JP6896413B2 - Image processing equipment, image processing methods, and programs - Google Patents

Description

The present invention relates to an image processing technique in a printer or the like.

There is a demand for a technique for efficiently holding information on bitmap format image data obtained by rendering processing on PDL data using data having a smaller amount of data than the image data. As such a technique, for example, in Patent Document 1, when the gradation property is emphasized, the intermediate language data is expanded on the memory as multi-valued data, while when the resolution is emphasized, the intermediate language data is used as binary data. Disclose the method of expanding on memory.

Japanese Unexamined Patent Publication No. 10-24482

However, Patent Document 1 does not disclose that the color information of the image data is retained when the resolution is emphasized. For example, in a business document, as shown in FIG. 1, an expression that emphasizes a character by arranging a light neutral-colored rectangle on the background of the character is generally used. When the method of Patent Document 1 is applied to such an image, the emphasized expression is lost as a result of causing the background rectangle to be missing in the area to be emphasized (the area where the character string "problem" exists in FIG. 1). A document that does not reflect the user's intention is printed.

Therefore, in view of the above problems, the present invention has a bit pattern for a first image area that reproduces image data at high resolution and a bit pattern for a second image area that reproduces image data at low resolution without losing color information. The purpose is to convert to data consisting of bit patterns including and.

The present invention is an image processing device that converts image data in a bit map format into data composed of a bit pattern including a first bit pattern and a second bit pattern, and reproduces the image data at the first resolution. Based on the pixel values of the pixels in the image area of, shape information indicating whether each pixel in the first image area is a foreground pixel or a background pixel is acquired, and based on the acquired shape information, The color of the foreground pixel is combined with the color of the foreground pixel by a color reduction process that reduces the number of gradations of the color of the foreground pixel and the color of the background pixel so that the number of gradations of the foreground pixel is smaller than the number of gradations of the background pixel. With respect to each pixel in the first image region based on the processing means for deriving the color information indicating the color of the background pixel, the shape information acquired by the processing means, and the derived color information. A bit indicating whether each pixel in the first image area corresponds to a foreground pixel or a background pixel, a bit indicating the color of the foreground pixel, and a bit indicating the color of the background pixel are included. With a first creating means for creating the first bit pattern in which the number of bits indicating the color of the background pixel is larger than the number of bits indicating the color of the foreground pixel, and a second resolution lower than the first resolution. The color information of the second image area represented by a number of bits larger than the color information of the first image area based on the pixel values of the pixels in the second image area having the same size as the first image area to be reproduced. Is stored, and the image processing apparatus is characterized by having a second creating means for creating the second bit pattern having the same bit length as the first bit pattern created by the first creating means. is there.

According to the present invention, the image data is composed of a bit pattern including a bit pattern for a first image area reproduced at a high resolution and a bit pattern for a second image area reproduced at a low resolution without losing color information. It becomes possible to convert it into data.

The figure explaining the subject of this invention Block diagram of the system including the image forming apparatus in the first embodiment Flowchart of processing executed by the printer in the first embodiment Flowchart of conversion processing in Example 1 and Example 2 The figure explaining the edge detection process in Example 1. The figure explaining the bit pattern of the edge region in Example 1. The figure explaining the bit pattern of the solid area in Example 1. The figure explaining how the image information is arranged in the memory after the conversion process for image data is completed. Flowchart of image processing in Example 1 Flowchart of recorded data creation process in Example 1 The figure explaining the mechanism concerning the image formation of the printer in Example 1. Bit pattern of edge region in Example 2 Bit pattern of solid region in Example 2 The figure which shows the VTF characteristic The figure explaining the color reduction processing performed using the dither method in Example 3. The figure explaining the binarization process The figure explaining the derivation method of color information

Hereinafter, preferred embodiments of the invention will be exemplified with reference to the drawings. However, the contents, relative arrangements, etc. of the components described below are not intended to limit the scope of the invention to those alone unless otherwise specified.

[Example 1]
FIG. 2 is a block diagram of a system including the image forming apparatus 200 in this embodiment. In this system, the image forming apparatus 200 and the host 210 are connected.

<About the image forming device>
Hereinafter, the configuration of the image forming apparatus 200 shown in FIG. 2 will be described. The CPU 201 uses the RAM 203 as a work memory to execute a program stored in the ROM 202, and comprehensively controls each component of the image forming apparatus 200 via the bus 207. As a result, various processes described later are executed. The ROM 202 stores programs and tables for performing printing processing, an embedded operating system (OS) program, and the like. In this embodiment, the program stored in the ROM 202 performs software control such as scheduling and task switching under the control of the embedded OS stored in the ROM 202. Further, a program for executing the flow in this embodiment as shown in FIG. 3 and the like is also stored in the ROM 202. The RAM 203 is composed of an SRAM (static RAM) or the like, and a work area is provided when the program is executed.

The head 204 ejects a coloring material to form an image on the recording medium in synchronization with the transfer of the recording medium (paper or the like). The interface (hereinafter, IF) 205 connects the image forming apparatus 200 and the external device (host 210 in this embodiment) of the image forming apparatus 200 by wire or wirelessly. Although not shown, the image forming apparatus 200 includes a mechanism such as a motor for driving the head 204 and a motor for conveying a recording medium. Further, the image forming apparatus 200 may include a DSP (Digital Signal Processor) 206 as a hardware apparatus for performing high-load processing such as image processing.

These components are electrically connected to each other via bus 207. Further, all or a part of these components may be mounted as a single LSI and made into parts as an ASIC.

In the following, a case where the image forming apparatus 200 is an inkjet printer including one CPU, ROM, and RAM will be described. However, the image forming apparatus 200 may be provided with a plurality of CPUs, ROMs, and RAMs, or may be a printer of any type such as an electrophotographic method. Further, the image forming apparatus in this embodiment is not limited to a dedicated machine specialized in a printing function, but is also a multifunction device that combines a printing function and other functions, or a manufacturing apparatus that forms an image or a pattern on a recording medium. Etc. are also included.

<About the host>
The image forming apparatus 200 is connected to the host 210 via the I / F 205. A host is a computer having processing power, and is assumed to be a general PC, a mobile phone, a smartphone, a tablet, a digital camera, and other mobile and stationary terminals. The breakdown of the devices provided by the host varies depending on the main purpose of each device, but the host generally includes a CPU, ROM, RAM, IF, input device, and output device.

