JP3098485B2 - Image decoding device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image decoding apparatus, and more particularly to a moving picture compression system in which a picture group including one first picture and a plurality of second pictures following the first picture is continuous. The present invention relates to an image decoding device that outputs while decoding data.

[0002]

2. Description of the Related Art As a conventional image decoding apparatus, an international standard moving picture encoding system (MPEG: Moving Picture Experts G
2. Description of the Related Art There is known an apparatus of a type that takes in a stream including compressed data of video or audio by roup), decodes the compressed data, and outputs the data in real time.

For example, when decoding and displaying compressed moving image data included in a stream, it is necessary that the decoded image data and audio data are output in synchronization. Therefore, in the above-described conventional image decoding apparatus, when it is determined that the audio data is ahead of the image data, the image data is skipped and fast-forwarded automatically to synchronize with the audio data.

FIG. 4 is a timing chart showing a state when decoding is performed by the conventional image decoding apparatus. MP
In the compressed video data according to the EG standard, an I picture (Intra Picture) which is an intra-frame coded image, and a plurality of P pictures (Predictive Picture) which are inter-frame forward prediction coded images and follow the I picture. Are consecutively included. I pictures such as I0 and I4 are images that are decoded without referring to other pictures, and P pictures such as P1 to P3 and P5 are images that are decoded while referring to the picture decoded immediately before. is there. The moving image compressed data in FIG.
3 pictures, and I4, P5.
And a picture group consisting of the following pictures:

When the conventional image decoding apparatus performs decoding while skipping compressed moving image data, for example,
When a skip command is input during the display of 0 picture, skip processing is realized by canceling the decoding of the P3 picture located immediately before the I4 picture and not being the target of prediction reference. As a result, images are displayed in the order of I0, P1, P2, and I4 pictures on the display unit of the television receiver or the like.

[0006]

As described above, in the conventional image decoding apparatus, even when the skip command is input during the display of the I0 picture, the skip operation is performed until the P3 picture after the P2 picture is input. It was not executed and the response to the skip command was extremely slow. Further, irrespective of the input timing of the skip command, only a specific picture that is not a target of prediction reference is always skipped, so that the displayed image does not operate smoothly and gives a sense of discomfort to the viewer.

SUMMARY OF THE INVENTION In view of the above, it is an object of the present invention to provide an image decoding apparatus which can quickly respond to a skip command when fast-forwarding during a decoding process, and in which a displayed image operates smoothly without a sense of incongruity. .

[0008]

In order to achieve the above object, an image decoding apparatus according to the present invention refers to one first picture which is decoded without referring to another picture, and refers to another picture. In the image decoding apparatus, which decodes and outputs compressed moving image data in which a group of pictures including a plurality of second pictures subsequent to the first picture are decoded, the decoded first or second picture is displayed. And a third memory for storing the decoded first or second picture for non-display, and in normal processing without skipping, the first and second pictures are successively decoded. A picture and the first
Alternatively, the second picture decoded with reference to another decoded picture stored in the second memory is alternately stored in the first and second memories, and the skipped decoded picture is stored in the first and second memories. Subsequent pictures stored in a third memory and decoded are stored in the first and second pictures.
The second picture is alternately stored in a memory, and the second picture at this time is decoded with reference to another decoded picture stored in the first, second, or third memory.

In the image decoding apparatus according to the present invention, an arbitrary picture in a group of pictures can be skipped, so that the response to the skip command is speeded up, and the display image at the time of the skip processing is smoothly operated without a sense of incongruity. it can.

Here, the first or second picture stored in the third memory and the first or second picture following the picture are stored.
For the first or second picture stored in the memory,
It is preferable to perform the decoding process at twice the normal speed within one display frame period. As a result, the time required for decoding the picture to be skipped and the subsequent picture can be contained within one frame period, and the flow of the time required for decoding and the movement of the display image can be matched.

In a normal process, a decode start instruction signal for decoding a picture of one frame is issued once in one display frame period. In the skip process, the decode start instruction signal is issued in one display frame period. Preferably, the start instruction signal is issued twice. As a result, the picture stored in the third memory and the picture following the picture are stored in the normal 2
Decoding at twice the speed can be realized.

