JP2011223145A - Image processing apparatus and image processing program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image processing apparatus in which a conversion table is stored in a cache memory to be referred to and a decrease in an image processing speed is prevented.SOLUTION: An image processing apparatus includes a first storage section to store a plurality of conversion tables each of which having a different size, and a processing section to store all of or a part of reference color conversion table in a second storage section from which faster data reading than the first storage section is possible and to perform conversion processing referring to all of or a part of the reference conversion table from the second storage section. When the speed of the conversion processing becomes slower, the processing section selects a small size conversion table as the reference conversion table. Thereby, input data with larger gradation width is able to be stored in the second storage section. A decrease in the conversion processing speed is thereby able to be prevented.

Description

  The present invention relates to an image processing apparatus that converts image data with reference to a conversion table, and in particular, a first storage unit that stores a conversion table and data can be read at a higher speed than the first storage unit. And an image processing apparatus that converts the image data with reference to a conversion table read from the first storage unit to the second storage unit or a part thereof.

  An image processing apparatus such as a personal computer performs image processing on bitmap data to generate print data, and supplies this to a printer. For such image processing, color conversion processing for converting the color of the bitmap data in accordance with the color system of the printer, or binarization (or multi-leveling) of the color of the bitmap data in accordance with the printing resolution of the printer. Includes halftoning. In image processing, a conversion table in which output data is associated with discrete input data is referred to. For example, at the time of color conversion processing, a color conversion table in which CMYK (cyan, magenta, yellow, black) gradation values are associated with RGB (red, green, blue) gradation values of pixels of bitmap data. Used. In the halftone process, a dither table in which dot on / off (or dot size) is associated with CMYK gradation values of pixels of bitmap data is used.

  In recent years, the printing speed of printers such as page printers has been increased. Therefore, the image processing apparatus is required to supply print data in time for the printing speed of the printer. Otherwise, there will be inconveniences such as blank paper being output or printing being stopped. Therefore, various methods for speeding up image processing have been proposed in order to prevent a delay in supplying print data. For example, during image processing, a conversion table read from a RAM (Random Access Memory) such as a DRAM (Dynamic Random Access Memory) is stored in a cache memory and referenced. Generally, the cache memory is composed of SRAM (Static Random Access Memory) or the like, and can read data at a higher speed than the DRAM, so that the image processing is speeded up. Techniques relating to such a memory usage method are disclosed in Patent Documents 1 and 2.

JP 2001-67266 A JP 2002-149150 A

  On the other hand, in recent years, the quality of print images by printers has also improved, and the gradation values of print data have become finer than before. Therefore, in the conversion table, the number of discrete input data is increasing, and the size (data amount) of the conversion table is increasing. On the other hand, the capacity of the cache memory is limited due to manufacturing costs. Furthermore, when another program is executed by time sharing, the data required for the execution is stored in the cache memory, so the area for the conversion table is compressed. Then, it may be difficult to store the entire conversion table in the cache memory.

In such a case, only a part of the conversion table is stored in the cache memory. At this time, if the input data corresponding to the data to be converted is stored in the cache memory, a good image processing speed can be maintained by reading the output data corresponding to the input data. However, when referring to input data not stored in the cache memory, it is necessary to read an area including the input data from the RAM. As the frequency of reading from the RAM increases, the time required for referring to the table increases accordingly, and the image processing speed decreases. Then, there is a possibility that the print data cannot be supplied in time for the printing speed of the printer.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image processing apparatus or the like that can store a conversion table in a cache memory and refer to it, and prevent a decrease in image processing speed.

  In order to achieve the above object, according to a first aspect of the present invention, an image processing apparatus that performs conversion processing of image data using a conversion table in which output data of a predetermined amount of data is associated with input data is provided. A first storage unit storing a plurality of the conversion tables having different table sizes, and reading all or part of the reference color conversion table selected from the plurality of conversion tables at a higher speed than the first storage unit And a processing unit that stores the data in a second storage unit having a predetermined capacity and refers to all or a part of the reference conversion table from the second storage unit. When the speed of the conversion process is the first speed, the unit selects the first conversion table as the reference conversion table, and the speed of the conversion process is a second speed that is lower than the first speed. When To selects the first conversion table from the table a second of said conversion table size is small as a conversion table for the reference.

