Merge pull request #293 from team-lab/gammaFilter

Gamma filter support

image.go

@@ -185,6 +185,12 @@ func (i *Image) Trim() ([]byte, error) {
 	return i.Process(options)
 }
 
+// Gamma returns the gamma filtered image buffer.
+func (i *Image) Gamma(exponent float64) ([]byte, error) {
+	options := Options{Gamma: exponent}
+	return i.Process(options)
+}
+
 // Process processes the image based on the given transformation options,
 // talking with libvips bindings accordingly and returning the resultant
 // image buffer.

options.go

@@ -222,5 +222,6 @@ type Options struct {
 	GaussianBlur   GaussianBlur
 	Sharpen        Sharpen
 	Threshold      float64
+	Gamma          float64
 	OutputICC      string
 }

resizer.go

@@ -125,6 +125,12 @@ func resizer(buf []byte, o Options) ([]byte, error) {
 		return nil, err
 	}
 
+	// Apply Gamma filter, if necessary
+	image, err = applyGamma(image, o)
+	if err != nil {
+		return nil, err
+	}
+
 	return saveImage(image, o)
 }
 
@@ -382,6 +388,17 @@ func imageFlatten(image *C.VipsImage, imageType ImageType, o Options) (*C.VipsIm
 	return vipsFlattenBackground(image, o.Background)
 }
 
+func applyGamma(image *C.VipsImage, o Options) (*C.VipsImage, error) {
+	var err error
+	if o.Gamma > 0 {
+		image, err = vipsGamma(image, o.Gamma)
+		if err != nil {
+			return nil, err
+		}
+	}
+	return image, nil
+}
+
 func zoomImage(image *C.VipsImage, zoom int) (*C.VipsImage, error) {
 	if zoom == 0 {
 		return image, nil

vips.go

@@ -723,3 +723,14 @@ func vipsDrawWatermark(image *C.VipsImage, o WatermarkImage) (*C.VipsImage, erro
 
 	return out, nil
 }
+
+func vipsGamma(image *C.VipsImage, Gamma float64) (*C.VipsImage, error) {
+	var out *C.VipsImage
+	defer C.g_object_unref(C.gpointer(image))
+
+	err := C.vips_gamma_bridge(image, &out, C.double(Gamma))
+	if err != 0 {
+		return nil, catchVipsError()
+	}
+	return out, nil
+}

vips.h

@@ -592,3 +592,8 @@ int vips_find_trim_bridge(VipsImage *in, int *top, int *left, int *width, int *h
 	return 0;
 #endif
 }
+
+int vips_gamma_bridge(VipsImage *in, VipsImage **out, double exponent)
+{
+  return vips_gamma(in, out, "exponent", 1.0 / exponent, NULL);
+}