JP2008022082A - Image forming apparatus and control method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus and a control method thereof capable of limiting a data amount after compression processing so as not to exceed a data amount before compression, eliminating the need for ensuring the capacity of a memory with a data size before the compression even in the case of spooling data to the memory, and executing compression processing with the memory of a small capacity and storing compressed data. <P>SOLUTION: In the control method of the image forming apparatus, necessary image processing is applied to obtained image data (S1105) when the PDL is rendered in the case of performing printing on the basis of PDL data (S1103). Compression processing is applied to the image data after the image processing (S1106). Data sizes before and after the compression are compared with each other and uncompressed data are stored to a memory when the size of the uncompressed data before the compression is smaller than the size of the compressed data. Further, the compression rate of the data in the memory is checked (S1107), and when the compression rate is 1/4 or below, pixels are interleaved to 1/4 (S1108). When the image data of one page have been stored in this way, the image data are expanded as required and printed (S1111, S1112). <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus having a function of temporarily storing data, such as a copying machine or a printer, and a control method therefor.

Conventionally, it is widely performed to store data in a storage device such as a hard disk or a memory, and to read and process them as necessary. In order to store a large amount of data in such a storage device, compression processing is performed on the data (see, for example, Patent Document 1). Various methods of compression processing have been proposed, but a method that can always compress all data at a good compression rate has not been developed yet. Depending on the data, the data size of the compressed data may be larger than the uncompressed data. In such a case, it is necessary to secure an extra memory area used by each module, and the memory capacity increases accordingly. In order to solve such a problem, the compressed data is stored in the first data buffer, and the uncompressed data is stored in the second data buffer. Thereafter, a configuration has been proposed in which the sizes of both data are compared and the smaller size is adopted.
Japanese Patent Laid-Open No. 11-198462

  However, the conventional example has the following problems. That is, it is necessary to prepare two data buffers for storing uncompressed image data before compression and compressed image data after compression. For this reason, unless the data unit to be compared is made small, a huge memory capacity is required and the cost increases. Furthermore, even if the data unit to be compared is reduced, if all data is finally spooled in the memory, the memory must be secured for the entire data size before compression.

  The present invention has been made in view of the above conventional example, and an object thereof is to solve the above problems. Specifically, the amount of data after compression processing does not exceed the amount of data before compression, and it is not necessary to secure a memory of the data size before compression when spooling data to memory, An object of the present invention is to provide an image forming apparatus capable of performing compression processing and storing compressed data with a small-capacity memory, and a control method thereof.

The present invention includes the following configuration in order to solve the above-described problems. An image forming apparatus that temporarily stores image data,
Image compression means for compressing uncompressed image data and converting it into compressed image data;
A storage control unit that compares the size of the target uncompressed image data with the size of the compressed image data converted from the target uncompressed image data by the image compression unit, and stores the smaller data in the memory; ,
When the compression ratio, which is the ratio of the size of the compressed image data to the size of the target uncompressed image data, does not reach the reference value, the image data generated by thinning out the pixels of the image data stored in the memory is generated. A reduction means,
The storage control means uses uncompressed image data that has not been reduced initially as uncompressed data of interest, and when the reduced image data generated by the image reduction means is stored in a memory, the reduced image Process the data as the uncompressed data of interest,
If the image data stored in the memory is compressed, the image reducing means expands the compressed image data and then reduces the compressed image data.

  According to the present invention, the amount of data after compression processing does not exceed the amount of data before compression, and it is not necessary to secure a memory of the data size before compression when spooling data to the memory. In addition, compression processing and storage of compressed data can be performed with a small-capacity memory.

[First Embodiment]
An overall configuration of a copying machine 100 according to an embodiment of the present invention will be described with reference to FIG. The copier 100 is also called a digital multi-function peripheral, and may be called an image forming apparatus or an image input / output system.

  A reader unit (image input device) 200 optically reads a document image and converts it into image data. The reader unit 200 includes a scanner unit 210 having a function for reading a document and a document feeding unit 250 having a function for transporting a document sheet. The scanner unit 210 is provided with a reader controller 222.

