JP2001204018A - Variable bit rate coder and coding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make deterioration in the image quality of a reproduced image hardly visually remarkable under consecutive scenes in the case that a video signal is coded and recorded with compression. SOLUTION: A capacity detector 107 detects a remaining recordable storage capacity of a recording medium 107. A code quantity assignment unit 100 receives the remaining recordable capacity of the recording medium 106 and unrecording time information 100a of an input video signal 1a and assigns a code quantity by each prescribed period depending on a conversion characteristic on both the inputs. A scene change detector 108 detects a scene change in the input video signal 1a. The code quantity assignment unit 100 receives an output of the scene change detector 108 to output the assigned code quantity in timing synchronously with the scene change in the input video signal 1a. Since the assigned code quantity is unchanged under a state of consecutive video scenes, a change in the image quality deterioration of the reproduced image is hardly visually remarkable at reproduction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a variable bit rate coding apparatus and a coding method for compressing and coding a video signal and recording it on a recording medium such as an optical disk or a magnetic disk.

[0002]

2. Description of the Related Art In recent years, in the field of digital recording devices such as DVD recorders, a technique for simultaneously realizing long-time recording and high image quality has attracted attention.

As a technique for efficiently compressing and recording a video signal on a recording medium in real time using a variable bit rate encoding technique, for example, a technique disclosed in Japanese Patent Application Laid-Open No. 8-149413 has been proposed.

FIG. 3 shows a block configuration of the conventional variable bit rate coding apparatus. Referring to FIG.
A recording medium 107 such as a VD; a recording capacity detector 107 for detecting a recordable recording capacity 107b of the recording medium 106;
0 is a code amount allocator, which is an input video signal 1 to be recorded.
The unrecorded time information 1000a of a is used as a first input, and the recording capacity 107b, which is the output of the recording capacity detector 107, is used as a second input. Performed and assigned code amount 1000b
Is output.

Reference numeral 103 denotes a quantization parameter 101b from a code amount controller 101 which will be described later.
, And outputs a quantized data 103b. A second-order quantizer 104 performs variable-length coding on the quantized data 103b output from the second-order quantizer 103, and
Secondary encoder for generating next encoded data 104b, 10
2 measures the secondary encoded data 104b every predetermined period,
This is a code amount measuring device that generates the encoded data amount 102b. 101 is a secondary quantizer 10 that reduces the difference between the allocated code amount 1000b of the code amount allocator 1000 and the coded data amount 102b of the code amount measuring device 102.
3 is a code amount controller for generating a quantization parameter 101b used in the third embodiment. 105 is the secondary encoded data 104
This is a recording signal processor that records “b” on the recording medium 106 as a recording signal 105b.

[0006] In the conventional variable bit rate coding apparatus configured as described above, the optimum allocated code amount 1000b is determined by the recordable recording capacity 107b of the recording medium 106 and the unrecorded time information 1000a of the video signal 1a to be recorded. Is generated and at the same time, the encoded data amount 1 of the secondary encoded data 104b that is encoded and recorded on the recording medium 106
02b is measured, and the quantized data of the secondary quantizer 103 is controlled by the code amount controller 101 so that the difference between the coded data amount 102b and the allocated code amount 1000b is reduced, so that the efficiency is improved. High-quality, long-time compression recording on the recording medium 106 was realized while encoding was performed in real time.

[0007]

However, in the conventional variable bit rate encoding apparatus, the recording capacity 107b of the recording medium 106 is smaller than the length of the unrecorded time information 1000a of the input video signal 1a to be recorded. In the case, that is, in the case where the encoding rate must be reduced and a static image and a video of a continuous scene are input as the input video signal 1a, as shown in FIG. In some cases, the amount changed in the middle of a continuous scene. As a result, when the recorded video signal is reproduced, there is a problem that the change in image quality deterioration becomes noticeable because the coding rate decreases and changes in the middle of a continuous scene.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and an object thereof is to provide a case where static images and continuous scene images are input as an input image signal when recording must be performed at a low encoding rate. Provide a variable bit rate encoding device that realizes compressed recording that can obtain a more natural and smooth reproduced video without changing the allocated code amount in the middle of a static scene even if Is to do.

