Read/Write PNG images in pure Crystal
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README.md

stumpy_png

Build Status

Documentation

Interface

  • StumpyPNG.read(path : String) : Canvas read a PNG image file from a path
  • StumpyPNG.read(io : IO) : Canvas read a PNG image file from any IO object
  • StumpyPNG.write(canvas, path : String, bit_depth: 16, color_type: :rgb_alpha) save a canvas as a PNG image file
  • StumpyPNG.write(canvas, io : IO, bit_depth: 16, color_type: :rgb_alpha) write a canvas as PNG data to any IO object
    • bit_depth is optional, valid values are 8 and 16(default)
    • color_type is optional, valid values are :grayscale, :grayscale_alpha, :rgb and :rgb_alpha(default)
  • StumpyPNG::PNG, helper class to store some state while parsing PNG files
  • Canvas and RGBA from stumpy_core

Usage

Install the stumpy_png shard

  1. shards init
  2. Add the dependency to the shard.yml file
...
dependencies:
  stumpy_png:
    github: stumpycr/stumpy_png
    version: "~> 4.4.1"
...
  1. shards install

Reading

require "stumpy_png"

canvas = StumpyPNG.read("foo.png")
r, g, b = canvas[0, 0].to_rgb8
puts "red=#{r}, green=#{g}, blue=#{b}"

Writing

require "stumpy_png"
include StumpyPNG

canvas = Canvas.new(256, 256)

(0..255).each do |x|
  (0..255).each do |y|
    # RGBA.from_rgb_n(values, bit_depth) is an internal helper method
    # that creates an RGBA object from a rgb triplet with a given bit depth
    color = RGBA.from_rgb_n(x, y, 255, 8)
    canvas[x, y] = color
  end
end

StumpyPNG.write(canvas, "rainbow.png")

PNG image with a color gradient

(See examples/ for more examples)

Reading PNG files

Color Types

  • Grayscale
  • Grayscale + Alpha
  • RGB
  • RGB + Alpha
  • Palette

Filter Types

  • None
  • Sub
  • Up
  • Average
  • Paeth

Interlacing Methods

  • None
  • Adam7

Ancillary Chunks

None are supported right now.

Writing

  • RGB with 8 or 16 bits
  • RGB + Alpha with 8 or 16 bits
  • Grayscale with 8 or 16 bits
  • Grayscale + Alpha with 8 or 16 bits

Troubleshooting

If you run into errors like

/usr/bin/ld: cannot find -lz
collect2: error: ld returned 1 exit status

make sure zlib is installed (Installing zlib under ubuntu).

Contributors

Thanks goes to these wonderful people (emoji key):


Chris Hobbs

💻

Ary Borenszweig

💻

Alex Muscar

💻

Dru Jensen

💻

kojix2

📖

obskyr

💻

r00ster

💻

This project follows the all-contributors specification. Contributions of any kind welcome!