grayscale converter

.gitignore

*.jpg
*.jpeg
*.png
*.gif

main.go

package main

import (
	"flag"
	"fmt"
	"image"
	"image/color"
	"image/gif"
	"image/jpeg"
	"image/png"
	"os"
)

func main() {
	flag.Parse()

	if flag.NArg() < 1 {
		fmt.Println("need atleast one image")
		return
	}

	file := flag.Arg(0)

	f, err := os.Open(file)
	if err != nil {
		panic(err)
	}
	defer f.Close()

	img, _, err := image.Decode(f)
	if err != nil {
		img, err = png.Decode(f)
		if err != nil {
			img, err = jpeg.Decode(f)
			if err != nil {
				img, err = gif.Decode(f)
				if err != nil {
					panic("decode my ass")
				}
			}
		}
	}

	oimg := image.NewGray(img.Bounds())
	for i := img.Bounds().Min.X; i < img.Bounds().Max.X; i++ {
		for j := img.Bounds().Min.Y; j < img.Bounds().Max.Y; j++ {
			c := img.At(i, j)
			nc := color.GrayModel.Convert(c)
			oimg.Set(i, j, nc)
		}
	}

	o, err := os.Create("output.png")
	if err != nil {
		panic(err)
	}
	defer o.Close()

	png.Encode(o, oimg)
}