Merge pull request #104 from nvartolomei/png-16bit-alpha-background

fixes #103 flattening with background for 16bit transparent pngs

vips.h

@@ -244,11 +244,21 @@ vips_webpsave_bridge(VipsImage *in, void **buf, size_t *len, int strip, int qual
 	);
 }
 
+int
+vips_is_16bit (VipsInterpretation interpretation) {
+	return interpretation == VIPS_INTERPRETATION_RGB16 || interpretation == VIPS_INTERPRETATION_GREY16;
+}
+
 int
 vips_flatten_background_brigde(VipsImage *in, VipsImage **out, double background[3]) {
+	background[0] *= 256;
+	background[1] *= 256;
+	background[2] *= 256;
+
 	VipsArrayDouble *vipsBackground = vips_array_double_new(background, 3);
 	return vips_flatten(in, out,
 		"background", vipsBackground,
+		"max_alpha", vips_is_16bit(in->Type) ? 65535.0 : 255.0,
 		NULL
 	);
 }