Golang how to concatenate/append images to one another

Question

Go has great image manipulation and data libraries however I\'m having trouble creating one big image from smaller ones. Does anyone know how to take two png or jpeg files

Answer 1

Your life would be much easier if you make a few things into functions and create a struct to make sense of each pixel.

// 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)
    }
}