I don’t think that it can be done directly in lcms since the main use case of
lcms is working with ICC profiles where everything is done as D50. If you want,
here is a list of transforms that may help you if you want to go from D65 to
D50 and then compute the RGB.
http://www.brucelindbloom.com/index.html?Eqn_ChromAdapt.html
-Isaac
From: Robert V Canning [mailto:robert.v.cann...@usa.dupont.com]
Sent: Wednesday, September 30, 2009 10:39 AM
To: Case, Isaac
Cc: lcms-user@lists.sourceforge.net
Subject: RE: [Lcms-user] XYZ to RGB Conversion
I apparently am not setting the illuminant and observer. I thought I was but,
in the larger code I have routines that convert Lab to RGB and I thought I was
changing the observer and illuminant for this as well (different profile). The
cmsCreateLabProfile allows me to set the white point,, the cmsCreateXYZProfile
doen't have an argument for the white point. Excuse my lack of experience
here, but how do I set the illuminant and observer.
-Bob
"Case, Isaac" <isaac.c...@xerox.com>
09/30/2009 10:30 AM
To
Robert V Canning/AE/dup...@dupont
cc
Subject
RE: [Lcms-user] XYZ to RGB Conversion
Where/how are you setting the illuminant and observer?
-Isaac
From: Robert V Canning [mailto:robert.v.cann...@usa.dupont.com]
Sent: Wednesday, September 30, 2009 10:23 AM
To: Case, Isaac
Subject: RE: [Lcms-user] XYZ to RGB Conversion
Thanks Isaac, that was the problem, I forgot the divide by 100. The conversion
seems to be in D50, I set the white point to D65 at 10 degrees but the results
always seem to be in D50 space 2 degree. I am comparing it to Lindblooms
calculator and I get the D50 answer not D65. Any clue?
Thanks again,
Bob
"Case, Isaac" <isaac.c...@xerox.com>
09/30/2009 09:50 AM
To
Robert V Canning/AE/dup...@dupont, <lcms-user@lists.sourceforge.net>
cc
Subject
RE: [Lcms-user] XYZ to RGB Conversion
What range of values are you passing in as XYZ. I just tried and got
X:0.5 Y:0.5 Z:0.5 -> R:190 G:185 B:207
However, if you are expecting a range of
X from 0 to 95.047
Y from 0 to 100.000
Z from 0 to 108.883
You’ll need to divide by 100 for everything.
-Isaac Case
From: Robert V Canning [mailto:robert.v.cann...@usa.dupont.com]
Sent: Wednesday, September 30, 2009 8:11 AM
To: lcms-user@lists.sourceforge.net
Subject: [Lcms-user] XYZ to RGB Conversion
Hi,
I want to be able to convert an XYZ value to RGB. I took the following
steps:
- created a XYZ profile used as input.
- created a sRGB profile used as output
- intent is set to perceptual
- created a transform
- loaded the XYZ values
- did the transform
The problem is no matter what the XYZ value I always get 255 for the RGB
values. What am I doing wrong?
Thanks for any help.
void XYZtoRGB(double X, double Y, double Z, unsigned char &red, unsigned char
&green, unsigned char &blue)
cmsCIEXYZ XYZ;
BYTE output[3];
XYZ.X = X;
XYZ.Y = Y;
XYZ.Z = Z;
cmsHTRANSFORM hXYZtoRGBTransform;
cmsHPROFILE hXYZProfile;
cmsHPROFILE hsRGBProfile;
hXYZProfile = cmsCreateXYZProfile();
hsRGBProfile = cmsCreate_sRGBProfile();
// Rendering intent is perceptual
hXYZtoRGBTransform = cmsCreateTransform(hXYZProfile, TYPE_XYZ_DBL,
hsRGBProfile, TYPE_RGB_8,
0,
cmsFLAGS_NOTPRECALC);
cmsDoTransform(hXYZtoRGBTransform, &XYZ, output, 1);
red = output[0];
green = output[1];
blue = output[2];
cmsDeleteTransform(hXYZtoRGBTransform);
cmsCloseProfile(hXYZProfile);
cmsCloseProfile(hsRGBProfile);
}
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