JP2008035511A - Image processing device, image processing method, and image processing program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent smashing of the fine portions of a letter due to the blur of ink by changing the gray in the edge portions of characters to a white side by image correction, if the gray density in the edge portions of the characters uses the ink in large quantities. <P>SOLUTION: An image processing device for an image constituted of a signal in at least one color and a plurality of pixels includes a corrected density acquiring means for acquiring the density after correction processing; a correction coefficient change means for changing a correction coefficient from a density value acquired by the corrected density acquiring means; an image correcting means for performing correction, by using the correction coefficient changed by the correction coefficient change means; and an image recording processing means for performing recording processing for the image corrected by the image correcting means, where the deterioration in the reproduction of edge portions due to recording device characteristics is reduced. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image processing apparatus that performs image correction on digitized image data and records the image data.

  The image copying apparatus includes an input device unit and an output device unit. An input document is optically read by a scanner which is an input device unit, subjected to predetermined image processing, and then printed by a predetermined recording method in an output device unit.

  The edge (contour) part of the image (multi-valued data) optically read by the scanner has a gentler density change compared to the edge part of the original image, and the sharpness is lost if printing is performed directly on the recording medium. It was an image.

  Conventionally, when the distribution shape of the image signal at the point of interest is convex upward, it is converted to an image enhancement signal larger than the image signal at the point of interest, and when it is convex downward, There is a technique for converting the image signal into a smaller image enhancement signal than the image signal in FIG. Then, there is a technique for converting to an original image signal or a signal replaced with an unsharp signal when neither convex upward nor convex downward (for example, Patent Document 1).

  In addition, there is a technique for replacing the value of the target pixel with a replacement pixel value generated using the target pixel of the image and a pixel adjacent to the target pixel (for example, Patent Document 2).

  Furthermore, not only the above-mentioned sharpness but also a method for avoiding the problem by changing the resolution of the data input device or the output device for the problem of missing dots or thin lines disappearing at the time of reduction (for example, Patent Document 3). ).

In addition, there is a technique in which an image magnification and an outline width can be freely adjusted (for example, Patent Document 4). For example, when the user enlarges or reduces the size, the width of the contour is changed, which is effective in suppressing the occurrence of a defect in the image of the edge portion due to scaling.
Japanese Patent No. 0620368 JP 07-288768 A Japanese Patent Laid-Open No. 2004-056252 Japanese Patent Laid-Open No. 10-200733

  However, performing the edge emphasis by the above-described method does not necessarily improve the output image quality.

  An example of a thick character is shown in FIG. The left side of the figure is a document, and the edge portion is blurred. The right side of the figure shows an image obtained by reading this image and outputting an image in which edge enhancement is performed on the pixels in the blurred portion by the recording apparatus. In the figure on the right, the details of the recorded characters are crushed and the legibility is poor. This problem is noticeable when a thick character is read as a character type or in a kanji manuscript with complicated characters.

  In addition, ink jet printers, which are beginning to become popular recently, cause further ink bleeding, which is a serious problem. Ink bleeding is affected by the characteristics of the ink and the characteristics of the recording medium. Therefore, even if the same printer device is used, the difference between the ink and the recording medium and the combination thereof vary. Therefore, there is a method of performing correction in consideration of the bleeding rate in advance in the combination, but there are cases where that alone is insufficient.

  The ink jet recording system has been made multi-colored with an increase in image quality. As a result, there are now few cases where only a single ink such as black ink is mounted, and even when copying a single document, it is common to use several types of ink. This is also true when copying a monochrome copy or a monochrome manuscript, and as a result a monochrome printed matter is obtained, but it is not uncommon to record with a so-called process color combining color inks.

  FIG. 13 shows an example of using a gray line ink using four color inks of cyan (C), magenta (M), yellow (Y), and black (K), but the highlight portion reduces graininess. It can be seen that, for adjusting the hue of gray and gray, the ink is composed of three colors of cyan, magenta, and yellow, and the black ink is gradually used. In addition, the total amount of ink is also shown. This represents the amount of ink applied on the paper. The total amount of ink increases as the density increases from the highlight, and decreases when it is replaced with black ink. FIG. 14 is a diagram in which a fine gray line gradation is recorded by this ink usage method. It can be seen that in conjunction with the increase in the total amount of ink, the fine line blur becomes noticeable in the middle (near the density 192). In other words, even if the bleeding rate is corrected only by a combination of the ink and the recording medium, the total amount of ink is not taken into consideration, so that preferable edge enhancement cannot always be realized. In particular, when scanned by a scanner, the original may be halftone, or may be transmitted due to an excessive amount of irradiation light compared to the paper thickness of the original, resulting in a decrease in image density. In such a case, if the character portion has a high ink density and a high bleeding rate, there is a problem that the readability of the recorded character is deteriorated. Furthermore, if it is a reduced copy, the output product will be less legible and will have serious consequences.

  In addition, in an ink jet recording device, it is also possible to increase the number of nozzles that discharge black ink more than color and to increase the speed by using the nozzles in monochrome printing. In that case, even in color printing, the read image as shown in FIG. 15 is determined in a certain region (called a band) in the main scanning direction, and when it is determined as a monochrome band, only black ink is used. If this is not the case, there is a method of recording with normal color or a combination of color and black ink. In this process, in addition to correction of the bleeding rate by density, it is necessary to consider the bleeding rate of the ink used according to the determination result for each band.

  In the above-described conventional technology, no solution to the problem due to the characteristics of the recording apparatus is mentioned. Also, other literatures do not disclose prevention of edge deterioration by such an ink usage method.

The present invention has been made to solve the above-described problems,
In an image processing apparatus for an image composed of at least one color signal and a plurality of pixels,
Correction density acquisition means for acquiring density after correction processing;
Correction coefficient changing means for changing a correction coefficient from the density value acquired by the correction density acquisition means;
Image correction means for correcting with the correction coefficient changed by the correction coefficient changing means;
Image recording processing means for executing recording processing on the image corrected by the image correcting means;
And reproducibility deterioration of the edge due to the characteristics of the recording apparatus.

