JP2021187137A - Image processing device, image processing method and test pattern - Google Patents

Abstract

To provide a technique for improving the streak unevenness detection accuracy by reducing an area occupied by a reference mark in a test pattern and increasing an area and gradation number of a patch.SOLUTION: An image processing device acquires an image obtained by reading a printed matter that is obtained by printing a test pattern including patches in different gradations by using a plurality of recording elements. The image processing device acquires an average pixel value including a pixel value corresponding to a position of a reference mark in the patch for each patch in the image, and acquires the recording characteristics of the recording element on the basis of the average pixel value acquired for each patch in the image.SELECTED DRAWING: Figure 3

Description

The present invention relates to a technique for acquiring recording characteristics in a recording element.

As a device for forming an image on a recording medium, there is an inkjet printer that forms an image on the recording medium by ejecting ink from an individual recording element (hereinafter, may be referred to as a nozzle). In an inkjet printer, due to variations in the ink ejection characteristics of multiple nozzles provided in the recording head and variations in the transport accuracy of the recording medium, streaks (uneven density) occur in the image on the printed matter as the output result. In some cases, there was a problem with print quality.

As a countermeasure, a test pattern for detecting shading is printed, and the recording density formed from each nozzle is made constant when printing a uniform image based on the image read by a scanning device such as a scanner. A head shading correction technique for correcting image data according to the characteristics of individual nozzles is known. In the following, head shading will be referred to as HS (abbreviation for Head Shading). Patent Document 1 discloses a sujimura detection technique using a test pattern in which a plurality of reference marks are arranged before and after each of a plurality of gradation patterns for detecting sujimura.

Japanese Unexamined Patent Publication No. 2005-141232

According to the technique of Patent Document 1, the detection accuracy of the sujimura can be improved by specifying the recording position of each nozzle for each gradation pattern in the read image of the test pattern. However, since the area of the reference mark provided between each gradation pattern occupies a certain area, the area to which the gradation pattern can be assigned is limited when the entire test pattern is stored in a test paper of a predetermined size. .. As a result, there is a problem that the number of gradations of the gradation pattern that can be arranged in the test pattern is lowered, and the accuracy of sujimura detection becomes insufficient.

The present invention provides a technique for improving the sujimura detection accuracy by reducing the area occupied by the reference mark in the test pattern and increasing the patch area and the number of gradations.

The uniformity of the present invention is a first acquisition means for acquiring an image obtained by reading a printed matter obtained by printing a test pattern including patches having different gradations using a plurality of recording elements, and for each patch in the image. Second acquisition, the average pixel value including the pixel value corresponding to the position of the reference mark in the patch is acquired, and the recording characteristics of the recording element are acquired based on the average pixel value acquired for each patch in the image. It is characterized by having means.

According to the configuration of the present invention, the area occupied by the reference mark in the test pattern can be reduced, and the patch area and the number of gradations can be increased to improve the sujimura detection accuracy.

Schematic diagram of an inkjet printer. The block diagram which shows the hardware configuration example of an image formation system. The block diagram which shows the functional structure example of a print processing circuit 216. The flowchart of the process performed by the host PC 20 and the printer 10 for HS process. (A) is a diagram for explaining a measurement curve and a target characteristic, and (b) is a diagram for explaining a method of acquiring a corrected input value. The flowchart which shows the detail of the process in step S402. The figure which shows an example of a test pattern. The figure explaining the reference mark area in a gradation patch. The figure explaining the detection method of the reference mark. The figure explaining the characteristic of a test pattern. The figure which shows the result of binarizing the multi-valued test pattern shown in FIG. 7 by the dither method. The figure which shows the result of omitting the region where the gradation value is uniform extremely. The figure which shows an example of the test pattern (the multi-valued test pattern which shows the ink value image). The figure explaining the reference mark area in a gradation patch. The figure which shows an example of the test pattern (the multi-valued test pattern which shows the ink value image). The figure which shows an example of the test pattern (the multi-valued test pattern which shows the ink value image). The figure which shows an example of the test pattern (the multi-valued test pattern which shows the ink value image).

Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. The following embodiments do not limit the invention according to the claims. Although a plurality of features are described in the embodiment, not all of the plurality of features are essential for the invention, and the plurality of features may be arbitrarily combined. Further, in the attached drawings, the same or similar configurations are given the same reference numbers, and duplicate explanations are omitted.

[First Embodiment]
First, an inkjet printer (hereinafter, simply referred to as “printer”), which is an example of the image forming apparatus used in the present embodiment, will be described with reference to the schematic diagram of FIG. The printer 10 includes a recording head 100 in its housing. The recording head 100 is a so-called full-line type recording head, and has four nozzle rows 101 to 104 corresponding to black, cyan, magenta, and yellow ink colors. In each nozzle row, nozzles for ejecting ink are arranged in the X direction (nozzle arrangement direction) at regular intervals. In the following description, the nozzle resolution of each nozzle row is 1200 dpi. For example, if the length of the nozzle row in the X direction is 10 inches, about 12000 nozzles are lined up in the X direction. At this time, the nozzle positions in the Y direction (the direction orthogonal to the X direction and the paper transport direction at the time of printing) do not have to be the same and may be staggered. It should be noted that each nozzle row may be prepared as a separate recording head and may be arranged in parallel in the Y direction.

The paper 106 as a recording medium is conveyed in the Y direction by the transfer roller 105 (and other rollers (not shown) rotated by the driving force of a motor (not shown). Then, while the paper 106 is conveyed, each nozzle of each of the nozzle rows 101 to 104 ejects ink according to the recording data, so that an image is formed on the paper surface of the paper 106. In the following description, the recording resolution in the Y direction is 1200 dpi.

Further, an in-line sensor 107 is provided at a position downstream of the recording head 100 in the Y direction. The in-line sensor 107 optically reads the color of the image on the paper 106 (printed) by the optical reading elements arranged at regular intervals in the X direction, and represents the read color in the RGB color space. Output. In the following description, the resolution of the optical reading element is 1200 dpi, and the reading resolution in the paper transport direction is 1200 dpi.

Next, a hardware configuration example of an image forming system including such a printer 10 will be described with reference to the block diagram of FIG. As shown in FIG. 2, the image forming system according to the present embodiment includes the printer 10 and a host PC (personal computer) 20 which is an example of an image processing device that acquires the recording characteristics of each nozzle in the printer 10. Have.

First, the host PC 20 will be described.

The CPU 201 executes various processes using computer programs and data stored in the RAM 202. As a result, the CPU 201 controls the operation of the entire host PC 20, and also executes or controls each process described as being performed by the host PC 20.

The RAM 202 has an area for storing computer programs and data loaded from the HDD (hard disk drive) 203, data received from the printer 10 via the data transfer I / F 204, and the like. Further, the RAM 202 has a work area used by the CPU 201 when executing various processes. As described above, the RAM 202 can appropriately provide various areas.

The HDD 203 stores an OS (operating system) and computer programs and data for causing the CPU 201 to execute or control various processes described as those performed by the host PC 20. The computer programs and data stored in the HDD 203 are appropriately loaded into the RAM 202 according to the control by the CPU 201, and are processed by the CPU 201.

The data transfer I / F 204 is a communication interface for performing data communication with the printer 10. As the connection method for this data communication, for example, USB or LAN is used.

The keyboard / mouse I / F205 is an interface for controlling a HID (Human Interface Device) of a keyboard, a mouse, or the like. The display I / F 206 is an interface for controlling the display of a display (not shown) such as a liquid crystal monitor or a touch panel screen.

