JP2004023372A - Method and device for encoding image - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To encode a high quality image with a high compression rate by a simple operation without requiring special data. <P>SOLUTION: An inputting part 1 receives an image signal, and an 8 × 8 block input circuit 2a divides the image into blocks of 8 × 8 pixels. An average calculation circuit 3a calculates the average of pixel values in a divided block, and a predictive error quantizer 4a calculates a predictive error from the calculated average and quantizes the predictive error. A predictive error inverse quantizer and a new average calculation circuit 5a dequantize the quantized error to calculate an error and add or subtract the error to/from the calculated error to calculate a new average. An error calculation circuit 6a compares the new average with all pixel values in the block to thereby calculate an error. An error comparison circuit 7a compares the calculated error with a threshold. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image encoding method and apparatus for encoding and processing image signals for transmission and storage, which are applied to videophones, surveillance cameras, and the like.
[0002]
[Prior art]
As a general compression standard for image signals, JPEG has been proposed for still images, and MPEG has been proposed for moving images. Typical image compression methods include predictive coding and vector quantization, in addition to orthogonal transform using DCT employed in JPEG and MPEG.
[0003]
In the case of MPEG, although the compression ratio is high, the amount of calculation is large due to the use of motion compensation (prediction) and DCT, and when executed by hardware, it is necessary to use dedicated hardware. For execution, it is necessary to use a high-performance CPU.
[0004]
Also, in the case of a profile using a B picture (Bidirectional predictive coded image), the amount of delay is large, and it is difficult to apply to a conversation such as a videophone.
[0005]
Predictive coding is coding that predicts the pixel value from pixels adjacent to each other and quantizes the prediction error.In this case, it is necessary to reduce the number of quantization levels as the compression ratio increases. As a result, the image quality is significantly deteriorated.
[0006]
Vector quantization is a method of replacing a plurality of pixel values with a predetermined representative vector, and is effective when the input image has a characteristic such as a videophone. Is input, it is difficult to generate a codebook (encoded data, that is, a table).
[0007]
[Problems to be solved by the invention]
As described above, DCT used in MPEG or the like has disadvantages in that complicated addition, subtraction, multiplication, and division operations are performed and the amount of operation is enormous. Further, in the case of predictive coding, when the compression ratio is increased, the deterioration of image quality becomes remarkable, and in the case of vector quantization, special data (codebook) is required.
[0008]
SUMMARY OF THE INVENTION An object of the present invention is to provide an image encoding method and an image encoding apparatus capable of encoding an image of high quality and a high compression rate with a simple and small operation amount without requiring special data. is there.
[0009]
[Means for Solving the Problems]
The image encoding method according to the present invention comprises:
An image encoding method for encoding and transmitting an image signal, comprising:
The entire screen is divided into predetermined pixel units,
Calculating the average of the pixel values in the block,
Calculating the error between the pixel value and the average value,
Based on whether these errors are within a predetermined value, determine whether to encode the block or to further divide the block,
It is characterized in that the encoding process is performed in an appropriate pixel unit block according to the result of the determination.
[0010]
According to the present invention, it is determined whether to perform encoding of a block divided into predetermined pixel units or to further divide a block, and perform encoding processing on an appropriate pixel unit block according to the result of the determination. Since it is performed, complicated addition, subtraction, multiplication, division, and an enormous amount of operation such as DCT are not required. Further, since it is not necessary to reduce the number of quantization levels as the compression rate is increased unlike in predictive coding, it is possible to perform high quality and high compression coding. Furthermore, no special data is required as in vector quantization.
[0011]
Preferably, a histogram is created in which the maximum value of the absolute value of the difference between the average value of the block and the pixel value in the block is obtained for each block, and the predetermined value is calculated from the histogram.
[0012]
An image encoding device according to the present invention includes:
An image encoding device for encoding and transmitting an image signal,
Block dividing means for dividing the entire screen into blocks of a predetermined pixel unit,
Average value calculation means for calculating an average value of pixel values in the block,
Error calculating means for calculating an error between the pixel value and the average value,
A determination unit configured to determine whether to encode the block or to further divide the block, based on whether these errors are within a predetermined value;
Encoding means for performing an encoding process on an appropriate pixel unit block according to the result of the determination.
