Image processing method and image processing apparatus

Abstract

To obtain compressed image data with a good balance between image quality and a compression ratio through simple image processing on original image data.SOLUTION: A data processing apparatus 51 divides an image area of input image data into a character area and a non-character area. The data processing apparatus 51 compresses each of a plurality of first data blocks corresponding to the character area, of a plurality of data blocks constituting the input image data, with an irreversible compression method by using a first compression parameter, to thereby generate a plurality of pieces of first post-compression data. The data processing apparatus 51 compresses each of a plurality of second data blocks corresponding to the non-character area, of the plurality of data blocks, with the irreversible compression method by using a second compression parameter, which is a compression parameter with a higher compressibility ratio than the first compression parameter, to thereby generate a plurality of pieces of second post-compression data. The data processing apparatus 51 composes the plurality of pieces of first post-compression data and the plurality of pieces of second post-compression data with each other.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an image processing method and an image processing device for compressing image data. [Background technology]

[0002] Image processing devices such as copying machines, facsimile machines, and multifunction peripherals have a function for compressing image data.

[0003] When image data is compressed using a lossless compression method, high-quality compressed image data is obtained, but the compression ratio is relatively low. On the other hand, when image data is compressed using a lossy compression method, the compression ratio is high, but noise may occur in some parts of the image based on the compressed image data.

[0004] It is also known that an image compression device divides image data into a plurality of blocks, compresses each of the blocks using a lossless compression means and a lossy compression means to generate two compressed block data, and selects one of the two compressed block data for each block (see, for example, Patent Document 1). For example, the image compression device selects data according to the cumulative amount of information generated by the lossless compression and the number of colors for each block. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 8-167030 Summary of the Invention [Problem to be solved by the invention]

[0006] Meanwhile, there is a need to obtain compressed image data that has a good balance between image quality and compression ratio by performing image processing on original image data as simply as possible.

[0007] An object of the present invention is to provide an image processing method and an image processing apparatus that can obtain compressed image data with a good balance between image quality and compression ratio by performing image processing on original image data as simply as possible. [Means for solving the problem]

[0008] An image processing method according to one aspect of the present invention includes a data processing device performing area segmentation processing to segment an image area of ​​input image data into character areas and non-character areas other than the character areas. The image processing method further includes the data processing device compressing, by a lossy compression method, a plurality of first data blocks corresponding to the character areas among a plurality of data blocks constituting the input image data, using a first compression parameter that is a compression parameter that affects a data compression rate, thereby generating a plurality of first compressed data. The image processing method further includes the data processing device compressing, by a lossy compression method, a plurality of second data blocks corresponding to the non-character areas among the plurality of data blocks constituting the input image data, using a second compression parameter that is a compression parameter having a higher compression rate than the first compression parameter, thereby generating a plurality of second compressed data. The image processing method further includes the data processing device combining the plurality of first compressed data and the plurality of second compressed data to generate output image data, which is compressed data of the input image data.

[0009] An image processing device according to another aspect of the present invention includes an image data acquisition device that acquires image data, and a data processing device that realizes the image processing method, in which data obtained by the image data acquisition device is processed as input image data. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide an image processing method and an image processing device that can obtain compressed image data with a good balance between image quality and compression ratio by performing image processing on original image data as simply as possible. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a block diagram showing the configuration of an image processing apparatus according to the first embodiment. [Figure 2] FIG. 2 is a block diagram showing the configuration of a plurality of processing modules included in the image processing unit in the image processing apparatus according to the first embodiment. [Figure 3] FIG. 3 is a block diagram showing the configuration of an image processing apparatus according to the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Note that the following embodiment is an example of the present invention, and does not limit the technical scope of the present invention.

[0013] [First embodiment] The image processing device 10 according to the first embodiment is capable of executing various types of image processing such as image formation processing, image reading processing, image transmission processing, etc. For example, the image processing device 10 is a copying machine, a facsimile machine, a multifunction peripheral, or the like.

[0014] In the example shown in FIG. 1, an image processing apparatus 10 includes a printing device 1, an image reading device 2, a user interface device 3, a communication device 4, a control device 5, and a secondary storage device 6.

[0015] The image processing device 10 is capable of communicating with other devices such as a host device 8 through a network 80. The network 80 includes a LAN (Local Area Network) and the Internet.

[0016] The printing apparatus 1 executes the image forming process by a predetermined method such as an electrophotographic method or an inkjet method. The image forming process is a process of forming an image on a sheet 91.

[0017] The printing apparatus 1 includes a sheet transport mechanism that transports a sheet 91 and a printing device that forms an image on the sheet 91 .

[0018] The image reading device 2 executes the image reading process. The image reading process is a process of reading an image from an original 92 and outputting data of the read image. The image reading device 2 includes an optical scanning mechanism that scans light onto the original 92, and an image sensor that receives light reflected from the original 92.

