RU2493668C1 - Method of encoding/decoding multi-view video sequence based on local adjustment of brightness and contract of reference frames without transmitting additional service data - Google Patents

Abstract

FIELD: information technology.

SUBSTANCE: method for local adjustment of brightness and contrast of a reference frame for encoding a multi-view video sequence including: obtaining pixel values of the current encoded block belonging to the encoded frame, and pixel values of a reference block belonging to a reference frame; obtaining restored pixel values neighbouring with respect to the current block of the encoded frame, and pixel values neighbouring with respect to the reference block of the reference frame; determining numerical relationships between pixel values of the reference block and pixel values neighbouring with respect to the reference block, and relationships between the restored pixel values, neighbouring with respect to the current encoded block, and pixel values neighbouring with respect to the reference block; numerical relationships found at the previous step are used to determine parameters for adjusting brightness and contrast for adjusting differences in brightness and contrast for the reference block compared to the current encoded block; and adjusting differences in brightness and contrast for the reference block using the found adjustment parameters.

EFFECT: high encoding efficiency.

13 cl, 10 dwg

Description

The present invention relates to a method for correcting differences in brightness and contrast that may occur between frames of a multi-angle video sequence. In particular, the present invention can be used in the encoding and decoding of multi-angle video sequences.

One of the methods used for coding multi-angle video sequences is to use frames belonging to neighboring views (angles), as well as frames synthesized using frames of neighboring views (angles) and depth maps. Such frames act as reference frames during prediction coding [1]. This eliminates the offset of the object in the current frame relative to one of the reference frames. Under the displacement can be understood the movement of the object or the difference in the position of the object between the current encoded frame and frames belonging to neighboring views (angles), or a synthesized frame. The purpose of eliminating this bias is to obtain a minimum inter-frame difference. The resulting inter-frame difference is then encoded (for example, by applying decorrelating transform, quantization, and entropy encoding) and placed in the output bitstream.

Possible differences in the parameters of the cameras used for shooting multi-angle video sequences, as well as the difference in the luminous flux coming from the objects being shot to the cameras, lead to a difference in brightness and contrast between frames belonging to different angles. The indicated differences in brightness and contrast also affect the characteristics of the synthesized frames. This can lead to an increase in the absolute values of the interframe difference, which negatively affects the coding efficiency.

To solve the above problem, the H.264 standard [2] uses a weighted forecast, which was originally intended for efficient coding of single-species (single-view) video sequences in which there are effects of smooth input and output of images, flicker or scene change. Weighted prediction eliminates the difference in brightness between the encoded frame and reference frames at the macroblock level. In this case, the same values of the weighting coefficients are used for all macroblocks belonging to the same layer. Weights can be determined during the encoding process and stored in the output bitstream (“explicit” weighted forecast) or calculated in the encoding / decoding process (“implicit” weighted forecast). However, in the case of multi-angle sequences, where local changes in brightness and / or contrast can be observed, this method may be ineffective.

Another solution to this problem is adaptive block correction of differences in brightness [3]. One of the methods that implements this approach is the method of one-step affine brightness correction for multi-angle video sequences (Multiview One-Step Affine Illumination Compensation - MOSAIC) [4, 5]. This method involves a combination of block correction of differences in brightness with the inter-frame prediction modes described in the H.264 standard. In the process of such coding, for each macroblock, the average pixel values of the current encoded block and the candidate reference block are calculated. For these blocks, modified blocks are formed by subtracting the average value for each pixel of the block. Then, for the blocks obtained, the sum of the absolute differences (Mean-Removed Sun of Absolute Difference - MRSAD) is calculated. The result of inter-frame prediction is the relative coordinates of the reference block (offset vector), which give the minimum value of the encoding, as well as the difference between the modified encoded block and the modified reference block. In this case, the calculation of the encoding cost is based on the calculated MRSAD value and an estimate of the bit cost of transmitting additional information necessary for subsequent decoding. In addition to the displacement vector, additional information includes the difference between the average values of the current and reference blocks. This difference is referred to as DVIC (Difference Value of Illumination Compensation) and is a brightness correction parameter. The DVIC value is differential encoded and placed in the output bitstream. It should be noted that in the case of the "P Skip" mode, the DVIC value is determined based on the DVIC values of neighboring macroblocks that were already encoded at the time of encoding the current macroblock. Thus, the above method does not completely eliminate the need for explicit transmission of additional information necessary for subsequent decoding.

The parameters necessary for correcting the differences in brightness and contrast can be obtained by analyzing the reconstructed (encoded and then decoded) areas of the frames. This helps to reduce the amount of additional information that must be encoded and explicitly placed in the output bitstream. The indicated approach was implemented in the method of weighted prediction using neighboring pixels (WPNP - Weighted Prediction using Neighboring Pixels) [6]. This method uses the pixel values of the encoded frame adjacent to the current encoded block and the pixel values of the reference frame adjacent to the reference block for pixel-by-pixel estimation of brightness changes. In this case, the brightness changes for the selected two neighboring pixels are multiplied by weighting factors and added up, forming an estimate of the brightness and contrast changes between the individual pixels of the current and reference blocks. It should be noted that weights are calculated separately for each pixel position of the encoded block. The values of the weighting coefficients are determined based on the mutual distance between the pixel of the encoded block and the selected neighboring pixels. The main disadvantage of the described method is that the reduction in the amount of additional information is achieved due to a possible decrease in the quality of correction. The reason for the decrease in quality is that a change in the brightness of pixels adjacent to the encoded and reference blocks may differ from a change in the brightness of pixels belonging directly to the encoded and reference blocks.

Another option that implements the approach associated with assessing the parameters of changing the brightness and contrast by analyzing the reconstructed (encoded, and then decoded) areas of the frames is described in US patent application 2011/0286678 [7]. The encoding method for multi-angle video sequences described in the application includes the correction of the brightness difference in the prediction encoding process. The correction parameters of the brightness change are estimated based on the assessment of the brightness change for adjacent areas with respect to the coded and reference blocks. Since these adjacent areas are available both in encoding and in decoding, there is no need to explicitly transmit correction parameters in the output bitstream. The resulting parameters are used to correct the reference block. The reliability of the estimation of brightness variation parameters is determined by adjusting the brightness for the region of the reference frame adjacent to the reference block, and comparing the obtained corrected region with the reconstructed (encoded and then decoded) region of the encoded frame adjacent to the current encoded block. The disadvantage of this method lies in the fact that the reliability of the correction of changes in brightness is determined only by analysis of adjacent areas. The data contained in the reference block are not used in the analysis of the reliability of the correction of brightness changes, which can lead to erroneous correction, thereby reducing its effectiveness.

Closest to the claimed invention is the method described in US patent application 2008/0304760 [8]. The specified method for correcting changes in brightness and contrast for the reference block includes the following steps: obtaining the restored pixel values adjacent to the current encoded block, and the restored pixel values adjacent to the reference block, as input information; predicting average values for the current encoded and reference blocks based on the restored pixel values adjacent to the current encoded block and the restored pixel values adjacent to the reference block; determining brightness correction parameters for the reference block based on the predicted average pixel value of the current encoded block, the predicted average value of the reference block and pixel values of the current encoded block and the reference block; and performing luminance correction for the reference block using a previously determined luminance correction parameter.

The disadvantage of the prototype is as follows. The reconstructed values of pixels adjacent to the current encoded block and the reference block are used solely to predict average values. This restriction does not allow the use of information contained in neighboring pixels. In addition, there is no analysis of the relationship between the pixel values of the reference block and the values of pixels adjacent to the reference block. Thus, possible differences in the correction parameters of changes in brightness and contrast between the considered blocks and areas adjacent to the considered blocks are not taken into account. This can lead to a decrease in the reliability of the procedure for correcting differences in brightness and contrast, which will negatively affect the encoding efficiency.