Also,
In an image processing apparatus for an image composed of at least one color signal and a plurality of pixels,
Ink color determination processing means for determining the ink color to be used from the value of the signal;
Correction density acquisition means for acquiring density after correction processing;
Correction coefficient changing means for changing a correction coefficient from the used ink information determined by the ink color determination processing means and the density value acquired by the correction density acquisition means;
Image correction means for correcting with the correction coefficient changed by the correction coefficient changing means;
Image recording processing means for executing recording processing on the image corrected by the image correcting means;
And reproducibility deterioration of the edge due to the characteristics of the recording apparatus.

  According to the present invention, the above-described problems are solved, and the ink bleeding of the ink jet recording apparatus is corrected for each density, so that more accurate correction can be realized and a good edge portion can be reproduced.

  Further, even when monochrome / color determination processing is performed and the ink used is switched for speeding up, proper correction processing can be realized with each ink.

  Further, even when zooming is set such as reduced copy, it is possible to suppress the collapse of characters due to reduction. As a result, it is possible to provide the user with higher character reproducibility and legibility.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  In the description of the embodiment of the present invention, the copy function of the multifunction printer apparatus will be described as an example. However, the present invention is not limited to this. Data sent from a computer apparatus (hereinafter referred to as a PC) can be transferred to the multifunction printer apparatus or printer apparatus. Even when printing with.

<MFP device>
1 is an overview perspective view of a multifunction printer apparatus (hereinafter, MFP apparatus) 1 according to an embodiment of the present invention. The MFP apparatus 1 has a function as a normal PC printer that receives data from a host computer (PC) and prints it, and a function as a scanner. It has a copy function for printing an image with a printer, a function for directly reading and printing image data stored in a storage medium such as a memory card, or a function for receiving and printing image data from a digital camera.

  In FIG. 1, an MFP apparatus 1 includes a reading device 34 such as a flat bed scanner, a printing device 33 using an ink jet method or an electrophotographic method, and an operation panel 35 including a display panel 39 and various key switches. In addition, a USB port (not shown) for communicating with the PC is provided on the rear surface of the MFP apparatus 1, and communication with the PC is performed. In addition to the above configuration, a card slot 42 for reading data from various memory cards, a camera port 43 for data communication with a digital camera, and an auto document feeder (hereinafter referred to as ADF) 31 for automatically setting a document on a document table Thus, the MFP apparatus 1 is configured.

  In FIG. 2, the CPU 11 controls various functions provided in the image processing apparatus, and executes an image processing program stored in the ROM 16 in accordance with a predetermined operation of the operation unit 15.

  A reading unit 14 having a CCD corresponds to the reading device 34 in FIG. 1, reads a document image, and outputs analog luminance data of red (R), green (G), and blue (B) colors. Note that the reading unit 14 may include a contact image sensor (CIS) instead of the CCD. Further, if the ADF 31 as shown in FIG. 1 is provided, the order sheets can be read continuously, which is more convenient.

  The card interface 22 also corresponds to the card slot 42 in FIG. 1, and for example, image data shot with a digital still camera (hereinafter referred to as DSC) and recorded on a memory card or the like is transferred in accordance with a predetermined operation of the operation unit 15. Read. Note that the color space of the image data read via the card interface 22 is changed from a DSC color space (for example, YCbCr) to a standard RGB color space (for example, NTSC-RGB or sRGB) by the image processing unit 12 if necessary. ). Also, based on the header information, the read image data is subjected to various processes necessary for the application such as resolution conversion to the effective number of pixels as necessary.

  The camera interface 23 also corresponds to the camera port 43 of FIG. 1 and is used for reading image data by directly connecting to the DSC.

  The image processing unit 12 performs image processing such as image conversion of read signal values, image correction / processing processing, conversion from a luminance signal (RGB) to a density signal (CMYK), scaling, gamma conversion, and error diffusion, which will be described later. The data thus obtained is stored in the RAM 17. When the correction data stored in the RAM 17 reaches a predetermined amount necessary for recording by the recording unit 13 corresponding to the printing apparatus 33 in FIG. 1, the recording operation by the recording unit 13 is executed.

  The nonvolatile RAM 18 is a battery-backed SRAM or the like, and stores data unique to the image processing apparatus. The operation unit 15 corresponds to the operation panel 35 of FIG. 1, selects image data stored in a storage medium (memory card), and prints a photo direct print start key for starting recording and an order sheet. Key, key to read order sheet, copy start key for monochrome copy or color copy, mode key to specify mode such as copy resolution and image quality, stop key to stop copy operation, etc. It consists of a numeric keypad and a registration key. The CPU 11 detects the pressed state of these keys and controls each part according to the state.

  The display unit 19 corresponds to the display panel 39 in FIG. 1, and includes a dot matrix type liquid crystal display unit (LCD) and an LCD driver, and performs various displays based on the control of the CPU 11. Also, thumbnails of the image data recorded on the storage medium are displayed. The recording unit 13 corresponds to the printing apparatus 33 of FIG. 1 and is configured by an inkjet type inkjet head, a general-purpose IC, and the like, and reads the recording data stored in the RAM 17 under the control of the CPU 11 and prints it out as a hard copy.

  The drive unit 21 includes a stepping motor for driving the paper supply / discharge roller, a gear for transmitting the driving force of the stepping motor, and a driver circuit for controlling the stepping motor in the operations of the reading unit 14 and the recording unit 13 described above. Etc.

  The sensor unit 20 includes a recording sheet width sensor, a recording sheet presence sensor, a document width sensor, a document presence sensor, a recording medium detection sensor, and the like. The CPU 11 detects the state of the original and the recording paper based on information obtained from these sensors.

