JP2008263549A - Moving picture coding apparatus and moving picture coding method - Google Patents

Abstract

A moving image encoding apparatus capable of reducing a processing amount required for prediction mode determination while suppressing deterioration in image quality is realized.
All prediction modes are evaluated for the first macroblock MB1. Then, the prediction mode with the lowest cost is determined as the prediction mode for MB1. For the mode determination of the macro block MB2, the mode determination result of the MB1 immediately before is used. In this case, the prediction mode determined for MB1 is selected as the initial prediction mode, and the cost when MB2 is encoded in the initial prediction mode is calculated first. When the calculated cost is equal to or less than the cost of MB1, the initial prediction mode is the prediction mode of MB2, and evaluation for other prediction modes is omitted. For the mode determination of the macroblock MB3, the mode determination result of the immediately preceding MB2 is used.
[Selection] Figure 3

Description

  The present invention relates to a moving image encoding apparatus and a moving image encoding method for encoding a moving image signal selectively using a plurality of prediction modes.

  In recent years, personal computers equipped with software encoders that encode moving images by software have begun to spread. Recently, as a next-generation video compression encoding technology, H.264 has been introduced. The H.264 / AVC (Advanced Video Coding) standard is drawing attention. This H. The H.264 / AVC standard is a compression encoding technique that is more efficient than conventional compression encoding techniques such as MPEG2 and MPEG4.

  H. In the H.264 / AVC standard inter-frame prediction encoding, a plurality of prediction modes having different prediction block shapes such as 16 pixels × 16 pixels, 16 pixels × 8 pixels, 8 pixels × 16 pixels, and 8 pixels × 8 pixels should be used. In addition, when the predicted block shape is 8 pixels × 8 pixels or more, the orthogonal transform can selectively use the block shape of 4 pixels × 4 pixels and 8 pixels × 8 pixels. H. In intra-frame coding according to the H.264 / AVC standard, nine prediction directions can be selected for prediction block shapes such as 4 pixels × 4 pixels and 8 pixels × 8 pixels, and 16 pixels × 16 pixels can be selected. Four prediction directions can be selected for the prediction block shape.

  In this way, H.C. In the H.264 / AVC standard, the prediction efficiency is improved by increasing the number of available prediction modes.

  However, on the other hand, H.C. In the encoding process corresponding to the H.264 / AVC standard, a larger amount of processing is required than in the conventional compression encoding technique such as MPEG2 or MPEG4. In particular, a large amount of processing is required for a prediction mode determination process for determining an optimal prediction mode from a plurality of prediction modes for each image block.

  For these reasons, there have been proposals for reducing the amount of moving image encoding processing.

For example, Patent Document 1 specifies a selectable prediction mode candidate from a plurality of prediction modes for intra-frame coding using frequency information and weighting factors of prediction modes of encoded neighboring blocks. A technique for limiting to the prediction mode is disclosed.
JP 2006-148419 A

  However, as mentioned above, H.P. In the H.264 / AVC standard, there are a plurality of prediction modes for inter-frame coding as well as prediction modes for intra-frame coding. For this reason, H.C. In order to reduce the amount of encoding processing according to the H.264 / AVC standard, a plurality of prediction modes including a prediction mode group for interframe prediction encoding and a prediction mode group for intraframe prediction encoding are selected. It is necessary to be able to efficiently determine one prediction mode to be applied.

  The present invention has been made in view of such circumstances, and provides a moving picture coding apparatus and a moving picture coding method capable of reducing the amount of processing required for prediction mode determination while suppressing deterioration in image quality. The purpose is to do.

