stumpy_png

Interface

• StumpyPNG.read(path) : Canvas read a PNG image file

• StumpyPNG.write(canvas, path) saves a canvas as a PNG image file

• StumpyPNG::RGBA, 16-bit rgba color

  • rgba.r red channel
  • rgba.g green channel
  • rgba.b blue channel
  • rgba.a alpha channel
  • rgba.to_rgba8 returns a tuple of 4 8-bit values { r, g, b, a}
  • rgba.to_rgb8 returns a tuple of 3 8-bit values { r, g, b }

• StumpyPNG::Canvas, two dimensional Array of RGBA value

  • canvas.width
  • canvas.height
  • canvas.set_pixel(x, y)
  • canvas.get_pixel(x, y)

• StumpyPNG::PNG, helper class to store some state while parsing PNG files

Usage

Reading

require "stumpy_png"

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

Writing

require "stumpy_png"

canvas = StumpyPNG::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 = StumpyPNG::RGBA.from_rgb_n([x, y, 255], 8)
    canvas.set_pixel(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

Only supports writing to a RGB + Alpha PNG image without any filters, interlacing or ancillary chunks.