Chapter V

Color tricks

Things are a bit more complex than they should be relating to the previous explanations.

The fact is that not all images can be converted.
Images with strong contrast zones are definitively not adapted.
They produce what stereo addicts call "ghosts".
Strong contrast zones produce anaglyphs with too close and too strong red and cyan spots.
This produce a very uncomfortable sensation through the red-cyan glasses.
Images with large zones of saturated colors will produce "ghosts" too. The exact name of this trouble (that produces a visual flashy effect quite different from the "ghosts" from contrast) is : retinal rivalry.
All the left information comes from one color, red.
If your image has large red zones, there will be no information (No green nor blue) for the right eye about those zones.
No stereo effect will appear there.
The same trouble happens with green and blue zones.
There is nothing to do for images with strong contrast (excepted creating the same image without the strong contrast . . .).
For example, you can change a black background into a grey background or you can try to change the lighting), even though it is still possible to use images with saturated colors.
If those saturated zones were gray there should be no problems as all the three bands should be the same on the zones.

Thus, We have to find a solution that will shift colors to grays but, yet respect the balance of space information between the two eyes.
This solution should also respect the original colors (if possible) and the three bands.
The solution will be to modify the saturation of the images.
Modifying saturation will allow us to modify the quantity of colors in an image by keeping for the resulting image only a few percentages of colors from the original image.
Notice that fully decreasing saturation turns the image into some kind of black and white version still coded on RGB.
The correct way to produce really black and white images is to use a dedicated tool as the formula used to get one value from three is not calculating the average value but using the following formula :
black and white = 0.30 red + 0.59 green + 0.11 blue.
0.30, 0.59 and 0.11 are values related to the sensitivity of the human eye.
A tool converting into black and white will allow us directly to produce black and white stereo images.

Here is an example of a picture with high saturated spots. The small balls inside the "meteor" are of bright red, green, blue and yellow :

If you directly convert the corresponding stereo pair to a color anaglyph, there are numerous saturated zones which are uncomfortable to view. If you first convert the stereo pair to black and white images then create the anaglyph, this anaglyph have, of course, no saturated zones which are uncomfortable to view and his fully comfortable :

On the left : direct RGB anaglyph, on the right B&W conversion first.

black and white conversion is the ultimate weapon against saturated spots.
The trouble is it wipes all colors.
It would be better if it were possible to modify the colors wiping only the spots that produce "ghosts".

A way to do this is to use an image processing software to change the hue or to reduce the saturation of the spots before producing the anaglyph.
The fact is that despite using an image processing software, fighting the ghosts "by hand" spot by spot or by try and error can be long.
This does not suit our original aim to produce stereo images in a quick way.
A way to speed-up color correction is to turn the reds into yellows. This is achieved by using the red layer of the right image to fill the green layer of the anaglyph.
This is OK if you have big red spots, such as in the Red Cross example below, but as it tends to turn the browns into yellows, and also saturated greens to black, it might not be suitable for most images.

A goof exemple of red to yellow stereo conversion.
Sample picture from http://www.geocities.com/lebouttedidier/avions.html

A not so good example of red to yellow stereo conversion

There is however another solution, still working by changing the whole color layers, allowing to produce "perfect" color anaglyphs in a snap, whatever the color spots.

"Perfect" anaglyphs in a snap : the Automateac method

Why "perfect" with quotes ? Because there are different levels of perfection. The Automateac method is perfect in the meaning : will automatically and easily solve ALL color troubles for ALL anaglyphs. Now, of course there will be color shifts and, in some cases, you might achieve a "better" result using another method, with "better" in the meaning : with more aesthetic contrasts and color shifts in your opinion.
Below is a sample showing you the kind of result achieved with the Automateac method. The idea is to turn the reds to the closest totally comfortable anaglyphic color, which is a dark brown. A side effect of the method is to reduce the saturation of greens and yellows, as brown is in fact a dark yellow, which itself is a mix of red and green.
Note that absolutely ALL flashing spots from the original image are removed in the "perfect" anaglyphic. Regarding brightness and constrasts, all colors are as close as possible to the original when you compare both pictures seen through anaglyphic glasses.

The original colors with color ghosting.	The "perfect automatic" anaglyph.

The table below compare the four anaglyphic solutions between them and to the original colors (in the middle). From left to right the four solutions are : direct RGB, Black & White, Red to Yellow and Automateac.

More "Perfect" anaglyphs
(but of course less perfect than mine, or i would not go publicly advertizing them ;-)

ChromaTune-3D™

ChromaTune-3D™ process of ByteMyzer is a very good one, mainly since it was improved due to my constructive critic that the green objects turned into somewhat the same color than the yellow objects. Below is was the difference on the green objects between the old ChromaTune-3D™ rendering and the Automateac rendering until january the 7th 2008 when i was given notice by ByteMyzer Softwerx that :

• The web page at http://french.cars.free.fr/do_3d/t_05.htm contains proprietary material pertaining to the ChromaTune-3D™ anaglyph rendering method, that the material in question was posted without the author's prior and express permission
• ChromaTune-3D is a trademark of ByteMyzer Softwerx; any and all materials relating and in reference to ChromaTune-3D™ may not be used without obtaining permission from ByteMyzer Softwerx
• Sample image referenced in the above mentioned web page is copyrighted by ByteMyzer Softwerx, and may not be published without the author's prior and express permission
• The above mentioned Web Page is in clear violation of the terms of Trademark and of the United States copyright term for Works Published Abroad After 1 January 1978
• The above mentioned Web Page must be revised immediately to exclude any and all materials and reference to ChromaTune-3D™

The ChromaTune-3D™ rendered the "fire-men" with an almost completely yellow uniform (helmet, jacket, gloves, belt, trousers and boots) when the Automateac process keeps the difference between the yellow gloves, belt and boots with the rest of the uniform which is green. The new version of ChromaTune-3D™ including my suggestion to keep the difference between the greens and yellows is now very similar to the Automateac rendering. ChromaTune-3D™ seems to increase luminosity, then on this example the Automateac image luminosity was increased by 25%.

Anabuilder

Should you whish to have much more (too much ?) choices about how to precisely tune each color, or would like to create many different anaglyph versions from a pair, you can use Anabuilder.

All those tricks should allow you to find quickly a comfortable anaglyphic version from most of your stereo pairs and choose the processing method that, in your opinion, keeps the best color definition for what a color anaglyph is supposed to be.