CN110717892A - Tone mapping image quality evaluation method - Google Patents
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Abstract
The invention discloses a tone mapping image quality evaluation method, which comprises the steps of taking the influence of bright area characteristics and dark area characteristics on tone mapping into consideration in a training stage, extracting bright and dark area characteristic vectors of a tone mapping image, extracting area contrast characteristic vectors of the tone mapping image, forming a global characteristic vector, training the global characteristic vectors of all tone mapping images in a training image set by using support vector regression, and constructing a quality prediction model; in the testing stage, the objective quality predicted value of the tone mapping image is obtained through calculating the global feature vector of the tone mapping image used for testing and predicting according to the quality prediction model constructed in the training stage, and because the obtained global feature vector information has stronger stability and can better reflect the quality change condition of the tone mapping image, the correlation between the objective evaluation result and the subjective perception is effectively improved.
Description
Technical Field
The invention relates to an image quality evaluation method, in particular to a tone mapping image quality evaluation method.
Background
With the rapid development of display technologies, High Dynamic Range (HDR) images have received increasing attention. The high dynamic range image has rich levels, and can achieve the light and shadow effect which is far closer to the reality than the common image. However, conventional display devices can only support low dynamic range display output. To solve the contradiction between the mismatch of the dynamic range of the real scene and the conventional display device, many Tone Mapping (Tone Mapping) algorithms for high dynamic range images are proposed. The aim of the tone mapping algorithm of the high dynamic range image is to compress the brightness of the high dynamic range image to a range acceptable by the traditional display equipment, meanwhile, the detail information of the original image is kept as much as possible, and image flaws are avoided. Therefore, how to accurately and objectively evaluate the performance of different tone mapping methods plays an important role in guiding content production and post-processing.
However, for the tone-mapped image quality evaluation, if the existing image quality evaluation method is directly applied to the tone-mapped image, the tone-mapped image has only a high dynamic range image as a reference, and thus the objective evaluation value cannot be accurately predicted. Therefore, how to effectively extract visual features in the evaluation process to enable objective evaluation results to be more perceptually accordant with the human visual system is a problem to be researched and solved in the process of carrying out objective quality evaluation on tone mapping images.
Disclosure of Invention
The invention aims to provide a tone mapping image quality evaluation method which can effectively improve the correlation between objective evaluation results and subjective perception.
The technical scheme adopted by the invention for solving the technical problems is as follows: a tone mapping image quality evaluation method is characterized by comprising a training stage and a testing stage;
the specific steps of the training phase process are as follows:
① _1, selecting N tone mapping images with width W and height H to form a training image set, and recording the kth tone mapping image in the training image set as
Wherein N is a positive integer, N is more than 1, k is a positive integer, the initial value of k is 1, and k is more than or equal to 1 and less than or equal to N;
① _2, dividing each tone mapping image in the training image set into light area, dark area and normal area
The bright area, the dark area and the normal area are correspondingly recorded asAnd
① _3 calculating a light and dark region feature vector for each tone-mapped image in the training image set based on the light and dark regions of each tone-mapped image in the training image set, the method comprising
The light and dark region feature vector is recorded as
And calculating the regional contrast characteristic vector of each tone mapping image in the training image set according to the bright region, the dark region and the normal region of each tone mapping image in the training image set, and calculating the contrast characteristic vector of each tone mapping image in the training image set according to the bright region, the dark region and the normal region
Is noted as the area contrast feature vector
Wherein the content of the first and second substances,
has a dimension of 3 x 1,
has a dimension of 8 × 1;
① _4, forming a global feature vector by the bright and dark region feature vector and the region contrast feature vector of each tone mapping image in the training image setIs noted as Fk，
Wherein, FkHas a dimension of 11X 1, symbol "[ 2 ]]"is a vector representing a symbol and,
show that
And
connected to form a vector;
① _5, forming a training sample data set by the global feature vectors and the average subjective score difference values of all tone mapping images in the training image set, wherein the training sample data set comprises N global feature vectors and N average subjective score difference values, then adopting support vector regression as a machine learning method to train all global feature vectors in the training sample data set, so that the error between the regression function value obtained by training and the average subjective score difference value is minimum, and the optimal weight vector obtained by fitting is obtainedAnd an optimal bias termThen using the optimal weight vector
And an optimal bias termStructural quality prediction model, as
Wherein the content of the first and second substances,
in functional representation, F is used to represent the global feature vector of the tone-mapped image, and as input vector to the quality prediction model,
is composed of
The transpose of (a) is performed,
is a linear function of F;
the test stage process comprises the following specific steps:
② for any tone-mapped image I used as a testtestAccording to the same operations from step ① _2 to step ① _4, I is obtainedtestGlobal feature vector of (2), noted as Ftest(ii) a Then, according to the quality prediction model pair F constructed in the training stagetestTesting and predicting to obtain FtestCorresponding predicted value is taken as ItestThe predicted objective quality value of (2) is marked as Qtest，
Wherein, ItestHas a width W 'and a height H', FtestHas a dimension of 11 x 1,
is represented by FtestIs a linear function of (a).