Next, the printer 10 will be described. The CPU 211 executes various processes using computer programs and data stored in the RAM 212 and the ROM 213. As a result, the CPU 211 controls the operation of the entire printer 10 and executes or controls each process described as what the printer 10 performs.

The RAM 212 has an area for storing computer programs and data loaded from the ROM 213 and data received from the host PC 20 via the data transfer I / F 214. Further, the RAM 212 has an area for storing the data output from the inline sensor 107 according to the control by the sensor controller 217. Further, the RAM 212 has a work area used by the CPU 211 to execute various processes. As described above, the RAM 212 can appropriately provide various areas.

The ROM 213 stores setting data of the printer 10, computer programs and data related to the startup of the printer 10, computer programs and data related to the basic operation of the printer 10, and the like.

The data transfer I / F 214 is a communication interface for performing data communication with the host PC 20. The head controller 215 controls the ink ejection operation in each nozzle row of the recording head 100 based on, for example, a binary-quantized halftone image stored in the RAM 212.

The print processing circuit 216 is a digital circuit specialized in image processing, and executes print-related image processing such as color conversion, color separation, HS, gamma correction, and quantization. The sensor controller 217 controls the individual optical reading elements of the inline sensor 107.

In this embodiment, the process of creating various parameters and test patterns required for printing and HS processing is performed on the host PC 20 side, and the processing executed at the time of printing including color conversion processing and quantization processing is performed on the printer 10 side. It shall be performed by the print processing circuit 216. However, all or part of the print-related image processing may be performed on the host PC 20 side, or may be executed by the CPU 211 of the printer 10. As described above, the subject of processing is not limited to a specific form.

Next, an example of the functional configuration of the print processing circuit 216 of the printer 10 will be described with reference to the block diagram of FIG. Each functional unit shown in FIG. 3 will be described as being implemented by hardware, but a part of the functional unit is implemented by software, and the corresponding functional unit functions are realized by executing the software by CPU 211 or the like. You may.

The color conversion unit 301 uses a three-dimensional look-up table (3D-LUT) to "color reproduce the printer 10" of the "image expressed in the RGB color space (input RGB image)" to be printed, which is input from the host PC 20. Convert to "RGB image corresponding to the area" (RGB image after color conversion).

It is assumed that all the resolutions of the images handled by the print processing circuit 216 are 1200 × 1200 dpi corresponding to the above-mentioned nozzle resolution of 1200 dpi and the recording resolution of 1200 dpi in the paper transport direction. Further, the bit depth of each color component of the image handled by the print processing circuit 216, including the input RGB image and the RGB image after color conversion, is 16 bits except for the halftone image output by the quantization unit 305. Suppose there is.

The color separation unit 302 converts the "RGB image after color conversion" into an "ink value image corresponding to each ink color used in the printer 10" using a 3D-LUT. When the printer 10 uses four color inks of cyan, magenta, yellow, and black, the color separation unit 302 displays the "RGB image after color conversion" with the ink consisting of four channels of cyan, magenta, yellow, and black. Convert to a value image.

The HS unit 303 performs HS processing according to the recording characteristics of each nozzle on the ink value image for each color plate output by the color separation unit 302. The details of the HS processing in the HS unit 303 will be described later.

The gamma correction unit 304 is a dot formed on a paper surface using a one-dimensional look-up table (1D-LUT) for an ink value image for each color plate that has been subjected to HS processing by the HS unit 303. Adjust the number of. Specifically, the gamma correction unit 304 performs HS processing so that the relationship between the number of dots formed by the ink droplets ejected by each nozzle and the brightness realized by the number of dots is substantially linear. Later ink value Change the pixel value of the image. As a result, the gamma correction unit 304 can generate an ink value image after gamma correction for each color plate.

The quantization unit 305 applies a known quantization process such as a dither method or an error diffusion method to the gamma-corrected ink value image for each color plate by the gamma correction unit 304, and turns the dots on or off in binary. Generates a halftone image represented by. Then, the quantization unit 305 stores this halftone image in the RAM 212. The halftone image stored in the RAM 212 is read out by the head controller 215, and the head controller 215 controls the ink ejection operation in each nozzle row of the recording head 100 based on the read out halftone image.

In the case of a printer that can control the size (dot size) of the ink droplets ejected by each nozzle, a halftone image is obtained by performing a process of quantizing to the number of gradations (bit depth) corresponding to the type of dot size. Just generate it. In this case, the head controller 215 controls the ink ejection operation of each nozzle based on a multi-valued halftone image such as a 4-value or 16-value image.

Next, the processing performed by the host PC 20 and the printer 10 for the HS processing will be described with reference to the flowchart of FIG. In step S401, the color conversion unit 301 converts the input RGB image input from the host PC 20 by using the 3D-LUT. The color separation unit 302 converts the RGB image converted by the color conversion unit 301 into an ink value image for each color plate using a 3D-LUT, and outputs the ink value image for each color plate to the HS unit 303. do. Then, the HS unit 303 acquires the ink value image for each color plate output by the color separation unit 302 as an input image.

In step S402, the measurement curve (recording characteristic) of each nozzle in the recording head 100 is acquired from the read image obtained by the in-line sensor 107 reading the “printed matter on which the test pattern is printed by the recording head 100”. The details of the process in step S402 will be described later.

Here, the measurement curve will be described with reference to FIG. 5A. In the graph of FIG. 5, the horizontal axis shows the input pixel value, and the vertical axis shows the pixel value of the scanned image. The dotted line 501 indicates the upper limit of the input pixel value. The curve 502 is a pixel value of a portion recorded by the nozzle of interest in the scanned image and a measurement curve obtained by interpolation processing. In the present embodiment, sectional linear interpolation is used for the interpolation processing, but there are various interpolation processings such as interpolation processing using a spline curve in the interpolation processing, and any interpolation processing may be applied. For example, for a nozzle with a larger discharge rate, the measurement curve shifts downward (darker direction).

In step S403, the HS unit 303 acquires the target characteristic corresponding to the measurement curve of the nozzle corresponding to the pixel (pixel of interest) to be corrected in the input image. FIG. 5A shows the target characteristic 504 corresponding to the curve 502. In the present embodiment, as shown in FIG. 5A, the measured value linear with respect to the gradation is set as the target characteristic.

In step S404, the HS unit 303 acquires the corrected pixel value (corrected input value) of the pixel of interest by using the measurement curve of the nozzle corresponding to the pixel of interest and the target characteristic acquired in step S403. .. Here, a method of acquiring the corrected input value will be described with reference to FIG. 5 (b). In FIG. 5B, the value of the target characteristic 504 corresponding to the pixel value 505 of the pixel of interest is acquired as the target value 506, and the value (gradation value) 507 of the curve 502 corresponding to the target value 506 is “the pixel of interest”. It is acquired as "corrected input value of". Then, the pixel value of the pixel of interest is replaced with the corrected input value. By performing the processes of steps S403 and S404 with each pixel in the input image as the pixel of interest, the HS process on the input image can be performed.

Next, the details of the process in step S402 will be described with reference to the flowchart of FIG. In step S601, the CPU 201 of the host PC 20 acquires a test pattern. The test pattern acquisition method is not limited to a specific acquisition method. For example, the CPU 201 may acquire a test pattern created by the user using a keyboard or a mouse, may acquire the test pattern by receiving a test pattern transmitted from an external device, or may be stored in advance in the HDD 203. You may get the test pattern you have. The test pattern is a multi-valued test pattern showing an ink value image. The details of the test pattern will be described later.