  A printer unit (image output device) 300 conveys recording paper, prints image data as a visible image thereon, and discharges the recording paper out of the device. The printer unit 300 includes a paper feed unit 360 having a plurality of types of recording paper cassettes, and a marking unit 310 having a function of transferring and fixing image data onto the recording paper. Furthermore, this example includes a paper discharge unit 370 that has a function of sorting and stapling printed recording papers and outputting them to the outside of the apparatus.

  The control device 110 is electrically connected to the reader unit 200 and the printer unit 300, and is further connected to host computers 401 and 402 via the network 400.

  The control device 110 controls the reader unit 200 to read image data of a document, and controls the printer unit 300 to output the image data to a recording sheet to provide a copy function. The control device 110 provides a scanner function that converts image data read from the reader unit 200 into code data and transmits the code data to the host computer via the network 400. The control device 110 provides a printer function that converts code data received from the host computer via the network 400 into image data and outputs the image data to the printer unit 300.

  The operation unit 180 is connected to the control device 110, is configured with a liquid crystal touch panel, and provides a user I / F for operating the image input / output system.

  FIG. 2 is a schematic view of the reader unit 200 and the printer unit 300. The document feeding unit 250 in the reader unit feeds documents one by one from the top to the platen glass 211 one by one, and discharges the documents on the platen glass 211 after the document reading operation is completed. When the document is conveyed onto the platen glass 211, the lamp 212 is turned on, and the movement of the optical unit 213 is started to expose and scan the document. Reflected light from the original at this time is guided to a CCD image sensor (hereinafter referred to as CCD) 218 by mirrors 214, 215, and 216 and a lens 217. In this way, the scanned original image 202 is read by the CCD 218.

  The reader controller unit 222 performs predetermined processing on the image data output from the CCD 218 and outputs the image data to the control device 110 via the scanner I / F 140.

  The printer image processing circuit unit 352 outputs an image signal sent from the control device 110 via the printer I / F 145 to the laser driver.

  A laser driver 317 of the printer unit 300 drives the laser light emitting units 313, 314, 315, and 316, and laser light corresponding to the image data output from the printer image processing unit 352 is emitted from the laser light emitting units 313, 314, and 315. 316 is caused to emit light. This laser light is applied to the photosensitive drums 325, 326, 327, and 328 by mirrors 340, 341, 342, 343, 344, 345, 346, 347, 348, 349, 350, and 351. As a result, latent images corresponding to the laser light are formed on the photosensitive drums 325, 326, 327, and 328. The developing devices 321, 322, 323, and 324 are developing devices for developing the latent image with black, yellow, cyan, and magenta toners, respectively, and the developed color toners are transferred to a sheet and printed in full color. Out.

  A sheet fed from one of the sheet cassettes 360 and 361 and the manual feed tray 362 at the timing synchronized with the start of laser light irradiation is attracted onto the transfer belt 334 via the registration roller 333 and conveyed. Then, the developer attached to the photosensitive drums 325, 326, 327, and 328 is transferred to a recording sheet. The recording paper on which the developer is placed is conveyed to the fixing unit 335, and the developer is fixed on the image recording paper by the heat and pressure of the fixing unit 335. The recording paper that has passed through the fixing unit 335 is discharged to a paper discharge tray 371 by a discharge roller 336. The paper discharge unit 370 bundles the discharged recording sheets and sorts the recording sheets, and staples the sorted recording sheets.

  If double-sided recording is set, the recording paper is conveyed to the discharge roller 336, and then the rotation direction of the discharge roller 336 is reversed and guided to the refeed conveyance path 338 by the flapper 337. The recording sheet guided to the refeed conveyance path 338 is fed to the transfer belt 334 at the timing described above.

<Explanation of reader controller>
FIG. 4 is a block diagram showing a detailed configuration of the reader controller unit 222. The CPU 402 controls the reader controller unit 222. The activation program for the CPU 402 is stored in the ROM 422 and operates based on the program stored in the memory 421. The high-speed serial bus control unit 403 is connected to the controller unit 110 and transfers communication commands and image data. A USB is generally used as a high-speed serial bus. The bus controller unit 404 connects the general-purpose external bus 423 and the internal local bus 412.

  Internal local buses 411 and 412 connect each module of the reader controller unit and the memory controller unit 410 to perform data transfer.

