JP2006264003A - Image forming apparatus and density setting method for image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that when an additional image is synthesized on an original image to output a print by using a plurality of machines with different printer engine characteristics, the density of the additional image is deviated on each machine. <P>SOLUTION: An image forming apparatus which synthesizes a visible additional image on the back ground of the original image to be an object for printing to output the print comprises a patch forming part 44 for forming a plurality of patches with different density outputting conditions, a patch density acquiring part 45 for acquiring respective patch densities formed on test charts based on their patch data, a density comparing part 46 for comparing respective patch densities acquired by this patch density acquiring part 45 with a reference density of the additional image specified between the kinds of the machines in advance, and a density setting part 47 for setting a patch density corresponding to the reference density as a target density of the additional image based on the result of comparison in this density comparing part 46. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile machine, and a multifunction machine and a density setting method thereof.

  Some conventional image forming apparatuses have a function of synthesizing an additional image with an original image (see, for example, Patent Documents 1 and 2). In this type of image forming apparatus, for the purpose of security management of an original image recorded on a sheet, a copy of a visible additional image, such as “copy prohibited” or “confidential”, is provided on the background portion (background portion) of the original image. Some of them have a function to print out management characters. Such an additional image is printed out at a density lower than that of the original image so as not to hinder the visibility of the original image (readability in the case of characters) as much as possible.

Japanese Patent No. 3530211 JP 2001-268356

  In general, in an image forming apparatus such as a copying machine, the density of an original image is optimized in accordance with the characteristics of each printer engine, so the density of an additional image also depends on the characteristics of each printer engine. Therefore, for example, when two machines A and B having different printer engine characteristics are set to the same density index level and an additional image is printed out on the paper, the additional information printed on the paper by the machine A is displayed. There may be a significant difference between the density and the density of the additional image printed on the paper by the machine B. As a result, depending on the machine used by the user, the density of the additional image may be too dark or too light.

  An image forming apparatus according to the present invention is an image forming apparatus that synthesizes a visible additional image with a background portion of an original image to be printed and prints it out, and forms a plurality of patches with different density output conditions on a test chart Patch forming means, an acquisition means for acquiring each patch density formed on the test chart by the patch forming means, each patch density acquired by the acquisition means, and a reference density of an additional image defined in advance between models And a setting means for setting the patch density corresponding to the reference density to the target density of the additional image based on the comparison result of the comparison means.

  In the image forming apparatus according to the present invention, a plurality of patches having different density output conditions are formed on the test chart by the patch forming unit, and each patch density formed on the test chart is acquired by the acquiring unit. Then, each acquired patch density and the reference density of the additional image defined in advance between the models are compared by the comparison means, and based on the comparison result, the patch density corresponding to the reference density is added by the setting means. Set to the target density.

  According to the present invention, even if machines having different printer engine characteristics are used, the target density of the additional image is set to the same level according to the common reference density on each machine without depending on the machine characteristics. Is done. Therefore, it is possible to reduce the density variation of the additional image between the models.

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

  FIG. 1 is a schematic diagram showing a configuration example of an image forming apparatus to which the present invention is applied. This image forming apparatus is mainly composed of a document holding unit 1, a scanner unit 2, a printer unit 3, and a paper tray unit 4 that have an automatic document feeder (ADF). The document pressing unit 1 presses the document set on the document table 5 from above, and is attached to the upper part of the scanner unit 2 so as to be openable and closable. The document is fed to the image reading position by the automatic document feeder while the document pressing unit 1 is closed, or is placed on the document table 5 by a user's manual operation involving opening / closing operation of the document pressing unit 1.

  The scanner unit 2 includes an optical scanning unit 6, a wire 7 for moving the optical scanning unit 6 in the sub-scanning direction (left-right direction in FIG. 1), a driving pulley 9 for driving the wire 7, and this driving pulley. And a motor (not shown) that rotates the motor 9. The optical scanning unit 6 optically reads and scans an original image. Although not shown, the optical scanning unit 6 includes a document image reading sensor (hereinafter referred to as “document reading sensor”) composed of a CCD (Charge Coupled Device) line sensor with a color filter, and an image reading on the document surface. A light source such as a halogen lamp for irradiating a line-shaped light is mounted. When the original image is full-color four colors, the original (color original) on which the color image is recorded (printed) is set for each of the light primary colors B (blue), G (green), and R (red). The document is read by a document reading sensor.

