Fotoxx Quick Guide  v.9.8

File menu	File Management
Image Gallery	Show thumbnail images - files in the current directory (more).
Open Image File	File open dialog - open an image file to view or edit (more).
Open Recent File	Choose from a list of the most recent files opened.
Save to Same File	Save modified image to the same file (overwrite) (more).
Save to New File	Save modified image to a new file (more).
Print Image File	Select printer / paper format / orientation, and print image (more).
Trash Image File	Move an image file into the fotoxx trash bin (more).
Rename Image File	Rename image files with optional sequence numbers (more).
Mass Rename Files	Rename many files using a base name and sequence number (more).
Quit fotoxx	Exit from fotoxx.
Area menu	Areas within images where edits are confined
Overview	Explanation of area editing (more).
Select	Select an area for subsequent editing (more).
Invert	Replace an area with everything outside the area (more).
Disable / Enable	Temporarily disable an area or enable it again (more)
Delete	Permanently remove an area (more).
Copy / Paste	Copy an area to memory and paste it somewhere else (more).
Edit menu	These functions modify image files  (more).
Adjust White Balance	Remove false color-cast from an image (more).
Flatten Brightness	Flatten the brightness distribution to enhance detail (more).
Retouch Image	Edit brightness, color, saturation, balance (more).
Brightness Ramp	Ramp brightness change across image (more).
Tone Mapping	Increase local contrast (more).
Remove Red Eyes	Click on a red-eye to remove it (more).
Blur Image	Blur an image (smoothen skin) (more).
Sharpen Image	Sharpen a blurred image (more).
Reduce Noise	Reduce noise (speckles) in low-light images (more).
Trim Image	Cut out a rectangular portion of an image (more).
Resize Image	Scale an image up or down (more).
Rotate Image	Rotate an image (level a tilted image or turn in 90° steps) (more).
Flip Image	Reverse an image horizontally or vertically (more).
Unbend Image	Fix perspective problems (more).
Warp Area	Distort image within an area by pulling with the mouse (more).
Warp Image (curvey)	Distort entire image by pulling with the mouse (more).
Warp Image (affine)	Distort entire image by pulling with the mouse (more).
Color Depth	Reduce color depth (posterize) (more).
Simulate Drawing	Transform a photo into a simulated pencil or chalk drawing (more).
Simulate Embossing	Transform a photo into a simulated metallic embossing (more).
Simulate Tiles	Transform a photo into tiles (make large pixels) (more).
Simulate Painting	Transform a photo into a simulated painting (more).
Edit Pixels	Edit pixels and paint lines or areas using the mouse (more).
Make HDR Image	HDR = high dynamic range (more).
Make HDF Image	HDF = high depth of field (more).
Panorama	Join overlapping images to make an ultra-wide image (more).
Tools menu	Utilities and setup functions.
Check Monitor	Display a color palette for tuning your monitor (more).
Index Tags and Thumbs	Re-index tags and thumbnails after file rearrangements (more).
Brightness Graph	Show brightness distribution graph of current image (more).
Clone fotoxx	Open a new window (e.g. to compare two images) (more).
Slide Show	Show images full screen (no menu or toolbar) (more).
Show RGB	Show RGB values at position of mouse click (more).
Grid Lines	Add or remove grid lines for image alignment (unbend, rotate) (more).
Lens Parameters	Edit parameters for your cameras and lenses (more).
Change Language	Change the GUI language (more).
Create Launcher	Create a desktop icon / launcher for fotoxx (more).
Convert RAW Files	Convert one or many RAW files to tiff (more).
Burn Images to CD/DVD	Select images and write them on a CD or DVD (more).
Tags menu	Manage tags (keywords) / star ratings / dates  (more)
Edit Tags	Add or change image date / stars rating / tags (keywords) (more).
Mass Add Tags	Add many tags to many images at once (more).
Search Tags	Find images with desired tags / star ratings / dates (more).
View EXIF Data	View image EXIF data (date, exposure data, tags) (more).
Help menu	User guide, README, change log  (more).
Toolbar buttons
Gallery	Show thumbnail images - files in the current directory (more).
Open	File open dialog - open an image file to view or edit.
Prev	Go to previous image in the current directory.
Next	Go to the next image in the current directory.
Save	Save modified image to the same file (overwrite).
Save As	Save modified image to a new file (more).
Undo	Undo (reverse) the results of the previous edit function.
Redo	Redo the previous undo. Undo/redo depth is 50 edits.
Zoom+	Magnify the image. A left mouse click also magnifies.
Zoom-	Reduce the image. A right mouse click also reduces.
Trash	Move an image file into the fotoxx trash bin (more).
Quit	Exit from fotoxx.

Keyboard Shortcuts

Main Window
left / right arrow keys	previous / next image
plus(+) / minus(-)  keys	zoom bigger / smaller
Z  key	zoom to 100% / fit to window
R / L  keys	rotate 90° right / left (temporary)
G  key	open image gallery window (thumbnails)
Delete key	move image to fotoxx trash
Escape key	Exit slide show mode or show RGB mode
Control + s	Save to original file (no questions asked)
Control + S	Save-as: dialog to choose a target file
Control + q or Q	Quit fotoxx
Image Gallery window
Home / End keys	move to first / last page of thumbnails
Page Up / Down keys	move to previous / next page of thumbnails
up / down arrow keys	move up / down by one row of thumbnails
left / right arrow keys	move to previous / next page of thumbnails
plus(+) / minus(-)  keys	bigger / smaller thumbnail image size
Escape key	close image gallery window
Dialogs for User Input
F1 function key	display user guide section for current function

Mouse Functions

left click	Zoom-in: magnify image 1.41x, 2 clicks for 2x, center at click position.
right click	Zoom-out: restore image to window size.
drag on image	Scroll image in opposite direction, like a normal scroll bar.

Some additional technical notes can be found here.

License and Warranty
Fotoxx is licensed under the GNU General Public License v3 (Free Software Foundation).
Fotoxx is not warranted for any purpose, but if you find a bug, I will try to fix it.

Origin and Contact
Fotoxx originates from the author's web site:  http://kornelix.squarespace.com/fotoxx
Other web sites may offer it for download. Modifications may have been made.

If you have questions, suggestions, or a bug to report: http://kornelix.squarespace.com/contact


File Menu

Navigation

Use the Image Gallery menu or the [gallery] toolbar button to create an image gallery window (thumbnails) showing image files in the current directory. Use this window to scroll around the directory and select files by clicking thumbnails. The buttons at the top allow scrolling forward or back by rows or pages. Use the [parent] and [open] buttons to jump to other locations. Use the [bigger] and [smaller] buttons to change the thumbnail size and the number of visible thumbnails. Pressing the [gallery] button in the fotoxx main window will bring the gallery window forward with the current file thumbnail in the upper left corner. Clicking on a thumbnail will bring the fotoxx main window forward with the selected image.


Open Image File

This function starts a standard file open dialog, allowing you to select an image file or navigate to another directory and select an image file. The selected file is opened in the fotoxx main window where you can view or edit the file using the menus and toolbar buttons. Drag and drop can also be used to open a file: drag a file from Nautilus (or other source) to the fotoxx window or to the fotoxx desktop launcher, and fotoxx will open the file. If text is dragged from gedit (or other program with drag sourcing), fotoxx will assume the text is a filespec and try to open it. Thus you can make a list of filespecs within a text file and use this list with fotoxx. Effectively, you can use Nautilus or text files to navigate a collection of images as an alternative to the fotoxx navigation system.


Save Image File

Menu: File > Save to Same File, or toolbar button [Save]: saves the current image file back to itself without confirmation. If the file is a JPEG file, the default quality (90) is used.

