JPH1141472A - Image data processor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image data processor which can properly compress image data outputted from an image reader. SOLUTION: When a compression system selection processing is started, an original is prescanned by an image read part (step S1) and a histogram regarding the density of respective pixels is generated. On the basis of the generated histogram, it is determined whether or not an original image is a binary or multi-valued image (step S2). When the original image is a binary image, it is determined that a 1st compression processing by the 1st compression processing part that a scanner is equipped with is performed for a horizontal scan data (step S3) and a run-length compression system is selected as the system of a secondary compression processing performed by an image data processor. When the original image is a multi-valued data, on the other hand, it is determined that a primary compression is not performed for the horizontal scan data, and a JPEG compression system is selected as the system of the secondary compression processing performed by the image data processor (step S10).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image data processing apparatus for compressing image data read by an image reading apparatus.

[0002]

2. Description of the Related Art Conventionally, data of an image read by an image reading device such as a scanner is stored in a disk storage device or the like provided in a computer, and the stored image data is stored in a disk as needed. There is provided a system in which data is read from a storage device, subjected to various image data processing by a computer, and then input to a printer or a display.

In such a system, a buffer memory capable of temporarily storing image data is provided in addition to the disk storage device, and image data output from the scanner is temporarily stored in the buffer memory through a computer. Is done. Then, the image data is sequentially read from the buffer memory and subjected to a compression process by a computer, and then the compressed image data is stored in the disk storage device. Thus, the amount of image data stored in the disk storage device can be reduced.

[0004]

However, in the above-mentioned system, a buffer memory having a large storage capacity is required to temporarily hold image data input from the scanner to the computer, and the apparatus becomes expensive. To reduce the cost of the device, a disk storage device that is cheaper than the buffer memory may be used instead of the buffer memory. However, the data writing speed of the disk storage device is lower than that of the buffer memory, and it takes a long time to store all the image data output from the scanner in the disk storage device.

Therefore, an image processing system has been proposed in which image data output from a scanner is subjected to compression processing by a computer, and the data after compression processing is stored in a buffer memory, thereby reducing the time required for storing image data. (See, for example, Japanese Patent Application Laid-Open No. 1-151875). However, depending on the type of image read by the scanner, even if compression processing is performed, the data amount may not be reduced much. , The image reading time may be rather lengthened by performing the compression process.

Further, in the system disclosed in the above publication, uniform compression processing is performed on all image data output from the scanner. Therefore, depending on the type of image, compressed image data is expanded. Even in such a case, it may not be possible to restore the image data output from the scanner. For example, the above-described compression processing is performed by forcibly removing lower bits from image data of a plurality of bits, thereby reducing the number of bits by one.
In the case of the binarization process of converting into multi-bit image data, when image data obtained by reading a multi-valued image such as a photographic image is binarized, the compressed image data is converted into the original image data. Cannot be restored.

An object of the present invention is to solve the above-mentioned technical problems and to provide an image data processing apparatus capable of reliably reducing the time required for storing image data in a disk storage device. . Another object of the present invention is to provide an image data processing apparatus capable of performing appropriate compression processing on image data output from an image reading apparatus.

[0008]

According to a first aspect of the present invention, there is provided an image data processing apparatus for compressing image data output by reading an original by an image reading apparatus. Compression processing means for performing compression processing on image data output by the image reading device, and prescan control means for prescanning the image reading device to read an image of a predetermined portion of the document,
Selecting means for selecting a compression processing method to be applied to image data output from the image reading device from among predetermined compression processing methods based on image data output by the image reading device at the time of pre-scanning It is characterized by the following.

According to the first aspect of the present invention, based on the image data output by the image reading device at the time of pre-scan,
A compression processing method to be applied to image data output from the image reading device is selected from predetermined compression processing methods. Therefore, the most appropriate compression processing method can be selected according to the type of image read by the image reading device. Therefore, the most efficient compression processing can be performed according to the type of image.