  The configuration of the scanner unit 2 is, for example, when the reading line direction of the document reading sensor (alignment direction of the pixel rows for reading) is the main scanning direction and the direction orthogonal thereto is the sub scanning direction. Two moving scanning bodies (carriages) in which the relative ratio of moving speeds (moving distances) in the scanning direction is set to 1: 2, and optical components (light source lamps, condensing mirrors, etc.) mounted on these two moving scanning bodies A configuration using a reflection mirror or the like and a lens system that forms an image of light guided by the optical component on the light receiving surface of the document reading sensor can be employed. In this case, an optical scanning unit is constituted by the two moving scanning bodies and the optical components mounted thereon. The two moving scanning bodies are also referred to as a full rate carriage on the high speed side and a half rate carriage on the low speed side. The full rate carriage includes optical components such as a light source lamp, a condensing mirror, and a full rate mirror. The half rate carriage includes optical components such as a pair of half rate mirrors whose mirror surfaces are arranged at right angles. The The moving method using these two carriages is also called a full half rate method.

  The printer unit 3 prints out an image to be printed on paper, and has a laser scanning unit (laser ROS; Laser Raster Output Scanner) 10 and a photosensitive drum 11. Around the photosensitive drum 11, a charger 12 for uniformly charging the surface of the photosensitive drum 11, and an electrostatic latent image written on the surface of the photosensitive drum 11 by the laser scanning unit 10 is developed into a toner image. A developing unit 13 that performs transfer, a transfer unit 14 that transfers a toner image to a sheet, a cleaner 16 that removes residual toner that has not been transferred to the sheet from the photosensitive drum 11, and the like are disposed.

  The photosensitive drum 11 is rotationally driven in the direction of the arrow in the figure by driving a motor (not shown). At that time, the charger 12 uniformly charges the surface of the photosensitive drum 11. Further, the laser scanning unit 10 generates a laser beam at the laser output unit 10 a and blinks (modulates) the laser beam according to the image data of each color from the scanner unit 2. The laser beam emitted from the laser output unit 10a is irradiated onto the surface of the photosensitive drum 11 through the polygon mirror 10b, the f / θ lens 10c, and the reflection lens 10d, and the photosensitive member is rotated according to the rotation of the polygon mirror 10b. Scanning is performed in the axial direction of the drum 11. As a result, an electrostatic latent image corresponding to the image of the original read by the scanner unit 2 is formed on the photosensitive drum 11.

  The electrostatic latent image thus formed on the photosensitive drum 11 is developed into a toner image by the developing unit 13, and this toner image is transferred to a sheet by the transfer unit 14. At this time, the toner (residual toner) remaining on the photosensitive drum 11 without being transferred to the paper is removed by the cleaner 16. Further, after the surface of the photosensitive drum 11 cleaned by the cleaner 16 is charged again by the charger 12, writing of electrostatic latent images of other colors is sequentially performed on the drum surface by driving the laser scanning unit 10. Done.

  The developing unit 13 is a rotary developing unit integrally including a yellow developing unit 13Y, a cyan developing unit 13C, a magenta developing unit 13M, and a black developing unit 13K. Each of the developing devices 13Y, 13C, 13M, and 13K is disposed around the rotation axis of the developing unit 13. For example, when developing the electrostatic latent image on the photosensitive drum 11 into a yellow toner image, the yellow developing device 13Y is disposed at a position (state shown in the drawing) facing (close to) the photosensitive drum 11. The yellow toner is supplied from the yellow developing unit 13Y to the surface of the photosensitive drum 11. When developing a cyan toner image, the developing unit 13 is rotated by approximately 90 °, and the cyan developing device 13C is disposed at a position facing the photosensitive drum 11. Similarly, when developing a magenta toner image, the magenta developer 13M is disposed at a position facing the photoconductor drum 11, and when developing a black toner image, the magenta toner image is placed at a position facing the photoconductor drum 11. A black developing device 13K is disposed.

