Selective Coloring

gistfile1.rb

require 'chunky_png'

module ChunkyPNG::Color
  LUMA_WEIGHTS = [0.30, 0.59, 0.11]
  #based on http://en.wikipedia.org/wiki/HSL_and_HSV

  def self.to_hcy_floats(i) #creates hue, chroma, luma tuple
    r,g,b = to_truecolor_bytes(i).map {|x| x/255.0}
    minx,maxx = [r,g,b].minmax 

    chroma = maxx-minx

    hue = if chroma == 0
      0
    else
      case maxx
        when r
          ((g-b)/chroma) % 6
        when g
          (b-r)/chroma + 2
        when b
          (r-g)/chroma + 4
      end * 60
    end

    luma = [r,g,b].zip(LUMA_WEIGHTS).map {|x,w| x*w}.inject(&:+)

    [hue,chroma,luma]
  end

  def self.hcy(hue,chroma,luma)
    segment = hue / 60
    h2 = (1 - ((segment % 2) - 1).abs) #h2 is the portion of hue from the second-largest component. it gives us the distance from the 'max' component, along a hexagon edge, to the actual hue angle. is a float in 0..1 range.

    rgb1 = [
      [1,h2,0],
      [h2,1,0],
      [0,1,h2],
      [0,h2,1],
      [h2,0,1],
      [1,0,h2]
    ][segment.floor].map {|x| chroma*x }

    m = luma - rgb1.zip(LUMA_WEIGHTS).map {|x,w| x*w}.inject(&:+)
    r,g,b = rgb1.map {|x| (x+m)}.map {|x| (x*255).to_i}

    rgb(r,g,b)
  end
end


if __FILE__ == $0 #unless we're being loaded as a library
  #TODO: get chunks and prompt
  colors = [0,36,75,205,240]
  tolerance = 19
  colors.each_with_index do |color,i|
    image = ChunkyPNG::Image.from_file("input.png")

    image.pixels.map! do |p| h,c,y = ChunkyPNG::Color.to_hcy_floats(p)
      if (h-color).abs < tolerance || (h-color+360).abs < tolerance
        p
      else
       ChunkyPNG::Color.hcy(h,0,y)
      end 
    end

    image.save("output_#{i+1}.png")
  end
end

output_1.png

output_2.png

output_3.png

output_4.png

output_5.png