  In order to solve the above-described problem, the present invention divides a moving image signal into a plurality of image blocks, and for each image block, a prediction mode group for inter-frame prediction encoding and prediction for intra-frame prediction encoding. A moving picture encoding apparatus that selects one prediction mode from a plurality of prediction modes including a mode group and encodes the image block in the selected prediction mode, the first image to be encoded First prediction mode determination processing for calculating a coding cost when a block is coded in each of the plurality of prediction modes, and determining a prediction mode with the smallest coding cost as the prediction mode of the first image block And a coding cost of the leading image block corresponding to the prediction mode determined by the first prediction mode determination unit. When it is equal to or less than a predetermined reference value, a prediction mode for encoding the image block to be encoded is set for each image block to be encoded subsequent to the head image block. Second prediction mode determination means for executing a second prediction mode determination process that is determined based on the prediction mode determination result for the immediately preceding image block, wherein the second prediction mode determination means includes the encoding When the prediction mode determined for the image block immediately before the target image block is set as the initial prediction mode of the encoding target image block, and the encoding target image block is encoded in the initial prediction mode Means for calculating the encoding cost of the image block, and the encoding cost of the calculated image block to be encoded is the code of the immediately preceding image block. Means for determining the initial prediction mode as a prediction mode for encoding the image block to be encoded, and the calculated encoding cost of the image block to be encoded is the immediately preceding When the coding cost of the image block is larger than the coding cost, the coding cost is calculated when the coding target image block is coded in a prediction mode other than the initial prediction mode, and the coding cost is minimized. Means for determining a prediction mode as a prediction mode of the image block to be encoded.

  According to the present invention, it is possible to reduce the amount of processing required for prediction mode determination while suppressing deterioration in image quality.

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

  FIG. 1 shows a configuration example of a video encoding apparatus according to an embodiment of the present invention. This moving image encoding apparatus is realized by a computer such as a personal computer, for example.

  As shown in FIG. 1, this computer includes a CPU 11, a north bridge 12, a main memory 13, a graphics controller 14, a VRAM 14A, an LCD 15, a south bridge 16, a BIOS-ROM 17, an HDD 18, an HD DVD 19, a sound controller 20, a speaker 21, An embedded controller / keyboard controller IC (EC / KBC) 22, a keyboard 23, a touch pad 24, a power supply circuit 25, a battery 26, a network controller 27, and the like are provided.

  The CPU 11 is a processor that controls the operation of each unit in the computer. The CPU 11 executes an operating system (OS) 100 loaded from the HDD 18 to the main memory 13 and various application programs including utilities that operate under the control of the OS 100. In these various application programs, a video encoder application 200 is included. The video encoder application 200 is software for encoding moving images. It operates as a software encoder corresponding to the H.264 / AVC standard. The CPU 11 also executes the BIOS stored in the BIOS-ROM 17.

  The north bridge 12 is a bridge device that connects the local bus of the CPU 11 and the south bridge 16. The north bridge 12 has a function of executing communication with the graphics controller 14 via a bus, and also includes a memory controller that controls access to the main memory 13. The graphics controller 14 is a display controller that controls the LCD 15 used as a display monitor of the computer. The graphics controller 14 generates a display signal to be sent to the LCD 15 from the image data written in the VRAM 14A.

  The south bridge 16 is a controller that controls various devices on the PCI bus and the LPC bus. The south bridge 16 is directly connected to the BIOS-ROM 17, the HDD 18, the HD DVD 19, and the sound controller 20, and has a function of controlling them. The sound controller 20 is a sound source controller that controls the speaker 21.

  The EC / KBC 22 is a one-chip microcomputer in which an embedded controller for power management and a keyboard controller for controlling the keyboard 23 and the touch pad 24 are integrated. The EC / KBC 22 cooperates with the power supply circuit 25 to control supply of power from the battery 26 or the external AC power supply to each unit. The network controller 27 is a communication device that executes communication with an external network such as the Internet.

  Next, the functional configuration of the software encoder realized by the video encoder application 200 operating on the computer having such a hardware configuration will be described with reference to FIG.

  The encoding process by the video encoder application 200 is H.264. As shown in the figure, the video encoder application 200 includes an input unit 201, a DCT / quantization unit 202, an entropy coding unit 203, an inverse quantization / inverse DCT unit 204, an intra-frame (Intra) prediction unit 205, deblocking filter 206, frame memory 207, motion detection unit 208, inter-frame (inter) prediction unit 209, encoding control unit 210, switch 212, subtraction unit 213, addition unit 214, prediction mode determination Unit 301, rate control unit 302, and the like.

  The video encoder application 200 divides each screen (picture) of the moving image signal input from the input unit 201 into a plurality of image blocks such as a macro block of 16 × 16 pixels, for example. Run in units. The prediction mode determination unit 301 controls the DCT / quantization unit 202, the inverse quantization / inverse DCT unit 204, the intra-frame (intra) prediction unit 205, the motion detection unit 208, the inter-frame (inter) prediction unit 209, and the like. For each image block such as a macroblock, a prediction mode group for intra-frame prediction coding (intra prediction coding) and a prediction mode group for motion compensation inter-frame prediction coding (inter prediction coding) One prediction mode is determined from a plurality of prediction modes including. Each macroblock is encoded in the prediction mode determined by the prediction mode determination unit 301 (intra prediction encoding or inter prediction encoding).

