CN102306374A - Method for rebuilding super-resolution human face image by position block nonlinear mapping - Google Patents
Method for rebuilding super-resolution human face image by position block nonlinear mapping Download PDFInfo
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Abstract
The invention relates to a method for rebuilding a super-resolution human face image by position block nonlinear mapping. The method comprises the following steps of: segmenting the human face image for training and testing high resolution and low resolution into corresponding high-resolution position block images and low-resolution position block images which are provided with overlapped regions from structural information and detail information of a roughly-aligned human face image; rebuilding super-resolution position block images corresponding to testing low-resolution position block images at each corresponding position by using a nonlinear mapping relation which is between the high-resolution position block images and the low-resolution position block images and learned from training data; and splicing the super-resolution position block images to obtain the final super-resolution human face image. According to experiments on a standard database, the method provided by the invention has a good visual effect and high objective estimation quality.
Description
Technical field
The invention belongs to image processing techniques, be specifically related to a kind of face image super-resolution reconstruction method of block of locations Nonlinear Mapping.
Background technology
(Super Resolution SR) is meant that (Low Resolution obtains a panel height resolution (High Resolution, HR) process of image in LR) from a width of cloth or a series of low-resolution image to image super-resolution.In recent years, video monitoring important resultant use widely on bank, airport etc.But in many cases, the facial image resolution that watch-dog obtains is too low, so that can't directly discern, so the research of face image super-resolution problem has realistic meanings.
The super-resolution algorithms of general nature image much enlightens for the face image super-resolution algorithm.But facial image is one type of special image, and its specific global structure is arranged.Therefore the general nature image super-resolution algorithm that will not examine rate global structure information is generalized to the face image super-resolution problem has certain limitation, and the effect of reconstruction also has the space of further improving.
Liu etc. have proposed the two-step approach of human face super-resolution first, are about to reconstruction two parts of human face super-resolution PROBLEM DECOMPOSITION behaviour face global information and local detail information, and global information and local detail addition are obtained final high-resolution human face image.Two-step approach is a good framework; The method of numerous human face super-resolutions is all based on this framework: to the expression of people's face global information; Main thought is to describe global characteristics with the particular constraints of facial image, all rebuilds global information through the relation of setting up between the high low-resolution image global characteristics mostly in the realization; For the expression of detail textures characteristic, main thought is to set up the image block of sample and the neighborhood relationships between the training set image block, and adopts various partial models to describe textural characteristics.
Two-step approach combines through setting up high low resolution people's face global characteristics relation and details compensation; The reconstruction recovery effects improves; But being everlasting often, the relation between high low resolution people's face global characteristics set up introduces pseudo-shadow in the reconstructed results; Reduced the performance of rebuilding, meanwhile two-step approach has been introduced the additional calculation amount, and rebuilding on the efficient also has certain decline.Based on this, Ma etc. have proposed the human face super-resolution algorithm of a kind of position-based piece reconstruct, with the global structure of the location information table traveller on a long journey face of image block, characterize detailed information with the content of image block.Yet the least square method that Ma adopts when recovering detailed information has only been considered the linear dependence component of height resolution position interblock; And ignored the nonlinear dependence component; In order to improve the performance of super-resolution rebuilding, need to seek better method and solve the problem that exists here.
Summary of the invention
The object of the present invention is to provide a kind of face image super-resolution reconstruction method of block of locations Nonlinear Mapping, to solve the problems referred to above that exist in the prior art.
In order to achieve the above object, the technical scheme taked of the present invention is:
1) at first, high low resolution facial image is divided into height resolution position piece image;
2) secondly, utilize the high-definition picture of RBF super-resolution rebuilding correspondence position piece.In the training stage; Utilize RBF by training image Nonlinear Mapping of height resolution position piece training for each position; Be used to represent the nonlinear relationship between the height resolution position piece of each position; At test phase, the nonlinear relationship of utilizing each position training to obtain estimates corresponding high-resolution position piece from test low resolution block of locations;
3) at last, the positional information according to each block of locations becomes corresponding super-resolution reconstruction image with the high-resolution position piece image mosaic of estimating to obtain.