[0019] The image sensor outputs data of the read image, which is an image read from the document 92.

[0020] The image processing device 10 also includes a frame memory 20 capable of storing image data. The image reading device 2 stores the read image data in the frame memory 20.

[0021] The user interface device 3 includes an operation device 3a and a display device 3b. The operation device 3a is a device that accepts human operations. For example, the operation device 3a includes operation buttons and a touch panel. The display device 3b is capable of displaying information. For example, the display device 3b includes a display panel such as a liquid crystal panel.

[0022] The communication device 4 is a communication interface device that communicates with other devices such as a host device 8 via a network 80. The control device 5 performs all data transmission and reception with the other devices through the communication device 4.

[0023] The printing device 1 executes the image forming process based on the scanned image data or the received print data, which is data included in a print request received from the host device 8 via the communication device 4.

[0024] The communication device 4 is also capable of executing the image transmission process, which is a process of transmitting the data of the scanned image to a specified destination via the network 80.

[0025] The control device 5 executes various calculations, data processing, and control of various electrical devices included in the image processing device 10. The control device 5 includes a CPU 51, a RAM (Random Access Memory) 52, and the like.

[0026] The secondary storage device 6 is a computer-readable non-volatile storage device. The secondary storage device 6 can store computer programs and various data. For example, one or both of an SSD (Solid State Drive) and a hard disk drive may be used as the secondary storage device 6.

[0027] The secondary storage device 6 stores the computer programs executed by the CPU 51 and data referenced by the CPU 51. The CPU 51 is an example of a processor.

[0028] The CPU 51 is a processor that executes the computer programs stored in the secondary storage device 6 to perform various data processing and control operations.

[0029] It is also conceivable that another processor such as a DSP may perform the data processing and control instead of the CPU 51.

[0030] The RAM 52 is a computer-readable volatile storage device that temporarily stores the computer programs executed by the CPU 51 and data output and referenced during the execution of the computer programs by the CPU 51.

[0031] The CPU 51 includes a plurality of processing modules that are realized by executing the computer programs, including a job control unit 5a and an image processing unit 5b.

[0032] The job control unit 5a controls the printing device 1, the image reading device 2, and the communication device 4. The job control unit 5a causes some or all of the printing device 1, the image reading device 2, and the communication device 4 to execute a job corresponding to a request input through the operation device 3a or the communication device 4.

[0033] The job includes some or all of the multiple types of image processing, and in this embodiment, the job includes an image scanning job, a print job, and a copy job.

[0034] The image reading job includes the image reading process executed by the operation of the image reading device 2. The print job includes the image forming process executed by the operation of the printing device 1. The copy job includes the image reading process and the image forming process executed by the operations of the image reading device 2 and the printing device 1. In other words, the job includes one or more types of image processing.

[0035] The image processing unit 5b executes various types of image processing on the image data stored in the frame memory 20. In this embodiment, the image processing unit 5b executes image data compression processing to compress the image data stored in the frame memory 20.

[0036] For example, the image reading job includes the image reading process and the image data compression process executed by the image processing unit 5b. In this case, the image processing unit 5b compresses the data of the read image stored in the frame memory 20 and outputs the compressed data of the read image.

[0037] Furthermore, the image reading job includes an image data saving process for saving the compressed data of the read image in a secondary storage device 6, or an image transmission process for transmitting the compressed data of the read image to another device such as a host device 8 via a communication device 4.

[0038] When image data is compressed using a lossless compression method, high-quality compressed image data is obtained, but the compression ratio is relatively low. On the other hand, when image data is compressed using a lossy compression method, the compression ratio is high, but noise may occur in some parts of the image based on the compressed image data.

[0039] Meanwhile, there is a need to obtain compressed image data that has a good balance between image quality and compression ratio by performing image processing on original image data as simply as possible.

[0040] In this embodiment, the image processing unit 5b performs image data compression processing on the original image data to obtain compressed image data with a good balance between image quality and compression ratio by performing image processing as simply as possible.

[0041] [Image data compression processing] The image data compression process performed by the image processing unit 5b will be described below with reference to Fig. 2. Fig. 2 shows the configuration of a plurality of processing modules included in the image processing unit 5b.

[0042] For example, the input image data D1 to be subjected to the image data compression process is data of the scanned image obtained by the image reading device 2. The input image data D1 may also be image data obtained by the communication device 4 from the host device 8.

[0043] The image reading device 2 and the communication device 4 are each an example of an image data acquisition device that acquires input image data D1.

[0044] The plurality of processing modules in the image processing unit 5 b include an edge image detection unit 501 , a character region division unit 502 , a block selection unit 503 , a parameter selection unit 504 , a data compression unit 505 and a synthesis processing unit 506 .

