chromab.c

#include <gd.h>

typedef struct {
    int rx, ry, gx, gy, bx, by;
} coloffset;

/* expect im and out to have the same dimensions */
void chromab(gdImagePtr im, gdImagePtr out, int frm,
             coloffset offsetfunc(int, int, int)) {
    int x, y, colin, colout, coldest, black, sx, sy,
        r, g, b, rx, ry, gx, gy, bx, by;
    coloffset co;

    black = gdImageColorResolve(out, 0, 0, 0);
    gdImageFilledRectangle(out, 0, 0, out->sx, out->sy, black);
    for (y=0; y<im->sy; y++)
        for (x=0; x<im->sx; x++) {
            co = offsetfunc(frm, x, y);
            rx = co.rx; ry = co.ry;
            gx = co.gx; gy = co.gy;
            bx = co.bx; by = co.by;
            colin = gdImageGetPixel(im, x, y);
            /* red */
            coldest = gdImageGetPixel(out, x+rx, y+ry);
            r = gdImageRed  (out, coldest) + gdImageRed(im, colin);
            g = gdImageGreen(out, coldest);
            b = gdImageBlue (out, coldest);
            r = r<255?r:255; g = g<255?g:255; b = b<255?b:255;
            colout = gdImageColorResolve(out, r, g, b);
            gdImageSetPixel(out, x+rx, y+ry, colout);
            gdImageColorDeallocate(out, colout);
            /* green */
            coldest = gdImageGetPixel(out, x+gx, y+gy);
            r = gdImageRed  (out, coldest);
            g = gdImageGreen(out, coldest) + gdImageGreen(im, colin);
            b = gdImageBlue (out, coldest);
            r = r<255?r:255; g = g<255?g:255; b = b<255?b:255;
            colout = gdImageColorResolve(out, r, g, b);
            gdImageSetPixel(out, x+gx, y+gy, colout);
            gdImageColorDeallocate(out, colout);
            /* blue */
            coldest = gdImageGetPixel(out, x+bx, y+by);
            r = gdImageRed  (out, coldest);
            g = gdImageGreen(out, coldest);
            b = gdImageBlue (out, coldest) + gdImageBlue(im, colin);
            r = r<255?r:255; g = g<255?g:255; b = b<255?b:255;
            colout = gdImageColorResolve(out, r, g, b);
            gdImageSetPixel(out, x+bx, y+by, colout);
            gdImageColorDeallocate(out, colout);
        }
}