In accordance with the description, the prototype [8] proposes a method of encoding digital images (frames) based on the use of correction of brightness changes. This method includes the following steps: determining a reference block for generating a prediction block for the current encoded block; determining a brightness correction parameter for correcting the found reference block; performing brightness correction of the found reference block based on the brightness correction parameter determined in the previous step; generating a prediction block for the current block being encoded using the adjusted reference block; encoding the difference between the generated prediction block and the current encoded block; generating an output bitstream and storing information about a brightness correction parameter in a predetermined location within the generated bitstream. The disadvantage of the described method is the need to save the correction parameters in the output bitstream.

The claimed invention is aimed at improving the coding efficiency of multi-angle video sequences in the case when a hybrid video coding model is used. The invention consists in the application of a more reliable adaptive procedure for evaluating the parameters of changing the brightness and contrast of the reference block, as well as the procedure for correcting the brightness and contrast of the reference block.

The technical result is achieved through the use of more data to assess the parameters of changes in brightness and contrast. In particular, in the claimed method, an analysis is made of the relationships between the pixel values of the reference block and the pixel values adjacent to the reference block, as well as the ratios between the restored pixel values adjacent to the current encoded block and the pixel values adjacent to the reference block. When implementing the method, it is also envisaged to use improved methods of encoding and decoding multi-angle video sequences, and such methods are based on the use of brightness and contrast correction, which allows to increase the compression efficiency due to the fact that when evaluating changes in brightness and contrast, pixel values are used that are available as during encoding , and when decoding. In this case, the brightness and contrast correction parameters can be accurately restored without the need for additional data to be transmitted in the output bitstream.

According to the main aspect of the claimed invention, a method for correcting differences in brightness and contrast between the reference block and the current encoded block when conducting inter-frame prediction for encoding a multi-angle video sequence, and this method includes:

- obtaining pixel values of the current encoded block belonging to the encoded frame, and pixel values of the reference block belonging to the reference frame;

- obtaining the restored (encoded and then decoded) pixel values adjacent to the current block of the encoded frame, and pixel values adjacent to the reference block of the reference frame;

- determination of the relationship between the pixel values of the reference block and the values of pixels adjacent to the reference block, as well as the ratios between the restored pixel values adjacent to the current encoded block and the pixel values adjacent to the reference block;

- determination of correction parameters for changing the brightness and contrast to correct differences in brightness and contrast between the reference block and the current encoded block based on the relationships found in the previous step, the pixel values of the reference block, the restored pixel values adjacent to the current encoded block, and pixel values adjacent to the support block;

- performing correction of differences in brightness and contrast between the reference block and the current encoded block based on the correction parameters found in the previous step.

In one of the embodiments of the claimed invention, a modification of the above method is proposed, which consists in the fact that the process of determining the relationship between the pixels of the current encoded frame and the reference frame, as well as the process of determining the brightness and contrast correction parameters, include:

- calculation of statistical characteristics for the restored values of pixels adjacent to the current encoded block, statistical characteristics for pixels of the reference block and statistical characteristics for pixels adjacent to the reference block;

- determination of the relationship between the statistical characteristics for the pixels of the reference block and the statistical characteristics for the restored values of pixels adjacent to the reference block;

- calculating an estimate of the value of the statistical characteristic for the current encoded block based on the calculated statistical characteristics and the relationships between them;

- determination of a correction parameter for changing brightness and contrast to correct differences in brightness and contrast between the reference and the current encoded blocks based on the found estimate of the statistical characteristics for the current block and the statistical characteristics of the reference block.

In another embodiment of the claimed invention, a modification of the above method is proposed, in which the process of calculating statistical characteristics, determining relationships between statistical characteristics and determining a correction parameter for changing brightness and contrast includes:

- calculation of the average value for the recovered pixels adjacent to the current encoded block and located to the left of the current encoded block, if any; calculating the average value for the restored pixels adjacent to the current encoded block and located above the current encoded block, if any, calculating the average value for the pixels of the reference block, calculating the average value for pixels adjacent to the reference block and located to the left from the reference block, if any, and calculating an average value for pixels adjacent to the reference block and located above the reference block, if any;

- in the case of the presence of restored pixels adjacent to the current encoded block and located to the left of the current encoded block, as well as the presence of pixels adjacent to the reference block and located to the left of the reference block, calculating the ratio between the average pixel value of the reference block and the average the value of pixels adjacent to the reference block and located to the left of the reference block; calculating the product of the obtained ratio and the average value of the restored pixels adjacent to the current encoded block and located to the left of the current encoded block; determining a correction parameter for changing the brightness and contrast as a relationship between the calculated product and the average value for the pixels of the reference block;

- otherwise, in the case of the presence of restored pixels adjacent to the current encoded block and located above the current encoded block, and the presence of pixels adjacent to the reference block and located above the reference block, calculating the ratio between the average pixel value of the reference block and the average value of pixels adjacent to the reference block and located above the reference block; calculating the product of the obtained ratio and the average value of the restored pixels adjacent to the current encoded block and located above the current encoded block; determining a correction parameter for changing the brightness and contrast as a relationship between the calculated product and the average value for the pixels of the reference block;

- otherwise, by using the Median Prediction Method to calculate an estimate of the average value of the current encoded block;

- determination of the correction parameter for changing the brightness and contrast as the ratio between the average value for the pixels of the current encoded block and the average for the pixels of the reference block.

Another modification of the claimed invention is that the method for correcting the brightness and contrast of the reference block in the process of coding a multi-angle video sequence includes:

- obtaining pixel values of the current block of the encoded frame and pixel values of the reference block of the reference frame;

- obtaining restored (encoded and then decoded) pixel values adjacent to the current block being encoded, and pixel values adjacent to the reference block;

пикселей, соседних по отношению к текущему кодируемому блоку, k=0, …, N-1, N - число пикселей, соседних по отношению к текущему кодируемому и опорному блокам;- calculating a first estimate estD _{i, j} for each position (i, j) of the pixel in the reference block; moreover, the first estimate estD _{i, j} is a function of a linear combination of reconstructed values $$T_k^D$$

pixels adjacent to the current encoded block, k = 0, ..., N-1, N is the number of pixels adjacent to the current encoded and reference blocks;

пикселей, соседних по отношению к опорному блоку, k=0, …, N-1;- calculating a second estimate estR _{i, j} for each position (i, j) of the pixel in the reference block; moreover, the second estimate estR _{i, j} is a function of a linear combination of values $$T_k^R$$

pixels adjacent to the reference block, k = 0, ..., N-1;

пикселей, соседних по отношению к текущему блоку, и на значениях $$T_k^R$$

пикселей, соседних по отношению к опорному блоку;- determination of correction parameters for changes in brightness and contrast for the correction of each pixel in the reference block; the determination of these parameters is based on the value of the first estimate estD _{i, j} , the value of the second estimate estR _{i, j} , as well as on the values R _{i, j of the} pixels of the reference block, on the restored values $$T_k^D$$

pixels adjacent to the current block and at the values $$T_k^R$$

pixels adjacent to the reference block;

- performing correction of changes in brightness and contrast for each pixel in the reference block using the parameters for correcting changes in brightness and contrast found in the previous step.