  According to the above aspect, when the conversion processing speed is relatively fast, the first conversion table having a large table size is selected to maintain a good quality of the color-converted image, while the conversion processing is performed. When the processing speed is relatively slow, the second conversion table having a small table size is selected. Therefore, even if the capacity of the second storage unit is limited, input data having a wider gradation width is stored in the second storage table. Can be stored in the department. Therefore, when the input data is not included in a part of the reference table, the frequency of referring to the reference table stored in the first storage unit can be reduced, and the conversion processing speed decreases. Can be prevented. Further, it is assumed that the capacity of the second storage unit is further restricted by the image processing apparatus executing a program other than the image data conversion process and storing data related to the execution of the program in the second storage unit. However, by selecting the second conversion table having a small table size as the reference conversion table, input data having a wider gradation width can be stored in the second storage unit.

  According to a preferred aspect of the above aspect, the processing unit switches the reference conversion table from the first conversion table to the second conversion table when the conversion processing speed falls below a threshold value. When the conversion speed becomes equal to or higher than the threshold value, the reference conversion table is switched from the second conversion table to the first conversion table. Therefore, by selecting the second conversion table having a small table size, the conversion processing speed can be avoided, but when the conversion processing speed does not decrease, the first conversion table having a large table size is used. By returning to, it is possible to avoid a decrease in conversion accuracy and an increase in processing load for compensating the conversion accuracy, and to improve the quality of the converted image.

It is a figure explaining the structure of the image processing apparatus in this embodiment. It is a figure explaining the various programs which CPU6 runs. It is the flowchart figure which showed the image processing procedure. It is a figure explaining the color conversion table LUT. It is a figure which shows typically the use condition of RAM12 and the cache memory 7 when a color conversion process is performed. FIG. 10 is a flowchart illustrating a procedure for referring to a reference color conversion table LUTr. It is a flowchart explaining the procedure which selects the conversion table for reference LUTr. It is a flowchart figure explaining the modification of the procedure shown in FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the technical scope of the present invention is not limited to these embodiments, but extends to the matters described in the claims and equivalents thereof.

  FIG. 1 is a diagram illustrating the configuration of an image processing apparatus according to this embodiment. FIG. 1 shows a configuration in which a host computer 2 constituted by a personal computer supplies print data to a printer 4. The host computer 2 corresponds to the “image processing apparatus”, and the printer 4 corresponds to the “image output apparatus”.

  In the host computer 2, a central processing unit (CPU) 6, a read only memory (ROM) 8, a hard disk drive 10, a RAM 12, a video circuit 14, and an interface 16 are connected via a data bus 17. The CPU 6 performs arithmetic processing according to a startup program stored in the ROM 8 and various programs stored in the hard disk of the hard disk drive 10. The various programs include an operating system OS, an application program APP for generating image data, a printer driver program PDR for generating print data by performing image processing on the image data, and a video for displaying and outputting images. A driver program VDR is included. In the present embodiment, the CPU 6 corresponds to a “processing unit” and the printer driver program PDR corresponds to an “image processing program”. Here, the printer driver PDR includes a print module of the operating system OS.

  The CPU 6 temporarily stores program modules and calculation data in the RAM 12 when executing various programs. The RAM 12 is constituted by a DRAM having a capacity of several megabytes to several gigabytes, for example. Further, the CPU 6 stores program modules and calculation data that are used particularly frequently in the cache memory 7. The cache memory 7 is configured by an SRAM having a capacity of several kilobytes to several megabytes, for example. The cache memory 7 is provided in the CPU 6 and connected to the processor of the CPU 6 through a bus in the CPU 6. Therefore, the data in the cache memory 7 can be read from the processor at a higher speed than when the data in the RAM 12 is read. Here, the RAM 12 corresponds to a “first storage unit”, and the cache memory 7 corresponds to a “second storage unit”.

  When executing various programs, the CPU 6 instructs the video circuit 14 to draw a display image in accordance with the video driver program VDR. The video circuit 14 executes the instructed drawing and outputs an image signal corresponding to the display image to the display device 18. The display device 18 is composed of, for example, an LCD (Liquid Crystal Display) or a CRT (Cathode Ray Tube), and displays an image corresponding to an image signal. Further, the CPU 6 receives an input signal from the operation input unit 20 via the interface 16. The operation input unit 20 is composed of, for example, a keyboard and a mouse, and sends an input signal corresponding to a user operation input to the interface 16.

