JP2577705B2 - Image compression / expansion apparatus and control method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image compression / decompression device for compressing and decompressing an image such as a still image or a moving image as an extended function of an information processing device such as a computer, and a control method thereof. .

[0002]

2. Description of the Related Art When realizing functions such as image compression and decompression, it is possible to select an algorithm for realizing the functions, which is a great advantage in improving the processing speed by processing with dedicated hardware. There is. On the other hand, in order to realize various image processing and other various functions, it is more convenient to use a device such as a computer that can freely set its operation algorithm. For this reason, an information processing device is often provided with an image compression or expansion function as an extended or built-in hardware function.

FIG. 6 shows an example of a conventional image compression / expansion apparatus constructed based on the above concept. Hereinafter, the image compression / decompression device will be described with reference to FIG. Here, in order to make the description easy to understand, only the case where decompression is performed will be described.

In FIG. 6, reference numeral 61 denotes a JPEG compression / expansion device for expanding compressed image data, 62 denotes an image memory for storing expanded image data, 63 denotes a FIFO memory, and 64 denotes a memory between the image memory 62 and the FIFO memory 63. , A main memory 65 for storing compressed data, a system bus 66 for transferring compressed data between the compression / expansion device 61 and the main memory 65, and a compression / expansion device 61
A CPU 68 for controlling the transfer of the compressed data between the main memory 65 and the main memory 65, and a compressed data buffer 68 for temporarily storing the compressed data.

Further, a compression / expansion system 60 is constituted by a JPEG compression / expansion device 61, an image memory 62, a FIFO memory 63, an image data transfer control device 64, and a compression data buffer 68, and a main memory 65, a system bus 6
6. A host system 69 is constituted by the CPU 67.

In the image compression / decompression algorithm used here, a variable-length coding technique is often used, and the amount of compressed data and the amount of decompressed data when the data is decompressed are not proportional. This can be said for the JPEG algorithm. In that case, a device for temporarily storing image data such as a FIFO memory 63 is indispensable between the encoding / decoding device and the image memory.

Next, the operation of the image compression / decompression device configured as described above will be described. The CPU 67 controls the transfer of one frame of the compressed data stored in the main memory 65 or a part of the compressed data to the compressed data buffer 68. Decompression processing is started when this transfer is completed. In the decompression process, compressed data is sent from the compressed data buffer 68 to the JPEG compression / decompression device 61 and sequentially decompressed, and the decompressed data is temporarily stored in the FIFO memory 63 as image data.

The image data temporarily stored in the FIFO memory 63 is transferred to the image memory 62. At this time, the image data transfer control device 64 controls the transfer speed of the compressed data from the compressed data buffer 68 to the JPEG compression / decompression device 61 so that the FIFO memory 63 does not overflow.
The transfer rate of image data from the IFO memory 63 to the image memory 62 is controlled.

In addition, when the image data is partially transferred from the main memory 65 to the compressed data buffer 68 instead of being collectively transferred for one frame, the CP
When transferring the compressed data, the U67 controls the transfer so that the compressed data buffer 68 transfers the data at a speed that does not cause overflow or underflow. FIFO
The overflow and underflow prevention control of the memory 63 may be performed by controlling the image data transfer control device 64 while the CPU 67 checks the state of the FIFO memory 63.

[0010]

However, the method of providing a buffer for temporarily storing compressed data on the compression / expansion system side of the conventional image compression / expansion apparatus configured as described above has the following problems. Have. First
In addition, the size of the compressed data buffer 68 itself and the peripheral circuits required for controlling and interfacing the compressed data buffer 68 are not small, and the size of the apparatus is increased and the cost is increased.

Second, on the host system 67 side or on the compression / decompression system 60 side, the control for preventing the underflow and overflow of the FIFO memory 63 becomes complicated, or the processing overhead is increased by performing buffering. It also increases and the processing speed decreases. Assuming that the decompression speed is the total speed until all the data for one frame is transferred from the main memory 65 to the image memory 62, in order to make the decompression speed the fastest, the main memory 65 needs to transmit the compressed data buffer 68 , Transfer of compressed data from the compressed data buffer 68 to the JPEG compression / decompression device 61, decompression by the JPEG compression / decompression device 61, and transmission from the FIFO memory 63 to the image memory 62.
All the transfer of the image data to the data must be performed in a well-balanced manner.

