From 2 colors, calculates the contrast ratio defined for WCAG 2.0.
Hexadecimal notation, RGB/HSL/HWB functions are supported as input formats.
Add this line to your application's Gemfile:
And then execute:
$ bundle install
Or install it yourself as:
$ gem install css_color_contrast
Calculate the contrast ratio
For example, if you want to calculate the contrast ratio between yellow and black:
require 'css_color_contrast' CssColorContrast.ratio('#ff0', [0, 0, 0]) # => 19.555999999999997 CssColorContrast.ratio('rgb(255, 255, 0)', 'black') # => 19.555999999999997 CssColorContrast.ratio('hsl(60deg, 100%, 50%)', 'hwb(60deg 0% 100%)') # => 19.555999999999997
The following formats are supported for the arguments of
- RGB values as an Array of Integers: [255, 255, 0], [0, 0, 0], etc.
- RGB values in hexadecimal notation: #ff0, #ffff00, #FF0, etc.
- RGB values in functional notation: rgb(255, 255, 0), rgb(255 255 0), etc.
- HSL colors in functional notation: hsl(60deg, 100%, 50%), hsl(60 100% 50%), etc.
- [Experimental] HWB colors in functional notation: hwb(60deg 0% 0%), hwb(60 0% 0%), etc.
- Extended color keywords: white, black, red, etc.
Calculate the relative luminance
You can also calculate the relative luminance of a given color as follows:
require 'css_color_contrast' CssColorContrast.relative_luminance('#ff0') # => 0.9278
A command-line tool,
css_color_contrast is provided for a demonstration purpose.
Invoke it as follows:
$ css_color_contrast To calculate the contrast ratio between 2 colors, enter the following command: > ratio: color1 color2 For the values of color1 and color2, hexadecimal notation, RGB/HSL/HWB functions and the extended color keywords are supported. To finish the program, enter 'exit'. >
Calculate the contrast ratio between two colors as in the next case:
> ratio: rgb(255 255 0) black 19.555999999999997 >
It takes 3 arguments, 2 colors and a contrast ratio to be satisfied.
In the example below, it tries to adjust the lightness of the second color so that the contrast ratio between the 2 colors is just above the target ratio.
> adjust: white red 4.5 #ee0000 >
Print the properties of a given color:
> info: #ff0 --- name: yellow hex: #ffff00 rgb: rgb(255,255,0) hsl: hsl(60.00,100.00%,50.00%) hwb: hwb(60.00,0.00%,0.00%) >
When the 3rd argument is omitted, it defaults to 4.5.
Assignment to a variable
You can assign a color value to a varible. Variable names begin with @.
> @deeper_red: #e00 #e00 > ratio: white @deeper_red 4.530325445433122 > info: @deeper_red --- name: #ee0000 hex: #ee0000 rgb: rgb(238,0,0) hsl: hsl(0.00,100.00%,46.67%) hwb: hwb(0.00,0.00%,6.67%)
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.
Bug reports and pull requests are welcome on GitHub at https://github.com/nico-hn/css_color_contrast. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the code of conduct.
The gem is available as open source under the terms of the MIT License.
Code of Conduct
Everyone interacting in the CssColorContrast project's codebases, issue trackers, chat rooms and mailing lists is expected to follow the code of conduct.