[0009]

In order to achieve the above object, according to the present invention, when a correlation between continuous information of an input video signal is equal to or more than a predetermined value such as a scene change,
The assigned code amount is fixed without being changed.

That is, the variable bit rate encoding apparatus according to the first aspect of the present invention uses a conversion characteristic according to the unrecorded time information of the input video signal to be recorded and the remaining recordable recording capacity of the recording medium. In a variable bit rate encoding device including a code amount allocating unit that allocates a code amount every predetermined period, a variable bit rate encoding device includes a detecting unit that detects correlation between continuous information of the input video signal, and the code amount allocating unit includes the code amount allocating unit. In response to the output of the means, every time when the correlation is equal to or more than a predetermined value is detected, the code amount allocated at the time of the detection is output.

According to a second aspect of the present invention, in the variable bit rate encoding apparatus according to the first aspect, the detecting means is a scene change detecting means for detecting a scene change of an input video signal to be recorded. It is characterized by the following.

Further, the variable bit rate encoding apparatus according to the third aspect of the present invention provides a capacity detecting means for detecting a remaining recordable recording capacity of a recording medium and a scene change of an input video signal to be recorded. A scene change detecting means, and a first input which outputs unrecorded time information of the input video signal;
The first and second inputs are the remaining recordable recording capacity detected by the capacity detection means as a second input and the scene change detection signal of the input video signal from the scene change detection means as a third input. Code amount allocation means for allocating a code amount for each predetermined period according to a conversion characteristic according to the above, and outputting the allocated code amount at the input timing of the third input; and quantifying the input video signal in accordance with a quantization parameter. Secondary quantization means for performing quantization processing and outputting quantized data, secondary encoding means for performing variable length encoding processing on the quantized data of the secondary quantization means to generate secondary encoded data, A code amount measuring unit that measures an amount of secondary encoded data generated by the secondary encoding unit at every predetermined period and outputs an encoded data amount; a code amount allocated by the code amount allocating unit and the code amount; Data Code amount control means for outputting the quantization parameter to the secondary quantization means, and a recording signal for recording the secondary encoded data of the secondary encoding means on the recording medium so that the difference between And processing means.

According to a fourth aspect of the present invention, in the variable bit rate encoding apparatus according to the second or third aspect, the scene change detecting means sets a plurality of thresholds for determining a scene change of the input video signal. And when the scene change is detected from the input video signal, the threshold value is switched according to the remaining recordable recording capacity of a recording medium.

According to a fifth aspect of the present invention, there is provided the variable bit rate encoding method according to the present invention, wherein the conversion characteristic according to the unrecorded time information of the input video signal to be recorded and the remaining recordable recording capacity of the recording medium. A code amount is assigned every predetermined period, and a correlation between continuous information of the input video signal is detected, and whenever a time when the correlation is equal to or more than a predetermined value is detected,
A code amount allocated at the time of the detection is output, and the allocated code amount is fixed while the correlation is less than a predetermined value.

As described above, according to the first to fifth aspects of the present invention, even when the compression rate is required to be reduced at a low code rate, the timing of the change of the allocated code amount is determined by the continuous timing of the input video signal. When the correlation between the pieces of information is greater than or equal to a predetermined value, for example, it is synchronized with the timing of a scene change, so that the input video signal is compressed and recorded without changing the allocated code amount in the middle of a continuous scene. Therefore, a change in image quality is hardly noticeable, and a natural and smooth reproduced image can be obtained.

In particular, in the invention according to the fourth aspect, a video signal in which the correlation determination such as a scene change is confusing, that is, a video signal having a correlation near the determination threshold value, in a state where the encoding rate is reduced and the compression recording is performed. Is input, the determination threshold is switched to a higher value, so that scene change detection and the like are stable, video signals are compressed and recorded with stable image quality, and images with stable reproduction image quality can be obtained.

[0017]

Embodiments of the present invention will be described below with reference to the drawings.

