JP2002152743A - Moving picture decoder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a moving picture decoder that employs a simple circuit so as to select a still picture output without a blue even when normal decoding is disabled caused by an error in input coded data or deficient supply of the coded data themselves due to a damage of a recording medium or a communication fault or the like. SOLUTION: The moving picture decoder is provided with a timer, and if control from a CPU is not applied to the timer in proper timing, the selector of a display section is automatically switched to select an output of a still picture generating section so as to provide an output of a still picture with high quality.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a moving picture decoding apparatus for decoding a digitally compressed moving picture.

[0002]

2. Description of the Related Art When a digital image is stored and transferred, encoding is generally performed to reduce the amount of data. In the case of a moving image, as a coding method, there is a method of reducing data using temporal and spatial redundancy. As a method using temporal redundancy, there is a method of dividing the image into a plurality of blocks, detecting the motion of the block between the images, and taking the difference between the blocks between the images, thereby reducing the code amount. On the other hand, as a method of utilizing spatial redundancy, there is a method of dividing an image into blocks, orthogonally transforming the inside of the block, and performing variable-length coding on this information.

[0003] MPEG2 (ISO / IEC13818-
2) The image coding method is a coding method using both of the two methods. In MPEG2, each frame constituting a moving image is divided into a plurality of blocks, and each block is sequentially encoded. Each block is
A similar block in the preceding and following frames is referred to, and a difference from the block is calculated. Also, the difference between the block to be coded on the frame at this time and the planar position of the referenced block on the frame is added to the coded information as a motion vector. The difference between the coded block and the reference block is orthogonally transformed and quantized, and then, for example, arranged in the order of frequency components and subjected to variable length coding.
When decoding the encoded data, by performing the reverse procedure sequentially, the encoded data can be decoded and a moving image can be obtained.

In each frame of MPEG2, there are three types of blocks in a frame by a method of referring to blocks in previous and subsequent frames. An I frame is a frame composed of blocks that are not referred to, and data of the blocks are directly subjected to orthogonal transform, quantization, rearrangement, and variable length coding. The P frame is a frame composed of a block that is not referred to like an I frame and a block that refers to a block in an I or P frame that is temporally past. The B frame is generated by averaging the blocks in the I or P frame in the future in time and the blocks in the I or P frame in the past and the future, in addition to the blocks equivalent to the P frame. This is a frame composed of blocks that refer to the block to be processed.

FIG. 5 shows an example of a frame structure of a moving image in MPEG2. The arc-shaped arrows in the figure indicate the direction of reference. As described above, an I frame can be constructed only from encoded data because constituent blocks do not make reference. The P frame is the immediately preceding I or P
Browse the frame. The B frame refers to the preceding or succeeding I or P frame.

A B frame refers to an I or P frame in the future in terms of time, but in order to refer to it, it is necessary to decode the image of the reference destination first. For this reason, MPEG2
Are not arranged in the order of display time, and when a B frame is included, a future I or P frame referred to by the B frame comes first. In the moving picture decoding apparatus, decoding is performed in the order of the encoded data. However, at the time of decoding, since the reference image is always decoded first, the B frame can be decoded without any problem. On the other hand, the display needs to be rearranged so that the display is not in the decoding order but in time order after decoding. This is called reordering.

FIG. 6 shows an example of the relationship between the structure of MPEG2 encoded data, the image to be referred to, and the display. In FIG. 6, symbols following I0, P3, and B1 indicate input coded data or decoded image data of each frame. I, P, and B at the beginning indicate the type of the frame, and numerals following the frame. Indicates the order of display time. As shown in the figure, the input encoded data is configured such that the frame order of the encoded data is not the temporal order but the reference image is decoded first.
In decoding, encoded data is sequentially decoded. In this case, decoded frames necessary at this time are represented as a forward reference frame and a backward reference frame in FIG. Have been. Finally, when a frame to be displayed on the display unit is specified, by specifying the display order, a moving image in which frames are sequentially displayed in a correct time order can be obtained.

An example of an actual moving picture decoding process will be described with reference to FIGS. FIG. 3 is a block diagram of the entire video decoding device. The input encoded data is read from a recording medium or a communication path,
1. The data is accumulated in the buffer memory 109 in the memory 110 via the memory control unit 108. CPU103
Instructs the decoding unit 102 to start encoding in accordance with the frame display cycle. The decoding unit 102 includes a memory 110
The encoded data stored in the buffer memory 109 in the memory controller 108 and the buffer controller 101
Input via. Among the encoded data input to the decoding unit 102, information on decoding control
Passed to. The CPU 103 appropriately controls the decoding unit 102 based on the information on the decoding control, and instructs the start of the decoding of the block.

