gifx is a drop-in replacement fork of the standard image/gif package with improved support for animated GIF files.

• Encode and decode images one at a time to reduce peak memory usage.
• Extract the first image from an animation without parsing the entire file.
• Store and retrieve comment and plain text extension data.
• Optimize output file size by only storing inter-frame changes.

Original code copyright 2013 The Go Authors. No changes have been made to the original reader.go and writer.go source files as forked from Go 1.18.

Decode example

Extract each frame from an animated GIF and save them to disk. Each image is eligible for GC before the next frame is decoded.

f, _ := os.Open("tmp.gif")
defer f.Close()
dec := gif.NewDecoder(f)
dec.ReadHeader()
i := 0
for {
    if blk, err := dec.ReadBlock(); err == io.EOF {
        break
    } else if frm, ok := blk.(*gif.Frame); ok {
        f, _ := os.Create(fmt.Sprintf("tmp%d.gif", i))
        gif.Encode(f, frm.Image, nil)
        f.Close()
        i++
    }
}

Encode example

Create a random 100 frame greyscale animated GIF using only a single allocated image.Paletted struct.

f, _ := os.Create("tmp.gif")
defer f.Close()
enc := gif.NewEncoder(f)
pal := make(color.Palette, 0x100)
for i := range pal {
    pal[i] = color.Gray{Y: uint8(i)}
}
enc.WriteHeader(image.Config{Width: 100, Height: 100, ColorModel: pal}, 0)
pm := image.NewPaletted(image.Rect(0, 0, 100, 100), pal)
for i := 0; i < 100; i++ {
    rand.Read(pm.Pix)
    enc.WriteFrame(&gif.Frame{Image: pm})
}
enc.WriteTrailer()
enc.Flush()

Optimize example

Optimize each frame by replacing unchanged pixels with the transparent palette entry and optionally cropping the image.

pal[0xff] = color.Transparent
opt := gif.NewOptimizer(0xff)
pm := image.NewPaletted(image.Rect(0, 0, 100, 100), pal)
for {
    // draw frame
    pm, _ := opt.Optimize(pm)
    _ = enc.WriteFrame(&gif.Frame{Image: pm})
}