JP2001320705A - Image data compression device for monitoring camera - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image data compression device for a monitoring camera which minimizes the capacity of a memory for temporary storage of compressed data when compressing the image data of a prescribed number of images picked up with the monitoring camera and transmitting them through digital transmission media. SOLUTION: The compression device has a memory part 15 for compressed data to store compressed picture data 22 obtained by compressing image data 21 from a camera part 11 in a compression part 13 and to output data an amount H for every input frame, and a CPU part 14 to calculate the difference D between the compressed data amount H and a reference value C and to accumulate the difference D for comparing it with thresholds F and -G. Each input image frame is compared and when a cumulative value E becomes a threshold F or more, the CPU part 14 raises the compression ratio of a compression part 13 and controls the compression part 13 so that the compressed data amount H of the following processing image frame becomes a reference value C or less. Besides, when the cumulative value E becomes a threshold -G or less, the CPU part 14 controls a compression part 13 when compressing the following image frame so that the compressed data amount H becomes a reference value C or more.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surveillance camera image data compression apparatus for compressing and storing image data of a predetermined number of images.

[0002]

2. Description of the Related Art For example, a remote monitoring camera system includes:
2. Description of the Related Art Some video data is transmitted using digital transmission media such as the Internet so that a captured video at a certain point can be viewed at another point. In a remote surveillance camera system, an image captured by a remote surveillance camera usually includes a predetermined m (natural number) images temporally before a specific timing when a shooting instruction is given, that is, a trigger point, and a trigger. A plurality of predetermined nm images after the dot are transmitted. Where n is
This is a natural number representing the number of monitoring images designated for transmission, and is a predetermined value. When these images are transmitted via a communication line by digital transmission media such as the Internet, compression processing is generally performed before transmission in order to efficiently transmit a huge amount of information of a video signal. .

[0003] In this compression processing, JPEG (Joint Photographic cod) for reducing redundancy by utilizing the properties of image data.
ing Experts Group). Each compressed video data is temporarily stored in a buffer memory functioning as a compressed data memory. The compressed data memory has a sufficient storage capacity for the number of images to be transmitted, the compressed image data is input in time series, and when the free storage area is exhausted, the oldest compressed image data is sequentially written from the area in which the data is written. Used as a ring buffer to overwrite the latest compressed image data.

When a transmission instruction (trigger) is output from the control unit of the remote monitoring camera system, the image data of m images before the trigger and nm images after the trigger are sequentially read from the compressed data memory, and temporarily stored in the transmission buffer. Write to memory. This transmission buffer memory, that is, the storage memory,
A buffer memory for matching the speed of the transmission line, reads out image data in conformity with communication conditions such as the transmission speed of the transmission line, and sends the image data to a remote place via a communication line such as the Internet.

[0005]

Generally, image data compressed by JPEG or the like is used to reduce the complexity of the picture to be compressed.
The amount of data per screen varies according to the state of each image. On the other hand, the compressed data memory needs to hold the required number of pieces of compressed image data regardless of the fluctuation of the compressed data amount. For that purpose, it is necessary to assume a maximum value of the compressed image data per screen and prepare a compressed image data memory having a storage capacity of n required images with respect to the assumed maximum value. As described above, it is necessary to prepare a compressed image data memory having an enormous memory capacity, so that the scale of the compressed data memory becomes large, and there is a problem that the configuration becomes complicated such as an increase in power consumption and cost.

The present invention focuses on the above points, and solves such disadvantages of the prior art and can reduce the storage capacity of a compressed image data memory for storing images before and after a trigger point. An object of the present invention is to provide an image data compression device for a surveillance camera.

[0007]

According to the present invention, in order to solve the above-mentioned problems, an image data compression device of a surveillance camera for compressing and storing image data of a predetermined number of images sequentially arrives. Compression means for compressing image data for each image at a variable compression rate, storage means for overwriting the compressed image data in order from oldest image data and cyclically storing the compressed image data, and storage means for storing the stored compressed image data Output means for reading and outputting the compressed image data, and control means for controlling the compression means, the storage means and the output means, wherein the control means calculates a difference between the data amount of the compressed image data and a predetermined first reference value. Then, a compression rate corresponding to the difference is set in the compression means, and the compression means compresses the image data at the set compression rate, and the compression rate is determined by the compressed image data stored in the storage means. Is set to such a value that does not exceed the number of fixed, control means outputs from sequentially reads output means from the storing means compressed image data of a predetermined number of sheets, including a read trigger time.