[0013]
According to the present invention, it is possible to perform high-quality and high-compression encoding without requiring complicated addition, subtraction, multiplication, division, and an enormous amount of computation such as DCT, and does not require special data.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment of an image encoding method and an image encoding apparatus according to the present invention will be described in detail with reference to the drawings.
[0015]
FIG. 1 is a flowchart of the operation of the embodiment of the image encoding method according to the present invention. In this case, the entire screen is divided into blocks having 8 pixels in the horizontal direction and 8 pixels in the vertical direction, that is, blocks of 8 × 8 pixels, and the block of 8 × 8 pixels thus divided is used as a reference. .
[0016]
The control routine shown in FIG. 1 is executed, for example, on the transmission side of the image monitoring system. First, in step S1, a threshold value for determination processing is calculated as preprocessing for encoding. Step S1 will be described later in detail with reference to FIGS.
[0017]
Next, in step S2, the number J of all blocks when the entire screen is divided into blocks of 8 × 8 pixels is set. The total number of blocks J is determined by the number of vertical and horizontal pixels. Next, in step S3, processing of an 8 × 8 pixel block, which will be described later in detail with reference to FIG. 5, is performed.
[0018]
Next, 1 is subtracted from the total number of blocks J (step S4), and thereafter, it is determined whether or not the processing of all the blocks is completed (step S5). If the processing has been completed, this routine ends. If not, the processing returns to step S3.
[0019]
FIG. 2 is a flowchart of the first half of the subroutine of step S1 in FIG. 1, and FIG. 3 is a flowchart of the second half of the subroutine of step S1 in FIG. In this embodiment, the reference block is composed of 8 × 8 pixel blocks. Since processing is performed on the basis of an 8 × 8 pixel block, the block is divided into 4 × 4 pixel blocks if it is divided in half vertically and horizontally, and further divided into 2 × 2 pixel blocks if it is further divided into half. Will be done. The subroutine in FIGS. 2 and 3 calculates the average value and the threshold value by proceeding with the calculation of the block of 4 × 4 pixels and the block of 8 × 8 pixels based on the block of 2 × 2 pixels.
[0020]
First, in steps S11 to S13, the number of all blocks J, the number of operations k for a block of 4 × 4 pixels, and the number of operations 1 for a block of 2 × 2 pixels are set as parameters. In this case, the numbers of operations k and l are both 4.
[0021]
Next, in step S14, the average value of the block of 2 × 2 pixels when the block of 8 × 8 pixels is divided into the block of 2 × 2 pixels is calculated. Since there are 2 × 2 pixels, the number of pixels is four. In order to obtain an average value of four pixels, it is sufficient to sum these pixel values and then divide by four. The division by 4 does not require a divider having a complicated configuration, since the digital calculation only requires shifting by 2 bits to the right. That is, if the pixel values are A1, A2, A3, and A4, respectively, the first average value (average value 2) is １ ／ (A1 + A2 + A3 + A4).
[0022]
Next, the absolute value of the difference between the average value 2 and each pixel is obtained (step S15), the maximum value of the obtained absolute values of the four differences is detected, and a first histogram (described later) is used. Histogram 1) is registered (step S16), 1 is subtracted from the number of operations l (step S17), and whether or not the number of operations 1 is 0, that is, the processing is completed for all blocks of 2 × 2 pixels Is determined. If the process has been completed, the process proceeds to the next step S19, whereas if the process has not been completed, the process returns to step S14.
[0023]
In step S19, the average value of the 4 × 4 pixel block is calculated using the processing result of the 2 × 2 pixel block. Since there are 4 × 4 pixels, the number of pixels is 16. In order to obtain the average value of 16 pixels, it is sufficient to use the above average value 2 to obtain the average of four 2 × 2 pixel blocks. Assuming that the average value of the four 2 × 2 pixel blocks is B1, B2, B3, and B4, the second average value (average value 4) is １ ／ (B1 + B2 + B3 + B4).
[0024]
Next, the absolute value of the difference between the average value 4 and each pixel is obtained (step S20), the maximum value of the obtained absolute values of the four differences is detected, and a second histogram (described later) Histogram 2) is registered (step S21), 1 is subtracted from the number of operations k (step S22), and whether or not the number of operations k is 0, that is, processing is completed for all blocks of 4 × 4 pixels Is determined. If the process has been completed, the process proceeds to the next step S24, whereas if the process has not been completed, the process returns to step S13.