  FIG. 3 shows functional blocks of the prediction mode determination unit 301.

  As illustrated in FIG. 3, the prediction mode determination unit 301 includes a first prediction mode determination unit 401 and a second prediction mode determination unit 402. The first prediction mode determination unit 401 performs normal prediction mode determination processing, and calculates each encoding cost when an image block (macroblock) to be encoded is encoded in each of a plurality of prediction modes. Then, a first prediction mode determination process is executed in which the prediction mode that minimizes the encoding cost is determined as the prediction mode for encoding the encoding target image block.

  Here, the encoding cost is a value indicating the encoding efficiency. For example, the total of the generated code amount (for example, the amount of encoded coefficient data including the motion vector amount and the amount of difference data between the predicted image and the original image) Value, etc.).

  Normally, the first prediction mode determination process by the first prediction mode determination unit 401 is executed for each of all macroblocks. In this embodiment, in order to reduce the processing amount of the prediction mode determination process. The first prediction mode determination process performed by the first prediction mode determination unit 401 is executed at least for the first macroblock of the current picture, but the prediction mode determined by the first prediction mode determination process. When the coding cost of the first macroblock corresponding to is less than or equal to a predetermined reference value, the prediction mode determination process by the second prediction mode determination unit 402 is used from the next macroblock.

  The second prediction mode determination unit 402 performs, for each encoding target macroblock subsequent to the macroblock for which the prediction mode has already been determined, the prediction mode determination result of the macroblock immediately before the encoding target macroblock ( Second prediction mode determination of determining a prediction mode for encoding the macroblock to be encoded based on the determined prediction mode and the encoding cost of the immediately preceding macroblock corresponding to the prediction mode) Execute the process.

  That is, the second prediction mode determination unit 402 first sets the prediction mode of the immediately preceding macroblock for which the prediction mode has been determined as the initial prediction mode for the next encoding target macroblock, and performs the encoding target in the initial prediction mode. The encoding cost when the macroblock is encoded is calculated. Then, the second prediction mode determination unit 402 calculates the encoding cost of the calculated macroblock to be encoded and the encoding cost of the immediately preceding macroblock (the prediction mode determined for the immediately preceding macroblock in the immediately preceding prediction mode). And the encoding cost when the macroblock is encoded).

  If the calculated encoding cost of the encoding target macroblock is equal to or less than the encoding cost of the immediately preceding macroblock, the second prediction mode determination unit 402 sets the initial prediction mode to the encoding target macroblock. Is determined as a prediction mode for encoding, and the encoding cost calculation process for each of the remaining prediction modes is omitted. On the other hand, if the encoding cost of the calculated macroblock to be encoded is higher than the encoding cost of the immediately preceding macroblock, the second prediction mode determination unit 402 uses the remaining prediction modes other than the initial prediction mode. The encoding cost when each encoding target macroblock is encoded is calculated, and the prediction mode that minimizes the encoding cost is determined as the prediction mode for encoding the encoding target macroblock.

  Many of the macroblocks that are consecutive in the coding order have a strong spatial correlation. Therefore, the prediction mode determination process is required by using the prediction mode determination result of the immediately preceding macroblock for the prediction mode determination of the next macroblock. The amount of processing can be reduced efficiently. Assume that four macroblocks MB1 to MB4 are sequentially encoded as shown in FIG. The macroblock MB1 is the first macroblock in a certain picture, and the macroblocks MB2 to MB4 are macroblock groups that follow the macroblock MB1 in the coding order. The first prediction mode determination process is applied to the macroblock MB1, and each prediction mode is evaluated. Then, the prediction mode with the lowest coding cost is determined as the prediction mode for the macroblock MB1.

  The second mode determination process is applied to the mode determination of the macroblock MB2, and the mode determination result of the macroblock MB1 immediately before the macroblock MB2 is used. The application of the second mode determination process to the macroblock MB2 is performed on the condition that the encoding cost of the leading macroblock MB1 is equal to or lower than a predetermined reference value, and the encoding cost of the leading macroblock MB1 is the reference value. Is larger than the first mode determination process, the first mode determination process is continuously applied to the mode determination of the macroblock MB2.