Said step 1) comprises following steps:
1) the low resolution facial image is adopted bilinear interpolation, make that the low resolution facial image resolution sizes after the interpolation is consistent with the high-definition picture resolution sizes.
2) adopt the window of p*p size respectively high low-resolution image to be carried out piecemeal, adopting has overlapping partitioned mode, and overlapping part is arranged between the piece of adjacent position up and down, and overlaid pixel is n between the adjacent block.Wherein p is an integer, and span is 2~16, and n is an integer and 0≤n≤p/2.The height resolution position piece that same level images of positions piece in the high low-resolution image is called corresponding same position.
Said step 2) utilize the high-definition picture of RBF super-resolution rebuilding correspondence position piece, its detailed process is following:
Use the high low resolution training block of locations of q position of
and
expression respectively;
and
representes the height resolution position piece image of q first training sample of position respectively; Wherein
and
is the column vector that block of locations gradation of image value is launched into; Subscript H and L represent high resolving power and low resolution respectively; First subscript q representes q position being partitioned into according to aforesaid block of locations dividing method; Second subscript 1~m representes the 1st~m training sample; Represent to be positioned at test low resolution block of locations and high-resolution position piece to be asked after the bilinear interpolation of position q with
and
respectively, then utilize RBF to try to achieve
calculating formula to be:
The wherein transposition computing of T representing matrix;
multidimensional quadric surface RBF for adopting, concrete calculation expression is:
W
qBe the weight matrix that the training stage obtains, calculation expression is:
Inv representing matrix inversion operation in the above-mentioned formula, τ are a very little positive constant, and span is 0.001~0.1, and E is a unit matrix, and φ is a matrix, are obtained by training height resolution position piece image calculation:
The repeating step aforementioned calculation is till the high-resolution position piece image of obtaining each position.
Said step 3) becomes corresponding super-resolution reconstruction image with high-resolution position piece image mosaic, and the average of when running into overlaid pixel, getting each this grey scale pixel value of high-resolution position piece is the final gray-scale value of overlaid pixel.
The positional information that the present invention has made full use of block of locations has kept the global structure of super-resolution human face rebuilding, utilizes the Nonlinear Mapping of RBF training to estimate corresponding high-resolution block of locations by the low resolution block of locations better.Therefore method of the present invention can keep the global structure of super-resolution rebuilding people face preferably, can recover the detailed information of people's face again preferably.
Description of drawings
Fig. 1 image block synoptic diagram
Fig. 2 human face super-resolution is rebuild comparison diagram
The PSNR contrast of Fig. 3 human face super-resolution reconstructed results
The SSIM contrast of Fig. 4 human face super-resolution reconstructed results
Embodiment
For making the object of the invention, technical scheme and advantage clearer,, the present invention is done further detailed description below in conjunction with accompanying drawing and instantiation.These instances only are illustrative, and are not limitation of the present invention.
The method that the present invention proposes may further comprise the steps:
(1) high low resolution facial image is divided into height resolution position piece image:
Because the resolution sizes of high low resolution facial image is different; Direct picture position with high low resolution people's face usually relates to the sub-pix rank when being mapped; Therefore need earlier the low resolution facial image to be adopted bilinear interpolation, make that the image resolution ratio size after the interpolation is consistent with the high-definition picture resolution sizes.Because the bilinear interpolation process is not introduced extra high-frequency information, still can image after the interpolation be regarded as low-resolution image.
Then, as shown in Figure 1, adopt the window of p*p size respectively high low-resolution image to be carried out piecemeal, adopting has overlapping partitioned mode, and overlapping part is arranged between the piece of adjacent position up and down, and overlaid pixel is n between the adjacent block.Wherein p is an integer, and span is 2~16, and n is an integer and 0≤n≤p/2.The height resolution position piece that same level images of positions piece in the high low-resolution image is called corresponding same position.