According to another modification of the claimed invention, the method provides that the calculation of the first and second estimates for each pixel position in the reference block and the determination of correction parameters for changing the brightness and contrast for each pixel position in the reference block includes:

- calculation of the first estimate estD _{i, j} as

, $$est{D}_{i,j}={\displaystyle {\sum }_{k=0...,N-\mathrm{one}}{W}_k\left(i,j\right)\cdot T_k^D}$$

,

, k=0, …, N-1 - это восстановленные значения пикселей, соседних по отношению к текущему кодируемому блоку, N - это число пикселей, соседних по отношению к текущему кодируемому и опорному блокам;where W _k (i, j), k = 0, ..., N-1 are weights, and $$T_k^D$$

, k = 0, ..., N-1 are the restored values of pixels adjacent to the current encoded block, N is the number of pixels adjacent to the current encoded and reference blocks;

- calculation of the second estimate estR _{i, j} as

$$est{R}_{i,j}={\displaystyle {\sum }_{k=0...,N-\mathrm{one}}{W}_k\left(i,j\right)\cdot T_k^R}$$

, k=0, …, N-1 - значения пикселей, соседних по отношению к опорному блоку;where W _k (i, j), k = 0, ..., N-1 are weights, and $$T_k^R$$

, k = 0, ..., N-1 are the values of pixels adjacent to the reference block;

, если вторая оценка estR_i,j не равна нулю. В противном случае α_i,j полагается равным 1.- determination of correction parameters for changes in brightness and contrast for each position (i, j) of the pixel in the reference block; this parameter is the ratio $${\alpha }_{i,j}=\frac{est{D}_{i,j}}{est{R}_{i,j}}$$

if the second estimate estR _{i, j is} not equal to zero. Otherwise, α _{i, j is} assumed to be equal to 1.

- performing correction of changes in brightness and contrast for the reference block by multiplying the values of each pixel of the reference block R _{i, j} by the corresponding correction parameter α _{i, j} .

Another modification of the claimed invention provides that the calculation of the first and second estimates for each pixel position in the reference block includes:

- calculation of the weighting coefficients W _k (i, j), k = 0, ..., N-1 for the first estimate estD _{i, j,} and the second estimate estR _{i, j} , for each position (i, j) of the pixel in the weight reference block the coefficient W _k (i, j) is equal to a non-increasing function of the absolute difference:

, $$\left|R_{i,j}-T_k^R\right|$$

,

(k=0, …, N-1) - значение пикселя, соседнего по отношению к опорному блоку; N - число пикселей, соседних по отношению к текущему кодируемому и опорному блокам.which provides an inversely proportional increase / decrease in the value of W _k (i, j) depending on the decrease / increase in the absolute difference. Here R _{i, j} is the pixel value of the reference block; $$T_k^R$$

(k = 0, ..., N-1) is the value of a pixel adjacent to the reference block; N is the number of pixels adjacent to the current encoded and reference blocks.

In another embodiment of the claimed invention, a modification of the above method is proposed, which provides that the calculation of the first and second estimates for each pixel position in the reference block includes:

- calculation of weighting factors W _k (i, j), k = 0, ..., N-1 for the first estimate estD _{i, j} and the second estimate estR _{i, j} ; for each position (i, j) of the pixel in the reference block, the weight coefficient W _k (i, j) is equal to a non-increasing function of the absolute difference:

, $$\left|R_{i,j}-T_k^R\right|$$

,

, где Thr - предопределенное пороговое значение; иначе W_k(i,j). Здесь R_i,j - значение пикселя опорного блока; $$T_k^R$$

(k=0, …, N-1) - значение пикселя, соседнего по отношению к опорному блоку; N - число пикселей, соседних по отношению к текущему кодируемому и опорному блокам.which provides an inversely proportional increase / decrease in the value of W _k (i, j) depending on the decrease / increase in the absolute difference; when $$\left|T_k^R-R_{i,j}\right|\le Thr$$

where Thr is a predetermined threshold value; otherwise W _k (i, j). Here R _{i, j} is the pixel value of the reference block; $$T_k^R$$

(k = 0, ..., N-1) is the value of a pixel adjacent to the reference block; N is the number of pixels adjacent to the current encoded and reference blocks.

When implementing the claimed invention, it makes sense to apply another modification of the above method, which provides that the calculation of the first and second estimates for each pixel position in the reference block includes:

- calculation of weight coefficients W _k (i, j), k = 0, ..., N-1 for the first estimate estD _{i, j} and the second estimate estR _{i, j,} for each position (i, j) of the pixel in the reference block, the weight coefficient W _k (i, j) is equal to the non-increasing function of the absolute difference:

, $$\left|R_{i,j}-T_k^R\right|$$

,

, где $$T_k^D$$

(k=0, …, N) - значение пикселя, соседнего по отношению к текущему кодируемому блоку, Thr1 - первый предопределенный порог; и $$\left|T_k^R-R_{i,j}\right|\le Thr2$$

, где Thr2 - второй предопределенный порог; иначе W_k(i,j)=0. Здесь R_i,j - значение пикселя опорного блока; $$T_k^R$$

(k=0, …, N - 1) - значение пикселя, соседнего по отношению к опорному блоку; N - число пикселей, соседних по отношению к текущему кодируемому и опорному блокам.which provides an inversely proportional increase / decrease in the value of W _k (i, j) depending on the decrease / increase in the absolute difference; when $$\left|T_k^R-T_k^D\right|\le Thr\mathrm{one}$$

where $$T_k^D$$

(k = 0, ..., N) is the value of a pixel adjacent to the current block being encoded, Thr1 is the first predetermined threshold; and $$\left|T_k^R-R_{i,j}\right|\le Thr2$$

where Thr2 is the second predetermined threshold; otherwise, W _k (i, j) = 0. Here R _{i, j} is the pixel value of the reference block; $$T_k^R$$

(k = 0, ..., N - 1) is the value of a pixel adjacent to the reference block; N is the number of pixels adjacent to the current encoded and reference blocks.

According to another embodiment of the claimed invention, a modification of the aforementioned method is proposed, which provides that the calculation of the first and second estimates for each pixel position in the reference block includes:

, где R_i,j - значение пикселя опорного блока, $$T_k^R$$

(k=0, …, N - 1) - значение пикселя, соседнего по отношению к опорному блоку, в случае $$\left|T_k^R-R_{i,j}\right|\le Thr$$

, где Thr - предопределенный порог; иначе W_k(i,j)=0.- calculation of weighting factors W _k (i, j), k = 0, ..., N - 1 for the first estimate estD _{i, j} and the second estimate estR _{i, j} ; for each position (i, j) of the pixel in the reference block, the weight coefficient W _k (i, j) is equal to W _k (i, j) = exp (-C · A _k (i, j)), where C is a predetermined constant greater than 0, and A _k (i, j) equals $$A_k\left(i,j\right)=\left|R_{i,j}-T_k^R\right|$$

where R _{i, j} is the pixel value of the reference block, $$T_k^R$$

(k = 0, ..., N - 1) is the value of a pixel adjacent to the reference block, in the case $$\left|T_k^R-R_{i,j}\right|\le Thr$$

where Thr is a predetermined threshold; otherwise, W _k (i, j) = 0.

As an alternative to the implementation of the claimed invention, a modification of the above method is proposed, which provides that the calculation of the first and second estimates for each pixel position in the reference block includes:

, где R_i,j - значение пикселя опорного блока $$T_k^R$$

(k=0, …, N - 1) - значение пикселя, соседнего по отношению к опорному блоку, в случае $$\left|T_k^R-T_k^D\right|\le Thr1$$

, где $$T_k^D$$

, k=0, …, N - 1 - значение пикселя, соседнего по отношению к текущему кодируемому блоку, Thr1 - первый предопределенный порог; $$\left|T_k^R-R_{i,j}\right|\le Thr2$$

, где Thr2 - второй предопределенный порог; иначе W_k(i,j)=0.- calculation of weighting factors W _k (i, j), k = 0, ..., N - 1 for the first estimate estD _{i, j} and the second estimate estR _{i, j} ; for each position (i, j) of the pixel in the reference block, the weight coefficient W _k (i, j) is equal to W _k (i, j) = exp (-C · A _k (i, j)), where C is a predetermined constant greater than 0, and A _k (i, j) equals $$A_k\left(i,j\right)=\left|R_{i,j}-T_k^R\right|$$

where R _{i, j} is the pixel value of the reference block $$T_k^R$$

(k = 0, ..., N - 1) is the value of a pixel adjacent to the reference block, in the case $$\left|T_k^R-T_k^D\right|\le Thr\mathrm{one}$$

where $$T_k^D$$

, k = 0, ..., N - 1 - the value of a pixel adjacent to the current block being encoded, Thr1 - the first predetermined threshold; $$\left|T_k^R-R_{i,j}\right|\le Thr2$$

where Thr2 is the second predetermined threshold; otherwise, W _k (i, j) = 0.