The CPU 6 receives various programs and data from the external storage device 22 via the interface 16. The external storage device 22 is, for example, a CD-ROM (Compact Disk R
OM) drive units, MO (Magneto Optic) drive units, FD (Floppy (registered trademark) Disk) drive units, and the like, which read programs and data from each storage medium and supply them to the interface 16. For example, the external storage device 22 is configured by a USB (Universal Serial Bus) interface. The USB interface reads a program and data from a removable USB memory or the like and supplies it to the interface 16.

  In the above configuration, the CPU 6 temporarily stores image data generated by executing the application program APP or image data read from the hard disk of the hard disk drive 10 or the external storage device 22 in the RAM 12. The CPU 6 performs image processing on the image data in response to an instruction input from the user, and generates print data. Image processing is performed by executing the printer driver program PDR. The generated print data is stored in the RAM 12. The print data is output from the RAM 12 to the printer 4 via the interface 16.

  In the printer 4, the CPU 30 executes arithmetic processing for controlling a printing operation according to a control program stored in a ROM 32 or an EEPROM (Electronically Erasable and Programmable ROM) 34. The CPU 30 temporarily stores arithmetic processing data in the RAM 36. Further, the CPU 30 receives print data supplied from the host computer 2 via the interface circuit 40 and stores it in the RAM 36. The RAM 36 functions as, for example, a page buffer that stores print data for one to several pages.

  The CPU 30 outputs the print data stored in the RAM 36 to the print engine 38 via the interface circuit 40. The print engine 38 includes a mechanism for transporting recording paper in the sub-scanning direction, a print head that operates in a main scanning direction orthogonal to the sub-scanning direction, and a drive / control circuit thereof. The print head scans the transported recording paper or photoconductor, forms an output image with a recording material such as ink or toner, and executes printing. Such a printing operation is executed at a uniform speed of 1 to several seconds per page of A4 paper, for example, when a multi-page print job is executed.

  FIG. 2 is a diagram for explaining various programs executed by the CPU 6. The CPU 6 executes an application program APP, a video driver program VDR, and a printer driver program PDR. The application program APP is, for example, a drawing / document creation program. The CPU 6 generates image data GD in response to an operation input by the user according to the application program APP. The image data GD is, for example, RGB bitmap data. At this time, the CPU 6 instructs the video circuit 14 to display an image according to the video driver program VDR.

  The printer driver PDR is a program for performing image processing on the image data GD and generating print data PD. The CPU 6 performs image processing by executing each program module of the printer driver PDR. Here, the image processing procedure will be described with reference to FIG.

  FIG. 3 is a flowchart showing an image processing procedure. The procedure in FIG. 3 is executed, for example, when a print execution instruction is sent from the application program APP. The print execution instruction is input from the operation input unit 20 by the user.

First, the resolution conversion module P2 receives RGB bitmap data from the application program APP (S2). Then, the resolution conversion module P2 performs resolution conversion processing for increasing or decreasing the number of pixels of the RGB bitmap data in accordance with the printing resolution of the printer 4 (S4). Next, the color conversion module P4 performs color conversion processing for converting the color of the pixels of the RGB bitmap data in accordance with the color system of the printer 4 (S6). For example, the RGB gradation value of each pixel is converted into a CMYK gradation value. At this time, the color conversion table LUT is referred to. In the color conversion table, CMYK gradation values are associated with RGB gradation values. Alternatively, the color conversion module P2 can convert CMYK gradation values in the reference color space into CMYK gradation values in the color system of the printer 4. In this case, a color conversion table LUT in which CMYK gradation values in the reference color space are associated with RGB gradation values, and CMYK gradation values in the color system of the printer 4 are associated with CMYK gradation values in the reference color space. The obtained color conversion table LUT is referred to.

  Next, the halftone module P6 performs halftone processing for converting the CMYK bitmap data into dot recording state data in the printer (S8). The dot recording state data is data defining dot on / off and dot size for each pixel of the CMYK bitmap data. At this time, the dither table DT is referred to. In the dither table DT, there is a threshold value for determining dot on / off or size with respect to the CMYK gradation value for each pixel of the CMYK bitmap data (or the dot recording rate in a fixed area based on the CMYK gradation value). Is set.

