JPH04336896A - Moving picture storage device - Google Patents

Abstract

PURPOSE:To attain high picture quality and high performance by preventing deterioration in picture quality for a prescribed period after a scene change and implementing sure coding processing without incurring information missing of a picture data of a scene change frame and storing the above coding data. CONSTITUTION:A scene change detection means 41 detects a scene change frame from a moving picture data to be inputted. A coded data S8a resulting from coding the picture data of the frame detected as the scene change frame at a variable length coding means 8 is tentatively stored in a storage means 52 able to input/output a high speed data. An input output control means 42 reads a coded data from the storage means 52 for a prescribed period from a frame succeeding to the scene change frame and stores it to a storage means 61 whose capacity is large but whose data input output speed is medium through a data bus 11.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a moving image storage device used in videophone calls, video conferences, etc., and particularly to a coding system for images immediately after a scene change.

0002

[Prior Art] Conventionally, technologies in this field include:
For example, there were some documents described in the following.

[0003]Reference 1: Ai Ii Transactions on Communications (
IEEE TRANSACTIONS ON COMM
UNICATIONS) COM-32 [3] (198
4-3) (US) H. H. CHEN et al. “Scene Adaptive Coder (Scene Adaptive C
order) ”P. 225-232 Reference 2; C.C.I.T.S.
GXV Recommendations (CCITT SGXV Recommendations)
dation)H. 261 Document 3; JP-A-2-222
No. 388 Publication Document 2 describes a standard moving image storage device that compresses and encodes information on moving image data. The configuration will be explained below using figures.

FIG. 2 is a functional block diagram showing an example of the configuration of a conventional moving image storage device.

[0005] This moving image storage device includes, for example, individual circuits,
Alternatively, it may be constructed under computer program control or the like, and has an image input means 1 for inputting a video signal (moving image signal) Si from a television camera or the like. Connected to the output side of the image input means 1 are an intra-frame/inter-frame determination means 2, a current frame image storage means 3, and an image selection means 5. A previous frame image storage means 4 is connected to the input side of the intra-frame/inter-frame determination means 2 and the image selection means 5.

Connected to the output side of the image selection means 5 are orthogonal transformation means 6, quantization means 7, and variable length encoding means 8 having a buffer. A code amount control means 9 is connected to the output side of the variable length encoding means 8, and a decoded image calculation means 10 is further connected to the output side of the quantization means 7. Further, an encoded data storage means 12 is connected to the output side of the variable length encoding means 8 via a data bus 11.

Next, the operation of FIG. 1 will be explained with reference to FIG.

FIG. 3 is a diagram showing an example of block division in FIG. 2, and this diagram shows an example of the number of divisions of 10. Note that the number of divisions may be any number.

In FIG. 2, when a moving image signal Si is input to the image input means 1, the image input means 1 performs analog/digital conversion (hereinafter referred to as A/D conversion) of the moving image signal Si. As shown in FIG. Image data S1 is spatially divided into a plurality of processing blocks.

The intra-frame/inter-frame determining means 2 selects the current frame image data S1 in the order of the divided processing blocks.
and previous frame image data S4, which is a decoded image of the image of the frame (predetermined unit time) immediately before the current frame image data S1, are input, and the gap between the current frame image data S1 and the previous frame image data S4 in the processing block is inputted. and the amount of density variation within the processing block of the current frame image data S1 are compared. When the correlation is large, the subsequent processing is performed using interframe difference data between the current frame image data S1 and the previous frame image data S4 (interframe mode), and when the correlation is small, the subsequent processing is performed using the interframe difference data of the current frame image data S1 and the previous frame image data S4 (interframe mode). Determine which is appropriate (intra-frame mode) using the current frame image data S1,
The intra-frame/inter-frame determination result S2 is output to the image selection means 5. An example of this intra-frame/inter-frame determination method will be described next.

