pura-bmp

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

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

Features

  • BMP decoding and encoding (24-bit RGB)
  • Image resizing (bilinear / nearest-neighbor / fit / fill)
  • No image-specific native extension or FFI dependency
  • CLI tool included

Installation

gem install pura-bmp

Usage

require "pura-bmp"

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

# Encode
Pura::Bmp.encode(image, "output.bmp")

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

CLI

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

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
pura-bmp 39 ms
ffmpeg (C) 59 ms

Encode

Encoder Time vs ffmpeg
pura-bmp 35 ms 0.6× — faster than ffmpeg!
ffmpeg (C) 58 ms —

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. Decoded pixels are RGB; any alpha channel is discarded. Encoding writes 24-bit RGB BMP.

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

License

MIT