JPH11205739A - Image reproduction method and system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reproduce coded moving images smoothly in the reverse direction. SOLUTION: A write control section 21 writes an image decoded in a forward direction to an area of a memory 17 assigned by an area assignment section 29. A reproduction sequence storage section 31 for the memory 17 stores a reproduction sequence of pluralities of images stored in the memory 17. In the case of reproducing the image in a reverse direction, a read control section 25 reads a decoded image stored in the memory 17 according to the reverse sequence stored in the reproduction sequence storage section 31. In the case that there is no idle area to be assigned by the area assignment section 29, a thinning control section 27 thin the decoded image or the displayed image stored in the memory 17 and overwrites the result on the image stored in the memory 17 to thin the image.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reproducing method and an image reproducing apparatus for reproducing encoded image data recorded on a disk medium such as a DVD or a magnetic tape or the like. The present invention relates to a method and apparatus for reproducing images smoothly.

[0002]

2. Description of the Related Art Conventionally, a discrete cosine transform for compressing an information amount by transmitting a coefficient subjected to a discrete cosine transform based on a spatial correlation of an input image has been known as an element technology for highly efficient coding of a moving image signal. (DCT), an inter-frame prediction method of compressing an information amount based on temporal correlation, and variable-length coding which is statistical information compression in which codewords are assigned in consideration of a symbol appearance probability are known. As an example of an advanced image compression encoding system combining these element technologies, a standard called MPEG2 standard ISO / IEC
13818-2.

In the MPEG2 system, an image divided into blocks of 8 × 8 pixels is DCT-transformed and intra-picture coded “I picture”, and an error predicted between frames based on “I picture” is transmitted. Accordingly, a “P picture”, which is a forward prediction image for reducing the amount of temporal information, and a “B picture”, which is a bidirectional prediction image for predicting an intermediate image from an I picture or a P picture, are used.

[0004] The image encoding / decoding system of the MPEG2 system will be described below.

[0005] First, on the encoding side, compressed image data is generated by obtaining image data including picture information and a motion vector that have been subjected to variable-length encoding from original image data, and adding header information to the image data.

[0006] The header information includes quantization step information indicating a unit of quantization when variable-length coding of picture information is performed. The motion vector information is 2
This shows the movement of the subject between two pictures.

Here, in the case of encoding an I picture,
While picture information is obtained only from an I picture, in the case of encoding a P picture, picture information is obtained using a difference between the P picture and an I picture or P picture that is a forward reference image thereof, In the case of a B picture, picture information is obtained using the difference between the B picture and its forward reference image and backward reference image.

Therefore, two B-pictures are usually continuous, but when decoding a B-picture, the preceding or succeeding I-picture or P-picture is required. It is necessary to encode and output a certain picture as an I picture or a P picture first. Therefore, when bidirectional predictive encoding is performed, encoding is performed with the temporal order between pictures interchanged.

In the MPEG system, a group of pictures (hereinafter abbreviated as GOP) as shown in FIG.
A unit composed of a plurality of pictures called a picture is used.
This is adopted to provide an entry point for access in order to realize random access to a moving image storage medium or to promptly display an image when a broadcast channel is switched. The structure in this GOP is
Although it can be arbitrarily composed of I, P, and B pictures, in general, an I picture is placed at the beginning, and then a fixed period (the period of the I or P picture is indicated by M), for example, 3 pictures , A periodic structure is used in which a P picture is placed and a B picture is sandwiched between the P pictures. GOP
Any length is possible, but in general, 10
A length (N) of about 15 pictures is used.

As shown in FIG. 6, when decoding image data which has been subjected to motion prediction encoding such as MPEG, a memory for holding a forward prediction reference image and a backward prediction reference image is provided. Images (P pictures, B pictures) that are predictively coded using the transformed reference pictures (I pictures, P pictures).
Picture).

Therefore, even when the motion-predicted coded image data is reproduced in the backward direction, it is necessary to decode the reference image first, so that the coded image signal having the GOP structure as shown in FIG. Is decoded, a decoded image cannot be obtained unless decoding of a number of reference images is repeated.

For example, in the example of FIG. 7, in order to decode P10 which is the first image of the reverse reproduction, I1,
P4 and P7 must be decoded, and the number of decoded images including P10 is four. Hereinafter, since the image decoding numbers of B9 and B8 are 1, P7 is held as a forward reference image, the image decoding number is 0, and when decoding B6,
The number of decoded images is 3 in order to decode 1 and P4. Although omitted below, the number of times of decoding when 10 images are reproduced in the reverse direction is 12 times.

For this reason, Japanese Patent Application Laid-Open Nos.
As disclosed in JP-A-79688, only I pictures (intra-frame encoded pictures) or only I pictures and P pictures (pictures encoded using forward prediction) in encoded data are picked up. And reverse playback was performed.

