pura-gif

A pure Ruby GIF decoder/encoder without additional image-processing libraries.

Part of the pura-* series — pure Ruby image codec gems.

Features

  • GIF decoding (LZW decompression)
  • GIF encoding with color quantization (median cut)
  • Image resizing (bilinear / nearest-neighbor / fit / fill)
  • No image-specific native extension or FFI dependency
  • CLI tool included

Installation

gem install pura-gif

Usage

require "pura-gif"

# Decode
image = Pura::Gif.decode("animation.gif")
image.width      #=> 400
image.height     #=> 400
image.pixels     #=> Raw RGB byte string
image.pixel_at(x, y) #=> [r, g, b]

# Encode (with color quantization)
Pura::Gif.encode(image, "output.gif")
Pura::Gif.encode(image, "output.gif", max_colors: 128)

# Resize
thumb = image.resize(200, 200)
fitted = image.resize_fit(800, 600)

CLI

pura-gif decode input.gif --info
pura-gif resize input.gif --width 200 --height 200 --out thumb.gif

Benchmark

These historical measurements include ffmpeg process startup. They do not compare against an in-process C codec or establish Rails pipeline throughput.

400×400 image, Ruby 4.0.2 + YJIT.

Decode

Decoder Time
ffmpeg (C) 65 ms
pura-gif 77 ms

Encode

Encoder Time vs ffmpeg Notes
ffmpeg (C) 59 ms —
pura-gif 377 ms 6.4× slower Includes color quantization

Why pure Ruby?

  • gem install and go — no brew install, no apt install, no C compiler needed
  • Part of pura-* — convert between JPEG, PNG, BMP, GIF, TIFF, WebP seamlessly
Gem Format Status
pura-jpeg JPEG ✅ Available
pura-png PNG ✅ Available
pura-bmp BMP ✅ Available
pura-gif GIF ✅ Available
pura-tiff TIFF ✅ Available
pura-ico ICO ✅ Available
pura-webp WebP ✅ Available
pura-image All formats ✅ Available

Pixel model and limitations

Images contain 8-bit RGB pixels. Only the first image is decoded, and encoding writes one image. Animation timing and subsequent frames are not preserved. Transparent pixels are flattened to a background color; the image model does not retain alpha.

crop(x, y, width, height) requires integer coordinates, positive dimensions, and a region entirely inside the image; invalid regions raise ArgumentError.

License

MIT