Said step ① _2
And
the acquisition process comprises the following steps:
① _2a, will
R, G, and B components in the RGB color space are expressed as
Then calculate
Is recorded as a dark channel image
Will be provided with
The pixel value of the pixel point with the middle coordinate position (x, y) is recorded as Wherein x is more than or equal to 1 and less than or equal to W, y is more than or equal to 1 and less than or equal to H, min () is a function for taking the minimum value, Cx,yRepresenting a set of coordinate positions of all pixel points within a 3 × 3 neighborhood range centered on a pixel point whose coordinate position is (x, y), (x1,y1) Is Cx,yAny one of the coordinate positions of (a) and (b),
to represent
The middle coordinate position is (x)1,y1) The pixel value of the pixel point of (a),
to represent
The middle coordinate position is (x)1,y1) The pixel value of the pixel point of (a),
to representThe middle coordinate position is (x)1,y1) The pixel value of the pixel point of (1);
① _2b, calculation
Distribution of gray histogram of (1), noted as { hk(j) J is more than or equal to 1 and less than or equal to 256 }; then will { h }k(j) The coordinate of the node with the minimum coordinate in all nodes with the non-zero histogram value in the [ 1 is not less than j is not more than 256 ] is recorded as XminWill { h }k(j) The coordinate of the node with the maximum coordinate in all nodes with the non-zero histogram value in the [ 1 is not less than j is not more than 256 ] is recorded as XmaxWill be
The middle pixel value belongs to [ Xmin,Xmid]The set of pixel values of all the pixels in the range is recorded as omega1Will be
Middle pixel value belongs to (X)mid,Xmax]The set of pixel values of all the pixels in the range is recorded as omega2(ii) a Wherein j is a positive integer, j is more than or equal to 1 and less than or equal to 256, and hk(j) Represents { h }k(j) J is more than or equal to 1 and less than or equal to 256, the histogram value of the node with the coordinate of j,
symbol
Is a rounding down operation symbol;
① _2c, by maximizing Ω1Obtain a first threshold, denoted as X1 *，
And by maximizing omega2Obtain a second threshold, denoted as X2 *，Wherein the content of the first and second substances,
express the finding such thatX when the value of (A) is maximum1Value of (A), X1Is omega1Of any one pixel value, Pf(X1) Represents omega1In (A) is [ X ]min,X1) Probability density function, mu, of all pixel values within a rangef(X1) Represents omega1In (A) is [ X ]min,X1) Mean, σ, of all pixel values in the rangef(X1) Represents omega1In (A) is [ X ]min,X1) Standard deviation, μ, of all pixel values within a rangeb(X1) Represents omega1In (A) is [ X ]1,Xmid]Mean, σ, of all pixel values in the rangeb(X1) Represents omega1In (A) is [ X ]1,Xmid]The standard deviation of all pixel values within the range,
express the finding such that
X when the value of (A) is maximum2Value of (A), X2Is omega2Of any one pixel value, Pf(X2) Represents omega2In (A) is [ X ]mid,X2) Probability density function, mu, of all pixel values within a rangef(X2) Represents omega2In (A) is [ X ]mid,X2) Mean, σ, of all pixel values in the rangef(X2) Represents omega2In (A) is [ X ]mid,X2) Standard deviation, μ, of all pixel values within a rangeb(X2) Represents omega2In (A) is [ X ]2,Xmax]Mean, σ, of all pixel values in the rangeb(X2) Represents omega2In (A) is [ X ]2,Xmax]Standard deviation of all pixel values within the range;
① _2d, will
Middle pixel value belongs to (X)2 *,Xmax]The area formed by all pixel points in the range is determined as a bright area
Will be provided withThe middle pixel value belongs to [ Xmin,X1 *) The area formed by all pixel points in the range is determined as a dark areaWill be provided with
The middle pixel value belongs to [ X1 *,X2 *]The area formed by all pixel points in the range is determined as a normal area
Said step ① _3
The acquisition process comprises the following steps:
① _3a 1. A. the method comprises the steps of
From the RGB color space to the CIELAB color space,
the three components in the CIELAB color space are a luma component, a first chroma component, and a second chroma component, respectively;
① _3b1, will
Dividing into M non-overlapping sub-blocks of size 8 × 8 if
The sub-blocks with the size of 8 multiplied by 8 can not be equally divided, and redundant pixel points are removed; then will be
The brightness components of all pixel points in each sub-block form a matrix with dimension of 8 x 8, and the matrix is divided into two parts
The matrix with dimension of 8 multiplied by 8 formed by the brightness components of all the pixel points in the t-th sub-block is marked as zt(ii) a Wherein M is a positive integer, M is more than 1, t is a positive integer, the initial value of t is 1, and t is more than or equal to 1 and less than or equal to M;
① _3c1, pairPerforming two-dimensional discrete cosine transform on a matrix with dimension of 8 multiplied by 8 and formed by the brightness components of all pixel points in each sub-block to obtain a corresponding discrete cosine transform coefficient matrix, and converting z into ztThe corresponding matrix of discrete cosine transform coefficients is denoted as Zt(ii) a However, the device is not suitable for use in a kitchenPost-calculation
The sum of all high frequency coefficients and all intermediate frequency coefficients in the discrete cosine transform coefficient matrix corresponding to each sub-block in the Z-transform coefficient matrix is obtainedtThe sum of all high frequency coefficients and all medium frequency coefficients in (1) is denoted as St(ii) a Wherein Z istHas a dimension of 8 × 8;
① _3d1, calculation
Is characterized by
① _3e1, calculation
The mean and standard deviation of the brightness components of all the pixels in (1) are correspondingly recorded as
And
① _3f1, will
Andvectors constructed in a sequential arrangement as
Wherein the symbol "[ alpha ],")]"is a vector representing a symbol and,
show that
And
connected to form a vector.