However, since the variable-length code is decoded, for each compressed data input to the JPEG compression / expansion device 61, a prediction is made of how large the data is expanded and output to the FIFO memory. Therefore, it is difficult for all of these transfer rates to follow the ever-changing processing speed of the JPEG compression / decompression device 61.

Third, when the compressed data buffer 68 is used, the space between the host system 69 and the compression / expansion system 60 is substantially cut off. Is difficult to do. That is, when the compressed data buffer 68 enters the middle of the transfer path from the main memory 65 to the image memory 62, the portion where the data transfer speed changes is caused by the compressed data buffer 68, the JPEG compression / decompression device 61, and the FIFO. There are three locations in the memory 63, and it is not easy to control these transfer rates in total.

Fourth, even when the compressed data buffer 68 is not used, control for preventing underflow and overflow of the FIFO memory 63 is generally performed only by the host system 69. When applied to
There occurs a period during which the control for preventing the underflow or overflow of the memory 63 cannot be performed, and the image data in the FIFO memory 63 is redundantly written or read, and the image data may be damaged.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems, and has been described as an extended function of an information processing device such as a computer when configuring a compression / expansion device for image data such as a still image or a moving image. It is an object of the present invention to provide an image compression / expansion apparatus in which the configuration and control are made simpler and smaller, and the speed of the compression / expansion apparatus can be arbitrarily controlled without destroying image data.

[0016]

To achieve the above object, an image compression / decompression apparatus according to the present invention comprises: an image memory for storing original image data or expanded image data;
Compression / expansion means for compressing or decompressing the image data obtained based on the variable length coding technique, and image data to be transferred from the image memory to the compression / expansion means or from the compression / expansion means to the image memory. Image data temporary storage means for temporarily storing data in a read-ahead read-out format, and for generating first to fourth control signals for notifying the amount of data to be stored therein based on first to fourth predetermined threshold values; Image data transfer control means for controlling transfer of image data between the image memory and the image data temporary storage means based on the first and second control signals; a main memory for storing compressed data; A system bus means for transferring compressed data to and from the main memory; and a system bus means for transferring compressed data between the compression and decompression means and the main memory based on third and fourth control signals. It is characterized in that a compression and expansion control means for controlling the transmission.

Further, the image compression / decompression device according to the present invention comprises:
In order to achieve the above object, the image data transfer control means determines that the amount of image data stored in the image data temporary storage means falls below the first threshold value by the first control signal during the image data compression operation. Only when it is recognized that the image data has been rotated, the image data to be compressed is transferred from the image memory to the image data temporary storage means. Only when it is recognized that the storage amount of the image data exceeds the second threshold value, is controlled to transfer the expanded image data from the image data temporary storage means to the image memory. It is.

Further, the image compression / decompression device according to the present invention comprises:
In order to achieve the above object, the compression / decompression control means performs a third control signal during a compression operation of image data.
Only when it is confirmed that the storage amount of the image data in the image data temporary storage means exceeds the third threshold value, the image data to be compressed is transferred from the image data temporary storage means to the compression / decompression means, Only when it is confirmed by the fourth control signal that the storage amount of the image data in the image data temporary storage means is below the fourth threshold value during the expansion operation of the compressed data, the compression from the main memory is performed. It is characterized in that control is performed such that the image data expanded through the expansion means is transferred to the image data temporary storage means.

Further, the image compression / decompression device according to the present invention comprises:
In order to achieve the above object, the image data transfer control means and the compression / decompression control means independently control the transfer of image data. The image data transfer control means and the compression / decompression control means The device is very simple because the means can be controlled without monitoring each other.

Furthermore, in the control method of the image compression / decompression device according to the present invention, in order to achieve the above object, at the time of image data compression, the image data is read from the image memory under the control of the image data transfer control means. The image data temporarily stored is temporarily stored in the data temporary storage means, and the temporarily stored image data is compressed and stored in the main memory under the control of the compression / decompression control means. The read compression data is decompressed and temporarily stored in the image data temporary storage means, and under the control of the image data transfer control means, the control method of the image compression / decompression device is such that the decompressed image data is stored in the image memory. Then, the image data temporary storage means informs the user of the amount of data stored internally based on the first to fourth predetermined threshold values. 1 to generate a fourth control signal,
The control by the image data transfer control means controls the transfer of image data between the image memory and the image data temporary storage means based on the first and second control signals, and the control by the compression / decompression control means controls the third and fourth control signals. The transfer of compressed data between the compression / expansion means and the main memory is controlled based on the control signal.

