JP2013244647A - Image forming apparatus, image forming method, computer program, and recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus in which detection and adjustment for density unevenness can be easily performed without using a complicated apparatus and which is suitable for density adjustment for a coloring material with high lightness, and to provide an image forming method, a computer program, and a recording medium therefor.SOLUTION: An image forming apparatus includes an image output device 6 which forms a test chart on a recording medium so as to detect difference between density of an original image and that of the image to be formed when the image is formed on the recording medium, a control unit 2 which receives an amount of adjustment for density, and a density adjustment part 21 which adjusts the density of the image to be formed in the image output device 6 based on the amount of adjustment for the received density. The image output device 6 forms, on the recording medium, a test chart including an image with high lightness which is colored with a coloring material with high lightness and constituted by a plurality of patterns and in which at least one pattern is more susceptible to the influence of variable factors of density than other patterns and an image with low lightness which is colored with a coloring material with low lightness and constituted by the other patterns.

Description

  The present invention relates to an image forming apparatus, an image forming method, a computer program, and a recording medium that can form an image having a uniform density.

  In recent years, image forming apparatuses such as copiers and printers that employ an electrophotographic process have been widely used. Such an image forming apparatus includes a photosensitive drum, a charger that charges the photosensitive drum to a predetermined potential, and a laser beam that emits a laser beam in accordance with image data received from outside to form an electrostatic latent image on the photosensitive drum. Laser writing device to be generated, developing device for supplying toner to an electrostatic latent image formed on the surface of the photosensitive drum for development, and transfer device for transferring the toner image formed on the surface of the photosensitive drum onto a sheet Etc., and an image desired by a user is formed on a recording medium by an electrophotographic method.

  In such an image forming apparatus, the charging characteristics depending on the position of the photosensitive drum, the amount of laser light emitted from the laser writing apparatus, the amount of toner transported in the developing unit, the distance between the developing unit and the photosensitive drum, and the like are not uniform. Thus, for example, there is a problem that density unevenness occurs in an image formed on a recording medium, and density non-uniformity appears depending on the formation position. If the density non-uniformity is not eliminated, the image density may differ depending on the formation position even if an image is formed on a recording medium based on image data to be formed with the same density as a whole.

  In order to eliminate the non-uniformity of density according to the formation position, in Patent Document 1, a test patch is printed, and the printed test patch is color-measured to obtain a correction amount for each position. A method for correcting image data is disclosed.

Japanese Patent No. 3405555

  However, since the method disclosed in Patent Document 1 requires a device for performing color measurement in order to correct the density non-uniformity at each position, the correction is performed when there is no color measurement device. I can't do it. To correct density non-uniformity without using a colorimetric device, a patterned test image is formed on the recording medium, and image formation is performed while checking the density non-uniformity by means such as visual observation. A method for setting the density adjustment of the apparatus is conceivable. However, a color material with high brightness, such as a yellow color material, has a problem that it is difficult to visually recognize density non-uniformity because the contrast with the ground color (for example, white) of the recording medium is low. .

  The present invention has been made in view of such circumstances, and an object thereof is to easily detect and adjust density non-uniformity without using a complicated device such as a colorimetric device. Another object of the present invention is to provide an image forming apparatus, an image forming method, a computer program, and a recording medium that are suitable for density adjustment relating to a high brightness color material.

  An image forming apparatus according to the present invention includes an image forming unit that forms a test image on a recording medium so as to detect a difference in density between the original image and the formed image when the image is formed on the recording medium; An image forming apparatus comprising: a receiving unit that receives the adjustment amount; and an adjusting unit that adjusts the density of an image to be formed by the image forming unit based on the adjustment amount related to the density received by the receiving unit. The image forming means is colored with a high brightness color material, is composed of a plurality of patterns, and at least one pattern is more susceptible to density fluctuation factors than other patterns, and a low brightness image It is characterized in that the test image, which is colored with a lightness color material and is composed of a low lightness image composed of the other patterns, is formed on a recording medium.

  The image forming apparatus according to the present invention is characterized in that the plurality of patterns are patterns formed by dots, and the dot arrangement of the low brightness image is different from the dot arrangement of the high brightness image.

  In the image forming apparatus according to the present invention, the at least one pattern is a dot dispersion type dither pattern or an error diffusion pattern, and the other pattern is at least one of a dot concentration type dither pattern and a line pattern. It is characterized by being.

  In the image forming apparatus according to the present invention, the high brightness color material is a yellow color material, and the low brightness color material is any one of a cyan color material, a magenta color material, and a black color material. To do.

  The image forming method according to the present invention is colored with a high-lightness color material, is composed of a plurality of patterns, and at least one pattern is more susceptible to a density variation factor than the other patterns. , And an image forming step for forming a test image made of a low-lightness image formed of the other pattern on the recording medium, and a receiving step for receiving an adjustment amount related to the density. And an adjustment step for adjusting the density of the image to be formed based on the adjustment amount.

  The computer program according to the present invention is a computer program in which a computer is colored with a high-lightness color material, is composed of a plurality of patterns, and at least one pattern is more susceptible to density variation factors than other patterns. Means for forming on the recording medium a test image made up of a low-intensity image and a low-intensity image composed of the other pattern, and means for accepting an adjustment amount relating to density; It is characterized by functioning as means for adjusting the density of an image to be formed based on the adjustment amount relating to the density.

  A computer-readable recording medium according to the present invention records the computer program of the above-described invention.