Said step ① _3
The acquisition process comprises the following steps:
① _3a 2. A. the method comprises the steps of
From the RGB color space to the CIELAB color space,the three components in the CIELAB color space are a luma component, a first chroma component, and a second chroma component, respectively;
① _3b2, calculationSum of luminance components of all pixel points in
The first regional contrast of the brightness components of all the pixels in (1), which is recorded as
And calculate
Sum of luminance components of all pixel points in
The second regional contrast of the brightness components of all the pixel points in (1), is recorded as
Wherein the symbol "|" is an absolute value symbol,
to represent
The average of the luminance components of all the pixel points in (a),
to representThe standard deviation of the luminance components of all the pixel points in (a),
to represent
The average of the luminance components of all the pixel points in (a),
to represent
The standard deviation of the brightness components of all the pixel points in the image is xi, which is a control parameter;
① _3c2, calculation
Sum of luminance components of all pixel points in
The first regional contrast of the brightness components of all the pixels in (1), which is recorded as
And calculateSum of luminance components of all pixel points in
The second regional contrast of the brightness components of all the pixel points in (1), is recorded as
Wherein the content of the first and second substances,
to represent
The average of the luminance components of all the pixel points in (a),to represent
The standard deviation of the luminance components of all the pixel points in (1);
① _3d2, calculationFirst chrominance component sum of all pixel points in
Of all the pixel pointsFirst regional contrast of the first chrominance component, denoted
And calculate
First chrominance component sum of all pixel points in
The second regional contrast of the first chrominance components of all the pixel points in (1) is recorded as
Wherein the content of the first and second substances,to represent
The average of the first chrominance components of all the pixels in (a),
to representThe standard deviation of the first chrominance components of all the pixel points in (a),
to represent
The average of the first chrominance components of all the pixels in (a),
to represent
The standard deviation of the first chrominance components of all the pixel points in (1);
① _3e2, calculation
First chrominance component sum of all pixel points inThe first regional contrast of the first chrominance components of all the pixel points in (1) is recorded as
And calculate
First chrominance component sum of all pixel points in
The second regional contrast of the first chrominance components of all the pixel points in (1) is recorded as
Wherein the content of the first and second substances,
to represent
The average of the first chrominance components of all the pixels in (a),
to represent
The standard deviation of the first chrominance components of all the pixel points in (1);
① _3f2, will
Vectors constructed in a sequential arrangement as
Wherein the symbol "[ alpha ],")]"is a vector representing a symbol and,
show that
And
connected to form a vector.
Compared with the prior art, the invention has the advantages that:
the method takes the influence of bright area characteristics and dark area characteristics on tone mapping into consideration, extracts bright and dark area characteristic vectors of a tone mapping image, extracts area contrast characteristic vectors of the tone mapping image at the same time, then constructs a global characteristic vector, and trains the global characteristic vectors of all tone mapping images in a training image set by using support vector regression to construct a quality prediction model; in the testing stage, the objective quality predicted value of the tone mapping image is obtained through calculating the global feature vector of the tone mapping image used for testing and predicting according to the quality prediction model constructed in the training stage, and because the obtained global feature vector information has stronger stability and can better reflect the quality change condition of the tone mapping image, the correlation between the objective evaluation result and the subjective perception is effectively improved.
Drawings
Fig. 1 is a block diagram of the overall implementation of the method of the present invention.
Detailed Description
The invention is described in further detail below with reference to the accompanying examples.