[0045] The image data compression process is executed by an edge image detection unit 501 , a character region division unit 502 , a block selection unit 503 , a parameter selection unit 504 , a data compression unit 505 and a synthesis processing unit 506 .

[0046] The image data compression process is an example of a process that realizes an image processing method. The CPU 51 including the image processing unit 5b is an example of a data processing device that realizes the image processing method.

[0047] The edge image detection unit 501 performs edge detection processing on the input image data D1 to detect an edge image made up of a plurality of continuous edge pixels.

[0048] For example, the edge detection process includes a differential value derivation process and an edge data derivation process. The differential value derivation process is a process of deriving differential values ​​in the X-axis direction and the Y-axis direction for a plurality of pixels in the input image data D1. The edge data derivation process is a process of deriving data consisting of the logical sum of binary data of the differential value in the X-axis direction and binary data of the differential value in the Y-axis direction for each of a plurality of pixels as edge data D11. The edge data D11 is data representing the edge image.

[0049] The character region segmentation unit 502 segments a rectangular region surrounding the edge image in the edge data D11 as a character region, and outputs character region coordinate data D12 representing the coordinates of the character region. The process of deriving the rectangular region surrounding the edge image is so-called bounding box processing.

[0050] The area other than the character area corresponding to the character area coordinate data D12 in the image area of ​​the input image data D1 is a non-character area.

[0051] Therefore, the processing by the edge image detection unit 501 and the character region division unit 502 is an example of region division processing that divides the image region of the input image data D1 into the character region and the non-character region other than the character region.

[0052] The block selection unit 503 selects each of the plurality of data blocks constituting the input image data D1 as a target block BD1. The target block BD1 is data to be subjected to data compression processing. The plurality of data blocks are data obtained by dividing the input image data D1 into predetermined unit areas.

[0053] For example, each of the plurality of data blocks is data for 64 pixels, consisting of 8 pixels in the X-axis direction and 8 pixels in the Y-axis direction. The block selection unit 503 sequentially selects each of the plurality of data blocks as a target block BD1 in a predetermined order.

[0054] The parameter selection unit 504 determines whether the data of the target block BD1 corresponds to the character area or the non-character area based on the coordinates of the sequentially selected target block BD1 and the character area coordinate data D12.

[0055] For example, if more than a predetermined number of pixels in the target block BD1 belong to the text region, the parameter selection unit 504 determines that the target block BD1 is the first data block corresponding to the text region.

[0056] On the other hand, if the number of pixels in the target block BD1 that exceeds the predetermined number does not belong to the character area, the parameter selection unit 504 determines that the target block BD1 is a second data block that corresponds to the non-character area.

[0057] Furthermore, the parameter selection unit 504 selects a compression parameter PA1 that affects the data compression rate from two candidate parameters depending on whether the target block BD1 is the first data block or the second data block.

[0058] The compression parameter PA1 is a parameter used in the data compression process using a lossy compression method executed by the data compression unit 505, which will be described later.

[0059] In this embodiment, the data compression unit 505 compresses the current block BD1 in the JPEG format. The compression parameter PA1 is a QUALITY parameter in the JPEG format.

[0060] The two candidate parameters include a first compression parameter and a second compression parameter, which are preset. The second compression parameter is a compression parameter PA1 that has a higher compression ratio than the first compression parameter.

[0061] For example, the value 90 of the QUALITY parameter is the first compression parameter, and the value 50 of the QUALITY parameter is the second compression parameter.

[0062] When data compression processing using a lossy compression method such as the JPEG method is performed with parameters for a high compression ratio, noise is likely to occur in character regions with many edges.

[0063] The parameter selection unit 504 selects the first compression parameter as the compression parameter PA1 when the current block BD1 is the first data block, and selects the second compression parameter as the compression parameter PA1 when the current block BD1 is the second data block.

[0064] The data compression unit 505 compresses the target blocks BD1 sequentially selected by the block selection unit 503 in JPEG format using the compression parameters PA1 sequentially selected by the parameter selection unit 504.

[0065] The data compression unit 505 sequentially generates and outputs compressed data blocks BD2 by performing JPEG compression processing on sequentially selected target blocks BD1.

[0066] That is, the data compression unit 505 generates a plurality of first compressed data by compressing each of the first data blocks among the plurality of data blocks constituting the input image data D1 in the JPEG format using the first compression parameter, where each of the first compressed data is a compressed data block BD2 obtained when the compression parameter PA1 is the first compression parameter.

[0067] Furthermore, the data compression unit 505 generates a plurality of second compressed data by compressing each of the second data blocks among the plurality of data blocks constituting the input image data D1 using the second compression parameter in the JPEG format, where each of the second compressed data is a compressed data block BD2 obtained when the compression parameter PA1 is the second compression parameter.

[0068] The synthesis processing unit 506 synthesizes the plurality of first compressed data and the plurality of second compressed data to generate output image data D2, which is compressed data of the input image data D1.

