Shadow Illuminator: Some Technical Details

Shadow Illuminator is an image processing software that intelligently compensates for illumination problems in digital pictures. The Shadow Illuminator has been developed at the Robotics Institute of Carnegie Mellon University to enable machines to approach visual capabilities of human eye.  Users will find that the results of Shadow Illuminator resemble what theirs eyes would see  if they viewed the environment instead of a camera.

From the original image the software estimates the illumination field that illuminated the scene when the picture was taken. Then it corrects every pixel to produce a result that would have been seen if the scene was uniformly illuminated.   The algorithm is intelligent in that it automatically "finds" where shadows start and stop just by "looking" at the original picture. By knowing where the shadow boundaries are, Shadow Illuminator produced results free of a highly objectionable artifact known as "halo" artifact.

Shadow Illuminator is not the "same thing" as other commonly used techniques

All of common techniques illustrated below gain some but also lose some.  Shadow Illuminator does not only improve visibility everywhere, it also enhances contrast of details.  It is just as if you had an additional light source at the photo shoot.  Best of all it is automatic; "one-click" does it all.  Try it for yourself.

Original Image	Global Brightness and Contrast Adjustment
Gamma Compression	Histogram Equalization
More advanced techniques produce halos and unnatural color	Shadow Illuminator Result

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Poor quality original produces poor quality result

An original that is compressed at low quality levels contains compression artifacts in shadows...	...that become visible once the shadows are "illuminated".
Image with a poor noise performance...	produce noisy results in deep shadows on the processed image.

Requesting less of shadow compensation from Shadow Illuminator, will hide some of this noise, at the expense of having some shadows remaining.  The best approach is to provide high quality originals.

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