Further, in order to achieve the above object, the control method of the image compression / decompression device according to the present invention, based on the control by the image data transfer control means, uses the first control signal during the image data compression operation. The image data to be compressed is transferred from the image memory to the image data temporary storage means only when it is recognized that the storage amount of the image data in the image data temporary storage means is less than the first threshold value. During the data decompression operation, the decompressed image data is deleted only when it is recognized by the second control signal that the storage amount of the image data in the image data temporary storage means exceeds the second threshold value. The image data is temporarily transferred from the image data temporary storage means to the image memory.

In order to achieve the above object, the control method of the image compression / expansion apparatus according to the present invention is based on the control of the compression / expansion control means, and during the image data compression operation, the image data temporary storage means is transferred from the main memory to the main memory. Each time the transfer of the compressed data is controlled, the storage amount of the image data stored in the image data temporary storage means is confirmed by the third control signal, and the storage amount of the image data in the image data temporary storage means The image data to be compressed is transferred from the image data temporary storage means to the compression / decompression means only when it is confirmed that the threshold value exceeds the threshold value of 3. Each time the transfer of the compressed data to the temporary storage means is controlled, the storage amount of the image data stored in the image data temporary storage means is changed to a fourth control. Only when it is confirmed by the signal that the storage amount of the image data in the image data temporary storage means is below the fourth threshold value, the image data expanded from the main memory via the compression / expansion means is deleted. It is characterized in that the image data is controlled to be transferred to the image data temporary storage means.

Further, in the control method of the image compression / decompression device according to the present invention, in order to achieve the above object, the image data transfer control means and the image data transfer control by the compression / decompression control means are independently performed. Since the image data transfer control means and the compression / decompression control means can control each other without monitoring each other, the control becomes very simple.

[0024]

The image compression / expansion apparatus and the control method thereof according to the present invention are constructed and operated as described above, so that a buffer for compressed data and its peripheral circuits are not required, so that the circuit scale is reduced. be able to. The control by the host system only needs to prevent underflow of the image data temporary storage means of the compression / decompression system during compression and prevention of overflow during decompression. In addition, it is necessary to constantly monitor underflow and overflow. However, since the control by the host system may be performed in a time-division manner, the image can be efficiently compressed and decompressed at an arbitrary speed.

Further, by using the main memory of the host system as a compressed data buffer, it is not necessary to consider a change in the compressed data size due to a change in the image size or the image compression ratio. In this way, the total control of the transfer speed of the image data becomes very simple, and there is no risk of destruction of the image data due to duplicate writing or the like.

[0026]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The accompanying drawings, FIGS.
An image compression / decompression apparatus according to an embodiment of the present invention and a control method thereof will be described in detail with reference to FIG. FIG.
FIG. 2 is a block diagram illustrating a configuration of an image compression / decompression device according to an embodiment of the present invention. FIG. 2 is a diagram illustrating a flow of processing during a compression operation performed by the image compression / decompression device according to the present embodiment.
FIG. 2A is a flow chart of control for preventing an underflow of the image data temporary storage means by the compression / decompression control means, and FIG. 2B is a flowchart for preventing an overflow of the image data temporary storage means by the image data transfer control means. It is a flowchart of control.

FIG. 3 is a diagram showing the flow of processing during the decompression operation by the image compression / decompression device in this embodiment. FIG. 3 (a) shows the overflow of the image data temporary storage means by the compression / decompression control means. 3 (b) is a flowchart of control for preventing an underflow of the image data temporary storage means by the image data transfer control means, and FIG. 4 is a flow chart of the control when the image compression / expansion apparatus in the present embodiment performs a compression operation. A conceptual diagram showing a range of a storage amount in which image data temporary storage means stores image data, and a threshold value managed by each of the compression / decompression control means and the image data transfer control means,
FIG. 5 shows a range of a storage amount in which the image data temporary storage means stores the image data when the image compression / expansion apparatus in the present embodiment performs the expansion operation, and a threshold managed by each of the compression / decompression control means and the image data transfer control means. It is a conceptual diagram which shows a value.

First, the configuration of an image compression / decompression device according to an embodiment of the present invention will be described with reference to FIG. In FIG. 1, reference numeral 11 denotes a compression / expansion means for compressing / expanding image data such as a still image or a moving image; 12, an image memory for storing source image data or expanded image data;
Reference numeral 3 denotes an image data temporary storage means for temporarily storing image data to be transferred from the image memory 12 to the compression / expansion means 11 or from the compression / expansion means 11 to the image memory 12 in a prefetching / readout format; And 15 is a main memory for storing compressed data. Further, 16 is a system bus means for transferring compressed data between the compression / expansion means 11 and the main memory 15, and 17 is a compression / expansion control means for controlling the transfer of compressed data between the compression / expansion means 11 and the main memory 15.