In a preferred embodiment, the compressed image data amount H of each frame (one screen) of the image is monitored, and a difference value D between the compressed data amount H of each image frame and a predetermined reference value C is calculated. This difference value D is sequentially accumulated, and when the accumulated value E becomes equal to or more than the upper limit threshold F,
The compression rate of the image compression process is increased so that the compressed data amount H of the frame image is controlled to be smaller than the reference value C. When the accumulated value E becomes equal to or less than the lower threshold value -G, the compression rate is reduced so that the compressed data amount H becomes larger than the reference value C.

By performing such a compression ratio control, the amount of data stored in the compressed data memory becomes a value Cxn +
It can be suppressed to α. Here, α is an overflow margin, and is advantageously set to be equal to the sum of the threshold value F and the maximum amount of compressed image data per image and the assumed data amount. Thus, the data amount in the compressed image data memory can be suppressed to a predetermined value or less.

[0010]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of a control of a compressed data memory of a surveillance camera according to the present invention. FIG. 1 is a functional block diagram showing the configuration of an embodiment of the surveillance camera system of the present invention. This surveillance camera system always captures an image of an object scene with the camera unit 11 and, when receiving a shooting instruction from the sensor unit 12 or an external network 18 which is a digital transmission medium such as the Internet, temporally before the trigger point. The imaging transmission system transmits image data representing m (natural number) images and a plurality of subsequent nm images to the external network 18 as compressed image data.

The camera section 11 has, for example, a solid-state image pickup device, thereby constantly taking an image of an object field to be monitored, and converting a video signal representing the object field into digital data finally. This is an imaging device that outputs from the output 21. An imaging output 21 from the camera unit 11 is connected to an input of the compression unit 13.

The compression unit 13 is a data compression function unit that takes in the image data 21 from the camera unit 11 at a rate of B (natural number) frames per second and compresses the image data 21 in frame units. In the present embodiment, the compression unit 13 employs a JPEG compression method for reducing redundancy by utilizing the properties of image data. The compression unit 13 includes MPEG (Moving Picture coding Experts
Other image data compression schemes such as up) are also advantageously applied. In this embodiment, the frame rate is set to
Control line from a CPU (Central Processor Unit)
It is configured to be set variably through 32.
Alternatively, the frame rate may be fixedly set in the camera unit 11. The compression unit 13 in the embodiment performs compression in units of frames, but is not limited to this. For example, the compression unit 13 may be configured to perform compression in units of fields. The compression unit 13 also receives a compression ratio control signal 26 from the CPU unit 14,
As a result, the compression ratio is variably set. The compression ratio can be changed by, for example, changing the quantization width of the quantization step of the compression unit 13. Output 22 of compression unit 13
Are connected to the compressed data memory unit 15.

The compressed data memory unit 15 is a buffer memory for temporarily storing compressed image data, and has a storage capacity enough to store compressed image data of n (natural number) of images to be transmitted. The storage device functions as a storage device. Number of transmitted images n per trigger
Is fixed in this embodiment, and the compressed data memory unit 15
Are configured to have a storage capacity commensurate with the number n of transmitted images. However, the number of transmitted images for one trigger may be variably set by the CPU unit 14 to a value equal to or less than the value n corresponding to the storage capacity. The compressed data memory unit 15 also has a function of outputting a data amount information signal 27 indicating the data amount of each frame of the compressed data 22 input from the compression unit 13 to the CPU unit 14. The compressed data output 23 of the compressed data memory unit 15 is connected to the storage unit 16.

The storage section 16 temporarily stores the compressed image data 23 read from the compressed data memory section 15 and outputs the compressed image data 23.
This is a buffer memory for adjusting the reading speed of the image data output from the transmission line 18 with the transmission speed in the transmission line 18 and the like. In the storage unit 16, parameters such as the speed required for transmission on the network 18 are set by a control signal 29 from the CPU unit 13. The transmission image data output 24 from the storage unit 16 is connected to the network interface unit 17. The network interface unit 17 is an interface function unit that performs various matchings on the transmission image data 24 and transmits the transmission image data 24 to the external network 18 for transmission to a line of the external network 18 such as the Internet. When receiving an image data transmission instruction, that is, a trigger signal from a remote place via the network 18, the network interface unit 17 converts this into a transmission instruction signal 30 as a CPU
It also has the function of transferring to

On the other hand, the sensor section 12 is a trigger detecting section for detecting characteristics such as movement, voice, temperature and the like in an object scene, that is, a monitoring place, and outputting the detection result as a trigger output 25. The output 25 is input to the CPU unit 14.

