JP5500969B2 - Image processing apparatus and method - Google Patents

Description

  The present invention relates to image processing that suppresses uneven gloss when an image is formed with a pigment-based color material.

  As inks for ink jet recording apparatuses, dye inks using dyes that are easily dissolved in water as color materials are widely used. In a dye ink containing water as a main component, a color material dissolved in a solvent easily penetrates into the fibers of the recording medium. Therefore, even after image recording, the surface shape of the recording medium is easily maintained, and the gloss of the recording medium itself is maintained as the gloss of the image. In other words, if an image is recorded on a recording medium excellent in gloss using a dye ink, an image excellent in gloss can be easily obtained. Therefore, in an ink jet recording apparatus using dye ink, the gloss of an image can be adjusted by adjusting the gloss of the recording medium.

  The dye ink generally has low light resistance, and the dye molecules of the coloring material are decomposed by light, and the image is faded. In addition, printed matter printed with dye ink generally has low water resistance, and when wetted with water, dye molecules that have penetrated into the fiber dissolve in water, and image blurring occurs.

  In order to solve the light resistance and water resistance problems that occur when using dye inks, in recent years, pigment inks using pigments as coloring materials have been developed. Unlike dyes that exist as molecules, pigment inks exist in a solvent as particles of several tens of nm to several μm. The color material particles of the pigment ink are larger than the color material particles of the dye ink, and a printed matter having high weather resistance can be obtained.

  The color material of the pigment ink hardly penetrates into the recording medium and is deposited on the surface of the recording medium. Therefore, the fine shape of the image surface is different between the region where the pigment ink is applied and the region where the pigment ink is not applied. Also, the amount of color material used varies depending on the density and color of the image. For this reason, the area where the color material covers the recording medium is different, and the reflectance of the color material and the surface reflectance of the recording medium are different. Therefore, the gloss differs depending on the area where the color material covers the recording medium.

  For the above-described reasons, when an image is recorded using pigment ink, a phenomenon called “gloss unevenness” occurs in which the glossiness varies depending on the density and color of the image. When gloss unevenness occurs, a gloss area where gloss is observed and a mat area where gloss is not observed are mixed in the same image, and in particular, a photographic image is recognized as an undesirable image.

  Uneven gloss occurs not only in an inkjet recording apparatus using pigment ink, but also in an electrophotographic recording apparatus that records an image by fixing toner on a recording medium. For example, the smoothness of the image surface is increased by fixing in a region where the toner adhesion amount is large. For this reason, if the plain paper has a low gloss, the area where the image exists is higher in gloss than the area where the surface of the recording paper where the image does not exist is exposed. It is known that the gloss of the area where the image exists changes depending on the amount of toner attached, the fixing temperature, the fixing speed, and the like.

  In order to suppress uneven gloss, a method using a substantially colorless and transparent ink (hereinafter, clear ink) that does not affect color reproduction is known. That is, the gloss unevenness is suppressed by applying clear ink or white ink to an area not covered with colored ink (for example, Patent Document 1).

  Also, there is a method of recording an image using pigment ink, and a method of applying an achromatic color ink (hereinafter, light gray ink) that is lighter than black to an area that is not covered with colored ink (for example, Patent Documents). 2).

  However, the invention of Patent Document 1 requires that a clear ink or white ink unnecessary for color reproduction be mounted on the recording apparatus, resulting in an increase in size and cost of the recording apparatus. The invention of Patent Document 2 also increases the number of inks and inevitably increases the size and cost of the recording apparatus. Furthermore, if light gray ink is recorded in an area that is not covered with colored ink, the color material is also recorded in the area where the input signal value (R, G, B) = (255, 255, 255) is not applied. As a result, the brightness of the highlight area is reduced and the color reproduction area is reduced.

  Also, in recording devices that use dye inks for cyan C, magenta M, and yellow Y, and pigment inks for black K, the difference in gloss between K and CMY The resulting pseudo contour becomes a problem. In order to solve this problem, Patent Document 3 determines the range in which the glossiness obtained by mixing the pigment ink K with respect to the glossiness printed with only the dye ink CMY is determined by visual observation or measurement of glossiness, A method for determining the maximum amount of pigment ink K applied is disclosed. However, since the pigment ink having high weather resistance is used only for the K color material, there is a problem that the color reproduction range without using the K color material has low weather resistance.

  The above prior art performs the same processing regardless of the input image. Uneven gloss suppression processing is executed even for an image where uneven gloss is not noticeable. Gloss unevenness suppression processing may have a trade-off relationship with the occurrence of image quality other than processing speed and gloss (granularity, streaky density unevenness (hereinafter, streaks), and in consideration of factors other than gloss unevenness, It is desired to execute processing suitable for the input image.

JP 2002-307755 A JP2005-096194 JP 2006-041949 A Japanese Patent No. 3938184 Roger P. Dooley and Rodney Shaw “Noise Perception in Electrophotography” Journal of Applied Photographic Engineering Vol. 5, p. 190-196 (1979)

  An object of the present invention is to predict the degree of occurrence of uneven glossiness of an image to be printed and to control printing processing according to the degree of occurrence of unevenness of gloss.

  The present invention has the following configuration as one means for achieving the above object.

  In the image processing according to the present invention, in the image processing of an image forming apparatus that prints an image using a pigment-based color material, image characteristics of an image to be printed are detected, and the image is printed based on the image characteristics. The degree of occurrence of gloss unevenness is predicted, and based on the degree of occurrence of gloss unevenness, it is determined whether or not to execute a process for suppressing gloss unevenness in the image printing process.

  According to the present invention, it is possible to predict the degree of occurrence of uneven glossiness of an image to be printed, and to control the printing process according to the degree of occurrence of unevenness of gloss.

