The module brings implementations of different image hashing algorithms.

クラス
class	cv::img_hash::AverageHash
	Computes average hash value of the input image [詳解]
class	cv::img_hash::BlockMeanHash
	Image hash based on block mean. [詳解]
class	cv::img_hash::ColorMomentHash
	Image hash based on color moments. [詳解]
class	cv::img_hash::ImgHashBase
	The base class for image hash algorithms [詳解]
class	cv::img_hash::MarrHildrethHash
	Marr-Hildreth Operator Based Hash, slowest but more discriminative. [詳解]
class	cv::img_hash::PHash
	pHash [詳解]
class	cv::img_hash::RadialVarianceHash
	Image hash based on Radon transform. [詳解]

列挙型
enum	cv::img_hash::BlockMeanHashMode { cv::img_hash::BLOCK_MEAN_HASH_MODE_0 = 0 , cv::img_hash::BLOCK_MEAN_HASH_MODE_1 = 1 }

関数
CV_EXPORTS_W void	cv::img_hash::averageHash (cv::InputArray inputArr, cv::OutputArray outputArr)
	Calculates img_hash::AverageHash in one call [詳解]
CV_EXPORTS_W void	cv::img_hash::blockMeanHash (cv::InputArray inputArr, cv::OutputArray outputArr, int mode=BLOCK_MEAN_HASH_MODE_0)
	Computes block mean hash of the input image [詳解]
CV_EXPORTS_W void	cv::img_hash::colorMomentHash (cv::InputArray inputArr, cv::OutputArray outputArr)
	Computes color moment hash of the input, the algorithm is come from the paper "Perceptual Hashing for Color Images Using Invariant Moments" [詳解]
CV_EXPORTS_W void	cv::img_hash::marrHildrethHash (cv::InputArray inputArr, cv::OutputArray outputArr, float alpha=2.0f, float scale=1.0f)
	Computes average hash value of the input image [詳解]
CV_EXPORTS_W void	cv::img_hash::pHash (cv::InputArray inputArr, cv::OutputArray outputArr)
	Computes pHash value of the input image [詳解]
CV_EXPORTS_W void	cv::img_hash::radialVarianceHash (cv::InputArray inputArr, cv::OutputArray outputArr, double sigma=1, int numOfAngleLine=180)
	Computes radial variance hash of the input image [詳解]

詳解

Provide algorithms to extract the hash of images and fast way to figure out most similar images in huge data set.

Namespace for all functions is cv::img_hash.

Supported Algorithms

• Average hash (also called Different hash)
• PHash (also called Perceptual hash)
• Marr Hildreth Hash
• Radial Variance Hash
• Block Mean Hash (modes 0 and 1)
• Color Moment Hash (this is the one and only hash algorithm resist to rotation attack(-90~90 degree))

You can study more about image hashing from following paper and websites:

• "Implementation and benchmarking of perceptual image hash functions" [zauner2010implementation]
• "Looks Like It" [lookslikeit]

Code Example

Performance under different attacks

Speed comparison with PHash library (100 images from ukbench)

As you can see, hash computation speed of img_hash module outperform PHash library a lot.

PS : I do not list out the comparison of Average hash, PHash and Color Moment hash, because I cannot find them in PHash.

Motivation

Collects useful image hash algorithms into opencv, so we do not need to rewrite them by ourselves again and again or rely on another 3rd party library(ex : PHash library). BOVW or correlation matching are good and robust, but they are very slow compare with image hash, if you need to deal with large scale CBIR(content based image retrieval) problem, image hash is a more reasonable solution.

More info

You can learn more about img_hash modules from following links, these links show you how to find similar image from ukbench dataset, provide thorough benchmark of different attacks(contrast, blur, noise(gaussion,pepper and salt), jpeg compression, watermark, resize).

Introduction to image hash module of opencv Speed up image hashing of opencv(img_hash) and introduce color moment hash

Contributors

Tham Ngap Wei, thamn.nosp@m.gapw.nosp@m.ei@gm.nosp@m.ail..nosp@m.com

列挙型詳解

BlockMeanHashMode

enum cv::img_hash::BlockMeanHashMode

列挙値
BLOCK_MEAN_HASH_MODE_0	use fewer block and generate 16*16/8 uchar hash value
BLOCK_MEAN_HASH_MODE_1	use block blocks(step sizes/2), generate 31*31/8 + 1 uchar hash value

関数詳解

averageHash()

CV_EXPORTS_W void cv::img_hash::averageHash	(	cv::InputArray	inputArr,
		cv::OutputArray	outputArr
	)

Calculates img_hash::AverageHash in one call

引数

inputArr	input image want to compute hash value, type should be CV_8UC4, CV_8UC3 or CV_8UC1.
outputArr	Hash value of input, it will contain 16 hex decimal number, return type is CV_8U

blockMeanHash()

CV_EXPORTS_W void cv::img_hash::blockMeanHash	(	cv::InputArray	inputArr,
		cv::OutputArray	outputArr,
		int	mode = BLOCK_MEAN_HASH_MODE_0
	)

Computes block mean hash of the input image

引数

inputArr	input image want to compute hash value, type should be CV_8UC4, CV_8UC3 or CV_8UC1.
outputArr	Hash value of input, it will contain 16 hex decimal number, return type is CV_8U
mode	the mode

colorMomentHash()

CV_EXPORTS_W void cv::img_hash::colorMomentHash	(	cv::InputArray	inputArr,
		cv::OutputArray	outputArr
	)

Computes color moment hash of the input, the algorithm is come from the paper "Perceptual Hashing for Color Images Using Invariant Moments"

引数

inputArr	input image want to compute hash value, type should be CV_8UC4, CV_8UC3 or CV_8UC1.
outputArr	42 hash values with type CV_64F(double)

marrHildrethHash()

CV_EXPORTS_W void cv::img_hash::marrHildrethHash	(	cv::InputArray	inputArr,
		cv::OutputArray	outputArr,
		float	alpha = 2.0f,
		float	scale = 1.0f
	)

Computes average hash value of the input image

引数

inputArr	input image want to compute hash value, type should be CV_8UC4, CV_8UC3, CV_8UC1.
outputArr	Hash value of input, it will contain 16 hex decimal number, return type is CV_8U
alpha	int scale factor for marr wavelet (default=2).
scale	int level of scale factor (default = 1)

pHash()

CV_EXPORTS_W void cv::img_hash::pHash	(	cv::InputArray	inputArr,
		cv::OutputArray	outputArr
	)

Computes pHash value of the input image

引数

inputArr	input image want to compute hash value, type should be CV_8UC4, CV_8UC3, CV_8UC1.
outputArr	Hash value of input, it will contain 8 uchar value

radialVarianceHash()

CV_EXPORTS_W void cv::img_hash::radialVarianceHash	(	cv::InputArray	inputArr,
		cv::OutputArray	outputArr,
		double	sigma = 1,
		int	numOfAngleLine = 180
	)

Computes radial variance hash of the input image

引数

inputArr	input image want to compute hash value, type should be CV_8UC4, CV_8UC3, CV_8UC1.
outputArr	Hash value of input
sigma	Gaussian kernel standard deviation
numOfAngleLine	The number of angles to consider