JP2006166176A - Image processor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce a feeling of roughness due to a random number components added in gradation smoothing. <P>SOLUTION: A system which performs image formation by using variable-density toner/ink is configured to superpose a random number component to be added only on light color components among color components for which variable-density components are usable. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image processing apparatus used for an image forming apparatus for forming an image with a plurality of inks or toners having the same hue used in a copying machine, a printer, and a FAX.

  The market needs for printers are increasing year by year, and image forming apparatuses having an increased number of ink or toner colors have been proposed and realized in comparison with the conventional four-color image forming apparatuses using ink or toner of color. For example, in an inkjet printer, in order to reduce graininess in addition to the conventional four colors of cyan, magenta, yellow, and black, image formation is performed with six colors of ink including light cyan and light magenta. What is to be performed has been realized, and as an electrophotographic printer, a six-color printer such as an inkjet method has been proposed (the following Patent Document 1, Patent Document 2, and the like).

  In addition, electrophotographic printers that use green and orange inks to expand the color gamut, and image formation using inks and toners that support special colors such as red, blue, green, gold, silver, and fluorescent colors Some of these have been realized and proposed.

  As described above, there are various types and formats of the image forming apparatus in which the number of colors of ink and toner is increased, and all of them are intended to improve the color reproducibility capability of the image output device itself.

On the other hand, a problem of gradation skip (pseudo contour) that becomes noticeable when a gradation in CG or the like is output has been known. This occurs when the input image gradation step size exceeds the gradation step size that can be expressed by the printer. In order to prevent this, mainly in an electrophotographic image forming apparatus, a technique (gradation smoothing technique) that adds a weak random number to an image, reduces gradation skip (pseudo contour) in a gradation portion, and smoothes the image (gradation smoothing technique). Known (Patent Document 3, Patent Document 4).
JP 2001-290319 A JP 2001-318499 A JP 2000-118044 A JP 2000-134475 A

  The gradation smoothing technique described above superimposes a weak random number component on the image to make the gradation skip less noticeable. On the other hand, the image quality sometimes deteriorated. Further, since the signal value of the random number component to be superimposed is low, a signal value having a characteristic that dot formation is unstable is used. For this reason, the random number component formed with an image may be further affected by instability, and may become more noticeable.

  Accordingly, an object of the present invention is to provide an image processing apparatus which can solve the above-described drawbacks and can further improve image quality when a conventional gradation smoothing technique and an image forming apparatus using dark and light ink / toner are combined. It is.

  A plurality of image forming means for forming an image using at least one set of similar color shades and a plurality of image signal components composed of the color components of the dark color, and a plurality of shades of the same color. Color separation means for converting the image signal component into the image signal component, and random number addition means for adding a random number to the color-separated image signal, wherein the random number addition means outputs the image signal corresponding to the light and dark color material. As an input, the image signal corresponding to the dark color material is used to define the absolute amount of the random number to be added, and the random number having the specified absolute amount is added to the image signal corresponding to the light color material. The above-described problem is solved by a featured image processing apparatus.

  Also, an image forming means for forming an image using at least one set of similar color shades and a plurality of image signal components composed of the color components of the dark color material, and the color shades of the same color are formed. Color separation means for converting into a plurality of image signal components, wherein the color separation means corresponds to a first conversion means for converting an input image signal into an image signal corresponding to a dark color material, and a light color material A random number adding means for adding a random number to the color-separated image signal. In the random number adding means, the input image signal is an absolute amount of a random number to be added. The above-mentioned problem is solved by an image processing apparatus, which is used to define an image signal and adds a random number having the specified absolute amount to an image signal corresponding to a light color material.

  As described above, according to the image processing apparatus of the present invention, when the gradation smoothing technique using random number addition is applied to an image forming apparatus using dark / light ink / toner, by adding a random number component to a light color signal, While making the banding inconspicuous, it is possible to obtain high image quality with suppressed roughness of the image due to random number addition.

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

<Configuration of image forming apparatus>
FIG. 1 is a schematic sectional view of a full-color image forming apparatus (a multi-function machine having both a copying function, a printer function, and a FAX function) according to an embodiment of the present invention. In this example, the digital color image reader unit 300 is provided in the upper part, and the digital color image printer unit 100 is provided in the lower part.

  In the reader unit 300, the original 30 is placed on the original table glass 31 and exposed and scanned by the exposure lamp 32, and the reflected light image from the original 30 is condensed on the full-color CCD sensor 34 by the lens 33, and the color separation image. Get a signal. The color-separated image signal passes through an amplifier circuit (not shown), is processed by a video processing unit (not shown), and is sent to the printer unit 100 via an image memory (not shown).