FIG. 2 is a block diagram for explaining a configuration example of an image processing apparatus according to the first embodiment. 6 is a flowchart for explaining processing of the image processing apparatus. FIG. 3 is a diagram illustrating details of a user interface provided by a printer driver. FIG. 6 is a diagram for explaining a change in glossiness in an output image of an electrophotographic printer. FIG. 4 is a schematic diagram illustrating a toner fixing state. The block diagram explaining the functional structural example of a glossiness nonuniformity estimation part. The figure explaining the calculation method of the brightness characteristic of an image. FIG. 9 is a diagram showing an example of a brightness histogram of an input image and a comparison of gloss unevenness index values of images having a brightness range shown in FIGS. 8 (a) and 8 (b). The figure which shows the relationship between a brightness range and a glossiness range. FIG. 11 is a diagram showing an example of spatial frequency characteristics of images, and a diagram showing comparison of gloss unevenness index values of images having the spatial frequency characteristics shown in FIGS. 10 (a) and 10 (b). The figure explaining the visual sensitivity curve in the observation distance of 350 mm, and the setting method of the spatial frequency in which visual sensitivity is less than a threshold value. The figure which shows a mode that an example of the input image and each object were isolate | separated into the high frequency object and the low frequency object. The figure which shows the typical brightness value of each object. The block diagram explaining the modification of a function structure of a glossiness nonuniformity estimation part. The figure which shows an example of a glossiness characteristic. The figure explaining an uneven glossiness suppression process. The figure explaining the change of the glossiness in the output image of the inkjet printer using a pigment ink. FIG. 3 is a block diagram for explaining an example configuration of an image processing apparatus and a printer according to a second embodiment. FIG. 3 is a diagram illustrating a configuration example of a recording head. 9 is a flowchart for explaining operations of the image processing apparatus and the printer according to the second embodiment. The figure explaining the setting method of Y coordinate Ycut which is a cutting position. The figure explaining the setting of recording data. The figure explaining the example of the relationship between brightness (signal value) and glossiness, and the setting method of an intermediate brightness area. The figure which shows the example of a relationship between lightness (signal value) and image clarity.

  Hereinafter, image processing according to an embodiment of the present invention will be described in detail with reference to the drawings.

  In the first embodiment, a case where the present invention is applied to an electrophotographic recording apparatus (hereinafter referred to as an electrophotographic printer) will be described.

[Device configuration]
A configuration example of the image processing apparatus according to the first embodiment will be described with reference to the block diagram of FIG.

  The image input unit 101 inputs image data representing an image to be printed. In FIG. 1, although a description of a host device (for example, a computer) that controls the printing apparatus is omitted, a printer driver operates on an operating system (OS) of the host device. Image data instructed to be printed by the user interface (UI) of the printer driver is input to the image input unit 101 via a general-purpose serial bus such as USB or IEEE1394. In some cases, an image that has been edited or processed by an application different from the printer driver is instructed to be printed from the application via the printer driver.

  The image input unit 101 is, for example, a general-purpose serial bus interface, and inputs image data from a host device or an image input device (for example, a digital camera or a scanner) via the serial bus. The image input unit 101 is, for example, a disk reader or a memory card reader, and may input image data stored in the memory card or image data recorded on the disk. Alternatively, the image input unit 101 is a network interface, for example, and may input image data from a server on the network.

  The uneven gloss prediction unit 102 predicts the degree of occurrence of uneven gloss in the input image before printing. The uneven gloss determination unit 103 determines whether to perform the uneven gloss suppression process according to the predicted occurrence of uneven gloss. The image output unit 104 performs an input image printing process according to the determination result of whether or not the gloss unevenness suppression process can be executed.

[Image processing]
The processing of the image processing apparatus will be described with reference to the flowchart of FIG. The image input unit 101 inputs image data representing an image to be printed (S201), and the uneven gloss prediction unit 102 calculates the degree of occurrence of uneven gloss when the input image is printed (hereinafter referred to as uneven gloss index value). (S202).

  The gloss unevenness determination unit 103 determines whether or not the gloss unevenness index value exceeds a predetermined threshold (hereinafter referred to as the gloss unevenness threshold). Instructs the image output unit 104 to execute the uneven gloss reduction process (S203). If the gloss unevenness index value is equal to or less than the gloss unevenness threshold (that is, the gloss unevenness is small), the non-execution of the gloss unevenness suppression process is instructed to the image output unit 104 (S203).

  The image output unit 104 executes print processing including gloss unevenness suppression processing when instructed to execute gloss unevenness suppression processing (S204), and executes normal print processing when non-execution of gloss unevenness suppression processing is instructed. (S205).

  The image output unit 104 performs printing corresponding to the printing speed, printing cost, and image quality other than gloss (granularity, streak generation, gradation, sharpness, etc.) set by the user when the uneven gloss reduction processing is not executed. Execute the process. Note that any one or a combination of printing speed, printing cost, and image quality (granularity, streak generation, gradation, sharpness, etc.) other than gloss may be set as the standard print processing.

[User interface]
Details of the user interface 301 provided by the printer driver will be described with reference to FIG. A UI 301 is a window for setting printing conditions, and is implemented in the printer driver as a graphical user interface (GUI). The user operates the input image field 302 to set image data to be printed. In addition, a recording medium for recording an image is set or selected by operating the paper type column 303.

  In the setting of the print mode column 304, the gloss unevenness index value calculated by the uneven gloss prediction unit 102 based on the characteristics of the image to be printed and the characteristics of the recording medium set by the user is equal to or less than the uneven gloss threshold, that is, no uneven gloss suppression processing is required. It becomes effective when it is judged. In other words, the user can select an item to be prioritized in the printing process of step S205 from the image quality (radio button 305), cost (same 306), and speed (same 307) by the print mode column 304.

  After the above settings are completed, the user presses the print button 308 to instruct execution of printing. When canceling printing, a cancel button 309 is pressed.

