Re: [Lcms-user] General question about CIE Lab and TIFF

[Mark A. <m.f...@pl...>]

I’ve had experience with old image file formats like TIFF but I’m just a LittleCMS user. So I don’t know the insides of LittleCMS and I'm not a color management expert. But my guesses follow... Keep in mind they're just guesses and you're probably better off spending some serious time with the LittleCMS documentation.


>>Is it possible with lcms to extract the illuminant and Lab range from the ICC
I haven't seen anything regarding a range of values in LittleCMS but I don't know every nook and cranny of it. I'd think you'd just have to write your own code to check the pixel values. LittleCMS has routines which can read ICC tags for you but I'm not knowledgeable enough to know which one(s) you want. I'd personally use LittleCMS to set up for a color conversion and follow the code in the debugger and watch the part where it figures it out. LittleCMS certainly knows how to do it. It may involve this routine: _cmsReadMediaWhitePoint but I don't really know the insides of LittleCMS. I'd follow it in the debugger once to make sure you get the right result. I’d just do what it does. I don’t see a public routine which does it for you but I may have missed it.


>>And vice-versa, when decompressing custom CIE, can I convert an illumanant with Lab range into an ICC profile?
These create LAB ICC profiles with a white point:

cmsHPROFILE cmsCreateLab2Profile(const cmsCIExyY* WhitePoint);
cmsHPROFILE cmsCreateLab4Profile(const cmsCIExyY* WhitePoint);

LittleCMS can write that profile to a stream or write it to a file for you so you can create an ICC profile. I'm not sure what J2K is after with the range part.