pura-png

A pure Ruby PNG decoder/encoder with zero C extension dependencies.

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

• Color types: Grayscale (0), RGB (2), Indexed (3), Grayscale+Alpha (4), RGBA (6)
• Bit depths: 1, 2, 4, 8, 16
• All 5 filter types: None, Sub, Up, Average, Paeth
• Zlib compression/decompression via Ruby stdlib
• Image resizing (bilinear / nearest-neighbor / fit / fill)
• No native extensions, no FFI, no external dependencies
• CLI tool included

gem install pura-png

require "pura-png"

# Decode
image = Pura::Png.decode("photo.png")
image.width      #=> 800
image.height     #=> 600
image.pixels     #=> Raw RGB byte string
image.pixel_at(x, y) #=> [r, g, b]

# Encode
Pura::Png.encode(image, "output.png")

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

# From raw pixels
image = Pura::Png::Image.new(width, height, rgb_pixels_string)
Pura::Png.encode(image, "output.png")

pura-png decode input.png --info
pura-png decode input.png --out pixels.dat
pura-png encode input.dat --width W --height H --out output.png
pura-png resize input.png --width 200 --height 200 --out thumb.png
pura-png resize input.png --fit 800x600 --out fitted.png

400×400 image, Ruby 4.0.2 + YJIT.

pura-png is slower than chunky_png for decoding, but supports more color types and bit depths, and is part of the pura-* ecosystem for seamless format conversion. Both use Ruby's built-in Zlib (a C extension) for compression.

• gem install and go — no brew install, no apt install, no C compiler needed
• Works everywhere Ruby works — CRuby, ruby.wasm, JRuby, TruffleRuby
• Full PNG support — all color types and bit depths, not just 8-bit RGB/RGBA
• Part of pura-* — convert between JPEG, PNG, BMP, GIF, TIFF, WebP seamlessly

MIT