Shaders and Texturing - An Introduction to Computer Graphics for Artists - page 190

Fig. 11.9 The three swatches on the left of this illustration were taken from three different areas
in the image, all of which are painted white

Hue shift will be evident in both the lit portion of your photo and the shadow side
of objects in your scene. A photograph taken indoors with carefully controlled light-
ing or outdoors at mid-morning on an overcast day will largely prevent any signifi -
cant amount of hue shift from occurring.
It is important to remove local hue shift lighting artifacts because they are the
equivalent of baking lighting into your texture map. This is because a texture shot in
an environment with yellow lighting will have a yellow cast to it. If it is adjacent to
a texture shot in violet lighting, its yellow hue shift will be highlighted by the CG
lighting in the scene and made more prominent by the contrast with the violet-
shifted adjacent texture. The effect of this is that any colors in the two maps will be
less prominent than the hue shift, and by placing them so that they are adjacent, the
contrast between the hue shifts in each map will be exaggerated.
This is not immediately evident to artists who are not trained to recognize hue
shift, because every color in a single photograph will be affected in exactly the same
way, to exactly the same degree. This will equalize the colors to your eye, and make
them appear normal. It is only when they are placed beside images taken in different
lighting conditions that hue shift errors become obvious.

11.5.3.6 Light Gradient/Falloff

The farther light travels, the less intense it becomes. This is known as falloff .
Depending on how much light is present in your scene, it can be diffi cult to detect a
falloff gradient , or a gradient tone shift along a surface in your scene (Fig. 11.10 ).
We are so accustomed to seeing this in our environments that, unless we are looking
for it, it is diffi cult to detect.
The result of having a falloff gradient in your photo is that it becomes diffi cult to
know the actual color of any given object in your picture, because it gradually