In the example disclosed in Japanese Patent Application Laid-Open No. 9-55946, the decoded image is down-sampled and the amount of image data is reduced and stored, thereby reducing the amount of memory required for normal decoding. 1GOP images are stored in a memory and read in reverse order to perform reverse reproduction.

[0015]

However, in the case of picking up only the conventional I-pictures or I-pictures and P-pictures and performing the backward reproduction, the reproduced picture is a skipped picture not including the B-picture. There has been a problem that the reverse reproduction image has awkward movement.

Further, the down-sampled image is held,
When reading in reverse order and performing reverse playback, in addition to deteriorating the image quality, in order to switch from normal playback to reverse playback, the mode must be switched and then the decoding of one GOP worth of images must be completed before the reverse playback is performed. Since the image cannot be output, there is a problem that the response from receiving the instruction of the backward reproduction to displaying the image is poor.

SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to provide an image reproducing method and apparatus capable of obtaining a reverse reproduced image having a smooth motion. It is another object of the present invention to provide an image reproducing method and apparatus capable of performing reverse reproduction without deteriorating image quality. The object of the present invention is
An object of the present invention is to provide a fast-response image reproducing method and apparatus in which the time from when an instruction for reverse reproduction is received until an image is displayed is reduced.

[0018]

SUMMARY OF THE INVENTION In order to achieve the above object, according to the present invention, a decoded image obtained by decoding encoded moving image data is written into a memory, and the decoded image is read from the memory to output a moving image. The image playback method
Image reproduction in which a plurality of forward-decoded images are stored in the memory, and a plurality of forward-decoded images stored in the memory are read out in reverse order and output to perform reverse reproduction of a moving image. Is the way.

According to the present invention, there is provided an image reproducing method for writing a decoded image obtained by decoding encoded moving image data to a memory, reading the decoded image from the memory and outputting a moving image. After displaying by reproduction, a plurality of displayed images are held in the memory, and at the time of reverse reproduction, the displayed plurality of images stored in the memory are read out in reverse order and output to output a moving image. This is an image reproducing method whose main purpose is to perform reverse reproduction.

The present invention also provides decoding means for decoding encoded moving image data, a memory for holding the decoded image decoded by the decoding means, and a method for reading out the decoded image held in the memory to read the moving image. In an image reproducing apparatus that outputs a region, an area allocating unit that allocates an area in the memory in which a forward decoded image is to be stored, and a reproducing order storing unit that stores a reproducing order of a plurality of images held in the memory. Read control means for controlling reading from the memory for image reproduction, and when performing reverse reproduction, the read control means holds the data in the memory in a reverse order of the order stored by the reproduction order storage means. An image reproducing apparatus has a gist of reading a decoded image that has been read.

The present invention also provides decoding means for decoding encoded moving image data, a memory for holding the decoded image decoded by the decoding means, and a method for reading the decoded image held in the memory to read the moving image. In an image reproducing apparatus that outputs the image, an area allocating unit that allocates an area in the memory in which a plurality of forward decoded images are to be stored so as to be able to hold the most recently reproduced image in the forward direction, Playback order storage means for storing the playback order of the plurality of images, and readout control means for controlling readout for image playback from the memory, and when performing reverse playback, the playback order storage means An image reproducing apparatus, wherein the read control unit reads a plurality of images including a reproduced image held in the memory in a reverse order of storage order.

[0022]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of an image reproducing apparatus according to the present invention.
An example in which image data encoded using is reproduced will be described.

In FIG. 1, an image reproducing apparatus 1 includes an input buffer 3 into which coded image data is input, a variable length decoding unit 5 for decoding variable length coded quantized transform coefficients, and quantization step information. , An inverse DCT unit 9 for decoding an intra-frame encoded image by inverse discrete cosine transform, a forward reference image, a backward reference image, and motion vector information. A motion compensating unit 11 for decoding an image subjected to inter-frame predictive coding, an output I / F unit 13, a memory I / F unit 15, and a memory 17 having a storage capacity for a plurality of frames.

The memory I / F unit 15 includes the write control unit 2
1, forward / reverse reproduction control unit 23, read control unit 2
5, a thinning control unit 27, an area allocating unit 29, and a reproduction order storage unit 31 for controlling the interface between the memory 17, the motion compensation unit 11, and the output I / F unit 13.

The write control unit 21 of the memory I / F unit 15
The image is written in the storage area of the memory 17 allocated by the area allocating unit 29 described later. Forward / reverse playback controller 2
3 is forward playback, slow playback, reverse playback,
It performs overall control of normal playback such as stop motion and trick play.