[0025]
Next, in step S24, the average value of the block of 8 × 8 pixels is calculated using the processing result of the block of 4 × 4 pixels. Since there are 8 × 8 pixels, the number of pixels is 64. In order to calculate the average value of 64 pixels, it is sufficient to calculate the average of four 4 × 4 pixel blocks using the average value 4 described above. Assuming that the average value of the four 4 × 4 pixel blocks is C1, C2, C3, and C4, the third average value (average value 8) is と (C1 + C2 + C3 + C4).
[0026]
Next, the absolute value of the difference between the average value 8 and each pixel is obtained (step S25), the maximum value of the obtained absolute values of the 64 differences is detected, and a third histogram (to be described later) is used. It is registered in the histogram 3) (step S26).
[0027]
Next, in step S27, 1 is subtracted from the total number J of blocks, and in step S28, it is determined whether the processing has been completed for all blocks, that is, the entire image (one screen). If the processing has been completed, the process proceeds to step S29. If the processing has not been completed, the process returns to step S12.
[0028]
In step S29, a threshold value and a quantization table number to be used in the subsequent processing are determined from the histograms 1, 2, and 3 and the free space after the previous frame processing in a buffer memory (not shown) connected to the subsequent stage, This subroutine ends.
[0029]
In this case, the threshold value is determined from the distribution of the histograms 1, 2, and 3 obtained as shown in FIG. 4, and is used for the block of 8 × 8 pixels, the block of 4 × 4 pixels, and the block of 2 × 2 pixels. Three types are required. Further, three types of quantization table numbers for quantizing the average value 8, the average value 4, and the average value 2 are determined.
[0030]
FIG. 5 is a flowchart of a subroutine of step S3 in FIG. This subroutine performs quantization in order to perform variable length coding.
First, in step S41, a prediction error of an average value of predetermined 8 × 8 pixels is quantized based on the quantization table calculated in step S29 of FIG.
[0031]
Next, in step S42, the quantized prediction error is inversely quantized to calculate the error, and the original average is corrected by performing addition and subtraction to calculate a new average.
[0032]
Next, the new average value is compared with the 64 pixels in the block (step S43), and based on the result of this comparison, within the threshold value for the block of 8 × 8 pixels obtained in step S29 in FIG. It is determined whether or not there is (step S44). If it is within the threshold value, this subroutine ends. If it is not within the threshold value, the process proceeds to step S45.
[0033]
Next, the number of operations k (in this case, 4) is set (step S45), and the difference between the new average value calculated in step S42 and the average value of the block of 4 × 4 pixels is quantized (step S46).
[0034]
Next, in step S47, the quantized error is inversely quantized to calculate the error, and the original average is corrected by performing addition and subtraction to calculate a new average (new average).
[0035]
Next, the new average value is compared with the 16 pixels in the block (step S48), and based on the result of this comparison, within the threshold value for the 4 × 4 pixel block obtained in step S29 in FIG. It is determined whether or not there is (step S49). If it is not within the threshold value, block processing of 2 × 2 pixels, which will be described in detail later with reference to FIG. 6, is performed (step S50), and then the process proceeds to step S51. If there is, the process directly proceeds to step S51.
[0036]
In step S51, 1 is subtracted from the number of operations k. Next, in step S52, it is determined whether or not the processing has been completed for all of the 4 × 4 pixel blocks. If it is determined that the processing has been completed, this subroutine is completed. If it is determined that the processing has not been completed, the process returns to step S46.
[0037]
FIG. 6 is a flowchart of a subroutine of step S50 in FIG. In this case, first, in step S61, the processing number L (4 in this case) of a block of 2 × 2 pixels is set as a parameter.
[0038]
Next, in step S62, the difference between the new average value of the 4 × 4 pixel block calculated in step S47 of FIG. 5 and the average value of the 2 × 2 pixel block is quantized. Next, in step S63, the quantized error is inversely quantized to calculate the error, the average value of the block of 2 × 2 pixels is corrected, and this is set as a new average value (new average value).
