Hi Paul,
Just change the line
value = (value * max)/numberOfEntries; // normalize to gamma range
to
value = (value * max)/(numberOfEntries-1); // normalize to gamma range
And youll get the same numbers
. The correct value for vInt at the end of
the loop is 65535.
Best regards,
Lorenzo
From: Paul Cezanne [mailto:p...@fineeyecolor.com]
Sent: terça-feira, 28 de setembro de 2010 18:34
To: Lcms Liste
Subject: [Lcms-user] Bug in LPGAMMATABLE? (LCMS 1)
I'm looking at a 1% error in what I expect my gamma to be and now I'm
wondering if it is an LCMS bug! Run this program.
#include "lcms.h"
int main (int argc, const char * argv[]) {
const int numberOfEntries = 100;
LPGAMMATABLE transferFunctionsDebug;
transferFunctionsDebug = cmsBuildGamma(numberOfEntries, 1.0);
int max = transferFunctionsDebug[0].GammaTable[numberOfEntries-1];
float value;
int vInt;
for(int i =0; i < 100; i++) {
value = i; // convert to float
value = (value * max)/numberOfEntries; // normalize to gamma range
vInt = (int) (value + 0.5);
fprintf(stdout, "%d\t%d\n", vInt,
transferFunctionsDebug->GammaTable[i]);
}
}
I get this output:
0 0
655 662
1311 1324
...
62914 63549
63569 64211
64224 64873
64880 65535
I would have expected the columns to be the same. Does cmsBuildGamma not
build a perfectly linear LUT?
=
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