Average Hash

Average hashing is based on four steps:

(1) Resize an image to be a squ ared image of height and width equal to a user defined input n_size_side.
(2) Construct an matrix img_resized_gray with the the gray values of the resized image.
(3) Compute the mean intensity of img_resized_gray and store it to mean_image_intensity.
(4) Build a matrix that contains a 1 in position k if img_resized_gray[k] >. mean_image_intensity, and a 0 otherwise.

The average hash vector for an image would be the flattenend matrix of step (4).

Example

Let us visualize the original image and hash and mathash of an image.

using TestImages
img = testimage("fabio_color_256.png");
img

An average mat hash (matrix hash) can be created using average_hash(image, size), as follows:

using TestImages, Images, ImageHashes
img = testimage("fabio_color_256.png");
mat_hash = average_mathash(img, 8)
mat_hash

8×8 BitMatrix:
 0  0  0  0  0  0  0  0
 0  0  1  1  1  0  0  0
 0  0  0  1  1  1  0  0
 0  1  0  1  1  1  0  0
 0  1  0  1  1  1  0  0
 0  1  0  1  1  1  0  0
 1  1  0  0  1  1  1  0
 1  0  0  0  1  1  1  1

We can visualize the hash using Gray..

using TestImages, Images, ImageHashes
img = testimage("fabio_color_256.png");
mat_hash = average_mathash(img, 8)
Gray.(mat_hash)

The bigger the mat hash is, the higher quality it can achive.

using TestImages, Images, ImageHashes
img = testimage("fabio_color_256.png");
mat_hash = average_mathash(img, 28)
Gray.(mat_hash)

A hash (vector hash) for an image can be created with the average_hash function.

using TestImages, ImageHashes
img = testimage("fabio_color_256.png");
img_hash = average_hash(img, 8)
img_hash

0x031e407c7f3f0301

Execution time and allocations

using TestImages, ImageHashes, BenchmarkTools
img = testimage("fabio_color_256.png");
benchmark = @benchmark average_hash($img, 8)
benchmark