arjan / pixels

Elixir library to read pixels from a PNG file, using libpng (using a NIF)

Pixels

Elixir NIF to read and write image data from/to PNG and JPEG files.

For PNG images, it uses the lodepng C library; for JPEG images, it uses the ujpeg C library.

Progressive or lossless JPEG files, as well as JPEG encoding are not supported by the underlying uJpeg.

Getting Pixel data

Pixels.read and Pixels.read_file allow you to decode a PNG / JPEG file into a %Pixels{} struct. The data component of this struct contains the RGBA data of the image, in row order. To get an individual pixel's value, you can calculate an offset into this data based on the x/y coordinate. For example:

{:ok, pixels} = Pixels.read_file("test.png")

# the pixel value you want to get:
x = 10
y = 3

# calculate offset into `pixels.data`
offset = (y * pixels.width + x) * 4

# binary-pattern-match the pixel value in the data:
<<_::binary-size(offset), r, g, b, alpha, _::binary>> = pixels.data

I need feature X!

Pull requests welcome! For a more feature-complete library you could also use image, however its license is LGPL so a bit more restrictive than the MIT license of Pixels.

Installation

If available in Hex, the package can be installed by adding pixels to your list of dependencies in mix.exs:

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

Documentation can be generated with ExDoc and published on HexDocs. Once published, the docs can be found at https://hexdocs.pm/pixels.

pixels's Issues

To get pixel value of an image

How am I get pixel values of an image in elixir?

$CROSSCOMPILE Issue on MacOS

Hey @arjan, I've got a question that hopefully will be a quick fix for you. I'm on MacOS and trying to compile an Elixir project using this package but I'm getting an issue with the makefile.

Makefile:11: *** PNG only works on Linux. Crosscompiling is possible if $CROSSCOMPILE is set.. Stop.

I was having trouble trying to figure out where $CROSSCOMPILE should be set. The configuration does seem to work as is on Windows with WSL. I'm assuming I need to set something in the .zshrc file but I'm not 100% sure. Hoping you can help out. Thanks!