  In the reader controller unit 222, the document image on the platen glass 211 is read by the CCD 218 and converted into an electrical signal. The CCD 218 may be one in which RGB color filters are mounted in-line in RGB order on a one-line CCD, or may be a three-line CCD in which an R filter, a G filter, and a B filter are arranged for each CCD. Further, the filter may be on-chip, or the filter may be configured separately from the CCD.

  An electrical signal (analog image signal) input to the scanner I / F unit 416 is A / D converted and converted into, for example, an RGB 8-bit digital signal. RGB 8-bit digital signals are input to the scanner image processing unit 415 via the scanner I / F unit 416, and after being subjected to predetermined image processing, are stored in the memory 421 via the local bus 411 and the memory controller unit 410. The scanner image processing unit 415 outputs image data and an image area flag indicating the characteristics of the image data. Examples of the image area flag include a flag indicating characters / non-characters and a flag indicating chromatic / achromatic colors.

  The image data stored in the memory 421 is converted into compressed data using a multi-value image compression / decompression unit 414. A compression method generally includes JPEG compression, and is used to transfer a scan image to the controller unit 110.

  When the binary image data is transferred to the controller unit 110, the multi-value data read by the binarization unit 417 is binarized, and the binary image compression / decompression unit 413 performs binary image compression. Generally, binary image compression methods include JBIG and MMR.

  The image area flag data output from the scanner image processing is subjected to lossless compression by the CPU 402 and transferred to the controller unit 110 together with the image data. The compression of the image area flag uses Packbits or the like.

<Description of Reader Image Processing Unit>
FIG. 6 is a block diagram showing a detailed configuration of the scanner image processing unit 415. The inter-line correction unit 601 adjusts the delay amount for each line in accordance with the reading speed, and corrects the RGB phase changed according to the reading speed. When the CCD 218 is a 3-line CCD, the inter-line correction corrects the signal timing so that the reading positions of the 3 lines are the same.

  The shading unit 602 performs shading correction and black correction. The digital signal whose reading position timing is corrected is subjected to a one-dimensional nonlinear conversion for each of the RGB image signals by the γ correction unit 603.

  The color space matching unit 604 performs color correction on the input RGB signal using a three-dimensional LUT. The MTF correction unit 605 corrects the difference in MTF for each color of the input signal RGB using data before and after the data of interest for each component. The spatial filter unit 606 performs matrix calculation to adjust the sharpness of the input image. After the RGB → LcaCb color space conversion is performed, a 7 × 7 operation is performed on the luminance component.

  The linear interpolation unit 607 performs zooming from 50 to 200%. The color space conversion unit 608 performs color space conversion from RGB to YUV according to the operation mode. The trimming unit 609 performs frame erasing processing and trimming / masking processing. The frame erase process is used for document frame erase, punch hole erase, book frame erase, and the like.

  The achromatic color determination unit 612 determines whether the input image signal includes a chromatic color. The black character determination unit 611 determines the character / non-character region and chromatic / achromatic color of the input image for each pixel from the edge direction of the image signal, etc., and creates an image region flag as a determination result to the memory 421. Forward.

<Description of control device>
The function of the control device 110 will be described based on the block diagram of the control device 110 shown in FIG. FIG. 5 shows a detailed block diagram of the main controller 111.

  The CPU 501 (FIG. 5) of the main controller 111 controls the overall operation of the control device 110, and the CPU 501 operates based on a program stored in the memory 121. The program also describes the operation of interpreting PDL (page description language) code data received from the host computer and developing it into raster image data. The interpretation of the code data is mainly performed by the CPU 502, and the raster image data development is processed by the rendering unit 508. The rendering unit creates raster image data based on the code data created by the CPU 502, and transfers the raster data after development to the memory 121 or the bus control unit 510. Examples of the color space of the image data created by the rendering unit include RGB and CMYK.

  The high-speed control unit 511 controls data transfer input / output from the printer image processing unit 151, and controls arbitration at the time of bus contention and DMA data transfer.

  A serial communication control unit 507 communicates with the CPU of the printer unit 300 by transmitting and receiving control commands via the serial bus. In the serial bus control unit 506, communication with the host computer and communication with various devices are performed via the connector 122. A serial bus is generally USB, and is used as an I / F that receives PDL data from a host computer. The serial bus connected to the connector 123 is connected to the reader controller 222 and is used for communication with the reader and transfer of image data.