Hereinafter, the configuration of the host 210 shown in FIG. 2 will be described. The CPU 211 uses the RAM 213 as a work memory to execute a program stored in the ROM 212, and comprehensively controls each component of the host 210 via the bus 217. The IF 214 connects the host 210 and the image forming apparatus 200 by wire or wirelessly. These components are electrically connected to each other via bus 217. Further, the host 210 includes an input device 215 for the user to input an instruction to the host and an output device 216 for outputting (presenting) information to the user, which are connected via the IF 214.

<About data transmission processing from the host to the image forming device>
Hereinafter, the data transmission process from the host to the image forming apparatus will be described by taking as an example a case where a document is printed from a smartphone using an inkjet printer.

When a user viewing a document on a smartphone wants to print the document being viewed, he / she operates the smartphone to input a print instruction. When a print instruction is input, the OS on the smartphone converts the document into image data in some format and then creates a print job according to the print protocol (for example, the document to be printed is converted into PDF data. Create an XML format print job that contains PDF data). The smartphone sends the created print job to the inkjet printer.

<About the processing executed by the inkjet printer>
Hereinafter, the processing executed by the inkjet printer will be described with reference to FIG.

In step S300, the CPU 201 analyzes the print job transmitted from the host such as the above-mentioned smartphone and acquires the print data. Specifically, the CPU 201 analyzes a print job using an XML parser, acquires setting information including information such as paper to be used and print quality, and data (PDL data) described in PDL, and obtains the data (PDL data). The acquired setting information and PDL data are stored in the RAM 203.

In step S310, the CPU 201 interprets the PDL data derived in step S300 to create an intermediate file called a display list. Then, the rendering process for the display list is executed, and each pixel creates a 2400 dpi × 2400 dpi bitmap image having a value of 16 bits for each channel of R (red), G (green), and B (blue). This bitmap image is abbreviated as "2400 dpi x 2400 dpi, 16 bit, 3ch bitmap image", and other bitmap images are also abbreviated in the same manner. The bitmap image created in this step is not limited to the 16-bit bitmap image, and a bitmap image (for example, a low-bit bitmap image such as 8-bit or 3ch) is created according to the processing capacity of the printer. You can do it. Further, the display list and the bitmap image may be created for the entire page at once, and in order to reduce the usage of the RAM 203, the display list and the bitmap image may be created in band units in response to the request from the subsequent step S330. You may do it. Further, this step may be executed by DSP 206 instead of CPU 201.

In step S320, the CPU 201 executes a conversion process for the bitmap image derived in step S310. In the conversion process, an area of 4 × 4 pixels in an image of 2400 dpi × 2400 dpi is treated as one tile, and it is determined whether the tile is an edge area or a solid area for each tile. Then, each tile is represented by a 32-bit bit pattern (FIG. 6A) according to the determination result. Specifically, the tile determined to be the edge region is represented by the 32-bit bit pattern shown in FIG. 6 (b), while the tile determined to be the solid region is represented by the 32-bit bit shown in FIG. 7 (a). It is represented by a pattern. As described above, in this embodiment, the information for all pixels in each image area is expressed by a 32-bit bit pattern in both the edge area and the solid area. The data amount (32 bits) of this bit pattern is smaller than the data amount (768 bits) of all the pixels constituting the edge region or the solid region. Here, the most significant bit b31 of the bit pattern stores an identification flag indicating whether it is an edge area or a solid area, and stores 0 in the case of the edge area and 1 in the case of the solid area. On the other hand, data corresponding to the information of each tile is stored in the lower bits other than the most significant bit. The conversion process in this step will be described later with reference to FIG.

In step S330, the CPU 201 executes image processing based on the data derived in the conversion process of step S320. By this step, image data in which each pixel has an ink color value is derived and developed on the RAM 203. This image data is, for example, 1 bit, 4 ch image data in which each pixel has a value of 1 bit for each channel of C (cyan), M (magenta), Y (yellow), and K (black). The image processing in this step will be described later with reference to FIG.

In step S340, the CPU 201 creates recorded data based on the image data derived in step S330. This recorded data is, for example, binary image data in which each pixel has a value of 0 or 1 for each channel of ink color (CMYK or the like). The recorded data created in this step is developed on the RAM 203 so as to form an image on the paper in the correct direction when transmitted to the head 204. The recorded data creation process in this step will be described later with reference to FIG.

In step S350, the CPU 201 transmits the recording data derived in step S340 to the head 204, drives the head 204 and the feeder based on the transmitted recording data, and performs an image forming process for actually forming an image on paper. Execute. The image forming process in this step will be described later with reference to FIG.

<About conversion processing>
Hereinafter, the conversion process (step S320 in FIG. 3) in this embodiment will be described with reference to FIG.

In step S400, the CPU 201 executes an edge detection process that applies an edge filter to the bitmap image derived in step S310. In this embodiment, the convolution operation using the 3 × 3 filter shown in FIG. 5A is executed. For example, when the filter shown in FIG. 5A is convoluted in the image shown in FIG. 5B, the edge image shown in FIG. 5C is derived.

In step S410, the CPU 201 initializes n, that is, sets the value of n to 1. Here, n is a parameter representing a tile of interest, which is a region to be processed, that is, a region of a predetermined size in the image data (a region of 4 × 4 pixels in an image of 2400 dpi × 2400 dpi in this embodiment). Since the subsequent processes of steps S420 to S460 are sequentially executed for each tile, initialization is performed in this step.

In step S420, the CPU 201 derives the edge amount of the region (attention region) corresponding to the tile of interest in the edge image derived in step S400. Here, the edge amount is a parameter used as an index when determining whether the tile of interest is an edge region (that is, an region to be reproduced with high resolution), and is the total of the pixel values of each pixel in the region of interest. In this embodiment, when the edge amount of an arbitrary region of interest is larger than the predetermined threshold Th1, the tile of interest corresponding to the region of interest is determined to be the edge region.