  In the present invention, the image forming means forms a test image on a recording medium, the accepting means accepts an adjustment amount relating to the density, and the adjusting means is based on the accepted adjustment amount relating to the density by the image forming means. The density of the image to be formed is adjusted. The image forming means is colored with a high brightness color material, is composed of a plurality of patterns, and at least one pattern is more susceptible to density variation factors than the other patterns, and low brightness A test image, which is colored with a color material and is composed of a low brightness image composed of the other patterns, is formed on a recording medium. The test image colored with the high brightness color material and the low brightness color material is visually recognized as an image of a hue in which the high brightness color material and the low brightness color material are mixed. A test formed by a low-lightness image colored by a low-lightness color material when the density of the one pattern colored by the high-lightness colorant changes due to the influence of density variation factors during image formation The hue of the image also changes. A change in hue occurring in the test image is detected by a simple method such as visual observation, and the density of the image is adjusted by an adjustment amount of the density of the high brightness color material based on the detection result. Thereby, without using a complicated device, it is possible to detect the non-uniformity of the density with respect to the high brightness color material by a simple method such as visual observation, and appropriately adjust the density of the image to be formed, An image having a uniform density is formed.

  In the present invention, the plurality of patterns constituting the test image are patterns formed by dots, and the dot arrangement of the low brightness image is different from the dot arrangement of the high brightness image. A test image is recorded by suppressing the overlapping of the dots of the low brightness color material and the high brightness color material so that the dots of the low brightness color material and the high brightness color material do not overlap as much as possible because the dot layout of the low brightness image and that of the high brightness image are different. Form on top. The test image formed on the recording medium can be visually recognized as an image in which dots of low brightness color material and dots of high brightness color material are optically mixed.

  In the present invention, at least one of a plurality of patterns constituting the test image is a dot dispersion type dither pattern or error diffusion pattern, and the other patterns are dot concentration type dither patterns and line patterns. At least one of the above. Dot-dispersed dither pattern and error diffusion pattern are easy to show density change because each dot formation state changes depending on density variation factors such as photoreceptor characteristics and laser light quantity at the time of image formation. It is suitable for use as the one pattern that is easily affected by the above. On the other hand, the dot-concentrated dither pattern and line pattern have a small density change as a whole of the concentrated dots even if some dots have changed due to density fluctuation factors such as photoreceptor characteristics and laser light quantity. It is suitable for use as the other pattern that is less affected by the density variation factor than the one pattern.

  In the present invention, the high brightness color material is a yellow color material. Since the image of the yellow color material has high brightness, the contrast with the ground color (for example, white) of the recording medium is lower than that of other color materials, and it is difficult to visually observe the change in density. For example, a test image consisting of a low brightness image colored with a magenta color material, which is a low brightness color material, and a high brightness image with a yellow color material, becomes an orange image, and the high brightness image with a yellow color material causes the density variation factor. If the density changes due to the influence of, the test image is visually recognized as a change in orange hue.

  According to the present invention, the image forming unit forms a test image on the recording medium, the receiving unit receives the adjustment amount relating to the density, and the adjusting unit is formed by the image forming unit based on the received adjustment amount relating to the density. Adjust the image density. The image forming means is colored with a high brightness color material, is composed of a plurality of patterns, and at least one pattern is more susceptible to density variation factors than the other patterns, and low brightness A test image, which is colored with a color material and is composed of a low brightness image composed of the other patterns, is formed on a recording medium. For this reason, it is possible to detect a change in hue occurring in a test image by a simple method such as visual observation, and appropriately adjust the density of the image without using a complicated apparatus to form an image having a uniform density. Can do.

1 is a block diagram illustrating a configuration example of a digital multifunction peripheral according to a first embodiment of the present invention. FIG. 6 is an explanatory diagram for explaining background area determination processing by a background determination processing unit of the digital multi-function peripheral according to Embodiment 1 of the present invention; It is a figure which shows an example of LUT used for exposure adjustment by the exposure adjustment part of the digital multi-functional peripheral concerning Embodiment 1 of this invention. It is a figure which shows the example of the pattern which comprises the test chart used for the digital multifunctional device which concerns on Embodiment 1 of this invention. It is a figure which shows the contrast of the pattern which comprises the test chart used for the digital multifunctional device which concerns on Embodiment 1 of this invention. It is a figure which shows the example of the pattern which comprises the test chart used for the digital multifunctional device which concerns on Embodiment 1 of this invention. It is a figure which shows the example of a setting of the dither pattern of the centralized dot used for the digital multi-functional peripheral concerning Embodiment 1 of this invention. It is a figure which shows the example of the dither pattern of the dispersion | distribution dot used for the digital multi-functional peripheral concerning Embodiment 1 of this invention. It is a figure which shows the example of the test chart output by the image output device of the digital multi-functional peripheral concerning Embodiment 1 of this invention. It is a figure which shows the example of the test chart output by the image output device of the digital multi-functional peripheral concerning Embodiment 1 of this invention. It is a figure which shows the example of the test chart output by the image output device of the digital multi-functional peripheral concerning Embodiment 1 of this invention. It is a figure which shows the example of the test chart output by the image output device of the digital multi-functional peripheral concerning Embodiment 1 of this invention. It is a figure which shows the example of the test chart output by the image output device of the digital multi-functional peripheral concerning Embodiment 1 of this invention. It is a figure which shows the example of the correction amount input screen displayed on the display apparatus of the digital multi-function peripheral which concerns on Embodiment 1 of this invention. 4 is a flowchart showing a processing procedure of the control device of the digital multi-function peripheral according to Embodiment 1 of the present invention. It is a figure which shows the example of the pattern which comprises the test chart used for the digital multifunctional device which concerns on the modification 1 of this invention. It is a figure which shows the example of the test chart output by the image output device of the digital multi-function peripheral which concerns on the modification 1 of this invention. It is a figure which shows the example of the test chart output by the image output device of the digital multi-function peripheral which concerns on the modification 2 of this invention. It is a figure which shows the example of the adjustment amount input screen displayed on the display apparatus of the digital multi-function peripheral which concerns on the modification 2 of this invention. It is a block diagram which shows the principal part structure of the digital multifunctional device which concerns on Embodiment 2 of this invention.

  Hereinafter, embodiments in which an image forming apparatus, an image forming method, a computer program, and a recording medium according to the present invention are applied to a digital multi-function peripheral having a copy function, a print function, and the like will be specifically described with reference to the drawings.

