Add simple (and naive) implementation of pixelate filter (#224)

* - add simple (and naive) implementation of pixelate filter

* - add golden

* - implement Pixelate as a non-receiver func

* - update golden

vips/image.go

@@ -1594,3 +1594,25 @@ const (
 	CodingLABQ  Coding = C.VIPS_CODING_LABQ
 	CodingRAD   Coding = C.VIPS_CODING_RAD
 )
+
+// Pixelate applies a simple pixelate filter to the image
+func Pixelate(imageRef *ImageRef, factor float64) (err error) {
+	if factor < 1 {
+		return errors.New("factor must be greater then 1")
+	}
+
+	width := imageRef.Width()
+	height := imageRef.Height()
+
+	if err = imageRef.Resize(1/factor, KernelAuto); err != nil {
+		return
+	}
+
+	hScale := float64(width) / float64(imageRef.Width())
+	vScale := float64(height) / float64(imageRef.Height())
+	if err = imageRef.ResizeWithVScale(hScale, vScale, KernelNearest); err != nil {
+		return
+	}
+
+	return
+}

vips/image_golden_test.go

@@ -878,6 +878,14 @@ func TestImage_QuantTable(t *testing.T) {
 	)
 }
 
+func TestImage_Pixelate(t *testing.T) {
+	goldenTest(t, resources+"jpg-24bit-icc-iec.jpg",
+		func(img *ImageRef) error {
+			return Pixelate(img, 24)
+		},
+		nil, nil)
+}
+
 func testWebpOptimizeIccProfile(t *testing.T, exportParams *WebpExportParams) []byte {
 	return goldenTest(t, resources+"has-icc-profile.png",
 		func(img *ImageRef) error {