[0039]
Next, the new average value obtained in step S63 is compared with all the pixels in the 2 × 2 pixel block (step S64), and whether all the pixel values are within the threshold value for the 2 × 2 pixel block. It is determined whether or not it is (step S65). If all the pixel values are not within the threshold value for the block of 2 × 2 pixels, the difference between the new average value and the four pixels is quantized (step S66), and then the process proceeds to step S67. If the value is within the threshold value for the block of 2 × 2 pixels, the process directly proceeds to step S67.
[0040]
Steps S41 to S52 in FIG. 5 are performed on all the divided blocks of 8 × 8 pixels. Each average value changes from the value calculated in step S1 due to the quantization error of the 2 × 2 pixel, 4 × 4 pixel, and 8 × 8 pixel blocks. The set values of the threshold value and the quantization table number in each block are adjusted with reference to the generated code amount.
[0041]
When encoding an image, using the correlation between each pixel, the prediction value of the pixel is calculated from the neighboring pixels, and simply quantizing the error from the actual pixel value increases the compression ratio. However, according to the present embodiment, the correlation between a plurality of pixels is obtained in advance, and if it is determined that there is a correlation, the average of those pixel values is used as a representative value, and this processing is performed with a relatively large value. This is realized by dividing into blocks.
[0042]
That is, the degree of correlation between pixels in the largest block that can be encoded is obtained, and when it is determined that there is a correlation, the average of the pixel values of the block is used as a representative value, and there is no correlation. If it is determined, the block is divided and the degree of correlation between pixels in the divided block is determined.
[0043]
The block division is repeated until it is determined that there is a correlation, and if it is determined that there is no correlation even if the block is divided into the smallest block, that is, a block of 2 × 2 pixels, other than the average pixel value of the block, Next, the error (residual error) between the average value and each pixel is quantized.
[0044]
Note that the image decoding process on the receiving side of the image monitoring system is performed by performing an operation reverse to the flowchart of FIG.
[0045]
7 to 10 are flowcharts of the operation of another embodiment of the image encoding method according to the present invention.
First, in step S101, the number J of all blocks when the entire screen is divided into blocks of 8 × 8 pixels is set.
[0046]
Next, in step S102, an average value of each of the 8 × 8 pixel blocks is calculated, and in step S103, a so-called prediction error of the average value calculated in step S102 is obtained and quantized.
[0047]
Next, in step S104, a new prediction error is obtained by performing inverse quantization to correct the prediction error quantized in step S103, and the new prediction error obtained by calculating with the average value calculated in step S102. Calculate the average value (new average value).
[0048]
Next, in step S105, the maximum value (absolute value) of the error between the new average value and each pixel is detected and stored in the first error table (error table 1), and the first histogram (error table 1) is used. Register in histogram 1).
[0049]
Next, 1 is subtracted from the total block number J (step S106), and thereafter, it is determined whether or not the processing for all blocks, that is, the processing for the entire image (one screen) is completed (step S107). When the process is completed, the process proceeds to step S108, whereas when the process is not completed, the process returns to step S102.
[0050]
In step S108, based on the free space after the previous frame processing of the buffer memory (not shown) connected to the subsequent stage, the information bit amount of the average value data of the 8 × 8 pixel block, the histogram 1, and the like, the 8 × 8 pixel block Calculate the threshold.
[0051]
Next, the error table 1 is compared with the threshold calculated in step S108 (step S109), and it is determined whether or not the error is within the threshold (step S110). If the error is within the threshold value, the average value of the block of 8 × 8 pixels is set as the representative value, and the process skips to step S118 described later.
[0052]
If the error is not within the threshold value, 4 is set as the number k of blocks when the 8 × 8 pixel block is divided into 4 × 4 pixel blocks in step S111 for processing of 4 × 4 pixel blocks. I do.
[0053]
Next, in step S112, the average value of each of the 4 × 4 pixel blocks is calculated, and in step S113, the error between the new average value of the 8 × 8 pixel block calculated in step S104 and the average value calculated in step S112. And quantize.
[0054]
Next, in step S114, a new error is obtained by performing inverse quantization to correct the error quantized in step S113, and the new average value obtained by calculating with the average value calculated in step S112. (New average).
[0055]
Next, in step S115, the maximum value (absolute value) of the error between the new average value and each pixel is detected and stored in the second error table (error table 2), and the second histogram (error table 2) is used. Register in histogram 2).
