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)

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)

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)

---

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

• Alex Clink - creator and maintainer