JP2004064210A - Recording apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a recording apparatus capable of reproducing images continuously without degrading image quality even when the images are intermittently recorded by using an inter-picture correlation like an MPEG system. <P>SOLUTION: The recording apparatus periodically extracts image data of one frame from a received image data stream, encodes the extracted image data in compliance with the MPEG system to record the data to a recording medium and is configured to insert at least one frame of image data the same as the extracted image data of one frame as a dummy frame and encodes the image data of the dummy frame by inter-picture encoding and records the result. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a recording apparatus, and more particularly, to an apparatus for intermittently recording image data.
[0002]
[Prior art]
2. Description of the Related Art Devices that intermittently record an image captured by a camera are known.
[0003]
For example, there is a so-called time lapse recorder for monitoring applications. The time lapse recorder intermittently extracts and records one or several frames from a series of input images, thereby enabling long-term monitoring.
[0004]
Due to recent advances in digital signal processing technology, even in an apparatus that performs such intermittent recording, an image signal is often encoded by an encoding method such as JPEG and the amount of information is compressed and recorded.
[0005]
On the other hand, as a method for encoding an image signal more efficiently, a high-efficiency encoding method called MPEG is well known, and is adopted in the DVD video standard and the like. This method is a method for obtaining a higher compression ratio by utilizing the correlation between frames in addition to the intra-frame encoding method represented by JPEG. The effect is particularly great when applied to a device for recording a moving image such as a camcorder.
[0006]
[Problems to be solved by the invention]
As described above, the MPEG encoding method can compress an image signal at a higher compression ratio than JPEG, and can reduce the amount of generated code. Therefore, a longer recording time is considered by applying the MPEG coding method to the intermittent recording apparatus described above.
[0007]
However, since the MPEG coding method originally uses a correlation between frames to improve coding efficiency, even if MPEG coding is simply applied to intermittent recording, intermittently extracted image If the correlation is small, the original compression ratio cannot be obtained.
[0008]
In the MPEG coding method, an upper limit of a coding rate (a code amount per unit time) is defined for compatibility of a decoder. Further, in a case of continuous reproduction, a recording medium such as a disk or a tape is used. The playback rate also has an upper limit.
[0009]
Therefore, when the encoding rate is suppressed so that the MPEG encoding apparatus satisfies the standard, the image quality may be insufficient. Alternatively, when recording is performed without adjusting the encoding rate, when the image is reproduced, the reproduction rate of the reproduction device is exceeded and continuous reproduction becomes impossible.
[0010]
For example, in a general TV image quality mode, 15 Mbps is defined as the upper limit of the coding rate.
[0011]
An object of the present invention is to solve such a problem.
[0012]
Another object of the present invention is to provide a process for enabling continuous reproduction without deteriorating image quality even when intermittent recording is performed by encoding an image signal using correlation between screens such as the MPEG encoding method. It is in.
[0013]
[Means for Solving the Problems]
In order to achieve the above object, according to the present invention, one screen of image data is intermittently extracted from an image data sequence including a plurality of frames, and the extracted one screen of image data is repeated a predetermined number of times. Extracting means for outputting, encoding means for encoding the image data output from the extracting means using an intra-screen encoding method and an inter-screen encoding method, and image data encoded by the encoding means. Recording means for recording on a recording medium.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described.
[0015]
First, the concept of the encoding process at the time of intermittent recording in the present embodiment will be described.
[0016]
As shown in FIG. 3, each frame encoded in the MPEG encoding is classified into three types of pictures called I picture, P picture, and B picture.
[0017]
An I picture is a frame for which intra-frame coding is performed, and can be coded / decoded independently without referring to information of another frame, but requires a large code amount. A P-picture is a frame for performing a so-called inter-frame predictive coding for coding a difference from a picture that has been motion-compensated and predicted from an I- or P-picture preceding one or more frame times, and greatly reduces the code amount as compared with an I-picture It is possible. A B-picture is a frame that performs bidirectional inter-frame predictive coding that predicts not only from a preceding I or P picture, but also from a subsequent I or P picture, and can reduce the code amount further than a P picture.
[0018]
In order to improve the coding efficiency, it is sufficient to use many P and B pictures. However, in consideration of the special reproduction and editing such as search, and the recovery performance at the time of error, the I picture is used at appropriate intervals as shown in FIG. Is generally inserted and encoded. A unit of a plurality of frames including an I picture as shown in FIG. 3 is called a GOP (Group Of Picture). The arrows in the figure indicate the direction of frame prediction.
[0019]
Next, FIG. 5A shows a state in which image data is intermittently extracted from an input image data sequence and MPEG-encoded. Although the B picture is omitted in FIG. 5 for simplicity of description, the use of the B picture does not affect the essence of the present invention.