(First Embodiment) FIG. 1 shows an example of a block diagram of a variable bit rate coding apparatus according to a first embodiment of the present invention.

In FIG. 1, reference numeral 100 denotes a code amount allocator (code amount allocating means); 101, a code amount controller (code amount control means); 102, a code amount measuring device (code amount measuring means);
3 is a secondary quantizer (secondary quantizing means), 104 is a secondary encoder (secondary encoding means), 105 is a recording signal processor (recording signal processing means), 106 is a recording medium, and 107 is a recording medium. A recording capacity detector (capacity detecting means) 108 is a scene change detector (detecting means and scene change detecting means). Except for the scene change detector 108 and the code amount allocator (code amount allocating unit) 100, the configuration is the same as that of the block diagram of the conventional example in FIG.

The configuration and operation of the scene change detector 108 will be described below with reference to FIGS.

FIG. 4 shows the scene change detector 108.
FIG. 2 is a block diagram showing an internal configuration of the device. In the figure, an input video signal 1a is delayed by one frame by a frame memory 1081, and a frame difference 108 from a currently input video signal 1a is input by a frame differentiator 1082.
2b is output. Further, in the absolute value comparator 1083,
Reference difference data (judgment threshold) 108 set in advance
3a is compared with the absolute value of the frame difference 1082b to determine whether or not the currently input video signal 1a is a scene switching frame, and the absolute value of the frame difference 1082b is compared with the reference difference data. 1083a
At this time, that is, when the correlation between continuous information of the input video signal 1a is equal to or greater than a predetermined determination threshold, it is determined that a scene change has occurred. This determination is made for each frame timing period as shown in FIG. The determination signal indicating that the scene change has occurred is a scene change detection signal 1
08b. In the present embodiment, the difference data information between the frames is determined. However, a configuration may be used in which the determination is performed using the average of the differences between the frames, the difference between adjacent pixels, or a combination thereof. .

The code amount allocator 100 shown in FIG. 1 includes unrecorded time information 100a of an input video signal 1a to be recorded,
A recording capacity 107b, which is an output of the recording capacity detector 107, is input, and a code amount is allocated according to conversion characteristics according to both inputs. This assignment is performed every predetermined period t. Further, upon receiving the scene change detection signal 108b from the scene change detector 108, at the reception timing of the scene change detection signal 108b, the code allocation result is updated as the allocated code amount 100b as shown in FIG. . In this embodiment, the unrecorded time information 1 of the input video signal 1a is transmitted to the code amount allocator 100.
Although 00a is input, the video signal 1a may be input, and the unrecorded time information 100a may be calculated in the code amount allocator 100 based on the input video signal 1a. In the code amount allocator 100, a predetermined time may be subtracted from the unrecorded time information 100a, and the unrecorded time information 100a used for allocating the code amount may have an offset.

Code amount allocator 100 having such a function
Is shown in FIG. In the code amount allocator 100 shown in FIG. 1, reference numeral 110 denotes a latch circuit for latching the value of the storage capacity 107b by a system clock 100c having a predetermined period t, and reference numeral 120 denotes the value of the unrecorded time information 100a of the input video signal 1a to be recorded. This is a latch circuit that latches according to the system clock 100c. 140 is a ROM
In this case, the optimum code amount as viewed from the system is stored in advance in accordance with a combination of both the recording capacity 107b and the unrecorded time information 100a. For example, if the unrecorded time information 100a is a constant value, the larger the recording capacity 107b, the larger the code amount. Also, the recording capacity 107b
Is a constant value, the larger the unrecorded time information 100a, the smaller the code amount. The ROM 140 receives the output 110b (the value of the storage capacity 107b) of the latch circuit 110 and the output 120b (the value of the unrecorded time information 100a) of the latch circuit 120, and uses these as addresses to code corresponding thereto. Output the quantity 140b. 13
Reference numeral 0 denotes a latch circuit, and the scene change detector 1
08, the code amount 140b output from the ROM 140 is latched at the time of receiving the scene change detection signal 108b, and is output as the allocated code amount 100b.