  Next, the print data generation module P8 generates print data from the dot recording state data (S10). The print data includes raster data indicating a dot recording state during main scanning and a feed amount in the sub-scanning direction. Then, the print data generation module P8 outputs the generated print data PD to the buffer area of the RAM 12 (S12). The print data PD is transferred from the RAM 12 to the printer 4.

  FIG. 4 is a diagram illustrating the color conversion table LUT. In the present embodiment, the color conversion table LUT corresponds to a “conversion table”. FIG. 4A schematically shows a color conversion table LUT for converting RGB gradation values into CMYK gradation values. The color conversion table LUT has grid points GRD (indicated by black circles) provided for discrete input data in the R, G, B coordinate space. Here, R, G, and B are expressed by 8 bits (1 byte) for each color, and have 256 gradation widths of 0 to 255. The grid points GRD are provided at a fixed interval, for example, for each gradation, with respect to the 256 gradation width of the input data. In each grid point GRD, RGB gradation values (r, g, b) as input data are associated with CMYK gradation values (c, m, y, k) as output data. When executing the color conversion module P4, the CPU 6 refers to the grid point GRD corresponding to the RGB gradation value for each pixel of the RGB bitmap data and converts it to the corresponding CMYK gradation value.

Here, C, M, Y, and K are also expressed by 8 bits (1 byte) for each color, and have 256 gradation widths of 0 to 255. Then, in the color conversion table LUT, 256 grid points GRD for each color of R, G, and B are provided. In each grid point GRD, output data of 4 bytes in total for each color of C, M, Y, and K is associated. It is done. Therefore, the size (data amount) of the color conversion table LUT is 256 ³ × 4 bytes = 67,108 kilobytes.

  Next, the size of the color conversion table with different density of the grid points GRD will be described with reference to FIG. Here, a case where CMYK gradation values in the reference color space are converted into CMYK gradation values in the color system of the printer 4 is taken as an example. Each color of C, M, Y, and K of the input data is expressed by 8 bits (1 byte) and has a 256 gradation width from 0 to 255. On the other hand, the colors C, M, Y, and K of the output data are expressed by 8 bits (1 byte) and have 256 gradation widths. That is, here, a four-dimensional color conversion table that converts input data consisting of four color gradation values into output data consisting of four color gradation values is taken as an example.

  FIG. 4B shows the number of grid points and the table size for the four color conversion tables. That is, for each color of the input data, a color conversion table LUT1 having 32 lattice points GRD for every 8 gradations in a 256 gradation width, and a color conversion table LUT2 having 24 lattice points GRD for every 10 gradations; The sizes of the color conversion table LUT3 having 16 grid points GRD for every 16 gradations and the color conversion table LUT4 having 8 grid points GRD for every 32 gradations are shown.

The color conversion tables LUT1 to LUT4 have a data amount of 8 bits (1 byte) for each color of CMYK for each grid point GRD. Therefore, the size of the color conversion table LUT1 is 32 ⁴ × 4 bytes = 4096 KB (kilobytes). Similarly, the size of the color conversion table LUT2 is 24 ⁴ × 4 bytes = 1296 kilobytes. Similarly, the size of the conversion table LUT3 is 16 ⁴ × 4 bytes = 256 kilobytes. Similarly, the size of the color conversion table LUT4 is 8 ⁴ × 4 bytes = 16 kilobytes. Therefore, the density of grid points in the gradation width of the input data decreases in the order of the color conversion table LUT1, the color conversion table LUT2, the color conversion table LUT3, and the color conversion table LUT4 (that is, the number of discrete input data decreases). As a result, the size of the table also decreases. In this example, the input / output data has 256 gradation widths of 8 bits for each color as an example, but 128 gradation widths of 0 to 127, 64 gradation widths of 0 to 63, or 32 of 0 to 31. Various gradation widths are possible depending on the data amount (number of bits) of each color, such as gradation width. Alternatively, the interval between gradations where input data is provided in the color conversion table LUT, that is, the interval between grid points GRD may not be constant within a single color conversion table LUT. For example, the interval can be small (large) in the low gradation portion, and the interval can be large (small) in the high gradation portion.

