Rbimg

Allows simple creation and reading of images (currently only PNG images).

Supports all required chunk types (IHDR, PLTE, IDAT, IEND)

All filtering methods for individual scanlines are supported for reading PNG images, but it will always write with a filtering method of 0 (so re-writing may give you a different format than the original image)

All bit depths for PNG images are supported. See PNG documentation or source code for specifics (ArgumentError thrown if an incorrect bit depth is used for a specific color type)

All PNG color types are supported: greyscale, greyscale with alpha, rgb, rgba, and palette. All with their respective bit_depth sizes.

As of now this gem will be able to retrieve the correct pixel information for all PNG images except for those with an interlace method other than 0, which, as far as I can tell, are most PNG images.

Non-required chunk types are not currently supported.

This gem is primarily for simple manipulation of images using pixel data.

You can easily write images from an array of pixel data, and retrieve pixel data from a PNG image.

Examples:

Write simple 100x100 green-blue image

pixels = []
100.times do
    pixels << Array.new(100, [0,255,255])
end
png = Rbimg::PNG.new(pixels: pixels.flatten, type: :rgb, width: 100, height: 100)
png.write(path: './green-blue')

Write simple 500x500 half blue half red rgba image

pixels = []
500.times do |row|
    if row >= 250
        pixels << Array.new(500, [0,0,255,127])
    else
        pixels << Array.new(500, [255,0,0,127])
    end
end
png = Rbimg::PNG.new(pixels: pixels.flatten, type: :rgba, width: 500, height: 500)
png.write(path: './blue-red-alpha')

Write simple 300x500 half white half black greyscale image

pixels = []
500.times do |row|
    if row >= 250
        pixels << Array.new(300, 255)
    else
        pixels << Array.new(300, 0)
    end
end
png = Rbimg::PNG.new(pixels: pixels.flatten, type: :greyscale, width: 300, height: 500)
png.write(path: './greyscale')

Write a greyscale-alpha version of the image above

pixels = []
500.times do |row|
    if row >= 250
        pixels << Array.new(300, [255,175])
    else
        pixels << Array.new(300, [0,175])
    end
end
png = Rbimg::PNG.new(pixels: pixels.flatten, type: :greyscale_alpha, width: 300, height: 500)
png.write(path: './greyscale_alpha')

Write a greyscale image from the MNIST dataset:

img_data = File.read("./data/t10k-images-idx3-ubyte").bytes
mag_num = img_data[0...4]
num_imgs = img_data[4...8]
num_rows = img_data[8...12]
num_cols = img_data[12...16]
pixels = img_data[16...(16 + 784)]
png = Rbimg::PNG.new(pixels: pixels, type: :greyscale, width: 28, height: 28)
png.write(path: 'mnist_test')

Read a PNG image and get the pixel array from a path

png = Rbimg::PNG.read(path: './data/smiley.png')
puts png.pixels

Read a PNG image and get the pixel array from raw data

data = File.read('./data/smiley.png')
png = Rbimg::PNG.read(data: data)
puts png.pixels

Write a 16-bit-depth rgba image with random colors and alpha:

height = 140
width = 123
r = Random.new
pixels = Array.new(3 * width * height) do |i|
    r.rand(2 ** 16)
end

png = Rbimg::PNG.new(pixels: pixels, type: :rgb, width: width, height: height, bit_depth: 16)
png.write(path: "./rgba_16bit")

Combine images in rows or columns:

Installation

Add this line to your application's Gemfile:

gem 'rbimg'

And then execute:

$ bundle install

Or install it yourself as:

$ gem install rbimg

Development

After checking out the repo, run bin/setup to install dependencies. Then, run rake spec to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to rubygems.org.

Contributing

The feature that will make this gem fully-functional for all PNG images is the implementation of interlaced PNGs. Any help is welcomed. This gem was developed using the documentation found and libpng.org/png/spec/1.2 Information about interlaced PNGs can be found there.

Bug reports and pull requests are welcome on GitHub at https://github.com/[USERNAME]/rbimg. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the code of conduct.

License

The gem is available as open source under the terms of the MIT License.

Code of Conduct

Everyone interacting in the Rbimg project's codebases, issue trackers, chat rooms and mailing lists is expected to follow the code of conduct.