Attachments	Size
colorspace.zip	65.47 KB

Added	29 Sep 2010
Updated	05 Sep 2011
Authors	Pascal Getreuer
OS	All OS
Language	C
Attachments	1 file(s)

This package converts colors between sRGB, Y'P_bP_r, Y'C_bC_r, JPEG-Y'C_bC_r, Y'UV, Y'IQ, Y'D_bD_r, HSV, HSL, HSI, CIE XYZ, CIE L*a*b* (CIELAB), CIE L*u*v* (CIELUV), and CIE L*ch (CIELCH), and CIE CAT02 LMS. It can be used either as part of a C/C++ program or compiled as a Matlab MEX function.

For use in C programs, an example command line program colorcalc is included.  For use in Matlab, colorspace is compiled as a MEX function by entering

mex colorspace.c

on the Matlab command console. As an alternative to MEX, a pure M-code version colorspace.m is also included.

To perform a color transformation, first call GetColorTransform, specifying the source and destination color spaces as "dest<-src" or "src->dest". Then call ApplyColorTransform to perform the transform:

num S[3] = {173, 0.8, 0.5};
num D[3];
colortransform Trans;
       
if(!(GetColorTransform(&Trans, "HSI -> Lab")))
{
    printf("Invalid syntax or unknown color space\n");
    return;
}   
       
ApplyColorTransform(Trans, &D[0], &D[1], &D[2], S[0], S[1], S[2]);

“num” is a typedef defined at the beginning of colorspace.h that may be set to either double or float, depending on the application.

The supported spaces are

"RGB"	sRGB IEC 61966-2-1
"YPbPr"	Luma (ITU-R BT.601) + Chroma
"YCbCr"	Luma + Chroma (digitized version of Y'PbPr)
"JPEG-YCbCr"	Luma + Chroma space used in JFIF JPEG
"YUV"	NTSC PAL Y'UV Luma + Chroma
"YIQ"	NTSC Y'IQ Luma + Chroma
"YDbDr"	SECAM Luma + Chroma
"HSV" or "HSB"	Hue Saturation Value/Brightness
"HSL" or "HLS"	Hue Saturation Luminance
"HSI"	Hue Saturation Intensity
"XYZ"	CIE XYZ
"Lab"	CIE L*a*b* (CIELAB)
"Luv"	CIE L*u*v* (CIELUV)
"LCH"	CIE L*C*H* (CIELCH)
"CAT02 LMS"	CIE CAT02 LMS

All transforms assume 2 degree observer and D65 illuminant. Color space names are case insensitive. When sRGB is the source or destination, it can be omitted. For example "yuv<-" is short for "yuv<-rgb".

Similarly in Matlab, B = colorspace(S,A) converts the color representation of image A where S is a string with the format S = 'dest<-src' or S = 'src->dest' specifying the transformation.

This material is based upon work supported by the National Science Foundation under Award No. DMS-1004694. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.