[0012] More preferably, a display data output unit is provided for taking in the first or second picture from the first or second memory and outputting it as a display image. This makes it possible to sequentially send the decoded image data to the display unit and display it smoothly.

Preferably, the first and second pictures are respectively composed of an I picture and a P picture in the compressed video data of the MPEG standard. In this case, it is possible to take in a stream including compressed data of video and audio by MPEG, and output the data in real time while decoding the compressed data.

[0014]

[0015]

[0016]

The present invention will be described in more detail with reference to the drawings. FIG. 1 is a block diagram showing an MPEG decoding device (image decoding device) according to the first embodiment of the present invention. The MPEG decoding device 11 includes a display storage device 12,
It comprises a stream supply unit 13, an MPEG decoding unit 14, a display data output unit 15, and an MPEG decoding control unit 16. The MPEG decoding device 11 outputs an I picture (: Intra Pictur) which is an intra-frame coded image in the MPEG standard.
e), and a P picture (: Predictive Pictu) which is a plurality of inter-frame forward predictive encoded images following the I picture
The function has a function of decoding and outputting compressed moving image data having a group of pictures including re).

The stream supply unit 13 separates required moving image compressed data from the input stream St and supplies the separated data to the data bus 20.

The display storage device 12 stores the first memory area 1
7, a second memory area 18, and a third memory area 19. The first memory area 17 and the second memory area 18
The decoded I picture or P picture is stored for display. The third memory area 19 is an area for storing the decoded I picture or P picture for non-display, and stores the I picture or P picture to be skipped at a predetermined timing when the skip command Sc is input. .

The MPEG decoder 14 has an operation clock set higher and operates according to a picture writing area instruction signal and a decode start instruction signal, which will be described later, sent from the MPEG decoder controller 16.

At the time of normal processing in which the skip command Sc is not input, the MPEG decoding control unit 16 specifies a picture writing area instruction to store successive I pictures and P pictures alternately in the first memory area 17 and the second memory area 18. The signal is issued to the MPEG decoding unit 14. Also, MP
At the time of the skip processing in which the skip command Sc is input, the EG decoding control unit 16 stores the picture to be skipped in the third memory area 19 and stores the succeeding picture in the first memory area 17 and the second memory area 18 alternately. A picture writing area instruction signal to the effect that the picture is written is issued to the MPEG decoding unit 14.

At the time of the normal processing, the MPEG decoding control section 16 issues a decoding start instruction signal for decoding a picture of one frame once within one display frame period. The decoding start instruction signal is issued twice during the period. As a result, the MPEG decoding unit 14 outputs the I picture or P picture stored in the third memory area 19 and the I picture transmitted immediately after this picture and stored in the first memory area 17 or the second memory area 18. Or for a P picture
The decoding process is performed at twice the normal speed within one display frame period. The MPEG decoding control unit 16 further controls the MPEG decoding unit 1 so that a new decoded picture is not written before the decoded picture stored in the first memory area 17 or the second memory area 18 is output for display.
4 is controlled.

The display data output unit 15 includes a data bus 20
The decoded image data is fetched from the display storage device 12 via the display unit and output to a display unit (not shown).
The video synchronization signal is supplied to the MPEG decoding control unit 16.

MPEG decoding unit 14, display data output unit 1
5 and the MPEG decoding control unit 16 refers to the decoding result of the first picture to be skipped, and decodes the next second picture when displaying the third picture sent prior to the first picture. Decoding means for continuously displaying the second picture without interruption is configured.

FIG. 2 is a timing chart showing a state when the moving image compressed data is simply decoded, and FIG. 3 is a timing chart showing a state when the moving image compressed data is decoded while performing the skip processing. 2 and 3,
I indicates an I picture, and P indicates a P picture, and the appended numbers indicate the order of decoding processing. Hereinafter, FIG.
The operation of the MPEG decoding device 11 according to this embodiment will be described with reference to FIG.

A virtual counter value for synchronizing with the audio data is added to the image data, and a judgment circuit (not shown) judges whether or not the image data is output in synchronization with the audio data. Is done. As a result, when the skip command Sc indicating that the skip process is to be performed is output, a process of skipping the set picture and synchronizing with the audio data is performed.