  The transfer unit 14 has a transfer drum 15. A sheet carrier made of a dielectric film is stretched around the outer periphery of the transfer drum 15. The transfer drum 15 is connected to a dedicated electric motor or a rotational drive system of the photosensitive drum 11 by a gear and is driven to rotate in the direction of the arrow shown in the drawing. Around the transfer drum 15, a transfer charger 17, a separation discharger 18, a toner charge control charger 19, a peeling claw 20, a static eliminator 21, a cleaner 22, a pressing roll 23, and an adsorption charger 25 are arranged. Has been. The sheet conveyed from the sheet tray section 4 via the sheet feed roller 4a and the sheet feed guide 4b waits at the registration position 4c for timing with the image (toner image), and then at a predetermined timing. 15 and is attracted to the dielectric film by corona discharge of the attracting charger 25.

  The transfer drum 15 rotates in synchronization with the photosensitive drum 11. For example, a toner image developed with yellow toner is transferred to the paper wound around the outer periphery of the transfer drum 15 by the transfer charger 17, and the other colors (cyan, magenta, black) are sequentially transferred by the rotation of the transfer drum 15. ) Is transferred (overlaid). When the transfer drum 15 rotates four times and toner images for four colors are transferred onto the paper, the discharge is performed by the separation discharger 18 provided inside and outside the transfer drum 15. As a result, the paper is separated by the peeling claw 20 and sent to the fixing device 29 by the transport belt 27. In the fixing device 29, the toner image is melted and fixed on the paper by the hot pressure roller 30. Thus, one copy cycle relating to color copying is completed. Incidentally, in the case of black-and-white copying, since it can be handled by only one development process using the black developing device 13K, the copy cycle is shorter than that of color copying.

  FIG. 2 is a block diagram showing a schematic configuration of the image forming apparatus according to the embodiment of the present invention. In the figure, an image input unit 31 inputs an original image to be printed. The image input unit 31 is configured by the scanner unit 2. In addition to the scanner unit 2, the image input unit 31 receives image data transmitted from an external device to the own device via a network such as a LAN (Local Area Network) in the case of a network compatible model, for example. Network communication unit (not shown). Here, the original image refers to an image that is a source for print output. More specifically, for example, image data read from an original in copy mode, or from an external device via a network in print mode or facsimile mode. This is the image data received at.

  The image processing unit 32 performs predetermined image processing on the image data of the original image input from the image input unit 31. In addition, the image processing unit 32 performs composition processing of an original image and a stamp image as one of image processing. The image output unit 33 outputs the image processed by the image processing unit 32 on paper. The image output unit 33 is configured by the printer unit 3.

  FIG. 3 is a block diagram showing an internal configuration of the image processing unit 32. In the figure, the color correction unit 34 converts the image data of the original image input from the image input unit 31 into R (red), G (green), B (blue) data is converted into C (cyan), M (magenta), Y (yellow), and K (black) data.

  The spatial filter unit 35 corrects the resolution of the original image converted into CMYK data by the color correction unit 34. For example, the spatial filter unit 35 performs processing such as edge enhancement, MTF correction, smoothing, and moire removal by matrix calculation. is there.

  The screen generation unit 36 generates a screen (halftone image) for printing out the original image processed by the spatial filter unit 35. This screen is generated for each color of CMYK. Further, the screen generation processing by the screen generation unit 36 is performed by halftone processing such as dither processing.

  The stamp generation unit 37 generates a stamp image that is a visible additional image. The stamp image is printed out in the form of being superimposed on the background of the original image when the original image is printed on paper. The image synthesizing unit 38 synthesizes the original image screen-processed by the screen generating unit 36 and the stamp image generated by the stamp generating unit 37 and outputs the synthesized image to the image output unit 33.

  The UI unit 39 accepts user input operations and displays various types of information to the user. The UI unit 39 includes, for example, a display unit including a touch panel display and an operation unit having various operation buttons and keys. The output condition of the stamp image generated by the stamp generation unit 37 can be arbitrarily selected by the user using a user interface unit (hereinafter referred to as “UI unit”) 39. Whether or not the stamp image is actually printed out can be arbitrarily selected by the user using the UI unit 39.