  A boot ROM 124 and a printer image processing unit 151 are connected to the bus control unit 510 via a custom bus 125. The boot ROM 124 stores a program to be started by the CPU 501, and in some cases, font data for PDL is stored. The raster image data developed by the rendering unit 508 is transferred from the main controller 111 to the printer image processing unit 151 via the bus control unit 510.

  The custom bus 125 operates at a low speed in the general-purpose bus mode when accessing the boot ROM 124, and operates at a high speed in the custom bus mode when transferring raster image data to the printer image processing unit 151.

  A general-purpose high-speed bus 130 is connected to the general-purpose high-speed bus control unit 509, and an expansion connector 135 for connecting an expansion board, an I / O control unit 136, and an HD controller 131 are connected. A general-purpose high-speed bus is a PCI bus.

  An image compression unit 504 and an image expansion unit 505 have a function of compressing and expanding a multi-value image and simultaneously performing color space conversion. The image compression / decompression / color space conversion is used, for example, when the image data read from the reader unit 200 is transferred to the host computer via the LAN 147 or the connector 122 and converted to the standard color space.

  The memory controller unit 503 controls access to the memory 121. The bus bridge 512 connects buses between modules in the main controller 111. The HD controller 131 is for connecting an external storage device. In this embodiment, the hard disk drive 132 is connected via this I / F. The hard disk 132 is used for storing programs and storing image data. The I / O control controller 136 controls the data bus 191 and controls ports and interrupts. The I / O control controller 136 includes a CPU 137 that controls port control 138, communication with the network controller 140 and the operation unit 180, communication with the modem 146, and the like.

  The network controller 180 is connected to the external network 147. The network is generally Ethernet (registered trademark), and is used for receiving PDL data from a host computer, transmitting a scanner image, remote management, and the like. The modem 146 is connected to the public line 149 and performs facsimile communication.

  The memory 139 is used as a work memory for the CPU 137, a work memory for image data to be displayed on the operation unit 180, and the like.

  The operation unit I / F 145 includes an I / F for displaying on the liquid crystal screen of the operation unit 180 and a key input I / F for inputting hard keys and touch panel keys. The operation unit 180 includes a liquid crystal display unit, a touch panel input device attached on the liquid crystal display unit, and a plurality of hard keys. A signal input from the touch panel or the hard key is transmitted to the CPU 137 via the operation unit I / F 147 described above, and the liquid crystal display unit displays image data sent from the operation unit I / F 147. The liquid crystal display unit displays function display, image data, and the like in the operation of the image forming apparatus. The fan 148 is connected to the I / O control controller 136 and is used to cool the controller unit 110.

  The SRAM 141 is backed up by a backup battery 144, and stores user mode, various setting information, file management information of the hard disk drive 132, and the like.

  The real-time clock module 143 is for updating / saving the date and time managed in the device, and is backed up by a backup battery 144.

  The printer image processing unit 151 is connected to the main controller 111 via a custom bus 125 and a high-speed bus 150. The high-speed bus 150 is connected in a ring shape by one-way communication.

  The printer image processing unit 151 is connected to the printer unit 300 via the connector 181, and has a function of performing predetermined image processing on the image data input from the main controller 111 and outputting the image data to the main controller 111 or the printer unit 300. . The memory 152 is used as a work area and delay buffer for the printer image processing 151.

<Description of Printer Image Processing Unit>
Next, a detailed description will be given with respect to the portion responsible for the printer image processing 153. FIG. 7 is a block diagram showing the detailed configuration of the printer image processing 151.

  An image signal sent from the main controller 111 via the custom bus 125 is first input to the data input unit 701. The data input unit 701 switches between raster image data input and access to the memory 152. When raster image data is input, the raster image data input to the color space compression unit 704 is transferred.

  A color space compression unit 704 compresses the color range of the input image data to a range that can be reproduced by a printer, and performs saturation adjustment, color phase adjustment, background adjustment, and black area adjustment. When the input color space is YUV, the color space compression unit 704 performs conversion to the RGB color space.

  The background removal / black-and-white conversion unit 705 has a function of performing nonlinear calculation on RGB image data to remove the background of the image. Further, it has a color / monochrome conversion function for converting image data from RGB to monochrome when the achromatic color determination unit 612 of the scanner image processing unit 415 determines that the color is achromatic.