Menu: File > Save to New File, or toolbar button [Save-as]: opens a dialog to save the current image file to a selected file, which can be the original file, another existing file, or a new file. An edited image file can be saved in three formats, JPEG, PNG, and TIFF. JPEG is normally the best option, since files are compressed to reduce space. You can choose a JPEG quality value in the range 1-100. Lower values give greater compression and less image quality. Values above 70 are generally hard to distinguish from 100 (highest quality, largest file size). PNG files are compressed without any loss of quality and are usually larger than JPEG files of the highest quality. TIFF files are uncompressed and larger than JPEG or PNG. TIFF files may be saved with 8 or 16 bits per color. The 16-bit TIFF format only makes sense for files converted from a RAW format supporting more than 8 bits per color (camera RAW files are typically 12 bits per color with noise in the lowest 2 bits). It is rare that the difference between 8 and >8 bits per color can be seen with the eye.
 
File sizes for a 10 megapixel image are roughly as follows (depending on amount of detail):

tiff-16	tiff-8	png	jpeg-100	jpeg-90	jpeg-80	jpeg-70
58 MB	19 MB	14 MB	7 MB	2 MB	1 MB	0.6 MB

Print Image File

The print menu brings up a dialog where you can select a printer, a paper format (e.g. letter, A4), and an orientation (portrait or landscape). Use the [print] button to print the current image using the selected printer and paper format. You may also choose a format "custom" where the paper width and height can be edited to any reasonable values, in centimeters. The format is "custom N.N x N.N cm" and you must not change this - just replace N.N with your centimeter values (as in the predefined formats). Depending on your print software and printer, you may be able to see a "print preview" before printing, and you may be able to select the type of paper (plain or photo) and the print quality. Some of the predefined formats may not work for some printers. Margins seem to be a bit random. You can compensate by changing the paper dimentions: use the custom format with increased dimensions to get reduced margins on the paper. I have only been able to test with CUPS and an HP Officejet printer. I suggest you experiment with plain paper before comitting expensive photo paper.


Trash Image File

The location and structure of "trash" varies with the different flavors of the Linux desktop, so fotoxx does not try to use the un-standard trash. Fotoxx puts discarded images into a desktop folder named "fotoxx-trash". You can delete it or move it to your distro-specific trash folder.


Rename Image File

This function can help automate the process of renaming a series of files using a root name (e.g. an event or place name) and a sequence number. It is good for renaming a series of files from a digital camera. Open the first file in the series, input a new name, and press the [rename to] button. The next file is then opened. You can use the same name again by pressing the [previous] button and then add a suffix or sequence number. If you are using sequence numbers, press the [ +1 ] button after the [previous] button to get the next sequence number added to the name.


Mass Rename Files

This function is helpful if you want many image files (perhaps with the same date or from the same event) to have the same names with an added sequence number. In the dialog, specify a base name, a starting sequence number, and an increment. For example, a base name of "arctic cruise", a starting sequence number of 100, and an increment of 1 will produce a series of file names like this: arctic cruise-100, arctic cruise-101, arctic cruise-102, etc. (file extensions will not be changed). Use the button [select files] to open a file chooser dialog to select as many files as you want. When done, press [rename files] to rename all the files at once. Don't use this function to rename non-image files, since fotoxx will also update file name and tag associations in the tag index file.


Area Overview

Edit functions normally apply to the entire image, but it is possible to edit part of an image and leave the rest unchanged. If a smaller image area has been selected, then the following edit functions will be carried out within the selected area: white balance, flatten brightness, brightness/color, tone mapping, warp area, sharpen, blur, reduce noise, and all art functions. The warp area function works only within a selected area, and the warp image function works only on the whole image. Other functions (trim, red-eye, rotate, resize, HDR, HDF, panorama, unbend) ignore a selected area. An area may be selected before starting an edit function, or while an edit function is active. The selected area is immediately active, prior edits are retained, and future edits (those listed above) will apply only within the area. If another edit function is started, the selected area remains active, so it is possible to carry out a series of edits on one area, or one edit function on a series of areas.


Area Select

In the select area dialog, start with the [Edit] button. If an area is already there, it will be shown. You can continue to edit this area or use [Delete] to delete it and start a new area. The [Pause] button is used to suspend editing and free the mouse for zooming or scrolling a zoomed image to another position in the window. Use [Edit] to resume editing the area. The [Hide] button removes the area outline (for better visibility of image edits and edge blending). The button changes to [Show] and can then be used to show the outline. The [Delete] button removes the area, allowing another area to be started. The select area dialog can be exited and re-started later. Press [Edit] to resume editing the area.

Several methods (described below) can be used to outline one or more spaces within the image. These enclosed spaces will belong to the selected area and will be the areas modified by subsequent edit functions.

When you are finished selecting the spaces, use the [Finish] button to complete the process. A popup dialog will ask you to click the mouse inside each enclosed space in sequence. This action launches a search for all pixels within the enclosed space, and these are mapped and saved. The enclosed space is temporarily blackened so you can see exactly what part of the image is being mapped. The dialog will show the status of the search, success or "there is a gap". If there is a gap in the outline (i.e. the space is not fully enclosed), an attempt is made to show where the gap is: you will see a line coming out of the blackened space to meet the edge of an imaginary rectangle enclosing the space. You may be able to follow this line back to the gap, but if the area is convoluted finding the gap can be difficult. Each use of [finish] will produce a different picture that may lead you to the gap. When all spaces have been mapped in this manner, close the popup dialog with the [Done] button.

There are four methods to enclose space that will belong to the final area. These may be used in any sequence to define spaces that are joined or detached. Choose the current method using the four corresponding radio buttons: Freehand draw: drag the mouse to draw lines to outline an enclosed space. Follow edge: like freehand draw, but the drawn line will tend to follow along the edges of image objects that are close to the dragged cursor. Color range: select space around a clicked position which also matches the color and brightness of the clicked position. Radius: select a circular area around the dragged mouse cursor. The following paragraphs explain the details of each method.

Freehand draw: Drag the mouse (left button down) to draw a freehand (curvey) line, or left-click to connect a straight line from the last point drawn to the point clicked. Continue around the target area until it is surrounded with connected curves and lines. Right click to remove previous lines (mistakes) in order to re-draw them. A right click will remove the previous clicked or dragged line, up to 50 pixels. Right click repeatedly to remove more. A new clicked line will always connect to the end of the previous line. A new dragged line will connect to the previous line if it is started close to the end of that line. If it is started elsewhere, a disconnected line will be drawn. You can start a new drag from far away and draw back to meet the previous line. If a clicked line connects to an undesired point (you don't want to connect to the last line drawn), right click to erase it and then use drag to start a new sequence of lines. A right-button drag can be used to erase small segments: right-drag closely along a line to erase it, then left-drag to re-draw the line. At the end, all lines must be connected with no gaps. Overlaps are OK. Gaps can be difficult to find and correct, so work at 100% image size or greater and be careful. A series of lines automatically connected with left clicks will not leave gaps, but deviation from this sequence is likely to create gaps. To reduce the possibility of gaps, use deliberate overlaps when manually connecting lines.

Follow edge: this modifies the behavior of click and drag: high-contrast pixels (likely object edges) in the direction of mouse movement are searched and connected. This is effective for hard edges that are straight or gently curved. Fuzzy and ragged edges may not work well and freehand draw will be needed if high precision is necessary. The rules for connecting lines are the same as explaned above.

