threshold_qerror.go

package main

import (
	"fmt"
	"image"
	"image/color"
	"image/png"
	"math"
	"os"
)

func Treshold(img image.Image, t float32) (image.Image, image.Image) {

    result := image.NewGray(img.Bounds())
    qerr := image.NewGray(img.Bounds())
    
    for y := img.Bounds().Min.Y; y < img.Bounds().Max.Y; y++ {
        for x := img.Bounds().Min.X; x < img.Bounds().Max.X; x++ {
            r, g, b, _ := img.At(x, y).RGBA()

            v := float32(uint8((r + g + b) / 3)) / 255.0
            
            var final uint8
            if v > t {
                final = 255
            }  else {
                final = 0
            }

            result.Set(x, y, color.Gray{ final })
            delta := math.Abs(float64(final) - float64(255.0 * v))
            qerr.Set(x, y, color.Gray{ uint8(delta) })
        }
    }

    return result, qerr
}

func main() {
    r, err := os.Open("image.png")
    if err != nil {
        panic(err)
    }

    img, err := png.Decode(r)
    if err != nil {
        panic(err)
    }
    
    out, qerr := Treshold(img, 0.6)

    w, err := os.Create("out.png")
    if err != nil {
        panic(err)
    }

    w2, err := os.Create("qerr.png")
    if err != nil {
        panic(err)
    }
    err = png.Encode(w, out)
    err = png.Encode(w2, qerr)

    if err != nil {
        panic(err)
    }

    fmt.Println("Dither")
}