  The LOG conversion unit 706 performs nonlinear conversion using a one-dimensional lookup table, and converts image data from RGB signals to CMY signals. The CMYK conversion unit 707 converts a CMY signal into a CMYK signal using a three-dimensional lookup table. When the color space of the image data input from the main controller 111 is CMYK, the input data is output as it is from the color space compression unit 704 to the CMYK conversion unit 707.

  The gamma correction unit 708 adjusts the density of the input CMYK signals independently using a one-dimensional lookup table. The halftone unit 709 converts the input multivalued image data into 4/2/1 bit gradation. The SST unit 710 detects and converts the edge portion of the image data by pattern matching, reduces jaggies and smoothes it. The video count unit 717 performs γ correction on the CMYK signal output from the CMYK conversion unit 707 and adds the corrected signal value. The addition result is used by the printer unit 300 to estimate the toner consumption.

  An image compression unit 711 performs lossless compression of the image data output from the SST unit. As a reversible compression method, JBIG compression is generally used. The compressed data is output from the image compression unit 711 to the bus controller 712, and at the same time, uncompressed image data is stored in the memory 152 via the memory access queue unit 716 and the memory controller unit. The uncompressed image data stored in the memory 152 is used when the compressed data is replaced with uncompressed data when the compression ratio exceeds 1 in the image compression unit 711.

  The bus controller 712 transfers the compressed / uncompressed image data input from the image compression unit 711 to the main controller. Also, the memory 152 stores image data input from the main controller and performs register access of each module in the printer image processing unit 151.

  The image decompression unit 714 decompresses the compressed data stored in the memory 152 and stores the decompressed image data in the memory 152 again.

  The printer controller unit 715 transfers the image data stored in the memory 152 to the printer unit 300 via the connector 181. The printer controller unit 715 has a memory for storing image data for one line, and has a function of performing reverse output. In addition, it has a function of frame erasing and masking.

  The gamma correction unit 708, the halftone unit 709, the SST unit 710, the video count unit 717, the image compression unit 711, the image expansion unit 714, and the printer controller unit 715 each have four circuits for independently processing CMYK signals. is doing.

  The memory controller unit 713 controls access to the memory 152. The memory access queue unit 716 switches access from the data input unit 701, the image compression unit 711, the bus controller unit 712, the image expansion unit 714, and the printer controller unit 715 to the memory 152.

<Operation section overview>
FIG. 8 shows the configuration of the operation unit 180, and FIG. 9 shows an example of the displayed screen. The LCD display unit 3001 has a touch panel sheet pasted on the LCD, displays a system operation screen 3010, and transmits position information to the controller CPU when a displayed key is pressed. A start key 3002 is used to start a document image reading operation. There is a green and red two-color LED in the center of the start key, and the color indicates whether the start key is ready for use. A stop key 3003 serves to stop an operation in operation. An ID key 3004 is used when inputting the user ID of the user. A reset key 3005 is used to initialize settings from the operation unit.

<Operation screen>
As shown in FIG. 9, the functions provided by the apparatus of the present invention are divided into six major categories: Copy / Send / Retrieve / Tasks / Management / Configuration. These correspond to six main tabs (COPY / SEND / RETREIVE / TASKS / MGMT / CONFIG) 3011-3016 displayed on the upper part of the operation screen 3010. By pressing these main tabs, switching to the screen of each category is performed. If switching to another category is not permitted, the display color of the main tab will change, and pressing the main tab will not respond.

  Copy includes a function for performing normal document copying using its own scanner and printer, and a function for performing document copying (remote copying) using a scanner connected to its own scanner via a network. . Send is a function for transferring a document placed on a scanner of the own apparatus to an e-mail, a remote printer, a fax, a file transfer (FTP), and a database, and a plurality of destinations can be designated. Retrieve is a function for acquiring an external document and printing it with a printer included in the own apparatus. WWW, e-mail, file transfer and fax can be used as document acquisition means. Tasks automatically processes a document sent from the outside such as a fax or an Internet print, and generates and manages a task for periodically performing a retrieve. Management manages jobs, address books, bookmarks, documents, account information, and the like. In the configuration, settings (network, clock, etc.) regarding the own device are performed.

