Goで複数の画像を1つに結合するにはどうすればよいですか?

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

func main() {
    // Load the images
    img1, err := os.Open("test1.jpg")
    if err != nil {
        fmt.Println(err)
    }
    img2, err := os.Open("test2.jpg")
    if err != nil {
        fmt.Println(err)
    }
    img1, _, err = image.Decode(img1)
    if err != nil {
        fmt.Println(err)
    }
    img2, _, err = image.Decode(img2)
    if err != nil {
        fmt.Println(err)
    }

    // Create the large image
    r1 := img1.Bounds()
    r2 := img2.Bounds()
    r := image.Rectangle{image.Point{0, 0}, r2.Max}
    rgba := image.NewRGBA(r)

    // Draw the images
    draw.Draw(rgba, r1, img1, image.Point{0, 0}, draw.Src)
    draw.Draw(rgba, r2, img2, image.Point{r1.Dx(), 0}, draw.Src)

    // Export the final image
    out, err := os.Create("output.jpg")
    if err != nil {
        fmt.Println(err)
    }
    
    var opt jpeg.Options
    opt.Quality = 80
    
    jpeg.Encode(out, rgba, &opt)
}