[Gloss unevenness in the output image of the electrophotographic printer]
For the evaluation of gloss of a recording medium, generally, a gloss meter measurement value based on a specular gloss measurement method (JIS Z 8741) for measuring the intensity of specular reflection light is used. In addition, for the evaluation of the gloss of a highly glossy object such as an automobile outer plate, a reflection haze measurement method (ISO13803, ASTM E 430) is used to measure the degree of fogging of the sample surface. In addition, the image clarity measurement method (JIS K 7105, JIS H 8686) for measuring the sharpness of the image of the object reflected on the sample surface is used.

  However, in electrophotographic printers, an ink jet type or sublimation type thermal transfer type recording device or a recording medium having a lower gloss than silver halide photography is used, and the gloss changes depending on the amount of toner used. The change in gloss is small as compared with the recording apparatus. Therefore, the measurement of the uneven glossiness of the output image of the electrophotographic printer is preferably a specular gloss measurement method, not the reflection haze measurement method or image clarity measurement method used for the measurement of a relatively high gloss sample.

  The change in glossiness in the output image of the electrophotographic printer will be described with reference to FIG. Fig. 4 (a) shows the change in glossiness (measurement value of glossmeter based on specular glossiness measurement method) with respect to input signal value when printing on a recording medium such as plain paper with relatively low gloss. 401 is shown. Reference numeral 403 indicates the glossiness of the recording medium, and reference numeral 404 indicates the glossiness obtained for the maximum signal value (for example, 255). FIG. 4B shows a change 402 in glossiness with respect to an input signal value when printing is performed on a recording medium such as coated paper having relatively high gloss.

  The fixing state of the toner will be described with reference to the schematic diagram of FIG. FIG. 5A shows a fixing state of the toner 502 of the recording medium 501 such as plain paper, which has a relatively low gloss, and corresponds to FIG. FIG. 5B shows a fixing state of the toner 504 on the recording medium 503 such as coated paper having a relatively high gloss, and corresponds to FIG. 4B.

  As shown in FIG. 5A, the surface of the toner 502 fixed on the recording medium 501 is (relatively) smoother than the surface of the recording medium 501. As the input signal value increases, the recording area having a smooth surface increases, and the smooth area increases in the entire output image. That is, due to the change in the area ratio of the recording medium 501 having a large unevenness and the smooth recording area, as shown in FIG.

  On the other hand, as shown in FIG. 5B, the unevenness of the surface of the toner 504 fixed on the recording medium 503 is (relatively) larger than the surface of the recording medium 503. As the input signal value increases, the recording area with large surface irregularities increases, and the area with large irregularities increases in the entire output image. That is, due to the change in the area ratio of the smooth recording medium 503 and the recording area with large unevenness, as shown in FIG. 4 (b), the glossiness decreases with the increase of the input signal value.

  It is known that the surface of toner fixed on a recording medium generally becomes smoother as the fixing speed is lower and the fixing temperature is higher.

[Gloss unevenness prediction method]
A functional configuration example of the uneven gloss prediction unit 102 will be described with reference to the block diagram of FIG. The uneven gloss prediction unit 102 detects an image characteristic 702 from the image data 701, and further calculates an uneven gloss index value 703 based on the image characteristic 702. The image characteristic 702 is information composed of an image brightness characteristic or an image brightness characteristic and an image spatial frequency characteristic.

  A method for calculating the brightness characteristic of an image will be described with reference to FIG. The brightness conversion unit 902 of the uneven gloss prediction unit 102 converts the RGB value of the image data 701 into an L * value of CIELab for each pixel using a lookup table (LUT). Then, a brightness image 903 composed of the brightness value L * of each pixel is obtained. The spatial frequency calculation unit 904 performs a Fourier transform on the brightness image 903 to calculate a spatial frequency distribution as the spatial frequency characteristic of the image. Note that the spatial frequency calculation unit 904 is not an essential component depending on the method of calculating the uneven gloss index value.

  The LUT used by the lightness conversion unit 902 is configured as a three-dimensional LUT (3DLUT) in which each RGB color component signal value is equally divided into n, for example. That is, a signal value corresponding to a grid point of 3DLUT is input to the image output unit 104, and a patch corresponding to the grid point is printed on a recording medium. Then, the brightness of each printed patch is measured by a colorimeter, and the measured brightness value is recorded as the output value of the corresponding grid point. If the grid point corresponding to the RGB value of the target pixel does not exist in 3DLUT, the L * value of the target pixel is calculated by interpolation from the output values of multiple neighboring grid points (for example, four grid points) surrounding the RGB value. Is calculated.

  In the above example, the L * value is calculated by 3DLUT. However, assuming that the relationship between the input signal value and the lightness value is expressed by a linear or non-linear curve such as a gamma curve, the lightness value is calculated. Also good. Alternatively, the XYZ value may be calculated using a RGB-to-XYZ conversion formula standardized by CIE, and the brightness value may be calculated from the Y value. Further, the dot arrangement when predetermined image processing is performed may be predicted, and the brightness value may be calculated using a prediction formula such as the Murray-Davies equation or the Neugebauer equation. The spatial frequency characteristics of the image can also be calculated by converting the input image into a gray scale image and Fourier transforming the gray scale image.

● Prediction method 1
A method of calculating the uneven gloss index value from the brightness characteristic of the input image will be described as “prediction method 1”.

  The uneven gloss prediction unit 102 creates a histogram (hereinafter, brightness histogram) representing the brightness distribution shown in FIG. 8 from the brightness image 903. FIG. 8 shows an example of the brightness histogram of the input image. Then, with reference to the lightness histogram, a lightness range exceeding a predetermined frequency is set as a lightness range representing the spread of lightness of the input image. In the lightness histogram 601 shown in FIG. 6A, a lightness range 604 having a frequency exceeding a predetermined frequency (threshold) 603 is the lightness range of the input image. Similarly, in the brightness histogram 602 of FIG. 6B, the brightness range 605 having a frequency exceeding the threshold 603 is the brightness range of the input image.

