JP4779977B2 - Image encoding / decoding device - Google Patents

Description

  The present invention relates to an image encoding / decoding device.

  As background art in this field, for example, there is JP-A-8-195680. In this publication, [[Purpose] Enables decoding of arithmetic codes at high speed. [Configuration] Change processing procedure to reduce the number of register updates. Increase code register stuffing bit width, code input The loop associated with is completely eliminated, the data is prefetched, two contexts depending on the preceding undetermined pixels are prepared and processed, and one is selected when the preceding pixel is determined, Is reduced to reduce the waiting time until the preceding pixel is determined "(see summary).

  Further, as background art in this field, for example, there is JP-A-8-46520. In this publication, “[Purpose] Reduces the processing time required to encode or decode an arithmetic code. [Configuration] When encoding or decoding an arithmetic code, the audend register AR and the code code register CR are used. In addition, the present invention has been found to be able to execute such processing during encoding or decoding processing in parallel. Parallel processing related to the register is performed, parallel processing related to the code code register is performed in the shift calculation unit 34A, and parallel processing related to the loop counter is performed in the count calculation unit 36A. A value is selected, and based on this value, the shift calculation units 32A and 34A and the count calculation unit 36A calculate By selecting the fruit, it has been described to. "Eliminating loop process as described above (see Abstract).

JP-A-8-195680 JP-A-8-46520

  An entropy code is used in an image encoding / decoding device, and one of the entropy codes is an arithmetic code (CABAC). In the arithmetic code, as shown in FIG. 9, there exists a feedback loop in which the decoding result up to immediately before affects the subsequent decoding processing. In FIG. 9, 1491 is a Bin decoder unit that performs arithmetic decoding processing to obtain a 1-bit value “Bin”, 1492 is a numerical value restoration unit that obtains a set of numerical values from a plurality of Bin columns, and 1493 is a Bin unit It is a Context calculation unit that calculates a parameter “Context value” used for the decoding process in the decoder unit. Since processing in this loop, particularly Context calculation, takes a certain amount of time, it is difficult to speed up the overall processing to some extent.

  Therefore, in the present invention, as an example, two systems of Context calculation units are provided, and the calculation is started in advance in preparation for the case where the previous calculation result is 0 and 1 (for binary processing, the previous calculation result “Bin "Is either 0 or 1), and the correct one is selected when the previous result is obtained.

  According to the present invention, as an example, it is possible to reduce the delay time of the loop as much as possible and to achieve high speed.

  Problems, configurations, and effects other than those described above will be described in the following embodiments.

  Hereinafter, embodiments will be described with reference to the drawings.

  FIG. 1 shows a block diagram of an image encoding / decoding device 1 which is an embodiment of the present invention. First, the operation during encoding will be described. A moving image is input from the image input terminal and received by the video I / F unit 12. The received moving image is temporarily stored in a buffer area provided in the SDRAM 2 via the SDRAM I / F unit 17. After a predetermined delay time, the moving image data is read from the buffer area in the SDRAM 2 and sent to the encoder unit 13. Encoder unit 13 performs an encoding process. The encoded data (elementary stream) after the encoding process is sent to the Mux / Demux unit 15. The System Mux / Demux unit 15 performs system stream processing such as header code, time stamp addition, and packetization. The encoded data that has been converted into the system stream is output as an encoded image to an external device via the Device I / F unit 16.

  Next, the operation at the time of decoding will be described. First, encoded image data is input to the Device I / F unit 16 from an external device. The encoded image data received by the Device I / F unit 16 is input to the System Mux / Demux unit 15. The System Mux / Demux unit 15 removes a header code from the input encoded image data and extracts an elementary stream. The extracted elementary stream is sent to the decoder unit 14. In the decoder unit 14, the elementary stream is decoded. The moving image data that has been decrypted is sent to the Video I / F unit 12. The moving image data sent to the Video I / F unit 12 is stored in a buffer area provided in the SDRAM 2 through a decoding process. After a predetermined delay time, the moving image data is read from the buffer area in the SDRAM 2 and output from the Video I / F unit 12 to the outside of the apparatus 1 as an image output.

  Further, as shown in FIG. 4, transcoding can be performed by using the Decoder unit 14 and the Encoder unit 13. In this case, encoded image data is input to the Decoder unit 14, decoded as described above, and moving image data is output. The moving image data is input to the Encoder unit 13, encoded as described above, and encoded image data is output. At this time, as shown in FIG. 4, by exchanging information regarding encoding between the processor of the decoder unit 14 and the processor of the encoder unit 13, the encoder unit 13 can perform more efficient encoding.