According to a second aspect of the present invention, there is provided a means for trially performing a compression process on the image data output by the image reading apparatus at the time of pre-scan according to the compression processing method selected by the selection means. Means for permitting execution of the selected compression processing by the compression processing means only when a compression rate equal to or higher than a predetermined compression rate is obtained in the compression processing that has been performed. An image data compression apparatus according to claim 1, wherein

According to the second aspect of the present invention, the image data obtained by pre-scanning is subjected to a test on the basis of the compression method selected by the selection means. If the compression ratio is equal to or higher than a predetermined compression ratio, compression processing is performed on image data output from the image reading device at the time of main scanning. This allows
For example, since the amount of image data to be stored in the disk storage device is reduced, the time required for writing the image data to the disk storage device is reduced.

On the other hand, as a result of trially performing compression processing on image data obtained by pre-scanning, if the data compression rate by the compression processing is less than a predetermined compression rate, the image reading apparatus sends No compression processing is performed on the output image data. Therefore, the image data output from the image reading device is stored in the disk storage device as it is. Therefore, by performing the compression process on the image data, the time required for storing the image data becomes longer than when the image data output from the image reading device is directly stored in the disk storage device. There is no.

According to a third aspect of the present invention, the image reading apparatus is provided with pre-compression processing means for compressing the image data by a predetermined compression method, based on the image data output by the image reading apparatus at the time of pre-scanning. 3. The image data processing apparatus according to claim 1, further comprising a determination unit that determines whether to perform image data compression by the pre-compression processing unit.

According to a fourth aspect of the present invention, the determining means determines whether or not the image read by the image reading device is a binary image, and the determining means determines whether the image read by the image reading device is a binary image. If it is determined that the image to be obtained is a binary image, it is determined that image data compression is to be performed by the pre-compression processing means. If it is determined that the image is not a binary image, image data compression by the pre-compression processing means is to be performed. 4. The image data compression device according to claim 3, further comprising means for determining not to perform the operation.

It is preferable that the pre-compression process is a relatively simple process such as a binarization process and a compression process in which it is difficult to restore the original data from the compressed data. In this case, the compression processing performed by the compression processing means is a more advanced compression processing than the pre-compression processing,
It is preferable that the original data can be almost accurately restored from the data after the compression processing.

Further, the image data processing apparatus further includes means for enabling or disabling the compression processing by the pre-compression processing means based on the determination of the determination means, so that the compression processing by the pre-compression processing means is automatically performed. Preferably, it is configured to be performed. According to the configuration of claim 3,
Whether or not to execute the compression processing by the pre-compression processing means
It is determined based on the image data obtained by the prescan. Specifically, as described in claim 4,
If the document image is a binary image, a pre-compression process is executed. As a result, compared to the case without compression processing,
The time required for transmitting image data from the image reading device to the image data processing device can be greatly reduced. In addition, the processing time of the compression processing performed by the image data processing device can be reduced.

If the original image is a multi-valued image, the pre-compression process is not performed, and the image data output from the image reading device is directly provided to the image data processing device. As a result, the multi-bit image data representing the multi-valued image is converted into, for example, 1-bit image data. For example, when an image is output by an image output device, the compressed image data is converted into the original multi-bit image data. There is no such thing that image data cannot be restored.

[0018]

An embodiment of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a block diagram showing a configuration of a system to which an image data processing device according to an embodiment of the present invention is applied. The system includes a scanner 1 as an image reading device, an image data processing device 2 for performing predetermined processing on data of an image read by the scanner 1, and an image data processed by the image data processing device 2. And an image output device 3 for outputting an image based on the image. The image output device 3 may be a printer that records an image based on image data provided from the image data processing device 2 on paper, or may be a display device that displays the image on a screen.

The scanner 1 reads a document image,
An image reading section 4 for generating digital image data representing the density of a document image, and a first compression processing section (pre-compression processing means) for performing a first compression process on the digital image data output from the image reading section 4 5 are included. The first compression processing unit 5 is connected to a CPU 6 (described later) provided in the image data processing device 2 via a control line 10, and based on a control signal input from the CPU 6, The image data provided from the image data can be switched between a case where the first compression is performed and a case where the first compression is not performed.

