golang read many images into one simegle image

// Create a struct to deal with pixel
type Pixel struct {
    Point image.Point
    Color color.Color
}

// Keep it DRY so don't have to repeat opening file and decode
func OpenAndDecode(filepath string) (image.Image, string, error) {
    imgFile, err := os.Open(filepath)
    if err != nil {
        panic(err)
    }
    defer imgFile.Close()
    img, format, err := image.Decode(imgFile)
    if err != nil {
        panic(err)
    }
    return img, format, nil
}

// Decode image.Image's pixel data into []*Pixel
func DecodePixelsFromImage(img image.Image, offsetX, offsetY int) []*Pixel {
    pixels := []*Pixel{}
    for y := 0; y <= img.Bounds().Max.Y; y++ {
        for x := 0; x <= img.Bounds().Max.X; x++ {
            p := &Pixel{
                Point: image.Point{x + offsetX, y + offsetY},
                Color: img.At(x, y),
            }
            pixels = append(pixels, p)
        }
    }
    return pixels
}

func main() {
    img1, _, err := OpenAndDecode("makey.png")
    if err != nil {
        panic(err)
    }
    img2, _, err := OpenAndDecode("sample.jpg")
    if err != nil {
        panic(err)
    }
    // collect pixel data from each image
    pixels1 := DecodePixelsFromImage(img1, 0, 0)
    // the second image has a Y-offset of img1's max Y (appended at bottom)
    pixels2 := DecodePixelsFromImage(img2, 0, img1.Bounds().Max.Y)
    pixelSum := append(pixels1, pixels2...)

    // Set a new size for the new image equal to the max width
    // of bigger image and max height of two images combined
    newRect := image.Rectangle{
        Min: img1.Bounds().Min,
        Max: image.Point{
            X: img2.Bounds().Max.X,
            Y: img2.Bounds().Max.Y + img1.Bounds().Max.Y,
        },
    }
    finImage := image.NewRGBA(newRect)
    // This is the cool part, all you have to do is loop through
    // each Pixel and set the image's color on the go
    for _, px := range pixelSum {
            finImage.Set(
                px.Point.X,
                px.Point.Y,
                px.Color,
            )
    }
    draw.Draw(finImage, finImage.Bounds(), finImage, image.Point{0, 0}, draw.Src)

    // Create a new file and write to it
    out, err := os.Create("./output.png")
    if err != nil {
        panic(err)
        os.Exit(1)
    }
    err = png.Encode(out, finImage)
    if err != nil {
        panic(err)
        os.Exit(1)
    }
}