First, when the MPEG decoding apparatus 11 starts operating by a predetermined operation, the stream supply unit 13 supplies necessary compressed moving image data separated from the input stream St to the data bus 20. Correspondingly,
The MPEG decoding control unit 16 issues a corresponding picture writing area instruction signal to the MPEG decoding unit 14,
A decoding start instruction signal is issued once. This gives M
The PEG decoding unit 14 decodes the I picture and the P picture in the picture group, and stores them alternately in the corresponding first memory area 17 and second memory area 18.

At this time, the MPEG decoding unit 14 decodes the first I0 picture and stores it in the first memory area 17 in accordance with the picture writing area instruction signal.
Referring to the I0 picture in the first memory area 17, P1
The picture is stored in the second memory area 18 while being decoded. Thereafter, the MPEG decoding unit 14 sets the second memory area 1
8, the P2 picture is decoded and stored in the first memory area 17 while referring to the P1 picture. Prior to this, the display data output unit 15 outputs the I
Since the 0 picture is received and output to the display unit, the decoded P2 picture is stored in the empty first memory area 17.

Next, the MPEG decoding section 14 refers to the P2 picture in the first memory area 17 and decodes and stores the P3 picture in the second memory area 18. Prior to this, the display data output section 15 receives the P1 picture from the second memory area 18 and outputs it to the display unit, so that the decoded P3 picture is stored in the empty second memory area 18. Further, the MPEG decoding unit 14 stores the I4 picture in the first memory area 17, but prior to this, the display data output unit 15 receives the P2 picture from the first memory area 17 and outputs it to the display unit. .

Next, the MPEG decoding unit 14 refers to the I4 picture in the first memory area 17 and decodes the P5 picture and stores it in the second memory area 18. The P3 picture is extracted from 18 and output to the display unit. Further, the MPEG decoding unit 14 refers to the P5 picture in the second memory area 18 and decodes the subsequent picture (not shown) and stores it in the first memory area 17.
The I4 picture is extracted from the memory area 17 and output to the display unit. By these processes, as shown in FIG. 2, an image based on the I0, P1 to P3, and I4 pictures is displayed on the display unit without skip processing.

For example, when the skip command Sc is input during the display of the I0 picture, the MPEG decoding control unit 16
Issues a corresponding picture write area instruction signal to the MPEG decoding unit 14 and issues a decode start instruction signal twice. Thus, MPEG decoding unit 14, while decoding the I and P pictures in the picture group, relative to the P3 picture followed by the P2 picture of an arrow A in FIG. 2 and the corresponding display end time of the I0 picture Decoding at twice the normal speed. As a result, the time required for decoding the P2 picture to be skipped and the P3 picture following the skipped P2 picture can be contained within one frame period, and the flow of time required for decoding can be matched with the movement of the display image. For other pictures, a normal process of alternately storing the pictures in the corresponding first memory area 17 and second memory area 18 is performed.

That is, when the skip command Sc is input during the display of the I0 picture, the MPEG decoding unit 14
Is the first memory area 17 while decoding the I0 picture.
, And then decode the P1 picture while
It is stored in the memory area 18. Further, the P2 picture is stored in the third memory area 19 while being decoded at twice the normal speed, and then the P3 picture is stored in the first memory area 17 while being decoded at twice the normal speed. When the P2 picture is stored, the third memory area 19 is empty, and the I0 picture is extracted from the first memory area 17 before the P3 picture is stored.

Furthermore, MPEG decoding unit 14, and stores the I4 picture in the second memory area 18, then stored in the first memory region 17 while decode the P5 picture. I
Prior to storing four pictures, the second memory area 18
, A P1 picture is extracted, and a P3 picture is extracted from the first memory area 17 before a P5 picture is stored. Moreover, MPEG decoding unit 14, but stores a picture (not shown) subsequent to the second memory region 18 while decode, prior to this, I4 picture is taken from the second memory region 18.

As described above, P for two consecutive frames
The two pictures and the P3 picture are decoded in one frame at double speed, and the P2 picture in the third memory area 19 is decoded.
Since the picture is not used for display, the displayed image is shown in FIG.
As shown in FIG.
Displayed as 1, P3 and I4.