  As shown in FIG. 4, it is generally known that the change in glossiness with respect to brightness in an electrophotographic printer monotonously increases or monotonously decreases. FIG. 9 shows the relationship between the brightness range and the gloss range. A line 610 shown in FIG. 9 shows a change in glossiness with respect to a change in brightness. In the case of the image shown in FIG. 9A (narrow brightness range 604), the glossiness range is indicated by reference numeral 611. On the other hand, in the case of the image shown in FIG. 9B (wide brightness range 605), the glossiness range is indicated by reference numeral 612. That is, the wider the brightness range, the wider the glossiness range. Therefore, the difference between the maximum brightness value and the minimum brightness value in the brightness range of the image can be used as the uneven gloss index value.

  FIG. 8 (c) shows a comparison of gloss unevenness index values of images having the brightness ranges shown in FIGS. 8 (a) and 8 (b). The gloss unevenness index value of the image in the brightness range 604 shown in FIG. 8A is denoted by reference numeral 1701, and the gloss unevenness index value of the image in the brightness range 605 shown in FIG. 8B is denoted by reference numeral 1702. Reference numeral 1703 indicates a gloss unevenness threshold set empirically. In the example of FIG. 8 (c), the gloss unevenness suppression process is executed on the image in the brightness range 605 shown in FIG. 8 (b) assuming that the gloss unevenness index value 1702 exceeds the gloss unevenness threshold value 1703.

● Prediction method 2
A method for calculating the gloss unevenness index value from the spatial frequency characteristics of the input image will be described as “prediction method 2”.

  FIG. 10 shows an example of the spatial frequency characteristics of the image. FIG. 10 (a) shows the spatial frequency distribution of an image with many low frequency components compared to high frequency components, and FIG. 10 (b) shows the spatial frequency distribution of an image with many high frequency components compared to low frequency components.

According to Non-Patent Document 1, it is clear that human visual sensitivity varies depending on the spatial frequency, and a visual sensitivity curve can be obtained according to the observation distance of the image. FIG. 11 (a) shows a visual sensitivity curve at an observation distance of 350 mm. The uneven gloss prediction unit 102 calculates the uneven gloss index value S by the product-sum operation (the following expression) of the spatial frequency characteristics of the image shown in FIG. 10 and the visual sensitivity curve shown in FIG.
S = ∫P (f) ・ VTF (f) df… (1)
Where P (f) is the power spectrum at spatial frequency f,
VTF (f) is the visual spatial frequency response at the spatial frequency f (in this example, the value indicated by the visual sensitivity curve at the observation distance of 350 mm and the spatial frequency f).

  As described above, it is generally known that the change in glossiness with respect to lightness in an electrophotographic printer monotonously increases or monotonously decreases. Accordingly, the gloss unevenness index value S can be calculated from the spatial frequency characteristics obtained with the lightness as a reference.

  FIG. 10 (c) shows comparison of gloss unevenness index values of images having the spatial frequency characteristics shown in FIGS. 10 (a) and 10 (b). The gloss unevenness index value of the spatial frequency characteristic image shown in FIG. 10 (a) is denoted by reference numeral 1501, and the gloss unevenness index value of the spatial frequency characteristic image shown in FIG. 10 (b) is denoted by reference numeral 1502. As shown in FIG. 10 (c), gloss unevenness is more likely to occur in an image with many low frequency components, and gloss unevenness is more easily recognized.

  Also, it is difficult to recognize a visual sensitivity below a certain value. Therefore, as shown in FIG. 11 (b), the spatial frequency fb at which the visual sensitivity curve becomes equal to or less than a predetermined value is calculated. In the example of FIG. 11 (b), for example, a threshold value is set to a visual sensitivity of 10% as a predetermined value, and the spatial frequency fb at which the visual sensitivity is equal to or less than the threshold value is 4.5 [cycle / mm]. The uneven gloss prediction unit 102 may separate the high frequency component and the low frequency component with the spatial frequency fb as a boundary, calculate the ratio of the low frequency component in the image, and use the ratio as the uneven gloss index value.

● Prediction method 3
A method for calculating the uneven gloss index value from the brightness characteristic and spatial frequency characteristic of the input image will be described as “prediction method 3”.

  The uneven gloss prediction unit 102 performs image area separation processing on the input image and divides the object. Then, each object is subjected to Fourier transform, and each object is separated into an object composed of a high-frequency spatial frequency component and an object composed of a low-frequency spatial frequency component, with the spatial frequency fb shown in FIG. 11 (b) as a boundary. Hereinafter, the separated objects are referred to as a high frequency object and a low frequency object.

  An example of the input image is shown in FIGS. 12 (a) and 12 (b). The difference between the image shown in FIG. 12 (a) and the image shown in FIG. 12 (b) is only the presence or absence of the object 1005. 12 (c) and 12 (d) show how each object is separated into a high frequency object and a low frequency object. In FIGS. 12 (c) and 12 (d), the hatched object is a high frequency object, and the other objects are low frequency objects. In the example of FIGS. 12C and 12D, the objects 1101 and 1103 are high-frequency objects, and the objects 1102, 1104, and 1105 are low-frequency objects.

  Next, the uneven gloss prediction unit 102 calculates a representative brightness value of each object with reference to the brightness image 903. FIG. 13 shows typical brightness values of each object.

  Next, the uneven gloss prediction unit 102 calculates the brightness difference between adjacent objects for the low-frequency component object. In the case of the object shown in FIG. 12C, the brightness difference between the objects 1102 and 1104, and 1104 and 1105 is calculated. In the case of the object shown in FIG. 12D, the brightness difference between the objects 1102 and 1104 is calculated. Then, the maximum value of the calculated brightness difference is set as the gloss unevenness index value.

  For example, it is assumed that the brightness difference between the white cloud object 1105 and the blue sky object 1104 is larger than the brightness difference between the tree trunk object 1102 and the object 1104. In this case, the gloss unevenness index value of the image shown in FIG. 12A is the brightness difference between the objects 1105 and 1104. Further, the gloss unevenness index value of the image shown in FIG. 12B is a brightness difference between the objects 1102 and 1104. In this example, uneven gloss tends to occur in the image shown in FIG.