  As a result, it becomes possible to start application of the second mode determination process from the macroblock next to the macroblock having a good prediction mode result determined by the first mode determination process, and the previous mode determination result is obtained. It is possible to execute the utilized second mode determination process with high accuracy.

  When the coding cost of the first macroblock MB1 is equal to or lower than a predetermined reference value, first, the prediction mode determined for the macroblock MB1 is selected as the initial prediction mode of the macroblock MB2, and the initial prediction mode is The encoding cost when the macroblock MB2 is encoded is first calculated. When the calculated encoding cost of the macroblock MB2 is equal to or less than the encoding cost of the macroblock MB1, the initial prediction mode is determined as the prediction mode of the macroblock MB2 at that time, and other prediction modes other than the initial prediction mode Evaluation of is omitted. On the other hand, when the calculated encoding cost of the macroblock MB2 is larger than the encoding cost of the macroblock MB1, the encoding cost when the macroblock MB2 is encoded in the remaining prediction modes other than the initial prediction mode, respectively. Are calculated, and the prediction mode that minimizes the coding cost is determined as the coding mode of the macroblock MB2.

  The second mode determination process is also applied to the mode determination of the macroblock MB3, and the mode determination result of the immediately preceding macroblock MB2 is used. In this case, the prediction mode determined for the macroblock MB2 is selected as the initial prediction mode, and the encoding cost when the macroblock MB3 is encoded in the initial prediction mode is calculated first. When the calculated encoding cost of the macroblock MB3 is equal to or less than the encoding cost of the macroblock MB2, the initial prediction mode becomes the encoding mode of the macroblock MB3. When the calculated encoding cost of the macroblock MB3 is larger than the encoding cost of the macroblock MB2, the encoding costs when the macroblock MB3 is encoded in each of the remaining prediction modes other than the initial prediction mode are respectively The prediction mode that is evaluated and minimizes the coding cost is the coding mode of the macroblock MB3.

  Similarly, the second mode determination process is applied to the mode determination of the macroblock MB4, and the mode determination of the macroblock MB4 is executed using the mode determination result of the macroblock MB3.

  As described above, in the present embodiment, the previous macroblock is recorded on the condition that the encoding cost when the encoding target macroblock is encoded in the initial prediction mode is equal to or less than the encoding cost of the immediately preceding macroblock. The prediction mode determined for the next macroblock is determined as the prediction mode, and evaluation for each of the remaining other prediction modes is terminated. The remaining prediction modes may include a prediction mode that has a lower coding cost than the initial prediction mode, but by adopting the above-mentioned truncation conditions, simply selectable prediction modes. Compared with the case where the number is limited, it is possible to reduce the processing amount required for the prediction mode determination process while preventing the image quality from being deteriorated.

  H. In the high profile of the H.264 / AVC standard, in the inter prediction, when the block size of the prediction mode is 8 pixels × 8 pixels or more, a DCT having a block size of 4 × 4 pixels and a DCT having a block size of 8 × 8 pixels are used. The most suitable one can be selected. Accordingly, if m types of prediction modes exist and n types of DCTs can be selected in a certain standard, m × n prediction mode candidates substantially exist only by inter prediction. Become. In such a situation, if all the prediction mode candidates are evaluated and the optimum prediction mode candidate is selected without any ingenuity, the processing amount required for the prediction mode determination of the inter prediction becomes enormous. End up. Therefore, the prediction mode determination process of this embodiment is extremely effective. Also, in intra prediction, there are nine prediction modes (prediction directions) for each prediction block shape of 4 pixels × 4 pixels and 8 pixels × 8 pixels, and there are 4 prediction modes for 16 pixels × 16 pixels. Since there are street prediction modes (prediction directions), the number of prediction modes for intra prediction is extremely large.

  In the present embodiment, since the prediction mode can be determined by a determination process at least once, the processing amount of the prediction mode determination process can be greatly reduced.