The first compression executed by the first compression processor 5
In the next compression process, for example, the lower 7 bits are converted from, for example, 8-bit digital image data output from the image reading unit 4.
Bits are forcibly deleted and converted to 1-bit image data. In other words, the primary compression process is a binarization process for converting a plurality of bits of image data into 1-bit image data.

The image data processing device 2 can be realized by, for example, a computer. Image data processing device 2
A CPU 6 for generally controlling the operation of each unit included in the system, a DRAM 7 for temporarily storing image data input from the scanner 1,
A second compression processing unit (compression processing means) 8 for performing a secondary compression process on image data input from the scanner 1 and a disk storage device 9 capable of storing a large amount of image data are included. I have.

The second compression processing section 8 performs secondary compression on the image data input to the image data processing device 2 based on the compression method selected by a compression method selection process (described later) executed by the CPU 6. Perform processing. The second compression processing unit 8 is realized by software processing executed by the CPU 6. Also, the disk storage device 9
Can be constituted by a hard disk or a floppy disk drive, for example. When the disk storage device 9 is constituted by a floppy disk drive, a floppy disk is mounted on the disk storage device 9 and image data is written on the floppy disk.

FIG. 2 is a flowchart showing the flow of the compression method selection process. This compression method selection processing determines whether or not to perform primary compression processing and secondary compression processing on image data input from the scanner 1 to the image data processing apparatus 2, and performs compression in the secondary compression processing. This is a process for determining the method. When a document is set on the scanner 1 and a start signal is input from, for example, a keyboard (not shown) connected to the image data processing device 2, the compression method selection process is started.

In the compression method selection processing described below, three flags F ₁ , F ₂ , and F ₃ are used. The flags F ₁ , F ₂ and F ₃ are reset to 0 at the start of the compression method selection processing. When the compression method selection process is started, prescanning of a document is performed by the image reading unit 4, and an image is read, for example, every fixed line (step S1). Image data obtained by pre-scanning (hereinafter referred to as “pre-scan data”)
Are stored in the DRAM 7 from the image reading unit 4 via the CPU 6. At this time, the first compression processing unit 5 and the second compression processing unit 8 are invalidated, and the image data output from the image reading unit 4 is stored in the DRAM 7 as it is.
The CPU 6 converts the image data stored in the DRAM 7
A histogram relating to the density of each pixel is created.

Next, the CPU 6 determines whether the original image is a binary image or a multi-valued image based on the created histogram (step S2). For example, even if the prescan data output from the image reading unit 4 is image data having a plurality of bits, the number of black data and white data is extremely large, and the number of image data representing a halftone is smaller than a predetermined number. If the number is small, it is determined that the document image is a binary image. On the other hand, if the number of image data representing halftones is equal to or more than the predetermined number in the pre-scan data, the document image is determined to be a multi-value image.

[0026] When the original image is determined to be a binary image, a binary image is determined whether the step S2 is affirmative, the flag F ₁ is rewritten to 1 (step S
3). The flag F ₁ is image data obtained by the main scan of the original image (hereinafter. Referred to as "the scan data") to a flag indicating whether to perform the primary compression process. Note that the main scan is a scan performed to convert all images in a desired area in a document image into image data.

[0027] flag F ₁ is 1, the primary compression process is performed on the prescan data stored in the DRAM 7 (step S4). The primary compression processing performed on the pre-scan data is performed by the CPU 6 as software. In the primary compression processing, the lower bits of the prescan data are forcibly deleted, and the prescan data is converted into 1-bit image data. The pre-scan data subjected to the primary compression processing is stored in the DRAM 7
Is stored in

The compression method in the secondary compression processing is
For example, if run-length compression is selected,
Lug F_TwoIs rewritten to 1 (step S5). Hula
F _TwoIs updated to 1
Data is subjected to secondary compression processing using run-length compression
It is acceptable to apply. Here, run length compression method
Means that white and black pixels are continuous in a binary image
Pay attention to the existence of the part,
By encoding the continuous length of elements (run length),
This is a method for compressing image data. Step S5
And the flag F_TwoIs rewritten to 1, in step S4
A run is added to the pre-scan data that has been subjected to the primary compression processing.
The secondary compression processing is experimentally performed by the length compression method.
(Step S6).