The read control unit 25 controls reading of a forward reproduced image, reading of a backward reproduced image, and reading of a forward reference image and a backward reference image referred to by the motion compensation unit 11. The area allocating unit 29 performs area allocation of the memory 17 in which the decoded image is to be written, and controls a displayed image to be stored in the memory 17.

When there is no more free area to be allocated by the area allocating section 29, the thinning control section 27 determines which image is to be thinned and instructs the area allocating section 29. The reproduction order storage unit 31 stores a forward reproduction order of a plurality of images decoded in the forward direction.

Encoded image data input from a disk device such as an external DVD player, a VTR, a VOD, etc. is input to an input buffer 3, a variable length decoding unit 5, an inverse quantization unit 7, an inverse DCT unit 9, Compensation unit 11, memory I / F1
5 is decoded on the memory 17 using the output I / F 13
The decoded image is output to a display device or the like via the.

FIG. 2 is an image reproduction diagram for explaining the operation of the image reproduction apparatus 1 of FIG.
The example which is comprised by the frame is shown. FIG. 2 (a)
Indicates an example of forward reproduction, and X, X + 1, X + 2, X +
Each GOP of 3, X + 4 is one I picture,
It is assumed that one P picture and two B pictures are included.

Each GOP is a closed GOP in which images in the GOP can be reproduced independently from other GOPs.
The data is read from the storage medium in the order of an I picture, a P picture, a B picture, and a B picture. The forward reproduction order is an I picture, a B picture, a B picture, and a P picture.

In reverse reproduction in a conventional image reproducing apparatus, for example, as shown in FIG. 2B, only I pictures are extracted from each GOP, and the same I picture is repeatedly displayed for the display period of each GOP. Therefore, the reverse reproduction image has a discontinuous motion.

When the coded image data shown in FIG. 2 is reproduced in the reverse direction, the coded image data is coded using motion compensation prediction, so that it can be read in the GOP unit in the reverse direction. The order of decoding within a GOP cannot be changed.

Therefore, in the present invention, the image areas of the memory 17 which have been displayed by the area allocating section 29 in FIG.
It operates so as to be re-allocated as a decoded image storage area (see FIG. 2), holds the decoded image in the memory 17, and controls the readout according to the reverse of the forward reproduction order stored in the reproduction order storage unit 31. The reading is performed by the unit 25 to perform reverse reproduction.

Here, in the case of the example of FIG. 2, the capacity of the memory 17 needs to be four frames, and the reference memory for holding the forward reference image and the backward reference image at the time of decoding. Note that a minute is included.

For forward reproduction, the area allocating unit 2
3, as shown in FIG. 3, the image area whose display has been completed is not immediately reallocated as the decoded image storage area, but is reallocated in the order from the oldest display end. By allocating the area of the memory 17 in this way,
When switching from forward playback to reverse playback mode,
Since the displayed images held in the memory can be displayed again in the reverse order, it is possible to output the reverse reproduction image without interruption.

When displaying the reverse reproduction image, GO
Since it is necessary to perform decoding from the beginning of P and read in reverse order, even if the mode is changed from the forward playback mode to the backward playback mode, the image decoded in the reverse playback mode cannot be displayed immediately. By holding the image decoded and displayed in the reproduction mode in the memory 17, the time lag from the switching to the reverse reproduction mode to the output of the reverse reproduction image can be absorbed.

Here, if the number of image frames in one GOP is large and the amount of memory for holding the decoded image is not enough, as shown in FIG. 5 from the thinning control unit 27 to the writing control unit 21 so as not to write the data into
As shown in (1), the thinning control unit 27 instructs the area allocation unit 29 to overwrite the held image. In this case, when performing reverse playback, smooth reverse playback is performed as long as the capacity of the memory 17 permits.

When the number of frames in one GOP is known in advance, as shown in FIG. 4B, the decoded image to be written in the memory 17 is sampled and held, so that the reproduced image is reproduced in the reverse direction. In addition, it is possible to reduce awkward reproduction.

In this embodiment, for simplicity of description, each GOP is assumed to be a closed GOP in which an image in a GOP can be reproduced independently from another GOP, and an I picture is arranged at the head of the GOP. Although the above example has been described, the present invention can be applied to a moving image having a GOP configuration other than the closed GOP.

As a decoding and display method at the time of reverse reproduction in this case, a B picture and a P picture transmitted prior to an I picture in each GOP are not decoded, and a substitute picture (I picture) is decoded. The GOP (n-1) is displayed, or the previous GOP (n-1) in chronological order is preempted and this GOP (n
It is sufficient to decode the I picture and P picture of -1) and decode the B picture or P picture at the head of GOP (n) using the decoded image as a forward reference image.