Color range:  Click the left mouse button somewhere on the image to define a target color to select. An area of the image around the mouse position will be selected. The color range slider defines the range of colors to select. Low values (left) define a narrow range and high values (right) a broad range. Clicking the right mouse button removes the last selection, and may be repeated to undo more previous selections. Adjust the color range slider to increase or decrease the area selected with each left click. It is important to understand the selection algorithm: all pixels contiguous with the mouse position and matching the color at the mouse position (within the specified range) are selected. The search for matching pixels stops at pixels not within the color range or at pixels already selected by the current or a previous selection. You can think of non-matching pixels and already selected pixels as "barriers" that cannot be penetrated by the search for new pixels. The search spreads out from every matching pixel to adjacent pixels, until a barrier is met. The mouse may also be dragged with the left button pressed. The selection algorithm is repeated for very pixel touched during the drag: this pixel and matching contiguous pixels are added to the selection. You can drag along the edge of an object with a narrow color range to define a barrier, and then increase the range to select a large area at once that will not cross the barrier. You will need some practice to get a feeling for this and be able to work efficiently. If an "island" is left out after a selection, you can likely eliminate it by clicking or dragging through it. Zoom the image to 100% or more to better see edge details. Sometimes getting the perfect color range is impossible: either too much will be selected, or many "islands" of excluded pixels will be created. The islands can be eliminated by clicking and draging over them using a large color range, but if there are hundreds of them this can get tiresome. Instead, use the "radius" method.

Radius: Enter a value in the radius control. A corresponding circle will appear around the mouse cursor. A left mouse click or drag will select all pixels within the circle, and a right mouse click or drag will un-select all pixels within the circle (i.e. those that were previously selected). Use a large radius to rapidly enclose large spaces, and a small one to carefully follow along the edge of a subject in the image.

Blend width: Edits made within an area can be blended with the surrounding image over a distance called "blend width". At the edge of the selected area, the image is the original image. At a distance of "blend width" from any edge into the area, the image is the edited image. For distances in-between, the pixels are a mix of original and edited pixels with a gradual transition. Use the Blend Width slider to set the blend width for the current or subsequent edit functions. The leftmost position of the slider is zero blend width, which gives a hard edge to the area edit. Moving the slider to the right increases blend width and makes the edges of the edit more gradual and harder to distinguish from the original image. Moving the slider for the first time after editing an area will cause the edge distance to be calculated for each pixel in the area. This is normally fast (a few seconds), but it may take minutes if the area is large and has a complex geometry (a very long edge). Whenever an area is re-edited or inverted, the edge calculation is discarded and must be repeated if blending is wanted. If the edge of a selected area is within 4 pixels of the image edge, it is no longer considered an edge for blending. If a selected area includes a portion of the image edge, and you do not want blending along this edge (the normal case), be sure the edge of the area is tightly bound to the image edge.


Area Invert

This function inverts an existing area: the entire image is selected except for the existing area. Using the function two times returns the original selected area. Inverting a selected area invalidates the edge calculation which must be repeated if edge blending is desired.


Area Disable / Enable

This function disables the current area and keeps the data so that it can be re-activated or re-edited. This allows you to alternate edits within a selected area and edits for the entire image.


Area Delete

This function permanently deletes the current area. The function is the same as the [Delete] button in the select area dialog.


Area Copy / Paste

Copy: The current selected area is copied and saved in memory.
Paste: The saved area is pasted into the current image. It can be moved around by dragging with the mouse. Use the buttons [+10%] etc. to resize the pasted object. Use the edge blend slider to make a blended edge if desired. Press the [done] button in the popup dialog. The pasted area now behaves like a selected area. You can edit within the area and use the [blend width] control in the Select Area dialog.



Image Edit Menus

General Editing Procedure

The image in the main window can be operated on with the edit menu functions. You can use these functions in any order, and the changes are accumulated for the current image and shown in the main window. The [undo] and [redo] buttons can be used to review the before/after results for the last 50 edits of the current image. These buttons do not work during an image edit function, but some of these functions have their own method to undo and redo changes during the edit. When finished with an image, use [save] to replace the original file or save to a new file.


Adjust White Balance

This function is an easy way to remove a false color-cast, e.g. the whole image has an overall blue or red tinge. After strarting the function, click somewhere on the image that should have no color - a white or gray area. If that location has any color other than white or gray, it will be used as a measure of overall false color, and this amount of color will be removed from the whole image. You can click around on various areas and see the impact instantly. Press the [done] button when you are satisfied, or [cancel] if not.


Flatten Brightness

This is a fast and easy way to compensate for a common limitation in photos: there is not enough range in the brightness to show good detail in all areas. This function finds where there are too many pixels with nearly the same brightness and spreads them apart, compressing other areas to make room. Technically, the brightness distribution is made more uniform (flatter). Move the slider and watch the image, which may lag a moment. Some images will show good results, others may not be helped or even become worse.


Brightness/Color

This function is used to change brightness, color intensity, color saturation, and color balance (relative RGB levels). You can adjust all of these items as a function of the original image pixel brightness. To illustrate, you could increase color saturation in darker image areas and leave it unchanged in brighter image areas.

There are 6 response curves for the 6 image attributes of brightness, color intensity, color saturation, and color balance (levels of red, green, and blue). The radio buttons select which curve is active and displayed. The curve represents a value (Y-axis) for each level of image brightness (X-axis). The middle Y-value is neutral (no change from the initial value). Higher and lower Y-values represent corresponding higher and lower settings for the 6 attributes. The initial curves are flat at the middle value.

The buttons [+++] etc. can be used to shift the whole curve in various ways. The curve can also be dragged up or down with the mouse. An anchor point (black dot) is added to the curve wherever it is pulled, and this becomes a constraint for subsequent pulls: the curve will continue to go through this point as other parts of the curve are pulled. Anchor points can be dragged, or deleted by right-clicking them.

The image changes in real-time as the curves are moved. Simply move the curves and observe the image until you are satisfied.

Changing brightness moves all RGB values by the same factor. Changing color intensity moves all RGB levels by the same factor within a pixel (no color shift), and the factor is greater for darker pixels. Changing color saturation changes the dominant RGB color(s) within each pixel and moves other colors in the opposite direction, so that overall brightness does not change.


Brightness Ramp

This function can be used to compensate for uneven lighting such as vignetting (darker image periphery), left/right or top/bottom brightness differences, etc. The function dialog displays two editable curves, horizontal and vertical. The horizontal curve adjusts brightness horizontally, and the vertical curve adjusts brightness vertically. Move the curves in the directions labeled "+" and "‒" to increase or decrease the image brightness in the corresponding image area. To remove vignetting in the image corners, move both ends of both curves in the "+" direction while fixing the middle areas or even moving them in the "‒" direction. To brighten the lower left corner, move the left end of the horizontal curve and the lower end of the vertical curve in the "+" direction.


Tone Mapping

Tone mapping can be used to improve the visible detail in images or image areas that have too little contrast. It brings out more detail by increasing the spread between darker and lighter pixels which are in close proximity. Other methods can also be used: adjusting the brightness curve can increase contrast for a selected brightness range (possibly at the expense of others). Flattening the brightness distribution can spread the available contrast more evenly. Increasing color intensity and saturation can also bring out more detail. These methods operate globally: all pixels of a color and brightness are processed the same. Tone mapping can process pixels differently depending on the brightness of surrounding pixels, and is more effective at enhancing detail.

Four tone mapping methods are available. All of them work globally or within a selected area.

Tonemap: base
This method is fast and interactive, and is somewhat different from what is normally called tone mapping. When the function is started, the mean brightness for the image (or currently selected area) is computed, which becomes the initial basis for contrast adjustment. Pixels darker or brighter than this value can be adjusted to be more dark or more bright, respectively - i.e. the existing contast is amplified. An editable curve spans the brightness range from black to white. If a portion of the curve is raised, pixels in the affected area are darkened if below the mean, or brightened if above. The left end of the curve affects darker pixels, the right end brighter pixels. Raising the middle will mostly increase the contrast for mid-brightness areas while affecting darker and brighter areas less. The slider below the curve can be used to move the base brightness value: where the transition between darkening and brightening occurs. Simply adjust the curve and slider while watching the image, until you are satisfied. If this is being done within a selected area, hide the area outline and use the "blend width" control to get rid of any edge effects.

