resize.go

package main

import (
	"fmt"
	"github.com/nfnt/resize"
	"image/jpeg"
	"io"
	"os"
)

func check(e error) {
	if e != nil {
		panic(e)
	}
}

func resizeJpeg(writer io.Writer, reader io.Reader, width uint) error {
	image, e := jpeg.Decode(reader)
	check(e)

	resizedImage := resize.Resize(width, 0, image, resize.Lanczos3)

	return jpeg.Encode(writer, resizedImage, nil)
}

func main() {
	fmt.Printf("%s => %s\n", os.Args[1], os.Args[2])

	reader, e := os.Open(os.Args[1])
	check(e)

	out, e := os.Create(os.Args[2])
	check(e)

	defer out.Close()
	defer reader.Close()

	resizeJpeg(out, reader, 800)
}