[0056]
Next, 1 is subtracted from the number k of blocks (step S116), and thereafter, it is determined whether or not the processing on the block of 4 × 4 pixels has been completed (step S117). If the process has been completed, the process proceeds to step S118, whereas if not, the process returns to step S112.
[0057]
When the processing for the block of 4 × 4 pixels is completed, or when it is determined in step S110 that the threshold value is larger than the error, in step S118, it is determined whether the processing for all blocks is completed.
[0058]
In step S119, a threshold value for the block of 4 × 4 pixels is calculated from the free space of the buffer memory after the previous frame processing, the information bit amount of the average value data of the block of 4 × 4 pixels, the histogram 2, and the like.
[0059]
Next, the error table 2 is compared with the threshold calculated in step S119 (step S120), and it is determined whether or not the error is within the threshold (step S121). If the error is within the threshold, the average value of the block of 4 × 4 pixels is set as the representative value, and the process skips to step S129 described later.
[0060]
If the error is not within the threshold value, 4 is set as the number l of blocks when the 4 × 4 pixel block is divided into 2 × 2 pixel blocks in step S122 for processing of the 2 × 2 pixel block. I do.
[0061]
Next, in step S123, the average value of each of the 2 × 2 pixel blocks is calculated. In step S124, the error between the new average value of the 4 × 4 pixel block calculated in step S114 and the average value calculated in step S123. And quantize.
[0062]
Next, in step S125, a new error is obtained by performing inverse quantization to correct the error quantized in step S124, and the new average value obtained by calculating the error with the average value calculated in step S123. (New average).
[0063]
Next, in step S126, the maximum value (absolute value) of the error between the new average value and each pixel is detected and stored in the third error table (error table 3), and the third histogram (histogram) Register in 3).
[0064]
Next, 1 is subtracted from the number of blocks l (step S127), and thereafter, it is determined whether or not the processing for the block of 2 × 2 pixels has been completed (step S128). If the process has been completed, the process proceeds to step S129. If the process has not been completed, the process returns to step S123.
[0065]
When the processing for the block of 2 × 2 pixels is completed or when it is determined in step S121 that the threshold value is larger than the error, whether or not the processing for all the blocks of 4 × 4 pixels is completed in step S129 Is determined.
[0066]
In step S130, a threshold value for a 2 × 2 pixel block is calculated from the free space of the buffer memory after the previous frame processing, the information bit amount of the average value data of the 2 × 2 pixel block, the histogram 3, and the like.
[0067]
Next, the error table 3 is compared with the threshold calculated in step S130 (step S131), and it is determined whether or not the error is within the threshold (step S132). When the error is within the threshold value, the average value of the block of 2 × 2 pixels is set as the representative value, and the process skips to step S134 described later.
[0068]
If the error is not within the threshold value, the error between the new average value and each pixel is quantized (step S133), and thereafter, it is determined whether or not the processing has been completed for all the 2 × 2 pixel blocks (step S134). ). When the process is completed, the control routine is terminated. When the process is not completed, the process returns to step S131.
[0069]
Note that the image decoding process on the receiving side of the image monitoring system is performed by performing an operation reverse to the flowcharts of FIGS.
[0070]
FIG. 11 is a block diagram of an embodiment of an image encoding device according to the present invention. This image coding apparatus is applied, for example, to the transmission side of an image monitoring system, and includes an input unit 1, an 8 × 8 block input circuit 2a, a 4 × 4 block input circuit 2b, and a 2 × 2 block input circuit 2c. , Average value calculation circuits 3a, 3b, 3c, prediction error quantizers 4a, 4b, 4c, prediction error inverse quantizer and new average value calculation circuits 5a, 5b, 5c, error calculation circuits 6a, 6b, 6c, error comparison circuits 7a, 7b, 7c, a quantizer 8, a controller 9, and a switch 10.
[0071]
The operation of the present embodiment will be described. A digitized image signal from a surveillance camera (not shown) is input to the input unit 1, and the 8 × 8 block input circuit 2a divides the image into blocks of 8 × 8 pixels.