Tonemap: local-1
This method is slower and works in a more conventional manner: an "unsharp mask" with a large radius. Here the base brightness for each pixel is computed from pixels within its neighborhood (radius), and the difference is amplified. This can do a better job of enhancing local contrast, but there are two problems: there may be "halos" around the edges of large uniform areas (e.g. where sky meets trees), and the computation time is longer. If you see halos, there are several possibilities to reduce them: (a) increase the radius, making the halos broader and less noticeable (but enhancement of local contrast is reduced), (b) reduce the amount of contrast adjustment, (c) use Select Area to operate on different image areas with different parameters.

Tonemap: local-2
This also uses the unsharp mask method, with additional controls. There are two radius inputs. The low radius governs halo suppression: a pixel with low contrast within its low radius neighborhood will have its contrast adjustment attenuated. The high radius governs the size of the neighborhood over which a pixel's brightness is compared for contrast amplification. The edit curve adjusts the amount of contrast amplification as a function of a pixel's initial contrast.

Tonemap: gradient
This is an entirely different approach which seems to work better for most of the images I use for testing. The horizontal and vertical gradient (slope) of brightness for each pixel is obtained, based on its neighbors. These values are amplified using an editable curve. The left end of the curve amplifies low gradient pixels, and the right end amplifies high gradient pixels (high contrast pixels). The amplified gradients are used to integrate a new brightness surface:
     this pixel brightness = prior pixel brightness + amplified gradient
This is done by row from top to bottom, left to right. Another pass is made in the opposite direction, and the results are averaged. If nothing else were done, this new brightness surface would go to extremes and be very unrealistic. Two variable factors ("constraints" in the dialog controls) tend to pull-in the extreme fluctuations and keep the new brightness surface closer to reality. The first constraint dampens an increasing (decreasing) brightness gradient when the brightness is already much greater (less) than the initial value. The second constraint pushes each pixel back in the direction of the initial brightness unconditionally, a little at a time with each new pixel calculation. Each pixel is used as the base for calculation of the next pixel, so these constraints have an effect that builds over a series of pixels. The pixel::pixel difference is dominated by the gradient, but over many pixels there is a drift in the direction of the neighborhood brightness. The constraint controls have a range of 0 (no constraint) to 1 (strong constraint). The curve can be dragged with the mouse and its effect on the image will show up in a few seconds (depending on image or area size and CPU speed). The constraint sliders also need a few seconds to show up in the image.


Remove Red Eye

This function reduces the red-eye effect from electronic flash photos. Two methods are provided. The first is faster but will not handle difficult cases (e.g. the eyelids are almost as red as the eye). The second method is more robust but also needs more time and care.

To use the first function, left-click on a red-eye one or more times until satisfied. If the darkened area is too small or off-center, do a right-click to undo the change and then left-click more precisely on the center of the red-eye. If a red-eye cannot be fixed correctly, right-click to undo the change and then use the second method.

The second method can better handle difficult cases where the red-eye is only slightly red and the color difference with the eyelids is too little for the automatic algorithm to distinguish. Place the cursor over the center of the red eye. Hold the left mouse button and drag the cursor down and to the right. A dotted ellipse will appear enclosing the red eye. Repeat if needed to get the red eye centered in the ellipse (roughly). Note that the shape of the ellipse depends on the direction of the drag, which can allow more precise enclosure of only the red-eye. Left-click inside the ellipse repeatedly while watching the red eye darken, and stop when it is dark enough. If you go too far, the eyelids may start to darken. Right-click to undo and repeat if necessary.


Blur image

This function can be used to blur or un-sharpen an image. Each pixel is mixed with neighboring pixels to reduce the differences, making edges fuzzy. Enter a value for blur radius and press [apply] to see the results. A small value mixes each pixel with its nearest neighbors and larger values mix more distant pixels. The contribution from each pixel decreases with distance, so the nearest pixels have the greatest contribution. This function is useful to smooth mottled skin tones. You can use "select area" to limit the blur to a face or part of a face. This is also a way to cure "banding" in sky areas (this can happen if the flatten, brightness, or tone mapping functions cause the distribution to spread out, making the brightness steps perceptible).


Sharpen Image

This function sharpens a blurry image. Three methods are implemented: edge detection, unsharp mask, and gradient. Edge detection: find adjacent pixels with the largest brightness difference (contrast) and increase the difference. This is repeated for several cycles, with the threshold for brightness difference decreased each cycle. Unsharp mask: a fast and effective method also found in Gimp and other tools. A technical description can be found via Google. Gradient: pixels are processed left to right and top to bottom. The brightness difference (contrast) between each pixel and its prior neighbors (left and above) is increased, and the pixel brightness is modified to match. This brightness change is propagated to the next pixel where the process is repeated.

The edge detection method gives sharper edges where the contrast is high and softer edges elsewhere, making it good for portraits (sharp eyes, smooth skin). For images that are partly sharp and partly blurred (e.g. depth of field or motion problem), the edge detection method primarily affects the blurry areas, whereas unsharp mask may put "halos" around edges that are already sharp. The gradient method works about as well as unsharp mask for slightly blurry images. It is experimental for now and may be revised or removed in the future. The radius value limits the distance over which pixels around an edge are changed. It should be small (1-2) for images that are slightly fuzzy and larger for poorer images. Threshold suppresses changes to low-contrast pixels: a higher values reduces the amplification of low-level irregularities.

For the edge detection method, enter the following parameters:
   cycles         number of iterations
   reduce        brightness reduction threshold per cycle, 80 means 0.80
   threshold    brightness change low cutoff threshold

For the unsharp mask method, enter the following parameters:
   radius          distance pixels around an edge are changed
   amount        amount of correction, 100 = normal
   threshold     brightness change low cutoff threshold

For the gradient method, enter the following parameters:
   amount        amount of correction, 100 = normal
   threshold     brightness change low cutoff threshold

Press the button for the method selected and wait a few seconds to see the result. The default values are suggested starting points. Make changes and repeat the process until satisfied. You can go back and forth among the methods to compare which is best for a given image. Use Select Area to operate on different parts of the image with different methods and parameters.


Reduce Noise

This function reduces the noise present in photos taken under poor lighting conditions, making uniform surfaces appear speckled. Choose one of the methods described below. Press the [reduce] button repeatedly while watching the image. If you go too far, sharpness and detail will be lost. The radius input determines the area around each pixel that is compared. A default radius is set when a method is selected, but other values may work better. For a large image, these algorithms may run a long time. To save time, select a small area and experiment with the different methods and radius settings until you make a decision, then clear the selected area and apply the chosen method to the whole image. There are four different methods, and each method applies to each RGB color independently.

• Flatten outliers by color: the highest and lowest pixel values within a radius are moderated slightly.
• Flatten outliers by color: pixels are compared to the mean and sigma of pixels within a radius. Those outside one sigma are moved back toward the mean by half the excess over one sigma.
• Set median brightness by color: pixels are set to the median value of their neighbors within a radius.
• Top hat: detect outliers by comparison with a band of pixels some distance away. The comparison distance is increased in steps from 1 pixel to the radius limit.

Trim Image

The HDR and panorama functions will leave some black margins around the edges where the images did not overlap. Use the trim function to remove these areas, or any other unwanted margins. An initial selection rectangle is drawn, encompassing about 60% of the image. Areas outside the rectangle will be cut off. Click or drag near any corner of the rectangle to move that corner. When done, press the [trim] button in the dialog box. The dialog box shows the current width/height ratio of the selection rectangle. If the box "lock ratio" is checked, then moving one corner of the rectangle will also move the opposite corner to keep the same ratio. You can also drag from the middle of the rectangle to shift the whole rectangle without changing its dimensions.