[0020]
For example, when shooting a flowering state of a flower with a video camera fixed on a tripod, the correlation between images is high even if the interval between frames to be encoded is long as shown in FIG. In addition, since the original compression efficiency by the MPEG encoding is exhibited, the generated code amount becomes as shown in FIG. 5B, and continuous reproduction can be performed without any problem.
[0021]
However, if the encoding process is performed on a fast-moving image in the same manner, the correlation between the frames becomes low, so that the code amount of the P picture using the frame correlation increases as shown in FIG. I will. Therefore, if the code amount is controlled at the time of encoding to suppress the entire code amount, the code amount becomes as shown in FIG. 5D, and as a result, the image quality is reduced. This is evident from the difference between the code amounts of the I pictures in FIGS. 5B and 5D.
[0022]
Also, when the encoded image data is recorded in the state of FIG. 5C with the target rate set high with emphasis on the image quality, the reading rate from the medium cannot be overrun during reproduction and the underrun may occur. There is also a problem.
[0023]
On the other hand, FIG. 6 shows a state of encoding according to the present embodiment. Although the frame intermittently extracted from the input image data sequence is MPEG-encoded, the image data of the extracted frame is encoded twice, as shown in FIG. Each of the second data 602a to 602e is encoded as a P picture. Since the P picture encodes the difference from the previous frame, the second image data 602a to 602e has no difference from the previous frame 601a to 601e, and substantially no code is generated (frame information such as a header). Is necessary, but here, the code amount by purely the image signal is considered).
[0024]
As a result, the generated code amount is as shown in FIG. In FIG. 6, although it appears that codes are generated in the P 'pictures 602a to 602e, this is because it is shown in a large scale for the sake of explanation, and almost no code amount is generated as described above.
[0025]
When encoded and recorded as described above, the number of frames to be decoded and output at the time of reproduction, that is, the reproduction time is doubled, so that the upper limit rate of the standard and the read rate of the medium are kept without sacrificing the image quality. It becomes easier. The doubling of the reproduction time itself has few problems for the purpose of the present invention.
[0026]
Next, an apparatus to which such an encoding process is applied will be described.
[0027]
FIG. 1 is a diagram showing a configuration of a recording apparatus to which the present invention is applied.
[0028]
In FIG. 1, an image input unit 101 inputs an image data sequence indicating a series of moving images obtained by a video camera or the like, and outputs the image data sequence to a frame memory 102 and a frame counter 105. The writing and reading operations of the frame memory 102 are controlled by the control unit 106 as described later, and the image data written in the frame memory 102 is output to the encoding unit 103.
[0029]
The frame counter 105 counts the number of frames of the input image data and outputs the count value to the control unit 106. The frame counter 105 counts the number of frames of the input image data from 1 to a predetermined frame number N, and then automatically resets it to 1.
[0030]
The control unit 106 controls the frame memory 102 according to the count value of the frame counter 105, writes image data from the image input unit 101 to the frame memory 102 for one frame in N frame periods, and writes the image data in other periods. Ban. That is, one frame of image data is extracted from the input image data every N frames and written into the frame memory 102. Specifically, for example, one frame in a period in which the count value of the frame counter 105 is 1 is written in the frame memory 102.
[0031]
The control unit 106 repeatedly reads out the image data of one frame written in the frame memory 102 for consecutive M frame periods of the N frame periods and supplies the data to the encoding unit 103. The encoding unit 103 is controlled to encode the image data of the M frames. In addition, the encoding process by the encoding unit 103 is stopped in a period other than the M frame period, that is, in the (N−M) frame period.
[0032]
The encoding unit 103 encodes the first frame of the M frame image data output continuously as an I picture or a P picture as shown in FIG. Encode as a picture. By performing encoding in this manner, encoded data with a difference of 0 is output from the second frame onward, and the code amount does not occur. At this time, the picture type of the first frame is determined in a predetermined order. In FIG. 6, the first extracted frame 601a is an I picture, and the two subsequently extracted frames 601b and 601c are P pictures.
[0033]
The data intermittently encoded by the encoding unit 103 is output to the recording unit 104. The recording unit 104 stores the encoded image data in an internal buffer memory, reads out the image data from the buffer memory at a timing when a predetermined amount of image data is stored, performs processing such as error correction encoding processing, and the like. In addition, the information is recorded on the recording medium M with synchronization according to the format, additional information such as ID data and a header. The recording medium M is not particularly limited, but a known magnetic tape, magnetic disk, memory card, or the like can be used.
