Support brightness and contrast

options.go

@@ -223,6 +223,8 @@ type Options struct {
 	Sharpen        Sharpen
 	Threshold      float64
 	Gamma          float64
+	Brightness     float64
+	Contrast       float64
 	OutputICC      string
 	InputICC       string
 	Palette        bool

resizer.go

@@ -142,6 +142,18 @@ func resizer(buf []byte, o Options) ([]byte, error) {
 		return nil, err
 	}
 
+	// Apply brightness, if necessary
+	image, err = applyBrightness(image, o)
+	if err != nil {
+		return nil, err
+	}
+
+	// Apply contrast, if necessary
+	image, err = applyContrast(image, o)
+	if err != nil {
+		return nil, err
+	}
+
 	return saveImage(image, o)
 }
 
@@ -610,3 +622,25 @@ func getAngle(angle Angle) Angle {
 	}
 	return Angle(math.Min(float64(angle), 270))
 }
+
+func applyBrightness(image *C.VipsImage, o Options) (*C.VipsImage, error) {
+	var err error
+	if o.Brightness != 0 {
+		image, err = vipsBrightness(image, o.Brightness)
+		if err != nil {
+			return nil, err
+		}
+	}
+	return image, nil
+}
+
+func applyContrast(image *C.VipsImage, o Options) (*C.VipsImage, error) {
+	var err error
+	if o.Contrast > 0 {
+		image, err = vipsContrast(image, o.Contrast)
+		if err != nil {
+			return nil, err
+		}
+	}
+	return image, nil
+}

vips.go

@@ -830,3 +830,25 @@ func vipsGamma(image *C.VipsImage, Gamma float64) (*C.VipsImage, error) {
 	}
 	return out, nil
 }
+
+func vipsBrightness(image *C.VipsImage, brightness float64) (*C.VipsImage, error) {
+	var out *C.VipsImage
+	defer C.g_object_unref(C.gpointer(image))
+
+	err := C.vips_brightness_bridge(image, &out, C.double(brightness))
+	if err != 0 {
+		return nil, catchVipsError()
+	}
+	return out, nil
+}
+
+func vipsContrast(image *C.VipsImage, contrast float64) (*C.VipsImage, error) {
+	var out *C.VipsImage
+	defer C.g_object_unref(C.gpointer(image))
+
+	err := C.vips_contrast_bridge(image, &out, C.double(contrast))
+	if err != 0 {
+		return nil, catchVipsError()
+	}
+	return out, nil
+}

vips.h

@@ -656,3 +656,13 @@ int vips_gamma_bridge(VipsImage *in, VipsImage **out, double exponent)
 {
   return vips_gamma(in, out, "exponent", 1.0 / exponent, NULL);
 }
+
+int vips_brightness_bridge(VipsImage *in, VipsImage **out, double k)
+{
+    return vips_linear1(in, out, 1.0 , k, NULL);
+}
+
+int vips_contrast_bridge(VipsImage *in, VipsImage **out, double k)
+{
+    return vips_linear1(in, out, k , 0.0, NULL);
+}