  In the image processing unit 32 configured as described above, the image data of the original image input from the image input unit 31 is sequentially processed by the color correction unit 34, the spatial filter unit 35, and the screen generation unit 36 and sent to the image composition unit 38. It is done. At this time, if the UI unit 39 is instructed to print out the stamp image, the stamp generation unit 37 generates a stamp image according to the content of the instruction, and this stamp image is sent to the image composition unit 38. As a result, the image composition unit 38 performs composition processing of the original image and the stamp image, and outputs the composite image to the image output unit 33. As a result, the image output unit 33 prints out the stamp image on the background portion of the original image.

  FIG. 4 is a block diagram showing an internal configuration of the stamp generation unit 37. In the figure, a stamp type setting unit 40 sets a stamp type applied to a stamp image. The stamp color setting unit 41 sets a stamp color to be applied to the stamp image. The stamp density setting unit 42 sets the density of the stamp applied to the stamp image.

  The stamp type, stamp color, and stamp density described above are set as one of output conditions when generating a stamp image. The output condition of the stamp image is selected by the user using the UI unit 39, and the stamp type, stamp color, and stamp density are set by the setting unit (40, 41, 42) corresponding to the selection condition. The configuration is set. The UI unit 39 has five stamp type selection candidates such as “copy prohibited”, “confidential”, “export prohibited”, “confidential”, and “register”. Of these, the characters “copy prohibited”, “confidential”, “export prohibited”, and “confidential” represent copy management characters of a document obtained by printing out an original image on paper. “Registration”, which is one of the stamp type selection candidates, is prepared for the user to specify (select) a desired character from a plurality of characters (including symbols) registered in advance by the user. Is. Note that the stamp image is not limited to the copy management character and the user registration character exemplified here, and may be a graphic or an image. Further, the UI unit 39 may be configured such that the size and layout of the stamp image can be specified (selected).

  In addition, the UI unit 39 prepares four candidates such as “black”, “red”, “blue”, and “arbitrary” as stamp color selection candidates, and “dark”, “normal”, and “light” as stamp densities. Four candidates such as “arbitrary” are prepared. Among these, “arbitrary” prepared as a stamp color selection candidate is prepared for the user to specify (select) a desired color from among a plurality of colors that can be output by the printer unit 3. “Arbitrary” prepared as a stamp density selection candidate is prepared for the user to specify (select) a desired density from a plurality of densities that can be output by the printer unit 3.

  On the other hand, the target density setting unit 43 sets a target density that serves as a reference (index) when the stamp density setting unit 42 sets the stamp density. The target density setting unit 43 sets the target density of the stamp image separately from the target density of the original image. Therefore, even if the target density setting unit 43 changes the setting of the target density of the stamp image, the density of the original image printed on the paper is not affected at all, and only the density of the stamp image changes. Become.

  The target density of the stamp image is set for each of the “dark”, “normal”, and “thin” density index levels prepared in the UI unit 39 as selection candidates for the stamp density. Therefore, for example, when the user selects the stamp density “high” in the UI unit 39, the stamp image is printed out with the target density set by the target density setting unit 43 corresponding to this “dark”. The stamp density setting unit 42 sets the stamp density. When the target density setting corresponding to “dark” is changed by the target density setting unit 43, the stamp density setting unit 42 prints the stamp image with the target density after the setting change. The density is set.

  FIG. 5 is a block diagram showing an internal configuration of the target density setting unit 43. In the figure, a patch generation unit 44 generates patch data for a plurality of patches having different density output conditions. The patch data generated by the patch generation unit 44 is sent to the printer 3. The printer unit 3 forms the plurality of patches on a test chart (paper) by performing a print output operation based on the patch data sent from the patch generation unit 44. The patch density acquisition unit 45 acquires each patch density formed on the test chart. The density comparison unit 46 compares each patch density acquired by the patch density acquisition unit 45 with a reference density defined in advance between models, and the density setting unit 47 compares the result of comparison by the density comparison unit 46. Is used to set the target density of the stamp image.