(2) utilize the high-definition picture of RBF super-resolution rebuilding correspondence position piece:
Because the algorithm of each position is consistent, the Nonlinear Mapping of just trying to achieve is inconsistent, is example with q position only, introduces correlative detail.Respectively
and
indicates the position of the q-th block and low resolution training positions.
and
representes the height resolution position piece image (
and
is the column vector that block of locations gradation of image value is launched into) of q first training sample of position respectively; Subscript H and L represent high resolving power and low resolution respectively; First subscript q representes q position being partitioned into according to aforesaid block of locations dividing method, and second subscript 1~m representes the 1st~m training sample.With
and
q, respectively, bilinear interpolation in position after the test block and the position of the unknown low-resolution high-resolution position blocks.Then utilize RBF to be in the hope of
calculating formula:
Wherein T is the matrix transpose computing;
is multidimensional quadric surface RBF, and concrete calculation expression is:
W
qBe the weight matrix that the training stage obtains, calculation expression is:
Inv representing matrix inversion operation in the above-mentioned formula, τ are a very little positive constant, and span is 0.001~0.1, and E is a unit matrix, and φ is a matrix, can be obtained by training height resolution position piece image calculation:
(3) splicing high-resolution position piece facial image:
According to the positional information of each block of locations with estimating that the high-resolution position piece that obtains is spliced into corresponding super-resolution reconstruction image.The average of when running into overlaid pixel, getting each this grey scale pixel value of high-resolution position piece is the final gray-scale value of overlaid pixel.
Fig. 2 rebuilds comparison diagram for human face super-resolution.Figure (a) is test low resolution facial image; Figure (b) proposes the facial image of method super-resolution rebuilding for the present invention; Figure (c) is the facial image of the method super-resolution rebuilding of Liu; (d) be the facial image of the method super-resolution rebuilding of Zhuang; Figure (e) is the original high resolution facial image.High-resolution human face image and the additive method that can be found out the method reconstruction that the present invention proposes by Fig. 2 contrast, and the gained visual effect is better, more near the original high resolution facial image.
Fig. 3 and Fig. 4 are the quality assessment contrast of human face super-resolution reconstructed results.Fig. 3 is the comparison diagram of Y-PSNR (PSNR), and Fig. 4 is the comparison diagram of structural similarity index (SSIM).Can find out the high-resolution human face image and the additive method contrast of the method reconstruction that the present invention proposes by Fig. 3 and Fig. 4; The gained evaluating objective quality is higher; Wherein Y-PSNR (PSNR) is higher; The error that shows method reconstructed results that the present invention proposes and original high resolution image is less, and (SSIM) is higher for the structural similarity index, shows that method that the present invention proposes has kept the structural information of people's face better.
In sum, the method for the present invention's proposition is compared the lifting that on subjective vision effect and evaluating objective quality, all has to a certain degree with existing method.
Should be appreciated that from foregoing description, under the situation that does not break away from spirit of the present invention, can make amendment and change each embodiment of the present invention.Description in this instructions is only used for illustrative, and should not be considered to restrictive.Scope of the present invention only receives the restriction of claims.
Claims (4)
1. the face image super-resolution reconstruction method of a block of locations Nonlinear Mapping is characterized in that: comprise following steps:
1) at first, high low resolution facial image is divided into height resolution position piece image;
2) secondly, utilize the high-definition picture of RBF super-resolution rebuilding correspondence position piece.In the training stage; Utilize RBF by training image Nonlinear Mapping of height resolution position piece training for each position; Be used to represent the nonlinear relationship between the height resolution position piece of each position; At test phase, the nonlinear relationship of utilizing each position training to obtain estimates corresponding high-resolution position piece from test low resolution block of locations;
3) at last, the positional information according to each block of locations becomes corresponding super-resolution reconstruction image with the high-resolution position piece image mosaic of estimating to obtain.