<Sequence when outputting PDL image>
FIG. 11 is a flowchart showing a procedure for outputting a PDL image in the present embodiment. In addition, S1101-S1111 in a figure shows each step. In the present embodiment, the “compression rate” represents the ratio of the data amount after compression to the data amount before compression. Therefore, the compression rate is a positive value. If it is less than 1, the data is reduced by compression, and if it exceeds 1, the data is increased. Further, the smaller the compression rate, the smaller the data after compression. A small compression rate may be expressed as a high compression rate, and a high compression rate may be expressed as a low compression rate.

  When outputting a PDL image, in step S1101, the user performs print settings for the PDL image output job on the PC 401. The contents of the print settings include the number of copies, the paper size, one side / both sides, page output order, sort output, presence or absence of stapling.

  In step S1102, a print instruction is given on the PC 401, and the driver software installed on the PC 401 converts the code data on the PC 401 to be printed into so-called PDL data. Then, along with the print setting parameter information set in S1101, the PDL data is transferred to the control device 110 of the copying machine 100 via the network 400.

  Steps S1103 and the subsequent steps are processing executed by the control device 110 of the copying machine 100. In S1103, the PDL data is developed (rasterized) into image data based on the print setting parameters. Here, the image data is raster image data in which an image is represented by pixels. In step S1104, the developed raster image data is input to the printer image processing unit 151 in dot order (raster scanning order).

  In step S1105, raster image data is subjected to image processing by the printer image processing unit 151, and halftone processing is performed to obtain binary image data.

  In S1106, the binary image data is compressed. Any known compression procedure may be used. For example, lossy compression such as JPEG and lossless compression such as Huffman coding can be employed. FIG. 12 shows the procedure of the compression processing in S1106. Note that S1201 to S1206 in FIG.

  In FIG. 12, in S1201, the binary image data subjected to image processing is transferred to the memory 152 as it is. This is because if the data size of the uncompressed data is smaller than the size of the compressed data, the amount of memory used can be reduced by storing the uncompressed data in the memory. In this way, even if the amount of image data increases due to compression, the upper limit of the amount of data to be stored is the amount of data before image compression. Therefore, the size of the image data area to be secured in the memory 152 is sufficient as the size of the uncompressed image data. By compressing image data for each area of a certain size (for example, a page or a certain rectangular area), the area to be secured in the memory is sufficient for the data size of that area. In short, the area to be secured in the memory may be an area of a fixed size called the uncompressed data size, that is, the size of the raw image data.

  In S1202, binary image data after halftoning is compressed by the image compression unit 711, and the data is transferred to the memory 121 in S1203. The image data to be output to the memory 121 is DMA-controlled by the bus controller 712, and is output as CMYK plane order.

  In S1204, it is determined whether or not the compression rate of the image data compressed by the image compression unit exceeds 1. If the compression rate becomes 1 or more (when it becomes large), the image data is stored in the memory 152 in S1205. Certain uncompressed data is transferred to the memory 121.

  In step S1206, the compression rate of image compression in the page is calculated, and it is determined whether the compression rate is equal to or less than a predetermined value. For example, 1/4 is selected as the predetermined value.

  By this procedure, the size of data stored in the memory 121 becomes the size of uncompressed data at the maximum. In S1203, identification data indicating that compressed image data is stored is stored in the memory 121 in S1205, and identification data indicating that uncompressed image data is stored in the memory 121.

  When the process in FIG. 12 is completed, the process returns to step S1107 in FIG. In S1107, if the result of determination in S1206 is that the compression ratio exceeds a certain value, for example, 1/4, the process branches to S1108. In step S1108, the image data stored in the memory 121 is subjected to thinning processing, and then the process proceeds to step S1109. If the stored data is compressed image data, the thinning-out procedure in S1108 is decompressed once. Thereafter, the resolution of the image data is reduced (reduced) at a constant rate, for example, to a half in the vertical and horizontal directions (1/4 in total). For example, the image data can be reduced to ¼ by thinning out every other pixel in the main scanning direction and thinning out one line in the sub-scanning direction. As a result, for example, image data of 8 bits / pixel at 600 dpi is reduced to 8 bits / pixel at 150 dpi, thereby reducing the amount of data information. Reduction is performed for each color plane. When thinning is performed, identification data indicating that is stored in the memory 121 together with the image data. In step S1111, the image data thinned out at 150 dpi by 8 bits / pixel is converted into resolution data (enlarged) by linear interpolation, for example, by the rendering unit 508 again at 600 dpi in order to match the printing resolution of the printer. ) The enlarged image data is transferred to the printer image processing unit 151.

