following images show: [a] an 8-bit 512x512 pixel abdominal ct-scan image. the large area on upper left is the liver. the brightness of each pixel is determined by shooting x-rays at many angles plus fancy backprojection math, free book online*. [b-d] visualization of brightness values at various scales extracted from
[a]. x-axis: pixel number [collapsing x-y position to a single dimension]. y-axis: brighness value [8-bit = 256 grey levels], with
0 = black toward bottom and 1=white, top. [b] pixel range 150k-160k, which is a closeup of [c] pixel range 100k-200k, which in turn is a closeup of [d]: pixels 0 to 262144 [=512x512].
as the scale increases, especially in [c,d] unforseen structure becomes visible: the dark horizontal bands correspond to missing brightness values at nearly equally
spaced brightness intervals. whereas the dark vertical areas evident in [b] are due to scanning the image repeatedly row by row,
the origin of the missing brightness values is mystery, maybe of significance for computer-aided tumor classification. you see the lesion in the liver?
[b] x-axis: pixels 150k-160k
[c] x-axis: pixels 100k-200k
[d] x-axis: pixels 0-262144