The operation of the image compression / decompression apparatus according to the present embodiment having the above-described configuration will be described below with reference to FIG. In the following description, the compression / decompression control means 17, the main memory 15, and the system bus means 16 are collectively referred to as a host system 19, and the compression / decompression means 11, the image memory 12, and the image data temporary storage means 1
3, and the image data transfer control means 14 are collectively referred to as a compression / decompression system 10.

In the case of compression, the image data temporary storage means 13
When the stored image data exceeds a certain amount, the image data temporary storage unit 13 stores the image data in the image data transfer control unit 1.
4, the image data transfer control means 14 stops writing the image data read from the image memory 12 to the image data temporary storage means 13, and the image data temporary storage means 13 When the value falls below the threshold, the writing to the image data temporary storage unit 13 is restarted.

Independently of this, the compression / decompression control means 17
Checks the amount of image data stored in the image data temporary storage means 13 every time the control of transfer of compressed data from the compression / expansion means 11 to the main memory 15 via the system bus means 16 is checked. When the amount of image data is smaller than a certain amount, the compression / decompression means 1
No transfer control of compressed data from 1 to the main memory 15 is performed, only the amount of image data stored in the image data temporary storage unit 13 is checked, and the amount of stored image data exceeds a certain amount. Is checked, the compression / expansion means 11 again sends the main memory 1
5 is controlled to transmit the compressed data.

However, the transfer of the image data from the image data temporary storage means 13 to the compression / expansion means 11 during the compression and the compression processing in the compression / expansion means 11 are as follows.
Each time compressed data is read from the compression / expansion means 11,
It is assumed that the processing is sequentially performed on the image data to be processed next.

In the case of decompression, the image data temporary storage means 1
When the image data stored in 3 falls below a certain amount,
The image data temporary storage means 13 transmits this to the image data transfer control means 14, and the image data transfer control means 14 stops writing the image data read from the image data temporary storage means 13 to the image memory 12, and temporarily stores the image data. When the image data stored in the means 13 exceeds a certain amount, the writing to the image memory 12 is restarted.

Independently of this, the compression / decompression control means 17
Each time the transfer of compressed data from the main memory 15 to the compression / expansion means 11 via the system bus 16 is controlled, the amount of image data stored in the image data temporary storage means 13 is checked and stored. When the amount of data exceeds a certain amount, the transfer control of the compressed data from the main memory 15 to the compression / expansion means 11 is not performed, and only the data amount stored in the image data temporary storage means 13 is checked. When it is confirmed that the amount of the image data is smaller than a certain amount, the control for transferring the compressed data from the main memory 15 to the compression / expansion means 11 is performed again.

However, during decompression, the decompression processing performed by the compression / decompression means 11 and the transfer of image data from the compression / decompression means 11 to the image data temporary storage means 13 are performed every time new compressed data is written to the compression / decompression means 11. Shall be performed.

The above operation is divided into a compression operation and a decompression operation, and the flowchart is viewed from each of the host system 19 side and the compression / expansion system 10 side. The processing flow and the processing flow during the decompression operation shown in FIG. 3 are shown. Hereinafter, each of them will be described in order.

FIG. 2A is a diagram showing a flow of control for preventing the underflow of the image data temporary storage means 13 by the compression / decompression control means 17 during the compression operation.
In this case, the compression / decompression control unit 17 checks only whether the amount of data stored in the image data temporary storage unit 13 is larger or smaller than １ ／ of the storable capacity (described later), The processing corresponding to each of them is performed.

When the storage amount exceeds 1/4, the compressed data is read out from the compression / expansion means 11, and
The image data to be compressed next is stored in the image data temporary storage unit 1.
3 is transferred to the compression / decompression means 11 and subjected to compression processing, and the image data in the image data temporary storage means 13 is reduced.

Conversely, when the storage amount falls below 1/4,
Since the reading of the compressed data is not performed, the image data in the image data temporary storage unit 13 does not decrease below that, and the image data transferred from the image memory 12 flows under the control of the image data transfer control unit 14. Only.