  In step S1109, it is determined whether the rendering process for one page has been completed. When the rendering process for one page is completed, the image data is transferred from the memory 121 to the memory 152 in S1110. The data transfer is DMA-controlled by the high-speed bus control unit 511, and is transferred for each color component in accordance with a request signal from the printer image processing unit 151. On the other hand, if it is determined in S1109 that the process has not ended, the remaining processing is performed from S1103. Of course, when batch processing is performed in units of pages, step S1109 is skipped and step S1110 is executed immediately.

  In step S <b> 1111, the compressed image data input to the memory 152 is decompressed, and the decompressed image data is returned to the memory 152. If it is compressed data, it is decompressed, and if it is thinned data, it is interpolated and returned to the original image data.

  In step S1112, the image data stored in the memory 152 is output from the printer controller unit 715 in synchronization with a control signal from the printer 300, and is printed out. The CMYK control signals input from the printer 300 are shifted in accordance with the positions of the photosensitive drums 325, 326, 327, and 328, and the shift amount for each color component between the drums is absorbed at the data output timing of the memory 121. To do.

  When the transfer of the image data is completed, that is, when the PDL job is finished, the print output is finished. Of course, when outputting a plurality of pages, the development of PDL data is repeated from S1103.

  In this way, print output is performed. In FIG. 11, the compression rate, which is the determination criterion in step S1107, is the same as the reduction rate due to thinning in step S1108. Therefore, if thinning is performed once in step S1108, even the uncompressed image data is reduced to a size that satisfies the criterion in step S1107 with respect to the size of the original image data. Note that the reduction rate by thinning out in step S1108 may be equal to or less than the compression rate that is the determination criterion in step S1107.

  Further, the area size for image data to be secured in the memory 121 is sufficient as the size of the image data before compression.

  In addition, the compression processing can reliably compress the image data at a compression rate equal to or lower than a predetermined value.

  In FIG. 11, the PDL process input from the computer has been described. However, the same process can be performed when copying a document. In this case, image data is input by a scanner instead of PDL input. Therefore, the processing before S1103 is not performed, and in S1104, image data is transferred from the reader controller unit 222 to the printer image processing unit 151. If image data for one page has been transferred together, the determination in S1107 always yields a positive result.

<Sequence when outputting copy image>
FIG. 10 is a flowchart showing a copy image output procedure in the present embodiment. In addition, S1001-S1007 in a figure shows each step.

  When outputting a copy image, in step S1001, the user performs copy settings for the copy image output job on the operation unit 180. The copy setting contents are the number of copies, paper size, single side / double side, enlargement / reduction ratio, sort output, presence of stapling, and the like.

  In step S <b> 1002, when a copy start instruction is given on the operation unit 150, the main controller 111 of the control device 110 controls the reader unit 200 via the connector 122 and performs an operation of reading document image data. First, the document feeding unit 250 feeds the placed documents one by one onto the platen glass 211, and simultaneously detects the size of the document. Image data is read by exposing and scanning the document based on the detected size of the document. When scaling processing is performed, image data is read from the CCD at the same magnification (100%), and the scaling processing is performed by the linear interpolation unit 607 of the scanner image processing unit 415 according to the enlargement / reduction setting. The read image data is temporarily stored as image data and an image area flag in the memory 421 of the reader unit, and is subjected to compression processing by the multi-value image compression / decompression unit 414 and the CPU 402 and stored in the memory 421.

  In S1003, the data on the memory 421 is transferred to the memory 121 of the control device 110. Data to be transferred to the control device 110 includes compressed image data and a compressed image area flag. In step S <b> 1004, the compressed image data on the memory 121 is expanded into a raster image by the image expansion unit 505 and transferred to the printer image processing unit 151 via the bus control unit 510 together with the image area flag data expanded by the CPU 501.

  In step S1005, the raster image data input to the printer image processing unit 151 is subjected to image processing with reference to the image area flag data to create a halftone image. The halftone image is stored in the memory 152 via the image compression unit 711. At this time, the image compression unit 711 does not perform image compression.

