Quick and dirty test - implementation of the sobel operator algo

sobel_operator.rb

class Img
  def initialize(img)
    @img = img
    @pixels = img.get_pixels(0, 0, img.columns, img.rows)
  end

  def at(x, y)
    pos = x + y * @img.columns
    @pixels[pos].red
  end
end

img = Img.new(cat2)

class MyMatrix < Matrix
  public :"[]=", :set_element, :set_component
end

edge = MyMatrix.build(cat2.columns, cat2.rows) { 0 }

(0..cat2.columns - 1).each do |x|
  (0..cat2.rows - 1).each do |y|
    if x == 0 || y == 0 || x > cat2.columns - 2 || y > cat2.rows - 2
      # edge[x, y] = [255, 255, 255].map { |a| a * 255 }
      cat2.pixel_color(x, y, Magick::Pixel.new(255 * 255, 255* 255, 255* 255))
      next
    end

    pixel_x = (sobel_x[0][0] * img.at(x-1,y-1)) + (sobel_x[0][1] * img.at(x,y-1)) + (sobel_x[0][2] * img.at(x+1,y-1)) +
              (sobel_x[1][0] * img.at(x-1,y))   + (sobel_x[1][1] * img.at(x,y))   + (sobel_x[1][2] * img.at(x+1,y)) +
              (sobel_x[2][0] * img.at(x-1,y+1)) + (sobel_x[2][1] * img.at(x,y+1)) + (sobel_x[2][2] * img.at(x+1,y+1))

    pixel_y = (sobel_y[0][0] * img.at(x-1,y-1)) + (sobel_y[0][1] * img.at(x,y-1)) + (sobel_y[0][2] * img.at(x+1,y-1)) +
              (sobel_y[1][0] * img.at(x-1,y))   + (sobel_y[1][1] * img.at(x,y))   + (sobel_y[1][2] * img.at(x+1,y)) +
              (sobel_y[2][0] * img.at(x-1,y+1)) + (sobel_y[2][1] * img.at(x,y+1)) + (sobel_y[2][2] * img.at(x+1,y+1))

    val = Math.sqrt((pixel_x * pixel_x) + (pixel_y * pixel_y)).ceil
    # edge[x,y] = [val, val, val]
    cat2.pixel_color(x, y, Magick::Pixel.new(val, val, val))
  end
end