  The PC interface 24 is an interface between the PC and the MFP apparatus 1, and the MFP apparatus performs operations such as printing and scanning from the PC via the PC interface 24.

  During the copying operation, the image data read by the reading device 34 is processed in the MFP device and printed by the printing device 33.

  When a copy operation is instructed by the operation unit 15, the reading unit 14 reads a document placed on the document table. The read data is sent to the image processing unit 12, subjected to image processing to be described later, and then sent to the recording unit 13 for printing.

<Image processing>
FIG. 3 is a flowchart of image processing executed at the time of copying. In the following, description will be given for each step, but details of processing methods that are not the essence of this proposal will be omitted.

  The data read and AD-converted by the reading unit 14 is subjected to shading correction for correcting variation of the image pickup device in STEP301.

  Thereafter, input device conversion is performed in STEP 302. As a result, the device-specific signal data is converted into standard color space regions such as sRGB defined by IEC (International Electrotechnical Commission) and Adobe RGB proposed by Adobe Systems. . Examples of the conversion method include a calculation method using a 3 × 3 or 3 × 9 matrix, a lookup table method in which a table describing conversion rules is referenced and determined based on the table.

  The converted data is corrected and processed in STEP 303. Examples of processing contents include edge enhancement processing that corrects blurring due to reading, character processing processing that improves character readability, and processing that removes show-through caused by reading by light irradiation. It is desirable to execute the processing that characterizes the proposal in this step.

  In STEP 304, enlargement / reduction processing is executed, and the magnification is converted to a desired magnification by the case where scaling is designated by the user or by allocation copying in which two originals are assigned to one sheet of paper. As a conversion method, methods such as bicubic and nearest neighbor are common.

  In STEP 305, data in a standard color space is converted into signal data unique to the output device. The present embodiment is an inkjet MFP apparatus, and in this case, conversion processing into ink color data such as cyan, magenta, yellow, and black is executed. For this conversion, a method similar to STEP 302 may be used.

  Further, in STEP 306, conversion to the number of recordable levels is performed. For example, if the ink dot is expressed with a binary value of whether or not the ink dot is applied, it may be binarized in a quantization method such as error diffusion. As a result, a data format that can be recorded by the printer is obtained, and a recording operation is executed based on the data format to form an image.

<Processing unit>
FIG. 4A is a diagram for explaining a processing unit when the processing that is the feature of the present proposal is performed.

  If a pixel marked with a circle in FIG. 4A is a target pixel (processing target pixel), an area composed of 7 × 7 pixels including the target pixel as shown by a thick line in FIG. 4A (7 × 7 area) Set. Image processing for the target pixel is executed using the image signal in the set 7 × 7 region. After the processing of the target pixel is executed, a pixel adjacent to the target pixel is set as the next target pixel, for example, a pixel marked with X in FIG. 4B, and the 7 × 7 region is set as described above. Set and execute image processing. Thereafter, similarly, the target pixel is sequentially moved one pixel at a time, and all the target pixels are corrected by setting a 7 × 7 area each time.

  FIG. 5 is a diagram for explaining the movement flow of processing units. STEP 501 is a processing target setting. Immediately after START, the first processing target is set. When returning from STEP 503 to STEP 501, the next processing target is set.

  STEP 502 is an image processing execution unit. Although details will be described later, a plurality of pixels including a processing unit (7 × 7 region in the above description) are set as described above, and image processing that is a feature of this specification is executed.

  STEP 503 is a final correction target determination. It is determined whether the processing unit is the last processing unit. If it is not the last processing unit (NO), return to STEP501. If it is the last processing unit (YES), it becomes END.

  In the CCD or CIS image sensor used in the reading device 34 described in FIG. 1 and the reading unit 14 in FIG. 2, one pixel does not always read one pixel equivalent of a document. In this embodiment, it is assumed that approximately 6 pixel ranges of a document are read. Even if the number of pixels is six, the reflected light from the document incident on the image sensor is variously affected by the float of the document from the document table, the unevenness of the document, and the like. Therefore, in practice, a range exceeding 6 pixels may be read. That is, the reflected light of one pixel of the original document affects a plurality of image sensors, which causes the blurring of the edge described in the background art and deteriorates the sharpness. In this embodiment, since the reading range is approximately 6 pixels, a 7 × 7 reference area is used. The reference area may be set as appropriate according to the number of pixels of the image sensor affected by one pixel of the document image, the spot diameter, the number of blurred pixels, the performance of the image sensor, such as MTF.

<Definition of words>
Here, in the description of the following examples, definitions and limitations of words are described below.

  The fluctuation information indicates the state of luminance change in the region of interest, and is represented by the number of fluctuations and the fluctuation amount described below.

  The number of fluctuations is described as the number of sign changes (the number of zero crossings) of signal value increase / decrease in the luminance change in the region, but is not limited to this, and is one of the values related to the image signal in the region of interest. It is defined as a value expressing the frequency of change of values related to the image signal, such as the number of zero-crossing points of the second derivative, the spatial frequency, and the number of changes in black and white after binarization.

  The fluctuation amount is described as the absolute value (edge amount) of the difference in luminance with respect to the pixel of interest, but is not limited to this, and is the absolute value of the first derivative of the value related to the image signal of the pixel of interest. It is defined as a value representing a difference (magnitude) of change, or a value representing a difference (magnitude) of change of a value related to the image signal in the region of interest.

  The variable acceleration is described as a value obtained by further taking a difference from the luminance difference in the region of interest in the following embodiment, but is not limited thereto, and is a value related to the image signal in the region of interest. It is defined as a value that expresses the acceleration of change, such as the second derivative of.

  The adaptively setting the correction strength means that the correction strength that differs for each value in each of the value regions that can be taken for the defined number of fluctuations, fluctuation amount, fluctuation acceleration, and saturation. Is defined to be set.

  Details of the examples will be described below. The range that the image signal can take will be described by taking 0 to 255 as an example. However, the range of the image signal is not limited to this, and may be set to be suitable for the MFP apparatus and image processing.

