PNG

Installation

  1. Add the dependency to your shard.yml:

    dependencies:
  png:
    github: sleepinginsomniac/png

  2. Run shards install

Usage

Reading

require "png"

canvas = PNG.read("examples/gradient.png")
canvas.header.color_type # => PNG::ColorType::RGB
canvas[0, 0]             # => Bytes[0, 255, 0]

Writing

require "png"

canvas = PNG::Canvas.new(255, 255)
0u8.upto(canvas.height - 1) do |y|
  0u8.upto(canvas.width - 1) do |x|
    canvas[x, y] = {x, 255u8, y}
  end
end

PNG.write("examples/gradient.png", canvas)

Color gradient

require "png"

canvas = PNG::Canvas.new(255, 255)

0.upto(canvas.height - 1) do |y|
  0.upto(canvas.width - 1) do |x|
    hue = (x / canvas.width) * 360.0
    value = 1 - (y / canvas.height)
    hsv = PNG::HSV.new(hue, 1.0, value)
    canvas[x, y] = PNG::RGB(UInt8).from_hsv(hsv)
  end
end

PNG.write("examples/test_pattern.png", canvas)

Test pattern

require "png"

# 1-bit black and white
canvas = PNG::Canvas.new(PNG::Header.new(10, 10, bit_depth: 1, color_type: PNG::ColorType::Grayscale))
0.upto(canvas.height - 1) do |y|
  0.upto(canvas.width - 1) do |x|
    canvas[x, y] = {1u8} if (x + y) % 2 == 0
  end
end

PNG.write("examples/1bit_checker.png", canvas)

1Bit B/W

ColorTypes

All PNG color types and bit depths are supported for reading / writing

| ColorType | 1bit | 2bit | 4bit | 8bit | 16bit | |----------------|------|------|------|------|-------| | Grayscale | r/w | r/w | r/w | r/w | r/w | | TrueColor | r/w | r/w | r/w | r/w | r/w | | Indexed | | | | r/w | | | GrayscaleAlpha | r/w | r/w | r/w | r/w | r/w | | TrueColorAlpha | r/w | r/w | r/w | r/w | r/w |

FilterMethods

| Name | Support | |---------|---------| | None | r/w | | Sub | r/w | | Up | r/w | | Average | r/w | | Paeth | r/w |

Interlacing

| Name | | |-------|-----| | None | r/w | | Adam7 | r/w |

Ancillary Chunks

| Name | Support | |------|---------| | cHRM | - | | gAMA | Yes | | iCCP | - | | sBIT | - | | sRGB | - | | bKGD | Yes | | hIST | - | | tRNS | Yes | | pHYs | Yes | | sPLT | - | | tIME | Yes | | iTXt | - | | tEXt | - | | zTXt | - |

Contributing

  1. Fork it (https://github.com/sleepinginsomniac/png/fork)
  2. Create your feature branch (git checkout -b my-new-feature)
  3. Commit your changes (git commit -am 'Add some feature')
  4. Push to the branch (git push origin my-new-feature)
  5. Create a new Pull Request

Contributors