Golang resize png images using different interpolations

imgrsz.go

package main

import (
	"image"
	"image/png"
	"log"
	"os"
	"time"

	"golang.org/x/image/draw"
)

const imgFile = "random.png"

func main() {
	src := openImage()
	// test different scalers;
	// scale down to 0.5x0.5 of origin
	for _, sc := range []struct {
		Name   string
		Scaler draw.Scaler
	}{
		{"NearestNeighbor", draw.NearestNeighbor},
		{"ApproxBiLinear", draw.ApproxBiLinear},
		{"BiLinear", draw.BiLinear},
		{"CatmullRom", draw.CatmullRom},
	} {
		// new size of image
		dr := image.Rect(0, 0, src.Bounds().Max.X/2, src.Bounds().Max.Y/2)
		// resize using given scaler
		var res image.Image
		{ // show time to resize
			tp := time.Now()
			// perform resizing
			res = scaleTo(src, dr, sc.Scaler)
			// report time to scaling to console
			log.Printf("scaling using %q takes %v time",
				sc.Name, time.Now().Sub(tp))
		}
		// open file to save
		dstFile, err := os.Create(sc.Name + ".png")
		if err != nil {
			log.Fatal(err)
		}
		// encode as .png to the file
		err = png.Encode(dstFile, res)
		// close the file
		dstFile.Close()
		if err != nil {
			log.Fatal(err)
		}
	}

}

func openImage() image.Image {
	fl, err := os.Open(imgFile)
	if err != nil {
		log.Fatal(err)
	}
	defer fl.Close()
	img, _, err := image.Decode(fl)
	if err != nil {
		log.Fatal(err)
	}
	return img
}

//
// for RGBA images
//

// src   - source image
// rect  - size we want
// scale - scaler
func scaleTo(src image.Image,
	rect image.Rectangle, scale draw.Scaler) image.Image {
	dst := image.NewRGBA(rect)
	scale.Scale(dst, rect, src, src.Bounds(), draw.Over, nil)
	return dst
}



// Timing

// NearestNeighbor      7.935489ms
// ApproxBiLinear      14.876478ms
// BiLinear          113.903067ms
// CatmullRom        115.972061ms