According to another embodiment of the claimed invention, a modification of the aforementioned method is proposed, in which it is provided that the positions of the restored pixel values adjacent to the current encoded block and the positions of the pixel values adjacent to the reference block are determined adaptively instead of the corresponding pixels in advance given positions.

The group of inventions related by a single concept also includes an original method of coding multi-angle video sequences based on correction of changes in brightness and contrast. This method includes:

- determining the reference block, which is used to form the prediction block for the current encoded block;

- determination of correction parameters for changes in brightness and contrast to correct differences in brightness and contrast between the reference block and the current encoded block during the search or upon completion of the search for the reference block;

- performing correction of changes in brightness and contrast of the found reference block through the use of the found correction parameters for changes in brightness and contrast;

- formation of a prediction block for the current encoded block through the use of a reference block adjusted for brightness and contrast;

- encoding the current block using the generated prediction block without encoding the found correction parameters for changing the brightness and contrast; encoding information about the reference block, if necessary for decoding;

wherein the determination of the correction parameters for changes in brightness and contrast includes:

- obtaining the restored (encoded and then decoded) pixel values adjacent to the current block of the encoded frame, and pixel values adjacent to the reference block of the reference frame;

- determination of the relationship between the pixel values of the reference block and the values of pixels adjacent to the reference block, as well as the ratios between the restored pixel values adjacent to the current encoded block and the pixel values adjacent to the reference block;

- determination of correction parameters for changing the brightness and contrast to correct differences in brightness and contrast between the reference block and the current encoded block based on the relationships found in the previous step between the pixel values of the reference block, the restored pixel values adjacent to the current encoded block, and pixel values adjacent to the support block.

Within the framework of a single concept, it is also envisaged to use an original method for decoding multi-angle video sequences based on correction of changes in brightness and contrast. This method includes:

- decoding information about the reference block, if necessary, in order to determine the reference block for the current decoded block; definition of the reference block;

- determination of correction parameters for changes in brightness and contrast for the found reference block;

- performing correction of changes in brightness and contrast of the found reference block using the found correction parameters for changes in brightness and contrast;

- the formation of a prediction block for the current decoded block by using the reference block, adjusted for brightness and contrast;

- decoding the current block through the use of the obtained prediction block and correction parameters for changes in brightness and contrast,

wherein the procedure for determining the brightness and contrast correction parameters includes:

- obtaining the restored (encoded and then decoded) pixel values adjacent to the current block of the encoded frame, and pixel values adjacent to the reference block of the reference frame;

- determination of the relationship between the pixel values of the reference block and the values of pixels adjacent to the reference block, as well as the ratios between the restored pixel values adjacent to the current encoded block and the pixel values adjacent to the reference block;

- determination of correction parameters for changing the brightness and contrast to correct differences in brightness and contrast between the reference block and the current encoded block based on the relationships found in the previous step between the pixel values of the reference block, the restored pixel values adjacent to the current encoded block, and pixel values adjacent to the support block.

Further, the invention is illustrated with the use of graphic materials.

Figure 1 is a structural diagram of a hybrid encoder multi-angle video sequences and the place of application of the claimed invention.

Figure 2 is a structural diagram of a part of a hybrid video encoder that implements the inventive method, which is part of the predictive coding process.

Figure 3 is a diagram explaining a method for correcting changes in brightness and contrast of a reference block in accordance with one example of the implementation of the claimed invention.

Figure 4 is a flowchart illustrating a method for correcting changes in brightness and contrast of a reference block, according to one example implementation of the claimed invention.

5 is a diagram illustrating a procedure for selecting input blocks in the current frame during the calculation of correction parameters for changes in brightness and contrast according to one example of the implementation of the claimed invention.

6 is a diagram illustrating a method for correcting changes in brightness and contrast for a reference block in accordance with another embodiment of the claimed invention.

7 is a flowchart illustrating a method of pixel-by-pixel correction of changes in brightness and contrast for a reference block according to one embodiment of the claimed invention.

Fig. 8 is a diagram explaining a method for correcting changes in brightness and contrast for a reference block in accordance with another embodiment of the claimed invention.

Fig.9 is a flowchart describing a method of encoding multi-angle video sequences based on the correction of changes in brightness and contrast according to one example implementation of the claimed invention.

Figure 10 is a flowchart describing a method for decoding multi-angle video sequences based on the correction of changes in brightness and contrast according to one example implementation of the claimed invention.

Figure 1 shows a structural diagram of a hybrid encoder multi-angle video sequences. The input to the hybrid multi-view video sequence encoder 105 includes the original view (encoded view) 101 and the already encoded and then decoded views (views) 102 that are part of the encoded multi-view video data. Already encoded / decoded views 102 and already encoded / decoded sequences of depth maps 103 are used to form a synthesized view (view) for the original view (encoded view) using synthesis procedure 104. The generated synthesized view (angle) is also input to the hybrid encoder 105.

Hybrid encoder 105 contains the following tools used to encode the original view: viewing reference frames 106, inter prediction 107, intra prediction 108, inter and intra compensation 109, spatial transform 110, optimizing the speed / distortion ratio 111, entropy encoding 112. Detailed information on the mentioned tools is contained in [9]. The inventive method can be implemented in the framework of inter prediction 107.

Figure 2 contains a diagram of a portion of a hybrid video encoder that implements the inventive method as part of predictive coding. The hybrid encoder includes a subtraction unit 201, a transform and quantization unit 202, an entropy encoding unit 203, an inverse transform and inverse quantization unit 204, a bias compensation and correction unit for brightness / contrast changes 205, a view synthesis unit 206, an addition unit 207 , a block 208 for buffering reference frames and depth maps, a block 209 for predicting compensation and correction parameters, a block for estimating an offset and changing the brightness / contrast 210, and a block 211 for deciding on a macroblock coding mode. Blocks 201-204, 207-209 and 211 are standard coding blocks that are used in the basic hybrid coding method [9]. A view synthesis block 206 is a block specific to multi-view coding. Block 206 synthesizes additional reference frames from already encoded / decoded frames and depth maps.

The inventive method can be implemented in blocks 205 and 210. These blocks implement a predictive block coding method, which includes the following steps:

- For the current block of the current encoded frame, a search is performed for the reference block, which minimizes the following expression:

$${\displaystyle \sum _{m=\mathrm{one}}^M{\displaystyle \sum _{n=\mathrm{one}}^N\left|I(m,n)-\Psi (R(m+i,n+j))\right|}}$$

where I (m, n) is the pixel brightness value with coordinates (m, n) inside the current block. The size of the current block being encoded is M × N, (i, j) defines a displacement vector (DV) that points to the reference block R within a predetermined search area. ψ (x) is a function that corrects for differences in brightness and contrast between the current block and the reference block. The described method is implemented in block 210. The found correction parameters for changing the brightness and contrast, along with the received DV, are transmitted to block 205 and to block 209.

- The found reference block is converted in accordance with the found correction parameters for changing the brightness and contrast (block 205). After that, block 201 forms a difference block. Then, the difference block is converted using the Discrete Cosine Transform (DCT), quantized (block 202) and encoded by an entropy encoder (block 203). Additional data (SI) required for subsequent decoding is also encoded by an entropy encoder (block 203).