The CPU section 14 is connected to the sensor section 25, the compression section 13, the compressed data memory section 15, the storage section 16, and the network interface section 17 as shown in the figure, and controls the operation of the entire surveillance camera. is there. More specifically, from the camera unit 11 to the storage unit 16 via the compression unit 13 and the compressed data memory unit 15 at a rate of B frames per second,
In other words, the image data 21 is captured and compressed at 1 / B second intervals, and the compressed image data 23 is accumulated by the ring buffer operation, but the CPU unit 14 receives the trigger signal 25 from the sensor unit 12 and the network interface unit 17 Transferred transmission instructions
Read control signal to compressed data memory unit 15 in response to 30
28, and has a control function of reading out image data representing n images before and after including the trigger point from the storage memory 16 and transmitting the image data to the external network 18. The CPU unit 14 also
The compression ratio control signal 26 is supplied to the compression unit 13 so that the compression ratio of the image data 21 can be variably set to the compression unit 13. CP
The U unit 14 further receives the data amount information 27 from the compressed data memory unit 15, and
The compression ratio control signal 26 that adaptively changes the compression ratio of the compression unit 13 based on a reference value C described later is generated by performing a difference operation on the data amount of the compressed data 22 input to. The adaptive control of the compression ratio of the compression unit 13 will be described in detail below.

The operation of adaptively controlling the compression ratio of the compression section 13 in this embodiment will be described in detail with reference to FIG. The operator inputs an instruction to set operating conditions of the apparatus to the apparatus from a remote place through the network 18 or by operating an operation unit (not shown) of the apparatus. In response to these instructions, the CPU unit 14 sends to the monitoring camera the values of various parameters such as the number of images m before the trigger, the number of images nm after the trigger, the image frame rate B / sec, and the initial value of the compression ratio. It is set (step S11).

Therefore, the camera unit 11 takes an image of the object scene,
The captured image data 21 is output to the compression unit 13 in frame units at a frame rate B / sec (S12). The compression unit 13 compresses the input captured image data 21 and outputs the compressed one-frame compressed image data 22 to the compressed data memory 15 (S
13) . The compressed image data 22 is stored in the compressed data memory 15
(S14). The compressed data memory 15 cyclically stores the set number n of compressed image data as a ring buffer. That is, the compressed image data is written in a time-sequential sequential storage position, and thereafter, the storage position where the oldest image data is stored is overwritten with the new compressed image data.

At this time, the compressed data memory unit 15 counts the data amount H (dimension is, for example, the number of bytes) of the input compressed image data of one frame, and sends a signal 27 indicating the count result to the CPU unit 14. (S15). The CPU 14 calculates a difference D = HC between the input count data amount H and a predetermined reference value C (S16), adds the difference value D to an accumulator (not shown), and adds the accumulated value E ( = ΣD)
(S17). Then, the CPU unit 14 compares the accumulated difference value E with a predetermined upper threshold value F, and determines whether the accumulated difference value E is equal to or larger than the threshold value F (S18).

If it is determined in step S18 that the accumulated difference value E is equal to or larger than the predetermined threshold value F, the CPU 14
Select a compression ratio that is higher than the compression ratio set in,
The compression unit 13 is instructed to increase the compression ratio (S19). More specifically, the CPU unit 14 sends an image compression control signal 26 for increasing the quantization width of the quantization step of the compression unit 13 to the compression unit 13. In general, the new compression ratio is selected so that the data amount H of the image data compressed at the compression ratio is equal to or smaller than the reference value C. Thereafter, the control returns to step S12, where the image data of the next frame is
Then, the flow from step S12 is repeated.

If it is determined in step S18 that the accumulated difference value E is smaller than the threshold value F, the CPU unit 14 determines whether the accumulated difference value E is equal to or smaller than another predetermined lower limit threshold value -G (S2).
0). Here, the value G takes a positive value. If the accumulated difference value E is not equal to or smaller than the threshold value -G, the control returns to step S12, and the flow from step S12 is repeated for the next frame to be input.