  FIG. 2 shows a block diagram of the encoder unit 13. It consists of a main processor 131 and a sub processor 132, and processing blocks 133 to 1310 controlled by these processors. The input image is input to the in-screen prediction unit 133 and the motion search unit 134. The intra-screen prediction unit 133 creates a predicted image of the partial image currently being processed from the already encoded portion in the screen. In addition, the motion search unit 134 searches for an image closer to the partial image currently being processed from other previously encoded images, and creates a predicted image. The more advantageous one of the predicted images output from the in-screen prediction unit 133 or the motion search unit 134 is selected. This selection decision is made with the main processor 131 involved. One block finally selected obtains the difference between the predicted image and the current image. The prediction error as a result is output to the DCT / quantization processing unit 135. The finally selected block outputs a prediction image to the motion compensation unit 137.

  The DCT / quantization processing unit 135 performs discrete cosine transform or a predetermined frequency transform process equivalent to the input prediction error. Subsequently, a quantization process using a quantization coefficient is performed. The processed result is output to the entropy encoding unit 139.

  The entropy encoding unit 139 performs a predetermined entropy encoding process based on an instruction from the sub processor 132. The processing result is output via the buffer unit 1310.

  The output of the DCT / quantization processing unit 135 is input to the inverse quantization / IDCT processing unit 136. The inverse quantization / IDCT processing unit 136 performs inverse quantization processing and inverse discrete cosine transform (or predetermined equivalent processing), obtains a prediction error, and outputs the result to the compensation unit 137.

  The motion compensation unit 137 adds the input prediction error and the predicted image to create a restored image. The restored image is output to the deblocking unit 138.

  The restored image input to the deblocking unit 138 is subjected to block boundary filtering. The local decoded image as a result is used in the motion search unit 134 in the future as a motion search image.

  The processing of the motion search unit 134 will be described with reference to FIG. Image 3 is an image that has been encoded in the past, and image 4 is an image that is currently being encoded. The macro block 41 is a partial image currently being encoded, and the macro block 31 is a macro block corresponding to the same position as the macro block 41 in the image 3. A region 32 having a width H and a height V around the macroblock 31 is taken as a motion search range.

  FIG. 6 shows the motion search range 32. The motion search unit 134 performs processing for finding a portion closest to the macroblock 41 within the motion search range 32. Here, if the ranges H and V can be made as large as possible, the possibility that similar images can be found in a wider range becomes higher. However, if H and V are unnecessarily large, the time required for the search increases in proportion thereto, and the processing time increases. Therefore, the following measures are taken.

That is, an image is prepared by thinning out pixels of the search range 32 and the macroblock 41 in units of 2 pixels in the horizontal direction. In this way, the number of pixels to be processed is H / 2 in the horizontal direction, and the processing time can be halved. Alternatively, if an image obtained by thinning out the pixels of the search range 32 and the macroblock 41 in units of 4 pixels in the horizontal direction is prepared, the processing time is similarly reduced to a quarter.
Alternatively, if the processing time is the same, it is possible to search a search range of 2 times or 4 times, respectively, and the image quality is improved. In particular, when encoding a high-definition television signal having a large number of pixels, it is necessary to ensure a wide search range. Therefore, a wide search range can be secured by selecting a unit of four pixels. In the case of a conventional television signal, it is possible to use thinning-out in units of two pixels by prioritizing a fine search over a wide search range.

As described above, according to the present invention, it is possible to adaptively select the search range decimation rate and the size of the search range in accordance with the image size.
In this manner, the motion search unit 134 searches for the closest search to the current image macroblock 41 in the motion search range 32.

  FIG. 7 is a diagram for explaining the continued operation of the motion search unit 134. The pixel position found above is further searched in a range of horizontal ± 2 pixels and vertical ± 2 pixels. A region A of 8 × 8 pixels in FIG. 7 is searched using a PE (processor element) group A capable of simultaneously performing a search for a total of 25 pixels including the central pixel. Similarly, the search is executed in parallel on PE-B, C, and D for adjacent B × 8 and D × 8 pixel regions B, C, and D.

  In this way, the nearest image is searched for each of the areas PE-A to D, and as a result, the respective position offsets, that is, motion vectors are obtained.

  Further, the motion search unit 134 searches the horizontal and vertical regions of ± 0.5 in the vicinity of the motion vector in increments of 0.25 pixels. The above-described PE-A to D are used again for this search.