Figure 3 contains a diagram explaining the essence of the method for correcting changes in brightness and contrast for the reference block in accordance with one embodiment of the claimed invention. In accordance with FIG. 3, at each iteration of the reference block search procedure for the current block 311 of the current encoded frame 310, a displacement vector (DV) 320 is determined. Vector 320 indicates the reference block 301 of the reference frame 300. According to the claimed method, the function ψ (x) of the correction of changes in brightness and contrast has the following form:

ψ (x) = α

The correction parameter for changes in brightness and contrast α is described by the following equation:

, $$\alpha =\frac{estMX}{refMX}$$

,

$$refMX=\frac{\mathrm{one}}{N\cdot M}\cdot {\displaystyle {\sum }_{m=\mathrm{one}}^M{\displaystyle {\sum }_{n=\mathrm{one}}^{N}S\left(m+i,n+j\right)}}$$

refMX is the average value of the reference block 301. (i, j) is the coordinate of the upper left corner of the reference block 301. S is the pixel of the reference frame 300. The value expressed as estMX is an estimate of the average value for the current encoded block 311.

Figure 4 contains a flowchart illustrating a method for correcting changes in brightness and contrast for a reference block, according to one embodiment of the invention. This method includes the following steps.

1. Obtaining input pixel values of blocks 301, 302, 303, 311, 312, 313 and 314 (Fig. 4, 401).

2. The calculation of the following average values (Figure 4, 402): calculation of the average value encMX_L block 312

, $$encMX\_L=\frac{\mathrm{one}}{P\cdot Q}\cdot {\displaystyle {\sum }_{p=\mathrm{one}}^P{\displaystyle {\sum }_{q=\mathrm{one}}^{Q}DI\left(p,q\right)}}$$

,

where DI (p, q) is the reconstructed (encoded and then decoded) pixel brightness value with coordinates (p, q) inside block 312. The dimensions of block 312 are P × Q.

The calculation of the average value encMX_A block 313

, $$encMX\_A=\frac{\mathrm{one}}{U\cdot V}\cdot {\displaystyle {\sum }_{u=\mathrm{one}}^U{\displaystyle {\sum }_{v=\mathrm{one}}^{V}DI\left(u,v\right)}}$$

,

where DI (u, v) represents the reconstructed (encoded and then decoded) brightness value of the pixel with coordinates (u, v) inside block 313. The dimensions of block 313 are U × V.

The calculation of the average refMX of the reference block 301.

Calculation of the average refMX_L of block 302:

. $$refMX\_L=\frac{\mathrm{one}}{P\cdot Q}\cdot {\displaystyle {\sum }_{p=\mathrm{one}}^P{\displaystyle {\sum }_{q=\mathrm{one}}^{Q}S\left(p+i,q+j-Q\right)}}$$

.

The dimensions of block 302 are equal to the dimensions of block 312.

Calculation of the average value of refMX_A block 303:

. $$refMX\_A=\frac{\mathrm{one}}{U\cdot V}\cdot {\displaystyle {\sum }_{u=\mathrm{one}}^U{\displaystyle {\sum }_{v=\mathrm{one}}^{V}S\left(u+i,-U,v+j\right)}}$$

.

The dimensions of block 303 are equal to the dimensions of block 313.

3. Verification of condition 1 (Fig. 4, 403): if block 302 and block 312 are available (that is, blocks 302 and 312 are located within the frame boundaries and, if the reference frame is a synthesized frame, then the pixels of block 302 do not belong to the region occlusion, and the value of at least one pixel of block 302 is different from 0), then we proceed to estimate the value of estMX (Fig. 4, 405) in accordance with the following expression:

. $$estMX=\frac{refMX}{refMX\_L}\cdot encMX\_L$$

.

Otherwise, they proceed to check condition 2 (Fig. 4, 404).

4. Verification of condition 2 (Fig. 4, 404): if block 303 and block 313 are available (that is, blocks 303 and 313 are located within the frame and, if the reference frame is a synthesized frame, then the pixels of block 303 do not belong occlusion area, and the value of at least one pixel of block 303 is different from 0), then we proceed to estimate the estMX value (Fig. 4, 407) in accordance with the following expression:

. $$estMX=\frac{refMX}{refMX\_A}\cdot encMX\_A$$

.

Otherwise, they proceed to estimate the estMX value (Figure 4, 406) in accordance with the following expression:

estMX = MAP (encMX_L, encMX_A, encMX_LA),

where MAP (x, y, z) is the well-known method of median prediction [10], encMX_LA is the average value of block 314:

$$encMX\_LA=\frac{\mathrm{one}}{U\cdot Q}\cdot {\displaystyle {\sum }_{u=\mathrm{one}}^U{\displaystyle {\sum }_{q=\mathrm{one}}^{V}DI(u,q)}}$$

The dimensions of block 314 are U × Q and equal to the corresponding sizes of blocks 312 and 313.

5. The calculation of the correction parameter changes in brightness and contrast α (Fig.4, 408) by using the obtained values estMX and refMX.

6. Performing correction of changes in brightness and contrast (Figure 4, 409) for the reference block 301 by using the calculated parameter α.

It should be noted that the reference frame 300, blocks 301, 302, 303 and reconstructed (encoded and then decoded) blocks 312, 313, 314 are available both during encoding and during decoding. 5 illustrates the relative position of the regions and blocks under consideration in the current frame 500. The region 501 of the current frame 500 is available during encoding and decoding of the current encoded block 502. Region 501 includes blocks 312, 313, and 314. Region 501 is sometimes referred to as a “pattern”. Region 503 is not present during decoding of the current block 502 and should not contain blocks 312, 313 and 314. In this regard, the method described above can be implemented both in the encoder and in the decoder, and does not require additional data to be transmitted to the output bit flow.

Another embodiment of the claimed invention provides for pixel-by-pixel correction of changes in brightness and contrast for the reference block in prediction coding. The key idea is to evaluate pixel-by-pixel the correction parameter for changes in brightness and contrast, moreover, the correction is based on the restored pixel values adjacent to the current block, the pixel values of the reference frame, and their mutual similarity. 6 illustrates a specific application of this technique.

. $$T_0^R\sim T_{15}^R$$

- пиксели, принадлежащие блокам 602 и 603. Блоки 602 и 603 являются соседними по отношению к опорному блоку 601 и ставятся в соответствие блокам 612 и 613. Следует также отметить, что общее число пикселей в блоках 612, 613 и 602, 603 является одинаковыми.6, at each iteration of the reference block search procedure for the current block 611 belonging to the current encoded frame 610, a displacement vector (DV) 620 is determined. DV indicates a reference block 601 of a reference frame 600. The current block 611 contains pixels, which are designated as A00 ~ A33. The reference block 601 contains pixels, which are designated as R00 ~ R33. The restored pixel values (blocks 612 and 613) adjacent to the current encoded block are indicated as $$T_0^D\sim T_{\mathrm{fifteen}}^D$$

. $$T_0^R\sim T_{\mathrm{fifteen}}^R$$

- pixels belonging to blocks 602 and 603. Blocks 602 and 603 are adjacent to the reference block 601 and are mapped to blocks 612 and 613. It should also be noted that the total number of pixels in blocks 612, 613 and 602, 603 are the same.

For each position (i, j) of the pixel in the reference block 601, the correction of changes in brightness and contrast is carried out in accordance with the following equation:

ψ (x _{i, j} ) = α _{i, j} x x _{i, j} .

Here, the parameter of pixel-by-pixel correction of changes in brightness and contrast (in case estR _{i, j is} not equal to 0) is described as:

, $${\alpha }_{i,j}=\frac{est{D}_{i,j}}{est{R}_{i,j}}$$

,

where estD _{i, j} is the first estimate for a pixel with coordinates (i, j) in the reference block; estR _{i, j} is the second pixel estimate with the coordinates (i, j) in the reference block. Otherwise, α _{i, j is} assumed to be equal to 1.