The decoding unit 102 receives an instruction to start block decoding from the CPU 103, performs variable-length encoded data decoding, scan conversion, inverse quantization, and inverse orthogonal transform. If there is a block to be referenced, A block in any one of the frame memories 111, 112, 113 and 114 in the memory 110 is stored in the memory control unit 10
8 to obtain the difference and obtain the decoded block. The decoded block is written from the decoding unit 102 to any of the frame memories 111, 112, 113, and 114 in the memory 110 via the memory control unit 108.

Next, the CPU 103 obtains information related to the decoding control of the next block from the decoding unit 102, controls the decoding unit 102 appropriately, and instructs the start of decoding of the block. In this way, the blocks constituting the frame are sequentially decoded, and the entire frame is decoded.

On the other hand, the CPU 103 sends the output frame to the display unit 104 in accordance with the frame period so that the decoded image is correctly displayed in the order of display time in the frame memory containing the image to be displayed. Instruct. Further, the CPU 103 controls the selector 106 in the display unit 104. The display unit 104 includes the memory control unit 10
8, the frame memory 11 in the memory 110
1, 112, 113, or 114, and the selector 106 outputs the frame data as it is or the frame data as the still image generation unit 10
The still image data output obtained by inputting the image data 5 to the video signal generator 107 is input to the video signal generator 107, which converts the image data into a video signal and outputs the video signal.

FIG. 10 is a time chart showing the processing procedure of the CPU 103. The CPU 103 controls the display unit and the decoding unit for each frame interval, displays one frame, and sequentially decodes one frame to obtain a moving image that changes every frame period. it can.

FIG. 4 shows an example of the details of the decoding unit. The input encoded data is input to the variable-length code decoding unit 120,
From the variable length code, the data is output as a data string (for example, from the lowest frequency component to the highest frequency component).
21. In the scan conversion unit 121, the blocks are arranged in the order of the orthogonally transformed blocks, and passed to the inverse quantization unit 122. The inverse quantization unit 122 performs inverse quantization to obtain orthogonal transform data, and passes the data to the inverse orthogonal transform unit 123.
The inverse orthogonal transform unit 123 performs an inverse orthogonal transform, obtains difference data of the block, and passes the data to the motion compensation unit 124. The motion compensating unit 124 calculates the difference from the block in the reference image, or outputs the block coded without reference without changing the difference. A decoded image can be obtained by sequentially performing the procedure of the variable-length code decoding, the scan conversion, the inverse quantization, the inverse orthogonal transform, and the motion compensation for all the blocks constituting the frame.

In some cases, the moving picture decoding apparatus does not merely display a moving picture by decoding, but also wants to freeze the display screen (display the same screen a plurality of times) during the moving picture decoding operation.
There is a case where the user wants to keep the screen being broadcast still, or a case where he wants to freeze a specific screen with a moving image player. Further, when there is an error in the encoded data, there is a case where it is desired to display a still image instead of a disturbed image in which an error has occurred in order to maintain display quality. Further, there is a case where the supply of the encoded data is temporarily stopped due to a failure such as a broadcast and the next image to be displayed cannot be generated.

There are two types of moving images: a method called interlace and a method called progressive. In the former, one screen (frame) is divided into two fields and displayed, and the first field and the second field are alternately arranged. In this case, the alternately upper field is called a top field, and the lower field is called a bottom field, and there is a time difference of half the frame period between the fields. That is, the frame period is 1 /
If it is 30 seconds, the period of the field is 1/60 seconds. When displaying a still image, data of one frame is repeatedly output. However, in the case of interlacing, a still image is displayed as blurred in a moving image having a change because there is a time difference between fields. I will. This will be described with reference to FIGS.

In FIG. 7, since the movement between fields is small, the still image output is also displayed as a beautiful still image. On the other hand, in FIG. 8, a still image is displayed blurred because there is movement between fields. Such a blurred image is not of good quality. To avoid this, as shown in FIG. 9, a method of repeatedly outputting the data of one field or a more advanced method of converting the frame data into a field data is used. There is a method of creating and displaying the data by the interpolation processing from the data of the above. With this method, a still image without blur can be obtained even with an interlaced image.