[Modified example of uneven gloss prediction method]
A modification of the functional configuration of the uneven gloss prediction unit 102 will be described with reference to the block diagram of FIG. The uneven gloss prediction unit 102 calculates an image characteristic 702 from the image data 701, and further calculates an uneven gloss index value 703 based on the image characteristic 702 and the gloss characteristic 704.

  A gloss characteristic 704 indicates the gloss characteristic of the color material used by the image output unit 104 and the gloss characteristic of the recording medium. The glossiness 403 with a signal value 0 shown in FIG. 4 (a) is the glossiness of a recording medium on which no color material is recorded. For example, the glossiness 404 with a signal value 255 is when the recording medium is completely covered with the color material. The glossiness, in other words, the glossiness of the color material. Accordingly, the glossiness 403 of the recording medium and the glossiness 404 of the color material are measured using a glossiness meter that conforms to the specular glossiness measurement method, and stored as gloss characteristics 704 in the memory. Further, a patch corresponding to each stage of the signal value is printed, and the glossiness is included in the gloss characteristic 704. An example of the gloss characteristic 704 is shown in FIG. FIG. 15 shows an example of a table showing the relationship between the input signal value and the glossiness for a certain recording medium, but it is easy to create a table in which the input signal value is replaced with the brightness value. Further, the table shown in FIG. 15 is prepared for each recording medium. If the image output unit 104 can use a plurality of sets of different color materials, they are prepared for each color material set and recording medium.

● Prediction method 4
With reference to the gloss characteristic 704, a glossiness range corresponding to the brightness range calculated in the above-mentioned “prediction method 1” is calculated, and the difference between the maximum glossiness and the minimum glossiness in the glossiness range is calculated as the uneven glossiness index value. To do. Alternatively, the standard deviation of the gloss range may be used as an uneven gloss index value.

● Prediction method 5
With reference to the gloss characteristic 704, a histogram (hereinafter referred to as glossiness histogram) indicating a glossiness distribution corresponding to the brightness histogram calculated in the “prediction method 1” described above is calculated. Then, a glossiness range exceeding a predetermined frequency threshold of the glossiness histogram is calculated, and a difference between the maximum glossiness and the minimum glossiness in the glossiness range is used as a gloss unevenness index value. Alternatively, the standard deviation of the gloss range may be used as an uneven gloss index value.

● Prediction method 6
With reference to the gloss characteristic 704, the brightness image 903 is converted into a gloss image, and the gloss frequency image is Fourier transformed to calculate the spatial frequency characteristics. Then, similarly to the “prediction method 2” described above, the value S calculated by giving the power spectrum at the spatial frequency f of the glossiness image as P (f) in the equation (1) is used as the gloss unevenness index value.

● Prediction method 7
With reference to the gloss characteristic 704, the glossiness information of the object corresponding to the brightness information of the object in the “prediction method 3” described above is calculated. Then, the maximum glossiness difference value between adjacent objects is set as the uneven glossiness index value.

  In the above description, the method for predicting the uneven glossiness from the brightness of the image has been described. However, it is possible to similarly predict the uneven glossiness by using an index representing brightness such as luminance and reflectance.

[Gloss unevenness suppression processing]
The gloss unevenness suppressing process will be described with reference to FIG.

  As shown in FIG. 5, the gloss of the output image of the electrophotographic printer depends on the surface state of the recording medium and the surface state of the fixed toner. When a low-gloss recording medium such as plain paper is selected, as indicated by a curve 401 in FIG. 4 (a), a gloss characteristic in which the glossiness increases as the signal value increases is shown. Therefore, the standard fixing speed and the fixing speed faster or lower than the fixing temperature on plain paper are changed to suppress the crushing of the toner, increase the unevenness of the surface of the toner after fixing, and gloss characteristics with respect to the signal value. This change is shown by a curve 1401 in FIG. That is, the change in the glossiness is smaller than the curve 401 indicating the change in the gloss characteristic with respect to the signal value at the standard fixing speed and fixing temperature on plain paper, and uneven gloss can be reduced.

  On the other hand, when a recording medium with high gloss such as coated paper is selected, as indicated by a curve 402 in FIG. 4B, the gloss characteristic that the glossiness decreases as the signal value increases is shown. Therefore, the standard fixing speed on the coated paper and the fixing speed lower or higher than the fixing temperature are changed to promote the crushing of the toner, reduce the unevenness of the surface of the toner after fixing, and the gloss characteristics with respect to the signal value. This change is shown by a curve 1402 in FIG. That is, the change in glossiness is smaller than the curve 402 indicating the change in gloss characteristics with respect to the signal value at the standard fixing speed and fixing temperature on the coated paper, and uneven gloss can be reduced.

  Note that the fixing speed and fixing temperature in the uneven gloss reduction processing are set based on experience values for each apparatus and recording medium.

  Alternatively, as a gloss unevenness suppressing process, a method of printing clear toner in an area where color dots are not printed without changing the fixing speed and the fixing temperature may be used.

  In this way, the degree of occurrence of uneven gloss is predicted according to the image characteristics of the input image (and further according to the gloss characteristics of the color material and the recording medium), and the uneven gloss suppression process is executed according to the occurrence degree of uneven gloss. Can be controlled. Therefore, an image with a high degree of gloss unevenness can be printed without performing the gloss unevenness suppression process, and an image with a low degree of gloss unevenness can be printed without performing the uneven gloss reduction process.

  The image processing according to the second embodiment of the present invention will be described below. Note that the same reference numerals in the second embodiment denote the same parts as in the first embodiment, and a detailed description thereof will be omitted.

  In Example 2, a case where the present invention is applied to an ink jet recording apparatus (hereinafter referred to as an ink jet printer) will be described.

[Gloss unevenness in output image of inkjet printer]
The uneven glossiness in the ink jet printer is caused by the fact that the gloss changes with the change in the brightness of the image when pigment-based ink is used as the color material. Further, when printing a photograph with an inkjet printer, glossy paper with high gloss is often used. As a result, a high level of gloss change occurs compared to the output image of the electrophotographic printer.