In step S430, the CPU 201 determines whether the edge amount of the region of interest is larger than the threshold Th1. If the result of the determination in step S430 is true, the tile of interest is determined to be an edge region, and the process proceeds to step S431. On the other hand, if the result of the determination in step S430 is false, the tile of interest is determined to be a solid area, and the process proceeds to step S435. The algorithm from edge detection to edge region determination is not limited to the above-mentioned method, and other methods may be used, or a known technique may be used in combination. For example, it may be determined whether the object is text based on the display list derived in step S310, and whether the object is an edge region or a solid region may be determined using the result of the determination.

Hereinafter, the case where the tile of interest is determined to be the edge region (YES in step S430) will be described. In this case, in step S431, the CPU 201 executes the quantization process for the tile of interest in the full-color image derived in step S310, and derives a bitmap pattern represented by only two colors, the foreground color and the background color. In deriving the bitmap pattern in this step, any method such as adaptive binarization may be used. Here, an example of adaptive binarization processing will be described with reference to FIG. First, the pixel values of the pixels constituting the two-dimensional image on the two-dimensional XY plane as shown by the reference numeral 1601 in the same figure are plotted in the RGB space as shown by the reference numeral 1602. On the other hand, using a clustering method (for example, k-means method), the color is divided into two groups as shown by reference numeral 1603, one of the divided two groups is the background color (bright color), and the other is the foreground color. Decide (dark color). When the result shown by reference numeral 1603 is fed back to the two-dimensional XY plane, a two-dimensional image composed of two types of pixels, a foreground pixel and a background pixel, is obtained as shown by reference numeral 1604. The pixel values of the foreground pixels and the background pixels are the average values of the colors of each group as shown by reference numeral 1605. By this step, shape information (16-bit data) indicating which pixel corresponds to the foreground pixel and which pixel corresponds to the background pixel among the 4 × 4 pixels constituting the tile of interest is acquired. Specifically, the shape information that takes a value of 1 when the pixel of interest corresponds to the foreground pixel and takes a value of 0 when the pixel of interest corresponds to the background pixel is a 32-bit bit pattern shown in FIG. 6 (b). It is stored in the last 16-bit area "map_4x4". As described above, in this step, the CPU 201 functions as a shape information deriving means.

In step S432, the CPU 201 executes a color reduction process for reducing the number of gradations for each of the two colors (16 bits and 3 channels, respectively) used in the bitmap pattern derived in step S431. Specifically, the foreground color is represented by 1 bit, 3 ch 3 bit data in which each RGB channel has a 1 bit value, while the background color is represented by 4 bit, 3 ch in which each RGB channel has a 4 bit value. It is expressed by 12-bit data. That is, as the foreground color, any one of eight pure colors of white, black, red, blue, green, cyan, magenta, and yellow can be specified. The RGB value of the foreground color after the color reduction processing is stored in the area "fg_rgb" for 3 bits of the bit pattern shown in FIG. 6B, and the RGB value of the background color after the color reduction processing is the area "bg_rgb" for 12 bits. Stored in. As described above, in this step, the CPU 201 functions as a color information derivation means. Here, the method for deriving the color information will be specifically described with reference to FIG. In this embodiment, each of the background color average value and the foreground color average value as shown by reference numeral 1701 described with reference to FIG. 16 is quantized using a dither table as shown by reference numeral 1702. .. The dither table has a threshold value for each tile in units of 4 × 4 pixels (= 1 tile). This quantization process may be performed using an already known algorithm. For example, when the background color average value is (0,10,230) and the foreground color average value is (0,0,5), the background color quantization is performed using the dither table shown by reference numeral 1702. The value is (0,1,13) and the foreground color quantization value is (0,0,0). After the quantization process, the quantization values obtained for each of the background color and the foreground color are stored in the corresponding parts of the bit pattern. Each bit pattern may be used as a palette color having a dictionary for each page. When the above-mentioned bit pattern is used as the palette color, any one of eight colors can be specified as the foreground color, and any one of 2 ^ 12 = 4096 colors can be specified as the background color. By switching the palette to be used according to the content of each page, it is possible to express colors according to the content of each page.

Next, a case where the tile of interest is determined to be a solid region (NO in step S430) will be described. In this case, in step S435, the CPU 201 derives the total value by summing the pixel values of each pixel in the tile of interest in the full-color image derived in step S310. As described above, in the present embodiment, the attention tile refers to the area of 4 × 4 pixels in the image of 2400 dpi × 2400 dpi, and each pixel constituting the attention tile has information of 16 bits and 3 channels. Therefore, in this step, as a result of totaling the pixel values of 16 pixels of pixels having a value in the range of 0 to 65535 per channel in the original image, the tile of interest has a value in the range of 0 to 1048560 per channel. Therefore, such a value can be expressed in 20 bits.

In step S436, the CPU 201 executes color reduction processing for reducing the number of gradations for each of the RGB values (20 bits each) derived in step S435, and derives 10 bit RGB values for each. The R value derived in this step is stored in the 10-bit area “r10” of the bit pattern shown in FIG. 7A, similarly, the G value is stored in the 10-bit area “g10”, and the B value is It is stored in the area "b10" for 10 bits. The 10-bit, 3ch information derived in steps S435 to S436 is treated as 1-pixel information in a 600 dpi × 600 dpi image in a subsequent step.

As described above, the data size (bit length) of the bit pattern (FIG. 6 (b)) representing the edge region and the bit pattern (FIG. 7 (a)) representing the solid region are both 32 bits. By setting the data formats of different image areas to the same data size in this way, it is possible to enable easy random access in the assigned format unit and improve the efficiency of data processing.

Returning to the explanation of the flow of FIG. In step S440, the CPU 201 arranges the bit pattern on the memory. FIG. 8 is a diagram for explaining how the image information is arranged in the memory after the conversion process for the image data is completed. Reference numeral 801 in FIG. 8 indicates image data composed of two types of image regions, an edge region and a solid region, and reference numeral 802 indicates how the image information is arranged in the memory after the conversion process is completed. .. In FIG. 8, the bit pattern of the edge region shown in FIG. 6 (b) is represented by the abbreviation format shown in FIG. 6 (c), and the bit pattern of the solid region shown in FIG. 7 (a) is shown in FIG. 7 (b). It is expressed in the abbreviation format shown in.

In step S450, the CPU 201 increments n.

In step S460, the CPU 201 determines whether n is greater than the total number of tiles. If the result of the determination in step S460 is true, the series of processes ends, while if the result of the determination is false, the process returns to step S420. The above is the content of the conversion process in this embodiment.