A still image generating unit 105 in the display unit 104 shown in FIG. 3 is a unit that generates a still image without blur from the frame image data. When the CPU 103 determines that the still image is to be displayed, The selector 106 selects a signal from the still image generation unit 105 and supplies the signal to the video signal generation unit 107 to provide a still image without blur.

[0018]

When a still image is displayed, two cases are conceivable. One of them is a case where the user makes an intention to display a still image on the moving picture decoding apparatus. In this case, the CPU 103 sends the display unit 104 Appropriate control can be performed by specifying the frame memory and directly controlling the selector 106. For example, when the same image is displayed for a period longer than one frame period, a beautiful still image without blur can be obtained by switching the selector 106 to select a signal from the still image generating unit 105.

An example of a time chart of this control is shown in FIG.
Shown in In normal playback, display control,
The decoding control is repeated, but when outputting a still image, the display control and the decoding control are also suspended until the still image is released. At this time, when the encoded data is interlaced, the CPU 103 switches the selector 106 of the display unit 104 to the still image side, so that a still image without blur can be displayed.

The other is a case where it is not based on the user's intention. For example, when an error occurs in the encoded data due to a scratch on the recording medium or disturbance of the broadcast,
The decoding process may not be performed normally, and the CPU 103 may need to spend a long time in the process until the next normal decoded image is obtained. In some cases, the input data may be insufficient, but at this time, the CPU 103 needs to wait for the next data. In such a case, the frame decoding and display processing for each frame time originally desired are delayed, and the display unit 104 displays a blurred unsightly image by repeatedly displaying the same frame.

An example of such a time chart is shown in FIG.
Shown in In this case, since the CPU 103 does not plan to display a still image, the selector 106 of the display unit 104 remains on the frame side, and as a result, a blurred image is seen. Particularly, in the case of MPEG, if an error occurs and decoding cannot be performed normally, the previously-decoded image is referred to, and due to the nature of the error, the screen disturbance generated in the reference source image due to the error occurs as a disturbance on the referencing side thereafter. Would.
If you skip over these distorted images without displaying them,
It may be necessary to display a blurred still image for a long time before decoding and displaying the next I frame.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and its purpose is to damage a recording medium,
Errors in input encoded data due to communication failures, etc.
It is an object of the present invention to make it possible to reliably switch to a still image in which blur is not visible by using a simple circuit even when the supply of encoded data itself is insufficient and a normal decoding operation cannot be performed.

[0023]

In a normal moving image display, the timing of display control from the CPU is determined, for example, once every 1/30 second depending on the frame rate of the moving image. However, when the broadcast signal is sometimes interrupted due to bad weather, or when there is an error in a moving image player, the input moving image data is incorrect at an unexpected timing or the supply is temporarily stopped. In this case, the decoding process cannot be performed normally, and an image is not generated at a time when the original display control is expected, so that the CPU cannot perform the display control. Therefore, a timer is provided, and if the control from the CPU cannot be performed at an appropriate timing with respect to the timer, the selector of the display unit is automatically switched to select the output of the still image generation unit. , So that a high-quality still image is output.

[0024]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a configuration of a video decoding device according to a first embodiment of the present invention. In FIG. 1, reference numeral 11 denotes a buffer control unit, 12 denotes a decoding unit,
3 is a CPU, 14 is a timer, 15 is a display unit, 16 is a still image generation unit in the display unit 15, 17 is a selector in the display unit 15, 18 is a video signal generation unit in the display unit 15, 19
Denotes a memory control unit, 21 denotes a memory, 20 denotes a buffer memory in the memory 21, and 22 to 25 denote image memories in the memory 21.

In the configuration shown in FIG. 1, input coded data is read from a recording medium or a communication path, and is stored in a buffer memory 20 in a memory 21 via a buffer control unit 11 and a memory control unit 19. Will be done. CP
U13 controls the decoding unit 12 in accordance with the display cycle of the frame.
To start encoding. The decoding unit 12 includes a memory 21
The coded data stored in the buffer memory 20 is input via the memory control unit 19 and the buffer control unit 11. Among the encoded data input to the decoding unit 12, information on decoding control is passed to the CPU 13. The CPU 13 uses the information on the decryption control,
The decoding unit 12 is appropriately controlled to instruct the start of decoding of the block.