The general implementation block diagram of the tone mapping image quality evaluation method provided by the invention is shown in fig. 1, and the method comprises two processes, namely a training stage and a testing stage;
the specific steps of the training phase process are as follows:
① _1, selecting N tone mapping images with width W and height H to form a training image set, and recording the kth tone mapping image in the training image set as
Wherein, N is a positive integer, N is more than 1, if N is 1000, k is a positive integer, the initial value of k is 1, and k is more than or equal to 1 and less than or equal to N.
① _2, dividing each tone mapping image in the training image set into light area, dark area and normal area
The bright area, the dark area and the normal area are correspondingly recorded as
And
in this embodiment, step ① _2
And
the acquisition process comprises the following steps:
① _2a, will
R, G, and B components in the RGB color space are expressed as
Then calculate
Is recorded as a dark channel image
Will be provided with
The pixel value of the pixel point with the middle coordinate position (x, y) is recorded as
Wherein x is more than or equal to 1 and less than or equal to W, y is more than or equal to 1 and less than or equal to H, min () is a function for taking the minimum value, Cx,yRepresenting a set of coordinate positions of all pixel points within a 3 × 3 neighborhood range centered on a pixel point whose coordinate position is (x, y), (x1,y1) Is Cx,yAny one of the coordinate positions of (a) and (b),to represent
The middle coordinate position is (x)1,y1) The pixel value of the pixel point of (a),
to represent
The middle coordinate position is (x)1,y1) The pixel value of the pixel point of (a),to represent
The middle coordinate position is (x)1,y1) The pixel value of the pixel point of (1).
① _2b, calculation
Distribution of gray histogram of (1), noted as { hk(j) J is more than or equal to 1 and less than or equal to 256 }; then will { h }k(j) The coordinate of the node with the minimum coordinate in all nodes with the non-zero histogram value in the [ 1 is not less than j is not more than 256 ] is recorded as XminWill { h }k(j) The coordinate of the node with the maximum coordinate in all nodes with the non-zero histogram value in the [ 1 is not less than j is not more than 256 ] is recorded as XmaxWill be
The middle pixel value belongs to [ Xmin,Xmid]The set of pixel values of all the pixels in the range is recorded as omega1Will be
Middle pixel value belongs to (X)mid,Xmax]The set of pixel values of all the pixels in the range is recorded as omega2(ii) a Wherein j is a positive integer, j is more than or equal to 1 and less than or equal to 256, and hk(j) Represents { h }k(j) J is more than or equal to 1 and less than or equal to 256, the histogram value of the node with the coordinate of j,symbol
To round the operator down.
① _2c, by maximizing Ω1Obtain a first threshold, denoted as X1 *，
And by maximizing omega2Obtain a second threshold, denoted as X2*，Wherein the content of the first and second substances,
express the finding such that
X when the value of (A) is maximum1Value of (A), X1Is omega1Of any one pixel value, Pf(X1) Represents omega1In (A) is [ X ]min,X1) Probability density function, mu, of all pixel values within a rangef(X1) Represents omega1In (A) is [ X ]min,X1) Mean, σ, of all pixel values in the rangef(X1) Represents omega1In (A) is [ X ]min,X1) Standard deviation, μ, of all pixel values within a rangeb(X1) Represents omega1In (A) is [ X ]1,Xmid]Mean, σ, of all pixel values in the rangeb(X1) Represents omega1In (A) is [ X ]1,Xmid]The standard deviation of all pixel values within the range,
express the finding such that
X when the value of (A) is maximum2Value of (A), X2Is omega2Of any one pixel value, Pf(X2) Represents omega2In (A) is [ X ]mid,X2) Probability density function, mu, of all pixel values within a rangef(X2) Represents omega2In (A) is [ X ]mid,X2) Mean, σ, of all pixel values in the rangef(X2) Represents omega2In (A) is [ X ]mid,X2) Standard deviation, μ, of all pixel values within a rangeb(X2) Represents omega2In (A) is [ X ]2,Xmax]Mean, σ, of all pixel values in the rangeb(X2) Represents omega2In (A) is [ X ]2,Xmax]Standard deviation of all pixel values within the range.
① _2d, will
Middle pixel value belongs to (X)2 *,Xmax]The area formed by all pixel points in the range is determined as a bright area
Will be provided withThe middle pixel value belongs to [ Xmin,X1 *) The area formed by all pixel points in the range is determined as a dark area
Will be provided withThe middle pixel value belongs to [ X1 *,X2 *]The area formed by all pixel points in the range is determined as a normal area
① _3 calculating a light and dark region feature vector for each tone-mapped image in the training image set based on the light and dark regions of each tone-mapped image in the training image set, the method comprising
The light and dark region feature vector is recorded as
And calculating the regional contrast characteristic vector of each tone mapping image in the training image set according to the bright region, the dark region and the normal region of each tone mapping image in the training image set, and calculating the contrast characteristic vector of each tone mapping image in the training image set according to the bright region, the dark region and the normal region
Is noted as the area contrast feature vector
Wherein the content of the first and second substances,
has a dimension of 3 x 1,
dimension (d) is 8 × 1.