FIG. 2B is a diagram showing a flow of control by the image data transfer control means 14 for preventing the image data temporary storage means 13 from overflowing during the compression operation. In this case, the image data transfer control unit 14 checks only whether the amount of data stored in the image data temporary storage unit 13 is more or less than １ ／ of the storable capacity (described later), The processing corresponding to each of them is performed.

When the storage amount is less than 1/2, a state signal generated from the image data temporary storage means 13 notifies the image data transfer control means 14 of the fact, and the image data transfer control means 14 The image data is transferred to the image data temporary storage unit 13, and the data amount in the image data temporary storage unit 13 increases.

Conversely, when the storage amount exceeds 1/2, a state signal generated from the image data temporary storage means 13 notifies the image data transfer control means 14 of the fact, and the image data transfer control means 14 The transfer of the image data from the storage unit 12 to the image data temporary storage unit 13 is stopped, and the data amount in the image data temporary storage unit 13 does not increase any more. Only the transferred image data flows out.

FIG. 3A is a diagram showing the flow of control by the compression / expansion control means 17 for preventing the image data temporary storage means 13 from overflowing during the expansion operation.
In this case, the compression / decompression control unit 17 checks only whether the amount of data stored in the image data temporary storage unit 13 is larger or smaller than ３ of the storable capacity (to be described later). Processing corresponding to each is performed.

When the storage amount is less than 3/4, the compressed data is written to the compression / decompression means 11, whereby the next compressed data to be decompressed is subjected to decompression processing by the compression / decompression means 11, and the image data is temporarily stored. Transferred to the storage means 13,
The image data in the image data temporary storage means 13 increases.

Conversely, when the storage amount exceeds 3/4,
Since the writing of the compressed data is not performed, the image data in the image data temporary storage unit 13 does not increase any more.
Only the image data transferred to the image memory 12 under the control of the image data transfer control means 14 flows out.

FIG. 3B is a diagram showing a flow of control by the image data transfer control means 14 for preventing an underflow of the image data temporary storage means 13 during the decompression operation. Also in this case, the image data transfer control means 14
Checks only whether the amount of data stored in the image data temporary storage unit 13 is larger or smaller than 1/2 of the storable capacity (described later), and performs processing corresponding to each.

When the storage amount exceeds 1/2, a state signal generated from the image data temporary storage means 13 notifies the image data transfer control means 14 of the fact that the image data transfer control means 14 temporarily stores the image data. The image data is transferred from the means 13 to the image memory 12, and the data amount in the image data temporary storage means 13 is reduced.

Conversely, when the storage amount falls below 1/2, a status signal generated from the image data temporary storage means 13 informs the image data transfer control means 14 of this, and the image data transfer control means 14 The transfer of the image data from the temporary storage unit 13 to the image memory 12 is stopped, and the amount of data in the image data temporary storage unit 13 does not decrease below that. Only the image data transferred from 11 flows in.

Referring now to FIGS. 4 and 5, for each of compression and decompression, the image data temporary storage means 13 has a storage capacity range for storing image data, a host system 19 and a compression / decompression system 10. , That is, the threshold value managed by each of the compression / decompression control means 17 and the image data transfer control means 14 will be described.

The hardware signal indicating the data amount stored in the image data temporary storage means 13 determines whether or not one level other than "full" and "empty" (described later) is satisfied. Is sufficient, and it is sufficient if the other levels can be known by reading registers and the like by software.

In this embodiment, the image data temporary storage means 1
3 (corresponding to the first control signal in the case of the compression processing and the second control signal in the case of the decompression processing). Threshold value and the second threshold value for the decompression process, but here the same threshold value).
Performs control, and a state signal (corresponding to a third control signal in the case of compression processing and a fourth control signal in the case of decompression processing) resulting from reading of the state register in the image data temporary storage means 13 is represented by 1 / A case in which the compression / expansion control means 17 performs control on the basis of levels 4 and 3/4 (respectively referred to as a third threshold value during compression processing and a fourth threshold value during expansion processing). I do.

However, "full" in the present embodiment means:
The data amount stored in the image data temporary storage means 13 indicates a state where the amount of data is full (Full).
Means that the amount of data stored in the image data temporary storage means 13 is empty.

Hereinafter, FIGS. 4 and 5 will be described. FIG. 4 shows the range of the amount of storage of the image data by the image data temporary storage means 13 at the time of compression and the threshold values managed by the host system and the compression / decompression system, ie, the compression / decompression control means 17 and the image data transfer control means 14. FIG. In FIG. 4, the compressed data is transferred from the image data temporary storage means 13 to the compression / decompression means 11 and flows out,
The image data is transferred from the image memory 12 and flows there.