  In the software encoder whose functional configuration is shown in FIG. 2, the intra prediction unit 205 performs prediction processing corresponding to each of a plurality of prediction modes for intra coding under the control of the prediction mode determination processing unit 301. Run selectively. In the intra prediction encoding mode, the prediction mode determination processing unit 301 uses the switch 212 to select the intra prediction unit 205. The intra prediction unit 205 generates a prediction signal of the encoding target block from several encoded blocks in the encoding target screen (picture) according to the prediction mode determined by the prediction mode determination processing unit 301. The subtraction unit 213 obtains a prediction error signal obtained by subtracting this prediction signal from the encoding target screen (picture). This prediction error signal is orthogonally transformed and quantized by the DCT / quantization unit 202. The quantized orthogonal transform coefficient is entropy encoded by the entropy encoding unit 203 together with intra prediction mode information and the like.

  On the other hand, in the inter prediction encoding mode, first, the motion detection unit 208 estimates the motion from the already encoded screen (picture) stored in the frame memory 207, and then the inter prediction unit 209 Then, a motion compensated inter-frame prediction signal corresponding to the encoding target screen is generated in a predetermined shape unit. Then, the DCT / quantization unit 202 performs orthogonal transform (DCT) and quantization on the prediction error signal obtained by subtracting the motion compensation inter-frame prediction signal from the encoding target screen (picture), and the entropy encoding unit 203 performs inter prediction. Encoding is performed by performing entropy encoding on the mode information and the quantized orthogonal transform coefficient.

  The inverse quantization / inverse DCT unit 204 performs inverse quantization and inverse orthogonal transform on the quantization coefficient of the orthogonally transformed and quantized image (picture), and the deblocking filter 206 reduces block noise. The deblocking filter process for performing is performed.

  The rate control unit 302 sets a quantization parameter and the like in order to adjust the rate (generated code amount) of the encoded stream output from the entropy encoding unit 203.

  FIG. 5 shows the encoding order of macroblocks in a picture.

  A picture is divided into a plurality of macroblocks and encoded in the order shown in FIG. 5A or the order shown in FIG. When encoding each macroblock, prediction mode determination is first performed.

  FIG. 6 shows the state of the prediction mode determination process when encoding is performed in the order shown in FIG.

  First, the prediction mode of the first macroblock MB1 is determined. In this case, the encoding cost when the macroblock MB1 is encoded in all prediction modes is calculated, and the prediction mode that minimizes the encoding cost is determined as the prediction mode of the macroblock MB1. Next, the prediction mode of the macroblock MB2 is determined. In the case of adjacent macroblocks, since the spatial correlation is large, the probability that the same prediction mode is selected is high. Therefore, when determining the prediction mode of the macroblock MB2, the prediction mode determination result of the immediately preceding macroblock MB1 is used.

  In the present embodiment, the first prediction mode determination process for evaluating all prediction modes is not performed only on the first macroblock, but the encoding cost corresponding to the determined prediction mode is predetermined. The first prediction mode determination process is executed in order from the first macroblock to be encoded until a macroblock having a reference value (mode determination threshold) or less is detected. By providing such a mode determination threshold, as described above, the second mode using the mode determination result of the immediately preceding macroblock only when the determined prediction mode result is good, that is, when the coding cost is low. Mode determination processing (simple mode determination processing) can be executed, and image quality deterioration can be suppressed.

  Furthermore, even when the simple mode determination process is started, the mode determination threshold is used, and when the minimum encoding cost calculated for a certain macroblock by the simple mode determination process is larger than the mode determination threshold, The mode determination method may be switched to the first prediction mode determination process again from the next macroblock.

  In this case, the prediction mode determination unit 301 determines whether or not the coding cost of the image block is larger than the mode determination threshold for each macroblock for which the prediction mode is determined by the simple mode determination process. Until the macroblock whose coding cost corresponding to the prediction mode determined in the first prediction mode determination process is equal to or less than the mode determination threshold is detected, the encoding cost is higher than the mode determination threshold by the simple mode determination process. The first prediction mode determination process is executed in order from the macro block to be encoded immediately after the macro block determined to be a macro block.

  Next, with reference to FIG. 7, an example of a specific procedure of the prediction mode determination process of the present embodiment executed for each picture will be described.

