MemeCode - Blog

Gamma correct scaling...

Date: 25/2/2010

Seems that scaling isn't as simple as I thought... apparently there are non-trivial issues with gamma involved.

I took some time today to revise the standard LGI scaling algorithm (most visible in i.Mage) to use 16 bits/component linear RGB internally using lookup tables (8.8 precision) into and out of sRGB. This fixes the scaler for these types of images and I keep the integer only internal loops for speed. Nice.

Comments:

jbw
03/03/2010 1:21pm

Not only scaling - please have a look at:

http://www.jbw.pl/cgi-bin/home/portal.cgi?loc=.home.gfx.gamma-bug

fret
03/03/2010 8:54pm

Hehe, awesome... well looks like I've got some more work to do eh?

I have some nice sRGB<->Linear lookup table generators now, and I have some experience in using 16bit components internally to the algorithm. Thanks for taking the time to report the issue.

jbw
03/03/2010 9:39pm

Honestly, I didn't know about the source of this problem before you mention it here. So, thank you. Of course I've noticed many times wrong antialiasing in GIMP, but cannot guess the reason. Now I'm happy to know how to hunt the bug and how to bypass it.

KID
05/03/2010 2:22pm

I am very liked I.Mage, I have this idea:
1. Add to the shortcut Open(Ctrl+O ),Save (Ctrl+S)...
2. Additional editing multiple images at once.
Thank you very much and I wish MemeCode development more !...

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