(Embodiment 1)
FIG. 1 is a block diagram showing a configuration example of a digital multi-function peripheral according to Embodiment 1 of the present invention. The digital multifunction peripheral 1 according to the first embodiment includes a control device 2, a storage device 3, an operation device 4, an image reading device 5, an image output device 6, an image processing device 7, and a display device 8. As a whole, the digital copy function, copy function, printer function, facsimile transmission function, scan function, etc. of the present invention are implemented.

  The control device 2 is, for example, a CPU, loads a predetermined program from the storage device 3 as necessary, and executes the loaded program so that the digital multi-function peripheral 1 operates as the image forming apparatus according to the present invention. It is.

  The storage device 3 is, for example, a non-volatile semiconductor memory, and includes a control program for controlling each part of the hardware by the control device 2, various image data processed by the image processing device 7, and the image output device 6. An adjustment amount for adjusting the density of an image to be output and a plurality of pattern data constituting a test chart (test image) for detecting density non-uniformity are stored.

  The operation device 4 includes function buttons such as “FAX”, “COPY”, “PRINT”, “MAIL”, etc. related to important functions of the digital multifunction device 1, a numeric keypad, and an enter key for confirming received instructions. I have.

  The image reading device 5 includes a light source that irradiates light to a reading document, for example, an image sensor such as a CCD (Charge Coupled Device), and performs optical reading of image data of the document. In the image reading device 5, an analog electric light imaged from a document set at a predetermined reading position on the image sensor and separated into RGB (R: Red, G: Green, B: Blue). A signal is output. The analog electrical signal output from the image reading device 5 is input to the image processing device 7.

  The image output device 6 generates a electrostatic latent image on the photosensitive drum by emitting a laser beam in accordance with image data received from outside, a photosensitive drum, a charger for charging the photosensitive drum to a predetermined potential, and externally received image data. A laser writing device, a developing device for supplying toner to the electrostatic latent image formed on the surface of the photosensitive drum for development, a transfer device for transferring the toner image formed on the surface of the photosensitive drum onto a recording medium, etc. An image is formed on a recording medium such as a recording sheet or an OHP film based on the image data from the image processing apparatus 7. The image output device 6 may be configured to perform image formation by an ink jet method, a thermal transfer method, a sublimation method, or the like, in addition to performing image formation by an electrophotographic method using a laser writing device.

  For example, the image processing device 7 generates digital image data based on an analog signal input from the image reading device 5, or reads out image data stored in the storage device 3. Density adjustment processing is performed. The adjusted output image data is output to the image output device 6 or a communication device (not shown). As shown in FIG. 1, the image processing apparatus 7 includes an A / D conversion unit 11, a shading correction unit 12, an input processing unit 13, a background determination processing unit 14, an exposure adjustment unit 15, an area separation unit 16, and a color correction unit 17. , A black generation / undercolor removal unit 18, a spatial filter unit 19, a halftone generation unit 20, a density adjustment unit 21, and a test chart creation unit 22.

  An analog signal of image data from the image reading device 5 is transmitted through the image processing device 7 through an A / D conversion unit 11, a shading correction unit 12, an input processing unit 13, a background determination processing unit 14, an exposure adjustment unit 15, and a region separation. Unit 16, color correction unit 17, black generation / undercolor removal unit 18, spatial filter unit 19, halftone generation unit 20, and density adjustment unit 21 in this order (in the direction of the arrow), and as CMYK digital color data, The image is output to the image output device 6.

  The A / D converter 11 converts RGB analog signals from the image reading device 5 into digital signals. The shading correction unit 12 performs processing for removing various distortions generated in the illumination system, the imaging system, and the imaging system of the image reading device 5 on the digital RGB signal from the A / D conversion unit 11. . The input processing unit 13 performs γ correction processing on each of the RGB signals from which various distortions have been removed by the shading correction unit 12.

The background determination processing unit 14 determines the background area of the image data acquired via the image reading device 5 by determining whether the background density exceeds a predetermined threshold, for example. When the background area is determined, first, image data input as RGB signals is separated into luminance signals and chromaticity signals by converting the image data into luminance signals using the following equation.
Y _j = 0.30R _j + 0.59G _j + 0.11B _j

Here, Y _j is a luminance signal of each pixel, and R _j , G _j , and B _j are color components of each pixel. Alternatively, the lightness signal may be obtained by converting to a uniform color space such as CIEL ^* a ^* b ^* signal (CIE: International Lighting Commission, L ^* : lightness, a ^* , b ^* : chromaticity). good. FIG. 2 is an explanatory diagram for explaining the background region determination processing by the background determination processing unit 14 of the digital multifunction peripheral 1 according to Embodiment 1 of the present invention. The background determination processing unit 14 creates a histogram as shown in FIG. 2 for the entire image based on the luminance signal or lightness signal obtained as described above, and uses the most frequently used luminance (lightness) based on the created histogram. ) Is regarded as a background area, the brightness (brightness) Y _{f at} this time is compared with a preset threshold th, and if Y _f <th, it is determined that the density of the background exceeds the threshold, In other cases, it is determined that the background is below a predetermined density.

  The exposure adjustment unit 15 switches an output luminance allocation table (LUT: Look Up Table) for a plurality of preset input luminances according to the user setting when the user selects to adjust the exposure. Thus, the RGB value of the input image is corrected to remove the background. FIG. 3 is a diagram showing an example of an LUT used for exposure adjustment by the exposure adjustment unit 15 of the digital multi-function peripheral 1 according to Embodiment 1 of the present invention. In the background removal processing, the background determination processing unit 14 may detect the background and perform background removal based on the detected background level. In this case, the processing of the exposure adjustment unit 15 is not performed.

  The region separation unit 16 determines whether each pixel of the input image data is a pixel belonging to any of a character region, a halftone dot region, a printing paper photograph region (continuous tone region), and the like, based on the RGB signals. It is. Based on the separation result, the region separation unit 16 outputs a region identification signal indicating to which region the pixel belongs to the black generation / undercolor removal unit 18, the spatial filter unit 19, and the halftone generation unit 20. It is like that.