  In addition to the signal from the reader unit 300, an image signal from a computer, an image signal from a FAX, and the like are similarly sent to the printer unit 100.

  Here, as an example, the operation of the printer unit 100 will be described based on a signal from the reader unit 300.

  The printer unit 100 is roughly divided into two image forming units, that is, a first image forming unit Sa including the first photosensitive drum 1a and a second image forming unit Sb including the second photosensitive drum 1b. Has been. These image forming portions Sa and Sb have substantially the same configuration (shape) from the viewpoint of cost reduction. For example, the configuration and shape of the developing unit described later are almost the same. As a result, the developing devices 41 to 46 can be interchanged with each other.

  Two drum-shaped photosensitive members (photosensitive drums) as image carriers, that is, a first photosensitive drum 1a and a second photosensitive drum 1b, are each supported rotatably in the direction of the arrow in the figure, and each of the arrows in the figure. Around the photosensitive drums 1a and 1b, pre-exposure lamps 11a and 11b, corona chargers (charging means) 2a and 2b, and a first exposure means 3a which is a laser exposure optical system. , Second exposure means 3b, potential sensors 12a and 12b, movable members (development rotary) 4a and 4b which are rotary developing device holding portions, and three developing devices each containing developer of different colors 41 to 43 and 44 to 46, primary transfer rollers 5a and 5b as primary transfer means, and cleaning devices 6a and 6b are arranged.

  Further, the number of developing units may be five or more in order to improve the image quality. In this embodiment, a configuration using six developing units 41 to 46 will be described.

  The developing unit is loaded with magenta toner 41, cyan toner 42, light magenta 43, yellow toner 44, black toner 45, and light cyan toner 46.

  Here, the dark and light color developers are prepared by changing the amount of the pigment having the same spectral characteristics. Accordingly, the light magenta toner has the same spectral characteristics as the magenta pigment but a low content, and the light cyan toner has the same spectral characteristics as the cyan pigment but a low content.

  In addition to these, it contains toners with different spectral characteristics of pigments from cyan, magenta, yellow and black, such as metallic toners such as gold and silver, and fluorescent toners containing fluorescent agents. It is also possible to mount a developing device (same shape as the above developing device) on the developing rotary.

  In addition, although the two-component developer used by mixing the toner and the carrier is loaded in the developing device, there is no problem even with the one-component developer composed only of the toner.

  Here, the use of dark and light colors for magenta and cyan is aimed at dramatically improving the reproducibility of light images such as human skin (to achieve a reduction in graininess). Is the aim).

  In the laser exposure optical systems 3a and 3b as exposure means, the image signal from the reader unit 300 is converted into an optical signal by a laser output unit (not shown), and the laser beam E converted into the optical signal is converted by the polygon mirror 35. The light is reflected and projected onto the exposure positions 38a and 38b on the surfaces of the photosensitive drums 1a and 1b through the lens 36 and the reflecting mirrors 37.

  At the time of image formation of the printer unit 100, the photosensitive drums 1a and 1b are rotated in the direction of the arrow A, and the photosensitive drums 1a and 1b after being neutralized by the pre-exposure lamps 11a and 11b are uniformly charged by the chargers 2a and 2b. A light image E is irradiated for each separation color to form latent images on the photosensitive drums 1a and 1b.

  Next, the rotary developing device holding section, that is, the first developing rotary 4a and the second developing rotary 4b, which are moving bodies, are rotated, and predetermined developing devices 41 and 44 are moved to the respective developing devices 41 to 41 on the photosensitive drums 1a and 1b. 43, or after moving to the common developing units 40a and 40b between the developing units 44 to 46, the developing units 41 and 44 are operated to invert the electrostatic latent images on the photosensitive drums 1a and 1b. Development is performed to form a developer image (toner image) on the photosensitive drums 1a and 1b using a resin and a pigment as a base. At this time, a developing bias is applied to the developing device.

  Further, as shown in the figure, the toner in the developing devices 41 to 46 is transferred from the toner storage units (hoppers) 61 to 66 for the respective colors disposed between and next to the laser exposure optical systems 3a and 3b. In order to keep the ratio (or toner amount) constant, it is replenished as needed at a desired timing.