[0011] The current frame image data S1 is converted to fc(i,j
) (i: horizontal pixel address, j: vertical pixel address), the previous frame image data S4 is fp(i, j),
When the horizontal start address of the processing block is xs, the horizontal end address is xe, the vertical start address is ys, and the vertical end address is ye, the intra-frame/inter-frame determining means 2 calculates the following equation (1), (2) A, B
Calculate. Then, if either condition (i) or (ii) of the following equation (3) is satisfied, it is determined that the mode is between frames, and if neither of them is satisfied, it is determined that the mode is intra-frame, and the intra-frame/inter-frame determination result S2 Output. (i) A≧B (ii) A≦THL1 (predetermined threshold)
...(3) The image selection means 5 selects the intra-frame/inter-frame determination result S2
Accordingly, when the intra-frame mode is determined, the current frame image data S1 is selected, and when the inter-frame mode is determined, inter-frame difference data between the current frame image data S1 and the previous frame image data S4 is calculated,
The orthogonal transform means 6 selects the calculated inter-frame difference data and uses the selection result as encoded input image data S5.
Output to.

[0012] The orthogonal transformation means 6 is based on the encoded input image data S5.
Transform (hereinafter referred to as DCT) calculation is performed to calculate the magnitude of the frequency spectrum of the image data based on the following equation (4), and orthogonal transform data S6 is output to the quantization means 7.

[0013]

[Math 1]

The orthogonal transformation data F(u,v) output as a result of the transformation process using equation (4) takes a relatively large value in an area where u, v are small, and a small value in an area where u, v is large. The general tendency is to take . This is because the density distribution of the image has large spatial redundancy, and the probability of occurrence of parts with extremely large fluctuations is low.

The quantization means 7 uses the orthogonal transform data S6 and the quantization step width S output from the code amount control means 9.
9, and outputs the quantized data S7 to the variable length encoding means 8 and the decoded image calculating means 10, for example, by a method according to the following equation (5).

[0016]

[Math 2]

However, QP; quantization step width QF(u,
v); Through the processing in the quantization data quantization means 7, the orthogonal transformation data F(
The quantized output becomes 0 for small components of u, v). The larger the number of 0s, the easier it is to compress data.

In the variable length encoding means 8, the quantized data S
7, a predetermined code is assigned so that the code length is relatively small with respect to the magnitude of the probability of occurrence of that value, and the assigned code is passed through the data bus 11 of the system as encoded data S8a. At the same time, the code amount S8b allocated to one processing block is output to the code amount control means 9.

The code amount control means 9 inputs the code amount S8b for each processing block, determines a quantization step width S9 considered to be appropriate, and outputs it to the quantization means 7. An example of the control direction of this quantization step width S9 is described in the above-mentioned document 1. The basic idea is as follows.

The standard code amount of one processing block is BS, and the code amount S8b when actually encoded is BR(m
)(m; block number), quantization step width S9 is qp
(m), this quantization step width qp(m) is obtained from the following equation. However, α is a positive number,
A value proportional to the reciprocal of the buffer capacity inside the device that buffers encoded data As shown in equation (6), when the sum of the code amounts S8b is larger than the sum of the standard code amounts BS, qp(m) is increased to reduce the amount of code for the next processing block. Conversely, when the sum of the code amounts S8b is smaller than the sum of the standard code amounts BS, the final code amount S9 can be made reasonable by decreasing qp(m) and increasing the code amount of the next processing block. value.

The decoded image calculation means 10 inputs the quantized data S7 of each processing block, and performs the following steps (i) and (ii).
), (iii), the decoded image is calculated and the contents of the previous frame image storage means 4 are updated as the previous frame image data S4.

(i) The inverse quantization processing block number is m, the quantization step width S9 used during quantization is qp(m), and the quantization data S7 is QF(
m) (u, v), and inverse quantized data IQF (u, v)
is obtained from the following equation (7). IQF(m)(u,v)=QF(m)(u
,v)×qp(m)...(7)(ii) Inverse DCT Perform the operation opposite to equation (4) to obtain the inverse DCT output data fi(
i, j) is obtained from the following equation (8).

