JP3034552B2 - Image signal recording device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image signal recording apparatus, and more particularly, to an image signal recording apparatus that records an image signal formed by an image signal forming unit such as an image sensor.

[Prior Art] A digital memory camera as an example of a conventional image signal recording apparatus will be described with reference to FIG. 12. When a subject image formed on an imaging surface of an image sensor 1 forming an image signal forming means is photoelectrically converted. The image signal obtained by the conversion is signal-processed by the analog processing circuit 2 and converted into a digital signal by the A / D converter 3, and then supplied to a buffer memory 5 formed of an SRAM or the like to be temporarily stored. You.

On the other hand, the image signal read out from the memory 5 at the time of non-shooting is compressed in the band by the encoding circuit 6 and recorded on the recording medium of the storage device 7. A control signal is sent from the system controller 8 which controls the sequence of each section of the digital memory camera to the image sensor 1 and the encoding circuit 6, and a signal is transmitted between the buffer memory 5 and the storage device 7. The exchange is performed.

[Problems to be Solved by the Invention] However, after temporarily storing image information in a buffer memory 5 formed of an SRAM or the like, the image information is read out from the memory, the band is compressed and transferred to the storage device 7. In the conventional example, a buffer memory 5 having a large storage capacity is required. In other words, a storage capacity that can store image signals for at least one screen is required. However, considering use in the continuous shooting mode, a buffer memory having a storage capacity multiplied by the number of continuous shootings is required. It will be.

SUMMARY OF THE INVENTION An object of the present invention is to provide an image signal recording apparatus which solves the above-mentioned problems and reduces the memory capacity of a buffer memory required for high-speed continuous shooting.

[Means for Solving the Problems] A first image signal recording apparatus according to the present invention is a first image signal for compressing an image signal formed by an image signal forming unit at a first compression rate via a buffer memory. An image signal recording device for supplying an image signal supplied to a compression means and recording the image signal compressed by the first image signal compression means on the applied image signal recording medium. The image signal is compressed at a second compression ratio lower than the first compression ratio and supplied to the buffer memory, and the image signal stored in the buffer memory is read out and restored, and the first image signal compression means And a second image signal compressing means for supplying the image signal to the second image signal.

According to a second image signal recording device of the present invention, in the first image signal recording device, the second image signal compression means includes an encoding circuit based on a DPCM encoding method.

Further, in the third image signal recording apparatus according to the present invention, in the first image signal recording apparatus, the buffer memory may include a supply repetition rate of image information sequentially supplied from the image signal forming means and the second image signal recording apparatus. This is selected so as to correspond to a plurality of images in accordance with the image compression processing speed of the image signal compression means.

[Operation] In this image signal recording apparatus, the image signal formed by the image signal forming means is compressed at a relatively low second compression ratio and then stored in the buffer memory. Can be stored. Therefore, high-speed continuous shooting is possible, and the memory capacity of the buffer memory required to store image information for one screen can be reduced in inverse proportion to the compression ratio. Also, the image stored in the buffer memory is read and restored, compressed at a first compression ratio higher than the second compression ratio, and then recorded on an image signal recording medium. The memory capacity required to store image information for one screen of the signal recording medium can be further reduced.

Hereinafter, the present invention will be described in detail with reference to the drawings. In the following embodiments, an example in which the image signal recording apparatus according to the present invention is applied to a digital memory camera will be described.

FIG. 1 is a block diagram of a first embodiment of the present invention. The first embodiment is largely different from the conventional example shown in FIG. 12 in that a second encoding circuit as a preliminary compression means having a low compression ratio but capable of high-speed operation is provided in the preceding stage of the buffer memory 5. 4 and the encoding circuit 6
(Adaptive Discrete Cosine Transform) There is no difference from the above-mentioned conventional example except for the point that the encoding circuit 6a is replaced with the encoding circuit 6a based on the encoding method. Omitted.