If it is determined in step S20 that the difference accumulated value E is equal to or smaller than the threshold value -G, the CPU unit 14 sends an image compression processing control signal 26 to the compression unit 13 so as to reduce the compression ratio of the compression unit 13. (S21). In response, the compression unit 13 narrows the quantization width of the quantization step. Hereinafter, step S1
2 Repeat the flow after that. As is clear from the above description of the operation, the comparison between the accumulated difference value E and the threshold value is performed on a frame basis, and the compression ratio is also controlled on a frame basis.

Referring to FIG. 3, there is illustrated an example of the relationship between the transmitted image frame, the state of the compression process, and the difference accumulated value E. When the image data is compressed while correcting the compression ratio as described above, the cumulative difference value E for the compressed image data 22 changes as shown in the lower part of FIG. In the figure, a state 40 is a state in which the above-described difference accumulated value E exceeds the threshold value F, and a state 42 is a state in which the difference accumulated value E is less than the threshold value -G. In state 40, the compression unit 13 is controlled to increase the compression ratio of the image data of the next incoming frame. On the other hand, in the state 42, the compression unit 13
Control is performed in such a manner that the compression ratio for the image data of the next input frame is reduced.

The above-mentioned reference value C and threshold values F and -G are selected and set in the present apparatus as follows. When designing the present apparatus, the storage capacity of the compressed data memory unit 15 is set to at least a value obtained by multiplying the required number n of images to be transmitted for one trigger by the reference value C and adding the safety coefficient α to this. . The reference value C is determined in consideration of the data amount of image data compressed at a compression ratio capable of reproducing an image having a resolution generally required for a surveillance camera.
In this embodiment, the safety coefficient, that is, the margin α, is set equal to the sum of the assumed maximum data amount of the compressed image data and the upper limit threshold F.

As described above, the camera section 11 constantly captures an image of the object field to be monitored, and supplies video signal data representing the object field to the compression section 13 from the output 21 thereof. Compression section
The unit 13 compresses the input image data into redundancy in frame units and temporarily stores the compressed image data in the compressed data memory unit 15. CPU part
14 monitors the state of the compressed data memory unit 15 as described above, and adaptively controls the compression ratio.

Thus, in the steady state after the start of the operation and after the n-frame image data has been stored in the compressed data memory unit 15, the monitoring image transmission instruction trigger is generated from the sensor unit 12 or the network interface unit 17. Then, images of m frames before the trigger point and n frames of nm frames after the trigger point can be transmitted at any time.

More specifically, as described above, n pieces of image data are constantly updated and written cyclically in the compressed data memory unit 15 as described above. When the sensor unit 12 detects a movement, a sound, or a change in temperature at a monitoring location, a detection output 25 is input to the CPU unit 14. When the network interface unit 17 receives an image data transmission instruction via the network 18, the transmission instruction signal 30
Is input to the CPU unit 14. In response to the sensor unit detection signal 25 or the instruction 30 for transmitting the captured image from the network, the CPU unit 14 reads the control signal to the compressed data memory unit 15.
Give 28. Thereby, from the compressed data memory unit 15,
The n pieces of compressed image data 23 including the trigger point are sequentially read out in the transmission order and stored in the storage unit 16. The CPU unit 14 also provides a control signal 29 to the storage unit 16, and the storage unit 16 reads the compressed image data 24 after correcting the time axis according to the speed required for transmission on the network 18 in response to the control signal 29. It is supplied to the interface unit 17. The network interface unit 17 converts the transmission image data of the input 24 into a signal format conforming to the communication line standard of the network 18 and sends the signal to the network 18.

As described above, according to this embodiment, the difference between the data amount H of the compressed image data for each frame stored in the compressed data memory unit 15 of the monitoring camera and the reference value C is accumulated, and the accumulated value E is The compression ratio of the image data of the next frame is changed accordingly, and thereafter, the image data compressed at the changed compression ratio is stored in the compressed data memory unit 15. Therefore, the storage capacity required for the compressed data memory unit 15 can be suppressed to the value Cxn + α. Therefore, unlike the conventional method, it is not necessary to prepare an image data memory having a storage capacity for the number of transmission images of the maximum expected data amount of image data, and the amount of memory can be reduced, thereby reducing power consumption and cost.