Resize Image

Sometimes called "rescale", this function allows setting a new image width and height in pixels, or as a percent of the original size. You can input the new width and height directly. Buttons are present for setting the new size to 3/4, 2/3, 1/2, 1/3, or 1/4 of the original size. Using one of these ratios will minimize loss of resolution. If the lock ratio box is checked, the original width / height ratio will be preserved, meaning that if one dimension is changed, the other dimension will be changed to match. After setting the new dimensions, use the [apply] button to perform the rescale. The window may look the same, but the image behind it is rescaled. The status bar shows the new dimensions. The file size is not updated until the modified image is saved.


Rotate Image

The rotate menu function starts a dialog to rotate the image clockwise (+) or counterclockwise (-) in steps of 0.1, 1, 10, or 90 degrees. For a tilted image, use the mouse to drag the right edge up or down until the image looks level. Use the 90 degree steps to convert an image taken in vertical format to horizontal. No resolution is lost with 90 degree rotation. For other angles, the loss of resolution varies up to about 1/2 pixel. The output image is increased to accommodate the rotated input image without size reduction - e.g. a 100 x 100 image rotated 45 degrees will be inside a new image box of 141 x 141 pixels, and the unused areas will be black. Use the [trim] button to remove these expanded margins.


Flip Image

Choose either horizontal or vertical flip from the dialog. The image is reversed vertically or horizontally. Repeating the flip restores the original image. Doing both a horizontal and vertical flip is the same as a 180 degree rotation.


Unbend Image

Panoramas of nearby subjects (typically buildings or interior rooms) may show straight lines that are curved, or buildings that are slanted. Bending of the images is necessary in the panorama process in order for the images to fit together. For remote subjects (esp. landscapes) this is not noticeable. The unbend function can be used to straighten curved lines and remove the slant from vertical lines. Vertical and horizontal dotted lines are drawn over the image, showing the unbend axes. Click or drag the mouse near the end of a line to move it. Input values for horizontal and vertical unbend and watch the effect on the image. Increase or decrease the values and repeat until satisfied. Move the axes to change the centers of unbending. See also "Warp Image" for another method of correcting perspective problems.


Warp Area

This function can be used to make distortions within an image. You can select an image area and drag the mouse to stretch this area with respect to the rest of the image. The image reacts as if made of rubber. The movement is maximum at the mouse pointer and declines to zero at the edges of the selected area. Many mouse drags of different lengths and directions can be combined to achieve the desired results. The [undo] button will remove the most recent stretch (up to the last 100). When finished, you can select another area and do some more warping, or select [done] to exit the function.


Warp Image (curvey)

This function is useful to correct perspective problems (see also "Unbend"). Drag the image from any edge, using the mouse. The entire image will be pulled or pushed in the direction of the mouse, but areas near the mouse are moved more than more distant areas. You can straighten curved lines or deliberately curve the image.


Warp Image (affine)

This function can be used to warp an image in interesting ways. Drag the image from a corner or edge using the mouse. The changes are purely linear so straight lines remain straight. This transform is called "affine". Technical details can be found with Google.


Color Depth

This function changes the normal 16 bits per RGB color (red, green, blue) to any value between 1 and 16 bits per color. At 8 bits per color, there are 16.8 million total color combinations. At 4 bits per color there are only 4096 total colors. Use 1-4 bits for an interesting "poster" effect.


Simulate Drawing

This function transforms a photo into a black and white high-contrast image or into a line drawing where only the edges of objects are shown as black lines on white background or white lines on black background. The sliding control "contrast" will deepen dark areas to black. The sliding control "threshold" will convert the image from gray-scale to black and white. The sliding control "outlines" will highlight high-contrast pixels (edges of objects) and suppress low-contrast pixels. This can be black on white or white on black, depending on the selection of the radio buttons "pencil" and "chalk". Manipulate both "threshold" and "outlines" to find the best balance.


Simulate Embossing

This function transforms a photo into a simulated relief or embossed image. The "radius" setting determines the feature size or level of detail. The "depth" setting determines how deep the features go into the surface.


Simulate Tiles

This function transforms a photo into an array of large monocolor tiles. You can control the tile size and the thickness of the space between tiles (caulk, grout).


Simulate Painting

This function transform a photo into something looking more like a painting. It reduces the number of colors, maps each contiguous pixel area having the same color, and then consolidates smaller areas into adjacent larger areas having the best color match. Four user settings control this process: "color depth" sets the number of colors to be used (bits per color). 1 = 8 colors, 2 = 64 colors ... 5 = 32768 colors;  "target group area" sets a lower limit for areas that will have their own color: areas smaller than this number of pixels will be absorbed into an adjacent area with the nearest color match; "req. color match" sets the minimum color match required for a smaller area to be consolidated into an adjacent larger area: 0 = don't care (maximum consolidation), 100 = perfect match required (no consolidation); "borders" determines whether the colored areas will be delineated with a thin black border, like irregular tiles in a mosaic. After using this function, using the "emboss" function can add interesting texture to the image.


Edit Pixels

This function changes individual pixels. There are three modes of operation: pick, paint, and erase. Pick mode: click anywhere on the image to set the current color. Paint mode: click or drag anywhere on the image to paint with the current color. Erase mode: click or drag anywhere on the image to restore modified pixels to their original color. The button [color] allows you to pick a color using a color wheel, and it always shows the current color. The "brush radius" control sets how large an area of pixels will be changed with each mouse click or drag. The "transparency" controls determine how intensely the color is applied at the center and edges of the brush. Zero transparency applies the full color immediately whereas a high transparency (90-99) applies a little color and allows you to gradually change the color using many clicks or drags (analogous to spray painting from a distance). Erase also works this way: use zero transparency to immediately erase, and high transparency to erase gradually. The [suspend] button releases the mouse so you can use the mouse to scroll or zoom the image. The button changes to [resume]. The [undo_last] button removes the last edit (modifications from the last click or drag operation), and this can be repeated to remove many recent edits. The memory for undo operations is limited to 100 megabytes, which can be reached if you make many edits using a large brush (every change to every pixel is saved). It is useful to save the image after each satisfactory change to free this memory. The amount of memory available is displayed in the dialog, so you can see when the limit is approaching. NOTE: zoom the image to 100% or more when using this function. If the mouse steps are larger than the image pixels and a small brush is being used, some pixels may be skipped by the mouse and cannot be painted.


Make HDR Image (high dynamic range)

HDR combines (overlays) multiple images of the same subject with different exposure levels. The combined image can show improved visibility of detail in both the darker and brighter areas, in effect using pixels from the brighter images for the darker areas, and from the darker images for the brighter areas. Many digital cameras do exposure bracketing: take multiple shots in quick succession with different exposure levels. You can combine such images to make a better one. If the camera is adjusted manually between shots, take care to keep it level and aim at the same point. Some misalignment of the two images can be tolerated. If things move between shots, fuzziness and ghosting cannot be avoided.

The HDR function can combine up to 10 files. Open one of the image files with the [open] button, then select the HDR menu function. A file open dialog is started to select up to nine more image files, which must all have the same pixel dimensions. The images are aligned and combined automatically, which may need a minute or more. When done, the combined image is shown, along with a dialog for manual adjustments. The contributions from the input images are shown as a series of editable curves. The horizontal scale represents pixel brightness, from dark to bright white. Each curve represents an image which contributes to the pixels. The image contribution at a given brightness level is proportional to the height of its curve at that level. The curves can be edited by dragging them with the mouse. The anchor points (small squares on a curve) can be pulled around while others remain fixed. The corresponding image contributions are changed accordingly, and you can see the results in quasi-real-time in the output image. Right-click on an anchor point to remove it. You will likely need practice to become effective at working the curves.

