crop_image.go

package main

import (
	"fmt"
	"image"
	"image/jpeg"
	"os"
)

func main() {
	f, err := os.Open("test.jpg")
	if err != nil {
		fmt.Println(err)
	}
	defer f.Close()

	img, _, err := image.Decode(f)
	if err != nil {
		fmt.Println(err)
	}
	imgY := img.(*image.YCbCr)
	imgBounds := imgY.Bounds()

	mX := imgBounds.Max.X
	mY := imgBounds.Max.Y

	for x := 0; x < mX; x += 256 {
		for y := 0; y < mY; y += 256 {
			subImg := imgY.SubImage(image.Rect(x, y, x+256, y+256)).(*image.YCbCr)
			fmt.Println(subImg.Bounds())

			imgName := fmt.Sprintf("img%dx%d.jpg", x+256, y+256)
			fo, err := os.Create(imgName)
			if err != nil {
				fmt.Println(err)
			}
			defer fo.Close()

			jpeg.Encode(fo, subImg, nil)
		}
	}
}