The decoding unit 12 receives an instruction to start block decoding from the CPU 13, performs variable-length coded data decoding, scan conversion, inverse quantization, and inverse orthogonal transform. If there is a block to be referenced, A block in any one of the frame memories 22, 23, 24 and 25 in the memory 21 is read out via the memory control unit 19, a difference is obtained, and a decoded block is obtained. The decoded block is sent from the decoding unit 12 via the memory control unit 19 to the frame memories 22, 23, 2 in the memory 21.
4 or 25 is written.

Next, the CPU 13 obtains information on decoding control of the next block from the decoding unit 12 and
2 is appropriately controlled to instruct the start of block decoding.
In this way, the blocks constituting the frame are sequentially decoded, and the entire frame is decoded.

On the other hand, the CPU 13 sends the output frame to the display unit 15 in accordance with the frame period so that the decoded image is displayed in the correct order of the display time in the frame memory containing the image to be displayed. Instruct. Further, the CPU 13 controls the selector 17 in the display unit 15 and resets the timer 14 at the same time. Display unit 15
Reads out any one of the frame memories 22, 23, 24, and 25 in the memory 21 via the memory control unit 19, and generates the still image or the frame data by the selector 17 as it is. The still image data output obtained by inputting to the section 16 is input to the video signal generation section 18 to convert the image data into a video signal and output.

The timer 14 is normally reset by the CPU 13 every frame period and does not function. However, if the timer 14 has not been reset from the CPU 13 and has not been reset for a period longer than the frame period,
It turns on, and switches the selector 17 in the display unit 15 to select the output of the still image generation unit 16. As a result, a video output of a still image with no blurring can be obtained without intervention from the CPU 13.

FIG. 13 shows an example of this time chart. Even if the CPU 13 continues the processing by the decoding unit 12, if the timer 14 determines that one frame period has passed, the selector 17 of the display unit 15 is switched to the still image display, so that a beautiful still image without blurring can be displayed. Obtainable.

FIG. 2 is a block diagram showing a configuration of a moving picture decoding apparatus according to a second embodiment of the present invention. In FIG. 2, components equivalent to those of the first embodiment shown in FIG. The same reference numerals are given. The present embodiment differs from the first embodiment shown in FIG. 1 in that a control line 30 for outputting a signal indicating that the signal is a progressive signal from the decoding unit 12 to the timer 14 is added.

In the configuration shown in FIG. 2, the input coded data is read from a recording medium or a communication path, and is stored in a buffer memory 20 in a memory 21 via a buffer control unit 11 and a memory control unit 19. To go. CPU
13 instructs the decoding unit 12 to start encoding in accordance with the display cycle of the frame. The decoding unit 12 inputs the encoded data stored in the buffer memory 20 in the memory 21 via the memory control unit 19 and the buffer control unit 11. Among the encoded data input to the decoding unit 12, information on decoding control is passed to the CPU 13.
The CPU 13 appropriately controls the decoding unit 12 based on the information on the decoding control, and instructs the start of the decoding of the block.

The decoding unit 12 receives an instruction to start block decoding from the CPU 13, performs variable-length encoded data decoding, scan conversion, inverse quantization, and inverse orthogonal transform. If there is a block to be referenced, A block in any one of the frame memories 22, 23, 24, and 25 in the memory 21 is read via the memory control unit 19, a difference is obtained, and a decoded block is obtained. The decoded block is sent from the decoding unit 12 via the memory control unit 19 to the frame memories 22, 23, 2 in the memory 21.
4 or 25 is written.

Next, the CPU 13 obtains information relating to the decoding control of the next block from the decoding unit 12 and
2 is appropriately controlled to instruct the start of block decoding.
In this way, the blocks constituting the frame are sequentially decoded, and the entire frame is decoded.

On the other hand, the CPU 13 sends the output frame to the display unit 15 in accordance with the frame period so that the decoded image is displayed in the correct order of display time in the frame memory containing the image to be displayed. Instruct. Further, the CPU 13 controls the selector 17 in the display unit 15 and resets the timer 14 at the same time. Display unit 15
Reads out any one of the frame memories 22, 23, 24, and 25 in the memory 21 via the memory control unit 19, and generates the still image or the frame data by the selector 17 as it is. The still image data output obtained by inputting to the section 16 is input to the video signal generation section 18 to convert the image data into a video signal and output.