  In the present embodiment, a plurality of color conversion tables LUT1 to LUT4 having different grid point densities and sizes are stored in the hard disk of the hard disk drive 10 as part of the printer driver program PDR. When the CPU 6 executes the printer driver program PDR, the color conversion tables LUT1 to LUT4 are stored in the RAM 12 together with the color conversion module P2. Further, when executing the color conversion module P2, the CPU 6 selects one of the color conversion tables LUT1 to LUT4 as a reference color conversion table. Then, the CPU 6 reads the selected reference color conversion table from the RAM 12 according to the operating system OS and stores it in the cache memory 7. Then, the CPU 6 refers to the reference color conversion table from the cache memory 7 and performs color conversion processing.

  FIG. 5 is a diagram schematically showing the usage state of the RAM 12 and the cache memory 7 when the color conversion process is performed. As shown in FIG. 5A, the RAM 12 stores color conversion tables LUT1 to LUT4 and bitmap data BMP_n for each page on which color conversion processing is performed (n is the number of pages 1, 2, 3,...). And the generated print data PD_n (number of n pages 1, 2, 3,...) Is stored.

  On the other hand, the cache memory 7 has a program area 7a, a color conversion table area 7b, and an input / output data area 7c. The CPU 6 secures the areas 7a, 7b, and 7c by executing the operating system OS. The CPU 6 stores, for example, a program module of the application program APP, a color conversion module P2 of the printer driver PDR, and the like in the program area 7a. Then, the reference color conversion table LUTr selected from the color conversion tables LUT1 to LUT4 is stored in the color conversion table area 7b. Further, the input data and output data of the reference color conversion table LUTr are stored in the input / output data area 7c.

Since the cache memory 7 has a program area 7a and an input / output data area 7c, the color conversion table area 7b is restricted accordingly. Here, FIG. 5B schematically shows the relationship between the color conversion tables LUT1 to LUT4 and the color conversion table area 7b. In FIG. 5B, the size of the color conversion tables LUT1 to LUT4 is represented by a rectangular area, and the size of the color conversion table region 7b is represented by the area of a region surrounded by a broken line. Here, for the size of the color conversion tables LUT1 to LUT4 shown in FIG. 4B, the color conversion table area 7b is, for example, 128 kilobytes. However, the relationship between the size of the color conversion tables LUT1 to LUT4 and the color conversion table area 7b is not limited to that shown here.

  First, when the color conversion table LUT1 is selected as the reference color conversion table LUTr, the size of the color conversion table LUT1 is larger than the color conversion table area 7b. Therefore, a part of the color conversion table LUT1, ie, the color conversion table area 7b. Only the overlapping part is stored in the color conversion table area 7b.

  Here, a procedure for referring to the reference color conversion table LUTr by the CPU 6 is shown in FIG. The CPU refers to the reference color conversion table LUTr stored in the cache memory 7 (S22). If grid points GRD (discrete input data) corresponding to the RGB gradation values to be converted are stored (YES in S24), that is, here, for the color conversion table of the color conversion table LUT1. If the grid point GRD to be referred to is included in the portion overlapping with the region 7b, the CPU 6 refers to the grid point GRD and outputs the corresponding CMYK gradation value (S26). By doing so, color conversion processing can be performed. However, if the grid point GRD corresponding to the RGB gradation value to be converted is not included (NO in S24), the CPU 6 refers to the color conversion table LUT1 stored in the RAM 12 (S28) and tries to convert it. The grid point GRD corresponding to the RGB gradation value to be read is read, and the corresponding CMYK gradation value is output (S30). Note that these procedures are usually executed as procedures incorporated in the operating system or hardware, so that the programmer need not be aware of them.

  As described above, when the grid point GRD to be referred to is not included in the color conversion table area 7b, it is necessary to read data from the RAM 12. However, since reading data from the RAM 12 takes longer than reading data from the cache memory 7, the image processing time increases accordingly. Therefore, there is a possibility that the supply of print data is delayed. Therefore, in this embodiment, when the supply of print data is likely to be delayed, a color conversion table LUT having a low grid point density and a small size is selected as a reference color conversion table LUTr, and all or a part thereof is stored in the cache memory 7. Store.