[0072]
The average value calculation circuit 3a calculates an average value of the pixel values in the divided blocks. Since the average value of 64 8 × 8 pixels can be obtained by addition and shift operations, the average value calculation circuit 3a can be configured with a simple circuit.
[0073]
The prediction error quantizer 4a obtains a so-called prediction error from the calculated average value and quantizes it. The number of data bits is reduced by the quantization by the prediction error quantizer.
[0074]
The prediction error inverse quantizer and the new average value calculation circuit 5a inversely quantizes the quantized error to obtain an error, and adds or subtracts the error to or from the average value calculated by the average value calculation circuit 3a to newly calculate the error. Calculate the average value.
[0075]
The error calculation circuit 6a calculates an error by comparing the new average value with all pixel values in the block, and the error comparison circuit 7a compares the error obtained by the error calculation circuit 6a with the threshold value. Do. If the error is within the threshold value, the controller 9 is controlled to output the output of the prediction error quantizer 4 a through the switch 10 using the average value of the block of 8 × 8 pixels as the representative value. On the other hand, when the error is outside the threshold, the block of 8 × 8 pixels is processed by the 4 × 4 block input circuit 2b and thereafter.
[0076]
The 4 × 4 block input circuit 2b further divides the block of 8 × 8 pixels into half, that is, the block of 4 × 4 pixels having 4 pixels in the horizontal direction and 4 pixels in the vertical direction.
[0077]
The average value calculation circuit 3b calculates an average value of pixel values in the divided blocks. Since the average value of 4 × 4 16 pixels can also be obtained by addition and shift operation, the average value calculation circuit 3b can also be constituted by a simple circuit.
[0078]
The prediction error quantizer 4b obtains a so-called prediction error from the calculated average value and quantizes it. The quantization by the prediction error quantizer 4b reduces the number of data bits (or quantizes the difference from the new average value of the new average value calculation circuit 5a).
[0079]
The prediction error inverse quantizer and the new average value calculation circuit 5b inversely quantize the quantized error to obtain an error, and add or subtract the error to or from the average value calculated by the average value calculation circuit 3b, and Calculate the average value.
[0080]
The error calculation circuit 6b calculates an error by comparing the new average value with all pixel values in the block, and the error comparison circuit 7b compares the error obtained by the error calculation circuit 6b with the threshold value. Do. When the error is within the threshold value, the controller 9 is controlled such that the average value of the block of 4 × 4 pixels is set as the representative value, and the output of the prediction error quantizer 4 b is output through the switch 10. On the other hand, if the error is outside the threshold, the block of 4 × 4 pixels is processed by the 2 × 2 block input circuit 2c and thereafter.
[0081]
The 2 × 2 block input circuit 2c further divides the block of 4 × 4 pixels into halves, that is, the block of 2 × 2 pixels having two pixels in the horizontal direction and two pixels in the vertical direction.
[0082]
The average value calculation circuit 3c calculates an average value of the pixel values in the divided blocks. Since the average value of 2 × 2 four pixels can also be obtained by addition and shift operation, the average value calculation circuit 3c can also be constituted by a simple circuit.
[0083]
The prediction error quantizer 4c obtains a so-called prediction error from the calculated average value and quantizes it. By the quantization by the prediction error quantizer 4c, the number of data bits is reduced (or the difference from the new average value of the new average value calculation circuit 5b is quantized).
[0084]
The prediction error inverse quantizer and the new average value calculation circuit 5c inversely quantize the quantized error to obtain an error, and add or subtract the error to or from the average value calculated by the average value calculation circuit 3c, Calculate the average value.
[0085]
The error calculation circuit 6c calculates an error by comparing the new average value with all pixel values in the block, and the error comparison circuit 7c compares the error obtained by the error calculation circuit 6c with the threshold value. Do. When the error is within the threshold value, the controller 9 is controlled to output the output of the prediction error quantizer 4c through the switch 10 using the average value of the block of 2 × 2 pixels as the representative value. On the other hand, if the error is outside the threshold, the quantizer 8 quantizes the error calculated by the error calculation circuit 6c.
[0086]
The signal output from the switch 10 is input on the receiving side to an image decoding device composed of elements similar to the elements shown in FIG. 11, and performs an operation opposite to the operation of the image encoding device shown in FIG. By doing so, it is decoded and output to, for example, a monitor.
