Module: Phash

Defined in:
lib/phash.rb,
lib/phash/image.rb,
lib/phash/version.rb

Defined Under Namespace

Classes: Image

Constant Summary collapse

CIMG_PI = 
3.14159265358979323846
CIMG_V = 
CIMG_PI / 2 / 32
CIMG_SCALE = 
2**8 + 1
VERSION = 
"0.3.1"

Class Method Summary collapse

Class Method Details

.distance(fingerprint1, fingerprint2) ⇒ Object 



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

def self.distance(fingerprint1, fingerprint2)
  (fingerprint1 ^ fingerprint2).to_s(2).count('1')
end

.fingerprint(path_or_img) ⇒ Object 



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

def self.fingerprint(path_or_img)
  img = path_or_img.is_a?(Vips::Image) ? path_or_img : Vips::Image.new_from_file(path_or_img)
  # Strip alpha channel if present (4-band images)
  img = img[0..2] if img.bands == 4
  #Y = (66*R + 129*G + 25*B + 128)/256 + 16
  img = img * [66.0 / 256, 129.0 / 256, 25.0 / 256]
  r, g, b = img.bandsplit
  img = r + g + b + 16.5

  mask = Vips::Image.new_from_array([[1.0] * 7] * 7)
  img = img.colourspace("grey16")
  img = img.conv(mask)
  mat = sample(img)
  dct = ph_dct_matrix
  dct_t = dct.transpose

  out = dct * mat * dct_t

  sub = out.minor(1..8, 1..8).to_a.flatten
  median = sub.sort[31..32].sum / 2

  sub.reverse.map {|i| i > median ? 1 : 0 }.join.to_i(2)
end

.large_image?(img) ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/phash.rb', line 54

def self.large_image?(img)
  img.width * img.height > 250_000
end

.ph_dct_matrix ⇒ Object 



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

def self.ph_dct_matrix
  @dct_matrix ||= begin
    v = 1 / Math.sqrt(32)
    c1 = Math.sqrt(2.0 / 32)

    Matrix.build(32, 32) do |y, x|
      (y < 1 ? v : c1 * Math.cos(CIMG_V * y * (2*x + 1))).round(6)
    end
  end
end

.sample(img) ⇒ Object 



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# File 'lib/phash.rb', line 58

def self.sample(img)
  w, h = img.width, img.height
  w_step = w / 32.0
  h_step = h / 32.0

  if large_image?(img)
    # Large images: use getpoint to avoid copying entire image to Ruby array
    Matrix.build(32, 32) do |y, x|
      img.getpoint((x * w_step).to_i, (y * h_step).to_i)[0] / CIMG_SCALE
    end
  else
    # Small images: to_a is faster than 1024 getpoint calls
    src = img.to_a
    Matrix.build(32, 32) do |y, x|
      src[(y * h_step).to_i][(x * w_step).to_i][0] / CIMG_SCALE
    end
  end
end