  The color correction unit 17 generates a CMY (C: cyan, M: magenta, Y: yellow) signal that is a correction of the RGB signal, and in addition, in order to improve color reproducibility, the spectrum of the CMY color material including an unnecessary absorption component Processing to remove color turbidity based on the characteristics is performed.

  The black generation / under color removal unit 18 generates a black (K) signal from the CMY three-color signals after color correction, and subtracts the K signal obtained by the black generation from the original CMY signal to generate a new CMY signal. The CMY three-color signal is converted into a CMYK four-color signal.

  The spatial filter unit 19 performs spatial filter processing using a digital filter on the image data of the CMYK signal input from the black generation / undercolor removal unit 18 based on the region identification signal, thereby correcting the spatial frequency characteristics. The output image is processed so as to prevent blurring and graininess deterioration.

  The halftone generator 20 performs, for example, gradation reproduction processing on the image data of the CMYK signal based on the region identification signal. The gradation reproduction process is performed so that the image is finally separated into pixels and each gradation can be reproduced. For example, in the region separated into characters by the region separating unit 16, the high frequency enhancement amount is increased by the sharp enhancement processing in the spatial filter processing by the spatial filter unit 19 in order to improve the reproducibility of black characters or color characters in particular. The At the same time, the halftone generation unit 20 selects a binarization or multi-value process on a high-resolution screen suitable for high-frequency reproduction.

  The density adjustment unit 21 stores various output image data such as CMYK image data output from the halftone generation unit 20 and various image data read from the storage device 3 in the storage device 3. Based on the adjustment amount, density adjustment processing is performed. The adjusted image data is output to the image output device 6.

  The test chart creation unit 22 reads pattern data stored in advance from the storage device 3, generates test chart data relating to a test chart for detecting image density non-uniformity, and the density adjustment unit 21. Is output.

  The display device 8 is, for example, a liquid crystal panel, and displays information to be notified to the user, a preview image, an adjustment amount input screen described later, and the like. When the preview is performed, the color correction unit 17 converts the RGB signal into an R′G′B ′ signal based on the display characteristics of the display device 8, performs spatial filter processing as necessary, and performs γ correction and display. To do. In this case, the processing of the black generation / undercolor removal unit 18, the halftone generation unit 20, and the density adjustment unit 21 is not performed. The display device 8 may be a touch panel that is also used as a part of the operation device 4.

  Hereinafter, the test chart used in the present embodiment will be described in detail with reference to FIGS. The test chart according to the present invention includes a pattern that is easily influenced by a density variation factor and a pattern that is not easily influenced by a density variation factor. In the first embodiment, a dot dispersion type dither pattern in which each dot is dispersed is used as the pattern that is easily affected by the density variation factor. A dot concentrated dither pattern in which dots are concentrated is used.

  FIG. 4 is a diagram showing an example of patterns constituting the test chart used in the digital multi-function peripheral according to Embodiment 1 of the present invention. 4, each of A and B is a dot dispersion type dither pattern (hereinafter simply referred to as a dot dispersion pattern) that is susceptible to the influence of density fluctuation factors and a pattern that is less susceptible to the influence of density fluctuation factors. A dot concentration type dither pattern (hereinafter simply referred to as a dot concentration pattern) is shown. As shown in FIG. 4A, the dot dispersion pattern is a halftone pattern that is designed so that dots are sparsely shot. When the characteristics of the photosensitive drum or the amount of laser light changes, the dots are dispersed. Since the formation state of the film changes, it tends to appear as a density change. As shown in FIG. 4B, the dot concentration pattern is composed of a dot aggregate formed by concentrating a plurality of dots, and is a halftone pattern designed so that some dots are densely packed. When the characteristics of the photosensitive drum or the amount of laser light varies, some of the dots constituting the pattern change, but the overall density hardly changes. That is, a dot dispersion pattern is a pattern that is more susceptible to density variation factors and has a relatively high sensitivity for detecting density fluctuations compared to a dot concentration pattern.

  Since the dot dispersion pattern tends to show density changes, it is possible to use only the dot dispersion pattern as a test chart. However, by outputting the dot concentration pattern together with the dot dispersion pattern, the density change is based on the dot concentration pattern. Can be easily detected. In the present embodiment, the test chart is composed of a dot dispersion pattern and a dot concentration pattern that have the same apparent density.For example, the dot distribution pattern and the dot concentration pattern are arranged in parallel in the sub-scanning direction. The entire image is a strip pattern extending along the main scanning direction. The density of the test chart may be set to a density at which fluctuations in the characteristics of the photosensitive drum and the amount of laser light can be easily detected. For example, when the image data is 8 bits (256 gradations), the density is about 18 ( Density value of CMYK color space). The test chart is preferably created for each of a plurality of concentrations (for example, 18, 32, 64, 88, 112). In this case, since the density value is in the CMYK color space, when the numerical value is large, the density becomes high, and there is a possibility that density unevenness is difficult to understand. For this reason, it is preferable to use a low density as the density of the test chart.

  Among the CMYK colors, the yellow color material, which is a high brightness color material, has a lower contrast with white paper than other color materials. As described above, the test chart uses a relatively low density halftone pattern in order to be susceptible to non-uniformity. However, the use of such a low density pattern further reduces the contrast of the yellow color material. For this reason, with a yellow color material, it is difficult to adjust the density uniformly by confirming a slight contrast when unevenness occurs.

  As a method for solving this, a test chart is formed by printing together with any one of cyan, magenta, and black color materials other than the yellow color material. Thereby, a slight change in the pattern due to the yellow color material having low visibility can be visually confirmed. For example, when printing is performed together with a magenta color material, the color is orange, the lightness is lower than that of the yellow color, and the contrast with white paper is higher than that of the yellow color material alone. When the yellow color material is affected by the non-uniformity, it appears as a change in orange hue, so that it can be visually confirmed.