In this embodiment, the compressed data memory unit
Although the capacity of the memory unit 15 is n frames, if the operation speed of the memory unit 15 is sufficiently high, it is obvious that the storage area necessary for storing the image data after the trigger point can be omitted or greatly reduced. is there.

Next, another embodiment of the present invention will be described with reference to FIG. In the above-described embodiment, the accumulated value E of the difference between the data amount H of the frame data and the reference value C is equal to the upper and lower thresholds F.
When the compression ratio of the compression unit 13 is changed in accordance with the departure from the range between -G, the image data of the next frame and subsequent images input from the camera unit 11 is compressed at the changed compression ratio. Was configured to. However, in the embodiment shown in FIG. 4, when the compression ratio of the compression unit 13 is changed in this manner, the difference accumulated value E is out of the range between the upper and lower thresholds F and -G. FIG. 1 shows that a new compression ratio is applied to the subsequent image data.
Are different from the embodiment shown in FIG. For this purpose, in the present embodiment, if it is determined that the accumulated difference value E is out of the range between the threshold value F and -G, the input image data 21 of the frame is compressed again with a new compression ratio. In order to hold the next input image data during the period, as shown in FIG.
An input buffer memory unit 52 is provided on the 21 side. In the following description, the same elements as those shown in FIG. 1 are denoted by the same reference numerals, and the same description will be omitted.

The buffer memory unit 52 is a temporary memory having a storage capacity for storing one or more frames of image data from the camera unit 11. The buffer memory 52 has a camera
The image data input from the output 60 of 11 is sequentially written for a plurality of frames, but when the storage area is full with the data thus stored, the buffer memory unit 52 overwrites the new data with the oldest frame data. This is a ring buffer.

Reading from the buffer memory unit 52 is performed by the CPU.
It is controlled by a read control signal 70 from the unit 14. CPU part
14 operates basically the same as the operation described with reference to FIG. 1 except that when the compression ratio of the compression unit 13 is changed, the input compressed image of the current frame supplied from the compressed data memory unit 15 Upon receiving the signal 27 indicating the data amount H of the data, the compression unit
It has a function of transmitting the compression ratio control signal 26 to the buffer 13 and transmitting a read control signal 70 to the buffer memory 52 to specify data to be read from the buffer memory 52.
The configuration of other parts may be the same as that of the embodiment shown in FIG.

The operation of this embodiment will be described with reference to FIG. Also in this flowchart, the same steps as those shown in FIG. 2 are denoted by the same reference numerals, and redundant description thereof will be omitted. FIG. 6 shows an example of the transition of the accumulated difference value in the present embodiment. Hereinafter, the operation of the present embodiment will be described in detail with reference to these.

When the operation is started and the CPU unit 14 is initialized S11, the frame data 60 of the captured image is sequentially input from the camera unit 11 to the buffer memory unit 52 at a frame rate B / sec (S112). Next, one frame worth of image data 21 is read from the frame memory 52 and input to the compression unit 13 (S113). Thereafter, the operation performed by the compression unit 13 and stored in the compressed data memory unit 15 is the same as the operation performed in step S13 described above.
The same as from to S17.

In step S18, if the accumulated difference value E is equal to or greater than the predetermined threshold value F, the CPU unit 14 increases the compression ratio of the compression unit 13 and instructs the compression unit 13 to increase the compression ratio (S19).
In the present embodiment, as the new compression ratio, a value is selected such that the compressed data amount H of the image data 21 of the frame, which is currently the object of compression by the compression unit 13, is equal to or smaller than the reference value C. CPU
The unit 14 sends the control signal 26 to the compression unit 13 so as to increase the compression ratio to a new value (S19), and sends the read control signal 70 to the buffer memory unit 52 to buffer the same image data 21 again. Read from the memory unit 52, and
Compresses the re-read image data 21 of the same frame at a new compression ratio (S121). The compression unit 13 overwrites and stores the compressed image data 22 in the compressed data memory 15 (S12
2). Thereafter, the control returns to step S113, in which the image data of the next frame is fetched from the buffer memory unit 52 into the compression unit 13, and thereafter, the flow from step S113 is repeated.

If it is determined in step S18 that the accumulated difference value E is smaller than the threshold value F, the CPU 14 proceeds to step S20. In step S20, the difference accumulated value E
If not -G, the control returns to step S113, and the flow from step S113 is repeated for the next frame to be input.