In the conversion process of this embodiment, in exchange for expressing the foreground color and the background color with low bits (low gradation) for the edge region, the shape is expressed with high resolution (1 pixel in an image of 2400 dpi × 2400 dpi). Express (in units). On the other hand, in the solid region, in exchange for expressing the shape with low resolution (in units of one pixel in an image of 600 dpi × 600 dpi), the color is expressed with high bits (with high gradation).

Here, the color reproduction ability in an image is determined based on the number of colors that can be used simultaneously in the image (three colors of R, G, and B in this embodiment) and the number of gradations that can be expressed by each color. On the other hand, the shape reproduction ability in an image depends on how finely the signal value of each pixel can be expressed (that is, at what high resolution). That is, in this embodiment, the shape reproduction ability is prioritized over the color reproduction ability in the edge region, the color reproduction ability is prioritized over the shape reproduction ability in the solid region, and the edge region and the solid region have the same data size. It is expressed by a bit pattern.

<About image processing>
Hereinafter, the image processing (step S330 in FIG. 3) in this embodiment will be described with reference to FIG. This image processing is executed for all the bit patterns in the memory arranged as shown in FIG.

In step S900, the CPU 201 initializes the value of m, that is, sets the value of m to 1. Here, m is a parameter representing a bit pattern to be processed (hereinafter, a bit pattern of interest). Subsequent processes of steps S910 to S960 are sequentially executed for each 32-bit bit pattern corresponding to one tile on the memory arranged as shown in FIG. 8, and therefore initialization is performed in this step. As described above, since both the edge area of one tile and the solid area of one tile are represented by a 32-bit bit pattern, high-speed processing for each bit pattern can be performed by, for example, burst transfer using a DMA controller. It is possible to execute sequentially.

In step S910, the CPU 201 determines whether the bit pattern of interest represents an edge region or a solid region. Specifically, it is determined whether the most significant bit (b31) of the attention bit pattern is 0, and if the result of the determination is true, it is determined that the attention bit pattern represents the edge region, and step S921. Proceed to. On the other hand, when it is determined that b31 is not 0, it is determined that the attention bit pattern represents the solid region, and the process proceeds to step S931.

Hereinafter, the case where it is determined that the bit pattern of interest represents the edge region (YES in step S910) will be described. In this case, in step S921, the CPU 201 executes a color conversion process for converting each of the foreground color and the background color represented by the attention bit pattern into colors in the recording color space of the image processing device in the printer. .. As the recording color space, a color space representing a color gamut (Gamut) that can be printed and expressed by a printer is used. By the color conversion process in this step, the input color outside the color gamut of the printer is converted into the color within the color gamut of the printer (Gamat compression). In step S432, the foreground color in the edge region is reduced to 3 bits (8 colors) and the background color is reduced to 12 bits (4096 colors). Therefore, a color conversion LUT that directly corresponds to these colors is prepared in advance. Therefore, the color conversion process of this step can be easily executed. That is, the linear interpolation calculation process after LUT reference, which occurs during the normal color conversion process, can be omitted.

In step S922, the CPU 201 executes a color separation process for converting the multi-value information of the color derived in step S921 into the multi-value information of the color material used in the printer for each of the foreground color and the background color. For example, in the case of an inkjet printer (hereinafter, CMYK inkjet printer) in which four color inks of C, M, Y, and K are used, the RGB value is converted into the CMYK value. For example, RGB (0,0,0) indicating black is converted to CMYK (0,0,0,255), and RGB (255,0,0) indicating red is converted to CMYK (0,255,255,0). Is converted to.

In step S923, the CPU 201 executes a gradation correction process for correcting the gradation of the signal value of each ink color after the color separation process derived in step S922 for each of the foreground color and the background color. The purpose of executing the gradation correction process in this step is as follows. Generally, in an inkjet printer, the larger the amount of ink ejected per unit area, the stronger the color of the ink appears on the paper surface. However, since there is a non-linear relationship between the amount of ink ejected and the color development on the paper surface (spectral reflectance, Lab value, etc.), gradation correction processing is executed in this step to correct this color development. To do. Since the ink ejection amount may change depending on the manufacturing intersection of the head 204, this error may be absorbed by the gradation correction process in this step. In that case, as a method for estimating the discharge amount of the head, any known technique such as a method for printing a test pattern by the user can be used.

In step S924, the CPU 201 executes a quantization process for binarizing the signal value of each ink color derived in step S923. Here, while the processing of steps S921 to S923 in the previous step is executed for each attention bit pattern, the quantization processing of this step is in pixel units in the tile corresponding to the attention bit pattern, that is, 2400 dpi × 2400 dpi. Must run at resolution. Specifically, based on the shape information stored in the bit pattern “map_4 × 4” shown in FIG. 6B, it is determined whether each pixel is a foreground pixel or a background pixel. Then, according to the result of this determination, a binarized signal value of each ink color (foreground color or background color) derived in step S923 is assigned to each pixel. For example, in the case of a CMYK inkjet printer, a total of 64 bits of output results corresponding to 16 pixels (that is, one tile) having values of 1 bit and 4 channels can be obtained by this step.

Next, a case where it is determined that the bit pattern of interest represents a solid region (NO in step S910) will be described. In this case, in step S931, the CPU 201 shifts the color represented by the values of r10, g10, and b10 (FIG. 7A) in the bit pattern of interest to the color in the recording color space of the image processing device in the printer. Execute the color conversion process to be converted.

In step S932, the CPU 201 executes a color separation process for converting the multi-value information of the color derived in step S931 into the multi-value information of the color material of the printer.

In step S933, the CPU 201 executes a gradation correction process for correcting the gradation of the signal value of each ink color after the color separation process derived in step S932.

In step S934, the CPU 201 executes a quantization process for converting the signal value of each ink color derived in step S933 into an ejection level that defines the ejection amount of ink per unit area. Here, the discharge level takes a value (0 to 15) in 16 steps. In this step, only the discharge level is derived, and in the subsequent index expansion process (step S935), the presence / absence and the number of discharges for each nozzle can be obtained. By the quantization process of this step, a value (any of 0 to 15) for each pixel in an image of 600 dpi × 600 dpi can be obtained.