  When a test chart is formed by printing a color material other than a yellow color material together with a yellow color material, a halftone pattern for printing a color material other than cyan, magenta, and black is not as shown in FIG. A centralized halftone pattern (halftone pattern for concentrating dots) that is not easily affected by uniformity is used. This is to make it easy to detect only the non-uniformity related to the yellow color material, and to make the other color materials less susceptible to the non-uniformity.

  FIG. 5 is a diagram showing a comparison of patterns constituting a test chart when printing a yellow color material together with other color materials, and FIG. 6 is a case where a yellow color material is printed together with other color materials. It is a figure which shows the example of the pattern which comprises this test chart. The dot-concentrated pattern using the yellow color material and the halftone pattern using the other color materials are configured so that the dots do not overlap (the number of overlapping dots is minimized). As shown in FIG. 5, when the concentrated pattern of the yellow color material and the concentrated dots of the other color materials overlap each other, the area where the yellow color material is formed by the distributed halftone pattern and the intermediate of the concentrated type The color changes in the region formed by the tone pattern, and the density unevenness cannot be detected properly visually. This is because in the area of dots formed with a distributed halftone pattern, yellow and other color material dots hardly overlap, so they are optically mixed, whereas in a concentrated halftone pattern This is because, in the formed region, color mixture is caused by superimposition of color materials, so that a difference occurs in the apparent color.

  On the other hand, as shown in FIG. 6, when the yellow color material and the other color materials are configured so that the dots formed in the concentrated halftone pattern do not overlap, the yellow color material is printed in a distributed manner. Since most of the optically mixed portions occupy both the area and the area printed in a centralized manner, the colors of the appearance match, and the influence of non-uniformity can be confirmed appropriately by visual observation.

  FIG. 7 is a diagram illustrating an example of setting a dither pattern of concentrated dots using a yellow color material and other color materials. The setting example shown in FIG. 7 shows a dither pattern in a case where the yellow color material and the concentrated dots of other color materials do not overlap. A dither matrix of concentrated dots for yellow color material and a dither matrix for other color materials are created. The numerical values in the dither matrix indicate the order in which dots grow, and indicate whether or not to print each pixel according to the input value. For example, when forming uniform image data on the entire surface consisting of pixels of the input value “10” or less in the growth order, since the dots below the input value are printed, numerical values from 1 to 10 in the matrix are described. The remaining pixels are printed, and the other pixels are not printed. The dither matrix of concentrated dots for yellow color material and the dither matrix for other color materials are made to have different growth orders at positions in the dither matrix.

  A pattern constituting the test chart is formed by arranging the dither matrix according to the matrix arrangement. FIG. 7 shows a pattern when printing is performed with a yellow color material and other color materials for pixels whose input value is “4” or less in the growth order, and the yellow color material and other color materials do not overlap. Is printed as follows. The setting of the pattern constituting the test chart shown in FIG. 7 is merely an example, and by other various setting methods, the concentrated dots formed by the halftone pattern using the yellow color material and the intermediate using the color material other than yellow are used. The effect of the present invention can also be obtained when control is performed so that concentrated dots formed by the tone pattern do not overlap.

  FIG. 8 is a diagram showing an example of a dither pattern of dispersed dots for yellow color material. A dither matrix of dispersed dots for yellow color material is created, and a dither pattern of dispersed dots of yellow color material is formed by arranging the dither matrix according to the matrix arrangement. The dither matrix of dispersed dots for yellow color material determines the growth order so that the dots grow in the order in which the dots are dispersed as much as possible. FIG. 8 shows a dither pattern in a case where a pixel having an input value “4” or less in the growth order is printed with a yellow color material.

  9 to 13 are diagrams showing examples of test charts output by the image output device 6 of the digital multi-function peripheral 1 according to Embodiment 1 of the present invention. Each drawing also outputs position information in the main scanning direction indicated by a to f so that the adjustment amount for each position in the main scanning direction substantially perpendicular to the conveyance direction of the recording medium can be visually determined. The density of the output test chart is expressed by, for example, dot density. Further, for convenience of explanation, an example in which the density of the dot dispersion pattern in the areas a and b is changed is shown. Here, the positions are indicated by a to f, but the present invention is not limited thereto, and any position that can determine the position may be used, and the density of the test chart is expressed by the dot density. However, the actually output test chart is not limited to the illustrated mode.

  The arrangement of the dot dispersion pattern and the dot concentration pattern may be any arrangement as long as the density unevenness can be visually confirmed. For example, FIG. 9 shows a test chart in which the dot dispersion pattern and the dot concentration pattern are arranged adjacent to each other. FIG. 10 shows a test chart in which the dot dispersion pattern and the dot concentration pattern are arranged so as to be slightly separated from each other. FIG. 11 shows a test chart in which dot dispersion patterns and dot concentration patterns are alternately arranged in the main scanning direction and also in the sub scanning direction. Here, the pattern arrangement is clearly shown. In order to express, the dot dispersion pattern is indicated by hatching, and the expression of density change is omitted. FIG. 12 shows a test chart in which two rows of dot concentration patterns are arranged and a dot dispersion pattern is arranged between the two rows. FIG. 13 shows a test chart in which dot dispersion patterns and dot concentration patterns are alternately arranged in two rows in the sub-scanning direction.

  Hereinafter, the procedure of the image density adjustment process will be described in detail. For example, when the user selects the test chart printing using the operation device 4, a message prompting user authentication such as password input is displayed on the display device 8. The digital multi-function peripheral 1 starts image density adjustment processing after user authentication.

  First, pattern data stored in advance from the storage device 3 is read by the test chart creation unit 22 and, for example, a test chart in which a dot dispersion pattern and a dot concentration pattern are installed adjacent to each other as shown in FIG. The test chart data according to the above is created and output to the density adjustment unit 21. The density adjustment unit 21 adjusts the test chart data from the test chart creation unit 22 based on the adjustment amount stored in the storage device 3, and outputs it to the image output device 6. Here, all the initial values of the adjustment amount for each position stored in the storage device 3 are set to “0”.

