static GdkPixbuf *pixbuf_gamma(GdkPixbuf *src, GdkPixbuf *dest, double gamma) {
    int has_alpha;
    int s_width, s_height, s_rowstride;
    int d_width, d_height, d_rowstride;
    guchar *s_pix;
    guchar *d_pix;
    guchar *sp;
    guchar *dp;
    int i, j, pix_width;
    double map[256] = {0.0,};

    for (i = 0; i < 256; i++)
        map[i] = 255 * pow((double) i / 255, 1.0 / gamma);

    g_return_val_if_fail(src != NULL, NULL);
    g_return_val_if_fail(dest != NULL, NULL);

    s_width = gdk_pixbuf_get_width(src);
    s_height = gdk_pixbuf_get_height(src);
    has_alpha = gdk_pixbuf_get_has_alpha(src);
    s_rowstride = gdk_pixbuf_get_rowstride(src);
    s_pix = gdk_pixbuf_get_pixels(src);

    d_width = gdk_pixbuf_get_width(dest);
    d_height = gdk_pixbuf_get_height(dest);
    d_rowstride = gdk_pixbuf_get_rowstride(dest);
    d_pix = gdk_pixbuf_get_pixels(dest);

    g_return_val_if_fail(d_width == s_width, NULL);
    g_return_val_if_fail(d_height == s_height, NULL);
    g_return_val_if_fail(has_alpha == gdk_pixbuf_get_has_alpha(dest), NULL);

    pix_width = (has_alpha ? 4 : 3);

    for (i = 0; i < s_height; i++) {
        sp = s_pix + (i * s_rowstride);
        dp = d_pix + (i * d_rowstride);
        for (j = 0; j < s_width; j++) {
            *(dp++) = map[*(sp++)];    /* red */
            *(dp++) = map[*(sp++)];    /* green */
            *(dp++) = map[*(sp++)];    /* blue */
            if (has_alpha) *(dp++) = map[*(sp++)];    /* alpha */
        }
    }

    return dest;
}