In step S935, the CPU 201 executes the index expansion process based on the discharge level derived in step S934. The index expansion process is a process of expanding one pixel in an image of 600 dpi × 600 dpi into a bitmap pattern of 4 × 4 pixels in an image of 2400 dpi × 2400 dpi. Specifically, a bitmap pattern is created by determining the pixel value of 4 × 4 pixels in the image of 2400 dpi × 2400 dpi based on the value of the ejection level of each ink color possessed by one pixel in the image of 600 dpi × 600 dpi. .. The index expansion process may be performed using a well-known technique. For example, the dot arrangement according to the discharge level may be stored in advance as a table, and the dot arrangement may be determined using the table according to the discharge level derived in step S934. By the index expansion process of this step, the final dot placement destination on the paper is determined. For example, when the head 204 can arrange dots on the paper surface at a resolution of 2400 dpi × 2400 dpi, it is determined whether or not to arrange the dots for each coordinate of dividing the paper surface into a grid of 2400 dpi × 2400 dpi. By this step, a total of 64 bits of output results corresponding to 16 pixels (that is, one tile) having values of 1 bit and 4 channels can be obtained.

In step S940, the CPU 201 stores the 64-bit output result obtained in step S924 or step S935 in the buffer on the RAM 203. When stored in the buffer in this step, both the edge region data and the solid region data are used as information for controlling whether or not to eject ink (On / Off) for each nozzle of the head 204 of 2400 dpi. It will have the same meaning. Therefore, for the processing after the recording data creation processing in the subsequent step S340, the same processing as the processing in the conventional printer may be executed.

In step S950, the CPU 201 increments m.

In step S960, the CPU 201 determines whether m is greater than the total number of bit patterns. If the result of the determination in step S960 is true, the series of processes ends, while if the result of the determination is false, the process returns to step S910. The above is the content of the image processing in this embodiment.

In step S923 or step S933, the same gradation correction may be realized in all the printer models by executing the gradation correction processing using the correction amount according to the printer model.

Further, in the above example, it is determined whether the edge region or the solid region corresponds to each tile of interest (bit pattern of interest), and different processes are executed according to the result of the determination. However, for all tiles (all bit patterns), the processing performed on the edge area and the processing performed on the solid area are separately executed, and the result of these processing is determined as the image area of the image (). It may be used properly based on the result of (determination of whether it is an edge region or a solid region). In this case, since it is not necessary to selectively execute the image processing, it is possible to prevent the printer circuit from becoming complicated, and since the image processing is performed without waiting for the result of the image area determination, the processing time can be shortened. ..

<About the recorded data creation process>
Hereinafter, the recorded data creation process (step S340 in FIG. 3) in this embodiment will be described with reference to FIG.

In step 1000, the CPU 201 executes the path decomposition process. In a serial head type inkjet printer, when the dot landing accuracy at the time of image formation is low, color unevenness and streaks caused by the dot landing position shift cause deterioration of image quality. In order to avoid this, it is effective to form an image by a plurality of head scans (multipath method) instead of forming an image by one head scan (single pass method). Therefore, in this step, recorded data for printing in the multipath method is created. Any known technique may be used as the path decomposition method.

The image processing so far has been performed by scanning the image in the raster direction and arranging the processing result on the RAM in the same direction. However, when transmitting the recorded data to the head 204, it is necessary to rearrange the image in the direction accepted by the head 204 (for example, the column direction). Therefore, in step 1010, the CPU 201 executes an HV conversion process that converts an image arranged in the raster direction into an image arranged in the column direction. The HV conversion process may be performed by accessing the RAM 203 by memory. Alternatively, in order to speed up the processing, the image arranged in the raster direction is directly input by burst transfer via the dedicated hardware, rearranged by the SRAM on the hardware, and the rearrangement result is directly output to the head 204. You may also transfer directly to. The above is the content of the recorded data creation process in this embodiment.

<About the process of forming an image>
Hereinafter, the process of forming an image (step S350 in FIG. 3) in this embodiment will be described with reference to FIG. FIG. 11 is a schematic view of a mechanism for forming an image by ejecting ink droplets onto paper in a general serial head type inkjet printer. In FIG. 11, the x direction represents the scanning direction of the carriage 1105, and the y direction represents the transport direction of the paper 1107.

As shown in the figure, the inkjet printer includes a paper feed shaft 1101 for feeding paper as a paper feed mechanism and a paper discharge shaft 1102 for discharging paper, and by rotating these shafts, the paper 1107 is transferred. Transport at a constant speed.

An ink tank 1104 for storing ink of each color of CMYK is installed on the carriage 1105, and the ink is supplied to the discharge head 1106 through a flow path in the carriage 1105. The carriage 1105 is mounted on the transport rail 1103 and can move along the transport rail 1103. The discharge head 1106 is connected to the bus 207 of the printer via a communication cable (not shown), and receives the recorded data derived by the above-mentioned HV conversion and the head discharge control information for controlling the ink discharge timing. .. An image is formed on the paper by ejecting ink based on the recorded data and the head ejection control information. Either a thermal method or a piezo method may be adopted as a method in which the ejection head ejects ink droplets onto the paper.

For example, 512 nozzles are arranged in a row on the head at intervals of 600 dpi corresponding to each ink color, and the inkjet printer can independently control ON / OFF of ejection for each nozzle.

The serial head type inkjet printer controls both the movement of the carriage and the transfer of the paper to move the head to an arbitrary position on the paper and eject the ink. For example, when printing on A4 size (8.5 inches wide x 11 inches long) paper using the single-pass method, ink is ejected while moving the carriage in the x direction, so that the width is 8.5 in one head scan. Image formation is performed on an area of inch × length 0.85 inch. Next, the paper is conveyed 0.85 inches in the y direction, and then the head scanning is performed again to form an image for the next region of 8.5 inches wide × 0.85 inches long. By repeating the head scanning and the paper transport in this way, the image forming process on the A4 size paper is completed by 13 head scannings in the single pass method. When printing in the multi-pass format, the image formation is performed by shortening the paper transport distance for each head scan and increasing the number of head scans as compared with the case of image formation in the single-pass format. For example, when printing on A4 size paper with 4 passes, the paper transport distance for each head scan is set to 0.21 inch, and the image formation process is completed by 52 head scans. The above is the content of the process for forming an image in this embodiment.