In step S602, the CPU 201 binarizes the multi-valued test pattern acquired in step S601 to generate a binary test pattern. Then, the CPU 201 outputs a print instruction including the binary test pattern and a print setting for printing the binary test pattern with only a single ink color to the printer 10.

In the print processing circuit 216 of the printer 10 that has received this print instruction, each process of the color conversion unit 301, the color separation unit 302, and the HS unit 303 is skipped, and the binary test pattern included in the print instruction received from the host PC 20 is used. Input to the gamma correction unit 304. Then, the halftone image obtained by the processing by the gamma correction unit 304 and the quantization unit 305 for the binary test pattern is printed on the paper by the nozzle row corresponding to the ink of a single color in the recording head 100. In the following, a case where the nozzle row corresponding to the single color ink is the “nozzle row (black) 101” will be described as an example. By this printing, a printed matter on which the test pattern is printed is obtained.

In step S603, the in-line sensor 107 reads the printed matter and generates a scanned image of the printed matter. The CPU 211 acquires the scanned image in three channels of RGB, and then converts it into a scanned image of one channel by a color conversion table prepared in advance according to the color characteristics of the inline sensor 107. In this embodiment, a color conversion table that converts a 16-bit value linear with respect to Y in the CIEXYZ color space is used. The color space of the scanned image is arbitrary, and may be L * of CIELab * or the density. Further, when the test pattern is recorded with color inks such as C, M, and Y, a value corresponding to saturation can be used instead of a value corresponding to brightness. For example, the values of the R, G, and B channels may be used as the values corresponding to the complementary colors of C, M, and Y.

In step S604, the HS unit 303 selects one unselected gradation patch from the plurality of gradation patches included in the scanned image obtained in step S603 as the attention gradation patch. In the present embodiment, the brightest gradation patch is selected in order, but the selection order is not limited to a specific order.

In step S605, the HS unit 303 includes a reference mark group for alignment embedded in the upper end region (one end region) of the attention gradation patch and the lower end region (the other end region) of the attention gradation patch. ) Is embedded in the reference mark group for alignment. The reference mark in the gradation patch will be described later. For example, it is assumed that the reference mark is a line-shaped mark (a line along the Y direction) corresponding to a total of 16 individual nozzles as shown in FIG. do. In this case, the area of interest (the area surrounded by the dotted line including 901) is assigned to each reference mark so as to include the reference mark, and the position of the center of gravity of the reference mark is calculated in each reference area. Detect the position of the mark.

In step S606, the HS unit 303 includes a reference mark group embedded in the upper end region of the attention gradation patch and a reference mark group embedded in the lower end region of the attention gradation patch for each pair of reference marks corresponding to each other. , Set a line through the position of one reference mark in the pair and the position of the other reference mark in the pair. The upper end of the line of each pair is the upper end of the attention gradation patch, and the lower end is the lower end of the attention gradation patch. That is, setting a line in the attention gradation patch for the attention pair is to specify the recording position of the nozzle corresponding to the attention pair in the attention gradation patch.

Then, the HS unit 303 obtains the average value (average pixel value) of the pixel values of the pixels on the line of the pair for each pair. In the nozzle row 101, when the nozzle 1, the nozzle 2, the nozzle 3, ... Are referred to in order from the nozzle at the left end (one end), the line of the pair at the left end is the dot row recorded by the nozzle 1, and the line of the second pair from the left end is. , The dot sequence recorded by the nozzle 2, and the line of the pair of N (N is an integer of 3 or more) from the left end is the dot sequence recorded by the nozzle N. That is, the average pixel value obtained for the attention pair is also the average pixel value corresponding to the nozzle corresponding to the attention pair.

In step S607, the HS unit 303 determines whether or not all the gradation patches included in the scanned image are selected as the attention gradation patches. As a result of this determination, when all the gradation patches included in the scanned image are selected as the attention gradation patches, the process proceeds to step S608. on the other hand. If a gradation patch that has not been selected as the attention gradation patch among the gradation patches included in the scanned image remains, the process proceeds to step S604.

In step S608, the HS unit 303 obtains a measurement curve for each nozzle. The method of obtaining the measurement curve of the nozzle of interest will be described below. Each gradation patch included in the scanned image is referred to as gradation patch 1, gradation patch 2, ..., Gradation patch N (N is an integer of 2 or more). In this case, the coordinate position in the coordinate system of FIG. 5A (the pixel value of the background of the gradation patch 1, the average pixel value obtained for the nozzle of interest in the gradation patch 1), and the coordinate position (the background of the gradation patch 2). Pixel value, average pixel value obtained for the attention nozzle in the gradation patch 2), ..., Coordinate position (background pixel value of the gradation patch N, average pixel value obtained for the attention nozzle in the gradation patch N), ... The curve to pass is obtained as the "measurement curve of the attention nozzle". The above interpolation technique is used to obtain this curve.

Next, a test pattern according to the present embodiment (a multi-valued test pattern showing an ink value image acquired in step S601) will be described. An example of the test pattern is shown in FIG. Here, for the sake of simplicity, a test pattern for four gradations for black ink will be described in a recording head having 256 nozzles. The number of gradations of the test pattern is not limited to four gradations, and may be any number of gradations such as 9, 17, 33, etc. in consideration of the size in a predetermined test paper. Further, regarding the number of nozzles, the size of the test pattern in the X direction may be determined according to the number of nozzles of the recording head.

As shown in FIG. 7, gradation patches 701 to 704 are arranged in the Y direction (paper transport direction) in the test pattern. The gradation patch 701 is the gradation patch with the brightest gradation, the gradation patch 702 is the gradation patch with the second brightest gradation, and the gradation patch 703 is the gradation patch with the third brightest gradation, the gradation patch 704. Is the fourth brightest gradation patch. In each of the gradation patches 701 to 704, a region having a uniform gradation value is set as a background region, and a reference mark for alignment is superimposed on the upper end region and the lower end region of the background region.

The gradation patch 701 has a background region 701b having a uniform gradation value A, and reference mark regions 701a and 701c in which a reference mark for alignment is superimposed on the background having the gradation value A. The reference mark region 701a is provided at the upper end of the gradation patch 701 in the paper transport direction (Y direction). The reference mark region 701c is provided at the lower end of the gradation patch 701 in the paper transport direction (Y direction).

In the gradation patch 702, the background region 702b having a uniform gradation value B (gradation value darker than the gradation value A) and the reference mark for alignment are superimposed on the background having the gradation value B. It has reference mark regions 702a and 702c. The reference mark region 702a is provided at the upper end of the gradation patch 702 in the paper transport direction (Y direction). The reference mark region 702c is provided at the lower end of the gradation patch 702 in the paper transport direction (Y direction).

In the gradation patch 703, a background region 703b having a uniform gradation value C (a gradation value darker than the gradation value B) and a reference mark for alignment are superimposed on the background having the gradation value C. It has reference mark areas 703a and 703c. The reference mark region 703a is provided at the upper end of the gradation patch 703 in the paper transport direction (Y direction). The reference mark region 703c is provided at the lower end of the gradation patch 703 in the paper transport direction (Y direction).

In the gradation patch 704, a background region 704b having a uniform gradation value D (a gradation value darker than the gradation value C) and a reference mark for alignment are superimposed on the background having the gradation value C. It has reference mark areas 704a and 704c. The reference mark region 704a is provided at the upper end of the gradation patch 704 in the paper transport direction (Y direction). The reference mark region 704c is provided at the lower end of the gradation patch 704 in the paper transport direction (Y direction).