[0034]
Further, the example shown in FIG. 6 corresponds to the case where M = 2 is fixed, but another value may be used, or dynamically changed to, for example, 2, 1, 2, 3,. Is also good. By selecting a sufficiently large value of M, it is possible to lower the upper limit encoding rate of the MPEG standard and the media read rate during reproduction. The setting unit 107 is a configuration for setting the value of M, and can be arbitrarily set by the user.
[0035]
As described above, according to the present embodiment, when one frame of image data is intermittently extracted from the input image data sequence and encoded and recorded by MPEG encoding, the extracted one frame of image data Is output to the encoding unit for repeating a predetermined number of frames, and the encoding unit encodes the P-picture as inter-frame encoding. That is, since a dummy frame that does not substantially generate a code amount is inserted into encoded data, intermittent recording using MPEG encoding can be realized without deteriorating image quality.
[0036]
Further, by inserting the dummy frame in this manner, when reproducing the image data, the reproduction rate of the reproducing device is not exceeded and continuous reproduction is not impossible.
[0037]
Next, a second embodiment will be described.
[0038]
In the above embodiment, the value of M is arbitrarily set by the user, but in this embodiment, the value of M is automatically changed. FIG. 2 is a block diagram illustrating a configuration of the recording apparatus according to the present embodiment. 2 is the same as the apparatus in FIG. 1 except for the processing related to the setting operation of M by the control unit 106, and thus detailed description is omitted.
[0039]
2, the control unit 106 controls the frame memory 102 in accordance with the count value of the frame counter 105, and writes image data from the image input unit 101 to the frame memory 102 for one frame during N frame periods. The configuration for prohibiting writing during the period is the same. Then, the control unit 106 reads out one frame of image data stored in the memory 102 and outputs the image data to the encoding unit 103 during the M frame period determined based on the output from the code amount comparison unit 108.
[0040]
The code amount comparison unit 108 detects the code amount of the encoded image data output from the encoding unit 103. Then, a data rate at the time of reproduction is calculated based on the code amount, and is compared with a predetermined reproduction rate R, and the result is output to the control unit 106.
[0041]
When the data rate based on the current code amount is larger than the reproduction rate R by the code amount comparison unit 108, the control unit 106 increases the value of M by one, and when the data does not exceed the reproduction rate R, the M value at that time is increased. Hold the value.
[0042]
As a result, when the frame correlation of the input image is high, M = 1, that is, an image of one frame is encoded every N frames. When the frame correlation is low and the generated code amount is large, the value of M is automatically increased, and the encoded data of the P picture indicating the difference 0 is inserted.
[0043]
As described above, in the present embodiment, the number of dummy frames to be inserted is set according to the code amount of image data. Therefore, the reproduction speed is not reduced without inserting unnecessary dummy frames.
[0044]
In the present embodiment, the value of M at the time when the reproduction rate calculated from the encoded image data becomes equal to or lower than the predetermined rate R is held. However, the value of M can be dynamically changed. .
[0045]
In this case, for example, after the value of M is determined as described above, the value of M is reduced by 1 after a predetermined period has elapsed. When the frame correlation of the image data encoded at that time is high and the occurrence of the code amount is small, even if the value of M is reduced, the code amount does not exceed the predetermined rate R.
[0046]
Here, the code amount control by the encoding unit 103 of FIG. 1 or 2 will be described.
[0047]
FIG. 4A shows image data obtained by adding and encoding one dummy frame P ′ every N frame periods as shown in FIG. 6A.
[0048]
According to the code amount control method of the MPEG coding, it is common to set a target code amount for each GOP, determine distribution of the target code amount for each picture in the GOP in advance, and perform feedback control. It is. For example, assuming that an I picture requires a code amount twice as large as that of a P picture, the code amount of one GOP is distributed to each picture as shown in FIG. Become.
[0049]
However, when the upper frame is inserted and inserted as described above, the picture indicated by P ′ has a frame difference of 0 and does not generate a code amount, so that the result shown in FIG. 4C is obtained. That is, since the code amount does not occur immediately after P ′ is encoded, the control is performed in a direction in which the code amount falls below the target code amount and the code amount increases thereafter. As a result, an extra code amount is used for an image portion from which a sufficient image quality can be obtained even if the code amount is not originally increased, thereby deteriorating efficiency as a whole.
[0050]
Therefore, in the present embodiment, since it is known in advance that the picture indicated by P ′ does not generate the code amount, the code amount is allocated to each picture as shown in FIG.
[0051]
That is, in this example, the GOP is composed of a total of six pictures of one I picture and five P pictures, but the control of the code amount is made of a total of three pictures of one I picture and two P pictures. A target code amount is assigned. As a result, the code amount is efficiently allocated, and an improvement in image quality can be expected as a whole.