A faster and easier alternative may work as well: after the images are combined, ignore the curves and exit from HDR. Then use the edit functions Flatten and Brightness/Color to tune the image, or use the tone mapping functions. Select Area (mouse) can be used to enclose any area in the image which needs more local contrast, so you can apply different methods and parameters to different areas.


Make HDF Image (high depth of field)

HDF combines (overlays) two photos of the same subject with different focus settings, near and far. The near-focus image has close objects sharply in focus and far objects blurred. The far-focus image has the opposite condition. The idea is to combine the images so that both near and far objects are sharp.

Making the two photos: choose a point for the center of the image. Aim the camera at a near object and depress the shutter button 1/2 way, to set the focus on this object. Hold the button at the 1/2 position, aim the camera at the chosen center, and snap the photo. Now choose a far object and do the same. The camera position should be nearly the same for both photos, which can be a challenge when the subject is very close. Camera movement can cause scaling and parallax problems (nearer objects shifted against farther objects), which may or may not be fixable within fotoxx.

Processing the photos: in fotoxx, open the first image file, choose the HDF menu function, and you will be asked to select the second image. The two images will now be aligned as well as possible. The output image is a 50/50 mix of the aligned input images. A small amount of camera movement between the photos is compensated, but this is limited, and parallax shifts are not compensated at all. When the alignment is complete, a dialog opens. You can select either input image and "paint" with the mouse on any area of the output image. This converts the 50/50 mix to the selected input image for the area being painted. The radius of the paintbrush can be 1-200 pixels, so you can paint large areas quickly and control fine detail when needed. If you have overlapping near and far objects, time and patience will be needed to make all of them sharp. The examples in the fotoxx gallery took about 5-10 minutes each, but the object overlaps are also minor.


Panorama

This function stitches two images together to make a wide image or panorama. The images must overlap by 10% or more, so that the program can find where they coincide and put them together.

Open the left image file first. Select the panorama menu function. A file open dialog is started to select the right image file. The two images are initially joined with a small transparent overlap. A dialog pops up asking you to move the right image into rough alignment with the left image. Do this with the mouse, dragging the right image leftwards until it is within a few pixels of the best match with the left image. Rotate the right image if needed, by dragging the right edge up or down.

The images should be correctly curved and fit together well. If they do not fit, you need to set the lens parameters as described under "Lens Parameters". You can adjust these parameters within the dialog until the images fit reasonably well, and this may be good enough for most panorama jobs.

Press [proceed] when rough alignment is finished, and the program will do fine alignment and join the images. Internally, the images are shifted and rotated and the degree of match is evaluated. This is done with increasing image sizes until the best match is found within a fraction of a pixel. The process needs 10 seconds to 3 minutes, depending on CPU speed and image size. A 2.4 GHz Intel Core 2 processor with 10 megapixel images needs about 30 seconds.

When fine alignment is complete, the combined image is displayed. A dialog pops up for fine adjustment of brightness and color match. You may see a sharp border because the two images do not have the same brightness and color balance. The [auto] button can be used to perform an automatic color match, which is usually the best starting point. This button toggles the auto color match on and off. The other controls allow you to make additional changes to better match the two images. Changes are made to both images, in opposite directions. Change the values for brightness and color and press the [apply] button to see the results. The "blend width" input governs how the two images are blended together: the color balance is gradually shifted over this many pixels, to mask imbalances that cannot be fully corrected. The default is 1 pixel, which makes any brightness or color differences look obvious. When done, you can use unbend, image warp, rotate, trim, and other functions for final adjustments.

Panoramas of three or more images
After joining the first two images, Start the panorama function again to open and join a 3rd image. In this manner you can string together several images. New images are always joined on the right.

Vertical Panoramas
Rotate the images 90° to make them match as a left-right pair. After doing the panorama, rotate them back.

Panorama Limitations
Panoramas including nearby objects can be tricky: when the two photos are made, be careful to turn the camera on a vertical axis through the lens, with minimum lateral movement, otherwise the images may align poorly due to movement of foreground objects against the background (parallax). This is not an issue when the subject is 50+ meters away, since a small lateral movement has little impact on the image.


Tools Menu

Check Monitor

Eight color bands are written across the screen with brightness from zero (black) to 100%. You can use this to adjust the brightness and gamma of your monitor. The left end of each stripe should be as black as possible, but you should start to see some color within a few mm from the left edge. If the completely black portion is wider than this, adjust the monitor. There are 255 brightness steps from black to 100% (8 bits per color). The steps are too small to distinguish with the eye. This evaluation should be done in a darkened room (no external light falling on the monitor screen).


Index Tags and Thumbs

You need to do this after first installing fotoxx, or if you move or reorganize image files and directories. Nothing is lost when image files are moved around, but tag searching will not work (see the tags section below), and the image gallery (thumbnail) windows will be slow. The index function regenerates the tags index file and the thumbnail images that make the gallery windows fast. A dialog will ask for the topmost directory of your image files. That directory and any subdirectories containing images will be processed (if you have multiple directories not in the same hierarchy, make one directory with links to all the others). The time required depends on computer speed and average image size. My (fast) development computer does about 800 images / minute. Once the images have been indexed, searching them using tags is almost instantaneous. Starting with v.8.4, this function works incrementally (after it has run one more time). If only a few images have been added or moved (unknown to fotoxx), then only these images are processed. The indexing should complete in seconds instead of minutes. The index is built in memory and then written to disk (at ~/.fotoxx/assigned_tags). There is a limit of 100K images. If you want to force a complete re-indexing of all files, delete this index file first.


Brightness Graph

This function opens a small window that shows a brightness distribution graph of the current image in the main window. This graph updates immediately as edit functions change the image.


Clone fotoxx

Start a new instance of fotoxx in a new window, starting with the current image file. This is useful to compare images or to work with more than one image at a time.


Slide Show

The image window is enlarged to the whole desktop, and the menu and toolbar are removed. A dialog pops up to ask for the time duration to show each slide. You can also use the keyboard for navigation (more). Use the escape key to get out of slide show mode. If a tag search is done before a slide show, these images are shown.


Show RGB

This function changes the mouse mode. When a point on the image is left-mouse clicked, the RGB values are shown in the status bar at the bottom. The values have the format xxx.ddd, where xxx is the upper 8 bits of the color value, with range 0-255, and .ddd is the lower 8 bits, with range .000 to .999. The lower 8 bits are zero unless the image has been edited. Only the edit functions for color and brightness affect the lower 8 bits, and this data is preserved only if the image is saved in 16-bit tiff format. A right-mouse click restores the normal mouse mode (click to zoom), or the escape key can also be used.


Grid Lines

This function adds or removes a set of horizontal and verticle lines across the image. The lines are useful when an image must be rotated for perfect horizontal alignment, or when an image is unbent or warped to straighten walls or other objects in the image.


Lens Parameters

This is a dialog for setting and saving the two lens parameters, lens_mm and lens_bow, which must be set for each camera/lens used for panoramas. These parameters govern how fotoxx "bends" the two panorama input images so that they can fit together accurately. Enter a name for the lens/camera and the two parameters. Up to four lens/cameras may be entered. Lens_mm is roughly the focal length of the lens (35mm film equivalent), and lens_bow is a factor to compensate for edge-curving distortion (barrel and pincushion distortion). How to set these parameters is described here, but you should read the section on making panoramas first, in order to better understand the following instructions.