In the conventional HS processing, the recording characteristics of each nozzle are acquired only from regions having uniform gradation values such as regions 701b, 702b, 703b, and 704b. On the other hand, in the present embodiment, the HS processing is performed using the entire area in the gradation patch including the reference mark area in addition to the area where the gradation value is uniform. That is, in the present embodiment, the HS processing is performed using the entire areas of the gradation patches 701, 702, 703, and 704. The recording characteristics of each nozzle, that is, the reason why the sujimura can be acquired even if the reference mark area is included will be described later.
When the inline sensor is read, the peripheral portion of the test pattern may be affected by so-called white cast, in which the read value (gradation value) becomes bright. In such a case, it is not necessary to apply the HS treatment to the nozzles in the range affected by the white cast. Alternatively, if the recording head has spare nozzles outside both ends of the commonly used nozzle row, those nozzles should be used at the periphery of the test pattern so as not to affect the HS processing of the normally used nozzle row. , A pattern may be provided to mitigate the influence of white fog.

Next, the reference mark area in the gradation patch will be described with reference to FIG. First, the reference mark regions 701a and 701c in the gradation patch 701 of FIG. 7 will be described with reference to FIG. 8A.

In the reference mark area 701a, the lines 701a-0 to 701a-3 are reference marks corresponding to the leftmost nozzle, the second nozzle from the left end, the third nozzle from the left end, and the fourth nozzle from the left end in the nozzle row, respectively. be. As described above, the reference mark region 701a is provided with a reference mark so that one line-shaped reference mark (black line) corresponds to each of 256 nozzles in the X direction.

In the reference mark area 701c, the lines 701c-0 to 701c-3 are reference marks corresponding to the leftmost nozzle, the second leftmost nozzle, the third leftmost nozzle, and the fourth leftmost nozzle in the nozzle row, respectively. be. As described above, the reference mark region 701c is provided with a reference mark so that one line-shaped reference mark (black line) corresponds to each of 256 nozzles in the X direction.

Therefore, the line passing through the line 701a-0 and the line 701c-0 (the upper end and the lower end of the line are the upper end and the lower end of the gradation patch 701, respectively) are the lines corresponding to the leftmost nozzle in the nozzle row.

The line passing through the line 701a-1 and the line 701c-1 (the upper end and the lower end of the line are the upper end and the lower end of the gradation patch 701, respectively) is a line corresponding to the second nozzle from the left end in the nozzle row.

The line passing through the line 701a-2 and the line 701c-2 (the upper end and the lower end of the line are the upper end and the lower end of the gradation patch 701, respectively) is the line corresponding to the third nozzle from the left end in the nozzle row.

The line passing through the line 701a-3 and the line 701c-3 (the upper end and the lower end of the line are the upper end and the lower end of the gradation patch 701, respectively) is the line corresponding to the fourth nozzle from the left end in the nozzle row.

Here, in the gradation patch 701, the pixel values of the background (701back) other than the reference mark (black line) are all the same gradation value. Further, the pixel value (black) of the reference mark (line) of the reference mark area 701a and the reference mark area 701c and the pixel value (gray) of the background are gradations so that the reference mark for alignment can be identified. The contrast of the values is high.

Next, the reference mark regions 704a and 704c in the gradation patch 704 of FIG. 7 will be described with reference to FIG. 8B. In the reference mark area 704a, the lines 704a-0 to 704a-3 are reference marks corresponding to the leftmost nozzle, the second leftmost nozzle, the third leftmost nozzle, and the fourth leftmost nozzle in the nozzle row, respectively. be. As described above, the reference mark region 704a is provided with a reference mark so that one line-shaped reference mark (black line) corresponds to each of 256 nozzles in the X direction.

In the reference mark area 704c, the lines 704c-0 to 704c-3 are reference marks corresponding to the leftmost nozzle, the second leftmost nozzle, the third leftmost nozzle, and the fourth leftmost nozzle in the nozzle row, respectively. be. As described above, the reference mark region 704c is provided with a reference mark so that one line-shaped reference mark (black line) corresponds to each of 256 nozzles in the X direction.

Therefore, the line passing through the line 704a-0 and the line 704c-0 (the upper end and the lower end of the line are the upper end and the lower end of the gradation patch 704, respectively) are the lines corresponding to the leftmost nozzle in the nozzle row.

The line passing through the line 704a-1 and the line 704c-1 (the upper end and the lower end of the line are the upper end and the lower end of the gradation patch 704, respectively) is the line corresponding to the second nozzle from the left end in the nozzle row.

The line passing through the line 704a-2 and the line 704c-2 (the upper end and the lower end of the line are the upper end and the lower end of the gradation patch 704, respectively) is the line corresponding to the third nozzle from the left end in the nozzle row.

The line passing through the line 704a-3 and the line 704c-3 (the upper end and the lower end of the line are the upper end and the lower end of the gradation patch 704, respectively) is the line corresponding to the fourth nozzle from the left end in the nozzle row.

Here, the difference between FIGS. 8A and 8C is that the pixel value of the reference mark line in the reference mark area 704a and the reference mark area 704c and the pixel value of the background are the reference marks for alignment. This is an inverted point so that can be identified. Here, the two gradations of FIGS. 8 (a) and 8 (b) have been described as an example, but the pixels of the gradation patch so that the reference mark for alignment embedded in each gradation patch can be identified. The gradation value is appropriately set so that the value and the pixel value of the reference mark have a contrast.

Next, the features of the test pattern according to this embodiment will be described with reference to FIG. In FIG. 10, the horizontal axis indicates the position of each nozzle in the nozzle row (position in the X direction), and the vertical axis indicates the average pixel value (average pixel value in the Y direction).

In FIG. 10A, the line segment 1001a represents the average pixel value in the section of the reference mark region 701a / 701c in the line in the gradation patch 701 of the nozzle at the position with respect to the position of each nozzle in the X direction. In FIG. 10A, the line segment 1001b represents the average pixel value in the line in the gradation patch 701 of the nozzle at the position with respect to the position of each nozzle in the X direction. In FIG. 10A, the line segment 1001c represents the average pixel value in the section of the region 701b in the line in the gradation patch 701 of the nozzle at the position with respect to the position of each nozzle in the X direction. Hereinafter, the distribution here will be referred to as a gradation value profile.

At this time, each gradation value profile has a constant value regardless of the position in the X direction, although the average pixel value in the Y direction is different. That is, the number of dots for each nozzle recorded in the gradation patch is equal. In particular, it is a feature of this embodiment that the gradation value profile of the gradation patch 701 in which the reference mark is embedded is constant, and even if the reference mark for alignment is embedded, the recording characteristics of each nozzle are acquired. , The recording amount for each nozzle can be kept constant. Therefore, the test pattern (test chart) of the present embodiment can be used for the HS processing without excluding the reference mark for alignment, as in the case of the uniform gradation patch used in the conventional HS processing. .. Moreover, since the background portion of the reference mark area is the gradation value of each gradation patch, it is possible to effectively acquire the recording characteristics from the reference mark area as well. As a result, it is possible to reduce the area occupied by the reference mark in the test pattern in the past, and improve the sujimura detection accuracy by increasing the area of the gradation pattern and the number of gradations.