In this embodiment, step ① _3
The acquisition process comprises the following steps:
① _3a 1. A. the method comprises the steps of
From the RGB color space to the CIELAB color space,the three components in the CIELAB color space are the luma component, the first chroma component (referred to as component a) and the second chroma component (referred to as component b), respectively.
① _3b1, will
Dividing into M non-overlapping sub-blocks of size 8 × 8 if
The subblocks with the size of 8 multiplied by 8 can not be equally divided, redundant pixel points are removed, namely the redundant pixel points are not considered; then will be
The brightness components of all pixel points in each sub-block form a matrix with dimension of 8 x 8, and the matrix is divided into two parts
The matrix with dimension of 8 multiplied by 8 formed by the brightness components of all the pixel points in the t-th sub-block is marked as zt(ii) a Wherein M is a positive integer, M is more than 1, t is a positive integer, the initial value of t is 1, and t is more than or equal to 1 and less than or equal to M.
① _3c1, pair
Performing two-dimensional discrete cosine transform on a matrix with dimension of 8 multiplied by 8 and formed by the brightness components of all pixel points in each sub-block to obtain a corresponding discrete cosine transform coefficient matrix, and converting z into ztThe corresponding matrix of discrete cosine transform coefficients is denoted as Zt(ii) a Then calculate
The sum of all high frequency coefficients and all intermediate frequency coefficients in the discrete cosine transform coefficient matrix corresponding to each sub-block in the Z-transform coefficient matrix is obtainedtThe sum of all high frequency coefficients and all medium frequency coefficients in (1) is denoted as St(ii) a Wherein Z istThe dimension of (2) is 8 multiplied by 8, the upper left corner part in the discrete cosine transform coefficient matrix is direct current and low frequency coefficients, the lower right corner part is high frequency coefficients, and the middle part is intermediate frequency coefficients.
① _3d1, calculationIs characterized by
① _3e1, calculation
The mean and standard deviation of the brightness components of all the pixels in (1) are correspondingly recorded as
And
① _3f1, will
And
vectors constructed in a sequential arrangement as Wherein the symbol "[ alpha ],")]"is a vector representing a symbol and,
show that
And
connected to form a vector.
In this embodiment, step ① _3
The acquisition process comprises the following steps:
① _3a 2. A. the method comprises the steps of
From the RGB color space to the CIELAB color space,
the three components in the CIELAB color space are the luma component, the first chroma component (referred to as component a) and the second chroma component (referred to as component b), respectively.
① _3b2, calculation
Sum of luminance components of all pixel points in
The first regional contrast of the brightness components of all the pixels in (1), which is recorded as
And calculate
Sum of luminance components of all pixel points in
The second regional contrast of the brightness components of all the pixel points in (1), is recorded as
Wherein the symbol "|" is an absolute value symbol,
to represent
The average of the luminance components of all the pixel points in (a),
to represent
The standard deviation of the luminance components of all the pixel points in (a),to represent
The average of the luminance components of all the pixel points in (a),
to representThe standard deviation of the luminance components of all the pixels in (1), ξ is a control parameter, which is 10 in this embodiment-6。
① _3c2, calculationSum of luminance components of all pixel points in
The first regional contrast of the brightness components of all the pixels in (1), which is recorded as
And calculateSum of luminance components of all pixel points in
Of all pixel points inRegional contrast, is
Wherein the content of the first and second substances,to represent
The average of the luminance components of all the pixel points in (a),
to represent
The standard deviation of the luminance components of all the pixel points in (1).
① _3d2, calculation
First chrominance component sum of all pixel points in
The first regional contrast of the first chrominance components of all the pixel points in (1) is recorded as
And calculate
First chrominance component sum of all pixel points in
The second regional contrast of the first chrominance components of all the pixel points in (1) is recorded as 
Wherein the content of the first and second substances,
to representThe average of the first chrominance components of all the pixels in (a),
to represent
The standard deviation of the first chrominance components of all the pixel points in (a),
to represent
The average of the first chrominance components of all the pixels in (a),
to represent
The standard deviation of the first chrominance components of all the pixel points in (1).
① _3e2, calculation
First chrominance component sum of all pixel points in
The first regional contrast of the first chrominance components of all the pixel points in (1) is recorded as
And calculate
First chrominance component sum of all pixel points inThe second regional contrast of the first chrominance components of all the pixel points in (1) is recorded as
Wherein the content of the first and second substances,
to represent
The average of the first chrominance components of all the pixels in (a),
to represent
The standard deviation of the first chrominance components of all the pixel points in (1).
