and 
then
the apparent brightnesses when a light of intensity I reflects off
of them, are: 
. The difference in the brightnesses is:More on Human Vision
We demonstrated in class that the human eye is not generally responsive to the absolute level of illumination, but to the relative changes of brightness at the edges between objects. This is because the visual response is approximately logarithmic so the diference between two signals is invariant with overall illumination changes.
So white is not necessarily MAX_BRIGHTNESS. See, for example, Debby Krim, The Colors of White
If two diffusely-reflecting objects have reflectivities and then
the apparent brightnesses when a light of intensity I reflects off
of them, are: . The difference in the brightnesses is:
which is independent of the illumination intensity I. As a corollary, to have objects appear to be equally spaced in brightness, the ratios of their reflectivities should be approximately constant.
When designing images, it is useful to accommodate this visual non-linearity.
Image Operations
Thresholding.
Contrast stretching
comet -- max brightness = 15
comet -- sqrt brightness
comet -- log brightness
comet -- max brightness = 255
comet -- stretch, sqrt
comet -- stretch, log
Histograms
comet
comet stretched
comet log
Bit planes
fire
fire -- bit plane 7 = msb
fire -- bit plane 6
fire -- bit plane 5
fire -- bit plane 4
fire -- bit plane 3
fire -- bit plane 2
fire -- bit plane 1
fire -- bit plane 0 = lsb
Color bit planes
EAP1
EAP1 -- bit plane 7 = msb
EAP1 -- bit plane 6
EAP1 -- bit plane 1
EAP1 -- bit plane 0 = lsb