  In step S1006, the image data stored in the memory 151 is printed out from the printer controller unit 715 in synchronization with a control signal from the printer 300. The CMYK control signals input from the printer 300 are shifted in accordance with the positions of the photosensitive drums 325, 326, 327, and 328, and the shift amount for each color component between the drums is absorbed by the memory 151.

  When the transfer of the image data is completed, that is, when the copy job is finished, the print output is finished.

  As described above, according to the present embodiment, the data amount after the compression process does not exceed the data amount when not compressed. Further, when all data is spooled in the memory, it is not necessary to secure the total data size before compression in the memory. For this reason, the memory capacity to be used can be reduced by ensuring only a predetermined data size in the memory.

It is a block diagram which shows the whole structure of this apparatus. 2 is an external view of a reader unit and a printer unit of the apparatus. FIG. It is a block diagram of the control-apparatus part of this apparatus. It is a block diagram of a reader image processing unit. It is a block diagram of a main controller. It is a block diagram of a portion related to image processing of a scanner I / F. 2 is a block diagram of a portion related to image processing of a printer I / F. FIG. It is a figure which shows the structural example of an operation part. It is a figure which shows the example of an operation part screen. It is a figure explaining the sequence at the time of a PDL image output. It is a figure explaining the compression process at the time of PDL image output. It is a figure explaining the sequence at the time of a COPY image output.

Claims (6)

An image forming apparatus that temporarily stores image data,
Image compression means for compressing uncompressed image data and converting it into compressed image data;
A storage control unit that compares the size of the target uncompressed image data with the size of the compressed image data converted from the target uncompressed image data by the image compression unit, and stores the smaller data in the memory; ,
When the compression ratio, which is the ratio of the size of the compressed image data to the size of the target uncompressed image data, does not reach the reference value, the image data generated by thinning out the pixels of the image data stored in the memory is generated. A reduction means,
The storage control means uses uncompressed image data that has not been reduced initially as uncompressed data of interest, and when the reduced image data generated by the image reduction means is stored in a memory, the reduced image Process the data as the uncompressed data of interest,
An image forming apparatus according to claim 1, wherein, when the image data stored in the memory is compressed, the image reducing means expands and compresses the compressed image data.   An image forming apparatus, further comprising: an image forming unit that decompresses the compressed image data stored in the memory and forms an image based on the image data.   3. The image forming apparatus according to claim 1, further comprising conversion means for converting print data received from a computer into uncompressed image data.   The image forming apparatus according to claim 1, wherein the image compression unit compresses uncompressed image data in units of a block having a certain size. An image forming apparatus control method comprising: an image compression unit; a memory; a storage control unit; and an image reduction unit;
An image compression step in which the image compression means compresses uncompressed image data and converts it into compressed image data;
The storage control means compares the size of the target uncompressed image data with the size of the compressed image data converted from the target uncompressed image data in the image compression step, and stores the smaller data in the memory. A storage control process to store;
When the compression ratio, which is the ratio of the size of the compressed image data to the size of the target uncompressed image data, does not reach a reference value, the image reduction means thins out the pixels of the image data stored in the memory and reduces the image data. An image reduction process for generating image data,
In the storage control step, uncompressed image data that has not been reduced initially is set as uncompressed data of interest, and when the reduced image data generated by the image reduction step is stored in a memory, the reduced image Process the data as the uncompressed data of interest,
In the image reduction process, if the image data stored in the memory is compressed, the compressed image data is expanded and then reduced. A program for causing a computer to function as an image forming apparatus that temporarily stores image data,
Image compression means for compressing uncompressed image data and converting it into compressed image data;
A storage control unit that compares the size of the target uncompressed image data with the size of the compressed image data converted from the target uncompressed image data by the image compression unit, and stores the smaller data in the memory; ,
When the compression ratio, which is the ratio of the size of the compressed image data to the size of the target uncompressed image data, does not reach the reference value, the image data generated by thinning out the pixels of the image data stored in the memory is generated. Let the computer function as a means of reduction,
The storage control means uses uncompressed image data that has not been reduced initially as uncompressed data of interest, and when the reduced image data generated by the image reduction means is stored in a memory, the reduced image Process the data as the uncompressed data of interest,
If the image data stored in the memory is compressed, the image reduction means expands and compresses the compressed image data.

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