Question

How I can change the colors from this:

into this:

I generated the output image using Gimp with the input image as layer one, and the background color from the image as layer two, in the Layers panel I selected the mode “colors”

I want preserve the background color, but want the colors be shades of brown.

Any ideas to do this with ChunkyPNG? Or should I use ImageMagick with color lookup tables?

Answer 1

Thanks for your ideas.

I found the one from Linuxios the most helpful Gimp layer modes

require "json"
require "httpclient"
require "chunky_png"

module ChunkyPNG::Color

  def h(value)
    r,g,b = r(value).to_f / MAX, g(value).to_f / MAX, b(value).to_f / MAX
    min, max = [r,g,b].minmax

    return 0 if max == min

    result = case max
      when r then (g - b) / (max - min) + (g < b ? 6 : 0)
      when g then (b - r) / (max - min) + 2
      when b then (r - g) / (max - min) + 4
    end

    result * 60
  end

  def s(value)
    min, max = [r(value), g(value), b(value)].minmax.map { |value| value.to_f / MAX }
    max == 0 ? 0 : (max - min) / max
  end

  def v(value)
    [r(value), g(value), b(value)].max.to_f / MAX
  end

  def hsv(h, s, v)
    h = h.to_f / 360
    i = (h * 6).floor
    f = h * 6 - i
    p = v * (1 - s)
    q = v * (1 - f * s)
    t = v * (1 - (1 - f) * s)

     case i % 6
      when 0 then r, g, b = v, t, p
      when 1 then r, g, b = q, v, p
      when 2 then r, g, b = p, v, t
      when 3 then r, g, b = p, q, v
      when 4 then r, g, b = t, p, v
      when 5 then r, g, b = v, p, q
    end

    rgb *[r,g,b].map {|value| (value * 255).round }
  end

end


module CoderWall

  module_function

  def badges(username)
    url = URI.escape("https://coderwall.com/#{username}.json")
    response = HTTPClient.get(url)

    json = JSON.parse(response.body)
    urls = json['badges'].map {|b| b['badge']}
    brown      = ChunkyPNG::Color.from_hex("#bf8a30")
    hue        = ChunkyPNG::Color.h(brown)
    saturation = ChunkyPNG::Color.s(brown)
    value      = ChunkyPNG::Color.v(brown)
    urls.each do |url|
      matches = url.match /(\w+)\-/
      response = HTTPClient.get(url)
      filename = "./tmp/coderwall/"+matches[1]+".png"
      File.open(filename,"w") {|f| f.write(response.body)}

      image = ChunkyPNG::Image.from_file(filename)

      image.pixels.map! do |pixel|
          v = ChunkyPNG::Color.v(pixel)
          unless ChunkyPNG::Color.a(pixel) > 0
            v = value
          end
          ChunkyPNG::Color.hsv(hue,saturation, v)
      end
      image.save(filename.gsub(/\.png/,"_brown.png"), :fast_rgba)
    end
  end
end

badges = CoderWall.badges("astropanic")

That above code consists from some snippets found around the web.

Here is the result: Stop doing new year resolutions. Make the change now !