  The toner images formed on the respective photosensitive drums 1a and 1b are superimposed on an intermediate transfer member (intermediate transfer belt) 5 as a transfer medium by primary transfer rollers 5a and 5b serving as primary transfer units. The primary transfer is sequentially performed so as to be formed. At this time, a primary transfer bias is applied to the primary transfer rollers 5a and 5b. As a result, the respective toner images are sequentially superimposed on the intermediate transfer belt 5 to form a full color toner image.

  Thereafter, the full-color toner image on the intermediate transfer belt 5 as a transfer medium is secondarily transferred collectively onto a sheet as a recording material. At this time, a secondary transfer bias is applied to the secondary transfer roller 54.

  The intermediate transfer belt 5 is driven by a driving roller 51 so that the transfer cleaning device 50 can be brought into contact with and separated from the driving roller 51 at a position facing the intermediate transfer belt 5.

  The photosensitive drums 1a and 1b are provided on the transfer surface t, which is the same plane portion formed by the intermediate transfer belt 5 stretched by two rollers 51 and 52. The photosensitive drums 1a and 1b are connected to the photosensitive drums 1a and 1b. Primary transfer rollers 5a and 5b, which are primary transfer units, are provided at opposing portions sandwiching the intermediate transfer belt 5.

  In addition, the roller that forms the transfer surface t is located downstream of the intermediate transfer belt 5 in the moving direction B and is opposed to the driven roller 52, and detects the positional deviation and density of the images transferred from the drums 1a and 1b. A sensor 53 is disposed, and control is performed to correct the image density, toner replenishment amount, image writing timing, image writing start position, and the like at each image forming unit Sa, Sb as needed.

  Further, the transfer cleaning device 50 facing the upstream drive roller 51 finishes superimposing images of necessary colors on the intermediate transfer belt 5, and then is pressed by the facing drive roller 51 and transferred to the recording material. The remaining toner on the intermediate transfer belt 5 is cleaned. After the cleaning is completed, the transfer cleaning device 50 is separated from the intermediate transfer belt 5.

  On the other hand, the recording material is conveyed one by one from the storage units 71, 72, 73 or the manual feed tray 74 by the respective paper feeding means 81, 82, 83, 84, and the skew is corrected by the registration rollers 85, and a desired timing is obtained. Then, the toner image on the intermediate transfer belt 5 is conveyed to a secondary transfer portion between the secondary transfer roller 54 and the intermediate transfer belt 5, which is a secondary transfer means for transferring the toner image onto the recording material.

  The toner image is transferred onto the recording material in the secondary transfer unit, the recording material passes through the conveyance unit 86, and the toner image is fixed by the heat roller fixing device 9, and the paper discharge tray 89 or a paper post-processing device (not shown). ).

  On the other hand, the intermediate transfer belt 5 after the secondary transfer is cleaned with the transfer residual toner by the transfer cleaning device 50 as described above, and again used for the primary transfer process of the image forming portions Sa and Sb.

  When images are formed on both sides of the recording material, the conveyance path switching guide 91 is driven immediately after the recording material passes through the fixing device 9, and the recording material passes through the conveyance vertical path 75 to the reversing path 76. After being guided, the reverse roller 87 is reversely rotated so that the rear end when the paper is fed is used as the head, and the paper is withdrawn in the direction opposite to the fed direction and sent to the double-sided conveyance path 77. After that, the paper passes through the double-sided conveyance path, skew correction and timing are performed by the double-sided conveyance roller 88, conveyed to the registration roller 85 at a desired timing, and an image is again formed on the other surface by the image forming process described above. Transcript.

<Configuration of controller unit and image processing unit>
FIG. 2 is a diagram illustrating a controller unit that controls the image forming apparatus illustrated in FIG. 1. The controller receives an instruction from the user, operates the apparatus and displays the apparatus state, the operation unit 205 for reading the image, the reader unit 206 for reading the image and sending the image signal to the image processing unit 207, and the received input image signal An image processing unit 207 that performs image processing suitable for image processing and output to a printer, sends the image to the printer unit 208, the printer unit 208 that forms an image on a paper medium, and an external host computer A network I / F 201 that receives PDL data and a PDL processing unit 202 that renders the PDL data received by the network I / F and sends the PDL data to the image processing unit. CPU 203 that performs. There are a number of components such as a FAX receiving unit in the controller, but a description thereof is omitted here.

