CSC111 Why 255?

--D. Thiebaut (talk) 16:14, 13 March 2014 (EDT)

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Sample Image

square.bmp

identify square.bmp
square.bmp BMP 20x20 20x20+0+0 8-bit sRGB 1.25KB 0.000u 0:00.000

ls -l square.bmp 
-rw-r--r--  1 thiebaut  wheel  1254 Mar 13 20:48 square.bmp

Octal Dump

od -t u1 square.bmp
0000000    66  77 230   4   0   0   0   0   0   0  54   0   0   0  40   0
0000020     0   0  20   0   0   0  20   0   0   0   1   0  24   0   0   0
0000040     0   0 176   4   0   0   0   0   0   0   0   0   0   0   0   0
0000060     0   0   0   0   0   0 240   0   0 240   0   0 240   0   0 240
0000100     0   0 240   0   0 240   0   0 240   0   0 240   0   0 240   0
0000120     0 240   0   0 100 100 100 100 100 100 100 100 100 100 100 100
0000140   100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100
0000160   100 100 240   0   0 240   0   0 240   0   0 240   0   0 240   0
...
0002200     0   0 255   0   0 255   0   0 255   0   0 255 100 100 100   0
0002220   250   0   0 250   0   0 250   0   0 250   0   0 250   0   0 250
0002240     0   0 250   0   0 250   0   0 250   0   0   0 255   0   0 255
0002260     0   0 255   0   0 255   0   0 255   0   0 255   0   0 255   0
0002300     0 255   0   0 255   0   0 255 100 100 100   0 250   0   0 250
0002320     0   0 250   0   0 250   0   0 250   0   0 250   0   0 250   0
0002340     0 250   0   0 250   0