The compression / expansion control means 17 determines whether or not a level (third threshold value) of 1/4 is satisfied by a status signal (third control signal) from the status register of the image data temporary storage means 13. The image data transfer control means 14 checks whether or not the external output signal or the state signal (first control signal) generated by the image data temporary storage means 13 indicates
It is determined whether level 2 (first threshold) is satisfied.

In the compression processing, the level used by the image data temporary storage means 13 is from “empty” to １ ／. At the start of compression, the amount of stored data simply increases from “empty”, and underflow and overflow control is started when the amount of image data exceeds ４. During the processing, the amount of image data is reduced from slightly less than ４ to 1 When all of the image data to be processed in the image memory 12 is transferred while changing the portion slightly over / 2, the image data is simply reduced to the “empty” level and is output.

FIG. 5 shows the image data temporary storage means 1 at the time of decompression.
Reference numeral 3 denotes a range of storage amount for storing image data, a host system and a compression / expansion system,
FIG. 5 is a conceptual diagram showing threshold values managed by the image data transfer control means 14 and the image data transfer control means 14. In FIG. 5, compressed data is transferred from the compression / expansion means 11 to the image data temporary storage means 13, and the image data is transferred to the image data temporary storage means 1.
3 to the image memory 12.

The compression / decompression control means 17 determines whether or not the level signal (fourth control signal) from the status register (fourth control signal) of the image data temporary storage means 13 satisfies the 3/4 level (fourth threshold value). The image data transfer control means 14 determines whether the external output signal or the state signal (the second control signal) generated by the image data temporary storage means 13 is 1 /
It is determined whether level 2 (second threshold value) is satisfied.

In the decompression processing, the level used by the image data temporary storage means 13 is from "empty" to 3/4. At the start of decompression, the amount of stored data simply increases from “empty”, and underflow and overflow control is started when the amount of data exceeds 3/4, and during processing, the amount of data is reduced from slightly less than 1/2 to 3/4. When the strong part fluctuates and all the predetermined compressed data is transferred to the compression / decompression means 11,
Data is simply reduced to the "empty" level and drained.

It is assumed that the image data transfer control means 14 inverts the interpretation of the signal output from the image data temporary storage means 13 on the basis of 1/2 corresponding to the time of compression and the time of expansion. In the present embodiment, the image data temporary storage unit 1
Although the threshold value at which the external output signal generated from 3 changes during compression and decompression is １ ／, another method is used as a threshold value, and the level differs between compression and decompression. Very good.

In this embodiment, the means for knowing the amount of image data temporarily stored in the image data temporary storage means 13 by the state signal from the state register is set to the 1/4 level and the 3/4 level. Is used as
Other levels than “full” and “empty” may be used as the threshold. However, the threshold value used to prevent overflow is equal to or larger than the maximum data size when the compressed data transferred in one transfer cycle under the control of the compression / expansion control means 17 is expanded by the compression / expansion means 11 to become image data. Must be set to a level lower than the “full” level.

Similarly, the threshold value used to prevent underflow is the maximum value required for the compression / expansion means 11 to generate compressed data transferred in one transfer cycle under the control of the compression / expansion control means 17. It is necessary to set the level higher than the “empty” level for the image data size or more.

As described above, in the operation of the image compression / expansion apparatus according to the present embodiment, the roles of control by software on the host system 19 side and control by hardware on the compression / expansion system 10 are completely separated. Host system 19 and compression / decompression system 1
It is sufficient that each of the 0s manages only one of the threshold values of the overflow or the underflow of the image data temporary storage means 13 and simple control is achieved.

From the viewpoint of the compression / expansion control means 17, the compression is performed when the compressed data is transferred from the compression / expansion means 11 to the main memory 15, and the compression is temporarily stopped when the transfer is temporarily stopped. Similarly, in the case of decompression, decompression is performed when the compressed data is transferred from the main memory 15 to the compression / decompression means 11, and decompression is also temporarily stopped when the data is temporarily stopped.

In the actual device according to the present embodiment, the compression / expansion means 11 is a JPEG compression / expansion LSI, the image memory 12 is a monitor video frame memory, the image data temporary storage means 13 is a FIFO memory, and the image data transfer control means. 14 is a device having a predetermined function, main memory 15 is a main memory of the computer, system bus means 16 is a system bus of the computer, and compression / expansion control means 17 is a CPU of the computer.