In FIG. 10B, the line segment 1002a represents the average pixel value in the section of the reference mark region 702a / 702c in the line in the gradation patch 702 of the nozzle at the position with respect to the position of each nozzle in the X direction. In FIG. 10B, the line segment 1002b represents the average pixel value in the line in the gradation patch 702 of the nozzle at the position with respect to the position of each nozzle in the X direction. In FIG. 10B, the line segment 1002c represents the average pixel value in the section of the region 702b in the line in the gradation patch 702 of the nozzle at the position with respect to the position of each nozzle in the X direction.

In FIG. 10 (c), the line segment 1003a represents the average pixel value in the section of the region 703b in the line in the gradation patch 703 of the nozzle at the position with respect to the position of each nozzle in the X direction. In FIG. 10 (c), the line segment 1003b represents the average pixel value in the line in the gradation patch 703 of the nozzle at the position with respect to the position of each nozzle in the X direction. In FIG. 10C, the line segment 1003c represents the average pixel value in the section of the reference mark region 703a / 703c in the line in the gradation patch 703 of the nozzle at the position with respect to the position of each nozzle in the X direction.

In FIG. 10D, the line segment 1004a represents the average pixel value in the section of the region 704b in the line in the gradation patch 704 of the nozzle at the position with respect to the position of each nozzle in the X direction. In FIG. 10D, the line segment 1004b represents the average pixel value in the line in the gradation patch 704 of the nozzle at the position with respect to the position of each nozzle in the X direction. In FIG. 10D, the line segment 1004c represents the average pixel value in the section of the reference mark region 704a / 704c in the line in the gradation patch 704 of the nozzle at the position with respect to the position of each nozzle in the X direction.

Next, acquisition of the target characteristic in step S403 will be described with reference to FIG. In the conventional HS processing, it is premised that the sizzle is acquired with a gradation patch having a uniform gradation value. Therefore, if the input gradation value and the output gradation value are linearly designed by the gamma correction unit 304, the average value of the gradation value profile in each gradation patch itself corresponds to the target characteristic. In the present embodiment, the average value of the entire gradation patch including the reference mark area for alignment corresponds to the target characteristic.

Therefore, in step S403, the relationship between the average value of the pixel values of the entire gradation patch and the original average gradation value of the gradation patch is calculated as the target characteristic. After calculating the average value of the gradation value profile of the reference mark area for alignment, the reference mark area and gradation value for alignment are calculated from the average value of the gradation value profile in the area where the gradation value is uniform. By subtracting (removing) the average value of the reference mark area for alignment based on the relative relationship (weight) of the size of the uniform area in the Y direction, the average value of the entire gradation patch Can also be calculated.

Next, the above binary test pattern will be described. In an actual image forming apparatus, since a multi-valued test pattern is binarized and then recorded, a binary test pattern represented by on or off of dots as shown in FIG. 11 is recorded. The binary test pattern shown in FIG. 11 is a binarized version of the multivalued test pattern shown in FIG. 7 by the dither method. 1101-1104, 1101a to 1101c, 1102a to 1102c, 1103a to 1103c, 1104a to 1104c correspond to 701 to 704, 701a to 701c, 702a to 702c, 703a to 703c, 704a to 704c, respectively, in FIG.

Since the binary test pattern shown in FIG. 11 has been described by taking a test pattern having a relatively small size as an example for the sake of simplicity, it seems that the reference mark is slightly broken. However, in an actual test pattern, such a state can be avoided by securing the size of the gradation patch and the size of the reference mark as much as necessary.

However, depending on the performance of the halftone processing, the gradation value profile described in FIG. 10 may be obtained by the binary test pattern as shown in FIG. 11 due to the influence of binarizing the test pattern. The value of may fluctuate slightly. For example, when the gradation value profile of the alignment reference mark areas 701a and 701c is significantly larger than the gradation value profile of the uniform gradation value area 701b, the alignment reference mark is used. Even if the binary pattern of the reference mark areas 701a and 701c for alignment is corrected so that the gradation value profile of the regions 701a and 701c is substantially equal to the gradation value profile of the region 701b having a uniform gradation value. good. Alternatively, the binary pattern of the alignment reference mark areas 701a and 701c or the area 701b may be changed so that the number of dots in the Y direction is substantially constant for each position in the X direction. In the above description, a bright gradation has been described as an example, but it goes without saying that the binary pattern can be similarly corrected for other gradations.

It should be noted that the larger the size in the Y direction of the region where the gradation value is uniform, the higher the accuracy of sizzle detection, and the size of the test pattern and the accuracy of sizzle detection are in a trade-off relationship. For example, when giving priority to reducing the size of the test pattern over the accuracy of sizzle detection, as shown in FIG. 12, the region where the gradation value is uniform may be extremely omitted. In that case, the areas above and below the reference mark for alignment are in contact with each other. However, since the gradation value of the background of the reference mark for alignment is equal to the gradation value that should have been provided in a uniform area, the reference mark for alignment does not have to be provided in an area where the gradation value is uniform. It is possible to detect the recording characteristics of each nozzle only in the area.

As described above, according to the present embodiment, the same alignment reference mark having the same number of dots for each nozzle to be recorded is embedded at the top and bottom of the gradation patch, and each nozzle is based on the reference mark. The recording position is specified, and the recording characteristics of each nozzle are acquired using the readings in the gradation patch including the reference mark for alignment. As a result, the area occupied by the reference mark in the test pattern can be reduced, and the area of the gradation pattern and the number of gradations can be increased, thereby improving the accuracy of sujimura detection.

[Second Embodiment]
In each of the following embodiments including the present embodiment, the differences from the first embodiment will be described, and unless otherwise specified below, the same as the first embodiment. In the first embodiment, the same alignment reference mark having the same number of dots for each nozzle to be recorded is embedded above and below the gradation patch, and the recording position of each nozzle is specified based on the reference mark. Then, the mode of acquiring the recording characteristics of each nozzle by using the reading value in the gradation patch including the reference mark for alignment was described.

In this embodiment, a test pattern in which reference marks for alignment with different arrangement patterns are embedded in the upper and lower parts of the gradation patch and the number of dots for each nozzle recorded by both the upper and lower reference marks is the same will be described. .. Even if the arrangement pattern of the reference mark for alignment is different between the upper and lower parts in the gradation patch, as in the first embodiment, Y for each position in the X direction including the reference mark for upper and lower alignment. When the average value of the pixel values is taken in the direction, a test pattern having a constant gradation value is used.

An example of a test pattern (a multi-valued test pattern showing an ink value image) according to the present embodiment will be described with reference to FIG. Similar to the first embodiment, in this embodiment as well, in order to simplify the explanation, it is common to explain using a test pattern for four gradations for black ink in a recording head having 256 nozzles.

As shown in FIG. 13, gradation patches 1301 to 1304 are arranged in the Y direction (paper transport direction) in the test pattern. The gradation patch 1301 is the gradation patch with the brightest gradation, the gradation patch 1302 is the gradation patch with the second brightest gradation, and the gradation patch 1303 is the gradation patch with the third brightest gradation, the gradation patch 1304. Is the fourth brightest gradation patch. In each of the gradation patches 1301 to 1304, a region having a uniform gradation value is set as a background region, and a reference mark for alignment is superimposed on the upper end region and the lower end region of the background region.

In the present embodiment, in each gradation patch, reference marks having different arrangement patterns are provided in the reference mark area at the upper end and the reference mark area at the lower end. In the example of FIG. 13, in the gradation patch 1301, reference marks having different arrangement patterns are provided in the reference mark area 1301a and the reference mark area 1301c. Further, in the gradation patch 1302, reference marks having different arrangement patterns are provided in the reference mark area 1302a and the reference mark area 1302c. Further, in the gradation patch 1303, reference marks having different arrangement patterns are provided in the reference mark area 1303a and the reference mark area 1303c. Further, in the gradation patch 1304, reference marks having different arrangement patterns are provided in the reference mark area 1304a and the reference mark area 1304c.

