JPH08331556A - Image coder and image coding method - Google Patents

Abstract

PURPOSE: To provide the moving image coder and its method applying high speed variable rate coding to a series of image data so as to be stored within a prescribed capacity. CONSTITUTION: A reproduction control section 20 and a reproduction section 30 interleave an image among a series of image data based on selection information from a selection section 10 to reproduce the data and a coding section 40 codes the data. A data interpolation section 60 estimates data production amount of image data not selected based on the data production amount of the coded image data. Thus, the data quantity for coding for each image is allocated based on the data production quantity of a series of image data, data production quantity of each image and a recording capacity of the recording medium. Then a VTR tape 9 is again reproduced and a quantization rate of a quantization section of the coding section 40 is controlled so that the data quantity of the coded bit stream is same data quantity allocated as above and the result is sequentially coded.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image coding apparatus for variable-speed coding image data and an image coding method.

[0002]

2. Description of the Related Art Considering the method of encoding an image in terms of controlling the amount of data, it is classified into fixed rate encoding and variable rate encoding. FIG. 5 is a diagram showing the relationship between the reproduction time and the encoding bit rate when certain continuous image data is encoded by the fixed rate encoding and the variable rate encoding, respectively. As shown in FIG. 5, in fixed rate coding, the bit rate is always constant. Further, in variable rate coding, the bit rate changes depending on the complexity of the scene. Since the period a is a relatively difficult scene period, the amount of generated data is large, and the periods b ₁ and b ₂ are relatively simple scenes, so that encoding can be performed at a low bit rate.

As described above, in variable rate coding, a large amount of data is assigned to a complicated image and a small amount of data is assigned to a simple image, so that encoding can be performed while maintaining a homogeneous image. On the other hand, in the fixed rate coding, in the period a in which the information generation amount is large, the information is insufficient as shown in the area A of FIG.
_{In 1} and b ₂ , excessive information is encoded as shown in area B in FIG. Therefore, when focusing on the image quality, the variable rate coding is generally considered to be a more effective coding method.

By the way, image data of a certain recording time is
When recording on a recording medium having a limited recording capacity, such as a digital video disc (DVD) device, the encoding rate must be controlled so that the image data can be recorded on the recording medium. In such a case, if fixed rate coding is performed, a bit rate R _f that satisfies Expression 1 is obtained, and the entire image data is coded at this bit rate R _f .

[0005]

[Number 1] _{R f × T ≦ S ··· (} 1) , however, R _f, coding bit rate, T is, Duration of the image data, S is a capacity of the recording medium.

When variable rate coding is performed,
In order to record all of the image data, a recording area is calculated backward from the recording capacity, a recording area is allocated to each image data, the encoding bit rate of each image is obtained based on the recording area, and encoding is performed at that bit rate. Specifically, for example, as shown in FIG. 6, the image data is divided into scenes for each time t, and for each scene i, a data amount d suitable for that scene
(I) is set, a bit rate satisfying, for example, Expression 2 is obtained for each scene based on the ratio of the data amount d (i) in all image data, and the bit rate of that scene is calculated at that bit rate. It will be encoded.

[0007]

## EQU00002 ## _R.sub.v (i) .times.t.ltoreq. (S.times. (D (i) / D)) (2) where _R.sub.v (i) is the coding bit rate of the image data of scene i, t is the time of the scene i, S is the capacity of the recording medium, i is the scene number, d (i) is the encoded data amount of the image data of the scene i, and D is the data amount of all the image data. D = Σd (i).

[0008]

However, when image data is recorded by variable rate coding on a recording medium having such a predetermined recording capacity, the amount of data in each scene of the image data as described above is increased. In order to allocate the data, it is necessary to investigate the data amount of each scene prior to the actual encoding, and there is a problem that the encoding process as a whole takes a very long time. That is, the image data is reproduced once, encoded, the amount of generated data is checked, and the amount of data is assigned to each scene based on the result,
Then, it is necessary to perform the process of reproducing the image data again and performing the variable rate coding, which requires a processing time about twice as long as the time for reproducing the image data. This is a major obstacle to efficient work when a program such as a movie is to be sequentially recorded on a recording medium such as a DVD by variable rate coding, and improvement is desired.

Therefore, an object of the present invention is to provide an image coding apparatus capable of performing a variable rate coding process of the supplied image data so that the entire image data has a predetermined capacity or less in a shorter time. It is in. Another object of the present invention is to provide an image coding method capable of performing such variable rate coding processing in a shorter time.

[0010]

In order to solve the above-mentioned problems, in the preliminary reproduction for investigating the data amount of each scene of the image data, the image data is selectively reproduced, that is, thinned and reproduced. The encoded data amount of each scene of the original image data is obtained based on the data generation amount of the reproduced image.

Therefore, the image coding apparatus of the present invention is
Image selecting means for selecting image data to be used for preliminary reproduction from continuous image data, and reproducing means for reproducing only the selected image data during preliminary reproduction and sequentially reproducing the continuous image data during main reproduction. An encoding means for variable-rate-encoding the reproduced image data, and the selected continuous image data based on the data generation amount of the selected image data variable-rate encoded at the time of preliminary reproduction. A data generation amount interpolating means for interpolating a data generation amount of image data other than image data, a data generation amount of each image data of continuous image data, and a limit value of the encoded data amount for the entire continuous image data. On the basis of,
A data amount determining means for allocating an encoded data amount to each image data, wherein the encoding means determines the data generation amount of each image data of continuous image data by the data amount determining means during main reproduction. Variable rate coding is performed so that the coded data amount assigned to each image data is equal to or less than the coded data amount.

Specifically, the image selecting means selects image data of continuous image data for each predetermined time, and the data generation amount interpolation means determines the data generation amount in the image data for each predetermined time. Based on this, the data generation amount in the image data at times other than the predetermined time is interpolated by linear interpolation.

More specifically, the image selection means is at least one for each continuous scene of continuous image data.
Select the image data of the frame.

More specifically, the image selecting means selects a plurality of image data from continuous image data based on the input image position information.

More specifically, the image selecting means selects predetermined image data based on an edit list having continuous image data management information.

In the image coding method of the present invention, a plurality of image data used for preliminary reproduction are selected from the continuous image data and reproduced, and the reproduced plurality of image data are variable-rate-encoded, respectively. Images other than the selected plurality of image data of continuous image data are detected based on the respective data generation amounts of the detected plurality of image data by detecting the data generation amounts of the plurality of rate-encoded image data. The data generation amount of the data is interpolated, the encoded data amount is assigned to each image data based on the data generation amount of each image data of the detected and interpolated continuous image data, and the continuous image data is The image is reproduced again, and each image of the continuous image data is variable rate encoded so that the data generation amount is equal to or smaller than the assigned encoded data amount.

[0017]

In the image coding apparatus of the present invention, first, the image selecting means generates information for appropriately selecting image data from continuous image data. The selection method includes sampling at predetermined intervals, selecting a representative image for each continuous scene, inputting by an operator from the outside, or an edit list created when creating image data. Take the method of extracting the appropriate position from such as. Then, the reproducing means reproduces only the image selected based on the selection information in the continuous image data, and the reproduced image is further encoded by the encoding means.

Based on the data generation amount of the coded image data, the data generation amount interpolation means interpolates the data generation amount of the image data other than the selected image data, and each of the continuous image data. Calculate the amount of data generated for an image. Based on the obtained data generation amount of each image, the data amount determination means allocates the encoded data amount when each image is encoded such that the entire continuous image data falls within the target data amount. . Then, during the main reproduction, the reproducing means sequentially reproduces the continuous image data, and the encoding means sequentially encodes the data so that the data amount of each image is equal to or less than the assigned data amount.

In the image coding method of the present invention, first, a plurality of image data are selectively reproduced at high speed from continuous image data, and the reproduced plurality of image data are each coded. Next, the data generation amount of each of a plurality of encoded image data is detected, and based on each data generation amount of the detected plurality of image data, the continuous image data of the unselected image data is detected. Interpolate the amount of data generated. Then, based on the detected and interpolated data generation amount of each image data, the data amount at the time of encoding is assigned to each image data, the continuous image data is reproduced again, and each image is assigned the above-mentioned Variable rate encoding is performed so that the data amount is equal to or less than the obtained data amount.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a moving picture coding apparatus according to an embodiment of the invention.
~ It demonstrates with reference to FIG. The moving picture coding apparatus according to the present embodiment records moving picture data on a recording medium having a predetermined recording capacity, such as a digital video disc (DVD), in other words, a recording medium having a limited recording capacity. Is a moving picture coding device for moving picture coding experts group (MPEG2).
Based on the video coding method), compression, quantization,
Variable rate coding is performed to generate an image bitstream.

First, the configuration of the moving picture coding apparatus according to the present embodiment will be described with reference to FIGS. Figure 1
It is a block diagram which shows the structure of the moving image coding apparatus of a present Example. The moving picture coding device 1 includes a selection unit 10, a reproduction control unit 20, a reproduction unit 30, a coding unit 40, a recording device 50, a data interpolation unit 60, and an allocation determination unit 70.

The selection unit 10 is means for deciding an image to be selectively reproduced in preliminary reproduction and outputting the information to the reproduction control unit 20. In this embodiment, a signal for instructing an image to be reproduced is output to the reproduction controller 20 so that the image is reproduced at a predetermined time interval t.

The reproduction control unit 20 is means for controlling the reproduction unit 30, and the reproduction unit 30 is means for actually reproducing the recording medium based on the control signal from the reproduction control unit 20. In the present embodiment, the reproducing section 30 is a reproducing apparatus for reproducing the image data recorded on the VTR tape, and therefore the reproduction control section 20 and the reproducing section 30 preliminarily reproduce the image data recorded on the VTR tape 9. Playback operation such as normal playback and normal operation, and handling operation such as fast forward and rewind of the VTR tape 9 are performed. The preliminary reproduction is
Based on the selection information input from the selection unit 10, the VTR
This is an operation of sequentially reproducing only a predetermined image selected from the continuous image data recorded on the tape 9. Parts other than the selected image are played back on the VTR tape 9 faster than the normal playback time by performing operations such as fast-forwarding and skipping.

The coding section 40 is a coding means for coding the image data reproduced by the reproducing section 30. Encoding unit 4
0 will be described with reference to FIG. FIG. 2 is a block diagram showing the configuration of the encoding unit 40. Encoding unit 40
Is an adder 101, a DCT unit 102, a quantization unit 103,
Variable-length coding unit 104, inverse quantization unit 105, inverse DCT unit 106, adder 107, frame memory 108, motion detection unit 109, motion compensation unit 110, switching circuit 111,
It has an external I / F 112 and a control unit 113.

The image data input to the encoding unit 40 is
The difference from the input from the switching circuit 111 is obtained in the adder 101, and the difference is output to the DCT unit 102. In the intra picture mode, since no significant image is input from the switching circuit 111, the adder 1
The image data input to 01 is directly applied to the DCT unit 102.
Is output to In the motion compensation prediction mode, image data based on the previous reproduced image is input from the switching circuit 111. Therefore, the difference is obtained by the adder 101,
The error is input to the DCT unit 102.

The DCT unit 102 applies a discrete cosine transform (DCT: D) to the image signal input from the adder 101.
iscrete Cosine Transform) to reduce spatial redundancy. The transform coefficient obtained as a result of the DCT is quantized by the quantizer 1.
It is input to 03. The quantization unit 103 quantizes the transform coefficient obtained by the DCT unit 102 according to the quantization rate input from the control unit 113, and outputs it to the variable length coding unit 104 and the inverse quantization unit 105. The variable length coding unit 104 performs variable length coding on the quantized transform coefficient, generates an image bit stream, and sequentially outputs the image bit stream.

The external I / F 112 is an interface circuit with the recording device 50. The external I / F 112 outputs the data amount of the bit stream generated by the variable length coding unit 104 to the recording device 50 for each image during preliminary reproduction. Further, at the time of actual reproduction, a signal indicating the amount of allocated data recorded in the recording device 50 is read and output to the control unit 113.

The control unit 113 is a control means for controlling the quantization rate of the quantization unit 103, recording of image data in the frame memory 108, which will be described later, and switching of the switching circuit 111. During the main reproduction, the control unit 113
Determines the quantization rate based on the data allocation amount for the image data recorded in the recording device 50 via the external I / F 112.

The transform coefficient quantized by the quantizer 103 is input to the inverse quantizer 105. The transform coefficient is inversely quantized by the inverse quantization unit 105, and further,
In the inverse DCT unit 106, the inverse discrete cosine transform (inverse DC
T) is performed. Then, in the mode in which the motion compensation prediction is performed, the adder 107 adds the image signal subjected to the inverse DCT and the image signal obtained by the motion compensation prediction to restore the original image signal, and the frame memory Record at 108. Intra-picture mode, inverse DCT
The image signal subjected to the inverse DCT in the unit 106 is recorded in the frame memory 108 as it is.

When performing motion compensation prediction, the image signal recorded in the frame memory 108 is used. That is, based on the image signal recorded in the frame memory 108, the motion detection unit 10 detects the next image source signal.
At 9, motion detection is performed to detect a motion vector.
Further, based on the motion vector, the motion compensation unit 11
At 0, motion compensated prediction is performed. Then, the image signal obtained by this motion compensation prediction is output to the adder 101 via the switching circuit 111, and the difference between the input image source signals is obtained.

In the recording device 50, the data generation amount of the selected image output from the encoding unit 40 during the preliminary reproduction, the data generation amount of each image interpolated by the data interpolation unit 60 based on the data, and Is a means for recording the allocation coded data amount for each image obtained by the allocation determining unit 70 based on the data amount, and is a hard disk device in this embodiment.

The data interpolating unit 60 selects between the selected images based on the data generation amount of the selected image data encoded by the encoding unit 40 and recorded in the recording device 50 by the preliminary reproduction. Interpolate the data generation amount for an image that has not been processed. In this embodiment, the data generation amount of those images is estimated by linear interpolation.

The allocation determining unit 70 includes a data interpolating unit 60.
The encoded data amount is assigned to each image based on the data generation amount of each image of the continuous image data obtained as a result of the interpolation and the recording capacity of the recording medium to be recorded. In this embodiment, the coded data amount of the image data within the time is determined for each time t that is the same as the image selection cycle in the selection unit 10 based on the three expressions.

[0034]

Dd (i) = S × (d (i) / D) (3) where dd (i) is the allocated data amount, i is the period number for each time t, and S is , Capacity of recording media, d (i)
Is the data amount of the period i in the interpolated data, D
Is the data amount of all images in the interpolated data.

Next, the operation of the moving picture coding apparatus 1 will be described with reference to FIGS. 3 and 4. 3A and 3B are diagrams for explaining the operation of the moving image encoding apparatus 1, where FIG. 3A is a diagram showing a normal reproduced image, FIG. 3B is a diagram showing the operation of the reproducing unit during preliminary reproduction, and FIG. FIG. 6A is a diagram showing a reproduced image at the time of preliminary reproduction, and FIG. 9D is a diagram showing a data generation amount of the image subjected to preliminary reproduction. FIG. 4 is a diagram showing a data interpolation method of the data interpolation unit of the moving picture coding apparatus 1.

When encoding the continuous image data as shown in FIG. 3 (A), the moving picture coding apparatus 1 performs a two-step process of preliminary reproduction and main reproduction. First, in the moving picture coding device 1, the reproduction control unit 20 and the reproduction unit 30 perform preliminary reproduction based on the selection information input from the selection unit 10. At this time, as shown in FIG. 3C, the reproducing unit 30 reproduces only the instructed selected image and fast-forwards the other parts. The selected and reproduced image data is encoded by the encoding unit 40, and the encoded data amount as shown in FIG. 4D is sequentially transferred to the recording device 50 via the external I / F 112 of the encoding unit 40. Will be recorded.

When the preliminary reproduction of the image data recorded on the VTR tape 9 is completed and the data generation amount for the selected image is obtained, based on the data generation amount,
The data interpolation unit 60 estimates the data generation amount for the image that is not selected. That is, FIG. 4 (D)
Linear interpolation is performed based on the data generation amount of the selected image as shown in FIG. 4 to obtain the data generation amount for each image in between as shown in FIG. When the data generation amount is obtained for each image, the allocation determination unit 70 allocates the data amount based on the recording capacity of the recording medium. That is, in order to record continuous image data on the recording medium, for each image data at a predetermined time t,
Allocate the amount of data using Equation 3.

After the allocation of the data amount to each image data is completed, the main reproduction is performed next. Playback unit 30 is VT
The R tape 9 is rewound and this time, all the images of the continuous image data as shown in FIG. 3A are reproduced again from the beginning, and are sequentially output to the encoding unit 40. In the encoding unit 40, motion compensation between frames is appropriately performed on each image, and DCT is performed to perform compression. Then, the quantizing unit 103 quantizes based on the data amount assigned to each image read from the recording device 50 to the control unit 113. Each quantized image data is variable-length coded by the variable-length coding unit 104 and sequentially output as an image bit stream.

As described above, in the moving picture coding apparatus 1 of the present embodiment, the preliminary reproduction is once performed to obtain the data generation amount of each image of the image data, and the image generation amount for each image data is calculated based on the data generation amount. Since the amount of data for recording is assigned, each image data is subjected to appropriate variable rate encoding while maintaining the image quality, and then the image data is appropriately applied to a recording medium having a limited recording capacity such as a DVD. Can be recorded exactly. Further, during the preliminary reproduction, the image data is thinned out and reproduced, and the data generation amounts of other images are interpolated from the data generation amount of the thinned image data, so that the preliminary reproduction is performed. It can be performed faster than normal playback.

The present invention is not limited to this embodiment, and various modifications can be made.

For example, the method of selecting the image data at the time of preliminary reproduction in the reproducing unit 30 is not limited to this embodiment. Any method may be used as long as it can be reproduced at a higher speed than normal reproduction and can select an image to the extent that the data amount can be appropriately estimated. For example, continuous scenes may be detected by a simple reproduction process, and an image may be selected for each continuous scene. Further, the continuous scene may be detected by using, if there is data such as an edit list at the time of creating image data. Such a method in which at least one image can be selected for each continuous scene, that is, for each continuous scene in which the amount of data is considered to be almost equal, is a preferable method from the viewpoint of accurately estimating the amount of data.

Also, when images are sequentially selected at predetermined time intervals as in the present embodiment, the time interval may be determined by a fixed interval determined in advance, or by the recording time of image data or the like. It may be determined based on the above, or may be determined by any suitable method. Further, the interpolation method in the data interpolation unit 60 is not limited to linear interpolation, and any interpolation method such as spline interpolation may be used. By using the selection method and the interpolation method that complement each other in the image selection method and the interpolation method during the preliminary reproduction, it is possible to obtain an accurate data generation amount with a smaller number of image selections. It is preferable to use each such method.

In the present embodiment, the image data of the source to be encoded is the image data recorded on the VTR tape, but in addition to this, a hard magnetic disk (HD), a magneto-optical disk (MO) is used. Any media, such as a digital video disc (DVD), may be used. Therefore, the reproducing unit 30 may also be a reproducing device corresponding to those media.

In the present embodiment, the encoding method in the encoding unit 40 is also the MPEG as shown in FIG.
However, the encoding method is not limited to this. DC
An encoding method that only performs T, an encoding method that does not perform motion compensation, or the like may be used, or any orthogonal transform method other than DCT may be used. Also, the allocation determination unit 7
In 0, the data amount for each image data is determined, but a method of determining up to the encoding bit rate based on the data amount and instructing the encoding unit 40 may be used.

[0045]

According to the moving picture coding apparatus of the present invention, continuous image data can be appropriately variable-rate-encoded with a predetermined capacity, and at that time, much more than before. Encoding can be performed at high speed. Therefore,
When various image data are to be compressed and recorded on a recording medium such as a DVD, recording can be sequentially performed at high speed, so that work efficiency is improved. Further, according to the moving picture coding method of the present invention, the variable rate coding processing of continuous image data so as to fit in a predetermined capacity can be appropriately and rapidly performed.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of a moving picture coding apparatus according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of a coding unit of the moving picture coding apparatus shown in FIG.

3A and 3B are diagrams for explaining the operation of the moving picture coding apparatus shown in FIG. 1, in which FIG. 3A is a diagram showing a normal reproduced image, and FIG.
FIG. 6A is a diagram showing an operation of a reproducing unit at the time of preliminary reproduction, FIG. 9C is a diagram showing a reproduced image at the time of preliminary reproduction, and FIG.

4A and 4B are diagrams showing a data interpolation method of a data interpolation unit of the moving picture coding apparatus shown in FIG. 1, FIG. 4D showing a data amount of a pre-reproduced image, and FIG. It is a figure which shows the data amount of each image after interpolation.

FIG. 5 is a diagram showing bit rates of fixed rate coding and variable rate coding.

FIG. 6 is a diagram illustrating a method of determining a bit rate in variable rate coding.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Moving image encoding apparatus 10 ... Selection part 20 ... Reproduction control part 30 ... Reproduction part 40 ... Encoding part 101 ... Adder 102 ... DCT part 103 ... Quantization part 104 ... Variable length coding part 105 ... Dequantization Unit 106 ... Inverse DCT unit 107 ... Adder 108 ... Frame memory 109 ... Motion detection unit 110 ... Motion compensation unit 111 ... Switching circuit 112 ... External I / F 113 ... Control unit 50 ... Recording device 60 ... Data interpolation unit 70 ... Allocation Decision part 9 ... VTR tape

Claims (6)

[Claims] 1. An image selecting means for selecting image data to be used for preliminary reproduction from continuous image data, only the selected image data is reproduced during preliminary reproduction, and the continuous image data is sequentially reproduced during main reproduction. Reproduction means for reproducing, encoding means for variable-rate encoding the reproduced image data, and the continuous operation based on the data generation amount of the selected image data that has been variable-rate encoded during the preliminary reproduction. Data amount interpolation means for interpolating the data generation amount of image data other than the selected image data of the general image data, the data generation amount of each image data of the continuous image data, and the continuous image A data amount determining means for allocating the encoded data amount to each of the image data based on a limit value of the encoded data amount for the entire data, At the time of the main reproduction, the encoding means makes the variable rate code so that the data generation amount of each image data of the continuous image data becomes equal to or less than the encoded data amount assigned to each image data by the data amount determination means. Image encoding device. 2. The image selecting means selects image data of the continuous image data for each predetermined time, and the data generation amount interpolating means based on the data generation amount in the image data for each predetermined time. The image coding apparatus according to claim 1, wherein the data generation amount in the image data other than the predetermined time is interpolated by linear interpolation. 3. The image coding apparatus according to claim 1, wherein the image selecting means selects at least one frame of image data for each continuous scene of the continuous image data. 4. The image coding apparatus according to claim 1, wherein the image selecting means selects a plurality of image data from the continuous image data based on the input image position information. 5. The image coding apparatus according to claim 1, wherein the image selecting means selects predetermined image data based on an edit list having management information of the continuous image data. 6. A plurality of image data used for preliminary reproduction are selected from continuous image data and reproduced, each of the reproduced image data is variable rate encoded, and each of the plurality of variable rate encoded is encoded. Data generation amount of image data is respectively detected, and data generation of image data other than the selected plurality of image data of the continuous image data is performed based on each data generation amount of the detected plurality of image data. An amount of data, and based on the data generation amount of each image data of the detected and interpolated continuous image data, allocate an encoded data amount to each image data, and reproduce the continuous image data. Then, the image coding method of performing variable rate coding on each image of the continuous image data so that the data generation amount is equal to or less than the allocated coded data amount.