In FIG. 1, a second encoding circuit 4 corresponds to a second image signal compression unit referred to in the claims, and includes, for example, DPCM (Di
A circuit that compresses the band to about 1/5 using a simple coding technology such as fferential pulse code modulation (coding), and performs appropriate arithmetic processing on past image signals to predict the next image signal. A predictor 4b for calculating a value, and a first for calculating a difference between an output signal of the predictor 4b and a current image signal.
Adder 4d, an encoder 4a that encodes an output signal of the adder 4d and applies it to the buffer memory 5, a decoder 4c that decodes a signal read from the buffer memory 5, and an output of the decoder 4c. The sum of the signal and the output signal of the predictor 4b,
That is, it is constituted by the second adder 4e for obtaining the original signal.

In addition, the encoding circuit 6a is provided with the first
The image information for one screen of a still image read out from the buffer memory 5 and decoded by the second encoding circuit 4 is stored in a frame incorporated in the encoding circuit 6a. This is a circuit that expands the data on the memory, encodes the data by the ADCT coding method, and compresses the band to 1/10 to 1/20. Note that, for each of the above DPCM and ADCT coding methods,
This is described in detail in "Trends in Still Image Coding Technology" by Tomohiro Ochi at the 18th Conference on Image Engineering in 987, and will not be described here.

In the first embodiment thus constructed, the image signal digitized by A / D conversion by the A / D converter 3 has a low compression ratio, but operates at a high speed in the second encoding circuit. At 4, the band is compressed to about 1/5 and then stored in the buffer memory 5. The image information compressed and stored in the buffer memory 5 is read out during non-shooting, decoded by the second encoding circuit 4, and reproduced into the original image signal before compression.
The image information reproduced in the original image signal has its operation speed reduced but its band is reduced by 1/10 to 1 /
After being compressed to 20, the data is recorded in the storage device 7 having a built-in recording medium.

Next, the recording operation of the image signal in the first embodiment will be described with reference to the flowcharts of FIGS.

In FIG. 2, when the power of the image signal recording apparatus is turned on, or when a start switch such as a single shooting mode or a continuous shooting mode is depressed, first in step S1, the buffer memory 5 (see FIG. 1) is read. Check if the memory area is free. If the memory area of the buffer memory 5 is vacant, the process proceeds to step S2 to determine whether the mode is the single shooting mode or the continuous shooting mode, and shifts to subroutines for the respective modes described later with reference to FIGS. On the other hand, if the memory area of the buffer memory 5 is not empty in step S1,
Proceeding to step S3, it is checked whether the recording medium of the storage device 7 is full. If the recording medium is full, a warning is issued to the user to urge the user to replace the medium (step S4). If the recording medium is not full, the memory information band-compressed from the memory area of the buffer memory 5 using the DPCM encoding method Is read (step S5), and the second encoding circuit 4 performs DPCM decoding (step S6). Then, the encoding circuit 6a performs encoding of the ADCT encoding method (step S
7) After compressing the band of the image information, the band-compressed image information is recorded on the recording medium of the storage device 7 (step S8). Thereafter, the process returns to step S1, and the routine of steps S1 to S8 is repeatedly executed.

FIG. 3 is a flowchart of the single shooting when the single shooting mode is determined in step S2 in FIG. In the figure, when the flow of the single shooting starts, the process first proceeds to step S11, and it is determined whether or not the memory area of the buffer memory 5 is already full. If the memory area of the memory 5 is full, a warning that the buffer memory is full is displayed (step S1).
2) Then, the mode shifts to the recording mode, and if it is not full, the process proceeds to step S13 to execute the shooting operation. After that, one image information obtained by this photographing operation is digitized,
The data is encoded by the DPCM encoding method in the second encoding circuit 4 (step S14), the band is compressed to about 1/5, and then recorded in the buffer memory 5 (step S15). Move to

FIG. 4 is a flowchart of the continuous shooting when the continuous shooting mode is determined in step S2 in FIG. In this continuous shooting, naturally, single shooting is repeatedly performed for the number of continuous shots. Therefore, in FIG. 4, the same steps as those in FIG. Description is omitted.