<Embodiment 1>
In the first embodiment, an example will be described in which the above-described problems are solved, and the edge deterioration is suppressed in consideration of the bleeding rate for each density.

  In the first embodiment, when printing is performed with a color having a large total amount of ink, ink bleeding becomes large, the edge portion is crushed, and the image deteriorates. Therefore, control is performed to prevent this.

  Possible control for edge deterioration prevention is to obtain the density corresponding to the brightness of the pixel after edge enhancement correction once, and perform edge enhancement correction so that the density of the ink is small in the vicinity of the density where the total amount of ink is large. This is a method of recalculation. However, in this control, since it is necessary to redo the calculation for edge enhancement correction, the amount of calculation increases and the time required for edge enhancement correction increases. Therefore, in this embodiment, instead of directly calculating the pixel density after the edge enhancement correction, the maximum luminance value and the minimum luminance value of the pixels arranged in the edge direction among the pixels in the predetermined range centered on the target pixel are obtained, The minimum luminance value is approximately the luminance of the pixel after edge enhancement correction. If the minimum luminance value is in the vicinity of the luminance corresponding to the density at which the total amount of ink increases, the edge enhancement condition is changed so that the target pixel is corrected to the maximum luminance value side at the time of edge enhancement correction.

  The following description is about a flowchart having the edge enhancement correction and the edge deterioration suppression control. However, if the increase in the amount of computation is not minded, the density corresponding to the luminance of the pixel after the edge enhancement correction is once obtained so that the density of the total ink amount is small in the vicinity of the density where the total ink amount is large. The edge enhancement correction may be recalculated.

  FIG. 16 shows a flowchart in the present embodiment. Hereinafter, the description will proceed along the steps described in the flowchart.

<STEP 1601: Processing Area Setting>
In an image composed of RGB multi-valued image signals, a processing area of 7 × 7 area composed of 7 pixels in the horizontal direction and 7 pixels in the vertical direction with the pixel of interest as the center is set, Luminance L is calculated according to equation (1), and a 7 × 7 processing region of L is generated.
L = (R + 2 × G + B) / 4 Formula (1)
Although the present embodiment uses the luminance L calculated by Expression (1), other luminance may be applied. For example, L * in the uniform color space L * a * b * may be the luminance, and Y of YCbCr may be the luminance.

  FIG. 8A1 shows the luminance when the black vertical line in the white background is read in the horizontal direction. FIG. 8A2 shows the luminance when the halftone dots arranged in the horizontal direction in the white background are read in the horizontal direction. For ease of explanation, FIG. 8 uses 12 pixels instead of 7 pixels.

<STEP 1602: Extraction in 4 directions>
As shown in FIG. 9, 7 pixels each in a total of 4 directions of 1 horizontal direction, 1 vertical direction, and 2 diagonal directions are extracted from the L processing region generated in STEP 1601.

<STEP1603: L difference calculation>
A difference Grd of L of 5 pixels in each direction is calculated from L in 4 directions extracted in STEP 1602 as shown in FIG. 10 and Expression (2). Here, the front pixel of the pixel L (i) is L (i−1), and the rear pixel is L (i + 1).
Grd (i) = L (i + 1) −L (i−1) (2)
The method of calculating the L difference is not limited to this, and may be a difference between adjacent pixels or a difference between pixels further away from the preceding and following pixels described above.

  8 (b1) and FIG. 8 (b2) show Grd obtained by applying Expression (2) to L in FIGS. 8 (a1) and 8 (a2), respectively.

<STEP 1604: Edge Direction Determination>
In the Grd in the four directions calculated in STEP 1603, the Grd absolute values in the four directions of the target pixel are obtained. Of the Grd absolute values in the four directions, the direction having the maximum Grd absolute value is determined as the edge direction of the target pixel.

<STEP 1605: Fluctuation Calculation>
For the edge direction determined in STEP 1604, the maximum absolute value is calculated as the variation amount (edge amount) of the target pixel from the five Grd pixels in the edge direction calculated in STEP 1603. The larger the fluctuation amount, the stronger the edge, and the weaker the fluctuation amount, the closer to the flatness.

<STEP 1606: Fluctuation count calculation>
The total number of changes in the four directions is calculated from the Grd in the four directions calculated in STEP 1603. In this embodiment, the number of times the sign of Grd changes from + to − or − to +, and the number of times the sign of Grd changes from + to 0 and the next pixel from − or − to 0 and the next pixel to + The number of fluctuations (number of zero crossings) is calculated.

<STEP 1607: Maximum / Minimum Luminance Position Determination>
Regarding the edge direction determined in STEP 1604, the pixel positions of the maximum L and the minimum L are determined from the seven pixels of L in the edge direction among the four directions extracted in STEP 1602.

<STEP 1608: Fluctuation acceleration calculation>
For the edge direction determined in STEP 1604, the fluctuation acceleration Lap of 3 pixels is calculated from the Grd in the edge direction calculated in STEP 1603. The calculation method of the fluctuation acceleration is Expression (3). However, the front pixel of the pixel Grd (i) is Grd (i−1) and the rear pixel Grd (i + 1). FIGS. 8 (c1) and 8 (c2) show Laps obtained by applying Equation (3) to Grd in FIGS. 8 (b1) and 8 (b2), respectively.
Lap (i) = Grd (i + 1) −Grd (i−1) (3)
The method for calculating the fluctuation acceleration is not limited to this, and a difference between adjacent Grds may be used.