  For example, returning to FIG. 5B, when the color conversion table LUT2 is selected as the reference color conversion table LUTr, the proportion of the portion stored in the color conversion table area 7b is larger than the color conversion table LUT1. Therefore, grid points corresponding to input data having a wider gradation width are stored in the color conversion table area 7b. Further, in the color conversion table LUT3, the proportion of the portion stored in the color conversion table area 7b is larger than the color conversion table LUT2. Therefore, grid points corresponding to input data having a wider gradation width are stored in the color conversion table area 7b. The entire color conversion table LUT4 is stored in the color conversion table area 7b. Therefore, grid points corresponding to all input data are stored in the color conversion table area 7b. Therefore, it is not necessary to refer to the RAM 12. As described above, the density of the grid points GRD decreases in the order of the color conversion tables LUT1, LUT2, LUT3, and LUT4. Therefore, the range of the corresponding input data increases, so that the necessity of referring to the RAM 12 is reduced. Therefore, an increase in image processing time can be avoided, and as a result, a delay in supplying print data can be prevented.

  FIG. 7 is a flowchart for explaining the procedure for selecting the reference conversion table LUTr. This corresponds to the subroutine of the color conversion process (step S6) shown in FIG.

  The CPU 6 selects the color conversion table LUT1 as the reference color conversion table LUTr, stores it in the cache memory 7, and starts the color conversion process (S102). Then, for example, at an arbitrary timer interrupt timing, it is checked whether the conversion processing speed, that is, the print data generation speed, is in time for the printer 4 (S104). Here, when the amount of the print data PD_n stored in the buffer area of the RAM 12 is equal to or greater than the threshold, it is determined that the print speed is in time, and when the amount is less than the threshold, it is determined that the print speed is not in time. As a threshold for such determination, an arbitrary value that increases the probability that the supply of the print data PD_n is delayed with respect to the printing speed of the printer 4 can be set in advance by an experiment or the like. Alternatively, the CPU 6 may measure the time required for color conversion processing for one page, or the time required for generating CMYK bitmap data or print data, and compare it with a predetermined threshold value. Further, the remaining amount of the print data PD_n in the RAM 36 may be acquired from the CPU 30 of the printer 4 and compared with a predetermined threshold value to determine whether it is in time.

  Here, the conversion processing speed does not necessarily depend on the data amount of RGB bitmap data. For example, even in the case of RGB bitmap data having a relatively large amount of data, if the gradation values of the pixels are uniform to some extent and the grid points GRD corresponding to the gradation values are stored in the cache memory 7, The conversion processing speed is kept at a certain level. On the other hand, even in the case of RGB bitmap data with a relatively small amount of data, if the gradation values of the pixels vary, the corresponding grid point GRD may not be stored in the cache memory 7. Then, since it is necessary to read from RAM12, the conversion processing speed falls.

  If the conversion processing speed is in time for the printing speed of the printer 4 (YES in S104), the color conversion processing is continued as it is. On the other hand, if not in time (NO in S104), the reference color conversion table LUTr is switched to a color conversion table that is one step smaller (S106). That is, the color conversion table LUT2 having a low density of grid points GRD and a small size is selected as the reference color conversion table LUTr and stored in the cache memory 7. Then, the CPU 6 continues the color conversion process.

  The CPU 6 further confirms whether the print data PD_n is full in the buffer area of the RAM 12 at an arbitrary timer interrupt timing (S108). If it is not full (NO in S108), the process is continued as it is. On the other hand, if it is full (YES in S108), since the supply of print data is in time for the printing speed of the printer 4, the reference color conversion table LUTr is switched to a color conversion table that is one step larger (S110). That is, the color conversion table LUT1 having a grid point density and size larger by one step is stored in the cache memory 7 as the reference color conversion table LUTr. Then, the CPU 6 continues the color conversion process, and repeats the procedure from step S104 to step S110 until the processing of the print data PD_n of the last page is completed (NO in S112).

  When the procedure from step S104 to step S110 is repeated in the next processing cycle, if the color conversion processing speed is not in time (NO in S104), a smaller color conversion table LUT3 is selected as the reference color conversion table LUTr to select the cache memory 7 (S106) and the color conversion process is continued. If the color conversion processing speed is not in time in the next processing cycle (NO in S104), the color conversion table LUT4 that is one step smaller is selected as the reference color conversion table LUTr and stored in the cache memory 7 (S106). ) Continue the color conversion process. Then, when the processing of the print data PD_n for the last page is completed (YES in S112), this processing procedure is ended.

