Colr: A color selector tool

README.md

Colr.rb

Colr selects colors based on hue calculations. It knows nothing about the image before initialization and works with any valid HTML color: red, green, aqua, brown, etc.

Colr allows you to adjust the tolerance and hue settings so you can select colors from any image!

Example:

@colr = Colr.new('input.png')
@colr.select(:red).save("red.png")

# To select all the colors:

Colr.new('input.png').select(:yellow, 40, -40).save("yellow.png")
Colr.new('input.png').select(:red).save("red.png")
Colr.new('input.png').select(:green, 30, -60).save("green.png")
Colr.new('input.png').select(:blue, 20, -50).save("blue.png")
Colr.new('input.png').select(:violet, 20, -70).save("violet.png")

blue.png

colr.rb

require 'chunky_png'

class Colr
  include ChunkyPNG::Color

  def initialize(png)
    @input = ChunkyPNG::Image.from_file(png)
  end

  # Converts each pixel of the image to grayscale except the given color. You
  # can use the tolerance and degrees (hues) to tune Colr to match any image!
  #
  # Example:
  #  @colr.select(:red)  #=> ChunkyPNG::Image
  #
  # Returns the resulting image
  def select(color, tolerance = 10, degrees = 0)
    hues = swatch(color, tolerance, degrees)
    @input.pixels.map! { |c| hues.include?( hue(c) ) ? c : to_grayscale(c) }
    @input
  end

  # Calculates a hue of the given color
  # Algorithm from http://en.wikipedia.org/wiki/HSL_and_HSV
  #
  # Example:
  #  @colr.hue(0xff000000)  #=> 0
  #
  # Returns the resulting integer value of the hue
  def hue(color)
    r,g,b = to_truecolor_bytes(color)
    min, max = [r,g,b].min, [r,g,b].max
    d = max - min
    h = case max
        when min; 0
        when r; 60 * (g-b)/d
        when g; 60 * (b-r)/d + 120
        when b; 60 * (r-g)/d + 240
        end % 360
  end

  # Calculates a range to hues given the color, tolerance, and
  #
  # Example:
  #   @colr.swatch(:red) #=> 0..10
  #
  # Returns a new Range of hues
  def swatch(color, tolerance, degrees)
    h = hue(PREDEFINED_COLORS[color.to_sym]) + degrees
    Range.new(h, h+tolerance)
  end

end

green.png

red.png

test_colr.rb

require 'minitest/autorun'
require File.join(File.dirname(__FILE__), 'colr.rb')

describe Colr do

  before do
    @colr = Colr.new('input.png')
  end

  it 'calculates hues for html colors' do
    @colr.hue(0xff000000).must_equal 0
  end

  it "returns a range for positive values" do
    @colr.swatch(:red, 10, 0).must_equal 0..10
  end

  it 'returns values for negative degrees' do
    @colr.swatch(:green, 30, -60).must_equal 60..90
  end

end

violet.png

yellow.png