Making gifs with Go

Aug 3 2013

Go's standard library has a gif decoder, but sadly no encoder. I found an encode on github here. Unfortunalty it written in the main package so i forked it and pulled it into its own package: Now we can easily decode a gif, play around with it and encode it back to a file.

For this example I'm going to do something pretty basic: Take a gif and mirror the animation. Below is my target gif:


Here's the code:

package main

import (

func main() {
    file, _ := os.Open("nom.gif")
    g, _ := gif.DecodeAll(file)

    for _, img := range g.Image { // iterate over frames
        for x := 0; x < img.Bounds().Max.X/2; x++ { // half of the x space
            for y := 0; y < img.Bounds().Max.Y; y++ { // all of the y space
                // find the mirror pixel's color
                c := img.At(img.Bounds().Max.X-x, img.Bounds().Max.Y-y)
                // set it
                img.Set(x, y, c)

    file, _ = os.Create("new_nom.gif")
    _ = gifencoder.EncodeAll(file, g)

Here's what we get: