Introduction to Color - Brown University
Introduction to Color - Brown University
Introduction to Color - Brown University
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Brightness<br />
CS123 | INTRODUCTION TO COMPUTER GRAPHICS<br />
Non-linearity of Visual System (4/4)<br />
<br />
But log function is based on subjective human<br />
judgments about relative brightness of various<br />
light sources in the human dynamic range<br />
<br />
Stevens’ power law approximates the<br />
subjective curve well in this range: S = c ⋅ I 0.4<br />
(or .42, for better imagery in a dark<br />
room, or .33, the value used in the CIE<br />
standard)<br />
<br />
Instead of encoding uniform steps in I in an<br />
image, better <strong>to</strong> encode roughly equal<br />
perceptual steps in S (using the power law) -<br />
called compression<br />
Idea behind encoding analog TV signals and<br />
JPEG images<br />
Intensity<br />
Andries van Dam <strong>Color</strong> 18/57