According to the above procedure, when the print data generation speed is not in time for the printer 4, the reference color conversion table LUTr stored in the cache memory 7 is switched to the color conversion table LUT having a smaller size. Therefore, color conversion can be performed on a wider range of input data without referring to the RAM 12, and delay in supplying print data can be prevented. Here, when the reference color conversion table LUTr is switched to a color conversion table LUT having a small size, the density of the grid points GRD is reduced, so that the conversion accuracy is lowered and the printed image becomes rough. However, by switching the reference table LUTr step by step, a decrease in conversion accuracy can be minimized, and a print image can be prevented from becoming drastically rough. In particular, when multiple pages are printed in one print job, for example, even when a photographic image that requires more processing time is sandwiched between consecutive text images, the print quality changes suddenly. Can be prevented.

  Alternatively, in the color conversion module P2, it is possible to compensate the print image for interpolation calculation of input values and output values. In this case, the processing load and the processing time for performing the interpolation calculation are generated. However, it is possible to avoid a sudden increase in the processing load and the processing time for the interpolation calculation by switching the reference table LUTr in stages.

  Alternatively, it is possible to provide a buffer memory on the output side (for example, the RAM 12 of the host computer or the RAM 36 of the printer 4), and store image-processed data of a plurality of pages. By doing so, even if there are pages that require more processing time than others in one print job, and the processing content of each page changes, image processing continues without switching the reference color conversion table LUTr it can. Therefore, it is possible to prevent the print quality from changing. In this case, the reference color conversion table LUTr is switched according to the number of pages of image-processed data stored in the buffer memory, specifically, when the threshold value of the preset number of pages falls below. Also good.

  On the other hand, when the supply of print data is in time for the printing speed of the printer, the reference color conversion table LUTr is switched to a color conversion table LUT having a large size. Therefore, such switching does not leave the conversion accuracy unilaterally lowered. Or even if it is a case where the fall of conversion accuracy is compensated by interpolation processing, the load and time for interpolation processing can be reduced. As a result, the optimum conversion accuracy can be maintained according to the print data supply speed.

  FIG. 8 is a flowchart for explaining a modification of the procedure shown in FIG. The procedure shown in FIG. 8 is preferably inserted between steps S106 and S108 in FIG. This procedure is a procedure for accelerating the color conversion process by releasing the program area 7a of the cache memory 7. That is, when the reference color conversion table LUTr is reduced by one step in step S106 of FIG. 7, the CPU 6 confirms again whether the color conversion processing speed is in time (S1071). The confirmation method is the same as in step S104. If it is in time (YES in S1071), the process proceeds to step S108 in FIG. On the other hand, if not in time (NO in S1071), it is checked whether a program that can be interrupted is operating in addition to the printer driver program PDR (S1072). If no interruptable program is operating (NO in S1072), the process proceeds to step S108 in FIG. On the other hand, if a program that can be interrupted is operating (YES in S1072), the program is interrupted (S1073). Such an operation is executed as a function of the print module of the operating system OS.

As a result, the program module and calculation data of the interrupted program are deleted from the program area 7a, and the area for holding calculation data for color conversion processing in the program area 7a can be expanded. Therefore, the frequency of reading / writing data from / to the RAM 12 can be reduced, and the speed of the color conversion process can be accelerated. As described above, by executing the procedure of FIG. 8 in addition to the procedure shown in FIG. 7, the speed of the color conversion process can be further accelerated, and the print data can be supplied in time for the printing speed of the printer 4.

  Among the above procedures, it is determined whether the conversion processing speed is in time in step S104 of FIG. 2 and step S1071 of FIG. Here, the threshold value used for the determination can be set by the user. For example, if the user wants to emphasize image quality even if the print data supply speed decreases, the threshold can be lowered. As a result, even if the conversion processing speed decreases to some extent, the reference color conversion table LUTr can be prevented from being switched to a color conversion table LUT having a smaller size. Further, according to the printer driver PDR that defines the above procedure, the reference color conversion table LUTr is switched depending on the amount of print data PD_n accumulated in the RAM 12, so that the environment is different without depending on the processing performance of the CPU 6. However, the print data PD_n can be supplied in time for the printing speed of the printer 4.

