image_analyzer.rb

# Perceptual image deduplication based on average intensity.

module ImageAnalyzer
  def intensities(image_path)
    image = CvMat.load(image_path, CV_LOAD_IMAGE_COLOR)
    image = image.smooth(CV_GAUSSIAN, 3, 3)

    half_x = (image.cols / 2).round
    half_y = (image.rows / 2).round

    nw_rect = image.sub_rect(0, 0, half_x, half_y)
    ne_rect = image.sub_rect((half_x + 1), 0, (image.cols - (half_x + 1)), half_y)
    sw_rect = image.sub_rect(0, (half_y + 1), half_x, (image.rows - (half_y + 1)))
    se_rect = image.sub_rect((half_x + 1), (half_y + 1), (image.cols - (half_x + 1)), (image.rows - (half_y + 1)))

    {
      average_intensity: rect_sum(image),
      nw_intensity: rect_sum(nw_rect),
      ne_intensity: rect_sum(ne_rect),
      sw_intensity: rect_sum(sw_rect),
      se_intensity: rect_sum(se_rect)
    }
  end

  def rect_sum(rect)
    sums = rect.sum
    r = (sums[0] / (rect.rows * rect.cols)) * 0.2126
    g = (sums[1] / (rect.rows * rect.cols)) * 0.7152
    b = (sums[2] / (rect.rows * rect.cols)) * 0.0772

    ((r + g + b) / 3).round(6)
  end
end