  Next, the procedure for setting the target density of the stamp image in the target density setting unit 43 will be described with reference to the flowchart of FIG. First, patch data for a plurality of patches having different density output conditions is generated by the patch generation unit 44, and the patch data is sent to the printer unit 3 for printing, whereby a plurality of patches having different density output conditions are printed on a sheet. A test chart formed is created (steps S1 and S2). The density output condition can be arbitrarily changed by appropriately changing the density output pattern applied to the patch formation. For example, as shown in FIG. 7, the density output pattern is constituted by a threshold matrix of 8 × 8 pixels. In this case, the density can be set in 65 levels from 0 to 64.

  Here, for example, if the patch density is changed step by step within the range of numbers (1 to 64) assigned to the threshold matrix, 64 patches having different density output conditions are formed on the test chart. become. However, the stamp image is printed out at a density sufficiently lower than that of the original image so as not to be noticeable on the paper. Therefore, when setting the target density of the stamp image, a plurality of representative patch densities are appropriately selected in the density range lower than the intermediate level of the density setting range (maximum set density to minimum set density). Only patches corresponding to the patch density need be formed (printed out) on the test chart.

  Therefore, in the present embodiment, three representative patch densities are selected in correspondence with the three density index levels of “dark”, “normal”, and “light” prepared as standard stamp density selection candidates. It was. That is, for the “dark” density index level, the density output pattern shown in FIG. 8A is selected as a representative patch density, and for the “normal” density index level, FIG. The density output pattern shown in FIG. 8C is selected as the representative patch density, and the density output pattern shown in FIG. 8C is selected as the representative patch density for the “thin” density index level. .

  Furthermore, for each representative patch density, a slightly darker patch density and a slightly thinner patch density were selected. That is, with respect to the “dark” density index level, a patch density slightly darker than that shown in FIG. As shown in FIG. 9D and FIG. 9E, as shown in FIGS. 9D and 9E, as shown in FIGS. 9D and 9E, as shown in FIGS. 9D and 9E, as shown in FIGS. In addition, the density output pattern of the 1-stage darker and 2-stage darker density output patterns in which the effective pixels are increased so that the overall dot shape tends to be vertically long is selected, and the patch density is slightly thinner than that. As shown in FIGS. 9 (F) and 9 (G), the density output patterns of the 1st and 2nd stages with the effective pixels reduced so that the overall dot shape tends to be horizontally long, Shown in (I) As such, it was decided to select the concentration output pattern of thin one-step diluted and 2-step overall dot shape has reduced the effective pixel to be the tendency of the vertical longitudinal.

  Similarly, with respect to the “normal” density index level, a patch density slightly higher than that shown in FIG. As shown in FIGS. 10D and 10E, as shown in FIGS. 10D and 10E, as shown in FIGS. 10D and 10E, as shown in FIGS. As shown in FIG. 10 (a), the first and second darker density output patterns in which the effective pixels are increased so that the overall dot shape tends to be vertically long are selected, and the patch density slightly thinner than that is selected. F) and (G), as shown in FIGS. 10H and 10I, the density output patterns of the first and second stages are thinned by reducing the effective pixels so that the overall dot shape tends to be horizontally long. As shown in Whole Tsu bets shape was decided to select a one-step dilution and two-stage dilute concentration output pattern with a reduced effective pixel so that the tendency of the vertical longitudinal.

  Further, with respect to the “thin” density index level, a patch density slightly darker than that shown in FIG. As shown in FIGS. 11D and 11E, as shown in FIGS. 11D and 11E, as shown in FIGS. 11D and 11E, as shown in FIGS. 11D and 11E, as shown in FIGS. In addition, the density output pattern of one-step darker and two-step darker increased in effective pixels so that the overall dot shape tends to be vertically long is selected, and patch density slightly thinner than that is selected as shown in FIG. ) And (G), as shown in FIGS. 11 (H) and (I), the density output patterns of the first and second stages are thinned by reducing the effective pixels so that the overall dot shape tends to be horizontally long. As shown Total bets shape was decided to select a one-step dilution and two-stage dilute concentration output pattern with a reduced effective pixel so that the tendency of the vertical longitudinal.

