Re: [Lcms-user] Gamut Checking for creating colour charts

[Marti Maria]

Hi,   This function is already in lcms, although not exposed in the API. If you are linking statically the library, could use it:   LPLUT  _cmsComputeGamutLUT(cmsHPROFILE hProfile, int Intent);   This returns a gamut-check LUT on the desired intent. You can then check values by doing:   WORD ValueToCheck[4]; WORD InGamut;   cmsEvalLUT(Lut, ValueToCheck, &InGamut);   Fill ValueToCheck with the CMYK (or whatever) you want to check. InGamut will return 0 if inside gamut and > 0 else.     Regards, Marti Maria The little cms project http://www.littlecms.com [EMAIL PROTECTED]   ----- Original Message ----- From: Glenn Wilton To: [EMAIL PROTECTED] Sent: Friday, March 26, 2004 10:09 PM Subject: Re: [Lcms-user] Gamut Checking for creating colour charts Cool, I was hoping it was correct.   What Ive done is write a small function where I pass a Lab value as cmsCIELAB and a profile handle and it returns the Delta E, It converts to 16 bit PCS then dows a double transforms and the checks the Delta E.   Is there any change this could be included in little CMS as a stnadard function, I would assime you could just to the transforms on a single profile using the A2B and B2A tables .. and not what I have to do and create a LAB profile plus two transforms   bool cmsLab2Device2Lab(cmsHPROFILE hProfile,LPcmsCIELab LabIn, LPcmsCIELab LabOut); hProfile - pointer to profile LabIn - Desired Lab colour LabOut - Resulting Lab colour on output device Intent ???? - Specify rendering intent to be used   This allows the freedome to choose the DeltaE method   Glenn Wilton > [EMAIL PROTECTED] <   ----- Original Message ----- From: Marti Maria To: Glenn Wilton ; [EMAIL PROTECTED] Sent: Saturday, March 27, 2004 7:41 AM Subject: Re: [Lcms-user] Gamut Checking for creating colour charts Hi,   This is more or less the algorithm littlecms is using for gamut checking.   The differences would be, I'm using relative colorimetric instead and the "Lab2" value is checked again across the profile to track white point displacements, but the basics are same.   It works to me. If anybody knows a better method, and want to share it, I would be glad to include it in the CMM.     Hue is an angle, so the range goes 0-360. Chroma can be any positive number.   Regards, Marti Maria The little cms project http://www.littlecms.com [EMAIL PROTECTED]     ----- Original Message ----- From: Glenn Wilton To: [EMAIL PROTECTED] Sent: Thursday, March 25, 2004 11:56 AM Subject: [Lcms-user] Gamut Checking for creating colour charts Im in the process of creating some custom colour charts for work, Theis is be based on LCH. I dont want to print all the colours in the LCH colourspace as this is too many and most are out of gamut (3600 colours at 360 step 10 and L/C step 0.1)  I want to limit the range to colours inside the gamut of the device. I have working code based on the below steps but I just want to check if this is the correct way   Firstly im converting from LCH to D50 LAB and calling this LAB1   Then im Converting from LAB1 to Device Colours via Absolute Colourmetric transform, Im then taking this Device Colour and converting it back from  the Device colour via Absolute Colourmetric transform and calling this LAB2.   Im then discarding all colours where the Delta E between LAB1 and LAB2 > 20 (The ensures im getting colours just outside the gamut)   Is this the best way?   Oh BTW is the range for Chroma and Hue H 0.0 to 1.0? Glenn Wilton > [EMAIL PROTECTED] <