Initial orientator

internal/detector/preprocess.go

@@ -0,0 +1,53 @@
+package detector
+
+import (
+	"image"
+	"image/color"
+	stddraw "image/draw"
+
+	xdraw "golang.org/x/image/draw"
+)
+
+const ImgSize = 1200
+
+// Preprocess implements the Python reference exactly:
+// 1. resize keeping aspect ratio to fit in 1200x1200 (Lanczos-equivalent CatmullRom)
+// 2. paste onto white 1200x1200 canvas at (0,0)
+// 3. normalize: (x/255 - 0.5) / 0.5
+// 4. HWC -> CHW with batch dim -> [1, 3, 1200, 1200]
+func Preprocess(img image.Image) []float32 {
+	bounds := img.Bounds()
+	w, h := bounds.Dx(), bounds.Dy()
+
+	scale := float64(ImgSize) / float64(w)
+	if s := float64(ImgSize) / float64(h); s < scale {
+		scale = s
+	}
+	newW := int(float64(w) * scale)
+	newH := int(float64(h) * scale)
+	if newW < 1 {
+		newW = 1
+	}
+	if newH < 1 {
+		newH = 1
+	}
+
+	canvas := image.NewRGBA(image.Rect(0, 0, ImgSize, ImgSize))
+	stddraw.Draw(canvas, canvas.Bounds(), &image.Uniform{C: color.RGBA{255, 255, 255, 255}}, image.Point{}, stddraw.Src)
+	xdraw.CatmullRom.Scale(canvas, image.Rect(0, 0, newW, newH), img, bounds, xdraw.Over, nil)
+
+	out := make([]float32, 3*ImgSize*ImgSize)
+	plane := ImgSize * ImgSize
+	pix := canvas.Pix
+	for y := 0; y < ImgSize; y++ {
+		row := y * canvas.Stride
+		base := y * ImgSize
+		for x := 0; x < ImgSize; x++ {
+			i := row + x*4
+			out[base+x] = float32(pix[i+0])/127.5 - 1
+			out[plane+base+x] = float32(pix[i+1])/127.5 - 1
+			out[2*plane+base+x] = float32(pix[i+2])/127.5 - 1
+		}
+	}
+	return out
+}