Add support for colourspace (fix #45)

image.go

@@ -134,6 +134,12 @@ func (i *Image) Convert(t ImageType) ([]byte, error) {
 	return i.Process(options)
 }
 
+// Colour space conversion
+func (i *Image) Colourspace(c Interpretation) ([]byte, error) {
+	options := Options{Interpretation: c}
+	return i.Process(options)
+}
+
 // Transform the image by custom options
 func (i *Image) Process(o Options) ([]byte, error) {
 	image, err := Resize(i.buffer, o)

image_test.go

@@ -262,6 +262,14 @@ func TestImageMetadata(t *testing.T) {
 	}
 }
 
+func TestImageColourspaceBW(t *testing.T) {
+	buf, err := initImage("test.jpg").Colourspace(B_W)
+	if err != nil {
+		t.Errorf("Cannot process the image: %#v", err)
+	}
+	Write("fixtures/test_image_colourspace_b_w.jpg", buf)
+}
+
 func TestFluentInterface(t *testing.T) {
 	image := initImage("test.jpg")
 	_, err := image.CropByWidth(300)

options.go

@@ -55,6 +55,20 @@ const (
 	VERTICAL   Direction = C.VIPS_DIRECTION_VERTICAL
 )
 
+type Interpretation int
+
+const (
+	ERROR Interpretation = C.VIPS_INTERPRETATION_ERROR
+	MULTIBAND Interpretation = C.VIPS_INTERPRETATION_MULTIBAND
+	B_W Interpretation = C.VIPS_INTERPRETATION_B_W
+	CMYK Interpretation = C.VIPS_INTERPRETATION_CMYK
+	RGB Interpretation = C.VIPS_INTERPRETATION_RGB
+	sRGB Interpretation = C.VIPS_INTERPRETATION_sRGB
+	RGB16 Interpretation = C.VIPS_INTERPRETATION_RGB16
+	GREY16 Interpretation = C.VIPS_INTERPRETATION_GREY16
+	scRGB Interpretation = C.VIPS_INTERPRETATION_scRGB
+)
+
 const WATERMARK_FONT = "sans 10"
 
 // Color represents a traditional RGB color scheme
@@ -97,4 +111,5 @@ type Options struct {
 	Watermark    Watermark
 	Type         ImageType
 	Interpolator Interpolator
+	Interpretation Interpretation
 }

resize.go

@@ -122,6 +122,7 @@ func Resize(buf []byte, o Options) ([]byte, error) {
 		Compression: o.Compression,
 		Interlace:   o.Interlace,
 		NoProfile:   o.NoProfile,
+		Interpretation: o.Interpretation,
 	}
 
 	// Finally save as buffer
@@ -143,6 +144,9 @@ func applyDefaults(o *Options, imageType ImageType) {
 	if o.Type == 0 {
 		o.Type = imageType
 	}
+	if o.Interpretation == 0 {
+		o.Interpretation = sRGB
+	}
 }
 
 func normalizeOperation(o *Options, inWidth, inHeight int) {

vips.go

@@ -37,6 +37,7 @@ type vipsSaveOptions struct {
 	Type        ImageType
 	Interlace   bool
 	NoProfile   bool
+	Interpretation Interpretation
 }
 
 type vipsWatermarkOptions struct {
@@ -227,6 +228,10 @@ func vipsSave(image *C.struct__VipsImage, o vipsSaveOptions) ([]byte, error) {
 	length := C.size_t(0)
 	err := C.int(0)
 	interlace := C.int(boolToInt(o.Interlace))
+	if o.Interpretation == 0 {
+		o.Interpretation = sRGB
+	}
+	interpretation := C.VipsInterpretation(o.Interpretation)
 
 	// Remove ICC profile metadata
 	if o.NoProfile {
@@ -235,7 +240,7 @@ func vipsSave(image *C.struct__VipsImage, o vipsSaveOptions) ([]byte, error) {
 
 	// Force RGB color space
 	var outImage *C.struct__VipsImage
-	C.vips_colourspace_bridge(image, &outImage)
+	C.vips_colourspace_bridge(image, &outImage, interpretation)
 
 	defer C.g_object_unref(C.gpointer(image))
 	defer C.g_object_unref(C.gpointer(outImage))

vips.h

@@ -135,9 +135,9 @@ vips_extract_area_bridge(VipsImage *in, VipsImage **out, int left, int top, int
 };
 
 int
-vips_colourspace_bridge(VipsImage *in, VipsImage **out)
+vips_colourspace_bridge(VipsImage *in, VipsImage **out, VipsInterpretation space)
 {
-    return vips_colourspace(in, out, VIPS_INTERPRETATION_sRGB, NULL);
+    return vips_colourspace(in, out, space, NULL);
 };
 
 gboolean