Next, the reference mark region in the gradation patch will be described with reference to FIG. First, the reference mark regions 1301a and 1301c in the gradation patch 1301 of FIG. 13 will be described with reference to FIG. 14A.

In the reference mark region 1301a, the lines 1301a-0 and 1301a-2 correspond to the (N × 4) th nozzle from the left end and the (N × 4 + 2) th nozzle from the left end, respectively, in the nozzle row (N is 0). With the above integers, the left end corresponds to the 0th). In this way, in the reference mark area 1301a, a line-shaped reference mark (black line) corresponds to the even-numbered (0-start) nozzle (even-numbered nozzle) at each of the 256 nozzle positions in the X direction. ) Are provided so that they correspond to each one.

In the reference mark area 1301c, the lines 1301c-1 and 1301c-3 correspond to the (N × 4 + 1) th nozzle from the left end and the (N × 4 + 3) th nozzle from the left end, respectively, in the nozzle row (N is 0). With the above integers, the left end corresponds to the 0th). In this way, in the reference mark area 1301c, a line-shaped reference mark (black line) corresponds to the odd-numbered (0-start) nozzle (odd-numbered nozzle) at each of the 256 nozzle positions in the X direction. ) Are provided so that they correspond to each one.

That is, when both the reference mark area 1301a and the reference mark area 1301c for alignment are traced in the Y direction, one reference mark is assigned to each of the 256 nozzle positions. Is created. More specifically, when the patterns of the reference mark region 1301a and the reference mark region 1301c are compared, the patterns are formed so that the two reference marks have different phases in the X direction.

As for the pixel values of the background (1301back) other than the reference mark (black line), the reference mark area 1301a and the reference mark area 1301c all have the same gradation value (bright color) as in the first embodiment. As for the pixel value (black) of the line of the reference mark and the pixel value (gray) of the background, the contrast of the gradation value is increased so that the reference mark area for alignment can be identified.

Next, the reference mark regions 1304a and 1304c in the gradation patch 1304 of FIG. 13 will be described with reference to FIG. 14 (b). In the reference mark area 1304a, the lines 1304a-0 and 1304a-2 correspond to the (N × 4) th nozzle from the left end and the (N × 4 + 2) th nozzle from the left end, respectively, in the nozzle row (N is 0). With the above integers, the left end corresponds to the 0th). In this way, in the reference mark area 1304a, a line-shaped reference mark (black line) corresponds to the even-numbered (0-start) nozzle (even-numbered nozzle) at each of the 256 nozzle positions in the X direction. ) Are provided so that they correspond to each one.

In the reference mark region 1304c, lines 1304-1 and 1304c-3 correspond to the (N × 4 + 1) th nozzle from the left end and the (N × 4 + 3) th nozzle from the left end, respectively, in the nozzle row (N is 0). With the above integers, the left end corresponds to the 0th). In this way, in the reference mark area 1304c, a line-shaped reference mark (black line) corresponds to the odd-numbered (0-start) nozzle (odd-numbered nozzle) at each of the 256 nozzle positions in the X direction. ) Are provided so that they correspond to each one.

That is, when both the reference mark area 1304a and the reference mark area 1304c for alignment are traced in the Y direction, one reference mark is assigned to each of the 256 nozzle positions. Is created. More specifically, when the patterns of the reference mark region 1304a and the reference mark region 1304c are compared, the patterns are formed so that the two reference marks have different phases in the X direction. As in the first embodiment, in the gradation patch of the dark portion, the reference mark for alignment is white or light color so that the contrast of the gradation value becomes large.

Next, the features of the test pattern according to this embodiment will be described. The test pattern according to the present embodiment is a test pattern in which reference marks for alignment having different arrangement patterns are embedded in the upper and lower parts of the gradation patch, and the number of dots for each nozzle is the same in both the upper and lower reference marks. Therefore, as in the first embodiment, even if the reference mark for alignment is embedded, the average value of the pixel values in the Y direction is taken for each position in the X direction in any gradation patch. It is characterized by having a constant gradation value. Since the test pattern according to the present embodiment has such characteristics, as described above, when acquiring the sizzle in each gradation patch, the reference mark area for alignment is included in the attention gradation patch. The recording characteristics of the nozzle can be obtained using the readings of the entire area of. As a result, it is possible to acquire the sizzle including the reference mark area for alignment. Therefore, also in this embodiment, the area occupied by the reference mark in the test pattern is reduced, and the area and gradation of the gradation pattern are obtained. By increasing the number, it is possible to improve the accuracy of sujimura detection.

In the first embodiment, two reference marks are assigned to each nozzle position in the Y direction in each gradation patch, but in the present embodiment, two reference marks are assigned to each nozzle. Only one is provided. Therefore, the size of the reference mark region in the Y direction can be made more compact than that of the first embodiment. However, as the size of the reference mark area in the Y direction becomes smaller, the recording characteristics calculated from the background of the reference mark area, that is, the detection accuracy of the sujimura may be lowered by that amount. In such a case, the detection accuracy of the sujimura component can be improved by lengthening the length of each reference mark in the Y direction to secure the size of the reference mark region in the Y direction. As a result, the length of the reference mark in the Y direction becomes long, which has a secondary effect of improving the alignment accuracy.

Next, a method of obtaining a measurement curve for each nozzle from the test pattern according to the present embodiment will be described. For example, in the reference mark area on the upper side of the gradation patch, at an intermediate position between the m-th reference mark (position x1 in the X direction) from the left end and the reference mark (m + 1) th (m + 1) th reference mark (position x2 in the X direction) from the left end. Set the virtual reference mark A. Then, a pair is formed by the reference mark whose position in the X direction is between x1 and x2 in the reference mark region below the gradation patch and the virtual reference mark A. Similarly, in the reference mark area on the lower side of the gradation patch, the mth reference mark from the left end (position x3 in the X direction) and the reference mark (m + 1) th from the left end (position x4 in the X direction) are intermediate. Set the virtual reference mark B at the position. Then, a pair is formed by the reference mark whose position in the X direction is between x3 and x4 in the reference mark region on the upper side of the gradation patch and the virtual reference mark B. Since each pair configured in this way corresponds to each nozzle in the nozzle row, the average pixel value for each pair is obtained in the same manner as in the first embodiment, and the average pixel for each gradation patch is obtained. Find the measurement curve based on the value.

As described above, according to the present embodiment, reference marks for alignment with different arrangement patterns are embedded at the top and bottom of the gradation patch, the recording position of each nozzle is specified based on them, and the reference mark for alignment is specified. The recording characteristics of each nozzle are acquired using the readings in the gradation patch including. As a result, the area occupied by the reference mark in the test pattern can be further reduced, and the area of the gradation pattern and the number of gradations can be increased, thereby improving the accuracy of sujimura detection.

[Third Embodiment]
In the first and second embodiments, reference marks for the same or different alignment with the same number of dots for each nozzle to be recorded are embedded above and below the gradation patch, and the recording position of each nozzle is set based on them. We have described how to acquire the recording characteristics of each nozzle using the readings in the gradation patch that are specified and include the reference mark for alignment.

In this embodiment, a test pattern in which a reference mark for alignment is embedded only in one place in the gradation patch, for example, the upper side, and the number of dots for each recorded nozzle is the same will be described. Similar to the first and second embodiments, when the average value of the pixel values is taken in the Y direction for each position in the X direction including the reference mark for alignment, the gradation value is constant. It is characterized in that a standard mark is embedded in only one place in the gradation patch.