[0023]

[Math 3]

[0024] However, N, C(u), C(v); Same as the definition of equation (4) (iii) Decoded image calculation Decoded image (reproduced image) is fr(i, j), previous frame image storage means Previous frame image data S4 read from S4
Let fm(i,j) be. When the intra-frame/inter-frame determination result S2 is (a) intra-frame mode fr(i,j)=fi(
i, j)...
(9) (b) When in interframe mode fr(i,j)=fi(
i, j)+fm(i, j)...(10)(a),
In the case of (b), in both cases, the decoded image fr for one block is
After calculating (i, j), the fr(i, j) is stored in the previous frame image storage means 4 as the previous frame image data S4.
Write to.

[0025] In the manner described above, encoding and storage of moving image data are performed.

Next, countermeasures taken immediately after a scene change will be explained.

On the screen immediately after the scene change, the intra-frame/inter-frame determination result S2 is output as intra-frame mode in most processing blocks, so the code amount S8b rapidly increases. The encoded data storage means 12 is composed of a hard disk, a magneto-optical disk, etc. Although such encoded data storage means 12 has a large storage capacity (
500 Mbytes to 16 bytes), and the data transfer rate is medium (1 Mbit/s to 10 Mbit/s).

Therefore, this encoded data storage means 12
Now, encoded data S8 with a code amount S8b that has rapidly increased.
It is impossible to accumulate the data a within a short time, and the data transfer time to the buffer in the variable length encoding means 8 is not enough, and the amount of encoded data remaining in the buffer (hereinafter referred to as the buffer) There is a risk that the remaining buffer capacity may overflow.

In order to avoid this overflow, in subsequent frames, the quantization step width S9 is increased or a processing block that stops encoding is generated, so that the remaining buffer capacity is free from the risk of overflow. Although attempts are made to keep it within a certain range, there is a problem in that overall image quality deteriorates.

Conventionally, in order to solve this problem, the technique disclosed in Document 3 takes the following measures. That is,
During a certain frame period after a scene change, the code amount S8 can be increased by increasing the quantization step width S9 or by taking the maximum value of the predetermined quantization step width S9.
Suppress the rapid increase in b. This eliminates the need for exceptional processing such as the occurrence of encoding aborted blocks.
The code amount S8b can be kept constant.

[0031]

However, the scene change countermeasure method described in Document 3 has the following problems.

Since the quantization step width S9 is set large for a certain period after a scene change, although the code amount S8b is stabilized, image quality deterioration cannot be avoided. In particular, since the screen after a scene change includes completely new information, deterioration in image quality is not desirable. In the conventional countermeasure, since the quantization step width S9 is set to a large value immediately after the scene change, the information of the original image is completely lost, and it takes a considerable amount of time to return to the encoding process until a high-quality restored image is obtained. It takes.

The present invention provides a moving image storage device that solves the problems of the prior art, such as image quality deterioration and performance deterioration.

[0034]

[Means for Solving the Problems] The present invention inputs moving image data frame by frame, compresses and encodes the data, and
In a video storage device that outputs the coded data to a data bus and stores it, the video storage device includes a scene change detection means for detecting the occurrence of a scene change during the input of the video data; The apparatus further includes a storage means for temporarily storing scene change frame encoded data in moving image data of a frame in which change occurrence is detected.

[0035]Furthermore, a first storage means that finally stores the encoded data of the scene change frame, and a second storage means that finally stores the encoded data of the moving image data of all frames except the scene change frame. reading out the scene change frame encoded data temporarily stored in the storage means during a certain period from the frame immediately after the scene change frame;
Input/output control means for causing storage to be stored in the first storage means via the data bus is provided.

[0036]

According to the present invention, since the moving picture storage device is configured as described above, the scene change detection means detects a scene change frame in the moving picture data that is being input. The encoded data for the image data of the frame detected as the scene change frame is temporarily stored in the storage means. The input/output control means reads the encoded data of the scene change frame stored in the storage means during a fixed period of time from the next frame of the scene change frame, and stores it in the first storage means via the data bus. As a result, the amount of encoded data remaining in the device can be kept constant, and encoding can be performed and the encoded data can be stored without causing information loss in the image data of the scene change frame. Therefore, the above problem can be solved.

[0037]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a functional block diagram of a moving image storage device showing an embodiment of the present invention, and elements common to those in the conventional FIG. 2 are given the same reference numerals.