Next, the number of pre-scan data after the primary compression processing is compared with the number of pre-scan data after the secondary compression processing (run-length compression), and the secondary compression processing is performed. It is determined whether or not the number of data of the subsequent pre-scan data is equal to or less than a reference value obtained by multiplying the number of data of the pre-scan data before the second compression processing by a predetermined compression rate α (%). Is performed (step S7). In other words, the data compression rate by the secondary compression processing is
It is determined whether or not the compression ratio is equal to or more than the compression ratio α. If the data compression rate by the secondary compression processing is equal to or more than the compression rate α, it is determined that the main compression data is to be subjected to the secondary compression processing, and the compression method determination processing is ended. At this time, the flag F ₂ is to remain 1.

If it is determined in step S7 that the data compression rate by the secondary compression processing is less than the predetermined compression rate α, the secondary compression processing is not performed on the main scan data. It is determined that the flag F ₂
Is reset to 0 (step S8). Then, the compression method determination processing ends. On the other hand, in the determination at step S2, the original image is when it is determined that the multi-valued image, the flag F ₁ is left 0 without being rewritten. That is, it is determined that the primary compression processing is not performed on the main scan data. Then, the JPEG compression scheme is selected as the compression method in the secondary compression process, the flag F ₃ is rewritten to 1 (Step S9). By flag F ₂ is rewritten to 1, it is allowed to the main scan data subjected to the second-order compression processing by the JPEG compression method. What is JPEG compression?
(Joint Photographic Experts Group) is a coding method of color image data, which divides image data into 8 × 8 matrices, encodes each matrix after performing discrete cosine transform (DCT), and then quantizes the matrix. This is a method for compressing image data. Further, after the flag F ₃ is rewritten to 1 in step S9, the prescan data stored in the DRAM 7, a secondary compression process is performed by the JPEG compression method (step S10).

When the compression processing by the JPEG compression method is performed in step S10, the process proceeds to step S7, where the data compression rate by the secondary compression processing (JPEG compression) is equal to or more than a predetermined compression rate α. It is determined whether or not.
Then, if the compression rate of the data by the secondary compression process the compression rate α or more, and that the secondary compression process is performed is determined in the scan data, while the flag F ₃ is 1, the compression method determination The process ends.

Further, in the judgment of step S7, the second
When the compression ratio of the data by the next compression process is determined to be less than the compression ratio α predetermined has been determined that the present scan data not subjected to secondary compression, the flag F ₃ is 0 (Step S8). Then, the compression method determination processing ends. When the pre-scan data is subjected to the compression processing by the JPEG compression method, a compression ratio β (%) different from the above-described predetermined compression ratio α may be adopted as a criterion of step S7. .

As described above, when the original image is a binary image such as a character image or a halftone image, it is determined that the first compression processing is performed on the main scan data. On the other hand, when the original image is a multi-valued image such as a photographic image, it is determined that the primary scan data is not subjected to the primary compression.
When the original image is a binary image, the run-length compression method is selected as the secondary compression processing method.
If the original image is a multi-valued image, the JPEG compression method is selected. Further, as a result of experimentally performing the secondary compression processing on the pre-scan data, if it is determined that the data compression rate by the secondary compression processing is less than a predetermined compression rate α, the main scan data Is determined not to be subjected to the secondary compression processing.

