get resized image pixel data

image_util.rb

require "RMagick"
include Magick

class Integer
  def to_hex
    self.to_s(16)[/^../] 
  end
end

class ImageUtil
  def initialize(path)
    @image =
      case path
      when Magick::Image; path
      else ImageList.new(path)
      end
    @col, @row = @image.columns, @image.rows
  end

  def resize(scale)
    img = @image.resize(@col*scale, @row*scale)
    ImageUtil.new(img)
  end
  
  # get pixels pos-x, pos-y and rgba info except base_color pixels
  def pixels(opt={})
    opt = {:reject_color => "#ffffff0"}.merge(opt)
    pixels = @image.get_pixels(0,0,@col,@row)
    pixels.map.with_index { |p, i|
              x, y = i.divmod(@col)
              r, g, b, a = p.red.to_hex, p.green.to_hex, p.blue.to_hex, p.opacity
              { x:x, y:y, color:"##{r}#{g}#{b}#{a}" }
            }
          .reject { |h| h[:color] == opt[:reject_color] }
  end

  def save(path='out.jpg')
    @image.write(path)
  end
end

if __FILE__ == $0
  img = ImageUtil.new("zelda.jpeg")
  p img.resize(0.25).pixels
  # img.resize(0.25).save('abc.jpg')
end