  Next, the image output device 6 outputs the test chart shown in FIG. 9 based on the test chart data from the density adjusting unit 21. As shown in FIG. 9, the density difference between the patterns is visually confirmed in the areas a and b. Accordingly, the user can determine that it is necessary to adjust the image density in the regions a and b based on the output test chart. As for a test chart for a yellow color material, for example, when a test chart is created together with a magenta color material, the density change of the yellow color material becomes a change in orange hue and is visually confirmed in the areas a and b. The Accordingly, the user can determine that it is necessary to adjust the density of the yellow color material of the image in the regions a and b based on the test chart for the yellow color material. In this case, for example, the user instructs to input the adjustment amount by using the operation device 4.

  The adjustment amount input screen is displayed on the display device 8. FIG. 14 is a diagram showing an example of a correction amount input screen displayed on the display device 8 of the digital multi-function peripheral 1 according to Embodiment 1 of the present invention. As shown in FIG. 14, on the adjustment amount input screen, an adjustment amount input frame for each region represented by a to f is set in association with the test chart. That is, the position information displayed on the adjustment amount input screen for inputting the adjustment amount is associated with the position information in the test chart. The adjustment amount is obtained by referring to a sample created in advance, for example. Specifically, an image is output in advance for a plurality of density values, and a sample in which the density change of the output image is associated with the adjustment amount is created. The user can easily obtain the adjustment amount by comparing the output test chart with the sample.

  The user manually inputs the adjustment amount on the adjustment amount input screen, thereby setting the adjustment amount of the region a as “+3” and the adjustment amount of the region b as “+2”. In the areas c to f, since the density difference between the patterns cannot be seen, the adjustment amount is set to “0”. When the input of the adjustment amount is completed, the user can instruct the end of the input of the adjustment amount with the operation device 4, for example. The adjustment amount input by the control device 2 is received and added to the adjustment amount stored in the storage device 3. In this manner, the adjustment amount stored in the storage device 3 is updated.

  Next, the test chart creation unit 22 reads pattern data from the storage device 3 again, creates test chart data, and outputs the test chart data to the density adjustment unit 21. Based on the adjustment amount stored in the storage device 3, the density adjustment unit 21 adjusts the density of the test chart data from the test chart creation unit 22 and outputs it to the image output device 6. The image output device 6 outputs a test chart based on the adjusted test chart data.

  The user visually determines whether or not there is a density difference between patterns in the output test chart (whether there is a difference in hue mixed with other colors in the case of a yellow color material). If it is determined that there is a density difference (hue difference), the above adjustment amount input and update, test chart data adjustment and output, etc. are performed again, and the density difference between the output test chart patterns The above process is repeated until (hue difference) disappears. When it is determined that there is no density difference (hue difference) between the patterns, the user can instruct the end of the adjustment with the operation device 4, for example. In response to a user instruction, the image density adjustment processing ends.

  For example, when the image output device 6 tries to output an image read by the image reading device 5, the density adjustment unit 21 performs processing by the halftone generation unit 20 based on the adjustment amount stored in the storage device 3. Adjust the image data. As a result, the image output device 6 outputs an image without density unevenness.

  FIG. 15 is a flowchart showing a processing procedure of the control device 2 of the digital multi-function peripheral 1 according to Embodiment 1 of the present invention. As shown in FIG. 15, the control device 2 instructs the test chart creation unit 22 to create test chart data (step S1). The test chart creation unit 22 reads pattern data stored in the storage device 3 in accordance with an instruction from the control device 2, creates test chart data, and outputs the test chart data to the density adjustment unit 21.

  The control device 2 instructs the density adjustment unit 21 to adjust the test chart data (step S2). The density adjustment unit 21 adjusts the test chart data from the test chart creation unit 22 based on the adjustment amount stored in the storage device 3. As described above, when the adjustment of the test chart data is started, the initial values of the adjustment amounts for each position stored in the storage device 3 are all “0”.

  The control device 2 instructs the image output device 6 to output the adjusted test chart data (step S3). The image output device 6 outputs a test chart based on the adjusted test chart data from the density adjustment unit 21 in accordance with an instruction from the control device 2.

  The control device 2 determines whether or not an adjustment amount input instruction from the user has been received (step S4). If it is determined that an adjustment amount input instruction has not been received (step S4: NO), the process proceeds to step S8. Proceed to

  When it is determined that the adjustment amount input instruction has been received (step S4: YES), the control device 2 instructs the display device 8 to display the adjustment amount input screen (step S5). The display device 8 displays an adjustment amount input screen in accordance with an instruction from the control device 2.

  The control device 2 determines whether or not the input of the adjustment amount by the user has been completed (step S6). When it is determined that the input of the adjustment amount has not been completed (step S6: NO), such determination is repeated until the input of the adjustment amount is completed.

  When it is determined that the input of the adjustment amount has been completed (step S6: YES), the control device 2 receives the input adjustment amount, and based on the adjustment amount stored in the storage device 3 and the received adjustment amount. Thus, the adjustment amount is updated (step S7).

  The control device 2 determines whether or not an instruction relating to the processing stop from the user has been received (step S8). If it is determined that an instruction relating to the process stop has not been received (step S8: NO), the process returns to step S1, and the operation of each step is repeated. If it is determined that an instruction relating to the process stop has been received (step S8: YES), the process ends.

  In the present embodiment, a test chart composed of a plurality of patterns and at least one pattern is more easily affected by a density variation factor than the other patterns is obtained visually from the output test chart. Input the adjustment amount to the adjustment amount input screen, adjust the density of the test chart to be output again based on the input adjustment amount, and perform the above operation until there is no density difference between the patterns in the output test chart. By repeating, it is possible to easily detect the density non-uniformity and obtain the density adjustment amount without using a complicated device such as a device for performing color measurement. Further, by adjusting the density of the image to be output by the image output device 6 based on the density adjustment amount thus obtained, an image having a uniform density can be easily output.

