ex_png

ExPng is a pure Elixir implementation of the PNG image format. It can read and write PNG files.

Installation

Add :ex_png as a dependency in your project’s mix.exs:

def deps do
  [
    {:ex_png, "~> 0.1.0"}
  ]
end

And run:

~$ mix deps.get

Features

• Decodes any image the PNG standard allows. This includes all standard bit depths, color modes, filtering and iterlacing options.
• Encodes using 8 bit depth, truecolor alpha color mode, default zlib compression, and no interlacing. Eventually ExPng will be able to choose encoding parameters based on the nature of the image (See Issue #11)
• Read/write access to the image’s pixels
• Implements Xiaolin Wu’s algorithm for drawing antialiased lines
• Works with all Elixir versions >= 1.7

Creating images

Images can be created by decoding an existing PNG file

{:ok, image} = ExPng.Image.from_file("adorable_kittens.png")

or by creating a blank image with a given width and height

image = ExPng.Image.new(200, 100)

Modifying images

Images can be edited by painting/clearing individual pixels, drawing lines, or erasing the entire canvas. These editing actions do not occur in layers, and change the underlying pixels, so be careful as changes cannot be undone.

{:ok, image} = ExPng.Image.from_file("adorable_kittens.png")

# Draws a pixel with the given color at the given coordinate
image = ExPng.Image.draw(image, {5, 8}, ExPng.Pixel.rgb(100, 100, 200))

# Draws a line between two points.
image = ExPng.Image.line(image, {0, 0}, {15, 8}, ExPng.Pixel.black())

# Sets a single pixel to opaque white
image = ExPng.Image.clear(image, {7, 3})

# Colors the entire canvas opaque white
image = ExPng.Image.erase(image)

Saving images

Images can be saved via

ExPng.Image.to_file(filename)

About

This library is written by Michael Berkowitz and released under the UNLICENSE.

The suite of test images in test/png_suite comes from Willem van Schaik’s PngSuite, with some additions made by Willem van Bergen as part of his work on ChunkyPNG, and some added by the author of this library.