Store the dominant color of an image with CarrierWave
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README.md

CarrierWave Color

Add the dominant color of an image to your database whenever you upload it with the CarrierWave gem on your Rails app.

This can be used to show the image's background color while it is loading or to index images for a "search by color" feature.

Installation

Add the following lines to your application's Gemfile:

# Detect the dominant color of images on upload
gem "carrierwave-color"

And then call:

$ bundle

Add a processor to your uploader

In your uploader, include the module and call the processor:

class PhotoUploader < CarrierWave::Uploader::Base
  include CarrierWave::Color

  process :store_dominant_color

  #
end

Add a dominant color attribute

To store the color, you need an attribute on the Rails model where you attach your uploader. Call it {uploader}_dominant_color.

For example if you have the following model:

class Article
  mount_uploader :photo, PhotoUploader
end

Then you would need to add a photo_dominant_color column to the articles table. You could create a migration by executing:

$ rails g migration AddPhotoDominantColorToArticles photo_dominant_color
$ rake db:migrate

Using your dominant color

An easy way of using your dominant colors is to put them as a background to your image tags:

<%= image_tag(article.photo.url(:thumb), style: "background: #{article.photo_dominant_color}") %>

For example, on cults3d:

Cults 3D Animated Screenshot with dominant colors during image load

Resizing

If you do any resizing or if you have several versions of your uploader, store the color on the smallest so that processing goes faster. For example:

#
version :medium do
  process resize_to_fill: [200, 200]
end

version :thumb, from_version: :medium do
  process resize_to_fill: [42, 42]
  process :store_dominant_color
end
#

Dominant color from a palette

If you wish to find the dominant color from a selection of colors, you can use the following processor with a {uploader}_palette_color field on your model:

process store_palette_color: ['ff0000', '00ff00', '0000ff']

Contributing

  1. Fork it ( https://github.com/sunny/carrierwave-color/fork )
  2. Create your feature branch (git checkout -b my-new-feature)
  3. Launch specs (bundle exec rspec)
  4. Commit your changes (git commit -am 'Add some feature')
  5. Push to the branch (git push origin my-new-feature)
  6. Create a new Pull Request

Releasing

  1. Update version.rb and commit
  2. Run rake release