  First, the prediction mode determination unit 301 sets the above-described mode determination threshold value EXE_thr (step S11). The value of the mode determination threshold EXE_thr is determined according to, for example, a quantization parameter QP for adjusting the encoding bit rate. The prediction mode determination unit 301 performs prediction mode determination processing on the first macroblock of the encoding target picture. In this case, the prediction mode determination unit 301 evaluates the prediction mode to be applied to the head macroblock for each of all the prediction modes, so that the encoding cost COST when all the prediction modes and the head macroblock are encoded with each prediction mode is evaluated. Are calculated respectively (step S12). Then, the prediction mode in which the coding cost COST is minimized is determined as the prediction mode of the first macroblock (step S13).

  Then, the prediction mode determination unit 301 compares the encoding cost COST of the first macroblock corresponding to the determined prediction mode with the mode determination threshold EXE_thr, and the encoding cost COST of the first macroblock is equal to or less than the mode determination threshold EXE_thr. It is determined whether or not there is (step S14).

  If the encoding cost COST of the first macroblock is larger than the mode determination threshold value EXE_thr (NO in step S14), the prediction mode determination unit 301 changes the encoding target macroblock sequentially, and the encoding cost COST is the mode. The processes in steps S12 and S13 are repeated until a macroblock that is equal to or less than the determination threshold EXE_thr is detected (step S15).

  When a prediction-determined macroblock whose coding cost COST is equal to or less than the mode determination threshold EXE_thr is detected (YES in step S14), the prediction mode determination unit 301 determines the prediction determined for the prediction-determined macroblock. The mode is set as the initial evaluation mode MODE_init of the next macroblock to be encoded, and the encoding cost of the prediction-determined macroblock corresponding to the determined prediction mode is set as the evaluation cost threshold COST_thr (step S16). ).

  Thereafter, the prediction mode determination unit 301 starts the simple mode determination process for the current macroblock to be encoded. First, the prediction mode determination unit 301 encodes the current macroblock to be encoded (evaluation cost) COST_init when encoding the current macroblock to be encoded in the prediction mode applied to the immediately preceding macroblock indicated by the initial evaluation mode MODE_init. Is calculated (step S18). Next, the prediction mode determination unit 301 compares the encoding cost COST_init with the evaluation cost threshold value COST_thr, and determines whether the encoding cost COST_init is equal to or less than the evaluation cost threshold value COST_thr (step S19).

  If the encoding cost COST_init is equal to or less than the evaluation cost threshold COST_thr (YES in step S19), the prediction mode determination unit 301 determines the initial evaluation mode MODE_init as a prediction mode for encoding the current macroblock. Then, the evaluation cost threshold value COST_thr is updated, and the value of the evaluation cost threshold value COST_thr is changed to the coding cost COST_init of the current macroblock obtained in step S18 (step S20). If there is an undetermined macroblock (NO in step S21), the processing from step S17 is executed for the next macroblock.

  On the other hand, if the coding cost COST_init is larger than the evaluation cost threshold COST_thr (NO in step S19), the prediction mode determination unit 301 codes the current macroblock in each of the other prediction modes other than the initial evaluation mode MODE_init. The encoding cost in the case of conversion is calculated (step S22). Then, the prediction mode that minimizes the coding cost among all prediction modes is determined as the prediction mode of the current macroblock (step S23). Thereafter, the prediction mode determination unit 301 proceeds to step S14, compares the coding cost COST of the determined macroblock corresponding to the determined prediction mode with the mode determination threshold EXE_thr, and determines the determined macroblock. It is determined whether or not the coding cost COST is larger than the mode determination threshold EXE_thr.

  When the coding cost COST of the determined macroblock is equal to or less than the mode determination threshold EXE_thr, the prediction mode determination result of the determined macroblock is used for the prediction mode determination of the next macroblock. The mode determination unit 301 sets the prediction mode determined for the determined macroblock as the initial evaluation mode MODE_init of the next macroblock to be encoded, and the determined mode corresponding to the determined prediction mode The encoding cost of the macroblock is set as the evaluation cost threshold value COST_thr (step S16).

  On the other hand, if the coding cost COST of the determined macroblock is larger than the mode determination threshold value EXE_thr, the simplified mode determination process is temporarily terminated, and from the next macroblock to be encoded again from step S12. Processing begins. When a macroblock whose coding cost COST is equal to or less than the mode determination threshold value EXE_thr is detected, the initial evaluation mode MODE_init and the evaluation cost threshold value COST_thr are set in step S16, and then the simple mode determination process in step S17 is started. The

  In addition, since most of the encoding processes other than entropy encoding are executed in the prediction mode determination process, by performing the remaining processes such as entropy encoding when the prediction mode determination to be applied is determined, Encoding can be performed efficiently.

