DarknetImage move float conversion into c code

imgTofloat32 + fill_image_f32 took more than double the time since tofloat created needless allocations and iterate over each pixel, and fill_image in c then iterate over each pixel*3 again just to move it into the c image.

image.c

@@ -11,3 +11,18 @@ void set_data_f32_val(float* data, int index, float value) {
     data[index] = value;
 }
 
+void to_float_and_fill_image(image* im, int w, int h, uint8_t* data) {
+    int x, y, idx_source;
+    int pixel_count = w * h;
+    int idx = 0;
+
+    for (y = 0; y < h; y++) {
+        for (x = 0; x < w; x++) {
+            idx_source = (y*w + x) * 4;
+            im->data[(pixel_count*0) + idx] = (float)data[idx_source] / 255;
+            im->data[(pixel_count*1) + idx] = (float)data[idx_source+1] / 255;
+            im->data[(pixel_count*2) + idx] = (float)data[idx_source+2] / 255;
+            idx++;
+        }
+    }
+}

image.go

@@ -14,61 +14,33 @@ import (
 type DarknetImage struct {
 	Width  int
 	Height int
-	ans    []float32
 	image  C.image
 }
 
 // Close and release resources.
 func (img *DarknetImage) Close() error {
 	C.free_image(img.image)
-	img.ans = nil
 	return nil
 }
 
-// https://stackoverflow.com/questions/33186783/get-a-pixel-array-from-from-golang-image-image/59747737#59747737
-func imgTofloat32(src image.Image) []float32 {
+func Image2Float32(src image.Image) (*DarknetImage, error) {
 	bounds := src.Bounds()
-	width, height := bounds.Max.X, bounds.Max.Y
-	srcRGBA := image.NewRGBA(src.Bounds())
-	draw.Copy(srcRGBA, image.Point{}, src, src.Bounds(), draw.Src, nil)
+	srcRGBA := image.NewRGBA(bounds)
+	draw.Copy(srcRGBA, image.Point{}, src, bounds, draw.Src, nil)
 
-	red := make([]float32, 0, width*height)
-	green := make([]float32, 0, width*height)
-	blue := make([]float32, 0, width*height)
-	for y := 0; y < height; y++ {
-		for x := 0; x < width; x++ {
-			idxSource := (y*width + x) * 4
-			pix := srcRGBA.Pix[idxSource : idxSource+4]
-			rpix, gpix, bpix := float32(pix[0])/257.0, float32(pix[1])/257.0, float32(pix[2])/257.0
-			red = append(red, rpix)
-			green = append(green, gpix)
-			blue = append(blue, bpix)
-		}
-	}
-	srcRGBA = nil
-
-	ans := make([]float32, len(red)+len(green)+len(blue))
-	copy(ans[:len(red)], red)
-	copy(ans[len(red):len(red)+len(green)], green)
-	copy(ans[len(red)+len(green):], blue)
-	red = nil
-	green = nil
-	blue = nil
-	return ans
+	return ImageRGBA2Float32(srcRGBA)
 }
 
 // Image2Float32 Returns []float32 representation of image.Image
-func Image2Float32(img image.Image) (*DarknetImage, error) {
-	// ans := imgTofloat32(img)
+func ImageRGBA2Float32(img *image.RGBA) (*DarknetImage, error) {
 	width := img.Bounds().Dx()
 	height := img.Bounds().Dy()
 	imgDarknet := &DarknetImage{
 		Width:  width,
 		Height: height,
-		ans:    imgTofloat32(img),
 		image:  C.make_image(C.int(width), C.int(height), 3),
 	}
-	C.fill_image_f32(&imgDarknet.image, C.int(width), C.int(height), 3, (*C.float)(unsafe.Pointer(&imgDarknet.ans[0])))
+	C.to_float_and_fill_image(&imgDarknet.image, C.int(width), C.int(height), (*C.uint8_t)(unsafe.Pointer(&img.Pix[0])))
 	return imgDarknet, nil
 }
 

image.h

@@ -3,4 +3,5 @@
 #include <darknet.h>
 
 extern void fill_image_f32(image *im, int w, int h, int c, float* data);
-extern void set_data_f32_val(float* data, int index, float value);
+extern void set_data_f32_val(float* data, int index, float value);
+extern void to_float_and_fill_image(image *im, int w, int h, uint8_t* data);