FIG. 3 is a flow chart showing the flow of image data compression processing executed subsequent to the above-mentioned compression method selection processing. When the compression method selection process ends, the CP
U6 operates the image reading unit 4 of the scanner 1 to execute the main scan of the original image (step T6).
1) determine the status of the flag F ₁ (step T2). If the flag F ₁ has been rewritten to ₁ in the compression method selection processing, the determination whether the flag F ₁ is 1 is affirmed, and the main scan data output from the image reading unit 4 is subjected to the first compression processing. Provided to part 5. The first compression processing unit 5
Based on a control signal input from the CPU 6, a first compression process is performed on the main scan data provided from the image reading unit 4 (step T3). The main scan data after the first compression processing is sequentially transmitted from the first compression processing unit 5 to the CPU 6.

[0035] Next, CPU 6 checks the status of the flag F _2, the flag F ₂ determines whether 1 (step T
4). When the flag F ₂ in the compression method selection process is rewritten to 1, the determination is affirmative in step T4,
The main scan data input to the CPU 6 is subjected to a secondary compression process by a run-length method. Then, the main scan data after the secondary compression processing is sequentially stored in the disk storage device 9, and the image data compression processing ends.

Further, when the flag F ₂ is zero, determination is negative in step T4, the secondary compression processing is not performed, the main scan data input to the CPU 6,
The data is sequentially stored in the disk storage device 9 as it is. When all the main scan data sent from the scanner 2 is stored in the disk storage device 9, the image data compression processing is completed.

On the other hand, in the determination at step T2, the flag F ₁ is determined to be 0, to the scan data output from the image reading section 4, the primary compression by the first compression processing unit 5 It is not applied and is given to the CPU 6 as it is. If the original image is a multi-valued image and a primary compression process is performed to remove the lower bits from the main scan data, the image output device 3 outputs the compressed image data based on the compressed image data. Image data cannot be restored. Thus, in this embodiment, when the document image is a multi-valued image, the image data is not subjected to the primary compression processing.

Next, CPU 6 checks the status of the flag F _3, the flag F ₃ is determined whether 1 (step T
6). If the flag F ₃ in the compression method selection process described above is rewritten to 1, the determination in step T6 is affirmative, for the present scan data input to CPU 6, the secondary compression processing by the JPEG method Is performed (step S7). Then, the main scan data after the secondary compression processing is sequentially stored in the disk storage device 9, and the image data compression processing ends.

Further, when the flag F ₃ is zero, is negative is determined in step T6, the scan data input to the CPU6 is sequentially stored in the disk storage unit 9 as it is. When all the main scan data sent from the scanner 2 is stored in the disk storage device 9, the image data compression processing is completed.

As described above, when the flag F ₁ has been rewritten to ₁ in the compression method selection process, that is, when the original image is a binary image, the main scan data is converted into 1-bit data. . As a result, the time required for transmission of the main scan data can be significantly reduced as compared with the case where the main scan data that is not subjected to the compression processing is transmitted from the scanner 1 to the image data processing apparatus 2 (CPU 6). In addition, the second processing executed by the image data processing device 2
The processing time of the next compression processing can be shortened.

On the other hand, if the flag F ₁ remains at 0,
That is, when the original image is a multi-valued image, the main scan data output from the image reading unit 4 is not subjected to the first compression processing and is directly provided to the CPU 6. As a result, the multi-bit image data representing the multi-valued image is forcibly converted into 1-bit image data. When the image output device 3 outputs the image, the compressed image data is converted into the original multi-bit image data. There is no such thing that the image data cannot be restored.

When the original image is a binary image, the length compression method is selected as the secondary compression processing method, and when the image is a multi-value image, the JPEG compression method is selected. , An appropriate compression method according to the type of image is selected. Therefore, the most efficient compression processing can be performed according to the type of image. Further, in the compression method selection processing, if the data compression rate of the secondary compression processing is equal to or more than a predetermined compression rate α as a result of experimentally performing the secondary compression processing on the prescan data, Secondary compression is performed on the scan data. Thus, the amount of main scan data to be stored in the disk storage device 9 is reduced, so that the time required for writing the main scan data to the disk storage device 9 is reduced.

