Canon 800II Installation Manual page 32

Chapter 2 Specifying the Scanner Settings
Preparing Gamma Curve Data
Gamma curve data consists of a 258-line text file (*.gmm) containing the output
values for the 256 levels of input values.
Always enter a connect as the first line of the gamma curve data and "256" in the
second line to indicate the number of data items.
Lines 3 onwards set the output values for each input value, starting with the output
values for "0" in line 3, "1" in line 4 and so on through to the output value for input
value "255" in line 258.
Smaller values in the gamma curve data give a darker image while larger values
produce a lighter image.
Example of Prepared Gamma Curve Data
Normally, the gamma curve leans to the right. However, the leftward-leaning gamma
curve shown in the lower figure below inverts all the output values so that the result-
ing image is also inverted.
Gamma curve data
1st line : gamma curve
2nd line : 256
3rd line : 0
4th line : 1
5th line : 2
253rd line : 250
254th line : 251
255th line : 252
256th line : 253
257th line : 254
258th line : 255
Gamma curve data (inverted)
1st line : inverted linear gamma curve
2nd line : 256
3rd line : 255
4th line : 254
5th line : 253
253rd line : 5
254th line : 4
255th line : 3
256th line : 2
257th line : 1
258th line : 0
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(Gamma curve)
255
Output value
0
Input value
(Gamma curve)
255
Output value
0
Input value
255
255