In this moving picture storage device, in place of the conventional intra-frame/inter-frame determining means 2 and code amount control means 9, intra-frame/inter-frame determining means 20 having a different configuration is used.
and code amount control means 30 are provided. Furthermore, the scene change control means 40 and output buffers 50 and 51 are connected to the output side of the variable length encoding means 8, and the output side of the output buffer 51 is connected to the data bus 11 via the storage means 52 and the output buffer 53. It is connected to the. Storage means 60 and 61 are connected to this data bus 11.

The scene change control means 40 inputs the current frame image data S1, the previous frame image data S4, and the code amount S8b, and detects a scene change and controls the input/output of encoded data for a certain period immediately after the scene change. It has the function of performing the following, and is composed of scene change detection means 41 and input/output control means 42. The scene change detection means 41 has a function of detecting the occurrence of a scene change during the input of moving image data and outputting an intraframe encoding command signal S41 to the intraframe/interframe determination means 20. The input/output control means 42 controls the input/output of encoded data for a certain period immediately after a scene change, so it sends a write command signal S42a, which is an encoded data output control signal.
Output S42b and S42c to output buffers 50 and 51
, 53 are turned on.

The storage means 52 is for temporarily storing scene change frame encoded data in the moving image data of the frame in which it is determined that a scene change has occurred, and is an IC memory or the like capable of high-speed data input/output. It is configured. The storage means (second storage means) 60 has a normal scene encoded data storage function to finally store encoded data for the moving image data of all frames except scene change frames, and has a data input/output speed. It is medium-sized, but consists of large-capacity hard disks and magneto-optical disks. Accumulation means (first accumulation means) 61
The storage means 60 finally stores the scene change frame encoded data, and like the storage means 60, the data input/output speed is moderate, but it is composed of a large-capacity hard disk, magneto-optical disk, or the like.

Next, the operation of FIG. 1 will be explained with reference to FIG.

FIG. 4 is a diagram showing an example of the operation of the encoded data output control method shown in FIG. 1, and shows the encoded data output operation waveform immediately after a scene change.

In FIG. 1, image input means 1, current frame image storage means 3, previous frame image storage means 4, image selection means 5, orthogonal transformation means 6, quantization means 7, variable length encoding means 8, and decoding means The operation in the image calculation means 10 is as follows:
The scene change detection operation (1) and encoded data output control operation (2), which are different from the conventional operation, will be explained below because they are almost the same as the conventional operation shown in FIG.

(1) Scene change detection operation Scene change detection means 41 in scene change control means 40
calculates the following equation (11) based on the current frame image data fc (i, j) and the previous frame image data fr (i, j), and determines whether the calculation result Err satisfies the following equation (12). Detect whether or not. However, xω: number of pixels in the horizontal direction of the image yω; number of pixels in the vertical direction of the image Err>THLS (predetermined threshold)
(12) When the equation (12) is satisfied, it is assumed that a scene change has been detected.

Note that the scale used for the judgment is (11), (
12), and the current frame image data fc (i, j) and the previous frame image data fr (i,
j) It is also possible to detect scene changes using other evaluation measures such as city distance, etc., as long as the evaluation measures express the correlation between the two.

(2) Encoded data output control operation When the scene change detection means 41 does not detect a scene change frame, that is, when it is not during the scene change frame encoding period, the scene change detection means 41 outputs a write command signal S42a to output the write command signal S42a to the output buffer 50. Turn on. Then, the encoded data S8a for the normal frame image other than the scene change scene outputted from the variable length encoding means 8 is transferred to the data bus 1.
1 and stored in the storage means 60.

When the scene change detection means 41 detects a scene change as shown in FIG. 4, it outputs an intraframe encoding command signal S41 to the intraframe/interframe determination means 20 during the scene change frame encoding period. do. The intra-frame/inter-frame determination means 20 outputs the intra-frame/inter-frame determination result S20 to the image selection means 5 while receiving the intra-frame encoding command signal S41, and specifies intra-frame encoding. This is because there is no correlation with the previous frame image data S4 in the scene change frame, so it is meaningless to use interframe difference data for encoding.