On the other hand, if the data compression rate of the secondary compression processing is less than a predetermined compression rate α as a result of the secondary compression processing performed on the prescan data on a trial basis, the scanner 1 The secondary scan processing is not performed on the main scan data sent to the image data processing device 2 from the, and the main scan data is stored in the disk storage device 9 as it is. Therefore, by performing the secondary compression processing on the main scan data, it does not take much longer than the time required to store the main scan data in the disk storage device 9 as it is.

Although the embodiment of the present invention has been described above, the present invention is not limited to the above embodiment. For example, in the above-described embodiment, the secondary compression processing executed by the computer is a run-length compression processing or a JPEG compression processing. However, the secondary compression processing is a compression processing by a compression processing method such as LZW encoding. You may.

In addition, various changes can be made within the scope described in the claims.

[0046]

According to the first aspect of the present invention, it is possible to select a compression processing method according to the type of image read by the image reading device. Therefore, compression processing can be performed most efficiently according to the type of image. According to the second aspect of the present invention, as a result of experimentally performing compression processing on image data obtained by pre-scanning by the compression method selected by the selection means, the data compression ratio by the compression processing is determined in advance. If the compression ratio exceeds
The compression processing is performed on the image data output from the image reading device during the main scan. Thereby, for example, the amount of image data to be stored in the disk storage device is reduced, so that the time required for writing the image data to the disk storage device is reduced.

On the other hand, as a result of trially performing compression processing on image data obtained by pre-scanning, if the data compression rate by the compression processing is less than a predetermined compression rate, the image reading device The output image data is not subjected to compression processing and is stored in the disk storage device as it is. Therefore, by performing the compression process on the image data, the time required for storing the image data becomes longer than when the image data output from the image reading device is directly stored in the disk storage device. There is no.

According to the third and fourth aspects of the present invention, when the original image is, for example, a binary image, the pre-compression processing is executed. The time required for transmitting image data from the image data processing apparatus to the image data processing apparatus can be greatly reduced. In addition, the processing time of the compression processing performed by the image data processing device can be reduced.

When the original image is, for example, a multi-valued image, the pre-compression process is not performed, and the image data output from the image reading device is directly provided to the image data processing device. As a result, the multi-bit image data representing the multi-valued image is converted into, for example, 1-bit image data. When the image output device outputs the image, the compressed image data is converted into the original multi-bit image data. There is no such thing that data cannot be restored.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a system to which an image data processing device according to an embodiment of the present invention is applied.

FIG. 2 is a flowchart illustrating a flow of a compression method selection process.

FIG. 3 is a flowchart illustrating a flow of image data compression processing.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Scanner 2 Image data processing apparatus 4 Image reading part 5 First compression processing part 6 CPU 8 Second compression processing part

Claims (4)

[Claims] An image data processing apparatus for compressing image data output from an image reading apparatus by reading an original, comprising: a compression processing means for performing compression processing on image data output by the image reading apparatus; A pre-scan control means for pre-scanning the image reading device to read an image of a predetermined portion of the document; and a predetermined compression processing method based on image data output by the image reading device at the time of pre-scanning. And a selecting unit for selecting a compression processing method to be applied to image data output from the image reading device. 2. A means for trially performing a compression process by the compression method selected by the selection means on image data output by the image reading apparatus at the time of pre-scanning. 2. The image data according to claim 1, further comprising means for permitting execution of said selected compression processing by said compression processing means only when a compression rate equal to or higher than a predetermined compression rate is obtained. Compression device. 3. An image reading apparatus comprising pre-compression processing means for compressing image data by a predetermined compression method, wherein said pre-compression processing is performed based on image data output by the image reading apparatus at the time of pre-scanning. 3. The image data processing apparatus according to claim 1, further comprising a determination unit that determines whether to perform image data compression by the unit. 4. The determining means for determining whether the image read by the image reading device is a binary image, and the image read by the image reading device by the determining means is a binary image. If it is determined that the image data is to be compressed by the pre-compression processing unit, and if it is determined that the image data is not a binary image, it is determined that the image data is not to be compressed by the pre-compression processing unit. 4. The image data compression apparatus according to claim 3, wherein: