calculation of the 'phash' of an image

Source: R/hash_functions.R

This function calculates the phash of an image

phash(
  gray_image,
  hash_size = 8,
  highfreq_factor = 4,
  MODE = "hash",
  resize = "nearest"
)

Arguments

gray_image

a (2-dimensional) matrix or data frame

hash_size

an integer specifying the hash size (hash_size * highfreq_factor should be less than number of rows or columns of the gray_image)

highfreq_factor

an integer specyfing the highfrequency factor (hash_size * highfreq_factor should be less than number of rows or columns of the gray_image)

MODE

one of 'hash' (returns the hash of the image), 'binary' (returns binary identifier of the image)

resize

corresponds to one of 'nearest', 'bilinear' (resizing method)

Value

either a hash-string or a binary vector

Details

The function is a modification of the 'phash' function of the imagehash package [ please consult the COPYRIGHT file ]. The phash algorithm extends the average_hash by using the discrete cosine transform.

Examples


image = readImage(system.file("tmp_images", "2.jpg", package = "OpenImageR"))

image = rgb_2gray(image)

res_hash = phash(image, hash_size = 6, highfreq_factor = 3, MODE = 'hash')

res_binary = phash(image, hash_size = 6, highfreq_factor = 3, MODE = 'binary')