  Next, the decoder unit 14 will be described with reference to FIG. It comprises a main processor 141 and sub-processor 142, and processing blocks 143 and 146 to 1410 controlled by these processors.

  The input elementary stream is buffered by the buffer unit 1410 and then input to the entropy decoding unit 149. As shown in FIG. 8, the entropy decoding unit 149 performs a predetermined entropy decoding process based on an instruction from the sub processor 142. The macroblock layer parameters and data, which are the processing results, are input to the inverse quantization / IDCT unit 146. Further, the upper layer such as a sequence or a picture header is analyzed by the sub processor 142 and output as upper layer information.

The inverse quantization / IDCT processing unit 146 performs inverse quantization processing and inverse discrete cosine transform (or predetermined equivalent processing), restores a prediction error, and outputs the result to the compensation unit 147.
The motion compensation unit 147 adds the input prediction error and the prediction image to create a restored image. Note that, as the predicted image here, either motion compensation or an intra-screen predicted image is used depending on the content of the code. In the case of the intra prediction image, the prediction image created by the intra prediction unit 143 is used. The restored image created by the motion compensation unit 147 is output to the deblocking unit 148.

  The restored image input to the deblocking unit 148 is subjected to block boundary filtering and output as an output image.

  Among the entropy codes that can be handled by the entropy decoding unit 149, arithmetic code decoding processing will be described with reference to FIG. In the figure, 1491 is a Bin decoder unit that performs arithmetic decoding processing to obtain a 1-bit value “Bin”, 1492 is a numerical value restoration unit that obtains a set of numerical values from a plurality of Bin columns, and 1493 is a Bin decoder unit It is a Context calculation part which calculates the parameter "Context value" used for the decoding process in.

  FIG. 10 illustrates the Context calculation unit 1494 of the present invention in more detail. A Context # 0 calculation unit 14941 and a Context # 1 calculation unit 14942 are incorporated therein. The Context # 0 calculation unit 14941 starts the Context calculation assuming that the result Bn-1 as the previous decoding result is 0 before the Bin value Bn-1 is finalized. Similarly, the Context # 1 calculation unit 14942 starts the Context calculation assuming that the result Bn-1 of the immediately preceding decoding result Bin is 1 before the value Bn-1 is determined. These results are input to the Bin decoder unit 1491 together as Context [0] and [1]. As soon as the previous decoding result Bn-1 is determined, the Bin decoder unit 1491 selects an appropriate one of the input Context [0] or [1] based on the value, and performs the next decoding. Use.

  As described above, according to the arithmetic decoding process of the present invention, since the Context operation can be started before the immediately preceding Bin decode value is determined, the processing time of the feedback loop inside the arithmetic decoding process can be shortened. It is possible to significantly increase the processing speed of the arithmetic decoding process.

1 is a block diagram of an image encoding / decoding device 1 according to an embodiment of the present invention. The block diagram of the Encoder part 13 is shown. The block diagram of the Decoder part 14 is shown. It is a figure which shows the Example in the case of transcoding. It is a figure explaining the process of the motion search part. A motion search range 32 is shown. FIG. 6 is a diagram for explaining the operation of a motion search unit 134. It is a figure explaining the entropy decoding part 149. FIG. It is a figure explaining the decoding process of an arithmetic code. It is a figure explaining the Context calculation part 1494. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Image encoding / decoding apparatus 2 ... SDRAM
12. ・ Video I / F
13 · Encoder unit 14 · Decoder unit 15 · System Mux / Demux unit 16 · Device I / F
17. · SDRAM I / F

Claims (1)

An image encoding / decoding device using an arithmetic code,
An input unit to which encoded image data is input;
A Bin decoder unit that performs arithmetic encoding processing on the input encoded image data to obtain Bin that is a value of 1 or 0;
A numerical value restoration unit for obtaining a numerical value from a plurality of Bin columns;
A context calculator that calculates a context value that is a parameter used for the decoding process in the Bin decoder;
With
The context calculation unit includes a first context calculation unit that calculates a context value when Bin is 1, and a second context calculation unit that calculates a context value when Bin is 0, and the Bin decoder Before the part calculates Bin, calculate the context value when Bin is 1 and the context value when Bin is 0,
When the Bin decoder section obtains Bin, the context value used for the next arithmetic coding process is output from the context calculation section when the Bin is 1 and the context value when Bin is 0. To choose the appropriate one,
An image encoding / decoding device characterized by the above.

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