Create an RGB -> RGB transform and re-sample it on a regular grid,
for instance like below (code is a bit older, still using lcms1, though).
Regards,
Gerhard
#define GRIDPOINTS 64
static GLushort clut[GRIDPOINTS][GRIDPOINTS][GRIDPOINTS][3];
static GLuint img_texture;
static GLuint clut_texture;
static GLfloat clut_scale;
static GLfloat clut_offset;
void
make_clut_texture(const char *profile_name)
{
int r, g, b, n = GRIDPOINTS;
cmsHPROFILE sRGB, monitor;
cmsHTRANSFORM xform;
sRGB = cmsCreate_sRGBProfile (); // image profile
monitor = cmsOpenProfileFromFile (profile_name, "r");
if (monitor == NULL) {
fprintf(stderr, "Cannot open display profile %s\n", profile_name);
exit(1);
}
xform = cmsCreateTransform (sRGB, TYPE_RGB_16, monitor, TYPE_RGB_16,
INTENT_PERCEPTUAL, cmsFLAGS_NOTPRECALC);
if (xform == NULL) {
fprintf(stderr, "Failed to create transformation\n");
exit(1);
}
clut_scale = (double) (n - 1) / n;
clut_offset = 1.0 / (2 * n);
for (r = 0; r < n; r++) {
for (g = 0; g < n; g++) {
for (b = 0; b < n; b++) {
unsigned short in[3];
in[0] = floor ((double) r / (n - 1) * 65535.0 + 0.5);
in[1] = floor ((double) g / (n - 1) * 65535.0 + 0.5);
in[2] = floor ((double) b / (n - 1) * 65535.0 + 0.5);
cmsDoTransform (xform, in, clut[b][g][r], 1);
}
}
}
cmsDeleteTransform (xform);
cmsCloseProfile (monitor);
cmsCloseProfile (sRGB);
glGenTextures (1, &clut_texture);
/* texture 1 = clut */
glActiveTextureARB (GL_TEXTURE0_ARB + 1);
glBindTexture (GL_TEXTURE_3D, clut_texture);
glTexParameteri (GL_TEXTURE_3D, GL_TEXTURE_WRAP_S, GL_CLAMP);
glTexParameteri (GL_TEXTURE_3D, GL_TEXTURE_WRAP_T, GL_CLAMP);
glTexParameteri (GL_TEXTURE_3D, GL_TEXTURE_WRAP_R, GL_CLAMP);
glTexParameteri (GL_TEXTURE_3D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameteri (GL_TEXTURE_3D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexImage3D (GL_TEXTURE_3D, 0, GL_RGB16, n, n, n,
0, GL_RGB, GL_UNSIGNED_SHORT, clut);
/* back to texture 0 = image */
glActiveTextureARB (GL_TEXTURE0_ARB);
}
Am 10.03.2015 um 00:09 schrieb Terence Tay:
Marti,
That is an interesting idea. Could you point out the relevant LCMS calls and
documentation to generate a 3D LUT from an ICC profile?
Terence
On Fri, Mar 6, 2015 at 6:08 PM, <marti.ma...@littlecms.com
<mailto:marti.ma...@littlecms.com>> wrote:
Quoting Noel Carboni <ncarb...@prodigitalsoftware.com
<mailto:ncarb...@prodigitalsoftware.com>>:
> Speaking of what the Adobe Color Engine can do... Is anyone
> considering porting Little CMS transformations to run on a GPU? :-)
Hi,
The trick is to use lcms2 to create a 3D Lut and then use the GPU and
trilinear interpolation. I think Media Player Classic is doing that.
Regards
Marti
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