In FIG. 4, when the single-shot shooting consisting of steps S11 to S15 is completed, the process proceeds to step S21, where it is determined whether or not a predetermined number of continuous shots has been reached. Execute repeatedly. Then, when the number reaches the predetermined number, the mode shifts to the recording mode.

According to the first embodiment described in detail with reference to FIGS. 1 to 4, (1) Prior to recording one screen of image information in the buffer memory 5, the DPCM operating at a low compression rate but operating at a high speed Since the bandwidth of the image information is compressed to about 1/5 by the second encoding circuit using a simple scheme such as the encoding scheme, the required memory capacity of the buffer memory 5 is reduced to about 1/5. be able to. Conversely, if the memory capacity of the buffer memory 5 is set to be the same as the conventional one, it is possible to record up to about five screens, so that continuous shooting is possible. At this time, the capacity of the buffer memory 5 may be appropriately selected according to the continuous shooting speed (supply repetition rate of the image information sequentially supplied from the image signal forming unit (image sensor 1)) and the compression processing speed of the image information. . In this case, adding the second encoding circuit 4 based on the DPCM encoding method can reduce the size of the apparatus and reduce the cost, rather than providing the buffer memory 5 for the number of continuous shots.

(2) Therefore, as a band compression means of an image signal for recording a large number of captured images in the storage device 7, the compression ratio is as high as that of the encoding circuit 6a using the ADTC encoding method, but it is complicated and time is required for transmission. Such a band compression method can be used.

(3) The storage device 7 uses a low-speed memory such as an E ² PROM or FPROM, which has a large storage capacity and a low memory cost per bit but requires a relatively low-speed writing operation. can do.

And the like.

FIG. 5 is a block diagram of a second embodiment of the present invention. In the image signal recording device of the present invention, the encoding circuit 6b and the second encoding circuit 4 are provided independently of each other,
In the first embodiment, the encoding circuit 6a is provided with the ADCT encoding method,
Although the DPCM encoding method is used for the second encoding circuit 4, in the second embodiment, the DPCM encoding method is used for the second encoding circuit 4.
The point of using the DPCM encoding method is the same as that of the first embodiment, except that a vector quantization method is used instead of the ADCT encoding method used in the encoding circuit 6a, and this is
Is different. Except for this point, since there is no difference from the first embodiment, there is no difference in the operation and effect. Therefore, the same components are denoted by the same reference numerals, and description thereof will be omitted.

The encoding method used in the encoding circuit 6b is as follows.
In addition to the vector quantization method, for example, a Hadamard transform method may be used. Each of these conversion methods is described in “Trends in Still Image Coding Technology” by Tomohiro Ochi in the 1987 18th Conference on Image Engineering, and the description is omitted here. .

As described above, according to each embodiment, the following effects are exhibited. (1) High-speed continuous shooting is possible, and the memory capacity of the buffer memory 5 can be reduced.

(2) The operation speed of the storage device 7, which is relatively high in density but cannot increase the writing speed so much, can be ignored.

(3) As the encoding circuit 6, a method with a high compression rate can be used, and the memory capacity of the storage device 7 can be reduced.

By the way, in each of the embodiments described above, an example in which the present invention is applied to a digital memory camera as an example of an image signal recording apparatus has been described. However, an analog signal is added to the image information output from the image signal forming means. The present invention is also applicable to an analog-type image signal recording apparatus that performs magnetic recording on a magnetic disk or the like after performing the processing. That is, prior to applying the image signal to the buffer memory 5, the band is compressed by the second encoding circuit 4 as a preliminary compression means operating at a low compression rate but operating at a high speed. The basic idea of the present invention of reducing the memory capacity of the buffer memory 5 can be applied to all kinds of image signal recording devices, whether digital or analog.

As described above, according to the present invention, the capacity of the buffer memory can be remarkably reduced in size, but the configuration of the above-described encoding circuits 6a and 6b applied in the device of the present invention is further reduced. An embodiment which further simplifies the entire apparatus by the above will be described below.

