package main

import (
	"fmt"
	"golang.org/x/image/tiff"
	"image"
	"image/color"
	_ "image/jpeg"
	"os"
)

func convert(i image.Image) image.Image {
	rect := i.Bounds()
	n := image.NewGray(rect)
	for x := 0; x < rect.Max.X; x++ {
		for y := 0; y < rect.Max.Y; y++ {
			p := color.GrayModel.Convert(i.At(x, y)).(color.Gray)
			if p.Y <= 130 {
				n.Set(x, y, p)
			} else {
				n.Set(x, y, color.White)
			}
		}
	}
	return n
}

func main() {
	in, err := os.Open(os.Args[1])
	if err != nil {
		fmt.Println(err)
		return
	}
	out, err := os.OpenFile(os.Args[2], os.O_RDWR|os.O_CREATE, 0644)
	if err != nil {
		fmt.Println(err)
		return
	}
	i, _, err := image.Decode(in)
	if err != nil {
		fmt.Println(err)
		return
	}
	err = tiff.Encode(out, convert(i), &tiff.Options{tiff.Uncompressed, false})
	if err != nil {
		fmt.Println(err)
	}
}