As shown in FIG. 8, the result of code assignment changes with a predetermined period t as a reference unit. However, scene change detection is performed so that the assigned code amount does not change during continuous scenes. Since the allocated code amount 140b is latched by the latch circuit 130 at the reception timing of the signal 108b, a change in the allocated code amount is output as the allocated code amount 100b in synchronization with the scene change of the input video signal 1a. Therefore, the encoding rate of the secondary encoded data 104b recorded after being variable-length encoded does not change in the middle of a continuous scene.
Since the coding rate changes in synchronization with the scene change of the input video signal 1a, deterioration in image quality during reproduction is not noticeable, and a natural and smooth reproduced image can be obtained.

(Second Embodiment) FIG. 2 is a block diagram showing the internal configuration of a variable bit rate encoding device according to a second embodiment of the present invention. In the figure, the configuration other than the scene change detector 109 is the same as that of the first embodiment, and has the same function, so that the description is omitted.

The configuration and operation will be described below with reference to FIGS. FIG. 5 shows a scene change detector 109.
FIG. 2 is a block diagram showing an internal configuration of the device. In the figure, an input video signal 1a is delayed by one frame by a frame memory 1091, and a frame difference 1092b from a currently input video signal 1a by a frame differentiator 1092.
Is output. Further, two absolute value comparators 1093, 1
In step 094, the absolute value of the frame difference 1092b and a preset reference correlation level (judgment threshold) 1093
a, a magnitude comparison with 1094a is performed, and a correlation output 109
3b and 1094b are output to the selector 1095.
The one reference correlation level 1093a is larger than the other reference correlation level 1094a. Residual capacity determiner 1
In step S096, the storage capacity 107b output from the storage capacity detector 107 is compared with a preset reference remaining capacity 1096a, and a selection signal 1096b indicating the comparison result is output to the selector 1095. When the remaining capacity is smaller than the reference capacity according to the selection signal 1096b, the selector 1095 selects the correlation output 1093b of the absolute value comparator 1093 corresponding to the large reference correlation level 1093a, and vice versa. In this case, the reference correlation level 1093 of the small value is used.
Correlation output 1094 of the absolute value comparator 1094 corresponding to b
b, and the selection result is the scene change detection signal 1
09b is output.

In the detection of a scene change in the input video signal 1a, when determining the correlation strength between frames of the input video signal 1a, the video signal 1a having a correlation strength near the determination threshold is input. In such a case, the scene change detection is likely to be unstable. As a result, a scene change detection signal frequently occurs, and the assigned code amount is updated in a scene that is not an original scene change. I will.

However, in the present embodiment, as shown in FIG. 10, when the residual capacity determiner 1096 determines that the recording residual capacity of the recording medium 106 is small, the absolute value on the side of the large reference correlation level 1093a is determined. The value comparator 1093 is selected, and the comparison output 1093b, which is compared with the reference correlation level 1093a, is output from the selector 1095. Therefore, the scene change can be detected by slightly increasing the strength of the frame correlation. On the other hand, when it is determined that the recording capacity is sufficient, the absolute value comparator 1094 on the side of the small reference correlation level 1094a is selected, and a scene change is detected with the normal frame correlation strength. You. Therefore, even when a video signal having a correlation strength near the scene change judgment threshold is input, the scene change judgment is performed by switching the correlation level threshold to compress the image with stable image quality. Recording can be enabled.

[0029]

As described above, according to the first to fifth aspects of the present invention, the timing of the change of the assigned code amount is synchronized with the timing of a scene change or the like, and the assigned code amount is changed during a continuous scene. Since the amount is fixed, a change in image quality is hardly noticeable, and a natural and smooth reproduced image can be obtained.

In particular, according to the fourth aspect of the present invention, even when the compression recording is performed at a low encoding rate,
Since the detection threshold for a scene change or the like is switched to a high value to stabilize the detection of a scene change or the like, a video signal can be compressed and recorded with a stable image quality, and a video with a stable reproduction image quality can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram of a variable bit rate encoding device according to a first embodiment of the present invention.

FIG. 2 is a block diagram of a variable bit rate encoding device according to a second embodiment of the present invention.