For example, if the skip command Sc is P
If the input is made during the display of two pictures, the I4 picture indicated by the arrow B in FIG.
Decoding is performed at double speed, and normal processing for alternately storing the other pictures in the corresponding first memory area 17 and second memory area 18 is performed on other pictures. Therefore,
By the same processing as described above, the continuous I4 picture and P
Five pictures are decoded at double speed, and the I4 picture stored in the third memory area 19 is not displayed.
For this reason, the display image is obtained by skipping the I4 picture.
0, P1, P2, P3 and P5.

As described above, in the present embodiment, a picture to be skipped in one display frame period and a picture following it are decoded, and the picture to be skipped is not used for display. Pictures can be skipped. Therefore, the response to the skip command can be sped up, and the display image at the time of the skip processing can be smoothly operated without a sense of incongruity.

In the present embodiment, the case is shown in which the picture is stored successively in the first memory area 17 and the second memory area 18 and then the next picture is stored in the third memory area 19. For example, the skip processing can be performed at a different timing. That is, if the timing of specifying a picture is advanced when the skip command Sc is input, the first memory area 17
After the picture is stored in the third memory area 19, the picture is stored in the first memory area 17, and the picture is further stored in the second memory area 18. In this case, when the picture is stored in the third memory area 19, the picture stored in the first memory area 17 is taken out for display. Is stored.

Although the present invention has been described based on the preferred embodiment, the image decoding apparatus of the present invention is not limited to the configuration of the above-described embodiment, but rather the configuration of the above-described embodiment. The image decoding apparatus in which various modifications and changes have been made from the above are also included in the scope of the present invention.

[0038]

As described above, according to the image decoding apparatus of the present invention, an arbitrary picture in a picture group can be skipped, so that the response to a skip command is speeded up, Can smoothly operate the displayed image at the time.

[Brief description of the drawings]

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

FIG. 2 is a timing chart showing how the MPEG decoding device of FIG. 1 simply decodes the compressed moving image data.

FIG. 3 is a timing chart showing how the MPEG decoding device of FIG. 1 decodes compressed moving image data while skipping the data.

FIG. 4 is a timing chart showing a situation when compressed moving image data is decoded by a conventional image decoding device.

[Explanation of symbols]

 Reference Signs List 11 MPEG decoding device 12 Display storage device 14 MPEG decoding unit 15 Display data output unit 16 MPEG decoding control unit 17 First memory area 18 Second memory area 19 Third memory area 20 Data bus Sc Skip command St stream

Continuation of the front page (56) References JP-A-8-163559 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H04N 5/91-5/956 H04N 7/24-7 / 68

Claims (5)

(57) [Claims] 1. A picture group including one first picture that is decoded without referring to another picture and a plurality of second pictures that are decoded with reference to another picture and follow the first picture. An image decoding apparatus that decodes and outputs compressed moving image data successively includes a first and second memory for storing the decoded first or second picture for display, and the first or second memory after decoding. A third memory for storing two pictures for non-display purposes, wherein during normal processing without skipping, the first picture after continuous decoding and another picture after decoding stored in the first or second memory And the second picture decoded with reference to the first and second memories is alternately stored in the first and second memories. Is stored in the third memory, and subsequent pictures after decoding are alternately stored in the first and second memories, and the second picture at this time is the decoding stored in the first, second, or third memory. An image decoding apparatus characterized in that decoding is performed with reference to another subsequent picture. 2. A display 1 for a first or second picture stored in the third memory and a first or second picture following the picture and stored in the first or second memory. 2. The image decoding apparatus according to claim 1, wherein decoding processing is performed at a speed twice as fast as that in a frame period. 3. During the normal processing, a decode start instruction signal for decoding a picture for one frame is issued once within one display frame period. At the skip processing, the decoding start instruction signal is issued within one display frame period. The image decoding apparatus according to claim 2, wherein the decoding start instruction signal is issued twice. 4. The display device according to claim 1, further comprising a display data output unit that fetches the first or second picture from the first or second memory and outputs the fetched image as a display image. 2. The image decoding device according to claim 1. 5. The method according to claim 1, wherein the first and second pictures are M
The image decoding apparatus according to any one of claims 1 to 4, comprising an I picture and a P picture in the compressed video data of the PEG standard.