Module: Blockhash

Defined in:
lib/blockhash.rb,
lib/blockhash/version.rb

Overview

Blockhash module

Constant Summary collapse

DEFAULT_BITS = 
16
VERSION = 
"0.1.0"

Class Method Summary collapse

Class Method Details

.calculate(img, bits = DEFAULT_BITS) ⇒ Object 



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# File 'lib/blockhash.rb', line 43

def self.calculate(img, bits = DEFAULT_BITS)
  even_x = (img.columns % bits).zero?
  even_y = (img.rows % bits).zero?
  return calculate_fast(img, bits) if even_x && even_y

  if img.alpha?
    total_value = method(:total_value_rgba)
    img_data = img.export_pixels(0, 0, img.columns, img.rows, "RGBA")
  else
    total_value = method(:total_value_rgb)
    img_data = img.export_pixels(0, 0, img.columns, img.rows, "RGB")
  end

  blocks = Array.new(bits**2, 0)
  block_width = img.columns / bits.to_f
  block_height = img.rows / bits.to_f

  (0...img.rows).each do |y|
    b_top, b_bottom, w_top, w_bottom = block_overlaps(y, img.rows, block_height, even_y)
    top_index = b_top * bits
    bottom_index = b_bottom * bits
    (0...img.columns).each do |x|
      value = total_value.call(img_data, img.columns, x, y)
      b_left, b_right, w_left, w_right = block_overlaps(x, img.columns, block_width, even_x)
      blocks[top_index + b_left] += value * w_top * w_left
      blocks[top_index + b_right] += value * w_top * w_right
      blocks[bottom_index + b_left] += value * w_bottom * w_left
      blocks[bottom_index + b_right] += value * w_bottom * w_right
    end
  end
  bits_to_hexhash(blocks_to_bits(blocks, block_width * block_height))
end

.calculate_fast(img, bits = DEFAULT_BITS) ⇒ Object 



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# File 'lib/blockhash.rb', line 17

def self.calculate_fast(img, bits = DEFAULT_BITS)
  if img.alpha?
    total_value = method(:total_value_rgba)
    img_data = img.export_pixels(0, 0, img.columns, img.rows, "RGBA")
  else
    total_value = method(:total_value_rgb)
    img_data = img.export_pixels(0, 0, img.columns, img.rows, "RGB")
  end
  blocksize_y = img.rows / bits
  blocksize_x = img.columns / bits
  # Loop through each block
  result = (0...bits).flat_map do |y|
    (0...bits).map do |x|
      # Sum all pixels in block
      (0...blocksize_y).sum do |iy|
        cy = (y * blocksize_y) + iy
        (0...blocksize_x).sum do |ix|
          cx = (x * blocksize_x) + ix
          total_value.call(img_data, img.columns, cx, cy)
        end
      end
    end
  end
  bits_to_hexhash(blocks_to_bits(result, blocksize_y * blocksize_x))
end

.calculate_from_path(path, bits = DEFAULT_BITS) ⇒ Object 



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# File 'lib/blockhash.rb', line 76

def self.calculate_from_path(path, bits = DEFAULT_BITS)
  calculate(Magick::Image.read(path).first, bits)
end

.distance(hash1, hash2) ⇒ Object 



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# File 'lib/blockhash.rb', line 9

def self.distance(hash1, hash2)
  (hash1.to_i(16) ^ hash2.to_i(16)).to_s(2).count("1")
end

.similar?(hash1, hash2, thresh = 10) ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/blockhash.rb', line 13

def self.similar?(hash1, hash2, thresh = 10)
  distance(hash1, hash2) < thresh
end