  As described above, according to the present embodiment, it is possible to efficiently determine the prediction mode with a small amount of processing while suppressing deterioration in image quality, and thus it is possible to encode a moving image signal in real time.

  Since all the encoding processes including the prediction mode determination process can be executed by the video encoder application 200, it is the same as the present embodiment only by installing this program on a normal computer through a computer-readable storage medium. The effect of can be easily realized.

  Further, the present invention is not limited to the above-described embodiments as they are, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

The block diagram which shows the structural example of the moving image encoder which concerns on one Embodiment of this invention. FIG. 3 is an exemplary block diagram illustrating a functional configuration of a software encoder realized by a video encoder application used in the moving image encoding apparatus according to the embodiment. The figure for demonstrating the function of the prediction mode determination part provided in the moving image encoder of the embodiment. The figure for demonstrating the basic principle of the prediction mode determination process performed by the moving image encoder of the embodiment. The figure which shows the example of the encoding order of the macroblock in the moving image encoder of the embodiment. The figure which shows the mode of the prediction mode determination process performed by the moving image encoder of the embodiment. The flowchart which shows the example of the specific procedure of the prediction mode determination process performed by the moving image encoder of the embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... CPU, 200 ... Video encoder application, 201 ... Input part, 202 ... DCT / quantization part, 203 ... Entropy encoding part, 204 ... Dequantization / inverse DCT part, 205 ... Intra prediction part, 208 ... Motion detection 209 ... inter prediction unit, 301 ... prediction mode determination unit, 401 ... first prediction mode determination unit, 402 ... second prediction mode determination unit.

Claims (7)

