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How does the luminance manipulate the color? (PTM-LRGB)


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Hello everyone! 

I got interested in the PTM format and wanted to "play around" with it a little bit and tried to write a PTM-reader in Java on my own.

I was able to get all the rgb-values and the luminance coefficences and I implemented the formular for calculating C (also regarding bias and scale) but from here on I really don't know how to proceed. How does the luminance C manipulate the colorvalues?

Am I using the formular " C = si * ( Craw - bi) " correctly this way?:

C = (((a1 * lu2) - b1 ) * s1)

+ (((a2 * lv2) - b2 ) * s2)

+ (((a3 * l* lu) - b3 ) * s3

+ (((a4 * lu) - b4 ) * s4

+ (((a5 * lv) - b5 ) * s5

+  ((a6 - b6) * s6

Or is my formula itself wrong?




Hope someone can help me.




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