① _3f2, will
Vectors constructed in a sequential arrangement as
Wherein the symbol "[ alpha ],")]"is a vector representing a symbol and,
show that
Andconnected to form a vector.
① _4, forming a global feature vector by the bright and dark region feature vector and the region contrast feature vector of each tone mapping image in the training image set
Is noted as Fk，
Wherein, FkHas a dimension of 11X 1, symbol "[ 2 ]]"is a vector representing a symbol and,
show that
Andconnected to form a vector.
① _5, forming a training sample data set by the global feature vectors and the average subjective score difference values of all tone mapping images in the training image set, wherein the training sample data set comprises N global feature vectors and N average subjective score difference values, and then training all global feature vectors in the training sample data set by adopting support vector regression as a machine learning method, so that the error between the regression function value obtained by training and the average subjective score difference value is causedThe difference is minimum, and the optimal weight vector is obtained by fitting
And an optimal bias term
Then using the optimal weight vector
And an optimal bias term
Structural quality prediction model, as
Wherein the content of the first and second substances,in functional representation, F is used to represent the global feature vector of the tone-mapped image, and as input vector to the quality prediction model,is composed of
The transpose of (a) is performed,as a linear function of F.
The test stage process comprises the following specific steps:
② for any tone-mapped image I used as a testtestAccording to the same operations from step ① _2 to step ① _4, I is obtainedtestGlobal feature vector of (2), noted as Ftest(ii) a Then, according to the quality prediction model pair F constructed in the training stagetestTesting and predicting to obtain FtestCorresponding predicted value is taken as ItestThe objective quality prediction value of (1) is recorded asWherein, ItestHas a width W 'and a height H', FtestHas a dimension of 11 x 1,
is represented by FtestIs a linear function of (a).
In the present embodiment, as the tone mapping image database, the TMID database established by the university of luugu, canada and the ESPL-LIVE database established by the austin division, university of texas, usa were used, and the TMID database included 120 tone mapping images and the ESPL-LIVE database included 1811 tone mapping images. 2 common objective parameters of the evaluation method for evaluating the image quality are used as evaluation indexes, namely Pearson Linear Correlation Coefficient (PLCC) and Spearman Rank Order Correlation Coefficient (SROCC) under the condition of nonlinear regression. The higher PLCC and SROCC indicate the better correlation between the evaluation results of the method of the invention and the difference of the average subjective scores. Table 1 shows the correlation between the objective quality prediction value obtained by the method of the present invention and the mean subjective score difference.
TABLE 1 correlation between objective quality prediction values and mean subjective score differences obtained by the method of the invention
| Database with a plurality of databases | PLCC | SROCC |
| TMID | 0.827 | 0.758 |
| ESPL-LIVE | 0.658 | 0.660 |
As can be seen from Table 1, the correlation between the objective quality prediction value of the tone mapping image obtained by the method of the present invention and the average subjective score difference is very high, which indicates that the objective evaluation result is more consistent with the result of human eye subjective perception, and is sufficient to illustrate the effectiveness of the method of the present invention.
Claims (4)
1. A tone mapping image quality evaluation method is characterized by comprising a training stage and a testing stage;
the specific steps of the training phase process are as follows:
① _1, selecting N tone mapping images with width W and height H to form a training image set, and recording the kth tone mapping image in the training image set as
Wherein N is a positive integer, N is more than 1, k is a positive integer, the initial value of k is 1, and k is more than or equal to 1 and less than or equal to N;
① _2, dividing each tone mapping image in the training image set into light area, dark area and normal area
The bright area, the dark area and the normal area are correspondingly recorded as
And
① _3 calculating a light and dark region feature vector for each tone-mapped image in the training image set based on the light and dark regions of each tone-mapped image in the training image set, the method comprisingThe light and dark region feature vector is recorded as
And calculating the regional contrast characteristic vector of each tone mapping image in the training image set according to the bright region, the dark region and the normal region of each tone mapping image in the training image set, and calculating the contrast characteristic vector of each tone mapping image in the training image set according to the bright region, the dark region and the normal region
Is noted as the area contrast feature vector
Wherein the content of the first and second substances,
has a dimension of 3 x 1,has a dimension of 8 × 1;
① _4, forming a global feature vector by the bright and dark region feature vector and the region contrast feature vector of each tone mapping image in the training image setIs noted as Fk，
Wherein, FkHas a dimension of 11X 1, symbol "[ 2 ]]"is a vector representing a symbol and,
show that
And
connected to form a vector;
① _5, forming a training sample data set by the global feature vectors and the average subjective score difference values of all tone mapping images in the training image set, wherein the training sample data set comprises N global feature vectors and N average subjective score difference values, then adopting support vector regression as a machine learning method to train all global feature vectors in the training sample data set, so that the error between the regression function value obtained by training and the average subjective score difference value is minimum, and the optimal weight vector obtained by fitting is obtained
And an optimal bias term
Then using the optimal weight vector
And an optimal bias term
Structural quality prediction model, as
Wherein the content of the first and second substances,in functional representation, F is used in tablesA global feature vector representing the tone-mapped image, and as an input vector to a quality prediction model,
is composed of
The transpose of (a) is performed,is a linear function of F;
the test stage process comprises the following specific steps:
② for any tone-mapped image I used as a testtestAccording to the same operations from step ① _2 to step ① _4, I is obtainedtestGlobal feature vector of (2), noted as Ftest(ii) a Then, according to the quality prediction model pair F constructed in the training stagetestTesting and predicting to obtain FtestCorresponding predicted value is taken as ItestThe predicted objective quality value of (2) is marked as Qtest，
Wherein, ItestHas a width W 'and a height H', FtestHas a dimension of 11 x 1,
is represented by FtestIs a linear function of (a).