  In the above description, the color conversion table LUT has been described as an example of the conversion table. However, the dither table DT may be a conversion table. That is, the present embodiment can also be applied to halftone processing performed using the dither table DT. The dither table DT includes a threshold value for determining dot on / off with respect to the gradation value (or dot recording rate) of each pixel of the CMYK bitmap data. Here, assuming that the gradation width of the input data is 256 gradations for each color, the dither table DT has a threshold value that is set for each of the predetermined gradations with respect to the 256 gradation width. Then, output data (that is, binary values of on / off or dot sizes such as large / medium / small) is associated with the gradation value of the input data at each grid point. Here, the present embodiment can be applied by providing a plurality of dither tables DT having different numbers of threshold values and different sizes depending on the number of threshold values.

  In the above description, the configuration in which the cache memory 7 is provided in the CPU 6 has been described. However, the cache memory 7 may be provided outside the CPU 6 as long as the data read speed from the CPU 6 to the RAM 12 is higher than that of the RMA 12. Further, in the above description, the host computer 2 is provided outside the printer 4 and the configuration in which the host computer 2 corresponds to the image processing apparatus has been described. However, even if the image processing apparatus is provided inside the printer 4. Good.

  As described above, according to the present embodiment, it is possible to prevent a decrease in image processing speed in an image processing apparatus that stores and refers to a conversion table in a cache memory.

2: host computer, 4: printer, 6: CPU, 7: cache memory, 12: RAM, PDR: printer driver program, P2: color conversion module, LUT: color conversion table

Claims (8)

An image processing apparatus that performs conversion processing of image data using a conversion table in which output data of a predetermined amount of data is associated with input data,
A first storage unit that stores a plurality of the conversion tables having different table sizes;
All or part of the reference color conversion table selected from the plurality of conversion tables is stored in a second storage unit having a predetermined capacity capable of reading data at a higher speed than the first storage unit. A processing unit that performs the conversion process with reference to all or part of the reference conversion table from a storage unit;
When the conversion processing speed is the first speed, the processing unit selects the first conversion table as the reference conversion table, and the conversion processing speed is lower than the first speed. When the speed is selected, the second conversion table having a smaller table size than the first conversion table is selected as the reference conversion table. In claim 1,
The processing unit refers to the reference table stored in the first storage unit when the input data is not included in a part of the reference table stored in the second storage unit. An image processing apparatus. In claim 1 or 2,
The processing unit switches the reference conversion table from the first conversion table to the second conversion table when the conversion processing speed falls below a threshold, and the conversion speed exceeds the threshold. When this happens, the reference conversion table is switched from the second conversion table to the first conversion table. In any one of Claims 1 thru | or 3,
Execute a program other than the image data conversion process,
The image processing apparatus, wherein the second storage unit further stores data related to execution of the program. In claim 4,
The image processing apparatus, wherein the processing unit deletes data related to execution of the program from the second storage unit when the conversion processing speed is slower than the second speed. In any one of Claims 1 thru | or 5,
The processing unit supplies the converted image data to an image output device that outputs an image based on the image data at a uniform speed, and the conversion-processed image for the image output speed by the image output device An image processing apparatus, wherein the conversion processing speed is obtained based on a data supply amount. In any one of Claims 1 thru | or 6.
The first conversion table has grid points in which the predetermined amount of output data is associated with input data at a first density, and the second conversion table has the grid points at the first density. An image processing apparatus having a lower second density. An image processing program for causing an image processing apparatus to perform image data conversion processing using a conversion table in which input data is associated with output data of a predetermined amount of data,
In the processing unit of the image processing apparatus,
A selection procedure for selecting a reference color conversion table from a plurality of the conversion tables having different table sizes stored in the first storage unit;
All or part of the reference color conversion table is stored in a second storage unit capable of reading data faster than the first storage unit, and all or part of the reference conversion table is stored in the second storage unit. The conversion process is performed with reference to a part, and when the input data is not included in a part of the reference table stored in the second storage unit, it is stored in the first storage unit A process procedure for performing the conversion process with reference to the reference table;
When the speed of the conversion process falls below a threshold value, the selection procedure changes the reference conversion table from the first conversion table to the second conversion table having a smaller table size than the first conversion table. An image processing program that switches the reference conversion table from the second conversion table to the first conversion table when the conversion speed becomes equal to or higher than the threshold.

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