  In Example 1, since the case where the gloss was relatively small was taken as an example, the example using the specular gloss measurement method was described. However, considering the case where a recording medium with high gloss like an ink jet printer is used, as disclosed in Patent Document 4, not only specular gloss but also image clarity (and reflection haze) is used to obtain gloss. The better the correspondence with the subjectivity of the observer of the image.

  A change in glossiness in an output image of an ink jet printer using pigment ink will be described with reference to FIG. Changes in glossiness (measured by a glossmeter based on the specular glossiness measurement method) 2701 (Fig. 17 (a)) and image clarity (image clarity measurement) with respect to image brightness when an image is recorded on glossy paper The change 2702 (FIG. 17 (b)) of the measurement value of the image clarity measuring instrument conforming to the law is shown. From the low brightness area to the intermediate brightness area, the glossiness and the image clarity increase as the brightness of the image increases. However, in the intermediate lightness region to the high lightness region, the glossiness decreases with an increase in the lightness of the image, and there is almost no change in image clarity or a moderate increase.

[Gloss unevenness prediction method]
The gloss unevenness prediction method and determination method in the second embodiment are the same as those in the first embodiment. However, when glossy paper with high gloss is used, reflection haze or image clarity can be used instead of specular gloss as gloss characteristics, but specular gloss and reflection haze, or a combination of specular gloss and image clarity are used. It is preferable.

[Device configuration]
A configuration example of the image processing apparatus and the printer according to the second embodiment will be described with reference to the block diagram of FIG.

  The image processing apparatus 180 and the printer 200 are connected via a serial bus or a network 190. The image buffer 181 of the image processing device 180 stores image data input from a host device (not shown). The color separation unit 182 refers to the color separation LUT 183 and separates the image data stored in the image buffer 181 into ink colors of the printer 200.

  The signal value determination unit 184 determines the signal value of each pixel of the image data stored in the image buffer 181. The recording data setting unit 185 refers to the determination result of the signal value determination unit 184 and the recording data setting LUT 186, sets the recording data for each pass, and stores the recording data for each pass in the recording data memory 187. A halftone (HT) processing unit 188 binarizes the multi-tone recording data by halftone processing, and stores the binarized image data in the HT image memory 189.

  The HT image memory 201 of the printer 200 stores image data output from the image processing apparatus 180. The ink color and ejection amount selection unit 202 selects the ink color from the ink color mounted on the recording head 204 and the ink ejection amount that can be ejected by the recording head 204 according to the value of the image data stored in the HT image memory 201. Select the color and discharge rate. Then, the selected ink color and ejection amount are output to the head controller 203.

  The head control unit 203 controls the movement of the recording head 204 via the moving unit 205, and controls ink ejection by the recording head 204 based on the selected ink color and ejection amount. That is, the recording head 204 is moved vertically and horizontally with respect to the recording medium 207 conveyed by the conveying unit 206 to form an image on the recording medium 207.

  FIG. 19 shows a configuration example of the recording head 204. The recording head 204 uses four colors of cyan C, magenta M, yellow Y, and black K, and light cyan Lc, which has a lower density than cyan C, and light magenta Lm, which has a lower density than magenta M. Ejects six colors of ink. FIG. 19 shows the recording head 204 in which nozzles are arranged in a line in the recording paper conveyance direction for the sake of simplicity, but the number and arrangement of nozzles are arbitrary. For example, nozzles having the same color and different discharge amounts may be provided, or a plurality of nozzles having the same discharge amount may be provided. Moreover, the structure by which the nozzle was arrange | positioned at the zigzag may be sufficient. Further, FIG. 19 shows a configuration in which the nozzle rows of each color are arranged in the head moving direction, but the nozzle rows of each color may be arranged in the recording paper conveyance direction.

[Image processing]
The operations of the image processing apparatus 180 and the printer 200 according to the second embodiment will be described with reference to the flowchart of FIG.

  First, the image buffer 181 stores input RGB image data (S301). As will be described in detail later, the signal value determination unit 184 determines the value of the target pixel of the image data stored in the image buffer 181 and a predetermined threshold value in order to obtain information for setting the output data value of each pass. The comparison result is output to the recording data setting unit 185 (S302). On the other hand, the color separation unit 182 uses the color separation LUT 183 to separate the RGB value of the pixel of interest stored in the image buffer 181 into an ink value CMYKLcLm representing the amount of ink used for each color (S303).

  Next, the recording data setting unit 185 sets the scan number k and the Y coordinate Ycut (k) that is the cut position of the color separation data (S304). Note that the initial value of the scan number k is 1, and although details will be described later, Ycut (k) is a cutting position (nozzle upper end coordinates) at the scan number k. Although details will be described later, referring to the recording data setting LUT 186, recording data for each scan is set from the image data after color separation (S305), and the set recording data is stored in the recording data memory 187 (S306). ).

  Next, the HT processing unit 188 executes halftone processing for reducing the number of gradations of the recording data stored in the recording data memory 187 (S307), and stores the recording data after the halftone processing in the HT image memory 189. (S308). Here, the gradation number of the recording data is 8 bits, and the gradation number of the recording data after halftone processing is 1 bit (binary).

  The halftone processing of the present embodiment generates binary data sequentially for the recording data stored in the recording data memory 187 having at least the number of nozzles of the nozzle array of the recording head 204 × the horizontal size of the image. To do. Accordingly, the HT image memory 189 similarly prepares a storage area corresponding to the number of nozzles in the nozzle row × the horizontal size of the image.

  In this way, halftone processing for a certain scan number k is completed, and as a result, binary images (hereinafter referred to as band data) of respective colors to be formed by one scan of the recording head 204 are stored in the HT image memory 189. Is done. The halftone process may be performed using an error diffusion method, but other methods such as a blue noise mask system, a Bayer system dither method, or a density pattern method may be used. Alternatively, a plurality of methods may be combined. Further, the processing from step S302 to S308 is repeatedly executed for the band data.