  By selecting the patch density under the above conditions, a plurality of patches corresponding to the respective density output patterns are formed as visible images on the test chart. FIG. 12 shows an example of a test chart. In this test chart, according to the density output pattern selection method described above, the reference density patch, the slightly darker patch, and the slightly lighter patch are set for each of the dark, normal, and light density index levels. Are formed in two stages by dividing into horizontally long and vertically long. In particular, depending on the characteristics of the printer engine, even if the number of effective pixels in the density output pattern is the same, the image density reproducibility (strength) is often different when the overall dot shape is horizontally long and vertically long. As described above, it is desirable to form a patch with density output patterns having different vertical and horizontal directions even with the same effective number of pixels.

  Subsequently, the density of each patch formed on the test chart is measured, and the measurement result is acquired by the patch density acquisition unit 45 (steps S3 and S4). The patch density is measured by, for example, setting a test chart on the document table 5 of the own apparatus, reading an image of each patch with the scanner unit 2, and based on the image data obtained thereby, the density (density) of each patch. Value). In addition to acquiring the density of the patch formed on the test chart by measuring the patch density on its own device, for example, setting the test chart on a device other than the own device (scanner etc.) and measuring the patch concentration However, the measurement data obtained thereby may be acquired by being taken into the apparatus.

  Next, each of the patch densities previously acquired by the patch density acquisition unit 45 is compared with a reference density defined in advance between models by the density comparison unit 46 (step S5). The standard density defined between models is a density that is commonly applied to machines with different printer engine characteristics, and is experimentally determined in advance as a density that is optimal for application to a stamp image. is there. The reference density is defined for each of the three density index levels “dark”, “normal”, and “light” prepared as stamp density selection candidates.

  Therefore, for example, the reference density corresponding to the “dark” density index level is “first reference density”, the reference density corresponding to the “normal” density index level is “second reference density”, and “light”. When the reference density corresponding to the density index level is “third reference density”, the density comparison unit 46 compares each patch density previously acquired by the patch density acquisition unit 45 with “first reference density”. Thus, the patch density closest to the “first reference density” in each patch density is compared with the “second reference density” in each patch density by comparison with the “second reference density”. By comparing the patch density closest to the “third reference density” with the patch density, the patch density closest to the “third reference density” is extracted from each patch density and extracted. Three patch densities as density comparison results Forces.

  Subsequently, the target density of the stamp image is set by the density setting unit 47 based on the comparison result of the density comparison unit 46 (step S6). That is, in the density setting unit 47, as a comparison result in the density comparison unit 46, the patch density that is closest to the “first reference density” is selected as the stamp when the “dark” density index level is selected. Set to the target density to be applied to the image. Also, the patch density that is closest to the “second reference density” is set as a target density to be applied to the stamp image when the “normal” density index level is selected, and the “third reference density” is set. The patch density closest to “density” is set to the target density to be applied to the stamp image when the “thin” density index level is selected.

  Incidentally, regarding the density comparison in the density comparison unit 46 (processing in step S5) and the target density setting in the density setting unit 47 based on the comparison result (processing in step S6), “dark” “normal” “ You may make it carry out in order for every three density | concentration index levels of "thin". That is, the patch density closest to the “first reference density” is extracted from each patch density acquired by the patch density acquisition unit 45, and the “dark” density index level is selected. In this case, the target density to be applied to the stamp image is set, and the patch density closest to the “second reference density” is extracted from each patch density acquired by the patch density acquisition unit 45, and the patch is extracted. The density is set to the target density to be applied to the stamp image when the “ordinary” density index level is selected, and then the “third standard” is selected from the patch densities acquired by the patch density acquisition unit 45. Uses a processing procedure such as extracting the patch density closest to “density” and setting the patch density to the target density to be applied to the stamp image when the “thin” density index level is selected. It may be.