[0052]
Further, the encoded data of the P picture indicating the frame difference 0 can be generated mechanically without directly encoding the image data. Therefore, by changing the firmware in the MPEG encoding means, the frame difference 0 can be obtained. Can be inserted.
[0053]
That is, after outputting one frame of image data from the frame memory 102 to the encoding unit 103, the control unit 106 outputs a control signal indicating how many more dummy frames should be inserted. Specifically, a value of M−1 obtained by subtracting the number of frames 1 already output to the encoding unit 103 from the value M described above is output to the encoding unit 103. The encoding unit 103 encodes one frame of image data output from the frame memory 102, and adds P-picture encoded data showing a difference of 0 to the encoded data for M-1 frames, and records the encoded data. Output to the unit 104.
[0054]
By not performing the encoding process on the dummy frame in this way, it is not necessary to read and write a large amount of image data to and from the memory at the time of encoding, so that the power consumption can be reduced.
[0055]
Although the frame memory is an independent block in FIGS. 1 and 2, the frame memory (for rearranging the frame order, etc.) in the encoding unit 103 can be substituted.
[0056]
Further, in the above-described embodiment, the intermittent recording process has been described. However, a normal continuous recording process can of course be performed. In this case, in the configurations of FIG. 1 and FIG. 2, since the encoding unit 103 can be operated continuously, it is possible to smoothly change from the continuous recording mode to the intermittent recording mode or vice versa.
[0057]
Further, the above-described extraction processing using the frame memory and the encoding processing including the dummy frame can also be realized by software processing using a microcomputer or a memory. The storage medium storing the computer program at this time is also included in the scope of the present invention.
[0058]
【The invention's effect】
As described above, according to the present invention, continuous playback images can be performed without deteriorating image quality even when intermittent recording is performed by encoding using the correlation between screens as in the MPEG encoding method. .
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of a recording apparatus to which the present invention is applied.
FIG. 2 is a diagram illustrating a configuration of a recording apparatus to which the present invention is applied.
FIG. 3 is a diagram showing an encoding process in the MPEG system.
FIG. 4 is a diagram illustrating a state of code amount control.
FIG. 5 is a diagram showing a state of encoded data at the time of intermittent recording.
FIG. 6 is a diagram showing a state of encoded data including a dummy frame at the time of intermittent recording.

Claims (30)

Extracting means for intermittently extracting image data of one screen from an image data sequence composed of a plurality of frames and repeatedly outputting the extracted image data of one screen a predetermined number of times;
Encoding means for encoding the image data output from the extraction means using an intra-screen encoding method and an inter-screen encoding method,
A recording device for recording the image data encoded by the encoding device on a recording medium. 2. The recording apparatus according to claim 1, wherein the encoding unit encodes the one-screen image data output from the extraction unit for the second time or later by an inter-screen encoding method. 3. The recording apparatus according to claim 2, wherein the encoding unit encodes the image data of the first screen output from the extraction unit for the first time by the intra-screen encoding method or the inter-screen encoding method. . 2. The apparatus according to claim 1, further comprising: setting means for arbitrarily setting the predetermined number of times; and control means for controlling the extracting means and the encoding means according to the number of times set by the setting means. Recording device. The extracting means has a memory for storing the input image data string, and the control means controls the memory to write one screen of image data for every N screens of the image data string in the memory. 2. The recording apparatus according to claim 1, wherein: 6. The recording apparatus according to claim 5, further comprising a counter that counts the number of screens of the image data, wherein the control unit controls writing and reading of the image data to and from the memory based on a count value of the counter. . 2. The recording apparatus according to claim 1, further comprising control means for determining the predetermined number of times based on the code amount of the encoded image data. 8. The recording apparatus according to claim 7, wherein the control unit determines the predetermined number of times so that a data rate obtained based on a code amount of the image data does not exceed a predetermined rate. 9. The image processing apparatus according to claim 8, wherein the control unit increases the number of times of reading out the image data of one screen repeatedly when the data rate obtained based on the code amount of the image data exceeds the predetermined rate. Recording device. 9. The method according to claim 8, wherein the extracting unit determines the predetermined number of times so that a data rate obtained based on a code amount of the image data does not exceed a rate at the time of reproducing the recorded image data. Recording device. The encoding means distributes and encodes a code amount for each screen of the image data in accordance with a target code amount, and further converts the image data of one screen output from the memory for the second time or later into a target code amount. 2. The recording apparatus according to claim 1, wherein the recording apparatus is excluded from distribution targets. Extracting means for intermittently extracting image data of one screen from an image data sequence composed of a plurality of frames;