A flowchart of a method for pixel-by-pixel correction of changes in brightness and contrast for a reference block is shown in FIG. 7. This method includes the following steps:

1. Obtaining pixel values of blocks 601, 602, 603 from the reference frame 600, block 611 and blocks 612, 613 belonging to the template area of the current encoded frame 610 (operation 701).

2. Calculation of weighting factors W _k (i, j), k = 0, ..., N - 1 for each position (i, j) of the pixel in the reference block 601 (operation 702). Weighting factors W _k (i, j) can be expressed as follows:

W _k (i, j) = exp (-CA A _k (i, j)),

, $$A_k\left(i,j\right)=\left|R_{i,j}-T_k^R\right|$$

. $$C=\frac{\sigma }{2}$$

, $$A_k\left(i,j\right)=\left|R_{i,j}-T_k^R\right|$$

.

, тем больше его вклад при определении параметра коррекции изменения яркости и контрастности для опорного блока.where σ> 0 is determined experimentally. Here N is the total number of pixels in blocks 612, 613 (or 602, 603). It should be noted that the weights reflect the fact that, than the value of R _{i, j is} closer to $$T_k^R$$

, the greater his contribution in determining the correction parameter for changes in brightness and contrast for the reference block.

3. The calculation of the values estD _{i, j} for each position (i, j) of the pixel in the reference block 601 (operation 703) in accordance with the following expression:

$$est{D}_{i,j}={\displaystyle {\sum }_{\begin{array}{c}k\in 0...N-\mathrm{one}\\ k:\left|T_k^R-T_k^D\right|\le Thr\mathrm{one}and\left|T_k^R-R_{i,j}\right|\le Thr2\end{array}}^{}{W}_k\left(i,j\right)\cdot T_k^D}$$

, соседних по отношению к текущему кодируемому блоку.Thr1 and Thr2 are predefined thresholds. Threshold values are used to exclude pixel values adjacent to the reference block, which differ significantly from the values of R _{i, j} and values $$T_k^D$$

adjacent to the current encoded block.

4. The calculation of the values estR _{i, j} for each position (i, j) of the pixel in the reference block 601 (operation 704) in accordance with the following expression:

. $$est{R}_{i,j}={\displaystyle \sum _{\begin{array}{c}k\in 0...N-\mathrm{one}\\ k:\left|T_k^R-T_k^D\right|\le Thr\mathrm{one}and\left|T_k^R-R_{i,j}\right|\le Thr2\end{array}}}{W}_k\left(i,j\right)\cdot T_k^R$$

.

The predefined threshold values Thr1 and Thr2 are the same as in the calculation for calculating estD _{i, j} .

5. The calculation of the correction parameter for changing the brightness and contrast α _{i, j} (operation 705) for each pixel with coordinates (i, j) in the reference block 601 based on the obtained values estD _{i, j} and estR _{i, j} in case estR _{i , j is} not equal to 0. Otherwise, α _{i, j is set} equal to 1.

6. Performing correction of changes in brightness and contrast (operation 706) for the reference block 601 based on the use of the calculated parameters α _{i, j} .

Another embodiment of the claimed invention is based on the following. Typically, as pixels adjacent to the reference block, a group of pixels adjacent to the reference block is selected. However, the search procedure for the reference block can select such a displacement vector that the pixel values in the indicated group will not be sufficiently similar to the corresponding pixel values adjacent to the current encoded block. Moreover, the values of pixels directly adjacent to the reference block may differ significantly from the pixel values of the reference block. In these cases, correction of changes in brightness and contrast may not be performed correctly.

To solve this problem, in an embodiment of the claimed invention, it is proposed to use the "floating" (relative to the reference block) position of said group of pixels adjacent to the reference block. Fig.8 explains the inventive method in accordance with one embodiment of the claimed invention. 8, at each iteration of the reference block search procedure for the current block 811 of the current encoded frame 810, a displacement vector (DV) 820 is determined. DV points to the reference block 801 of the reference frame 800. The coordinates of the group of pixels of the reference frame (which are formed by the pixels of the blocks 802 and 803) are determined using an additional refinement offset vector 804. The bias refinement vector 804 is the result of an additional bias estimation procedure. In this case, such a displacement vector 804 is determined that gives the minimum value of the penalty function that determines the degree of similarity of blocks 812, 813 and blocks 802, 803, respectively. Such a well-known function as the root mean square error, the sum of the absolute differences, the sum of the absolute differences for signals with a zero mean, and so on can serve as a penalty function. Vector 804 can be implicitly determined during the encoding and decoding process without transmitting additional information in the output bitstream.

Figure 9 presents a flowchart that describes a method for encoding multi-angle video sequences based on the correction of brightness and contrast according to one embodiment of the claimed invention. At 901, a reference block is determined which is used to form the predicted block. At 902, the correction parameters for changing the brightness and contrast for the found reference block are determined. Determining the correction parameters for changes in brightness and contrast includes:

- obtaining restored (encoded and then decoded) pixel values adjacent to the current block and pixel values adjacent to the reference block of the reference frame;

- determining the numerical relationships between the pixel values of the reference block and the pixel values adjacent to the reference block, and the ratio between the restored pixel values adjacent to the current encoded block and the pixel values adjacent to the reference block;

- determination of correction parameters for changing the brightness and contrast for correcting differences in brightness and contrast for the reference block based on the numerical relationships found in the previous step, the pixel values of the reference block, the restored pixel values adjacent to the current block being encoded, and the pixel values adjacent to in relation to the support block.

At 903, using the found correction parameters for changing the brightness and contrast, a correction is performed for the reference block. At 904, using the brightness and contrast-adjusted reference block, a prediction block is generated for the current block. At 905, using the generated prediction block, the current block is encoded. In particular, information about the reference block is encoded, if necessary for decoding. It should be noted that the found correction parameters for changes in brightness and contrast are not encoded and are not placed in the output bitstream.

Figure 10 illustrates a method for decoding multi-angle video sequences based on the correction of changes in brightness and contrast, according to one example implementation of the claimed invention. 10, information about a reference block is decoded if decoding is required. The decoded information can be used to determine the reference block at step 1001. At step 1002, correction parameters for changing the brightness and contrast for correcting the reference block are determined. The procedure for determining the correction parameters for changes in brightness and contrast includes:

- obtaining restored (encoded and then decoded) pixel values adjacent to the current block and pixel values adjacent to the reference block of the reference frame;

- determination of numerical ratios between the pixel values of the reference block and the values of pixels adjacent to the reference block, and the ratio between the restored pixel values adjacent to the current encoded block and the pixel values adjacent to the reference block;

- determination of correction parameters for changing the brightness and contrast for correcting differences in brightness and contrast for the reference block based on the numerical relationships found in the previous step, the pixel values of the reference block, the restored pixel values adjacent to the current block being encoded, and the pixel values adjacent to in relation to the support block.

At step 1003, using the found correction parameters for changing the brightness and contrast, the correction of the reference block is performed. At step 1004, using the brightness and contrast-adjusted reference block, a prediction block is generated for the current decoded block. At 1005, using the generated prediction block, the current block is decoded.

In practice, the claimed invention can be used in the encoding and decoding of multi-angle video sequences.

The embodiments of the claimed invention described above are provided for purposes of illustration only and are not restrictive. The scope of protection of the invention is determined by the attached claims.

References

[1] Yea, S .; Vetro, A., “View Synthesis Prediction for Multiview Video Coding”, Image Communication, ISSN: 0923-5965, Vol.24, Issue 1-2, pp.89-100, January 2009.

[2] ITU-T Rec. H.264. Advanced video coding for generic audiovisual services. 2010.

[3] US Patent 7,924,923. Motion Estimation and Compensation Method and Device Adaptive to Change in Illumination. April 2011.

[4] Y. Lee, J. Hur, Y. Lee, R. Han, S. Cho, N. Hur, J. Kirn, J. Kirn, P. Lai, A. Ortega, Y.Su, P. Yin and C. Gomila. CE11: Illumination compensation. Joint Video Team (JVT) of ISO / IEC MPEG and ITU-T VCEG JVT-U052, Oct. 2006.

