animate.sh

for n in {10..85}; do
   ./pixmaker -s $n -src ~/heartbleed.png ~/frame$n.png
done

gifme --reverse ~/Desktop/frame*.png

pixmaker.go

package main

import (
	"flag"
	"image"
	"image/color"
	"image/draw"
	"log"
	"os"

	"image/png"
)

func dominate(im image.Image, r image.Rectangle) color.Color {
	colors := make(map[color.Color]int)
	for y := r.Min.Y; y < r.Max.Y; y++ {
		for x := r.Min.X; x < r.Max.X; x++ {
			c := im.At(x, y)
			if v, exists := colors[c]; exists {
				colors[c] = v + 1
			} else {
				colors[c] = 1
			}
		}
	}

	var color color.Color
	max := -1
	for k, v := range colors {
		if v > max {
			color = k
			max = v
		}
	}

	return color
}

var src = flag.String("src", "", "source image (must be PNG)")
var dest = flag.String("dest", "", "destination image (must be PNG)")
var SIZE = flag.Int("s", 10, "width / height of box")

func main() {
	flag.Parse()

	if *src == "" && *dest == "" {
		log.Fatal("neither src nor dest can be empty")
	}

	reader, err := os.Open(*src)
	if err != nil {
		log.Fatal(err)
	}
	defer reader.Close()

	writer, err := os.Create(*dest)
	if err != nil {
		log.Fatal(err)
	}
	defer writer.Close()

	m, _, err := image.Decode(reader)
	if err != nil {
		log.Fatal(err)
	}

	bounds := m.Bounds()

	images := make(map[color.Color]image.Image)

	pt := image.Pt(0, 0)
	out := image.NewRGBA(bounds)

	for y := bounds.Min.Y; y < bounds.Max.Y; y = y + *SIZE {
		for x := bounds.Min.X; x < bounds.Max.X; x = x + *SIZE {
			rect := image.Rect(x, y, x+*SIZE, y+*SIZE)
			color := dominate(m, rect)
			if _, exists := images[color]; !exists {
				images[color] = image.NewUniform(color)
			}
			pt.X = x
			pt.Y = y
			draw.Draw(out, rect, images[color], pt, draw.Src)
		}
	}

	png.Encode(writer, out)
}