Setting Lens Parameters Automatically

The [search] button in the panorama pre-alignment dialog initiates an automated search for optimum lens parameters. Use a suitable image pair: the subject is 50+ meters away, the images have a low horizon difference and little relative rotation, and there is plenty of high-contrast detail in the overlap area. Input your nominal lens focal length for lens_mm. Use zero for lens_bow. After doing a decent pre-align, press the [search] button and wait a while for the results. Do this a second time and observe the changes. If the values remain consistent, you can use them for your panoramas. The search function steps through a range of values for lens_mm, lens_bow, and the image alignment offsets for x, y, and theta. It searches for the lens values that give the best alignment results for the given images. The process needs a minute or more, but you only need to do this once to characterize a given camera lens. Be sure to save the results using the lens parameters menu.

Setting Lens Parameters Manually

Make a panorama image of a brick or tile wall with about 40% image overlap. Within the panorama pre-align process, adjust lens_mm and lens_bow until the overlapping bricks or tiles coincide. When making the two images, be sure to turn the camera on a vertical axis through the lens, minimizing lateral movement and rotation in other axes - otherwise the images may fit poorly and your factors may not be optimum.


Change Language

This function allows you to change the GUI to one of the available languages. If your language is not available and you know enough English, consider making a translation, which is not difficult (more).


Create Launcher

This function puts a fotoxx icon / launcher on the desktop and enters fotoxx in the menu system in the category "Graphics". Your system must be LSB compliant (Linux Standards Base).


Convert RAW Files

This function converts one or more RAW files to tiff-16 format, using the program "ufraw". A file chooser dialog is opened. Choose one or more RAW files (hold down the CTRL key to select multiple files). The files are converted one at a time and displayed in the main window. Depending on the number of files, this can take a long time (my 2.67 GHz processor does about 9 files per minute using a mix of raw file types).


Burn Images to CD/DVD

This function enables you to choose image files and burn them into a CD or DVD. When the function starts, a dialog is started and an image gallery window (thumbnails) is displayed. The dialog shows a list of images for burning which is initially empty. To select an image, click its thumbnail and it will be added to the list. You can navigate the image gallery window to other directories and choose images randomly. Click on a file in the list to show its thumbnail in the dialog and also set the current position for subsequent adds and deletes. The next image added will be inserted at this position. If the [delete] button is pressed, the current image will be deleted, and if the [insert] button is pressed, the last deleted image will be inserted at the current position. To move an image to a new position in the list: click the image file (its thumbnail will be shown), press [delete], click another image and press [insert] - the deleted image will be inserted before the selected image. The list can also be edited directly: you can use cut and paste to get the sequence you wish, but be careful to always cut and paste entire lines only. The [add_all] button will add all the files in the current image gallery. Thus you can use the Search Tags function to create an image gallery, add them all, and than make adjustments if wanted. The [burn] button will send the list of files to Brasero to burn a CD or DVD.


Tags Menu

Tags - General Principles

Image files can have classification tags (categories, keywords) assigned to them. These can be used to search a large image library for those images having desired tags. Typical tags: the main subject of a photo, the associated event, the location, the person(s), etc. Tags reside inside the image (in the EXIF data) and are independent of its file name or directory location. You can use a directory hierarchy to make a physical organization of your images, e.g. directory names corresponding to year or location or other scheme. You can use file names for the main subject of the image. Such physical organizations are useful but optional: you can also put all your images in one giant directory and keep the numeric file names that come out of the camera. Regardless of the physical organization, "tags" can be used to create other organizations, e.g. label all the images of one person over all years, events, locations, etc. All images having a desired tag or tags can be found quickly and displayed in a pageable image gallery window (thumbnails), where you can further review the images and choose those for viewing, editing, or changing their tags. If you have used directory and file names in a meaningful way, you can keep using these, and you can also search for images using these names as well as tags.

Images may have a date which is pulled from the image EXIF data, if present, or manually set. Images may have a "star rating" for the importance of an image. Dates and star ratings can also be used as search criteria.

The package "exiftool" must be installed for tag editing. This program is used by fotoxx to read and write the EXIF data within image files.

There is a tag database used for searching, which makes it very fast (thousands of images per second are searched). The database is generated from the tags data inside the image EXIF data. Thus you can rearrange your image directories and files without losing anything - you must only regenerate the database, which is simple and fast. See the section Index Tags and Thumbs.

Limitations and Practical Tips
The following are the default limits for tags. These are compile time constants which can be easily increased if needed, although I believe they are large enough to exceed practical limits:
    o   max. tag length: 50 characters per tag
    o   max. tags for one image file: 1000 characters
    o   max. tags for all images: 2000 unique tags up to 50000 total characters
    o   max. tags in a search: 200 characters
The practical limit for the overall number of tags is in the range 100-200. Exceeding this range is possible but will lead to some practical problems: The window showing available tags will be large and tags will become hard to find (although ordered alphabetically), and the point and click method of adding tags will become more cumbersome. Typing the tags manually will work, but this may lead to typos and other tag redundancies. This is a bigger problem when tags are initially being defined for a library with thousands of images, and less of a problem afterwards when new images are added in small batches. Searching tags is also more cumbersome if the window of available tags is huge. If the tags are broadly defined and fewer in number, the search results will be larger, but using the search results (image gallery window) to find a smaller set of images is also quite fast. Physical file organization is also preserved in the gallery window (files located together in their directories will also appear together in the gallery window). All in all, my recommendation for the casual photographer is to use fewer and broader tag categories.


Edit Tags

Open an image file and then select the edit tags menu. Existing tags are shown in "current tags". Available tags are shown in the "assigned tags" window below. One of these tags can be added by pointing and clicking with the mouse. A tag can be deleted by pointing and clicking within the current tags. Tags recently added are shown in "recently added". This is a convenience to make adding tags to a new batch of images easier, assuming that many of the same tags will be used repeatedly. Point and click the same way. New tags that have never been used before (and do not appear in the list) can be added by typing them in and pressing [create tag].  The date of the image, if available, is shown as "image date". This may be entered if missing, or changed. You can enter a full date in the format yyyymmdd or a shorter format yyyy or yyyymm. A missing month or day is logically equivalent to "01" for search purposes. The [use last] button fills-in the date from the last date entered or shown. This is to allow easy dating of a series of images. You may enter an optional "stars" rating in the stars field. Use numeric values, e.g. 5 for a 5-star rating. The dialog remains open if you navigate to a new image, and the current tags are filled-in from that image.


Mass Add Tags

When adding tags to a large number of images having many of the same tags (i.e. the same event or subject matter), use this function to speed up the process. In the dialog, use the [select files] button to open a file chooser dialog where you can select as many image files as you want. Specify tags to add to the images by clicking tags in the "assigned tags" list. If you need a new tag, input the tag and press [create tag] to add it to the list. When done specifying files and tags, press [add tags] to add all the tags to all the files.


Search Tags

Use the search tags menu to find images having desired tags. Available tags are shown and can be chosen with point and click. Use the radio buttons to select "match all tags" or "match any tag". Press the [search] button to perform the search. Matching images are displayed in a pageable image gallery window (thumbnails). Choose images to view or edit by clicking the thumbnails. The set of matching images will remain in effect for image navigation (the buttons [prev], [next], [next page], etc.) until you use the [file] or [folder] buttons to establish a new image gallery set, which will be all images in the same directory as the chosen file.

A date range may be optionally entered, to further restrict the search to images within the date range. The format is yyyymmdd. Images are selected which have a date on or after the first date, if present, and on or before the second date, if present. Missing mm or dd default to 01.

A pair of star ratings may be optionally entered to restrict the results to images having a star rating within the given range. A missing low value implies zero, and a missing high value means unlimited.