<STEP 1609: Correction Value Setting Based on Density>
In this step, the Lap (i) value obtained in STEP 1608 is changed based on the density after recording, thereby performing processing for improving the reproducibility of the edge on the output image. The correction method is shown in equation (4). This is realized by subtracting the correction value BLUR from the value of Lap (i) obtained in STEP 1608 to update Lap (i) to Lap ′ (i). Here, since the correction value BLUR is a value determined in advance according to the luminance, it is described as BLUR (luminance) below. In this embodiment, BLUR (luminance) values corresponding to the respective luminance values are stored in a table.
Lap ′ (i) = Lap (i) −BLUR (luminance) (4)
Hereinafter, the correction value BLUR (luminance) will be described. Note that if this correction value is a large value, Lap ′ (i) becomes a small value, so that it is easy to be corrected to the minimum luminance side in STEP1610 described later, and the edge portion tends to become white.

  Here, the features of the present embodiment will be described. In this embodiment, for the edge enhancement, the replacement pixel position is determined in S1610, which will be described later, but the maximum or minimum L pixel is selected as the replacement pixel position. When the minimum L is selected in S1610, when the strongest correction is applied by the intensity setting in S1611 to S1613 described later, the target pixel is replaced with the value of the minimum L pixel. As can be seen from FIG. 13, in this embodiment, the point where the total amount of ink is maximized is on the higher density side. In other words, the point where the total amount of ink is maximized is on the low luminance side. If the pixel of interest is replaced with the value of the pixel of the minimum L and the minimum L is the luminance that maximizes the total amount of ink, the pixel of interest is recorded with the maximum density of the total amount of ink with a large bleeding rate. Similarly, if the replacement pixel position is determined to be the minimum L, the minimum L is the luminance in the vicinity of the maximum point of the total ink amount, and the correction intensity in S1611 to S1613 is close to the maximum, the target pixel after the edge enhancement correction Is a value in the vicinity of the minimum L. Therefore, in this embodiment, the minimum L is approximately used as the luminance of the target pixel after the edge enhancement correction. That is, in this embodiment, the method for acquiring the density of the target pixel after the edge enhancement correction is to obtain the minimum L. If the density of the pixel of interest after the edge enhancement correction is in the vicinity of the maximum point of the total ink amount, the density is recorded with a high blurring rate. To prevent this, the replacement pixel position by the edge enhancement correction is changed to the maximum L. Then, the target pixel is replaced with the maximum L. The processing for this is S1608, which can be realized by determining the value of BLUR (luminance) as shown in FIG.

  FIG. 6 shows an example of the correction value BLUR (luminance) table. In the graph, the horizontal axis represents the luminance, and the vertical axis represents the BLUR (luminance) value which is a correction value corresponding to each luminance. The recording apparatus is an ink jet recording apparatus equipped with four colors of cyan, magenta, yellow, and black described in the prior art, and the table example is based on the method of creating the gray line described in FIG. . Here, the gray line is a gray line (band) recorded by changing the density continuously from a low density (white) to a high density (black) in the mixed colors of the four colors in FIG. The minimum L in the edge direction acquired in STEP 1607 is the luminance on the horizontal axis in FIG. Then, as indicated by point A in FIG. 6, the density corresponding to the luminance having a large BLUR (luminance) value has a high bleeding rate, as will be described later. In other words, the BLUR (luminance) value, which is a correction value, is increased at a luminance with a high ink bleeding rate. This is because if the minimum L determined in STEP 1607 is the luminance near the point A in consideration of recording the edge portion of the character, if the minimum L pixel is selected as the replacement pixel position in STEP 1610 described later, The corrected pixel is recorded with a density near a high bleeding rate, and the edge is blurred and the character is easily crushed. Therefore, by increasing BLUR (brightness), the edge portion of the character portion is corrected to become white by STEP1611 described later, and deterioration of the character due to ink bleeding is prevented.

  The BLUR (brightness) table is obtained by outputting a fine gray gradation image as shown in FIG. 7A by the recording apparatus and obtaining an output result as shown in FIG. 7B. This is scanned and obtained as a digital value, and the number N of pixels corresponding to the distance of the point where the density is reduced by a certain ratio from the central density value may be obtained. In the present application, the number N of pixels is referred to as ink bleeding rate. When the density is high, N increases, and when the density is low, N decreases. The correction value BLUR (luminance) may be set while referring to the value of N for each predetermined density.

  The correction value BLUR (brightness) table may be stored in advance in the ROM of the copying apparatus. However, a user interface is used to output a predetermined pattern as shown in FIG. 7 and guide the user to perform scanning. It is good. As a result, it is possible to absorb variations in ink ejection of the recording apparatus, and to provide a high-quality output by the user.

<STEP 1610: Replacement Pixel Position Determination>
The replacement pixel position is determined from the maximum L and minimum L pixel positions determined in STEP 1607 and the fluctuation acceleration Lap ′ calculated in STEP 1609. When the sign of Lap is + as in (c1) and (c2) of FIG. 8, the value of the target pixel L is closer to the minimum L than the maximum L, and when the sign of Lap is-, the target pixel L tends to be closer to the maximum L than the minimum L. Therefore, as shown in Table 1, the target pixel can be replaced with an appropriate replacement target pixel by determining the replacement pixel position with respect to the sign of Lap ′.

  In this embodiment, the replacement pixel position is determined as shown in Table 1. However, the handling of the edge center where the Lap ′ of the target pixel is 0 is not limited to Table 1, and the Lap ′ of the target pixel is 0. For example, the maximum L pixel position may be used, and conversely, the minimum L pixel position may be set. Further, although the maximum L and minimum L pixel positions in the edge direction are used, the maximum L and minimum L around the target pixel may be set without considering the edge.

