obskyr / stumpy_png

Read/Write PNG images in pure Crystal

stumpy_png

Documentation

Interface

• StumpyPNG.read(path) : Canvas read a PNG image file
• StumpyPNG.write(canvas, path, bit_depth: 16, color_type: :grayscale) saves a canvas as a PNG image file
  • 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: "~> 4.2"
...

3. 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

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")

(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

• tRNS
• cHRM
• gAMA
• iCCP
• sBIT
• sRGB
• tEXt
• zTXt
• iTXt
• bKGD
• hIST
• pHYs
• sPLT
• tIME

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 📖

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