The compression / expansion means 11 and the image data temporary storage means 13 are JP
An EG compression / expansion LSI was used. Although the compression / expansion means 11 and the image data temporary storage means 13 can be realized with different configurations, they can be realized with a simple configuration by using one chip.

The fact that the host system 19 can arbitrarily control the compression and decompression by the configuration and control method of the image compression and decompression device according to the present invention is particularly effective in the case of a multi-process operating system. This is because the compression / expansion system 10 does not require regular control from the host system 19, and due to the operating system, the time during which the compression / expansion system 10 cannot be controlled occurs irregularly. This is because the image data temporary storage means 13 does not cause overflow or underflow, and no problem such as destruction of image data occurs.

On the contrary, if the configuration and the control method of the present invention are used in a single-process operating system such as a personal computer, the image can be compressed and decompressed at an arbitrary speed intended by the compression / decompression control means. This feature can be easily applied to special effects of image display, averaging of processing time for each frame when compressing and decompressing moving images, and the like. Also, since the buffering of the compressed data is not performed, there is almost no processing overhead between the image memory 12 and the main memory 15, and the transfer rate of the slowest transfer path in the transfer path immediately becomes the highest transfer rate, and is stable. And a high-speed system can be realized.

Although the present embodiment does not have any means dedicated to bus control, a configuration having bus control means dedicated to bus control is not excluded from the scope of the present invention.
Although the CPU has been described as an example of the compression / expansion control means, the configuration using another device that can be a bus master such as a DMA controller is the same as the above.

[0069]

To achieve the above object, the image compression / decompression apparatus and the control method according to the present invention are configured as described above, and do not require a buffer for compressed data and its peripheral circuit. It is possible to realize a reduction in circuit size, a reduction in cost, and an increase in processing speed due to no processing overhead due to buffering. In addition, the control by the host system only needs to prevent the underflow of the FIFO memory during compression and the overflow during decompression, and the control is simple and simple software is required, so that the cost of software development can be reduced. .

Further, the image compression / expansion apparatus and the control method thereof according to the present invention can be performed at any speed depending on the host system, and still perform the compression / expansion without destroying the image data by duplicate writing or redundant reading. be able to. Therefore, even when the operating system such as a multi-process or a single process such as a workstation or a personal computer is different, it can be realized without changing the control method, and application to a special effect of image display and the like is possible.

As described above, the control by the host system may be time-division, and the main memory of the host system is used for storing the compressed data. There is an advantage that it is not necessary to consider the fluctuation of

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an image compression / decompression device according to an embodiment of the present invention.

FIG. 2 is a diagram showing a flow of processing during a compression operation by the image compression / decompression device according to the present embodiment, and FIG. 2 (a) is a flowchart of control for preventing an underflow of the image data temporary storage means by the compression / decompression control means; (B) is a flowchart of control for preventing overflow of the image data temporary storage means by the image data transfer control means.

FIG. 3 is a diagram showing a flow of a process at the time of a decompression operation by the image compression / decompression device according to the present embodiment, and FIG. b) is a flowchart of control for preventing underflow of the image data temporary storage means by the image data transfer control means.

FIG. 4 is a diagram illustrating a range of a storage amount in which image data temporary storage means stores image data, and each of the compression / decompression control means and the image data transfer control means, when the image compression / decompression device in the present embodiment performs a compression operation. Conceptual diagram showing thresholds

FIG. 5 is a diagram illustrating a range of a storage amount in which image data temporary storage means stores image data, and each of the compression / decompression control means and the image data transfer control means, when the image compression / decompression device in this embodiment performs a decompression operation. Conceptual diagram showing thresholds

FIG. 6 is a block diagram showing a configuration of a conventional image compression / decompression device.