<About the effect of this example>
In this embodiment, multi-valued color information is represented by a bit pattern in a predetermined format for both the edge region and the solid region in the image (FIGS. 6 (b) and 7 (a)). Since this bit pattern does not depend on the characteristics of the printer (the composition of the ink used in the printer, the output characteristics of the head, etc.), it is not necessary to consider the output destination printer when creating the bit pattern. It is useful. Especially in commercial printing, it is necessary to keep the operating rate of the equipment always high by connecting a plurality of printer engines in parallel via a network and allocating print jobs evenly. For that purpose, it is important whether the rendering process (step S310) and the conversion process (step S320) can be executed regardless of the printer.

Further, the RIP process for creating a raster image by the rendering process based on the PDL data is generally performed using a dedicated RIP server. By using the RIP server as a common resource for all printers without associating it with a specific printer, it is possible to always execute processing with maximum performance regardless of the operating status of individual printers.

Furthermore, if the printer specified as the output destination becomes unusable due to a failure, etc., in order to minimize downtime, it is required to immediately send the data after RIP processing to another usable printer. Be done. Even in such a system, by adopting the format of this embodiment as the data format after the RIP processing, the data after the RIP processing can be commonly used by each printer, and the productivity can be improved.

In this embodiment, the case where the image area in which the shape reproduction ability is prioritized over the color reproduction ability is the edge area for designating the foreground color and the background color has been described, but the bit pattern corresponding to such an image area has been described. The number of colors specified by is not limited to 2. When the shape information of the bit pattern specifies which of the three or more types of pixels each pixel is, the number of colors specified in the color information of the bit pattern is three or more. That is, in the bit pattern, a number of colors is specified according to the type of pixels specified in the shape information, and this number may be smaller than the total number of pixels in the image area, which is a unit of shape information, and larger than 1.

Further, in this embodiment, the case where the number of gradations of both the foreground color and the background color specified by the bit pattern of the edge region is smaller than the number of gradations of the color specified by the bit pattern of the solid region has been described. However, it is sufficient that at least one gradation number of the foreground color and the background color specified by the bit pattern of the edge region is smaller than the gradation number of the color specified by the bit pattern of the solid region.

Further, in this embodiment, the case where the image area in which the resolution is more important than the gradation is the edge region and the image area in which the gradation is more important than the resolution is the solid region has been described. However, the combination of the image area in which the resolution is more important than the gradation and the image area in which the gradation is more important than the resolution is not limited to the combination of the edge area and the solid area.

[Example 2]
In the conversion process in the first embodiment, the foreground color is represented by 1 bit and 3 ch 3 bit data and the background color is represented by 4 bit and 3 ch 12 bit data by the color reduction process (step S432) for the edge region (FIG. 6 (b). )).

On the other hand, in this embodiment, the size of the tile to be processed is expanded, and the conversion process of treating the area of 8 × 8 pixels in the image having the resolution of 2400 dpi × 2400 dpi as one tile is executed. By the conversion process of this embodiment, both the edge area of one tile and the solid area of one tile are represented by a 128-bit bit pattern. This makes it possible to express the foreground color and background color of the edge region in full color (30 bits). In the following, the difference from the first embodiment will be mainly described, and the description of the same configuration and the same processing as that of the first embodiment will be omitted as appropriate.

<About conversion processing>
Hereinafter, the conversion process in this embodiment will be described with reference to FIG.

In step S400, the CPU 201 executes an edge detection process that applies an edge filter to the bitmap image derived in step S310. In this embodiment as well as in the first embodiment, the 3 × 3 filter shown in FIG. 5 (a) is used.

In step S410, the CPU 201 initializes n, that is, sets the value of n to 1. Here, n is a parameter representing a tile of interest, which is an area to be processed (in this embodiment, an area of 8 × 8 pixels in an image of 2400 dpi × 2400 dpi).

In step S420, the CPU 201 derives the edge amount of the region of interest in the edge image derived in step S400. In this embodiment, when the edge amount of an arbitrary region of interest is larger than the predetermined threshold Th2, the tile of interest is determined to be an edge region.

In step S430, the CPU 201 determines whether the edge amount of the region of interest is larger than the threshold Th2. If the result of the determination in step S430 is true, the tile of interest is determined to be an edge region, and the process proceeds to step S431. On the other hand, if the result of the determination in step S430 is false, the tile of interest is determined to be a solid area, and the process proceeds to step S435.

Hereinafter, the case where the tile of interest is determined to be the edge region (YES in step S430) will be described. In step S431, the CPU 201 executes the quantization process for the tile of interest in the full-color image derived in step S310, and derives a bitmap pattern represented by only two colors, the foreground color and the background color. In deriving the bitmap pattern in this step, any method such as adaptive binarization may be used. By this step, shape information (64-bit data) indicating which pixel corresponds to the foreground pixel and which pixel corresponds to the background pixel among the 8 × 8 pixels constituting the tile of interest is acquired. This shape information is stored in the 64-bit area “map_8 × 8” at the end of the 128-bit bit pattern shown in FIG.

In step S432, the CPU 201 executes a color reduction process for reducing the number of gradations for each of the two colors (16 bits and 3 channels, respectively) used in the bitmap pattern derived in step S431. Specifically, both the foreground color and the background color are represented by 30-bit data of 10-bit and 3ch in which each RGB channel has a value of 10-bit. The RGB values of the foreground color after the color reduction processing are stored in the bit pattern areas “fg_r10”, “fg_g10”, and “fg_b10” shown in FIG. It is stored in "bg_g10" and "bg_b10". As described above, in the first embodiment, the foreground color is represented by 3 bit data and the background color is represented by 12 bit data by the color reduction processing for the input 16 bit, 3 ch color information. Therefore, in the first embodiment, the background color can be expressed in full color, but the foreground color cannot be expressed in full color. On the other hand, in this embodiment, both the foreground color and the background color after the color reduction processing can be expressed in full color (30-bit data).

Next, a case where the tile of interest is determined to be a solid region (NO in step S430) will be described. In this case, in step S435, the CPU 201 sums the pixel values of each pixel for each 4 × 4 pixel area (sub tile) obtained by dividing the attention tile (8 × 8 pixel area) in the full-color image derived in step S310. To derive the total value for each subtile. As a result of totaling the pixel values of 16 pixels of pixels having a value in the value range of 0 to 65535 per channel in the original image, the subtile has a value in the value range of 0 to 1048560 per channel. As a result of this step, data for one subtile that can be represented by 20 bits and 3 channels is acquired for four subtiles. This is synonymous with acquiring a value of 20 bits and 3 channels as a pixel value corresponding to each pixel in the region of 2 × 2 pixels in an image of 600 dpi × 600 dpi.