When the input coded data is progressive (non-interlaced), the input coded data includes a progressive sequence signal (flag indicating that the data is progressive) which means that the data is progressive. When the decoding unit 12 detects this progressive sequence signal, it outputs a timer control signal corresponding to the progression sequence signal to the timer 14 via the control line 30 so that the decoding unit 12 is not reset for a period longer than the frame period. However, the timer 14 is not turned on (function). The timer 14 is normally reset by the CPU 13 every frame period and does not function. However, when the progressive sequence is not progressive, that is, when the timer 14 is interlaced,
In addition, when the reset from the CPU 13 is not performed and the reset is not performed for a period longer than the frame period, the switch is turned on, and the selector 17 in the display unit 15 is switched to select the output of the still image generating unit 16. . As a result, as described above, a video output of a still image with no blur can be obtained without intervention of the control from the CPU 13. When the input coded data is progressive, the selector 17 does not switch so as to select the signal of the still image generating unit 16. In this case, the processing that passes through the unnecessary still image generating unit 16 is unnecessary. It is possible to avoid this and obtain a beautiful still image that is faithful to the input encoded data.

FIG. 14 shows an example of this time chart.
Even if the CPU 13 continues the processing by the decoding unit 12, the timer 14 does not function, so that the selector 17 of the display unit 15 does not switch to the still image generation unit side. An image can be obtained.

[0038]

As described above, according to the present invention, errors in input coded data and insufficient supply of coded data themselves occur due to damage to a recording medium, communication failure, etc., and a normal decoding operation can be performed. Even in the case where it cannot be performed, switching to a still image in which blur is not visible can be reliably performed with a simple circuit.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a video decoding device according to a first embodiment of the present invention.

FIG. 2 is a block diagram illustrating a configuration of a video decoding device according to a second embodiment of the present invention.

FIG. 3 is a block diagram illustrating a configuration of a video decoding device according to a conventional technique.

FIG. 4 is a detailed configuration diagram of a decoding unit.

FIG. 5 is a diagram illustrating MPEG2 image reference.

FIG. 6 is a diagram illustrating MPEG2 decoding processing.

FIG. 7 is a diagram illustrating an interlaced image.

FIG. 8 is a diagram illustrating an interlaced image.

FIG. 9 is a diagram illustrating a field image still image.

FIG. 10 is an explanatory diagram illustrating an example of a time chart of a decoding process.

FIG. 11 is an explanatory diagram showing an example of a time chart of still image display according to a user's intention.

FIG. 12 is an explanatory diagram showing an example of a time chart of still image display due to delay in decoding processing.

FIG. 13 is an explanatory diagram showing an example of a time chart of still image display by timer control.

FIG. 14 is an explanatory diagram illustrating an example of a time chart of a still image display of a progressive image.

[Explanation of symbols]

 Reference Signs List 11 buffer control unit 12 decoding unit 13 CPU 14 timer 15 display unit 16 still image generation unit 17 selector 18 video signal generation unit 19 memory control unit 20 buffer memory 21 memory 22, 23, 24, 25 image memory 30 progressive sequence signal Control line 120 Variable-length code decoding unit 121 Scan conversion unit 122 Inverse quantization unit 123 Inverse orthogonal transformation unit 124 Motion compensation unit

Claims (2)

[Claims] 1. A memory for storing coded data and decoded image data, and coded data input thereto, decoding the coded data with reference to the decoded image data in the memory, A decoding unit that outputs decoded image data, a display unit that appropriately reads the decoded image data in the memory, converts the image data into a video signal, and outputs the image data, and a CPU that controls the decoding unit and the display unit. A timer that is reset by a reset signal from the CPU; a still image generation unit that is provided in the display unit and that performs processing to make a portion having a motion specific to an interlaced frame less noticeable than frame image data; And a selector for selecting one of the frame image data and the output of the still image generation unit. In a race, if the timer has not been reset for a predetermined time by the CPU, the timer switches the selector so as to select the output of the still image generation unit, and displays a still image without blur. A moving image decoding apparatus characterized in that the decoding is performed. 2. The apparatus according to claim 1, wherein a flag indicating progressive recorded in the input encoded data obtained by the decoding unit is detected, and when the input encoded data is progressive, a still image display is performed. A moving image decoding apparatus that controls the selector so that the output of the still image generating unit is not selected.