2. The method for evaluating the quality of a tone-mapped image according to claim 1, wherein said step ① _2 is
And
the acquisition process comprises the following steps:
① _2a, will
R, G, and B components in the RGB color space are expressed as
Then calculate
Is recorded as a dark channel image
Will be provided with
The pixel value of the pixel point with the middle coordinate position (x, y) is recorded as
Wherein x is more than or equal to 1 and less than or equal to W, y is more than or equal to 1 and less than or equal to H, min () is a function for taking the minimum value, Cx,yRepresenting a set of coordinate positions of all pixel points within a 3 × 3 neighborhood range centered on a pixel point whose coordinate position is (x, y), (x1,y1) Is Cx,yAny one of the coordinate positions of (a) and (b),
to represent
The middle coordinate position is (x)1,y1) The pixel value of the pixel point of (a),
to represent
The middle coordinate position is (x)1,y1) The pixel value of the pixel point of (a),
to represent
The middle coordinate position is (x)1,y1) The pixel value of the pixel point of (1);
① _2b, calculation
Distribution of gray histogram of (1), noted as { hk(j) J is more than or equal to 1 and less than or equal to 256 }; then will { h }k(j) The coordinate of the node with the minimum coordinate in all nodes with the non-zero histogram value in the [ 1 is not less than j is not more than 256 ] is recorded as XminWill { h }k(j) The coordinate of the node with the maximum coordinate in all nodes with the non-zero histogram value in the [ 1 is not less than j is not more than 256 ] is recorded as XmaxWill be
The middle pixel value belongs to [ Xmin,Xmid]The set of pixel values of all the pixels in the range is recorded as omega1Will be
Middle pixel value belongs to (X)mid,Xmax]The set of pixel values of all the pixels in the range is recorded as omega2(ii) a Wherein j is a positive integer, j is more than or equal to 1 and less than or equal to 256, and hk(j) Represents { h }k(j) J is more than or equal to 1 and less than or equal to 256, the histogram value of the node with the coordinate of j,
symbol
Is a rounding down operation symbol;
① _2c, by maximizing Ω1Obtain a first threshold, denoted as X1 *，
And by maximizing omega2Obtain a second threshold, denoted as X2 *，
Wherein the content of the first and second substances,express the finding such thatX when the value of (A) is maximum1Value of (A), X1Is omega1Of any one pixel value, Pf(X1) Represents omega1In (A) is [ X ]min,X1) Probability density function, mu, of all pixel values within a rangef(X1) Represents omega1In (A) is [ X ]min,X1) Mean, σ, of all pixel values in the rangef(X1) Represents omega1In (A) is [ X ]min,X1) Standard deviation, μ, of all pixel values within a rangeb(X1) Represents omega1In (A) is [ X ]1,Xmid]Mean, σ, of all pixel values in the rangeb(X1) Represents omega1In (A) is [ X ]1,Xmid]The standard deviation of all pixel values within the range,
express the finding such that
X when the value of (A) is maximum2Value of (A), X2Is omega2Of any one pixel value, Pf(X2) Represents omega2In (A) is [ X ]mid,X2) Probability density function, mu, of all pixel values within a rangef(X2) Represents omega2In (A) is [ X ]mid,X2) Mean, σ, of all pixel values in the rangef(X2) Represents omega2In (A) is [ X ]mid,X2) Standard deviation, μ, of all pixel values within a rangeb(X2) Represents omega2In (A) is [ X ]2,Xmax]Mean, σ, of all pixel values in the rangeb(X2) Represents omega2In (A) is [ X ]2,Xmax]Standard deviation of all pixel values within the range;
① _2d, will
Middle pixel value belongs to (X)2 *,Xmax]The area formed by all pixel points in the range is determined as a bright areaWill be provided with
The middle pixel value belongs to [ Xmin,X1 *) The area formed by all pixel points in the range is determined as a dark area
Will be provided with
The middle pixel value belongs to [ X1 *,X2 *]The area formed by all pixel points in the range is determined as a normal area
3. A tone mapping image quality evaluation method according to claim 1 or 2, characterized in that in said step ① _3
The acquisition process comprises the following steps:
① _3a 1. A. the method comprises the steps of
From the RGB color space to the CIELAB color space,the three components in the CIELAB color space are a luma component, a first chroma component, and a second chroma component, respectively;
① _3b1, willDividing into M non-overlapping sub-blocks of size 8 × 8 if
The sub-blocks with the size of 8 multiplied by 8 can not be equally divided, and redundant pixel points are removed; then will be