  By setting the target density of the stamp image in accordance with the processing procedure as described above, even for machines having different printer engine characteristics, the UI unit 39 can set the density index level prepared as a stamp density selection candidate. The target density is set so that each machine has the same output density (print density). Therefore, if the UI unit 39 selects the same stamp density (for example, “normal”) and instructs printing of the stamp image, the stamp image is printed at the same density on each machine without depending on the printer engine characteristics. Is printed out. Thus, in each machine, it is possible to reduce the variation in the density of the stamp image between the models without changing the density of the original image with the optimum conditions. Also in a single machine, the target density of the stamp image is periodically set (updated) in accordance with the above-described processing procedure, so that the density when the stamp image is printed out is maintained at a constant level for a long time. be able to.

  In addition, if the target density of the stamp image can be set for each color such as black, red, blue, or any color prepared as a candidate for the stamp color, for example, the target density for each stamp color Concentration settings can be optimized. Therefore, no matter what stamp color is selected, the quality of the copy management character can be maintained satisfactorily by adjusting the density of the stamp image to the target density.

  In addition, a halftone dot screen applied to halftone dot printing has a plurality of screens depending on differences in screen angle and screen shape (dot screen, line screen, etc.), so a stamp is provided for each halftone dot screen. In the case where the target density of the image can be set, the target density setting can be optimized for each halftone screen. As a result, image quality deterioration such as moire can be effectively avoided.

1 is a schematic diagram illustrating a configuration example of an image forming apparatus to which the present invention is applied. 1 is a block diagram illustrating a schematic configuration of an image forming apparatus according to an embodiment of the present invention. It is a block diagram which shows the internal structure of an image process part. It is a block diagram which shows the internal structure of a stamp production | generation part. It is a block diagram which shows the internal structure of a target density | concentration setting part. It is a flowchart which shows the setting procedure of target density | concentration. It is a figure which shows an example of the density | concentration output pattern applied to patch formation. It is a figure which shows an example of the density output pattern corresponding to the typical patch density applied to patch formation. It is a figure which shows an example of the density | concentration output pattern of the patch applied with respect to a density index level of "dark". It is a figure which shows an example of the density output pattern of the patch applied with respect to a "normal" density index level. It is a figure which shows an example of the density | concentration output pattern of the patch applied with respect to a density index level of "light". It is a figure which shows an example of a test chart.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 2 ... Scanner part, 3 ... Printer part, 31 ... Image input part, 32 ... Image processing part, 33 ... Image output part, 37 ... Stamp production | generation part, 38 ... Image composition part, 39 ... UI part, 40 ... Stamp type setting 41 ... Stamp color setting unit 42 ... Stamp density setting unit 43 ... Target density setting unit 44 ... Patch generation unit 45 ... Patch density acquisition unit 46 ... Density comparison unit 47 ... Density setting unit

Claims (7)

An image forming apparatus that synthesizes a visible additional image with a background portion of an original image to be printed and prints it out,
Patch forming means for forming a plurality of patches with different density output conditions on a test chart;
Acquisition means for acquiring each patch density formed on the test chart by the patch forming means;
Comparison means for comparing each patch density acquired by the acquisition means with a reference density of an additional image defined in advance between models;
An image forming apparatus comprising: a setting unit that sets a patch density corresponding to the reference density to a target density of the additional image based on a comparison result of the comparison unit. The image forming apparatus according to claim 1, further comprising a measurement unit that measures a patch density of the test chart. The image forming apparatus according to claim 1, wherein the setting unit can set a target density of the additional image for each color. The image forming apparatus according to claim 1, wherein the setting unit can set a target density of the additional image for each halftone screen. The image forming apparatus according to claim 1, wherein the setting unit sets a target density of the additional image separately from a target density of the original image. The image forming apparatus according to claim 1, wherein the additional image represents a copy management character. A density setting method for an image forming apparatus that synthesizes a visible additional image with a background portion of an original image to be printed and prints it out,
A patch forming process for forming a plurality of patches with different density output conditions on a test chart;
An acquisition step of acquiring each patch density formed on the test chart in the patch formation step;
A comparison step of comparing each patch density acquired in the acquisition step with a reference density of an additional image defined in advance between models;
A density setting method for an image forming apparatus, comprising: setting a patch density corresponding to the reference density as a target density of the additional image based on a comparison result in the comparison process.

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