  Next, FIG. 3 shows the configuration of the image processing unit. In the reader unit, the luminance image signal obtained by reading the document with the CCD is input to the image processing unit as a digital image signal. In many cases, 8 bits (= 256 gradations) are often used for one pixel. The RGB signal thus input is subjected to white reference correction by the shading correction unit 301 and subjected to a process called input masking by the input color processing unit 302 to remove the color blur caused by the spectral characteristics of the CCD. .

  Next, the frequency characteristics of the image input by the spatial filter unit 303 are corrected, and the LOG processing unit 304 inverts the RGB signal, which is a luminance signal, and converts it into a density signal, thereby obtaining a CMY signal. The output color processing unit 305 converts the CMY signal into a CMYK signal using a known output masking method or a three-dimensional LUT interpolation calculation and inputs the CMY signal to the gamma correction unit. The gamma correction unit 306 receives the image signal from the reader or the CMYK image rendered by the PDL unit, and performs tone correction using a one-dimensional LUT for each color component. Next, in the color separation unit 307, image signals suitable for the image forming apparatus, that is, cyan (C), light cyan (LC), magenta (M), yellow (Y), black (K) are input from the input CMYK signals. ) Is generated. More specifically, the four-color component signal is obtained by decomposing cyan and light cyan using cyan as input (C → C, LC) and decomposing magenta and light magenta using input magenta (M → M, LM). Is converted into a six-color component signal. The color signals thus color-separated are input to the random number addition processing unit 308, and the output of the random number addition processing unit is sent to the printer unit. For simplicity of explanation, it is assumed that each image signal flowing through the image processing unit is an 8-bit signal and the resolution is 600 dpi. Accordingly, it is assumed that an 8-bit, 600 dpi image signal of each color composed of six color components of C, LC, M, LM, Y, and K is sent to the printer unit.

  FIG. 4 shows an example of an input signal-density value characteristic of dark and light toner. Here, cyan and light cyan are illustrated, but the same applies to magenta and light magenta. Reference numeral 41 denotes a density value with respect to the cyan input signal level, and reference numeral 42 denotes a density value with respect to the light cyan input signal level. Since light cyan and cyan have such a toner density relationship, a typical example of C → C, LC color separation performed by the color separation unit 307 is as shown in FIG.

  The horizontal axis shows the level of the input cyan signal, and the vertical axis shows the level of the output signal. As shown by 52, the output level of light cyan increases in the low density part, and as it goes to the high density part, Control to increase the output level of cyan. The light cyan output level is attenuated from the middle density portion to the high density portion in order to keep the toner loading limit. Again, the color separation has been described for cyan and light cyan, but the same is true for magenta and light magenta.

  FIG. 6 is a diagram for explaining a gradation expression method in the printer unit. The image forming apparatus of the present invention has a resolution of 600 dpi for both main scanning and sub-scanning, and has a gradation expression capability of 256 gradations for each pixel by a pulse width modulation method (PWM). An overview of the scheme is shown in FIG. When a sawtooth wave a is generated in one pixel period and threshold processing is performed with a rectangular wave b in one pixel period corresponding to the level of each pixel, a rectangular wave c having a width corresponding to the level of each pixel is obtained. can get. With this width, 8-bit gradation expression is performed. In the printer unit, a laser is emitted according to the high level of the rectangular wave c and projected onto the surface of the photosensitive drum 1a or 1b.

<Configuration of random number addition processing section>
FIG. 7 shows the configuration of the random number addition processing unit in the present embodiment. The random number addition processing unit inputs a signal having both dark and light color components, in this embodiment dark cyan and light cyan, or dark magenta and light magenta, and calculates a random number to be added based on the dark color signal. The calculated random number component is added to the light color signal and output.

  As shown in FIG. 7, the random number addition processing unit includes a random number generation unit 701 that generates random number data that is a source of a random number signal to be added to image data, and a random number maximum value restriction that suppresses random number data to the maximum value of the random number signal. Unit 702, random number addition amount control unit 703 that adjusts the value of the random number to be added according to the gradation of the input dark color image, random number addition unit 704 that adds the adjusted random value to the input light color image signal, and random number addition It comprises a selector 705 for outputting either the light color image signal or the input light color image signal.

  The random number generator 701 generates a random number in the range of −127 to 127 using a known method. Examples of the random number generation method include a method using pseudo-random number generation such as an M-sequence random number method and a method of picking up hardware noise and converting it into a random number signal, but this method is not limited in this embodiment. Next, the random number maximum value limiting unit 702 multiplies the random number data generated by the random number generating unit with a preset absolute value of the absolute value of the random number (referred to as Rmax), so that −Rmax to Rmax or less. To suppress. Since the random number data is finally added to the light color image signal, the value of Rmax may be set larger than the case of adding the random number to the dark color signal. By doing so, the stability of the dots formed is increased, and a light color can be formed stably.