An example of a test pattern (a multi-valued test pattern showing an ink value image) according to the present embodiment will be described with reference to FIG. Similar to the first and second embodiments, this embodiment also has a common point of explaining using a test pattern for four gradations for black ink in a recording head having 256 nozzles in order to simplify the explanation. ..

As shown in FIG. 15, gradation patches 1501 to 1504 are arranged in the Y direction (paper transport direction) in the test pattern. The gradation patch 1501 is the gradation patch with the brightest gradation, the gradation patch 1502 is the gradation patch with the second brightest gradation, and the gradation patch 1503 is the gradation patch with the third brightest gradation, the gradation patch 1504. Is the fourth brightest gradation patch. In each of the gradation patches 1501 to 1504, a region having a uniform gradation value is set as a background region, and a reference mark for alignment is superimposed only on the upper end region of the background region.

The gradation patch 1501 is obtained by omitting the reference mark region 701c from the gradation patch 701. The gradation patch 1502 is obtained by omitting the reference mark region 702c from the gradation patch 702. The gradation patch 1503 is obtained by omitting the reference mark region 703c from the gradation patch 703. The gradation patch 1504 omits the reference mark region 704c from the gradation patch 704.

Next, the features of the test pattern according to this embodiment will be described. As can be seen from FIG. 15, even in the test pattern according to the present embodiment, when the average value of the pixel values in the Y direction is taken for each position in the X direction including the reference mark for alignment, it is constant. The test pattern is created so as to have the gradation value of.

Next, a method of obtaining a measurement curve for each nozzle from the test pattern according to the present embodiment will be described. In the present embodiment, unlike the first and second embodiments, the reference mark is embedded in only one place in the gradation patch. Therefore, when specifying the recording position of the nozzle from the reference mark, the reference mark of the adjacent gradation patch is used.

For example, the recording position of the nozzle in the gradation patch 1502 of FIG. 15 is specified as follows. The reference mark region 702a in the gradation patch 1502 is defined as the first region, and the reference mark region 703a in the gradation patch 1503 or the reference mark region 701a in the gradation patch 1501 is defined as the second region. Then, for each pair of reference marks corresponding to the reference mark group in the first region and the reference mark group in the second region, the position of one reference mark in the pair and the position of the other reference mark in the pair pass through. Set the line. Here, the upper end of the line of each pair is the upper end of the gradation patch 1502, and the lower end is the lower end of the gradation patch 1502. After that, in the same manner as in the first embodiment, the average pixel value is obtained for each pair, and the measurement curve is obtained based on the average pixel value for each gradation patch.

In the present embodiment, since the reference mark area is set to one place, the size of the test pattern can be made smaller than that in the first and second embodiments. As the area of the reference mark is made smaller, the signal component of the sujimura obtained from the background of the area of the reference mark is reduced. Therefore, in order to maintain the sujimura detection accuracy, a region having a uniform gradation value (region 701b in FIG. 15). The Y-direction size of 702b, 703b, 704b) may be increased.

As described above, according to the present embodiment, the reference mark is embedded in only one place in the gradation patch, the recording position of each nozzle is specified based on them, and the gradation patch including the reference mark for alignment is included. The recording characteristics of each nozzle are acquired using the readings in. As a result, the area occupied by the reference mark in the test pattern can be reduced, and the area of the gradation pattern and the number of gradations can be increased, thereby improving the accuracy of sujimura detection.

[Fourth Embodiment]
In the first to third embodiments, the same or different alignment reference marks having the same number of dots for each nozzle to be recorded are embedded in the upper and lower parts or only one place in the gradation patch, and each of them is based on them. An embodiment in which the recording position of the nozzles is specified and the recording characteristics of each nozzle are acquired by using the reading value in the gradation patch including the reference mark for alignment has been described.

In the present embodiment, reference marks for alignment designed so that the pixel values cancel each other with respect to the gradation value in the region in the gradation patch are embedded above and below the gradation patch, and each nozzle is used. The mode of the test pattern having the same number of dots will be described.

An example of a test pattern (a multi-valued test pattern showing an ink value image) according to the present embodiment will be described with reference to FIG. In this embodiment as well, as in the first to third embodiments, in order to simplify the explanation, a test pattern for black ink in a recording head having 256 nozzles is used, and the following is an example of the first floor of the bright part in the test pattern. A gradation patch with only tuning will be described. The same description can be applied to other gradation patches as well.

The gradation patch 1601 has a region 1601b having a uniform gradation value A, and reference mark regions 1601a and 1601c in which a reference mark for alignment is superimposed on a background having a gradation value A. The reference mark region 1601a is provided at the upper end of the gradation patch 1601 in the paper transport direction (Y direction). The reference mark region 1601c is provided at the lower end of the gradation patch 1601 in the paper transport direction (Y direction).

Here, the gradation value A (pixel value) in the region 1601b = 64. Further, the pixel value of the line 1603 in the reference mark area 1601a is 0. Further, the pixel value of the line 1604 in the reference mark area 1601c is 128. Line 1603 and line 1604 are lines corresponding to the same nozzle.

In such a gradation patch 1601, when the average value of the pixel values is obtained in the Y direction, the gradation value becomes equal to 64, which is the pixel value of the uniform region 1601b. That is, the average value of the pixel value "0" of the line of the reference mark area 1601a and the pixel value "128" of the line of the reference mark area 1601c becomes equal to the pixel value "64" of the area 1601b having a uniform gradation value. As a result, the pixel value is canceled.

By setting the pixel values in the alignment reference mark region to be canceled in this way, the pixel value itself in the region 1601b where the gradation value is uniform becomes the target characteristic of the gradation patch. Therefore, when a plurality of gradation patches are provided, there is an advantage that a test pattern having uniform target characteristics among gradations can be designed.

In the description of FIG. 16, only one gradation has been described, but similarly, even in a gradation patch having other gradation values, if the pixel values of the reference marks for alignment are set to cancel each other. good.

Further, if the dot ratio of the reference mark (the ratio at which the dots are turned on) is generated so as to be the dot ratio of the gradation patch (for example, the length of the dot ON and the length of the dot OFF are adjusted), the reference mark is used. The concentration does not change even if it is embedded. With such a reference mark, the influence on the reading value of the gradation patch can be minimized, so that it becomes easy to embed the required number of marks at arbitrary positions on the test pattern.

As described above, according to the present embodiment, the reference mark for alignment designed so that the pixel values cancel each other with respect to the gradation value of the region in the gradation patch at the top and bottom of the gradation patch. Is embedded, the recording position of each nozzle is specified based on them, and the recording characteristics of each nozzle are acquired using the reading value in the gradation patch including the reference mark for alignment. As a result, the area occupied by the reference mark in the test pattern can be reduced, and the area of the gradation pattern and the number of gradations can be increased, thereby improving the accuracy of sujimura detection.

[Fifth Embodiment]
In the first to fourth embodiments, the embodiment in which the reference mark is a line-shaped mark has been described. In this embodiment, an example of a test pattern using a mark other than the line-shaped mark as a reference mark will be described. As described in the first to fourth embodiments, when the average value of the pixel values is taken in the Y direction with respect to each position in the X direction including the reference mark for alignment, a constant gradation value is obtained. As long as it is a reference mark having the above, the pattern can be any shape. An example of a test pattern (a multi-valued test pattern showing an ink value image) according to the present embodiment will be described with reference to FIG.