  Next, when the band data equivalent to the number of nozzles × the horizontal size of the image is accumulated, the HT image memory 189 outputs the band data to the printer 200 (S309).

  The printer 200 to which the band data is input stores the band data in the HT image memory 201, selects an ink color and an ejection amount that match the band data, and starts image formation (S310). Image formation is performed by recording dots on the recording medium 207 by driving each nozzle at a predetermined driving interval while moving the recording head 204 from the left to the right with respect to the recording medium 207. In the present embodiment, a multi-pass recording method is used in which an image is recorded by scanning the recording medium 207 a plurality of times with the recording head 204.

  When band data image formation is started, the recording data setting unit 185 determines whether or not processing of all the image data stored in the image buffer 181 has been completed (S311), and there is unprocessed image data. If so, the process returns to step S302. By repeating the above processing, image formation for multi-tone image data is completed.

● Ycut setting method The Y coordinate Ycut setting method, which is the cutting position, will be described with reference to FIG. FIG. 21 shows four-pass printing in which an image is formed by four scans with respect to the same main scanning region on the image, using a recording head 204 in which eight nozzles are arranged in a row. Although the present embodiment can be realized even if the paper feed amount LF (k) after scanning at the scan number k is not constant, a case where the paper feed amount LF (k) is constant will be described for simplicity.

  As shown in FIG. 21, in general four-pass printing, an image is formed by using 1/4 nozzles at the lower end of the nozzle 2501 (that is, nozzle numbers n7 and n8) at a scan number k = 1. Subsequently, at scan number k = 2, paper feed is performed for 1/4 of the nozzle length with respect to scan number k = 1 (that is, LF (1) = 2), and 1/2 of the lower end of nozzle 2501. The nozzles (that is, n5 to n8) are used to form an image. Subsequently, at scan number k = 3, paper feed is performed for 1/4 of the nozzle length with respect to scan number k = 2 (that is, LF (2) = 2), and 3/4 of the lower end of the nozzle ( That is, an image is formed using n3 to n8). The above image formation is repeated to form an output image corresponding to the recording data 2502.

As shown in FIG. 21, the Y coordinate Ycut (1), which is the color separation data cut-out position at the scan number k = 1, is −6, the Ycut (2) at the scan number k = 2 is −4,. When the paper feed amount LF (k) is constant, Ycut (k) is generalized by the following equation.
Ycut (k) = -Nzzl + (Nzzl / Pass) × k… (2)
Where Nzzl is the number of nozzle rows,
Pass is the number of print passes.

  The Y coordinate Ycut (k), which is the color separation data cut-out position at the scan number k, is recorded in the recording data setting LUT 186.

Recording Data Setting Method Recording data setting (S305) will be described with reference to FIG. FIG. 22B shows the division ratio of input data for each nozzle. In other words, the horizontal axis of FIG. 22 (b) indicates a division ratio that takes a real value from 0 to 1 when the input duty is 1. The division ratio for each nozzle is determined by the number of passes, the paper feed amount, and the number of used nozzles, and is recorded in the input duty division table (record data setting LUT 186). In the present embodiment, for the sake of simplicity, an example in which the paper feeding amount is constant is shown.

  The recording data shown in FIG. 22 (c) is set as the product of the color separation data shown in FIG. 22 (a) and the division ratio shown in FIG. 22 (b). However, when the image Y address corresponding to the nozzle is outside the image area, the recording data is set to 0. For example, in the scan number k = 1, as shown in FIG. 21, the image Y address corresponding to the 3/4 nozzles at the upper end of the nozzle row becomes a negative value, and 0 is set as the recording data corresponding to these nozzles. Is done. In addition, a significant value is set in the recording data corresponding to the 1/4 nozzle at the lower end.

  Note that Ycut (k), which is the color separation data cut-out position, depends on the scan number k. Therefore, when the scan number k = 1 to 7, the print data is set as shown in FIG. 22 (c). The recording data in FIG. 22 (c) is determined by the product of the color separation data and the division ratio stored in the recording data setting LUT 186. When the product is taken while feeding paper, the scan number k = 1 to The total value of one raster formed by four scans of 4 is the same as the color separation data. Similarly, in the areas 2, 3, and 4, the total value of one raster is the same as the color separation data.

[Gloss unevenness suppression processing]
When recording an image with a predetermined amount of ink, if the recording is divided into a large number of passes, the gloss tends to be smaller than when recording with a small number of passes. For this reason, the number of passes is determined based on the range of signal values, and uneven glossiness with different glossiness depending on the density and color of the reproduced image is reduced.

  FIG. 23 (a) shows an example of the relationship between lightness (signal value) and glossiness. A curve 2701 represented by a thin solid line shows the relationship between the brightness (signal value) and glossiness of an image when recorded with a small number of passes (for example, 2 passes), as in FIG. 17 (a). On the other hand, a curve 2101 represented by an alternate long and short dash line shows a relationship between brightness (signal value) and glossiness of an image when recording is performed with as many passes as possible (for example, 4 passes). In the example shown in FIG. 23 (a), recording is performed with as few passes as possible in a high brightness area equal to or higher than the brightness indicated by reference numeral 2104 and a low brightness area equal to or lower than the brightness indicated by reference numeral 2103. Then, if recording is performed by dividing into as many passes as possible in the remaining intermediate brightness range, a glossiness curve represented by a thick solid line can be obtained, and a change in glossiness with respect to the brightness (signal value) of the image can be suppressed. And uneven gloss can be suppressed.

  The curve 2701 is obtained by plotting the measured values of the glossiness of a plurality of color charts (patches) having different lightness values that are adjusted to a predetermined lightness by performing two-pass printing on a predetermined recording medium. . A curve 2101 is obtained by plotting the measured values of the glossiness of a plurality of patches having different lightness values that have been adjusted to a predetermined lightness by performing 4-pass printing on the same recording medium. Each patch may be printed with a fixed signal value or ink amount without adjusting to a predetermined brightness.