<STEP 1611: Replacement intensity setting based on the fluctuation acceleration absolute value>
The replacement strength Cl is adaptively set according to the absolute value of the fluctuation acceleration calculated in STEP 1608. FIG. 19C can be obtained by setting Cl = 1 regardless of the absolute value of the fluctuation acceleration. However, jaggies may be conspicuous if Cl = 1 is always set. Therefore, here, a description will be given of a replacement example in which the edge can be emphasized more than in FIG. FIG. 20A is a diagram for explaining the Cl setting in STEP 1611. The horizontal axis indicates the variable acceleration absolute value, and the vertical axis indicates Cl. In the case of a fluctuating acceleration smaller than the ninth threshold value near the edge center, Cl is set to 0 so as not to be replaced. Setting so as not to replace the vicinity of the edge center is intended to make the occurrence of jaggy inconspicuous. If the absolute value of the fluctuation acceleration is larger than the tenth threshold value away from the edge center, Cl is set to 1 for replacement. In the case of a variable acceleration absolute value that is greater than or equal to the ninth threshold value and less than or equal to the tenth threshold value, Cl = 0 when the variable acceleration absolute value = the ninth threshold value, Different Cl is adaptively set for each variable acceleration absolute value so that Cl = 1. Specifically, it can be set adaptively by referring to FIG. 20A or the following equation (5).
Cl = (variable acceleration absolute value−9th threshold value) / (10th threshold value−9th threshold value) Expression (5)

<STEP 1612: Replacement intensity setting based on the number of fluctuations>
The replacement strength Cz is adaptively set according to the number of fluctuations calculated in STEP 1606. Using the eleventh threshold and the twelfth threshold, Cz is adaptively set with the characteristics shown in FIG. When the number of fluctuations is a thick line smaller than the eleventh threshold, Cz = 1, for thin lines and halftone dots larger than the twelfth threshold, Cz = 0, and when equal to or greater than the eleventh threshold and equal to or smaller than the twelfth threshold, the equation (6) is applied. Can be set automatically.
Cz = (12th threshold value−number of fluctuations) / (12th threshold value−11th threshold value) Expression (6)

<STEP 1613: Replacement intensity setting based on variation>
The replacement strength Ce is adaptively set according to the fluctuation amount calculated in STEP 1605. Using the thirteenth and fourteenth thresholds, Ce is adaptively set with the characteristics shown in FIG. When the fluctuation amount is smaller than the thirteenth threshold value, Ce = 0, when it is larger than the fourteenth threshold value, Ce = 1, and when it is greater than or equal to the thirteenth threshold value and less than or equal to the fourteenth threshold value, it can be set adaptively by equation (7).
Ce = (variation amount−13th threshold) / (14th threshold−13th threshold) Expression (7)

<STEP 1614: Substitution amount calculation>
The replacement amount is calculated using the pixel value at the replacement pixel position determined in STEP1610. The RGB value at the replacement pixel position determined in STEP 1610 is extracted from the RGB 7 × 7 region set in STEP 1601. If the target pixel value is N0, the pixel value at the replacement pixel position is C0, and the replacement amount is ΔC, ΔC can be calculated using Equation (8).
ΔC = C0−N0 (8)

<STEP1615: Replacement amount correction>
The replacement amount ΔC calculated in STEP 1614 is corrected with the replacement strengths Ce, Cl, and Cz set in STEP 1611 to 1613. The corrected replacement amount ΔC ′ is calculated using equation (9).
ΔC ′ = Ce × Cl × Cz × ΔC (9)

<STEP 1616: Replacement Processing>
By adding the replacement amount ΔC ′ calculated in STEP 1615 to the target pixel value N0 as shown in Expression (10), the target pixel value Nc with edge enhancement by replacement is calculated.
Nc = N0 + ΔC ′ (10)

  As described above with reference to the processing flow, according to the first embodiment of the present invention, the blurring rate for each ink density is taken into consideration and reflected in the replacement process, which is particularly likely to occur in an inkjet MFP. It is possible to suppress crushing due to blurred characters and provide a more suitable image to the user.

  If the increase in the amount of computation is not concerned, the following may be performed. First, in the first edge enhancement correction, BLUR (luminance) is calculated as 0 in equation (4) of S1609 up to S1616 to obtain a pixel value after edge enhancement correction. Further, the density (or luminance) of the pixel value is obtained, and the value of BLUR (luminance) is obtained from the density (or luminance) of the pixel value by the table of FIG. Then, the obtained BLUR (luminance) is substituted into equation (4) of S1609, the edge enhancement correction conditions are changed, and the second edge enhancement correction up to S1616 is performed again.

  Thus, the density corresponding to the luminance of the pixel after the edge enhancement correction is once obtained, and the edge enhancement correction can be recalculated so that the density of the total ink amount is small in the vicinity of the density having the large total ink amount.

<Embodiment 2>
In the second embodiment, in addition to the correction of the bleeding rate based on the ink density described in the first embodiment, the correspondence to the high-speed processing used in the ink jet recording apparatus will be described. The correction based on the ink density is the same as that in FIG. 16 of the first embodiment, and the correction relating to the used ink switching in the present embodiment can be realized by correcting STEP 1609.

  FIG. 18 is a diagram illustrating ink discharge nozzles of the recording apparatus according to the proposed embodiment. Since the number of nozzles ejecting black ink is larger than the number of nozzles ejecting color, it can be seen that the length of the nozzle row is increased. This makes it possible to achieve high-speed recording when using only black ink during monochrome printing. It is particularly effective for increasing the speed of monochrome text document printing. On the other hand, when printing a document containing both black and white characters, photographs, and illustrations, where monochrome and color are mixed, the monochrome area is recorded using black ink nozzles, and the area containing color is recorded using both normal black and color inks The method is desirable. In that case, as shown in FIG. 15, the number of rasters in the main scanning direction of the head called a band is considered as one unit, and is it recorded only with black ink or with black ink and color ink in combination? Will be judged.

  This used ink determination process is executed by the image processing flow STEP 303 in FIG. 3 of the first embodiment, and the table of STEP 306 is switched according to the determination result. If it is determined that the band is a monochrome band, it may be converted into data of only black ink.

  Next, the used ink determination process will be described with reference to FIG. FIG. 17 is a flow for performing the band ink usage determination process. A description will be added for each step.

<STEP 1701: Obtaining Pixel Signal Value>
The pixel value in the target band is acquired. If reading is performed using a scanner, the signal is generally in RGB format.

