[argyllcms] Re: help with camera profile

  • From: Nikolay Pokhilchenko <nikolay_po@xxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Fri, 20 Jul 2012 13:31:08 +0400

Alberto, did You check the saturation level of Your camera sensor? The sensor 
saturation may be the reason of the yellow cast.
Just shot any white object with the same shutter speed but with much higher 
brigtness than the white on the target. Convert the raw image by dcraw into 
linear 16bit TIFF without debayerization and without brigtening ("document 
mode"). Use the parameters -k 0 and -s 65535. Then check the saturation level 
on oversaturated areas of the test shot (the 16-bit tolerance is preferrable).
The level of saturation that RAW converter uses should be slightly lower than 
measured actual saturation level. It's possible that some of sensor channels 
are saturated while You shoot the target but You didn't see it because 
incorrect saturation level inside the converter.
After You've find actual sensor saturation level, You may use it with dcraw: 
for example, the saturation found at 15340. You can set the -s parameter of 
DCRAW sligtly lower (by 1..3%), for example, -s 15000 to guarantee that 
oversaturation will not be overseen. Then try to find new, correct exposure. 
The aim for exposure is the white level just under (but not at) the maximum 
while using -s parameter witn new saturation level defined.

I tried another profile by shooting the target in artificial light (a
430EX flash). The result is not much different, even though there is a
little bit less yellow in the images.

Any further help will be highly appreciated.


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