new simple downscaling ideas

pkg/dithering/grid.go

@@ -7,6 +7,7 @@ import (
 
 const side = 16
 
+// tile
 type grid struct {
 	color.Gray
 	Factor float64

pkg/downscale/downscale.go

@@ -1,4 +1,4 @@
-package main
+package downscale
 
 import (
 	"errors"

pkg/downscale/grid.go

@@ -0,0 +1,68 @@
+package downscale
+
+type sub struct {
+	image.Image
+	image.Rectangle
+}
+
+func (sub sub) ColorModel() color.Model { return sub.Image.ColorModel() }
+func (sub sub) Bounds() image.Rectangle { return sub.Rectangle }
+func (sub sub) At(x, y int) color.Color {
+	return sub.Image.At(x, y)
+}
+
+type GridDownscale struct {
+	image.Image
+	newBounds image.Rectangle
+}
+
+func blend(c1, c2 color.Color) color.RGBA {
+	r1, g1, b1, a1 := c1.RGBA()
+	r2, g2, b2, a2 := c2.RGBA()
+
+	r := r1/2 + r2/2
+	g := g1/2 + g2/2
+	b := b1/2 + b2/2
+	a := a1/2 + a2/2
+
+	return color.RGBA{
+		R: uint8(r >> 8),
+		G: uint8(g >> 8),
+		B: uint8(b >> 8),
+		A: uint8(a >> 8),
+	}
+}
+
+func avgColor(img image.Image) (c color.Color) {
+	dx, dy := img.Bounds().Dx(), img.Bounds().Dy()
+	for y := 0; y < dy; y++ {
+		for x := 0; x < dx; x++ {
+			c = blend(c, img.At(x, y))
+		}
+	}
+	return
+}
+
+func (grid grid) ColorModel() color.Model { return grid.Image.ColorModel }
+func (grid grid) Bounds() image.Rectangle { return grid.NewBounds }
+func (grid grid) At(x, y int) color.Color {
+	b := grid.Image.Bounds()
+	dx, dy := b.Dx(), b.Dy()
+	cellBounds := image.Rect(
+		0, 0,
+		dx/grid.newBounds.Dx(),
+		dy/grid.newBounds.Dy(),
+	)
+
+	r := grid.Image.Bounds().Intersect(
+		// move cell
+		cellBounds.Add(
+			image.Point{
+				x * cellBounds.Dx(),
+				y * cellBounds.Dy(),
+			},
+		),
+	)
+
+	return avgColor(sub{grid.Image, r})
+}

pkg/downscale/grid_test.go

@@ -0,0 +1 @@
+package downscale

pkg/downscale/main.go

@@ -1,21 +0,0 @@
-package main
-
-import (
-	"image/jpeg"
-	"image/png"
-	"os"
-)
-
-func main() {
-	// open image
-	img, err := jpeg.Decode(os.Stdin)
-	if err != nil {
-		panic(err)
-	}
-	// no pre-processing needed so we just
-	// write image
-	err = png.Encode(os.Stdout, Downscaled{img, 3})
-	if err != nil {
-		panic(err)
-	}
-}