The image selection means 5 selects the block-divided current frame image data S1 and outputs it to the orthogonal transformation means 6 in the form of encoded input image data S5. The orthogonal transformation means 6 converts D based on the encoded input image data S5.
The orthogonal transformation data S6 is quantized by means 7 of performing CT calculations, etc.
Output to. The quantization means 7 quantizes the orthogonal transformation data S6 based on the encoding step width S30 output from the code amount control means 30 and outputs quantized data S7 to the variable length encoding means 8 and the decoded image calculation means 10. do.

The variable length encoding means 8 converts the quantized data S7
Based on this, a predetermined code is assigned so that the code length is relatively small with respect to the magnitude of the probability of occurrence of that value, and the assigned code is output to the buffer 51 as encoded data S8a for the scene change frame image. Output to.

The input/output control means 42 in the scene change control means 40 outputs the write command signal S42b to turn on the output buffer 51 during the scene change frame encoding period. As a result, the encoded data S8 of the scene change frame output from the variable length encoding means 8
a is written into the storage means 52. The scene change control means 40 inputs the code amount S8b of the scene change frame for each processing block output from the variable length encoding means 8, and performs the encoding of the scene change frame by cumulatively adding the code amount S8b. Calculate the amount of data.

As shown in FIG. 4, the input/output control means 42 in the scene change control means 40 controls the encoding start time t of the frame image input next to the scene change frame.
When it becomes 0, the write command signal S42c is output to turn on the output buffer 53. Then, the encoded data of the scene change frame image stored in the storage means 52 is stored in the storage means 61 via the data bus 11. Thereafter, as shown in FIG. 4, when the output end time t1 of the encoded scene change frame data stored in the storage means 52 is reached, the write command signal S4 of the input/output control means 42 is reached.
2c is completed, and the output buffer 53 is turned off.

In FIG. 4, encoded data is output to both storage means 60 and 61 via data bus 11 from time t0 to time t1. However, the data transfer capacity of the data bus 11 is large and high-speed transfer (100Mb
It/s), the input/output control means 42 can transfer data to both the storage means 60 and 61 in a time-sharing manner. Therefore, even in a scene change scene, the encoded data can be stored in the storage means 60 without deteriorating the image quality.
61, and the performance of the moving image storage device can be improved.

[0053] Note that the present invention is not limited to the above embodiments,
Various modifications are possible, such as configuring storage means 60 and 61 with the same storage medium, for example.

[0054]

As described above in detail, according to the present invention, a scene change detection means detects a scene change frame for moving image data that is being input, and a code that encodes the image data of the scene change frame is detected. The converted data is temporarily stored in a storage means capable of high-speed data input/output. Then, the input/output control means reads the encoded data of the scene change frame stored in the storage means during a fixed period of time from the next frame of the scene change frame, and transfers it to the first storage means via the data bus. The data is stored at a speed corresponding to the data transfer speed of the storage means. Therefore, encoding can be performed and the encoded data can be stored in the first and second storage means without causing information loss in the image data of the scene change frame. Therefore, it is possible to realize a moving image storage device with high image quality and high performance.

[Brief explanation of the drawing]

FIG. 1 is a functional block diagram of a moving image storage device showing an embodiment of the present invention.

FIG. 2 is a functional block diagram of a conventional moving image storage device.

FIG. 3 is a diagram showing an example of block division in FIG. 2;

FIG. 4 is a diagram illustrating an operation example of the encoded data output control method of FIG. 1;

[Explanation of symbols]

Claims (1)

[Claims] [Claim 1] Inputting moving image data for each frame,
In a video storage device that compresses and encodes data and outputs the encoded data to a data bus for storage, scene change detection means detects the occurrence of a scene change during input of the video data. , storage means for temporarily storing encoded scene change frame data in the moving image data of the frame in which the occurrence of a scene change has been detected by the scene change detection means; and a storage means for finally storing the encoded scene change frame data. a second storage means for finally storing encoded data in the moving image data of all frames except the scene change frame; A moving image characterized by comprising: input/output control means for reading out the encoded scene change frame data temporarily stored in the storage means and storing it in the first storage means via the data bus. Image storage means.