FIG. 6 is a conceptual diagram for explaining an operation of encoding (compressing) a frame image of one screen S by the encoding circuit described above. A frame image of one screen S is composed of a set of pixels PX, PX, as image constituent units.
The reading of the image signal from the image sensor is normally performed sequentially by repeating horizontal scanning (return lines are indicated by broken lines) as indicated by solid arrows in the drawing. On the other hand, encoding of image information of one screen S is performed for each unit area (block indicated by a dashed line in the figure) PU composed of M × N pixels of M in the vertical direction and N in the horizontal direction. This is performed by associating a predetermined number of pieces of information representing the block. The whole area of one screen S is covered by a plurality of these blocks PU in accordance with a predetermined unit area M × N. The setting of the unit area M × N is selected, for example, as 8 × 8. If it is possible to instantly encode the image information for each block PU, if a buffer memory for M lines (8 lines) is provided in front of the means having such an encoding function, If image information for each PU is fetched into such a buffer memory, the entire area of one screen S should be able to be encoded by repeating the encoding operation sequentially. However, in practice, coding by DCT or ADCT requires a considerable amount of processing time.
Thus, it was not possible to encode the entire area of one screen S only by providing a small buffer memory.

FIG. 7 is a block diagram showing a configuration example of a general encoding circuit applied to this type of apparatus. This encoding circuit
In 6a, since encoding by DCT to ADCT requires a considerable processing time as described above, the encoder 62a
A frame memory 61a is provided as a buffer memory in the previous stage (based on DCT to ADCT). In this type of conventional apparatus, as shown by solid arrows in FIG. 6, an image signal is supplied to the encoding circuit 6a at a relatively high transmission rate so as to correspond to repetition of horizontal scanning. Therefore, this image signal is once taken into the memory 61a in frame units,
After that, it was necessary to sequentially encode each block PU indicated by a dashed line in FIG. That is, a storage state of the image information similar to the screen of FIG. 6 occurs once in the frame memory 61a, and the encoder 62a stores the stored and held image information for each block PU indicated by a one-dot chain line in FIG. The operation of scanning, reading, and encoding as shown by the broken arrow is sequentially executed for all the blocks PU. The encoding circuit 6a of FIG. 7 can of course be applied to the apparatus of the present invention shown in FIGS. 1 and 5, but the apparatus of the present invention, on the other hand, uses the buffer memory 5 (FIG. 1). Since the supply of image information to the encoding circuit 6a can be performed at a low speed or intermittently as required by the system controller 8,
This encoding circuit can be downsized.

FIG. 8 is a block diagram showing the configuration of a smaller-scale encoding circuit applied to the apparatus of the present invention. In the encoding circuit 62c in FIG. 8, a line memory 61c is provided as a buffer memory in a stage preceding the encoder 62c similar to the encoder 62a in the encoding circuit 6a in FIG. This line memory 61c has a capacity of M lines corresponding to the block PU in FIG. As described above, the buffer memory 5 (first
The image information supplied to the line memory 61c is supplied to the M × N pixels since the system controller 8 can supply the image information to the encoding circuit 6a at low speed or intermittently as required. Are sequentially encoded by the encoder 62c for each block PU corresponding to.

FIG. 9 is a diagram showing the operation timing of a system to which the encoding circuit 62c of FIG. 8 is applied. As shown, the operations of decoding (DPCM decoding) of information read from the buffer memory 5 (FIG. 1) and writing to the line memory 61c, and reading and encoding (DCT) of the line memory 61c are performed by the system controller. 8 (FIG. 1). In other words, the encoding circuit of FIG.
In 62c, the encoding itself is performed intermittently. On the other hand, if two line memories are provided, coding can be executed effectively continuously.

