IDF--CTF

红与黑.go

package main

import (
	"image"
	"image/color"
	"image/jpeg"
	"log"
	"os"
)

var (
	fn = "idf_game_stego_059.jpg"

	newf = "tmp.jpg"
)

func main() {
	log.Println("hello")
	f, err := os.Open(fn)
	if err != nil {
		log.Fatal(err)
	}
	defer f.Close()
	j, err := jpeg.Decode(f)
	if err != nil {
		log.Fatal(err)
		return
	}

	img := image.NewRGBA(image.Rect(0, 0, j.Bounds().Max.X, j.Bounds().Max.Y))
	for x := 0; x < j.Bounds().Max.X; x++ {
		for y := 0; y < j.Bounds().Max.Y; y++ {
			c := j.At(x, y)
			r, g, b, _ := c.RGBA()
			nc := color.RGBA{225, 225, 225, 225}
			if (g == 0 && b == 0) || !(r == b && b == g && b > 400) {
				nc = color.RGBA{0, 0, 0, 225}
			}
			img.Set(x, y, nc)
		}
	}

	writeJpg(img)
}

func writeJpg(i *image.RGBA) {
	os.RemoveAll(newf)
	f, err := os.OpenFile(newf, os.O_CREATE|os.O_EXCL|os.O_WRONLY, 0644)
	if err != nil {
		log.Fatal(err)
		return
	}
	defer f.Close()

	err = jpeg.Encode(f, i, &jpeg.Options{100})
	if err != nil {
		log.Fatal(err)
		return
	}
}