In step S20, when the accumulated difference value E is equal to or smaller than the threshold value -G, the CPU unit 14 executes step S21 and outputs the image compression processing control signal 26 so as to reduce the compression ratio of the compression unit 13. The data is sent to the compression unit 13. In response, the compression unit 13 narrows the quantization width of the quantization step.
Then, the CPU unit 14 sends the control signal 26 to the compression unit 13 so as to lower the compression ratio to a new value (S21), and, similarly to the above-described steps S121 to S122, the buffer memory unit 52.
And the same image data 21 is read out again. The compression unit 13
The image data 21 of the same frame read out again is compressed at a new compression ratio (S125). The compression unit 13 overwrites the compressed image data 22 on the compressed data memory 15 (S126). Thereafter, the control returns to step S113, where the buffer memory unit 52
Fetches the image data of the next frame into the compression unit 13 from
Hereinafter, the flow from step S113 is repeated.

When the image data is compressed while the compression ratio is corrected in this way, the accumulated difference value E for the compressed image data 22 becomes the upper and lower thresholds F and -G as illustrated in FIG.
Fluctuates within the range between

In this embodiment, when the difference accumulated value E is out of the range between the two thresholds F and -G, the compressed data amount H
Is changed to a new compression ratio such that is smaller than the reference value C,
The image data of the frame that has been subjected to the compression is compressed again. Because doing such a process, the storage capacity of the compressed data memory unit 15 can be suppressed to a value Cxn + alpha _1. In this embodiment, this margin α ₁ is
Advantageously, it is set to twice the value of the threshold value F. Thus, in the present embodiment, the memory capacity can be further reduced as compared with the embodiment shown in FIG.

In the present embodiment described here, the compression ratio is changed when the accumulated difference value E becomes equal to or smaller than the threshold value -G. However, in this case, the process may return to step S113 immediately without changing the compression ratio. In that case, the transmission speed is improved.

By the way, in the embodiment shown in FIG.
The U unit 14 may be configured to execute a compression ratio control operation as shown in FIG. This compression ratio control is different from the compression ratio control described with reference to FIG. 5 in that the difference value D is directly used to determine the change of the compression ratio without using the difference accumulated value E. Hereinafter, the compression ratio control operation will be described with reference to FIG.

As can be seen from the flowchart of FIG.
This compression ratio control operation is different from the flow shown in FIG. 5 in that step S118 in FIG. 5 is not provided, and the subsequent control uses the difference value D instead of the difference accumulation value E. Therefore, up to step S117 in FIG. 7 is the same as the flow in FIG.

When the difference value D (= HC) of the compressed image data amount H with respect to the reference value C is calculated in step S117, the control proceeds to step S219, and the CPU unit 54 determines that the difference value D is a predetermined reference value. In this embodiment, it is determined whether the value is “0” or more.
If the difference value D is less than 0, the process returns to step S113, reads the image data 21 of the next frame from the buffer memory unit 52, and repeats the control from step S114. This reference value may be a value other than 0.

On the other hand, in step S219, the difference value D becomes 0
In the above case, the control moves to step S120, and the CPU unit 14
Sends a compression ratio control signal 26 to the compression unit 13 to increase the compression ratio so that the data amount H after compression is equal to or less than the reference value C (S124). FIG. 8 shows an example of transition of the difference value D between the compressed image data H and the reference value C in the case of the control method shown in FIG. 7, but the above-described state corresponds to the state 80 in FIG. Therefore, the process proceeds to step S125, and the image data of the same frame is read from the buffer memory 52 again and compressed as described above. New compressed image data 22
Is overwritten and stored in the compressed data memory 15 (S126), and the process returns to step S113. Thereafter, the image data 21 of the next frame is read out from the buffer memory unit 52, and the control from step S114 is repeated.

According to such a compression ratio control operation, since the difference value D of the compressed image data does not become 0 or more,
The storage capacity of the compressed data memory unit 15 can be suppressed to the value Cxn or less. Therefore, the memory capacity can be further reduced, and the power consumption and cost of the device can be reduced.

[0046]

As described above, according to the present invention, the difference value of the data amount of the compressed image data for each frame stored in the compressed data memory of the surveillance camera with respect to the reference value is calculated, and based on the value, the difference value of the image data is calculated. By changing the compression ratio and storing the image data compressed at the new compression ratio in the compressed data memory, the storage capacity required for the compressed data memory is reduced, and the maximum expected data There is no need to prepare image data memories for the number of transmitted images. Therefore, the configuration is simplified, and power consumption and cost are reduced.