2. the face image super-resolution reconstruction method of block of locations Nonlinear Mapping according to claim 1 is characterized in that: said step 1) comprises following steps:
1) the low resolution facial image is adopted bilinear interpolation, make that the low resolution facial image resolution sizes after the interpolation is consistent with the high-definition picture resolution sizes.
2) adopt the window of p*p size respectively high low-resolution image to be carried out piecemeal, adopting has overlapping partitioned mode, and overlapping part is arranged between the piece of adjacent position up and down, and overlaid pixel is n between the adjacent block.Wherein p is an integer, and span is 2~16, and n is an integer and 0≤n≤p/2.The height resolution position piece that same level images of positions piece in the high low-resolution image is called corresponding same position.
3. the face image super-resolution reconstruction method of block of locations Nonlinear Mapping according to claim 1 is characterized in that: said step 2) utilize the high-definition picture of RBF super-resolution rebuilding correspondence position piece, its detailed process is following:
Use the high low resolution training block of locations of q position of
and
expression respectively;
and
representes the height resolution position piece image of q first training sample of position respectively; Wherein
and
is the column vector that block of locations gradation of image value is launched into; Subscript H and L represent high resolving power and low resolution respectively; First subscript q representes q position being partitioned into according to aforesaid block of locations dividing method; Second subscript 1~m representes the 1st~m training sample; Represent to be positioned at test low resolution block of locations and high-resolution position piece to be asked after the bilinear interpolation of position q with
and
respectively, then utilize RBF to try to achieve
calculating formula to be:
The wherein transposition computing of T representing matrix;
multidimensional quadric surface RBF for adopting, concrete calculation expression is:
W
qBe the weight matrix that the training stage obtains, calculation expression is:
Inv representing matrix inversion operation in the above-mentioned formula, τ are a very little positive constant, and span is 0.001~0.1, and E is a unit matrix, and φ is a matrix, are obtained by training height resolution position piece image calculation:
The repeating step aforementioned calculation is till the high-resolution position piece image of obtaining each position.
4. the face image super-resolution reconstruction method of block of locations Nonlinear Mapping according to claim 1; It is characterized in that: said step 3) becomes corresponding super-resolution reconstruction image with high-resolution position piece image mosaic, and the average of when running into overlaid pixel, getting each this grey scale pixel value of high-resolution position piece is the final gray-scale value of overlaid pixel.
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CN103514580A (en) * | 2013-09-26 | 2014-01-15 | 香港应用科技研究院有限公司 | Method and system used for obtaining super-resolution images with optimized visual experience |
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CN106709945A (en) * | 2017-01-09 | 2017-05-24 | 方玉明 | Super-resolution image quality evaluation method |
CN107135335A (en) * | 2016-02-29 | 2017-09-05 | 致伸科技股份有限公司 | Obtain the method for image and the Extraction of Image device and electronic installation of application this method |
CN108171124A (en) * | 2017-12-12 | 2018-06-15 | 南京邮电大学 | A kind of facial image clarification method of similar sample characteristics fitting |
CN110580680A (en) * | 2019-09-09 | 2019-12-17 | 武汉工程大学 | face super-resolution method and device based on combined learning |
CN110967302A (en) * | 2019-11-06 | 2020-04-07 | 清华大学 | Microbial panoramic smear detection device and detection method |
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CN106709945A (en) * | 2017-01-09 | 2017-05-24 | 方玉明 | Super-resolution image quality evaluation method |
CN106709945B (en) * | 2017-01-09 | 2018-03-06 | 方玉明 | A kind of quality evaluating method for super-resolution image |
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CN110580680A (en) * | 2019-09-09 | 2019-12-17 | 武汉工程大学 | face super-resolution method and device based on combined learning |
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CN110967302A (en) * | 2019-11-06 | 2020-04-07 | 清华大学 | Microbial panoramic smear detection device and detection method |
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