  A method for setting the intermediate brightness area will be described with reference to FIG. As described above, a patch is printed by two-pass printing, the glossiness for each lightness is measured, and the average glossiness 2201 at the time of two-pass printing is calculated from the measured glossiness value. Next, a patch is printed by 4-pass printing, the glossiness for each lightness is measured, and the average glossiness 2203 at the time of 4-pass printing is calculated from the measured glossiness value. Then, an average value 2202 of the average glossiness is calculated.

  Next, for a certain lightness, calculate the difference between glossiness and average value 2202 during 2-pass printing, calculate the difference between glossiness and average value 2202 during 4-pass printing, and calculate the number of passes with the smaller difference. The number of paths for the brightness (signal value) is determined. If such a determination is made for each lightness, lightness 2103 and 2104 where two buses and four passes are switched are obtained, and an intermediate lightness region between lightness 2103 and 2104 for performing four-pass printing can be set. Then, the recording pass number determination table is stored in the recording data setting LUT 186 so that the number of passes becomes 4 in the intermediate brightness range between the brightnesses 2103 and 2104.

  In the above, examples of 2-pass printing and 4-pass printing have been given, but the same argument holds for all n types of passes (n ≧ 2).

  In the above description, the method of switching the number of passes from the change in the glossiness with respect to the brightness has been described. However, the number of passes may be switched from the change in the image clarity. Also, the number of passes may be switched using the change in glossiness and the change in image clarity so that these changes are minimized.

  FIG. 24 shows an example of the relationship between brightness (signal value) and image clarity. A curve 2702 represented by an alternate long and short dash line shows the relationship between image brightness (signal value) and mapping properties when recording is performed with a relatively large number of passes (for example, 4 passes), as in FIG. On the other hand, a curve 2301 represented by a thin solid line shows the relationship between image brightness (signal value) and image clarity when recorded with a relatively small number of passes (for example, two passes). In the example shown in FIG. 24, recording is performed with a small number of passes in a high lightness area equal to or higher than the lightness indicated by reference numeral 2104 and a low lightness area lower than the lightness indicated by reference numeral 2103. Then, if recording is performed by dividing into as many passes as possible in the remaining intermediate brightness range, a glossiness curve represented by a thick solid line can be obtained, and a change in glossiness with respect to the brightness (signal value) of the image can be suppressed. And uneven gloss can be suppressed.

  In this way, the degree of occurrence of uneven gloss is predicted according to the image characteristics of the input image (and further according to the gloss characteristics of the color material and the recording medium), and the uneven gloss suppression process is executed according to the occurrence degree of uneven gloss. Can be controlled. Therefore, an image with a high degree of gloss unevenness can be printed without performing the gloss unevenness suppression process, and an image with a low degree of gloss unevenness can be printed without performing the uneven gloss reduction process.

[Other Examples]
The present invention can also be realized by executing the following processing. That is, software (program) that realizes the functions of the above-described embodiments is supplied to a system or apparatus via a network or various storage media, and a computer (or CPU, MPU, etc.) of the system or apparatus reads the program. It is a process to be executed.

Claims (11)

An image processing apparatus of an image forming apparatus that prints an image using a pigment-based color material,
Detecting means for detecting image characteristics of the image to be printed;
Predicting means for predicting the degree of occurrence of uneven glossiness when the image is printed based on the image characteristics;
An image processing apparatus comprising: a determination unit configured to determine whether or not to perform a gloss unevenness suppression process in the image printing process based on a degree of occurrence of the uneven gloss.   2. The detection unit according to claim 1, wherein the detection unit creates a brightness image of the image as the image characteristic, and the prediction unit predicts the degree of occurrence of the gloss unevenness from the spread of the brightness distribution of the brightness image. Image processing device.   The detecting means creates a brightness image of the image and calculates a spatial frequency distribution of the brightness image as the image characteristics, and the predicting means calculates the uneven glossiness from a ratio of a low frequency component and a high frequency component indicated by the spatial frequency distribution. 2. The image processing apparatus according to claim 1, wherein a degree of occurrence is predicted. The detecting means calculates the spatial frequency characteristic and brightness of the object as the image characteristic to the object dividing the image, the prediction means visual sensitivity consists spatial frequency components on a predetermined value or more, between adjacent objects 2. The image processing apparatus according to claim 1, wherein the occurrence degree of the gloss unevenness is predicted from a difference in brightness. And a memory for storing a table indicating a relationship between brightness and glossiness according to the color material and recording medium used by the image forming apparatus,
The detection means creates a lightness image of the image as the image characteristics, and the prediction means refers to the table, converts the lightness distribution of the lightness image into a glossiness distribution, and from the spread of the glossiness distribution 2. The image processing apparatus according to claim 1, wherein the degree of occurrence of uneven gloss is predicted.   6. The image forming apparatus according to claim 1, wherein the image forming apparatus changes a fixing temperature of the color material when it is determined to execute the gloss unevenness suppressing process. Image processing device.   6. The image forming apparatus according to claim 1, wherein the image forming apparatus changes a fixing speed of the color material when it is determined to execute the gloss unevenness suppressing process. Image processing device.   6. The image processing apparatus according to claim 1, wherein the image forming apparatus changes the number of recording passes when it is determined to execute the gloss unevenness suppressing process. . An image processing method of an image forming apparatus for printing an image with a pigment-based color material,
Detect the image characteristics of the image to be printed,
Based on the image characteristics, predict the degree of occurrence of uneven gloss when the image is printed,
6. An image processing method, comprising: determining whether or not gloss unevenness suppression processing is to be executed in the image printing process based on a degree of occurrence of uneven glossiness.   9. A non-transitory computer-readable storage medium storing a program for controlling a computer device to function as each unit of the image processing device according to claim 1.   11. A computer-readable recording medium on which the program according to claim 10 is recorded.

Images