The brightness components of all pixel points in each sub-block form a matrix with dimension of 8 x 8, and the matrix is divided into two partsThe matrix with dimension of 8 multiplied by 8 formed by the brightness components of all the pixel points in the t-th sub-block is marked as zt(ii) a Wherein M is a positive integer, M is more than 1, t is a positive integer, the initial value of t is 1, and t is more than or equal to 1 and less than or equal to M;
① _3c1, pair
Performing two-dimensional discrete cosine transform on a matrix with dimension of 8 multiplied by 8 and formed by the brightness components of all pixel points in each sub-block to obtain a corresponding discrete cosine transform coefficient matrix, and converting z into ztThe corresponding matrix of discrete cosine transform coefficients is denoted as Zt(ii) a Then calculate
The sum of all high frequency coefficients and all intermediate frequency coefficients in the discrete cosine transform coefficient matrix corresponding to each sub-block in the Z-transform coefficient matrix is obtainedtThe sum of all high frequency coefficients and all medium frequency coefficients in (1) is denoted as St(ii) a Wherein Z istHas a dimension of 8 × 8;
① _3d1, calculation
Is characterized by
① _3e1, calculation
The mean and standard deviation of the brightness components of all the pixels in (1) are correspondingly recorded as
And
① _3f1, will
And
vectors constructed in a sequential arrangement as
Wherein the symbol "[ alpha ],")]"is a vector representing a symbol and,
show that
And
connected to form a vector.
4. The method for evaluating the quality of a tone-mapped image according to claim 3, wherein said step ① _3 is
The acquisition process comprises the following steps:
① _3a 2. A. the method comprises the steps of
From the RGB color space to the CIELAB color space,
the three components in the CIELAB color space are a luma component, a first chroma component, and a second chroma component, respectively;
① _3b2, calculation
Sum of luminance components of all pixel points in
The first regional contrast of the brightness components of all the pixels in (1), which is recorded as
And calculate
Sum of luminance components of all pixel points in
The second regional contrast of the brightness components of all the pixel points in (1), is recorded as
Wherein the symbol "|" is an absolute value symbol,
to represent
The average of the luminance components of all the pixel points in (a),to represent
The standard deviation of the luminance components of all the pixel points in (a),to represent
The average of the luminance components of all the pixel points in (a),to represent
The standard deviation of the brightness components of all the pixel points in the image is xi, which is a control parameter;
① _3c2, calculation
Sum of luminance components of all pixel points in
The first regional contrast of the brightness components of all the pixels in (1), which is recorded as
And calculateSum of luminance components of all pixel points in
The second regional contrast of the brightness components of all the pixel points in (1), is recorded as
Wherein the content of the first and second substances,
to represent
The average of the luminance components of all the pixel points in (a),
to represent
The standard deviation of the luminance components of all the pixel points in (1);
① _3d2, calculation
First chrominance component sum of all pixel points in
The first regional contrast of the first chrominance components of all the pixel points in (1) is recorded as
And calculate
First chrominance component sum of all pixel points in
The second regional contrast of the first chrominance components of all the pixel points in (1) is recorded as
Wherein the content of the first and second substances,
to represent
The average of the first chrominance components of all the pixels in (a),
to represent
The standard deviation of the first chrominance components of all the pixel points in (a),
to represent
The average of the first chrominance components of all the pixels in (a),to represent
The standard deviation of the first chrominance components of all the pixel points in (1);
① _3e2, calculation
First chrominance component sum of all pixel points in
The first regional contrast of the first chrominance components of all the pixel points in (1) is recorded as
And calculate
First chrominance component sum of all pixel points inThe second regional contrast of the first chrominance components of all the pixel points in (1) is recorded as
Wherein the content of the first and second substances,to represent
The average of the first chrominance components of all the pixels in (a),to represent
The standard deviation of the first chrominance components of all the pixel points in (1);
① _3f2, will
Vectors constructed in a sequential arrangement as
Wherein the symbol "[ alpha ],")]"is a vector representing a symbol and,
show that
And
connected to form a vector.
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