[Brief description of the drawings]

FIG. 1 is a functional block diagram showing the configuration of an embodiment of an image data compression device for a surveillance camera according to the present invention.

FIG. 2 is a flowchart illustrating an operation example of the embodiment illustrated in FIG. 1;

FIG. 3 is an explanatory diagram for explaining difference accumulation values and compression ratio control in the embodiment.

FIG. 4 is a functional block diagram similar to FIG. 1, showing the configuration of another embodiment of the present invention.

FIG. 5 is a flowchart similar to FIG. 2 for explaining an operation example of the embodiment shown in FIG. 4;

FIG. 6 is an explanatory diagram illustrating a state of a transition of a cumulative difference value in the embodiment illustrated in FIG. 4;

FIG. 7 is a flowchart similar to FIG. 5, for explaining an operation example of a modification in the embodiment shown in FIG. 4;

8 is an explanatory diagram similar to FIG. 6, illustrating a state of transition of a difference value according to the operation control flow shown in FIG. 7;

[Explanation of symbols]

 11 Camera section 12 Sensor section 13 Compression section 14 CPU section 15 Compressed data memory section 16 Storage section 17 Network interface section 18 Network 52 Buffer memory section

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference) BB01 BC01 BC02 BC14 BC22 BD02

Claims (6)

[Claims] An image data compression device for a surveillance camera for compressing and storing image data of a predetermined number of images,
A compression means for compressing sequentially arriving image data for each image at a variable compression ratio; a storage means for sequentially overwriting the compressed image data in order from oldest image data and cyclically storing the compressed image data; Output means for reading and outputting the stored compressed image data from the storage means; and control means for controlling the compression means, storage means and output means, wherein the control means comprises: Calculating a difference with respect to a predetermined first reference value of the amount, setting a compression rate according to the difference in the compression unit, the compression unit compresses the image data at the set compression ratio, The compression ratio is set to a value such that the amount of compressed image data stored in the storage unit does not exceed the predetermined number, and the control unit sets the predetermined number of images including a read trigger time. Image data compression apparatus of the compressed image data of the surveillance cameras and outputs from the sequentially reads the output means from said storage means. 2. The apparatus according to claim 1, wherein the control means accumulates the difference value such that when the accumulated value is out of a predetermined range, the accumulated value is included in the predetermined range. An image data compression apparatus, wherein a value of the compression ratio is set in the compression means. 3. The apparatus according to claim 2, wherein, when the compression rate is changed, the control means compresses image data subsequently input to the compression means at the changed compression rate. Characteristic image data compression device. 4. The apparatus according to claim 2, wherein, when the compression ratio is changed, the control unit re-displays the image when the accumulated value falls outside a predetermined range. An image data compression device for compressing data at the changed compression ratio. 5. The apparatus according to claim 1, wherein the control unit is configured to prevent the difference value from exceeding a second reference value when the difference value exceeds a predetermined second reference value. When the value of the compression ratio is set in the compression unit and the compression ratio is changed, the compression unit again changes the image data when the difference value exceeds the second reference value. An image data compression device for performing compression at a compression ratio. 6. An object scene is photographed to form image data of a predetermined number of images, the image data is compressed and stored, and the stored image data is output in response to an input trigger. In a surveillance camera device, the device includes: an imaging unit that captures the object scene and sequentially forms image data of a predetermined number of images; and a compression unit that compresses the image data for each image at a variable compression ratio. Storage means for sequentially overwriting the compressed image data in order from oldest image data and cyclically storing the compressed image data; output means for reading and outputting the stored compressed image data from the storage means; Input means for outputting a trigger for instructing output of image data, and control means for controlling the compression means, storage means and output means in response to the trigger means, wherein the control means Calculating a difference between the data amount of the obtained image data and a predetermined first reference value, and setting a compression rate according to the difference to the compression unit; and the compression unit sets the image at the set compression ratio. Compressing data, the compression ratio is set to a value such that the number of compressed image data stored in the storage unit does not exceed the predetermined number, and the control unit receives the trigger from the input unit. Then, the predetermined number of compressed image data including the input point of the trigger is sequentially read from the storage unit and output from the output unit.