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The perceptual-hashes Reference Manual
This is the perceptual-hashes Reference Manual, version 0.1, generated automatically by Declt version 4.0 beta 2 "William Riker" on Wed Jun 15 05:31:30 2022 GMT+0.
Table of Contents
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1 Introduction
perceptual-hashes
perceptual-hashes library computes perceptual hashes for images (supported formats include formats supported by imago + jpeg). Perceptual hashes are a measure of similarity between images.
Installation
You can install perceptual-hashes from Ultralisp repository. Add Ultralisp repository to quicklisp (if you haven't already):
(ql-dist:install-dist "http://dist.ultralisp.org/"
:prompt nil)
and install perceptual-hashes:
(ql:quickload :perceptual-hashes)
Supported algorithms
The following algorithms are supported:
- aHash: An algorithm based on whenever each pixel of an image is brighter or darker than the average luminance of all pixels.
- dHash: An algorithm based on whenever each pixel of an image is brighter or darker than its neighbours.
You can find more information here.
Examples
(defconstant +threshold+ 45
"The distance between hashes can vary from 0 to (length hash) =
1024. If it is small enough (<= ~45) the images are similar")
(defun images-similar-p (image-name-1 image-name-2)
(let ((hash1 (perceptual-hashes:ahash image-name-1))
(hash2 (perceptual-hashes:ahash image-name-2)))
(< (perceptual-hashes:hamming-distance hash1 hash2)
+threshold+)))
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2 Systems
The main system appears first, followed by any subsystem dependency.
2.1 perceptual-hashes
Perceptual hash algorithms for images
- Author
Vasily Postnicov <shamaz.mazum@gmail.com>
- License
2-clause BSD
- Version
0.1
- Dependencies
- imago/pngload (system).
- jpeg-turbo (system).
- array-operations (system).
- Source
- Child Components
- src/package.lisp (file).
- src/conditions.lisp (file).
- src/load-image.lisp (file).
- src/hashes.lisp (file).
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3 Files
Files are sorted by type and then listed depth-first from the systems components trees.
3.1 Lisp
- perceptual-hashes/perceptual-hashes.asd
- perceptual-hashes/src/package.lisp
- perceptual-hashes/src/conditions.lisp
- perceptual-hashes/src/load-image.lisp
- perceptual-hashes/src/hashes.lisp
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3.1.1 perceptual-hashes/perceptual-hashes.asd
- Source
- Parent Component
perceptual-hashes (system).
- ASDF Systems
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3.1.2 perceptual-hashes/src/package.lisp
- Source
- Parent Component
perceptual-hashes (system).
- Packages
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3.1.3 perceptual-hashes/src/conditions.lisp
- Dependency
src/package.lisp (file).
- Source
- Parent Component
perceptual-hashes (system).
- Public Interface
- hash-error (condition).
- hash-unknown-format (condition).
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3.1.4 perceptual-hashes/src/load-image.lisp
- Dependency
src/conditions.lisp (file).
- Source
- Parent Component
perceptual-hashes (system).
- Internals
read-jpeg-grayscale (function).
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3.1.5 perceptual-hashes/src/hashes.lisp
- Dependency
src/load-image.lisp (file).
- Source
- Parent Component
perceptual-hashes (system).
- Public Interface
- ahash (function).
- dhash (function).
- hamming-distance (function).
- Internals
- +thumb-size+ (constant).
- get-image (function).
- thumbnail-pixels (function).
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4 Packages
Packages are listed by definition order.
4.1 perceptual-hashes
- Source
- Use List
- array-operations/all.
- common-lisp.
- imago.
- jpeg-turbo.
- Public Interface
- ahash (function).
- dhash (function).
- hamming-distance (function).
- hash-error (condition).
- hash-unknown-format (condition).
- Internals
- +thumb-size+ (constant).
- get-image (function).
- read-jpeg-grayscale (function).
- thumbnail-pixels (function).
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5 Definitions
Definitions are sorted by export status, category, package, and then by lexicographic order.
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5.1 Public Interface
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5.1.1 Ordinary functions
- Function: ahash (image) ¶
-
Return aHash (average hash) of an @c(image) which can be a string, a pathname or an @c(imago:image) object. If @c(image) is a string or a pathname, the image is loaded using this pathname.
This algorithm is based on whenever a pixel is brighter or darker than the average luminance of all pixels.- Package
- Source
- Function: dhash (image) ¶
-
Return dHash (gradient hash) of an @c(image) which can be a string, a pathname or an @c(imago:image) object. If @c(image) is a string or a pathname, the image is loaded using this pathname.
This algorithm is based on whenever a pixel is brighter or darker than the neighbour pixels.- Package
- Source
- Function: hamming-distance (hash1 hash2) ¶
-
Calculate Hamming distance between two hashes.
- Package
- Source
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5.1.2 Conditions
- Condition: hash-error ¶
-
- Package
- Source
- Direct superclasses
- error.
- simple-condition.
- Direct subclasses
- Condition: hash-unknown-format ¶
-
- Package
- Source
- Direct superclasses
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5.2 Internals
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5.2.1 Constants
- Constant: +thumb-size+ ¶
-
The image will be resized to a small square with a side +thumb-size+ before a hash is calculated.
- Package
- Source
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Appendix A Indexes
A.2 Functions
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A.3 Variables
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C |
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+thumb-size+: | Private constants | ||
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| C | |||
Constant, +thumb-size+: | Private constants | ||
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C |
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A.4 Data types
| Jump to: | C F H P S |
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