In order to encode the image data of one screen output from the extracting means by an intra-screen encoding method or an inter-screen encoding method, and to output the same image data as the one-screen image data a predetermined number of times during decoding Encoding means for adding the inter-screen encoded data to the encoded one-screen image data and outputting the image data;
A recording unit for recording the image data output from the encoding unit on a recording medium. 13. The apparatus according to claim 12, further comprising: setting means for arbitrarily setting the predetermined number of times, and control means for controlling the extracting means and the encoding means according to the number of times set by the setting means. Recording device. The extracting means has a memory for storing the input image data string, and the control means controls the memory to write one screen of image data for every N screens of the image data string in the memory. 13. The recording apparatus according to claim 12, wherein: 15. The recording apparatus according to claim 14, further comprising a counter for counting the number of screens of the image data, wherein the control unit controls writing of the image data to the memory based on a count value of the counter. 13. The recording apparatus according to claim 12, further comprising control means for determining the predetermined number of times based on a code amount of the encoded image data. 17. The recording apparatus according to claim 16, wherein the control unit determines the predetermined number of times so that a data rate obtained based on a code amount of the image data does not exceed a predetermined rate. 18. The recording apparatus according to claim 17, wherein the control unit increases the predetermined number of times when the data rate obtained based on the code amount of the image data exceeds the predetermined rate. 18. The method according to claim 17, wherein the extracting unit determines the predetermined number of times so that a data rate obtained based on a code amount of the image data does not exceed a rate at the time of reproducing the recorded image data. Recording device. An apparatus which periodically extracts one frame of image data from an input image data string, encodes the extracted image data by an MPEG method, and records the encoded image data on a recording medium,
A recording apparatus, wherein at least one frame of the same image data as the extracted one frame of image data is inserted as a dummy frame, and the image data of the dummy frame is coded by inter-screen coding and recorded. Extracting means for intermittently extracting image data of one screen from an image data sequence composed of a plurality of frames;
The one-screen image data output from the extracting means is encoded by an intra-screen encoding method or an inter-screen encoding method, and the inter-screen encoded data indicating a difference 0 with respect to the one-screen image data is encoded by Encoding means for adding and outputting the encoded one-screen image data;
A recording unit for recording the image data output from the encoding unit on a recording medium. 22. The recording apparatus according to claim 21, wherein the encoding unit outputs the inter-frame encoded data indicating the difference 0 for M screens. Control means for determining the value of M in accordance with the code amount of the image data, wherein the control means determines the value of M so that the data rate obtained based on the code amount of the image data does not exceed a predetermined rate. 23. The recording apparatus according to claim 22, wherein the value is determined. Control means for determining the value of M according to the code amount of the image data, wherein the control means sets a data rate obtained based on the code amount of the image data when reproducing the recorded image data. 23. The recording apparatus according to claim 22, wherein the value of M is determined so as not to exceed the rate. 23. The recording apparatus according to claim 22, further comprising setting means for arbitrarily setting the value of M. An extraction process of intermittently extracting image data of one screen from an image data sequence composed of a plurality of frames and repeatedly outputting the extracted image data of one screen a predetermined number of times;
An encoding process of encoding the image data output from the extraction unit using an intra-screen encoding method and an inter-screen encoding method;
A recording process for recording the image data encoded by the encoding means on a recording medium. An extraction process for intermittently extracting image data of one screen from an image data sequence composed of a plurality of frames;
In order to encode the image data of one screen output from the extracting means by an intra-screen encoding method or an inter-screen encoding method, and to output the same image data as the one-screen image data a predetermined number of times during decoding Encoding processing for adding the inter-screen encoded data to the encoded image data of one screen and outputting the data;
A recording process of recording the image data output from the encoding unit on a recording medium. A method of periodically extracting one frame of image data from an input image data sequence, encoding the extracted image data by an MPEG method, and recording the encoded image data on a recording medium,
A recording method, comprising inserting at least one frame of the same image data as the extracted one frame of image data as a dummy frame, and encoding and recording the image data of the dummy frame by inter-screen encoding. An extraction process for intermittently extracting image data of one screen from an image data sequence composed of a plurality of frames;
The one-screen image data output from the extracting means is encoded by an intra-screen encoding method or an inter-screen encoding method, and the inter-screen encoded data indicating a difference 0 with respect to the one-screen image data is encoded by An encoding process for adding and outputting the encoded image data of one screen;
A recording process for recording the image data output from the encoding means on a recording medium. A storage medium storing a computer program for realizing the method according to claim 26 using a computer.

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