FIG. 10 is a block diagram showing a configuration of a simple encoding circuit applied to the apparatus of the present invention, which can execute encoding effectively continuously. Encoding circuit 60 in FIG.
In 0, two line memories (A, B) 611 and 612 are provided as buffer memories in the preceding stage of the encoder 620 similar to the encoder 62a in the encoding circuit 6a of FIG. The two line memories 611 and 612 are controlled by the system controller 8 (FIG. 1) so that when one of the information is read, the other is read by the switches SA and SB provided on their input and output sides.

FIG. 11 is a diagram showing operation timing of a system to which the encoding circuit 600 of FIG. 10 is applied. As shown,
By switching the switches SA and SB, the two line memories (A) and (B) are temporally alternately controlled so that when information is read into one, the other performs information read.
As a result, the encoding circuit 620 can execute encoding effectively and continuously. Therefore, it is possible to execute the continuous encoding process with a circuit having a much smaller configuration than the general encoding circuit described with reference to FIG. 7, and the implementation described above with reference to FIGS. The apparatus as a whole will be further simplified while having the same functions as the example.

[Effects of the Invention] As described above, according to the present invention, the image signal formed by the image signal forming means is compressed at a relatively low second compression ratio and then stored in the buffer memory. The data can be stored in the buffer memory at high speed. Therefore, high-speed continuous shooting is possible, and the memory capacity of the buffer memory required to store image information for one screen can be reduced in inverse proportion to the compression ratio. Also, the image stored in the buffer memory is read and restored, compressed at a first compression ratio higher than the second compression ratio, and then recorded on an image signal recording medium.
The memory capacity required to store the image information for one screen of the image signal recording medium can be further reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram of a first embodiment in which an image signal recording apparatus according to the present invention is applied to a digital memory camera. FIG. 2 is a flowchart of an operation of recording the image signals in the storage apparatus in FIG. FIGS. 3 and 4 are flowcharts of respective recording operations in the single shooting mode and the continuous shooting mode in the buffer memory in FIG. 2, and FIG. 5 is a block diagram of a second embodiment of the present invention. FIG. 6 is a conceptual diagram for explaining an operation of encoding (compressing) a frame image of one screen S by the encoding circuit described above, and FIG. 7 is a general view applied to this type of apparatus. FIG. 8 is a block diagram showing a configuration example of a simple encoding circuit, FIG. 8 is a block diagram showing a configuration of a further downsized encoding circuit applied to the apparatus of the present invention, and FIG. Of the system to which the optimization circuit 62c is applied FIG. 10 is a block diagram showing a configuration of a simple encoding circuit applied to the apparatus of the present invention, which can execute encoding effectively continuously, and FIG. FIG. 10 is a diagram showing operation timings of a system to which the encoding circuit 600 shown in FIG. 10 is applied. FIG. 12 is a block diagram of a conventional digital memory camera. DESCRIPTION OF SYMBOLS 1 ... Image sensor (image signal formation means) 4 ... Second encoding circuit (second image signal compression means) 5 ... Buffer memory 6,6a-6d ... Encoding circuit (first image signal) Compression means)

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H04N 5/91-5/956 H04N 5/225 H04N ^7/ 24-7/68

Claims (3)

(57) [Claims] An image signal formed by an image signal forming means is supplied to a first image signal compressing means for compressing the image signal at a first compression rate via a buffer memory, and is compressed by the first image signal compressing means. An image signal recording device for recording the applied image signal on the applied image signal recording medium, wherein the output image signal of the image signal forming means is a second compression ratio lower than the first compression ratio. And a second image signal compressing means for supplying the compressed image data to the buffer memory, reading and restoring the image signal stored in the buffer memory, and supplying the restored image signal to the first image signal compressing means. Image signal recording device. 2. The image signal recording apparatus according to claim 1, wherein said second image signal compression means includes an encoding circuit based on a DPCM encoding method. 3. The image processing apparatus according to claim 1, wherein said buffer memory is adapted to handle a plurality of images in accordance with a supply repetition rate of image information sequentially supplied from said image signal forming means and an image compression processing speed in said second image signal compressing means. 2. The image signal recording apparatus according to claim 1, wherein the image signal recording apparatus has been selected to be used.