Adds Recomb for ImageRef (#377)

* Add recombination functionality to image processing

A new function add img.Recomb support has been added to the ImageRef structure

* Add tests on ImageRef_Recomb

* Trigger CI

---------

Co-authored-by: Benny <benny.think@gmail.com>

vips/conversion.c

@@ -126,6 +126,10 @@ int flip_image(VipsImage *in, VipsImage **out, int direction) {
   return vips_flip(in, out, direction, NULL);
 }
 
+int recomb_image(VipsImage *in, VipsImage **out, VipsImage *m) {
+  return vips_recomb(in, out, m, NULL);
+}
+
 int extract_image_area(VipsImage *in, VipsImage **out, int left, int top,
                        int width, int height) {
   return vips_extract_area(in, out, left, top, width, height, NULL);

vips/conversion.go

@@ -212,6 +212,18 @@ func vipsFlip(in *C.VipsImage, direction Direction) (*C.VipsImage, error) {
 	return out, nil
 }
 
+// https://libvips.github.io/libvips/API/current/libvips-conversion.html#vips-recomb
+func vipsRecomb(in *C.VipsImage, m *C.VipsImage) (*C.VipsImage, error) {
+	incOpCounter("recomb")
+	var out *C.VipsImage
+
+	if err := C.recomb_image(in, &out, m); err != 0 {
+		return nil, handleImageError(out)
+	}
+
+	return out, nil
+}
+
 // https://libvips.github.io/libvips/API/current/libvips-conversion.html#vips-extract-area
 func vipsExtractArea(in *C.VipsImage, left, top, width, height int) (*C.VipsImage, error) {
 	incOpCounter("extractArea")

vips/conversion.h

@@ -20,6 +20,8 @@ int embed_multi_page_image_background(VipsImage *in, VipsImage **out, int left,
 
 int flip_image(VipsImage *in, VipsImage **out, int direction);
 
+int recomb_image(VipsImage *in, VipsImage **out, VipsImage *m);
+
 int extract_image_area(VipsImage *in, VipsImage **out, int left, int top,
                        int width, int height);
 int extract_area_multi_page(VipsImage *in, VipsImage **out, int left, int top,

vips/image.go

@@ -1774,6 +1774,55 @@ func (r *ImageRef) Flip(direction Direction) error {
 	return nil
 }
 
+// Recomb recombines the image bands using the matrix provided
+func (r *ImageRef) Recomb(matrix [][]float64) error {
+	numBands := r.Bands()
+	// Ensure the provided matrix is 3x3
+	if len(matrix) != 3 || len(matrix[0]) != 3 || len(matrix[1]) != 3 || len(matrix[2]) != 3 {
+		return errors.New("Invalid recombination matrix")
+	}
+	// If the image is RGBA, expand the matrix to 4x4
+	if numBands == 4 {
+		matrix = append(matrix, []float64{0, 0, 0, 1})
+		for i := 0; i < 3; i++ {
+			matrix[i] = append(matrix[i], 0)
+		}
+	} else if numBands != 3 {
+		return errors.New("Unsupported number of bands")
+	}
+
+	// Flatten the matrix
+	var matrixValues []float64
+	for _, row := range matrix {
+		for _, value := range row {
+			matrixValues = append(matrixValues, value)
+		}
+	}
+
+	// Convert the Go slice to a C array and get its size
+	matrixPtr := unsafe.Pointer(&matrixValues[0])
+	matrixSize := C.size_t(len(matrixValues) * 8) // 8 bytes for each float64
+
+	// Create a VipsImage from the matrix in memory
+	matrixImage := C.vips_image_new_from_memory(matrixPtr, matrixSize, C.int(numBands), C.int(numBands), 1, C.VIPS_FORMAT_DOUBLE)
+
+	// Check for any Vips errors
+	errMsg := C.GoString(C.vips_error_buffer())
+	if errMsg != "" {
+		C.vips_error_clear()
+		return errors.New("Vips error: " + errMsg)
+	}
+
+	// Recombine the image using the matrix
+	out, err := vipsRecomb(r.image, matrixImage)
+	if err != nil {
+		return err
+	}
+
+	r.setImage(out)
+	return nil
+}
+
 // Rotate rotates the image by multiples of 90 degrees. To rotate by arbitrary angles use Similarity.
 func (r *ImageRef) Rotate(angle Angle) error {
 	width := r.Width()

vips/image_test.go

@@ -672,6 +672,38 @@ func TestImageRef_CompositeMulti(t *testing.T) {
 	require.NoError(t, err)
 }
 
+func TestImageRef_Recomb(t *testing.T) {
+	Startup(nil)
+
+	image, err := NewImageFromFile(resources + "png-24bit.png")
+	require.NoError(t, err)
+
+	matrix := [][]float64{
+		{0.3588, 0.7044, 0.1368},
+		{0.2990, 0.5870, 0.1140},
+		{0.2392, 0.4696, 0.0912},
+	}
+
+	err = image.Recomb(matrix)
+	require.NoError(t, err)
+}
+
+func TestImageRef_Recomb_Error(t *testing.T) {
+	Startup(nil)
+
+	image, err := NewImageFromFile(resources + "png-24bit.png")
+	require.NoError(t, err)
+
+	matrix := [][]float64{
+		{0.3588, 0.7044, 0.1368, 0},
+		{0.2990, 0.5870, 0.1140, 0},
+		{0.2392, 0.4696, 0.0912, 0},
+	}
+
+	err = image.Recomb(matrix)
+	require.Error(t, err)
+}
+
 func TestCopy(t *testing.T) {
 	Startup(nil)