As an application example of the present invention, when the MP @ ML MPEG2 decoder is used to decode the MP @ ML encoded image data, the decoding memory provided for the HL has an extra capacity. Using this extra decode memory, without the need for additional memory,
Since an ML image of about 5 frames can be held in the memory, smooth reverse reproduction and fast response reverse reproduction can be realized.

[0042]

As described above, according to the present invention, it is possible to provide an image reproducing method and apparatus capable of obtaining a reversely reproduced image having a smooth motion. Further, according to the present invention, it is possible to provide an image reproducing method and apparatus capable of performing reverse reproduction without deteriorating image quality. Further, according to the present invention, it is possible to provide a fast-response image reproducing method and apparatus in which the time from when a reverse reproduction instruction is received to when an image is displayed is reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of an image reproducing apparatus according to the present invention.

FIG. 2 is a diagram illustrating dynamic area allocation of a memory when performing reverse reproduction according to the embodiment.

FIG. 3 is a diagram illustrating dynamic allocation of memory when shifting from forward reproduction to reverse reproduction.

FIG. 4 is a diagram illustrating a method of thinning out a decoded image according to the embodiment when storing the decoded image in a memory.

FIG. 5 is a diagram illustrating a method of performing overwriting when a decoded image is stored in a memory according to the embodiment.

FIG. 6 is a diagram showing the order of encoding and decoding of an image in MPEG.

FIG. 7 shows a GOP for each image in a conventional image reproducing apparatus.
It is a figure which shows the procedure at the time of performing the reverse reproduction | regeneration within.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Image reproduction apparatus, 3 ... Input buffer, 5 ... Variable length decoding part, 7 ... Inverse quantization part, 9 ... Inverse DCT part, 11 ... Motion compensation part, 13 ... Output I / F part, 15 ... Memory I / Part F, 17
.., Memory 21, write controller 23, forward / reverse playback controller 25, read controller 27, thinning controller 29, area allocator 31, playback order storage

Claims (8)

[Claims] 1. An image reproducing method for writing a decoded image obtained by decoding encoded moving image data to a memory, reading the decoded image from the memory and outputting a moving image, comprising the steps of: An image reproducing method, comprising: performing reverse reproduction of a moving image by storing the plurality of forward-decoded images stored in the memory in a reverse order and storing the same in a memory; 2. An image reproducing method for writing a decoded image obtained by decoding encoded moving image data to a memory, reading the decoded image from the memory and outputting a moving image, wherein the decoded image is displayed by forward reproduction. Thereafter, the displayed plurality of images are held in the memory, and when the image is played in the backward direction, the displayed plurality of images held in the memory are read out in reverse order and output to output the moving image in the reverse direction. An image reproducing method characterized by performing reproduction. 3. The image reproduction according to claim 1, wherein when the forward-decoded image is written to the memory or the displayed image is held in the memory, the image is decimated. Method. 4. When writing a forward-decoded image in the memory or holding a displayed image in the memory, if there is no free space in the memory, the image already stored in the memory is overwritten. 4. The image reproducing method according to claim 1, wherein the image is decimated by performing image thinning. 5. A decoding means for decoding encoded moving image data, a memory for holding a decoded image decoded by the decoding means, and a decoded image held in the memory is read to output a moving image. In the image reproducing device, an area allocating unit that allocates an area in the memory in which the forward-decoded image is to be stored; a reproducing order storing unit that stores a reproducing order of a plurality of images stored in the memory; Read-out control means for controlling read-out for image reproduction, and when performing reverse reproduction, the read-out control means is held in the memory in reverse order of the order stored by the reproduction order storage means. An image reproducing apparatus for reading a decoded image. 6. A decoding means for decoding encoded moving image data, a memory for holding a decoded image decoded by the decoding means, and a decoded image held in the memory is read to output a moving image. In the image reproducing apparatus, an area allocating unit that allocates an area in the memory in which a plurality of forward-decoded images are to be stored so as to be able to hold the most recently reproduced image in the forward direction, and a plurality of areas held in the memory. A reproduction order storage unit that stores an image reproduction order; and a read control unit that controls reading from the memory for image reproduction. When the reproduction is performed in the reverse direction, the reproduction order storage unit stores the order. An image reproducing apparatus, wherein the read control unit reads a plurality of images including a reproduced image held in the memory in reverse order of the above. 7. The image reproducing apparatus according to claim 5, wherein the area allocating unit performs image thinning when instructing to hold the decoded image in the memory. 8. The area allocating means, when instructing the storage of the decoded image in the memory, if there is no free area in the memory, overwrites the area in which the decoded image or the reproduced image is already stored. 8. The image reproducing apparatus according to claim 5, wherein the area is allocated so as to perform the following.