In step S436, the CPU 201 executes color reduction processing for reducing the number of gradations for each of the RGB values (20 bits each) for each subtile derived in step S435, and derives 10 bit RGB values for each. The R values of the four subtiles derived in this step are stored in the 10-bit areas "a11_r10", "a10_r10", "a01_r10", and "a00_r10" of the bit pattern shown in FIG. 13, respectively. Similarly, the G values of the four subtiles are stored in the 10-bit areas "a11_g10", "a10_g10", "a01_g10", and "a00_g10" of the bit pattern shown in FIG. 13, respectively. Similarly, the B values of the four subtiles are stored in the 10-bit areas "a11_b10", "a10_b10", "a01_b10", and "a00_b10" of the bit pattern shown in FIG. 13, respectively. The four sets of 10-bit, 3ch information derived in steps S435 to S436 are treated as 2 × 2 pixel information in a 600 dpi × 600 dpi image in the subsequent step. The above is the content of the conversion process in this embodiment.

As described above, the data sizes of the bit pattern representing the edge region (FIG. 12) and the bit pattern representing the solid region (FIG. 13) are both 128 bits. By having different information with the same data size in this way, it is possible to enable easy random access in the assigned format unit and improve the efficiency of data processing.

In the conversion process of this embodiment, the color is expressed in low resolution in exchange for expressing the shape in high resolution in the edge region. Specifically, the color information between the foreground and the background is shared in units of one pixel in an image of 300 dpi × 300 dpi. On the other hand, in the solid region, in exchange for expressing the shape with a low resolution, the solid color can be expressed with a higher resolution than the edge region (in units of one pixel in an image of 600 × 600 dpi). That is, in this embodiment as in the first embodiment, the shape reproduction ability is prioritized over the color reproduction ability in the edge region, the color reproduction ability is prioritized over the shape reproduction ability in the solid region, and the edge region and the solid region are prioritized. It is represented by a bit pattern of the same data size.

In this embodiment, the case where both the foreground pixel color and the background pixel color are expressed by 30-bit data has been described, but if each of the foreground pixel color and the background pixel color is expressed in full color, Well, the data used is not limited to 30-bit data. That is, the bit length of the bit region allocated to the color of the foreground pixel and the color of the background pixel may be appropriately changed according to the bit length of the bit pattern to be used.

[Example 3]
In the first embodiment, in the conversion process, the edge region and the solid region are represented by bit patterns in different formats (FIGS. 6 (b) and 7 (a)). On the other hand, in this embodiment, in the conversion process, the solid region is represented by the same bit pattern as the edge region (FIG. 6B). That is, the image data is represented only by the bit pattern shown in FIG. 6 (b) without using the bit pattern shown in FIG. 7 (a).

Specifically, the area of 4 × 4 pixels in the image of 2400 dpi × 2400 dpi is treated as one tile. When the tile to be processed (the tile of interest) is determined to be a solid region, the solid color is represented by 10 bits and 3 channels in the first embodiment (FIG. 7 (a)), whereas the solid color is 4 bits in the present embodiment. , Expressed in 3ch. This is synonymous with expressing a solid color with 4 bits and 3 channels (each RGB channel has 16 gradations) in a 1 × 1 pixel region in a 600 dpi × 600 dpi image. In this embodiment, the gradation property is ensured by executing the color reduction processing (color reduction processing to 16 gradations) for deriving the solid color of 4 bits and 3 channels by using the dither method. In the following, the difference from the first embodiment will be mainly described, and the description of the same configuration and the same processing as that of the first embodiment will be omitted as appropriate.

It is known that human visual characteristics (Visual Transfer Function) with respect to periodic changes in brightness can be identified only by large changes in brightness in high-frequency images, while even slight changes in brightness can be identified in low-frequency images. There is.

FIG. 14 shows the relationship (VTF curve) between the sensitivity and the frequency, which is the discriminating ability of human gradation change. If the number of gradations in the image exceeds this VTF curve, it can be said that the number of gradations is sufficient.

Hereinafter, a case where image data of 600 dpi × 600 dpi (each pixel is represented by 16 gradations) is created by dither will be examined as an example. Here, one pixel in the image data of 300 dpi × 300 dpi corresponds to 2 × 2 pixels in the image data of 600 dpi × 600 dpi. Further, one pixel in the image data of 150 dpi × 150 dpi corresponds to 4 × 4 pixels in the image data of 600 dpi × 600 dpi. Since each pixel in the image data of 600 dpi × 600 dpi can represent 16 values of 0 to 15, one pixel in the image data of 300 dpi × 300 dpi uses 4 pixels in the image data of 600 dpi × 600 dpi and is 0 to 60 (= 15 ×). The 61 value of 4) can be expressed. Similarly, one pixel in the image data of 150 dpi × 150 dpi can represent a 241 value of 0 to 240 (= 15 × 16) by using 16 pixels in the image data of 600 dpi × 600 dpi. Generalizing the above contents, when 600 dpi is used as a reference, X dpi can express 15 × (600 / X) ^ 2 + 1 gradation. That is, in area gradation, finer gradation can be expressed in exchange for a decrease in resolution.

Based on the above, FIG. 15 is a plot of the relationship between the area gradation value by dither and the frequency in FIG. As shown in FIG. 15, the value of the area gradation by dither exceeds the number of gradations that can be recognized by humans (the number of gradations indicated by the VTF curve) at any resolution, and the area gradation by dither is exceeded. It can be seen that sufficient gradation can be obtained by using it. Taking advantage of this, in this embodiment, only the format shown in FIG. 6B is used.

<About conversion processing>
Hereinafter, the conversion process (step S320 in FIG. 3) in this embodiment will be described with reference to FIG. In this embodiment, only the color reduction treatment in step S436 is different from that of the first embodiment.

