dither/main.go

package main

import (
	"fmt"
	"image"
	"image/color"
	_ "image/jpeg"
	"image/png"
	"math/rand"
	"os"
	"time"
)

type coord struct {
	x, y int
}

// provided x, y, and color at location, return a color
type quantizerFunction func(int, int, color.Color) color.Color

// apply sequentially applies a quantizing function to an image and returns the result
func apply(i image.Image, f quantizerFunction) image.Image {
	out := image.NewRGBA(image.Rect(0, 0, i.Bounds().Max.X, i.Bounds().Max.Y))

	b := out.Bounds()
	for y := b.Min.Y; y < b.Max.Y; y++ {
		for x := b.Min.X; x < b.Max.X; x++ {
			out.Set(x, y, f(x, y, i.At(x, y)))
		}
	}

	return out
}

func main() {
	if len(os.Args) == 1 || len(os.Args) > 4 || os.Args[1] == "help" {
		fmt.Printf(`usage: %s <path/to/image.ext> <dither_option> <path/to/output.png>
  Supported dither options are: noop; naive; randomnoise; bayer{0,1}; bayer{0,1}n
  Supported input image formats are jpg, png
`, os.Args[0])
		os.Exit(0)
	}

	filename := os.Args[1]
	ditherer := os.Args[2]
	outfile := os.Args[3]

	i, codex, err := loadImage(filename)
	if err != nil {
		fmt.Printf("error loading %s; %v\n", filename, err)
		os.Exit(255)
	}
	fmt.Printf("loaded %s using %s\n", filename, codex)

	t := time.Now()

	var new image.Image
	switch ditherer {
	case "noop":
		new = apply(i, noOp)
	case "naive":
		new = apply(i, naiveBW)
	case "palette":
		new = apply(i, naivePalette(sixteencolors))
	case "randomnoise":
		rand.Seed(time.Now().UnixNano())
		new = apply(i, randomNoise)
	case "noisepalette":
		rand.Seed(time.Now().UnixNano())
		new = apply(i, randomNoisePalette(sixteencolors))
	case "bayer0":
		new = apply(i, bayerDithering(0, false))
	case "bayer0p":
		new = apply(i, colorBayer(0, sixteencolors))
	case "bayer0n":
		new = apply(i, bayerDithering(0, true))
	case "bayer1":
		new = apply(i, bayerDithering(1, false))
	case "bayer1n":
		new = apply(i, bayerDithering(1, true))
	case "bayer1p":
		new = apply(i, colorBayer(1, sixteencolors))
	case "simpleerror":
		new = apply(i, simpleErrorDiffusion())
	case "floydsteinberg":
		new = apply(i, floydSteinberg())
	case "jjn":
		new = apply(i, jarvisJudiceNinke())
	case "atkinson":
		new = apply(i, atkinson())
	default:
		fmt.Printf("unknown ditherer option: %s\n", ditherer)
		os.Exit(2)
	}

	fmt.Printf("dithering took %s\n", time.Since(t))

	err = saveImage(outfile, new)
	if err != nil {
		fmt.Printf("error saving %s; %v\n", outfile, err)
		os.Exit(255)
	}
	fmt.Printf("saved output to %s\n", outfile)
}

func loadImage(filename string) (image.Image, string, error) {
	r, err := os.Open(filename)
	if err != nil {
		return nil, "", err
	}
	return image.Decode(r)
}

func saveImage(filename string, img image.Image) error {
	f, err := os.Create(filename)
	if err != nil {
		return err
	}

	if err := png.Encode(f, img); err != nil {
		f.Close()
		return err
	}

	if err := f.Close(); err != nil {
		return err
	}

	return nil
}