<STEP 1702: Saturation Value Calculation>
A saturation value is calculated from the pixel signal value acquired in STEP1701. First, the CaCb value is obtained using the following formula.
Ca = (R−G) / 2 Formula (11-1)
Cb = (R + G-2B) / 4 Formula (11-2)
The CaCb obtained from the above equation is then converted to saturation according to the following equation to obtain the saturation value S of the target pixel.
S = (Ca * Ca + Cb * Cb) ^ (1/2) (12)

<STEP 1703: Achromatic Color Pixel Determination>
The saturation value S of the pixel obtained in STEP 1702 is compared with a determination threshold value Th_S prepared in advance. If it is equal to or less than the threshold value, it is determined as an achromatic pixel, and if not, it is determined as a color pixel.

<STEP 1704: Increment of achromatic counter>
Only when it is determined in STEP 1703 that the pixel is an achromatic pixel, the process proceeds to STEP 1704 and the counter MonoCount is incremented by one. Although not specifically described, MonoCount is initialized with 0 before this flow starts.

<STEP 1705: Pixel End Determination>
It is determined whether or not the processing of STEPs 1701 to 1704 has been completed for all the pixels in the block. If it is not completed for all the pixels, the process returns to STEP 1701 and the same processing is executed.

<STEP 1706: Use Ink Determination>
After the processing of STEPs 1701 to 1705 is completed, the ink used in the target block is determined using MonoCount. The determination threshold value Th_M prepared in advance is compared with the MonoCount, and if it is equal to or greater than the threshold value, it is determined as a monochrome band, otherwise it is determined as a color band.

<STEP 1707: Color band certification>
If the color band is determined in STEP 1706, the color band is recognized and the result is output to a register or the like.

<STEP 1708: Monochrome band certification>
If the monochrome band is determined in STEP 1706, the monochrome band is recognized and the result is output to a register or the like.

  By referring to the output result according to the above-described flow, and further performing the replacement process in consideration of the blurring rate due to the density, high-quality output can be realized.

In STEP 1609 of the first embodiment, the correction value BLURCOL (luminance) for the color band and the correction value BLURMONO (luminance) for the monochrome band are prepared as the correction value BLUR (luminance). If the target pixel is in the color band,
Lap ′ (i) = Lap (i) + BLURCOL (luminance) Expression (13-1)
To find Lap '(i) and if you are in the monochrome band,
Lap ′ (i) = Lap (i) + BLURMONO (luminance) (13-2)
Thus, Lap ′ (i) is obtained.

  This is a table of BLURCOL (luminance) and BLURMONO (luminance). For BLURCOL, FIG. 6 described in the first embodiment may be used. In addition, BLURMONO may be obtained by scanning the actually recorded data in the same manner as in BLUCOL. Although an example is shown in FIG. 11, since only a single ink is used, the amount of ink decreases monotonously as the brightness increases, and it does not have a peak like a process color. Also in FIG. 11, the luminance on the horizontal axis is the minimum L determined in S1607 as in FIG.

  As described above, according to the second embodiment of the present invention, it is possible to perform appropriate correction even in a recording apparatus that performs monochrome and color determination in band units and switches the ink to be used to increase the printing speed. Therefore, it is possible to prevent the reproduction deterioration of the edges of characters and the like, and to provide an image suitable for the user at high speed.

<Embodiment 3>
In the third embodiment, a case will be described in which the user changes the magnification ratio through the user interface together with the correction of the bleeding rate based on the ink density and the used ink switching process described in the first and second embodiments.

The processing of this embodiment can be realized by changing STEP 1609 in FIG. If only the correction by the density described in the first embodiment,
Lap ′ (i) = Lap (i) + BLUR (luminance) × K (magnification ratio) Expression (14)
Thus, in the switching of the ink used for speeding up described in the second embodiment, Lap ′ (i) = Lap (i) + BLUCOL (luminance) × K (magnification) for color band and monochrome band determination ... Formula (15-1)
Lap ′ (i) = Lap (i) + BLURMONO (luminance) × K (magnification ratio) Expression (15-2)
It is represented by

  Here, K (magnification ratio) is a coefficient that depends on the magnification ratio, and is set to 1 when the magnification ratio is equal to or larger than the magnification ratio, and may be increased from there as the reduction ratio increases. That is, when the reduction ratio is high and finer characters are crushed and become difficult to see due to blurring or the like, the correction value BLUR is increased to facilitate the replacement of the edge portion to the background color and improve legibility.

  Although the example in which the user sets the scaling ratio has been described, the present invention is not limited to this. For example, the present invention is also applied to a case where the document is necessarily reduced, for example, an A4 size document is output on a B5 size sheet. Needless to say.

  As described above, according to the third embodiment of the present invention, it is possible to prevent deterioration in reproduction of edges of characters and the like by considering the magnification of the image together with the correction of the bleeding rate depending on the ink density and the type of ink used. Thus, it is possible to provide an image suitable for the user at high speed.

  The present invention has been described by taking the copy function of a multifunction printer as an example. However, the present invention is not limited to this, and can be implemented even when data sent from a computer (PC) is printed by the multifunction printer or printer. . Further, the present invention can be implemented even when a scanner is connected to a computer device (PC), image data read by the scanner is transferred to the PC, and the data is sent from the PC to the multifunction printer device or printer device for printing. In these cases, the processes of the first to third embodiments may be executed by the multifunction printer apparatus or the printer apparatus. However, a program for executing these processes is stored in a storage unit such as a PC memory and the PC. It may be executed by the CPU. Furthermore, a part of the processing of the first to third embodiments may be executed by the PC, and the rest may be executed by the multifunction printer device or the printer device.