[5] J.H. Kirn, P. Lai, J. Lopez, A. Ortega, Y.Su, P. Yin, and C. Gomila. New coding tools for illumination and focus mismatch compensation in multiview video coding. IEEE Trans. on Circuits and Systems for Video Technology, vol. 17, no. 11, pp. 1519-1535, Nov. 2007.

[6] T. Yamamoto, T. Ikai, "Weighted prediction using neighboring pixels," ITU-T Q.6 / SG16 VCEG, Proposal VCEG-AH19, January 2008.

[7] US Patent Application 2011/0286678. Multi-view Image Coding Method, Multi-view Image Decoding Method, Multi-view Image Coding Device, Multi-view Image Decoding device. Multi-view Image Coding Program, and Multi-view Image Decoding Program. November, 2011.

[8] US patent application 2008/0304760. Method and Apparatus for Illumination Compensation and Method and Apparatus for Encoding and Decoding Image Based on Illumination Compensation. December, 2008.

[9] Richardson I.E. The H.264 Advanced Video Compression Standard. Second Edition. 2010.

[10] Martucci S.A. “Reversible compression of HDTV images using median adaptive prediction and arithmetic coding”, in IEEE Int. Symp on Circuits and Systems, 1990.

Claims (13)

1. A method for local correction of changes in the brightness and contrast of the reference frame for encoding a multi-angle video sequence, which includes the following steps:
- get the pixel values of the current encoded block belonging to the encoded frame, and the pixel values of the reference block belonging to the reference frame;
- get restored, that is, encoded and then decoded, the values of pixels adjacent to the current block of the encoded frame, and the values of pixels adjacent to the reference block of the reference frame;
- determine the numerical relationship between the pixel values of the reference block and the pixel values adjacent to the reference block, and the ratio between the restored pixel values adjacent to the current encoded block and the pixel values adjacent to the reference block;
- on the basis of the numerical relationships found in the previous step, the pixel values of the reference block, the restored pixel values adjacent to the current encoded block, and the pixel values adjacent to the reference block, brightness and contrast correction parameters are determined to correct for differences in brightness and contrast for the reference block in comparison with the current encoded block;
- perform correction of differences in brightness and contrast for the reference block using the found correction parameters. 2. The method according to claim 1, characterized in that the procedure for determining the numerical ratios for the pixels of the current encoded frame and the reference frame, as well as the procedure for determining the correction parameters for changing the brightness and contrast, include the following steps:
- calculate the statistical characteristics for the restored pixel values adjacent to the current encoded block, the statistical characteristics for the pixel values of the reference block and the statistical characteristics for the pixel values adjacent to the reference block;
- determine the numerical relationship between the statistical characteristics for the pixels of the reference block and the statistical characteristics for the restored values of pixels adjacent to the reference block;
- based on the calculated statistical characteristics and the relationships between them, an estimate is made of the value of the statistical characteristic for the current encoded block;
- calculate the correction parameter changes in brightness and contrast to correct differences in brightness and contrast between the reference and the current encoded blocks based on the found estimates of the statistical characteristics for the current block and the statistical characteristics of the reference block. 3. The method according to claim 2, characterized in that the calculation of statistical characteristics, determining the ratios for statistical characteristics and determining a correction parameter for changes in brightness and contrast include the following steps:
- if there are recovered pixels adjacent to the current encoded block and located to the left of the current encoded block, an average value is calculated for them; in the case of the presence of restored pixels adjacent to the current encoded block and located above the current encoded block, the average value is calculated for them, the average value for the pixels of the reference block is calculated, in the case of the presence of pixels adjacent to the reference block and located to the left of reference block, the average value is calculated for them, and also in the case of pixels adjacent to the reference block and located above the reference block, the average value is also calculated for them;
- in the case of the presence of restored pixels adjacent to the current encoded block and located to the left of the current encoded block, and the presence of pixels adjacent to the reference block and located to the left of the reference block, calculate the ratio between the average pixel value of the reference block and the average value pixels adjacent to the reference block and located to the left of the reference block; calculate the product of the found ratio and the average value of the restored pixels adjacent to the current encoded block and located to the left of the current encoded block; determining a correction parameter for changes in brightness and contrast as the ratio between the calculated product and the average value for the pixels of the reference block;
- otherwise, if there are recovered pixels adjacent to the current block to be encoded and located above the current block to be encoded and if there are pixels adjacent to the block and located above the reference block, the ratio between the average pixel value of the reference block is calculated and the average value of pixels adjacent to the reference block and located above the reference block; calculating the product of the found ratio and the average value of the recovered pixels adjacent to the current encoded block and located above the current encoded block; determining a correction parameter for changes in brightness and contrast as the ratio between the calculated product and the average value for the pixels of the reference block;
- otherwise, use the median prediction method to calculate an estimate of the average value of the current encoded block; determine the correction parameter for changes in brightness and contrast as the ratio between the average estimate for the pixels of the current encoded block and the average for the pixels of the reference block. 4. The method according to claim 1, characterized in that the procedure for determining the ratios for the pixels of the current encoded frame and the reference frame, determining a correction parameter for changing the brightness and contrast, and also performing correction of differences in brightness and contrast of the reference block in comparison with the current encoded block include The following steps are required:
- calculate the first estimate estD _{i, j} for each position (i, j) of the pixel in the reference block; moreover, the first estimate estD _{i, j} is a linear combination of the restored values $$T_k^D$$

pixels adjacent to the current encoded block, k = 0, ..., N-1, N is the number of pixels adjacent to the current encoded and reference blocks;
- calculate the second estimate estR _{i, j} for each position (i, j) of the pixel in the reference block; moreover, the second estimate estR _{i, j} is a linear combination of values $$T_k^R$$

pixels adjacent to the reference block, k = 0, ..., N-1;
- determine, based on the first estimate estD _{i, j} , the second estimate estR _{i, j} , the values of R _{i, j} pixels of the reference block, the restored values $$T_k^D$$

pixels adjacent to the current block being encoded and values $$T_k^R$$

pixels adjacent to the reference block, a correction parameter for changing the brightness and contrast for each pixel position in the reference block;
- perform correction of changes in brightness and contrast for each pixel of the reference block using the previously defined correction parameters. 5. The method according to claim 4, characterized in that the procedure for calculating the first and second estimates for each pixel position in the reference block and determining the correction parameters for changing the brightness and contrast for each pixel position in the reference block includes the following steps:
- calculate the first estimate estD _{i, j} as $$est{D}_{i,j}={\displaystyle {\sum }_{k=0...,N-\mathrm{one}}{W}_k\left(i,j\right)\cdot T_k^D}$$

, where W _k (i, j), k = 0, ..., N-1 are weights, and $$T_k^D$$

, k = 0, ..., N-1 - restored values of pixels adjacent to the current encoded block, N - number of pixels adjacent to the current encoded and reference blocks;
- calculate the second estimate estR _{i, j} as $$est{R}_{i,j}={\displaystyle {\sum }_{k=0...,N-\mathrm{one}}{W}_k\left(i,j\right)\cdot T_k^R}$$

, where W _k (i, j), k = 0, ..., N-1 are weights, and $$T_k^R$$

, k = 0, ..., N-1 are the values of pixels adjacent to the reference block;
- in the event that the second estimate estR _{i, j is} not equal to zero, the correction parameter for changing the brightness and contrast is determined to correct the difference in brightness and contrast for each pixel in the reference block; this parameter is a relation: $${\alpha }_{i,j}=\frac{est{D}_{i,j}}{est{R}_{i,j}}$$

otherwise, the correction parameter α _{i, j} is set to 1;
- perform correction of the brightness and contrast of the reference block by multiplying the values of each pixel of the reference block R _{i, j} by the corresponding correction parameter α _{i, j} . 6. The method according to claim 5, characterized in that the procedure for calculating the first and second estimates for each position of the pixel in the reference block includes the following steps:
- calculate the weight coefficients W _k (i, j), k = 0, ..., N-1 for the first estimate estD _{i, j} and for the second estimate estR _{i, j} ; for each position (i, j) of the pixel in the reference block, the weight coefficient, W _k (i, j) is equal to the non-increasing function of the absolute difference:
$$\left|R_{i,j}-T_k^R\right|$$

