a new function

floatimg.h

@@ -122,6 +122,7 @@ int fimg_cos_010(FloatImg *s, FloatImg *d, double maxval);
 
 
 int fimg_mix_rgb_gray(FloatImg *img, float mix);
+int     fimg_shift_to_zero(FloatImg *s, FloatImg *d, float coefs[6]);
 
 
 /*	module funcs/geometry.c		*/

funcs/saturation.c

@@ -41,4 +41,26 @@ for (y=0; y<img->height; y++) {
 return 0;
 }
 
+/* -------------------------------------------------------------- */
+int     fimg_shift_to_zero(FloatImg *s, FloatImg *d, float coefs[6])
+{
+int             sz, idx;
+
+sz = s->width * s->height;
+
+if (FIMG_TYPE_RGB != img->type) {
+	fprintf(stderr, "%s bad type\n", __func__);
+	return -6;
+	}
+
+for (idx=0; idx<sz; idx++) {
+	d->R[idx] = s->R[idx] - coefs[0];
+	d->G[idx] = s->G[idx] - coefs[2];
+	d->B[idx] = s->B[idx] - coefs[4];
+	}
+
+return 0;
+}
+
+
 /* -------------------------------------------------------------- */