[Explanation of symbols]

 Reference Signs List 10 compression / decompression system 11 compression / decompression means 12 image memory 13 image data temporary storage means 14 image data transfer control means 15 main memory 16 system bus means 17 compression / decompression control means 19 host system 60 compression / decompression system 61 JPEG compression / decompression device 62 image memory 63 FIFO memory 64 Image data transfer control device 65 Main memory 66 System bus 67 CPU 68 Compressed data buffer 69 Host system

Claims (8)

(57) [Claims] An image memory for storing original image data or decompressed image data, and compression / decompression means for decompressing the compressed data obtained by compressing or compressing the image data based on a variable length coding technique. Temporarily storing image data to be transferred from the image memory to the compression / expansion means or from the compression / expansion means to the image memory in a prefetching / readout format, and internally storing the data based on first to fourth predetermined threshold values Image data temporary storage means for generating first to fourth control signals for notifying the amount of data storage to be performed, and between the image memory and the image data temporary storage means based on the first and second control signals. Image data transfer control means for controlling transfer of image data, a main memory for storing compressed data, and compression between the compression / decompression means and the main memory. System bus means for transferring data, and compression / expansion control means for controlling the transfer of compressed data between the compression / expansion means and the main memory based on the third and fourth control signals. Characteristic image compression / decompression device. 2. The image data transfer control means according to the first control signal during a compression operation of image data.
Only when it is recognized that the storage amount of the image data in the image data temporary storage means is below the first threshold value, the image data to be compressed is transferred from the image memory to the image data temporary storage means. In the transfer and expansion of compressed data, when the second control signal recognizes that the storage amount of the image data in the image data temporary storage means exceeds the second threshold value, 2. The image compression / decompression device according to claim 1, wherein only the decompressed image data is controlled to be transferred from the image data temporary storage means to the image memory. 3. The image processing apparatus according to claim 2, wherein said compression control means controls the amount of image data stored in said image data temporary storage means to exceed the third threshold value by said third control signal during a compression operation of the image data. Only when it is confirmed that the image data has been rotated, the image data to be compressed is transferred from the image data temporary storage means to the compression / expansion means. Only when it is confirmed that the storage amount of the image data in the data temporary storage means is lower than the fourth threshold value, the image data expanded from the main memory via the compression / expansion means is converted into the image data. 3. The image compression / decompression device according to claim 1, wherein the image compression / decompression is controlled so as to be transferred to a temporary storage unit. 4. The image compression / decompression device according to claim 1, wherein the image data transfer control means and the compression / decompression control means perform image data transfer control independently of each other. 5. At the time of image data compression, image data is read from an image memory under the control of image data transfer control means and temporarily stored in image data temporary storage means. The compressed image data is compressed and stored in the main memory, and when the compressed data is expanded, under the control of the compression and expansion control means, the compressed data read from the main memory is expanded and temporarily stored in the image data temporary storage means. A method for controlling an image compression / expansion apparatus, wherein the image data is stored in the image memory under the control of the image data transfer control means. And generating first to fourth control signals indicating the amount of data to be stored internally with reference to a predetermined threshold value of Wherein the control by the feed control means first
And controlling the transfer of image data between the image memory and the image data temporary storage means based on a second control signal, and controlling the compression / decompression control means based on the third and fourth control signals. A method for controlling an image compression / expansion apparatus, wherein a transfer of compressed data between compression / expansion means and said main memory is controlled. 6. The control by the image data transfer control means, wherein the amount of image data stored in the image data temporary storage means is controlled by the first threshold in accordance with the first control signal during a compression operation of the image data. Only when it is recognized that the value is below the value, transfer the image data to be compressed from the image memory to the image data temporary storage means,
During the expansion operation of the compressed data, the expansion is performed only when it is recognized by the second control signal that the storage amount of the image data in the image data temporary storage means exceeds the second threshold value. 6. A control method for an image compression / decompression apparatus according to claim 5, wherein the control is performed to transfer the image data obtained from the image data temporary storage means to the image memory. 7. The control by the compression / decompression control means includes the step of controlling the image data temporary storage means every time the transfer of the compressed data from the image data temporary storage means to the main memory is controlled during the compression operation of the image data. The third control signal is used to confirm the storage amount of the image data stored in the storage device, and it is confirmed that the storage amount of the image data in the image data temporary storage means exceeds the third threshold value. Only when the image data to be compressed is transferred from the image data temporary storage means to the compression / expansion means, and during the operation of expanding the compressed data, the transfer of the compressed data from the main memory to the image data temporary storage means is performed. Each time the control is performed, the storage amount of the image data stored in the image data temporary storage unit is confirmed by the fourth control signal, Only when it is confirmed that the storage amount of the image data in the data temporary storage means is less than the fourth threshold value, the image data expanded from the main memory via the compression / expansion means is converted into the image data. 7. The control method for an image compression / decompression device according to claim 5, wherein control is performed to transfer the data to a temporary data storage unit. 8. The image data transfer control means and the compression / decompression control means perform image data transfer control independently of each other.
A control method of the image compression / decompression device according to the above.