,
which provides an inversely proportional increase / decrease W _k (i, j) depending on the decrease / increase in the absolute difference. Here R _{i, j} is the pixel value of the reference block; $$T_k^R$$

(k = 0, ..., N-1) is the value of a pixel adjacent to the reference block; N is the number of pixels adjacent to the current encoded and reference blocks. 7. The method according to claim 5, characterized in that the procedure for calculating the first and second estimates for each pixel position in the reference block includes the following steps:
- calculate the weight coefficients W _k (i, j), k = 0, ..., N-1 for the first estimate estD _{i, j} and the second estimate estR _{i, j} ; for each position (i, j) of the pixel in the reference block, the weight coefficient W _k (i, j) is equal to a non-increasing function of the absolute difference:
$$\left|R_{i,j}-T_k^R\right|$$

,
which provides an inversely proportional increase / decrease W _k (i, j) depending on the decrease / increase in the absolute difference; in case when $$\left|T_k^R-R_{i,j}\right|\le Thr$$

where Thr is a predetermined threshold; otherwise, W _k (i, j) = 0. Here R _{i, j} is the pixel value of the reference block, $$T_k^R$$

(k = 0, ..., N-1) is the value of a pixel adjacent to the reference block. 8. The method according to claim 5, characterized in that the procedure for calculating the first and second estimates for each pixel position in the reference block includes the following steps:
- calculate the weight coefficients W _k (i, j), k = 0, ..., N-1 for the first estimate estD _{i, j} and the second estimate estR _{i, j} ; for each position (i, j) of the pixel in the reference block, the weight coefficient W _k (i, j) is equal to a non-increasing function of the absolute difference:
$$\left|R_{i,j}-T_k^R\right|$$

,
which provides an inversely proportional increase / decrease W _k (i, j) depending on the decrease / increase in the absolute difference; when $$\left|T_k^R-T_k^D\right|\le Thr\mathrm{one}$$

where $$T_k^D$$

(k = 0, ..., N-1) - the value of a pixel adjacent to the current block being encoded, Thr1 is the first predetermined threshold; $$\left|T_k^R-R_{i,j}\right|\le Thr2$$

where Thr2 is the second predetermined threshold; otherwise W _k (i, j) = 0; here R _{i, j} is the pixel value of the reference block, $$T_k^R$$

(k = 0, ..., N-1) is the value of a pixel adjacent to the reference block. 9. The method according to claim 5, characterized in that the procedure for calculating the first and second estimates for each position of the pixel in the reference block includes the following steps:
- calculate the weight coefficients W _k (i, j), k = 0, ..., N-1 for the first estimate estD _{i, j} and the second estimate estR _{i, j} ; for each position (i, j) of the pixel in the reference block, the weight coefficient W _k (i, j) is equal to W _k (i, j) = exp (-C · A _k (i, j)), where C is a predetermined constant greater than 0, and A _k (i, j) equals $$A_k\left(i,j\right)=\left|R_{i,j}-T_k^R\right|$$

where R _{i, j} is the pixel value of the reference block, $$T_k^R$$

(k = 0, ..., N-1) is the value of a pixel adjacent to the reference block; when $$\left|T_k^R-R_{i,j}\right|\le Thr$$

where Thr is a predetermined threshold; otherwise, W _k (i, j) = 0. 10. The method according to claim 5, characterized in that the procedure for calculating the first and second estimates for each position of the pixel in the reference block includes the following steps:
- calculate the weight coefficients W _k (i, j), k = 0, ..., N-1 for the first estimate estD _{i, j} and the second estimate estR _{i, j} ; for each position (i, j) of the pixel in the reference block, the weight coefficient W _k (i, j) is equal to W _k (i, j) = exp (-C · A _k (i, j)), where C is a predetermined constant greater than 0, and A _k (i, j) equals $$A_k\left(i,j\right)=\left|R_{i,j}-T_k^R\right|$$

where R _{i, j} is the pixel value of the reference block, $$T_k^R$$

(k = 0, ..., N-1) is the value of a pixel adjacent to the reference block, in the case $$\left|T_k^R-T_k^D\right|\le Thr\mathrm{one}$$

where $$T_k^D$$

, (k = 0, ..., N-1) is the value of a pixel adjacent to the current block being encoded, Thr1 is the first predetermined threshold; and $$\left|T_k^R-R_{i,j}\right|\le Thr2$$

where Thr2 is the second predetermined threshold; otherwise, W _k (i, j) = 0. 11. The method according to claim 1, characterized in that the positions of the restored pixel values adjacent to the current block being encoded, and the positions of the pixel values adjacent to the reference block are determined adaptively instead of the corresponding pixels with the predetermined positions. 12. A method of encoding multi-angle video sequences based on local correction of the brightness and contrast of the reference block, which includes the following steps:
- determine the reference block, which is used to form the prediction block for the current encoded block;
- determine the correction parameters for changes in brightness and contrast to correct differences in brightness and contrast between the reference block and the current encoded block in the search process or at the end of the search for the reference block;
- perform correction of changes in brightness and contrast of the found reference block by using the found correction parameters for changes in brightness and contrast;
- form a prediction block for the current encoded block by using the corrected brightness and contrast reference block;
- encode the current block using the generated prediction block without encoding the found correction parameters for changing the brightness and contrast; encoding information about the reference block, if necessary for decoding;
characterized in that the procedure for determining the brightness and contrast correction parameters includes the following steps:
- get restored, that is, encoded and then decoded, the values of pixels adjacent to the current block of the encoded frame, and the values of pixels adjacent to the reference block of the reference frame;
- determine the numerical relationship between the pixel values of the reference block and the pixel values adjacent to the reference block, and the ratio between the restored pixel values adjacent to the current encoded block and the pixel values adjacent to the reference block;
- on the basis of the numerical relationships found in the previous step, the pixel values of the reference block, the restored pixel values adjacent to the current encoded block, and the pixel values adjacent to the reference block, the correction parameters for changing the brightness and contrast to correct the difference in brightness are determined and contrast for the reference block. 13. A method for decoding multi-angle video sequences based on the correction of brightness and contrast, which includes the following steps:
- decode information about the reference block, if necessary in order to determine the reference block of the current block, and determine the reference block;
- determine the correction parameters for changes in brightness and contrast for correcting brightness and contrast for the found reference block;
- perform the correction of differences in brightness and contrast for the found reference block using the found correction parameters for changes in brightness and contrast;
- form a prediction block for the current decoded block using the reference block, adjusted for brightness and contrast;
- decode the current block using the generated block prediction and the found correction parameters for changes in brightness and contrast;
characterized in that the procedure for determining the brightness and contrast correction parameters includes the following steps:
- get restored, that is, encoded and then decoded, the values of pixels adjacent to the current block of the encoded frame, and the values of pixels adjacent to the reference block of the reference frame;
- determine the numerical relationship between the pixel values of the reference block and the pixel values adjacent to the reference block, and the ratio between the restored pixel values adjacent to the current encoded block and the pixel values adjacent to the reference block;
- on the basis of the numerical relationships found in the previous step, the pixel values of the reference block, the restored pixel values adjacent to the current encoded block, and the pixel values adjacent to the reference block, the correction parameters for changing the brightness and contrast to correct the difference in brightness are determined and contrast for the reference block.

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