  In the present embodiment, the image output device 6 forms a test chart on the recording medium so as to detect a difference in density between the original image and the formed image when the image is formed on the recording medium. The image output device 6 is colored with a high brightness color material, is composed of a plurality of patterns, and at least one pattern is more susceptible to density fluctuation factors than other patterns, and a low brightness image. A test chart which is colored with a lightness color material and is composed of a low lightness image composed of the other pattern is formed on a recording medium. The test chart colored with the high brightness color material and the low brightness color material is visually recognized as an image of a hue in which the high brightness color material and the low brightness color material are mixed. A test formed by a low-lightness image colored by a low-lightness color material when the density of the one pattern colored by the high-lightness colorant changes due to the influence of density variation factors during image formation The hue of the chart also changes. A change in hue occurring in the test chart is detected by a simple method such as visual observation, and the density of the image is adjusted by an adjustment amount of the density of the high brightness color material based on the detection result. Thereby, without using a complicated device, it is possible to detect the non-uniformity of the density with respect to the high brightness color material by a simple method such as visual observation, and appropriately adjust the density of the image to be formed, An image having a uniform density can be formed.

  In this embodiment, a plurality of patterns constituting the test chart are formed by dots, and the dot arrangement of the low brightness image is different from the dot arrangement of the high brightness image. The test chart is formed on the recording medium so that the dots of the low brightness color material and the high brightness color material do not overlap with each other because the dot layout of the low brightness image and the dot layout of the high brightness image are different. The test chart formed on the recording medium can be visually recognized as an image in which dots of low brightness color material and dots of high brightness color material are optically mixed.

  In the present embodiment, at least one of a plurality of patterns constituting the test chart is a dot dispersion type dither pattern or an error diffusion pattern, and the other patterns are dot concentration type dither patterns and line patterns. At least one of them. Dot-dispersed dither pattern and error diffusion pattern are easy to show density change because each dot formation state changes depending on density variation factors such as photoreceptor characteristics and laser light quantity at the time of image formation. It is suitable for use as the one pattern that is easily affected by the above. On the other hand, the dot-concentrated dither pattern and line pattern have a small density change as a whole of the concentrated dots even if some dots have changed due to density fluctuation factors such as photoreceptor characteristics and laser light quantity. It is suitable for use as the other pattern that is less affected by the density variation factor than the one pattern.

  In the present embodiment, the high brightness color material is a yellow color material. Since the image of the yellow color material has high brightness, the contrast with the ground color (for example, white) of the recording medium is lower than that of other color materials, and it is difficult to visually observe the change in density. For example, a test chart composed of a low brightness image colored with a magenta color material that is a low brightness color material and a high brightness image with a yellow color material becomes an orange image, and the high brightness image with a yellow color material has a density. When the density changes due to the influence of the fluctuation factor, it can be visually recognized as a change in orange hue on the test chart.

(Modification 1)
In the first modification, the test chart is configured with three types of patterns. FIG. 16 is a diagram showing an example of patterns constituting a test chart used in the digital multi-function peripheral 1 according to the first modification of the present invention. A and B in FIG. 16 are the dot dispersion pattern that is easily affected by the density variation factor and the dot concentration pattern that is hardly affected by the density variation factor, similar to A and B in FIG. Is a line pattern that is not easily affected by concentration fluctuation factors.

  FIG. 17 is a diagram illustrating an example of a test chart output by the image output device 6 of the digital multifunction peripheral 1 according to the first modification of the present invention. The test chart is composed of a dot dispersion pattern, a dot concentration pattern, and a line pattern with the same apparent density. For example, these three types of patterns are sub-scanned in the order of the dot concentration pattern, the dot dispersion pattern, and the line pattern. The strips are arranged in parallel in the direction, and are formed in a strip pattern extending along the main scanning direction. In FIG. 17, the dot concentration pattern, the dot dispersion pattern, and the line pattern are expressed as pattern 1, pattern 2, and pattern 3, respectively, and the densities of the three types of patterns are all expressed by dot density.

  In the first modification, the example in which the pattern that is easily affected by the density variation factor is configured by only the dot dispersion type dither pattern is not limited thereto, but the pattern that is easily affected by the density variation factor is the dot. A distributed dither pattern and / or an error diffusion pattern may be included. Further, only one of the dot concentration type dither pattern and the line pattern may be used as the pattern which is hardly affected by the density variation factor.

  In Modification 1, by using a test chart composed of three types of patterns, the density difference between patterns (the difference in hue mixed with other colors in the yellow color material test chart) can be more visually confirmed. Therefore, the density adjustment amount can be obtained quickly.

(Modification 2)
In the second modification, a test chart having a plurality of densities is output to one recording medium, and an adjustment amount is obtained for each density. FIG. 18 is a diagram illustrating an example of a test chart output by the image output device 6 of the digital multifunction peripheral 1 according to the second modification of the present invention. As shown in FIG. 18, three test charts having different densities are formed on one recording medium (represented by density 1, density 2, and density 3, respectively). For example, it is composed of a dot dispersion pattern and a dot concentration pattern. Based on FIG. 18, the density 1 test chart has a density difference between patterns in areas a and b, and the density 2 test chart has a density difference between patterns in area a. 3, it is determined that there are density differences between patterns in the areas a, b, and c. In the test chart for yellow color material, it is determined that there is a difference in hue mixed with other colors at density 1, density 2, and density 3.

  FIG. 19 is a diagram showing an example of an adjustment amount input screen displayed on the display device 8 of the digital multi-function peripheral 1 according to the second modification of the present invention. The adjustment amount input screen shown in FIG. 19 is provided with an input frame for adjustment amounts for each density and each position in association with the test chart. By referring to the sample, the user can obtain the adjustment amount at the position where the density difference exists, and if the adjustment amount is input to the corresponding input frame, an appropriate adjustment is made based on the density of the image to be output. The concentration can be easily adjusted by the amount.

