Concatenate Images in Go: A Comprehensive Guide

In Go, manipulating images is a breeze thanks to its powerful image libraries. However, if you want to merge multiple images into one large canvas, things can get confusing. Here's a step-by-step guide to handle this task like a pro.

Loading Images

To kick things off, load the images you wish to concatenate. Here's a code snippet to do that:

// Open the first image
imgFile1, err := os.Open("test1.jpg")
if err != nil {
    fmt.Println(err)
}
// Decode the image
img1, _, err := image.Decode(imgFile1)
if err != nil {
    fmt.Println(err)
}

// Open the second image
imgFile2, err := os.Open("test2.jpg")
if err != nil {
    fmt.Println(err)
}
// Decode the image
img2, _, err := image.Decode(imgFile2)
if err != nil {
    fmt.Println(err)
}

Creating a New Image

Next, let's create a spacious new image to accommodate both loaded images. Determine the dimensions of this new canvas by adding the widths of both images:

r := image.Rectangle{image.Point{0, 0}, img1.Bounds().Dx()   img2.Bounds().Dx(), img1.Bounds().Dy()}
rgba := image.NewRGBA(r)

Drawing the Images

Now comes the fun part: assembling the images within this new canvas. Determine the position where you want to place the second image, and then draw both images onto the canvas:

// Starting point of the second image (bottom left)
sp2 := image.Point{img1.Bounds().Dx(), 0}
// Rectangle for the second image
r2 := image.Rectangle{sp2, sp2.Add(img2.Bounds().Size())}

// Draw the first image
draw.Draw(rgba, img1.Bounds(), img1, image.Point{0, 0}, draw.Src)
// Draw the second image
draw.Draw(rgba, r2, img2, image.Point{0, 0}, draw.Src)

Saving the Result

Finally, let's immortalize this concatenated masterpiece by saving it as a new image file:

out, err := os.Create("./output.jpg")
if err != nil {
    fmt.Println(err)
}

var opt jpeg.Options
opt.Quality = 80

jpeg.Encode(out, rgba, &opt)

That's it! You've successfully merged multiple images into a cohesive whole. Go forth and conquer the world of image manipulation.