Illustration of MFP device Control explanation diagram of MFP apparatus Flow chart of image processing of MFP apparatus Illustration of processing unit Flow chart of processing unit movement BLUR table for 4-color ink Diagram for obtaining the BLUR table Illustration of luminance, first derivative, ternary processing, second derivative Explanatory diagram of 4-way extraction Illustration of L difference BLUR table for black ink only Figure showing an example of blurred characters Gray line ink usage example Diagram of thickening of fine lines by concentration Illustration explaining the concept of the band Processing flowchart of embodiment 1 Used ink determination processing flowchart of Embodiment 2 Illustration of recording head Illustration of edge enhancement Illustration of replacement strength setting method

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 MFP apparatus 33 Printing apparatus 34 Reading apparatus 35 Operation panel 11 CPU
12 Image processing unit 13 Recording unit 14 Reading unit 15 Operation unit

Claims (25)

In an image processing apparatus for an image composed of at least one color signal and a plurality of pixels,
Correction density acquisition means for acquiring density after correction processing;
Correction coefficient changing means for changing a correction coefficient from the density value acquired by the correction density acquisition means;
Image correction means for correcting with the correction coefficient changed by the correction coefficient changing means;
Image recording processing means for executing recording processing on the image corrected by the image correcting means;
An image processing apparatus comprising:   The image processing apparatus according to claim 1, wherein the correction density acquisition unit is a unit that acquires the density of a pixel selected from a region around the target pixel.   The correction density acquisition unit is an edge detection unit that detects an edge direction from a region around a target pixel, and a unit that acquires the density of a pixel selected from the edge direction detected by the edge detection unit. The image processing apparatus according to claim 1.   The image processing apparatus according to claim 1, wherein the correction coefficient changing unit changes the correction coefficient based on a bleeding rate at a different density.   2. The image processing according to claim 1, wherein the correction coefficient changing unit obtains and changes a correction coefficient from a relationship between a bleeding rate at a different density and a scaling factor for changing an input image to an output image size. apparatus.   The image processing apparatus according to claim 1, wherein the image correction is a replacement process.   The image processing apparatus according to claim 1, wherein the replacement target pixel in the replacement process is changed by the correction coefficient changed by the correction coefficient changing unit. In an image processing apparatus for an image composed of at least one color signal and a plurality of pixels,
Ink color determination processing means for determining the ink color to be used from the value of the signal;
Correction density acquisition means for acquiring density after correction processing;
Correction coefficient changing means for changing a correction coefficient from the used ink information determined by the ink color determination processing means and the density value acquired by the correction density acquisition means;
Image correction means for correcting with the correction coefficient changed by the correction coefficient changing means;
Image recording processing means for executing recording processing on the image corrected by the image correcting means;
An image processing apparatus.   The ink color determination processing unit determines whether or not the fixed region in the main scanning direction including the target pixel can be determined as only an achromatic color pixel, and when the determination is an achromatic color, uses only black ink. The image processing apparatus according to claim 8, wherein, if not, it is determined that only color ink is used or a mixture of black ink and color ink is used.   The image processing apparatus according to claim 8, wherein the correction coefficient changing unit changes the correction coefficient based on a bleeding rate in the used ink determined by the ink color determination processing unit.   The image processing apparatus according to claim 8, wherein the correction density acquisition unit is a unit that acquires the density of a pixel selected from a region around the target pixel.   The correction density acquisition unit is an edge detection unit that detects an edge direction from a region around a target pixel, and a unit that acquires the density of a pixel selected from the edge direction detected by the edge detection unit. The image processing apparatus according to claim 8.   9. The image according to claim 8, wherein the correction coefficient changing unit changes the correction coefficient based on a bleeding rate in the used ink determined by the ink color determination processing unit and a bleeding rate at a different density. Processing equipment.   The correction coefficient changing means is a correction coefficient based on the relationship between the bleeding rate in the used ink determined by the ink color determination processing means, the bleeding rate at different densities, and the scaling factor for changing the input image to the output image size. The image processing apparatus according to claim 8, wherein the image processing apparatus is obtained and changed.   15. The image processing apparatus according to claim 8, wherein the image correction is a replacement process.   16. The image processing apparatus according to claim 8, wherein the replacement target pixel in the replacement process is changed by the correction coefficient changed by the correction coefficient changing unit. In an image processing method for an image composed of at least one color signal and a plurality of pixels,
A correction density acquisition step for acquiring density after correction processing;
A correction coefficient changing step of changing a correction coefficient from the density value acquired in the correction density acquisition step;
An image correction process for correcting with the correction coefficient changed in the correction coefficient changing process, an image recording process for executing a recording process on the image corrected by the image correction process,
An image processing method comprising:   18. The image processing method according to claim 17, wherein the correction density acquisition step is a step of acquiring the density of a pixel selected from an area around the target pixel.   The correction density acquisition step is an edge detection step of detecting an edge direction from a region around the target pixel, and a step of acquiring the density of a pixel selected from the edge direction detected by the edge detection step. The image processing method according to claim 17.   The image processing method according to claim 17, wherein the correction coefficient changing step changes the correction coefficient based on a bleeding rate at a different density.   The image processing according to claim 17, wherein the correction coefficient changing step obtains and changes a correction coefficient from a relationship between a bleeding rate at a different density and a scaling factor for changing an input image to an output image size. apparatus.   The image processing method according to claim 17, wherein the image correction is a replacement process.   The image processing method according to any one of claims 17 to 21, wherein a pixel to be replaced in the replacement process is changed by the correction coefficient changed in the correction coefficient changing step. In an image processing method for an image composed of at least one color signal and a plurality of pixels,
An ink color determination process for determining the ink color to be used from the value of the signal;
A correction density acquisition step for acquiring density after correction processing;
A correction coefficient changing step of changing a correction coefficient from the used ink information determined by the ink color determination processing step and the density value acquired by the correction density acquisition step;
An image correction process for correcting with the correction coefficient changed in the correction coefficient changing process, an image recording process for executing a recording process on the image corrected by the image correction process,
An image processing method comprising:   An image processing program for causing a computer to execute the method according to any one of claims 17 to 24.

Images