pura-image

Pure Ruby image processing library with zero C extension dependencies. Bundles all pura-* format gems and provides an ImageProcessing adapter for Rails Active Storage.

Why this exists (in 30 seconds)

Stop installing system libraries just to resize an image in Rails.

# Gemfile
  gem "image_processing"
+ gem "pura-image"

# config/application.rb
config.active_storage.variant_processor = :pura

# Dockerfile
- RUN apt-get install -y libvips-dev imagemagick

That's it. No brew install vips. No apt install imagemagick. No C compiler. Works on macOS, Linux, Windows, Docker, CI, ruby.wasm — anywhere Ruby runs.

✅ Drop-in for ImageProcessing::Vips / ImageProcessing::MiniMagick
✅ 7 formats — JPEG, PNG, BMP, GIF, TIFF, ICO/CUR, WebP
✅ Some operations are faster than C (no process-spawn overhead — see Benchmark)
✅ Runs on ruby.wasm, JRuby, TruffleRuby

Supported Formats

Format	Decode	Encode	Gem
JPEG	✅	✅	pura-jpeg
PNG	✅	✅	pura-png
BMP	✅	✅	pura-bmp
GIF	✅	✅	pura-gif
TIFF	✅	✅	pura-tiff
ICO/CUR	✅	✅	pura-ico
WebP	✅	✅	pura-webp

Format auto-detection by magic bytes — no extension guessing needed for decode.

Installation

gem install pura-image

Usage

require "pura-image"

# Load any format (auto-detected from magic bytes)
image = Pura::Image.load("photo.jpg")
image = Pura::Image.load("logo.png")
image.width   #=> 800
image.height  #=> 600

# Save to any format (detected from extension)
Pura::Image.save(image, "output.png")

# Convert between formats
Pura::Image.convert("input.bmp", "output.jpg", quality: 85)
Pura::Image.convert("photo.tiff", "photo.png")

Image Operations

All operations from the image_processing gem are supported:

image = Pura::Image.load("photo.jpg")

# Resize
image.resize_to_limit(800, 600)   # downsize only, keep aspect ratio
image.resize_to_fit(400, 400)     # resize to fit, keep aspect ratio
image.resize_to_fill(400, 400)    # fill exact size, center crop excess
image.resize_and_pad(400, 400)    # fit within bounds, pad with black
image.resize_to_cover(400, 400)   # cover bounds, no crop

# Transform
image.crop(10, 10, 200, 200)      # crop region
image.rotate(90)                   # rotate 90/180/270 degrees
image.grayscale                    # convert to grayscale

# Chain operations
result = Pura::Image.load("photo.jpg")
  .resize_to_limit(800, 600)
  .rotate(90)
  .grayscale

Pura::Image.save(result, "thumb.jpg", quality: 80)

Rails Active Storage Integration

Drop-in replacement for libvips/ImageMagick:

# Gemfile
gem "image_processing"
gem "pura-image"

# config/application.rb
config.active_storage.variant_processor = :pura

Models and views stay exactly the same:

class User < ApplicationRecord
  has_one_attached :avatar do |attachable|
    attachable.variant :thumb, resize_to_limit: [200, 200]
  end
end

<%= image_tag user.avatar.variant(:thumb) %>

No brew install vips. No apt install imagemagick. Just gem install and go.

ImageProcessing::Pura API

require "image_processing/pura"

# Same API as ImageProcessing::Vips
processed = ImageProcessing::Pura
  .source("photo.jpg")
  .resize_to_limit(400, 400)
  .convert("png")
  .call(destination: "output.png")

# Pipeline branching
pipeline = ImageProcessing::Pura.source("photo.jpg")
large  = pipeline.resize_to_limit(800, 800).call(destination: "large.jpg")
medium = pipeline.resize_to_limit(500, 500).call(destination: "medium.jpg")
small  = pipeline.resize_to_limit(300, 300).call(destination: "small.jpg")

# Validation
ImageProcessing::Pura.valid_image?("photo.jpg")  #=> true

Benchmark

400×400 image, Ruby 4.0.2 + YJIT vs ffmpeg (C + SIMD).

Decode

Format	pura-*	ffmpeg	vs ffmpeg
TIFF	14 ms	59 ms	🚀 4× faster
BMP	39 ms	59 ms	🚀 1.5× faster
GIF	77 ms	65 ms	~1× (comparable)
PNG	111 ms	60 ms	1.9× slower
JPEG	304 ms	55 ms	5.5× slower

Encode

Format	pura-*	ffmpeg	vs ffmpeg
TIFF	0.8 ms	58 ms	🚀 73× faster
BMP	35 ms	58 ms	🚀 1.7× faster
PNG	52 ms	61 ms	🚀 faster
JPEG	238 ms	62 ms	3.8× slower
GIF	377 ms	59 ms	6.4× slower

5 out of 11 operations are faster than C (ffmpeg process-spawn overhead).

Why pure Ruby?

gem install and go — no brew install, no apt install, no C compiler
Works everywhere Ruby works — CRuby, ruby.wasm, mruby, JRuby, TruffleRuby
Edge/Wasm ready — browsers (ruby.wasm), sandboxed environments, no system libraries needed
Perfect for dev/CI — no ImageMagick/libvips setup. rails new → image upload → it just works
7 formats, 1 interface — unified API across JPEG, PNG, BMP, GIF, TIFF, ICO, WebP

License

MIT