Directory and file names may also be searched, with simple wildcard matching. Example: in the input field labeled /path*/file*, enter *egypt*cairo* to select all files with "egypt" and "cairo" in the directory or file names. The matching rule is simple: * matches any sequence of characters anywhere in the full /pathname/filename. Example: the file  /home/jack/aaa/bbb/xxx.jpg  would match *aaa* and *xxx* and *aaa*xxx* but would not match aaa* or *xxx or *aaa/xxx*. You can enter multiple file search strings separated by blanks, and files matching any of the strings will be selected. Name matching is not sensitive to case: both *aaa* and *AAA* would match the previous example. Note: only the files that have been indexed (menu: tools > index tags and thumbs) are searched. This is NOT a general file search function that covers the entire file system.

To find all images with no tags, search with all-blank tags, stars, dates, and file names.


View EXIF Data

If the package exiftool is installed, the View EXIF menu will display EXIF data in the current image file, if available. EXIF data contains the date and time of a photo, shutter speed, focal length, pixel dimensions, etc. Most cameras store this data inside the image. If the image is edited and then saved, the EXIF data is updated and stored with the new image. NOTE THAT THE EXIFTOOL PACKAGE IS REQUIRED IF YOU WANT TO RETAIN EXIF DATA WHEN AN IMAGE IS MODIFIED AND SAVED.


Help Menu

About
This displays a short message about the fotoxx version number, license, home page, and credits.

User Guide
The user guide (this document) is displayed (created using the WYSIWYG HTML editor SeaMonkey).

README
Displays the README file distributed with fotoxx, which may contain new information about installation or dependencies. When you install a new release of fotoxx, you should look at README and the Change Log to check if there is anything special you need to be aware of.

Change Log
Displays the change log file distributed with fotoxx, containing details about functional changes, additions, or bug fixes for the current and previous releases.

Translate
Displays a short text file which explains how to make a new translation or change an existing one. This involves editing a text file that contains English text messages with corresponding translations (more).

Home Page
Shows the fotoxx home page from the Internet. Look here for program updates.



Technical Notes

Translations
See the menu  Help > Translations  or the text file TRANSLATIONS for guidance on how to modify an existing translation or make a new one. This is a fairly simple process: edit a text file with English text strings followed by their corresponding translations. See one of the existing translations as an example, e.g. /usr/local/share/fotoxx/locales/fr (the French translation file). A new translation for language code xx would be saved at /usr/local/share/fotoxx/locales/xx. After making such a file, you can test it by starting fotoxx on the command line: $ fotoxx -l xx.

Hardware and Software Requirements
Fotoxx works best on a fast computer with at least one gigabyte of memory. Multiple CPU cores are utilized for compute intensive functions (e.g. sharpen, rotate, warp, tone mapping). Smaller computers (notebooks, netbooks) will work, but will be quite slow for some functions. Screens smaller than 1200x800 will feel confining for some functions. The typical notebook screen with limited brightness and color should not be used for image retouching.

Packages Required by Fotoxx
Fotoxx requires the following libraries and programs to function at run time:
   libtiff4                read and write tiff files, 8 and 16 bits per color
   xdg-utils            open text or html files with user's assigned application
   exiftool              read and write EXIF data, including user-defined image tags
   ufraw                 import raw image files from a digital camera
   brasero              burn a CD or DVD with selected images

Packages Required for Fotoxx Source Build
See the README file for instructions on compiling fotoxx from source.
In addition to the programs listed above, the following are also needed:
   g++                       GNU C++ compiler
   libgtk2.0-dev         Gnome GTK/GDK/Pixbuf/etc. development files
   libtiff4-dev             tiff library development files

Command Line Options
   fotoxx /.../imagefile.jpg      #  initial image directory or file to open
   fotoxx -l lc                          #  language code to use for GUI (de, fr ...)
   fotoxx -v                             #  output version and build date and exit

Status Bar Information
   navigation:      1234x987x24 0.45MB 56%  edits: 3
   HDR/pano:       align: 2345  offsets: +12.3 -23.4 +0.0023 ...  match: 0.91234
Explanations:
   1234x987x24   image width x height x depth (bits per pixel)
   0.45MB             image file size (updated when a modified image is saved)
   56%                  zoom status, image % size
   edits: 3             3 prior versions are saved in the undo stack
   2345                 HDR or panorama alignment cycles done (progress indicator)
   +12.3 etc.        alignment offsets: x, y, theta, 4 corner warp values
   0.91234            image match (creeps up as alignment improves, reset each stage)

File Types Supported
Fotoxx uses two libraries to support reading and writing of image files: the GDK pixbuf library and libtiff. Pixbuf supports JPEG, PNG, ICO and BMP files, all with 3 RGB colors and 8 bits per color. Libtiff supports TIFF files with 1-bit depth (bi-level), 8-bit and 16-bit grayscale, and 3 RGB colors with 8 or 16 bits per color. Other TIFF formats are not supported by fotoxx, although they could be added if there is a need. Bi-level and grayscale images are treated as RGB inside fotoxx, with all RGB colors set to the same value. Fotoxx converts camera RAW files to TIFF RGB with 16 bits per color.

Color Depth
8-bit color, as supported by JPEG, is the norm for image files and is usually adequate. LCD monitors are limited to 8-bits, and the brightness range for photo paper is even less. 16-bit color can be useful if a narrow brightness range within an image has been expanded (e.g. the brightness distribution was flattened or tone-mapping was applied). This expansion within a narrow range can lead to visible "banding" or "picket fence distribution". If the image has a 16-bit color depth, this effect can be reduced, even after the image is truncated back to 8 bits for storage (JPEG) or display on a monitor.

Alignment Algorithm
5000 high-contrast or "edge" pixels are selected to control alignment in HDR, HDF, and Panorama. The actual pixels used are shown in red during the alignment process, which is also entertaining. For Panorama and HDF, one image is systematically warped various small amounts and the fit with the other image is tested. This is done becuase two photos made with slightly different horizons or rotations will not fit perfectly with simple translation and rotation.

Alpha Channels
Images having alpha channels (transparency information) can be processed, but the alpha channel is lost when the processed file is saved.

Image Deterioration From Repeated Editing
If you save an edited image file and then use this file later to perform additional edits, pixel resolution may be lost. It is better if you do all edits when the image files are first processed, to minimize image deterioration (or go back to the originals if you still have them). The following edit functions reduce resolution about 1/2 pixel, and this error can accumulate from repeated edits: rotate (other than 90 degrees), HDR, HDF, panorama, unbend, warp. Resize to a smaller size will of course reduce resolution, but using the fraction 1/2, 1/3, or 1/4 gives the best results. The following functions do not reduce resolution: flatten, brightness/color, tone mapping, red eye, sharpen, reduce noise, trim, and all art functions.

Source Code
The C++ source code is heavily commented in the hope that others can understand and use the code for their own projects. If you have a technical question about how something works, or a better idea to pass along, you can  contact me at: http://kornelix.squarespace.com/contact

Questions and Problems
If you have a question or run into a problem, contact me at: http://kornelix.squarespace.com/contact
If you send any images that work poorly, I can use these to try to improve fotoxx. If there is a traceback dump on the screen, or error messages in the log file ( /home/<user>/.fotoxx/fotoxx.log ), please send these also.

Technical Reference Book
I recommend the book "Introduction to Image Processing and Analysis" by Russ and Russ, CRC Press. It is clear and concise. The following algorithms were adapted from this book: flatten brightness distribution, unsharp mask, noise reduction (median smoothing, top hat), simulated embossing. The affine transform method for image distortion or rotation was found via Google.

Acknowledgements
The programs  libtiff, ufraw, exiftool and brasero  have helped fotoxx evolve much faster than otherwise possible. Of course this also applies to GTK, GDK, the pixbuf library, the GNU tools and libraries, and the entire Linux ecosystem. Thanks to those who have donated their time for translations and testing (see Help > About), and those who have donated their ideas for development.