  In the second modification, the example in which each density test chart is configured with a dot dispersion pattern and a dot concentration pattern has been described. However, the present invention is not limited to this, and any test chart described above may be used.

(Embodiment 2)
FIG. 20 is a block diagram showing a main configuration of the digital multi-function peripheral 1 according to Embodiment 2 of the present invention. The digital multi-functional peripheral 1 according to the second embodiment is configured such that a program for performing an operation can be provided on a portable storage medium A such as a CD-ROM via an external recording medium I / F 9. ing. Furthermore, the digital multi-function peripheral 1 according to the second embodiment is configured such that the computer program can be downloaded from an external device (not shown). The contents will be described below.

  The digital multi-functional peripheral 1 according to the second embodiment includes an exterior (or interior) storage medium reader (not shown). The storage medium reader causes the test chart creator 22 to create test chart data. A program for causing the density adjustment unit 21 to adjust the test chart data, causing the image output device 6 to output the adjusted test chart data, accepting the input adjustment amount, and adjusting the density based on the adjustment amount is recorded. For example, this program is installed in the storage device 3 by inserting the portable storage medium A. Such a program is loaded into a RAM (not shown) of the control device 2 and executed. Thus, the image forming apparatus according to the first embodiment functions as the image forming apparatus of the present invention.

  As the storage medium, a memory (not shown) such as a ROM itself may be a program medium because processing is performed by a microcomputer, a tape system such as a magnetic tape and a cassette tape, a flexible disk, With magnetic disk such as hard disk and optical disk such as CD-ROM / MO / MD / DVD, card system such as IC card (including memory card) / optical card, or mask ROM, EPROM, EEPROM, flash ROM, etc. It may be a medium that carries a fixed program code including a semiconductor memory.

  It may be a medium that fluidly carries the program code so as to download the program code from the communication network via a communication device (not shown). When the program is downloaded from the communication network in this way, the download program may be stored in the main device in advance, or may be installed from another storage medium. The present invention can also be realized in the form of a computer data signal embedded in a carrier wave in which the program code is embodied by electronic transmission.

  In the above embodiment, the density adjustment unit 21 is provided in the image processing apparatus 7 and the density adjustment is performed on the output image data. However, the present invention is not limited to this. The adjustment unit 21 is provided in the image output device 6, and the density is adjusted by adjusting parameters related to the density such as the pulse width for driving the laser beam of the image output device 6 and the output of the laser beam. Also good.

  Further, in the above embodiment, density non-uniformity corresponding to the position in the main scanning direction is detected using a test chart in which a plurality of patterns are arranged in parallel in the sub-scanning direction and the whole extends along the main scanning direction. However, the present invention is not limited to this. However, the present invention is not limited to this, and a plurality of patterns are arranged in parallel in the main scanning direction, and the density of the density corresponding to the position in the sub scanning direction is measured using a test chart extending along the sub scanning direction. The density may be adjusted by detecting the uniformity.

  In the above embodiment, the case where the test chart data is created by the test chart creating unit 22 has been described. However, the present invention is not limited to this, and the test chart data is stored in the storage device 3 in advance and the test chart is output. In this case, the test chart data may be read from the storage device 3.

  In short, the above embodiments are merely examples and should not be considered as restrictive. The scope of the present invention is defined by the terms of the claims, rather than the meanings described above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

1 Digital MFP (image forming device)
2 Control device (accepting means)
3 Storage Device 4 Operating Device 5 Image Reading Device 6 Image Output Device (Image Forming Unit)
7 Image processing device 8 Display device 9 External recording medium I / F
21 Density adjustment unit (adjustment means)

Claims (7)

Image forming means for forming a test image on the recording medium so as to detect a difference in density between the original image and the formed image when the image is formed on the recording medium;
Accepting means for accepting an adjustment amount relating to density;
In an image forming apparatus comprising: an adjusting unit that adjusts a density of an image to be formed by the image forming unit based on an adjustment amount relating to the density received by the receiving unit.
The image forming means is colored with a high brightness color material, is composed of a plurality of patterns, and at least one pattern is more susceptible to density fluctuation factors than other patterns, and a low brightness image An image forming apparatus, characterized in that the test image, which is colored with a lightness color material and is composed of a low lightness image composed of the other patterns, is formed on a recording medium. The plurality of patterns are patterns formed by dots,
The image forming apparatus according to claim 1, wherein the low brightness image has a dot arrangement different from that of the high brightness image. The at least one pattern is a dot dispersion type dither pattern or an error diffusion pattern;
The image forming apparatus according to claim 1, wherein the other pattern is at least one of a dot concentrated dither pattern and a line pattern.   The high lightness color material is a yellow color material, and the low lightness color material is any one of a cyan color material, a magenta color material, and a black color material. The image forming apparatus according to any one of the above. Colored with a high-lightness colorant, composed of multiple patterns, and at least one pattern is colored with a high-lightness image and a low-lightness colorant that are more susceptible to density fluctuation factors than other patterns. An image forming step of forming a test image consisting of a low brightness image composed of the other pattern on a recording medium;
An accepting step for accepting an adjustment amount relating to density;
An image forming method comprising: an adjustment step of adjusting a density of an image to be formed based on an accepted adjustment amount. The computer is colored with a high-lightness color material, is composed of a plurality of patterns, and at least one pattern is more susceptible to density fluctuation factors than other patterns, and a low-lightness color material. Means for forming, on a recording medium, a test image that is colored and comprises a low-lightness image composed of the other pattern;
A computer program that functions as means for receiving an adjustment amount relating to density, and means for adjusting the density of an image to be formed based on the adjustment amount relating to the received density.   A computer-readable recording medium on which the computer program according to claim 6 is recorded.

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