[0087]
According to the above embodiment, a flat and small change portion such as a road or a wall in the image of the surveillance camera is processed by a block of 8 × 8 pixels, and a portion with a large change is 2 × 2 pixels. By performing the processing of the above blocks, a suitable image monitoring system can be configured.
[0088]
In the case where the number of flat images is relatively large, a high compression transmission system can be configured by performing processing of a block larger than a block of 8 × 8 pixels, for example, a block of 16 × 16 pixels.
[0089]
The present invention is not limited to the above embodiment, and many modifications and variations are possible.
For example, the image coding method and device according to the present invention can be used on the transmission side of any transmission system, and the corresponding image decoding method and device can be used on the reception side of the corresponding system. .
[0090]
In addition, the processing was performed in the order of the block of 8 × 8 pixels, the block of 4 × 4 pixels, and the block of 2 × 2 pixels. ⁿ × 2 ⁿ It can be applied to a block of pixels (n: natural number). For example, processing is performed in the order of a block of 16 × 16 pixels, a block of 8 × 8 pixels, a block of 4 × 4 pixels, and a block of 2 × 2 pixels. You can also.
[0091]
In the above embodiment, the process of quantizing the average value data of the 8 × 8 pixel block, the 4 × 4 pixel block, and the 2 × 2 pixel block and converting the data into variable-length bits is performed. By performing transmission using fixed-length bits without performing such operations, the amount of calculation can be reduced.
[0092]
Further, the case of the intra-frame processing has been described, but the inter-frame processing may be combined. That is, when processing a block of an arbitrary size, an inter-frame process can be easily added by inserting a process for comparing with a previous frame.
[Brief description of the drawings]
FIG. 1 is a flowchart of an embodiment of an image encoding method according to the present invention.
FIG. 2 is a flowchart of a part of a subroutine of step S1 in FIG.
FIG. 3 is a flowchart of a part of a subroutine of step S1 in FIG. 1;
FIG. 4 is a diagram illustrating a relationship between an average value, an absolute value of a difference between pixels, and the number of blocks.
FIG. 5 is a flowchart of a subroutine of step S3 in FIG. 1;
FIG. 6 is a flowchart of a subroutine of step S50 in FIG.
FIG. 7 is a part of a flowchart of an operation of another embodiment of the image encoding method according to the present invention.
FIG. 8 is a part of a flowchart of an operation of another embodiment of the image encoding method according to the present invention.
FIG. 9 is a part of a flowchart of an operation of another embodiment of the image encoding method according to the present invention.
FIG. 10 is a part of a flowchart of an operation of another embodiment of the image encoding method according to the present invention.
FIG. 11 is a block diagram of an embodiment of an image encoding device according to the present invention.
[Explanation of symbols]
1 Input section
2a 8 × 8 block input circuit
2b 4 × 4 block input circuit
2c 2 × 2 block input circuit
3a, 3b, 3c Average value calculation circuit
4a, 4b, 4c prediction error quantizer
5a, 5b, 5c prediction error inverse quantizer and new average value calculation circuit
6a, 6b, 6c Error calculation circuit
7a, 7b, 7c error comparison circuit
8 Quantizer
9 Controller
10 Switch

Claims (3)

An image encoding method for encoding and transmitting an image signal, comprising:
The entire screen is divided into predetermined pixel units,
Calculating the average of the pixel values in the block,
Calculating the error between the pixel value and the average value,
Based on whether these errors are within a predetermined value, determine whether to encode the block or to further divide the block,
An image encoding method, comprising: performing an encoding process on an appropriate pixel-unit block according to a result of the determination. 2. A histogram in which a maximum value of an absolute value of a difference between an average value of the block and a pixel value in the block is obtained for each block, and the predetermined value is calculated from the histogram. Image coding method as described in the above. An image encoding device for encoding and transmitting an image signal,
Block dividing means for dividing the entire screen into blocks of a predetermined pixel unit,
Average value calculation means for calculating an average value of pixel values in the block,
Error calculating means for calculating an error between the pixel value and the average value,
A determination unit configured to determine whether to encode the block or to further divide the block, based on whether these errors are within a predetermined value;
An image encoding device comprising: an encoding unit that performs an encoding process on a block in an appropriate pixel unit according to a result of the determination.

Images