A video signal is divided into a plurality of image blocks, and each image block is selected from a plurality of prediction modes including a prediction mode group for inter-frame prediction encoding and a prediction mode group for intra-frame prediction encoding. A video encoding device that selects one prediction mode and encodes the image block in the selected prediction mode,
Coding costs are calculated when the first image block to be encoded is encoded in the plurality of prediction modes, and the prediction mode that minimizes the encoding cost is determined as the prediction mode of the first image block. First prediction mode determination means for executing a first prediction mode determination process;
When the encoding cost of the head image block corresponding to the prediction mode determined by the first prediction mode determination unit is equal to or lower than a predetermined reference value, the image block to be encoded following the head image block Second prediction mode determination processing for determining a prediction mode for encoding an image block to be encoded based on a prediction mode determination result for an image block immediately before the image block to be encoded for each of them Second prediction mode determination means to execute,
The second prediction mode determination means includes
The prediction mode determined for the image block immediately before the encoding target image block is set as the initial prediction mode of the encoding target image block, and the encoding target image block is encoded in the initial prediction mode. Means for calculating the encoding cost when
When the calculated encoding cost of the encoding target image block is equal to or less than the encoding cost of the immediately preceding image block, the initial prediction mode is used to encode the encoding target image block. Means to determine
When the encoding cost of the calculated image block to be encoded is larger than the encoding cost of the immediately preceding image block, the encoding target image block is encoded in a prediction mode other than the initial prediction mode, respectively. And a means for calculating a coding mode in which the coding cost is minimized and determining a prediction mode that minimizes the coding cost as the prediction mode of the image block to be coded. The first prediction mode determination unit is configured to detect the first prediction until an image block whose coding cost corresponding to the prediction mode determined in the first prediction mode determination process is equal to or less than the reference value is detected. Means for executing mode determination processing in order from the first image block to be encoded;
The said 2nd prediction mode determination means performs the said 2nd prediction mode determination process with respect to each image block of the encoding target subsequent to the said detected image block. Video encoding device. Means for determining whether or not the encoding cost of the image block is greater than the reference value for each image block for which the prediction mode is determined by the second prediction mode determination process;
When it is determined that the encoding cost is greater than the reference value, the first prediction mode determination unit performs encoding subsequent to the image block for which the encoding cost is determined to be higher than the reference value. For each target image block, the first prediction mode determination is performed until an image block whose coding cost corresponding to the prediction mode determined in the first prediction mode determination process is equal to or less than the reference value is detected. The moving image encoding apparatus according to claim 2, wherein the process is executed. A video signal is divided into a plurality of image blocks, and each image block is selected from a plurality of prediction modes including a prediction mode group for inter-frame prediction encoding and a prediction mode group for intra-frame prediction encoding. A video encoding method for selecting one prediction mode and encoding the image block in the selected prediction mode,
Coding costs are calculated when the first image block to be encoded is encoded in the plurality of prediction modes, and the prediction mode that minimizes the encoding cost is determined as the prediction mode of the first image block. A first prediction mode determination step for executing a first prediction mode determination process;
When the encoding cost of the head image block corresponding to the prediction mode determined by the first prediction mode determination process is equal to or less than a predetermined reference value, the image block to be encoded following the head image block Second prediction mode determination processing for determining a prediction mode for encoding an image block to be encoded based on a prediction mode determination result for an image block immediately before the image block to be encoded for each of them A second prediction mode determination step to be executed,
The second prediction mode determination step includes
The prediction mode determined for the image block immediately before the encoding target image block is set as the initial prediction mode of the encoding target image block, and the encoding target image block is encoded in the initial prediction mode. A step of calculating a coding cost when
When the calculated encoding cost of the encoding target image block is equal to or less than the encoding cost of the immediately preceding image block, the initial prediction mode is used to encode the encoding target image block. Steps to determine
When the encoding cost of the calculated image block to be encoded is larger than the encoding cost of the immediately preceding image block, the encoding target image block is encoded in a prediction mode other than the initial prediction mode, respectively. And a step of calculating a coding cost in each case and determining a prediction mode that minimizes the coding cost as a prediction mode of the image block to be coded. In the first prediction mode determination step, the first prediction mode is detected until an image block whose coding cost corresponding to the prediction mode determined in the first prediction mode determination process is equal to or less than the reference value is detected. The mode determination process is executed in order from the first image block to be encoded,
The said 2nd prediction mode determination step performs the said 2nd prediction mode determination process with respect to each image block of the encoding target subsequent to the said detected image block, The said 2nd prediction mode determination step is characterized by the above-mentioned. Video encoding method. Determining whether the coding cost of the image block is larger than the reference value for each image block for which the prediction mode is determined by the second prediction mode determination process;
When it is determined that the encoding cost is higher than the reference value, the first encoding block for each of the encoding target image blocks subsequent to the image block for which the encoding cost is determined to be higher than the reference value. And a step of executing the first prediction mode determination process until an image block is detected in which the coding cost corresponding to the prediction mode determined in one prediction mode determination process is equal to or less than the reference value. The moving picture encoding method according to claim 5, wherein: A video signal is divided into a plurality of image blocks, and each image block is selected from a plurality of prediction modes including a prediction mode group for inter-frame prediction encoding and a prediction mode group for intra-frame prediction encoding. A program that selects one prediction mode and causes a computer to execute a process of encoding the image block in the selected prediction mode,
Coding costs are calculated when the first image block to be encoded is encoded in the plurality of prediction modes, and the prediction mode that minimizes the encoding cost is determined as the prediction mode of the first image block. A first prediction mode determination procedure for executing a first prediction mode determination process;
When the encoding cost of the head image block corresponding to the prediction mode determined by the first prediction mode determination process is equal to or less than a predetermined reference value, the image block to be encoded following the head image block Second prediction mode determination processing for determining a prediction mode for encoding an image block to be encoded based on a prediction mode determination result for an image block immediately before the image block to be encoded for each of them A second prediction mode determination procedure to be executed, wherein the prediction mode determined for the image block immediately before the encoding target image block is set as an initial prediction mode of the encoding target image block; A procedure for calculating an encoding cost when the image block to be encoded is encoded in an initial prediction mode, and the calculated A procedure for determining the initial prediction mode as a prediction mode for encoding the encoding target image block when the encoding cost of the encoding target image block is equal to or less than the encoding cost of the immediately preceding image block; When the encoding cost of the calculated image block to be encoded is larger than the encoding cost of the immediately preceding image block, the encoding target image block is encoded in a prediction mode other than the initial prediction mode, respectively. A second prediction mode determination procedure including a step of calculating a coding cost in the case of encoding, and determining a prediction mode that minimizes the coding cost as the prediction mode of the image block to be encoded, A program characterized by being executed by a computer.

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