[0069] By employing the image data compression process, it is possible to obtain output image data D2 with a good balance between image quality and compression ratio by performing relatively simple image processing on the input image data D1.

[0070] [Second embodiment] Next, an image processing device 10A according to a second embodiment will be described with reference to Fig. 3. In Fig. 3, the same components as those shown in Fig. 1 are denoted by the same reference numerals.

[0071] The image processing device 10A has a configuration in which a compression circuit 7 is added to the image processing device 10. The compression circuit 7 is a circuit that realizes, by hardware, the edge image detection unit 501, the character region division unit 502, the block selection unit 503, the parameter selection unit 504, the data compression unit 505, and the synthesis processing unit 506 shown in FIG.

[0072] That is, the compression circuit 7 includes an edge image detection circuit that realizes the processing of the edge image detection unit 501, a character area division circuit that realizes the processing of the character area division unit 502, a block selection circuit that realizes the processing of the block selection unit 503, a parameter selection circuit that realizes the processing of the parameter selection unit 504, data compression that realizes the processing of the data compression unit 505, and a synthesis processing circuit that realizes the processing of the synthesis processing unit 506.

[0073] The compression circuit 7 is an example of a data processing device that realizes the image processing method. When the image processing device 10A is used, the same effects as when the image processing device 10 is used can be obtained.

[0074] [Notes on the Invention] The following is a summary of the invention extracted from the above-described embodiment. Note that the configurations and processing functions described in the following supplementary notes can be selected and combined as desired.

[0075] <Appendix 1> a data processing device executing an area division process for dividing an image area of ​​the input image data into a character area and a non-character area other than the character area; the data processing device generates a plurality of first compressed data by compressing each of a plurality of first data blocks corresponding to the character region among a plurality of data blocks constituting the input image data using a lossy compression method using a first compression parameter, which is a compression parameter that affects a data compression rate; the data processing device generates a plurality of second compressed data by compressing each of a plurality of second data blocks corresponding to the non-character regions among the plurality of data blocks constituting the input image data using the lossy compression method with a second compression parameter that is the compression parameter having a higher compression ratio than the first compression parameter; The image processing method includes the data processing device generating output image data that is compressed data of the input image data by combining the plurality of first compressed data and the plurality of second compressed data.

[0076] <Appendix 2> The region division process includes: the data processing device performs edge detection processing on the input image data to detect an edge image made up of a plurality of continuous edge pixels; The image processing method according to claim 1, further comprising: dividing a rectangular area surrounding the detected edge image into the character area.

[0077] <Appendix 3> the lossy compression method is the JPEG method, The image processing method according to claim 1 or 2, wherein the compression parameter is a QUALITY parameter in the JPEG format.

[0078] <Appendix 4> an image data acquisition device that acquires image data; and a data processing device that implements the image processing method according to any one of Supplementary Note 1 to Supplementary Note 3, which processes data obtained by the image data acquisition device as input image data.

[0079] <Appendix 5> 5. The image processing device according to claim 4, wherein the image data acquisition device is an image reading device that reads an image from a document. [Explanation of symbols]

[0080] 1: Printing device 2: Image reader 3: User interface device 4: Communication equipment 5: Control device 6 :Secondary storage device 7: Compression circuit (data processing device) 10: Image processing device 10A: Image processing device 20: Frame memory 51: CPU (Data Processing Unit)

Claims

1. a data processing device executing an area division process for dividing an image area of ​​the input image data into a character area and a non-character area other than the character area; the data processing device generates a plurality of first compressed data by compressing each of a plurality of first data blocks corresponding to the character region among a plurality of data blocks constituting the input image data using a lossy compression method using a first compression parameter, which is a compression parameter that affects a data compression rate; the data processing device generates a plurality of second compressed data by compressing each of a plurality of second data blocks corresponding to the non-character regions among the plurality of data blocks constituting the input image data by the lossy compression method using second compression parameters, which are compression parameters having a higher compression ratio than the first compression parameters; the data processing device generating output image data that is compressed data of the input image data by combining the plurality of first compressed data and the plurality of second compressed data.

2. The region division process includes: the data processing device performs edge detection processing on the input image data to detect an edge image made up of a plurality of continuous edge pixels; The image processing method according to claim 1 , further comprising: dividing a rectangular area surrounding the detected edge image into the character area by the data processing device.

3. the lossy compression method is the JPEG method, 3. The image processing method according to claim 1, wherein the compression parameter is a quality parameter in the JPEG format.

4. an image data acquisition device that acquires image data; 3. An image processing apparatus comprising: a data processing apparatus that implements the image processing method according to claim 1 or 2, and processes data obtained by the image data acquisition apparatus as input image data.

5. The image processing apparatus according to claim 4 , wherein the image data acquisition device is an image reading device that reads an image from a document.

Images