FIG. 3 is a block diagram of a conventional variable bit rate encoding device.

FIG. 4 is a block diagram illustrating an internal configuration of a scene change detector according to the first embodiment of the present invention.

FIG. 5 is a block diagram showing an internal configuration of a scene change detector according to a second embodiment of the present invention.

FIG. 6 is a block diagram illustrating an internal configuration of a code amount allocator according to the first embodiment of the present invention.

FIG. 7 is a waveform diagram showing a timing relationship between code assignment and scene change in a conventional example.

FIG. 8 is a waveform diagram showing a timing relationship between code assignment and a scene change in the first embodiment of the present invention.

FIG. 9 is a diagram showing operation waveforms of the code assignment and scene change detector according to the first embodiment of the present invention.

FIG. 10 is a diagram illustrating code assignment and operation waveforms of a scene change detector according to the second embodiment of the present invention.

[Explanation of symbols]

REFERENCE SIGNS LIST 100 code amount allocator (code amount allocating means) 101 code amount controller (code amount controlling means) 102 code amount measuring device (code amount measuring means) 103 secondary quantizer (secondary quantizing means) 104 secondary code Transformer (Secondary encoding means) 105 Recording signal processor (Recording signal processing means) 106 Recording medium 107 Capacity detector (Capacity detecting means) 108 Scene change detector (Detecting means and scene change detecting means) 110, 120 Latch Circuit 130 Latch circuit 140 ROM 1081 Frame memory 1082 Frame differencer 1083 Absolute value comparator 1095 Selector 1096 Residual capacity determiner

Claims (5)

[Claims] 1. A code amount allocating means for allocating a code amount every predetermined period according to a conversion characteristic according to unrecorded time information of an input video signal to be recorded and a remaining recordable recording capacity of a recording medium. A variable bit rate encoding device, comprising: detecting means for detecting a correlation between continuous information of the input video signal, wherein the code amount allocating means receives an output of the detecting means, and the correlation is equal to or more than a predetermined value. A variable bit rate encoding device, wherein every time a time is detected, an assigned code amount at the time of the detection is output. 2. The apparatus according to claim 1, wherein said detecting means is a scene change detecting means for detecting a scene change of an input video signal to be recorded.
A variable bit rate encoding device according to claim 1. 3. A capacity detecting means for detecting a remaining recordable recording capacity of a recording medium; a scene change detecting means for detecting a scene change of an input video signal to be recorded; The first input, the remaining recordable recording capacity detected by the capacity detecting means as a second input, and the scene change detection signal of the input video signal from the scene change detecting means as a third input. Code amount allocating means for allocating a code amount for each predetermined period according to conversion characteristics corresponding to the first and second inputs, and outputting the allocated code amount at an input timing of the third input; Secondary quantization means for performing quantization processing according to the quantization parameter and outputting quantized data; and performing variable-length encoding processing on the quantized data of the secondary quantization means to perform secondary encoding data. A coding amount measuring means for measuring a generation amount of the secondary coded data of the secondary coding means for each of the predetermined periods, and outputting a coded data amount; A code amount control unit that outputs the quantization parameter to the secondary quantization unit so that a difference between the code amount allocated by the allocation unit and the encoded data amount is small; A variable signal rate encoding device comprising: recording signal processing means for recording next encoded data on the recording medium. 4. The scene change detecting means has a plurality of thresholds for judging a scene change of an input video signal, and detects a scene change from the input video signal, and detects a remaining recording capacity of a recording medium when detecting a scene change from the input video signal. 4. The variable bit rate encoding device according to claim 2, wherein the threshold value is switched according to the following. 5. A code amount is allocated every predetermined period by a conversion characteristic according to unrecorded time information of an input video signal to be recorded and a remaining recordable recording capacity of a recording medium, and Detects a correlation between continuous information, and outputs a code amount allocated at the time of detection each time when the correlation is equal to or more than a predetermined value, and continues the situation where the correlation is less than a predetermined value. In the variable bit rate encoding method, the code amount is fixed in the middle.