In step S436, the CPU 201 executes color reduction processing for reducing the number of gradations for each of the RGB values (each 20 bits) derived in step S435, and derives each 4 bits of RGB values. Here, in this embodiment, the color reduction processing is performed by using the dither method. Instead of executing the color reduction process using the dither method, the color reduction process may be executed using the error diffusion method. The reason is as follows.

In the first embodiment, the color of the solid region is expressed with a sufficient number of bits (10 bits, 3 channels) (FIG. 7 (a)). On the other hand, in this embodiment, the color of the solid region is represented by 4 bits and 3 channels (FIG. 6 (b)). When the color reduction process for deriving the color information of the solid region is executed by using the dither method, there is a possibility that an adverse effect may occur. For example, when the quantization process in the subsequent step S924 is executed by using the dither method, the dither process is executed a plurality of times for the same region, so that the dither pattern interferes with the graininess. Get worse. Therefore, it is possible to avoid the occurrence of interference by performing the color reduction processing using the error diffusion method. Alternatively, when using the dither method, a pattern may be set in advance so that the dither pattern used in the color reduction processing and the dither pattern used in the quantization processing do not interfere with each other.

The color information of 4 bits and 3 channels derived by the color reduction processing is stored in the 12-bit area “bg_rgb” area of the bit pattern shown in FIG. 6 (b). Further, 0 is stored as a value indicating that the pixel is a background pixel for all the bits of the area “map_4 × 4”. Although the foreground color information is stored in the area "fg_rgb" in the first embodiment, it is not referred to in the present embodiment, so that an arbitrary value such as an indefinite value may be stored.

According to this embodiment, by creating a bit pattern similar to the edge region for the solid region, it is not necessary to execute the processes of steps S931 to S935 in FIG. 9, so that the configuration of the image processing apparatus in the printer is simplified. Can be converted.

[Other Examples]
The present invention supplies a program that realizes one or more functions of the above-described embodiment to a system or device via a network or storage medium, and one or more processors in the computer of the system or device reads and executes the program. It can also be realized by the processing to be performed. It can also be realized by a circuit (for example, ASIC) that realizes one or more functions.

200 Image forming apparatus 201 CPU

Claims (12)

An image processing device that converts image data in a bitmap format into data consisting of a bit pattern including a first bit pattern and a second bit pattern.
Based on the pixel values of the pixels in the first image area reproduced at the first resolution, shape information indicating whether each pixel in the first image area is a foreground pixel or a background pixel is acquired, and shape information is acquired. Color reduction that reduces the number of gradations between the color of the foreground pixel and the color of the background pixel so that the number of gradations of the foreground pixel is smaller than the number of gradations of the background pixel based on the acquired shape information. A processing means for deriving color information indicating the color of the foreground pixel and the color of the background pixel by processing, and
Based on the shape information acquired by the processing means and the derived color information, for each pixel in the first image area, each pixel in the first image area is a foreground pixel and a background pixel. A bit indicating which of the above is applicable, a bit indicating the color of the foreground pixel, and a bit indicating the color of the background pixel are included, and the number of bits indicating the color of the background pixel indicates the color of the foreground pixel. A first creation means for creating the first bit pattern, which is larger than the number of bits, and
The number of bits larger than the color information of the first image area based on the pixel values of the pixels in the second image area of the same size as the first image area reproduced at the second resolution lower than the first resolution. A second creating means for creating the second bit pattern having the same bit length as the first bit pattern created by the first creating means, in which the color information of the second image region indicated by is stored. An image processing device characterized by having and. Data amount of the data consisting of the bit pattern including the first bit pattern and the second bit pattern, according to claim 1, characterized in that less than the data amount of the image data of the bitmap format Image processing equipment. The image processing apparatus according to claim 1 or 2, wherein the first image region is an edge region, and the second image region is a solid region. The image processing apparatus according to claim 3 , further comprising a determining means for determining which of the edge region and the solid region is for each of the image regions of a predetermined size in the image data. Before Symbol color information of the first image area, the color of the background pixel and the color of the foreground pixel is specified,
The image processing apparatus according to claim 3 or 4 , wherein the solid color of the solid region is specified by the color information of the second image region. The image processing apparatus according to claim 5 , further comprising a shape information derivation means for executing a quantization process for the pixel value of each pixel in the edge region and deriving the shape information. A first color information deriving means for deriving the color information of the edge region,
The image processing apparatus according to claim 6 , further comprising a second color information deriving means for deriving color information in the solid region. The quantization process is a binarization process, and is
The image processing apparatus according to claim 7, wherein the first color information deriving means executes a color reduction process for reducing the number of gradations of colors. Any one of claims 5 to 8 , wherein the number of gradations of the solid color is larger than at least one of the number of gradations of the color of the foreground pixel and the number of gradations of the color of the background pixel. The image processing apparatus according to the section. In the second bit pattern, a solid color for each image area obtained by dividing the second image area is specified.
The image processing apparatus according to any one of claims 5 to 8, wherein the color of the foreground pixel and the color of the background pixel are expressed in full color. An image processing method for converting image data in a bitmap format into data consisting of a bit pattern including a first bit pattern and a second bit pattern.
Based on the pixel values of the pixels in the first image area reproduced at the first resolution, shape information indicating whether each pixel in the first image area is a foreground pixel or a background pixel is acquired, and shape information is acquired. Color reduction that reduces the number of gradations between the color of the foreground pixel and the color of the background pixel so that the number of gradations of the foreground pixel is smaller than the number of gradations of the background pixel based on the acquired shape information. A processing step of deriving color information indicating the color of the foreground pixel and the color of the background pixel by processing, and
Based on the shape information acquired by the processing step and the derived color information, for each pixel in the first image area, each pixel in the first image area is a foreground pixel and a background pixel. A bit indicating which of the above is applicable, a bit indicating the color of the foreground pixel, and a bit indicating the color of the background pixel are included, and the number of bits indicating the color of the background pixel indicates the color of the foreground pixel. The first creation step of creating the first bit pattern, which is larger than the number of bits, and
The number of bits larger than the color information of the first image area based on the pixel values of the pixels in the second image area of the same size as the first image area reproduced at the second resolution lower than the first resolution. A second creation step in which the color information of the second image area indicated by is stored and the second bit pattern having the same bit length as the first bit pattern created in the first creation step is created. An image processing method characterized by having and. A program for operating a computer as the image processing device according to any one of claims 1 to 10.

Images