FIG. 17A shows an example of a reference mark for alignment included in the gradation patch on the bright side in the recording head 1701 having 16 nozzles arranged in the X direction. When referring to the pixel value of the dot in the Y direction recorded by each nozzle, there are five black pixels (pixels having a specified pixel value) constituting the reference mark in each nozzle (excluding the nozzle at the end). Exists equally with.

Further, FIG. 17B shows an example of a reference mark for alignment included in the gradation patch on the dark portion side. Similar to FIG. 17A, when the pixel values of the dots in the Y direction recorded by each nozzle are referred to, there are five white pixels (pixels having a specified pixel value) constituting the reference mark in each nozzle. (Excluding the nozzle at the end), which exists equally.

As in the case of the line-shaped reference mark described in the first to fourth embodiments, even if the mark is other than the line-shaped reference mark, the reference mark for alignment is included for each position in the X direction. When the average value of the pixel values is taken in the Y direction, it has a characteristic that it has a constant gradation value.

The reference mark may be any mark as long as it satisfies the above characteristics. More specifically, at each position in the X direction, when viewed from the Y direction, a predetermined number of positions are determined, and the reference mark is folded (pasted) at those positions to form a reference mark area. Can be created. At that time, an arbitrary distance may be provided between the reference marks so that the adjacent reference marks do not overlap.

In the case of a halftone gradation patch, it may be difficult to make a difference in the contrast of the gradation value between the reference mark and the background, and it may be difficult to detect. In such a case, in order to clarify the boundary with the uniform background, the reference mark may have a gradation value different from the gradation value of the uniform background around the reference mark. Even in that case, if the average value of the pixel values is taken in the Y direction for each position in the X direction, including the reference mark for alignment, the reference mark has a constant gradation value. It should be.

Further, if the average value of the pixel values is taken in the Y direction for each position in the X direction, including the reference mark for alignment, the X has a constant gradation value. The shape of the reference mark may be different at each position in the direction.

As described above, according to the present embodiment, when the average value of the pixel values is taken in the Y direction for each position in the X direction, a reference mark having an arbitrary shape having a constant gradation value is formed. It is embedded in the gradation patch, the recording position of each nozzle is specified based on them, and the recording characteristics of each nozzle are acquired by using the reading value in the gradation patch including the reference mark for alignment. As a result, the area occupied by the reference mark in the test pattern can be reduced, and the area of the gradation pattern and the number of gradations can be increased, thereby improving the accuracy of sujimura detection.

<Modification example>
In the first to fifth embodiments, an inkjet printer is used as the image forming apparatus, but the image forming apparatus is not limited to the full-line type inkjet printer. For example, the image forming apparatus may be a so-called serial type inkjet printer that forms an image by scanning the recording head in a direction intersecting the paper transport direction. Further, the nozzle spacing in each nozzle row and the recording resolution in the paper transport direction are not limited to 1200 dpi. Similarly, the resolution of the optical reading element of the inline sensor 107 and the reading resolution in the paper transport direction are not limited to 1200 dpi.

Further, the method for forming an image is not limited to the inkjet method, and the image forming apparatus may be a printer that uses an LED or a heating element as a recording element. Specifically, the image forming apparatus is an electrophotographic printer that uses an LED array as a light source for exposure, and a sublimation printer that uses a thermal head in which minute heating elements are lined up as a heat source for vaporizing solid ink. May be.

Further, the reference marks described in the first to fifth embodiments do not have to be applied to all the gradations in the test pattern, and are necessary for tracing the nozzle position due to the characteristics of the position shift due to the transfer of paper or the like. Deformation such as applying only to the gradation patch formed at a suitable position is also possible.

The numerical values, processing timings, processing orders, etc. used in the above description are given as an example for specific explanation, and are not intended to be limited to this example.

In addition, some or all of the above-described embodiments may be used in combination as appropriate. Further, a part or all of each of the above-described embodiments may be selectively used.

(Other embodiments)
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.

The invention is not limited to the above embodiment, and various modifications and modifications can be made without departing from the spirit and scope of the invention. Therefore, a claim is attached to publicize the scope of the invention.

301: Color conversion unit 302: Color separation unit 303: HS unit 304: Gamma correction unit 305: Quantization unit

Claims (14)

A first acquisition means for acquiring an image obtained by reading a printed matter obtained by printing a test pattern including patches having different gradations using a plurality of recording elements.
The average pixel value including the pixel value corresponding to the position of the reference mark in the patch is acquired for each patch in the image, and the recording characteristics of the recording element are obtained based on the average pixel value acquired for each patch in the image. An image processing apparatus including a second acquisition means for acquiring the image. The one-sided end region of the patch is the first end region, the other end region is the second end region, and the first end region and the second end region are each the plurality. The image processing apparatus according to claim 1, wherein a reference mark corresponding to each of the recording elements of the above is provided. The arrangement pattern of the reference mark in the first end region and the arrangement pattern of the reference mark in the second end region are the same.
The image processing apparatus according to claim 2, wherein each reference mark in the first end region and each reference mark in the second end region correspond to each of the plurality of recording elements. The arrangement pattern of the reference mark in the first end region is different from the arrangement pattern of the reference mark in the second end region.
Each reference mark in the first end region corresponds to an even-numbered recording element from one end in the plurality of recording elements.
The image processing apparatus according to claim 2, wherein each reference mark in the second end region corresponds to an odd-numbered recording element from one end in the plurality of recording elements. The second aspect of the present invention is characterized in that the average pixel value of the pixel value of the reference mark in the first end region and the pixel value of the reference mark in the second end region is the background pixel value in the patch. The image processing device described. The one-sided end region of the patch is the first end region, the other end region is the second end region, and the first end region is a reference corresponding to each of the plurality of recording elements. The image processing apparatus according to claim 1, wherein a mark is provided and the reference mark is not provided in the second end region. The image processing apparatus according to any one of claims 1 to 6, wherein the reference mark is a line along a transport direction at the time of printing the test pattern. The reference mark is characterized in that the number of pixels having a specified pixel value in the transport direction at the time of printing the test pattern is the same for each recording element. The image processing apparatus according to any one of the following items. The image processing apparatus according to any one of claims 1 to 8, wherein the patches having different gradations are arranged in the transport direction at the time of printing the test pattern. The image processing apparatus according to any one of claims 1 to 9, wherein the number of dots for each recording element recorded in the patch is the same. In addition,
The image processing apparatus according to any one of claims 1 to 10, further comprising means for correcting the pixel value of a pixel in an input image based on the recording characteristics of the recording element corresponding to the pixel. It is an image processing method performed by an image processing device.
A first acquisition step of acquiring an image obtained by reading a printed matter in which a first acquisition means of the image processing apparatus prints a test pattern including patches having different gradations using a plurality of recording elements.
The second acquisition means of the image processing device acquires the average pixel value including the pixel value corresponding to the position of the reference mark in the patch for each patch in the image, and the average acquired for each patch in the image. An image processing method comprising a second acquisition step of acquiring the recording characteristics of a recording element based on a pixel value. It is a test pattern that includes patches with different gradations.
The patches having different gradations are arranged in the transport direction at the time of printing the test pattern.
A reference mark corresponding to each of the plurality of recording elements for printing the test pattern is provided in the one-sided end region and / or the other-side end region of the patch.
A test pattern characterized in that the number of dots for each recording element recorded in the patch is equal. A computer program for making a computer function as each means of the image processing apparatus according to any one of claims 1 to 11.

Images