jpg2png.go

// 【TRY】画像変換コマンドを作ろう
package main

import (
	"fmt"
	"image/jpeg"
	"image/png"
	"log"
	"os"
	"path/filepath"
)

func main() {
	path := "hoge.jpg"
	basename := getBasename(path)
	println(basename)
	if err := jpg2png(path); err != nil {
		log.Fatal(err)
	}
}

func getBasename(path string) string {
	lenBasename := len(path) - len(filepath.Ext(path))
	return filepath.Base(path[:lenBasename])
}

func jpg2png(path string) error {
	f, err := os.Open(path)
	if err != nil {
		return err
	}
	defer f.Close()

	jpgImg, err := jpeg.Decode(f)
	if err != nil {
		return err
	}

	basename := getBasename(path)

	pngImgName := fmt.Sprintf("%s.png", basename)
	d, err := os.Create(pngImgName)
	if err != nil {
		return err
	}
	defer d.Close()

	err = png.Encode(d, jpgImg)
	if err != nil {
		return err
	}
	return nil
}