map2_rgb
Tcl_Obj* imageObj
Tcl_Obj* redMapImageObj
Tcl_Obj* greenMapImageObj
Tcl_Obj* blueMapImageObj
int redControlChannel
int greenControlChannel
int blueControlChannel

/*
 * This operation is a generalized per-pixel transformation, mapping pixel
 * values to other pixel values in a completely arbitrary way. In contrast to
 * the map_* family of primitives here the mapping for one channel is
 * controlled by the data in a second channel. I.e. instead of a 256x1 table
 * we have 256 of these, in a single 256x256 map, with one channel selecting
 * the map to use for the other. Effects possible with this are hue-dependent
 * changes to saturation or value, value dependent color-shifts, etc.
 *
 * Important: For the sake of convenience the map is not provided as a (Tcl)
 * list (of values), or array, but as an _image_ itself, a 256x256 (WxH)
 * grey8. We have constructors for such images (read-tcl primitive).
 */

crimp_image*     result;
crimp_image*     image;
crimp_image*     redMap;
crimp_image*     greenMap;
crimp_image*     blueMap;
int              x, y;

crimp_input (imageObj,         image,    rgb);
crimp_input (redMapImageObj,   redMap,   grey8);
crimp_input (greenMapImageObj, greenMap, grey8);
crimp_input (blueMapImageObj,  blueMap,  grey8);

if (!crimp_require_dim (redMap, 256, 256)) {
    Tcl_SetResult(interp, "bad image dimension for red map, expected 256x256", TCL_STATIC);
    return TCL_ERROR;
}

if (!crimp_require_dim (greenMap, 256, 256)) {
    Tcl_SetResult(interp, "bad image dimension for green map, expected 256x256", TCL_STATIC);
    return TCL_ERROR;
}

if (!crimp_require_dim (blueMap, 256, 256)) {
    Tcl_SetResult(interp, "bad image dimension for blue map, expected 256x256", TCL_STATIC);
    return TCL_ERROR;
}

if (!RANGEOK (redControlChannel,2)) {
    Tcl_SetResult(interp, "bad control for red map, expected index in (0...2)", TCL_STATIC);
    return TCL_ERROR;
}

if (!RANGEOK (greenControlChannel,2)) {
    Tcl_SetResult(interp, "bad control for green map, expected index in (0...2)", TCL_STATIC);
    return TCL_ERROR;
}

if (!RANGEOK (blueControlChannel,2)) {
    Tcl_SetResult(interp, "bad control for blue map, expected index in (0...2)", TCL_STATIC);
    return TCL_ERROR;
}

result = crimp_new_like (image);

for (y = 0; y < result->h; y++) {
    for (x = 0; x < result->w; x++) {

	/*
	 * Run the pixel value of the input image through the map to
	 * produce the value for the output.
	 */

      R (result, x, y) = GREY8 (redMap,   R (image, x, y), CH (image, redControlChannel,   x, y));
      G (result, x, y) = GREY8 (greenMap, G (image, x, y), CH (image, greenControlChannel, x, y));
      B (result, x, y) = GREY8 (blueMap,  B (image, x, y), CH (image, blueControlChannel,  x, y));
    }
}

Tcl_SetObjResult(interp, crimp_new_image_obj (result));
return TCL_OK;


/* vim: set sts=4 sw=4 tw=80 et ft=c: */
/*
 * Local Variables:
 * mode: c
 * c-basic-offset: 4
 * fill-column: 78
 * End:
 */