The random number addition amount control unit 703 controls the maximum absolute value of the random data to be added as shown in FIG. 8 according to the gradation of the input dark color image signal. That is, the maximum value of the random number signal to be added is controlled to a certain value or less as shown in FIG. That is, if the input dark color image signal value is x and the input random number signal is rnd,
if (x <N1) then rnd = rnd · | Rmax · (x−N1) / (N2−N1) |
if (x> N3) then rnd = rnd · | Rmax · (x−N4) / (N3−N4) |
otherwise rnd = rnd
The value is clipped to [-127: 127] and rnd is output.

  Here, N1, N2, N3, and N4 are constants arbitrarily set by the CPU 203. Here, the gradation is divided into three sections, but it may be divided into other section division numbers. . By controlling in this way, the amount of random numbers to be added is reduced in the low density portion of the input image so as not to feel a harsh feeling due to noise. In addition, control is performed so as to reduce the amount of added random numbers even in a high density portion where gradation skip is originally not conspicuous.

  Thus, after the amount of random numbers to be added is determined, the random number addition unit 705 adds the light color signal and the random number. The internal processing is such that after simple addition of the image signal value and the random number signal, when the image signal exceeds the range of [0: 255], the value is clipped to [0: 255]. I do.

  The selector 705 selects and outputs the random number addition signal output from the random number addition unit and the input light color image signal. Upon selection, for example, if there is an instruction from the operation unit 205 to perform random number addition to the image signal, the random number addition signal is selected, or if the image signal is external PDL data, the random number addition signal is selected, When the image signal includes gradation, the CPU 203 sets so as to select a random number addition signal when detected by an external detection means.

  FIG. 9 shows the configuration of the random number addition processing unit in the present embodiment when there is no gray signal such as black or yellow. In this case, the image signals input to the random number addition amount control unit 703 and the random number addition unit 704 are image signals with no distinction between light and shade. The other configurations are the same and will not be described.

  In the first embodiment, an example in which random number addition is performed on grayscale image data after color separation has been described. However, in this embodiment, an example in which the color separation unit 307 includes a random number addition processing unit 308 is illustrated. Show.

  The color separation unit shown in FIG. 10 further includes a dark color signal LUT 1006 and a light color signal LUT 1007 in addition to the configuration of FIG. In FIG. 10, an input image signal (here, cyan) before color separation into dark and light image data is input to a dark color signal LUT 1006 and a light color signal LUT 1007. As shown in FIG. A simple LUT operation is performed to output cyan and light cyan, respectively. The input image signal is input to the random number addition amount control unit 1003 before being converted into the dark color image signal, and is used for the random number addition amount control. Since the components 1001 to 1005 correspond to the components 701 to 705 in the first embodiment and perform the same functions, description thereof will be omitted.

  Compared with the first embodiment, in this embodiment, the random number addition amount is determined using the signal before being separated into the gray signal, so that the light color signal itself is more random than the case where the color separated signal is used. Roughness can be reduced and image quality can be further improved.

  In the description of the present invention, the color signals to be decomposed into light and dark signals have been described as cyan and magenta. However, black and yellow are also decomposed into dark and light signals, and the same smoothing circuit is applied to the developing device. May be output to an image forming apparatus in which the number is further increased. In the image forming apparatus, when one developing device is added, the number of developing devices is seven. Therefore, three or four developing devices may be arranged on the developing rotary, and when two developing devices are added. In this case, four developing devices may be arranged in the developing rotary.

  Further, the image forming apparatus according to the present invention has been described as using the PWM method as a gradation expression method, but the same applies to a printer having gradation expression of 2 or more and less than 8 bits. At this time, a pseudo halftone expression method such as a dither method or an error diffusion method may be used as a gradation expression method.

  Furthermore, in the description of the present invention, an electrophotographic printer is used as an example of an image forming apparatus. However, an output using an edge smoothing apparatus can be similarly applied to an ink jet printer that forms an image using dark and light inks. Needless to say.

The drawing which shows the example of the schematic sectional drawing which shows one Example of the image forming apparatus used by this invention Drawing showing controller configuration example Drawing showing configuration example of image processing unit Drawing showing examples of density toner characteristics (density-signal value characteristics) Drawing showing an example of dark-to-dark color separation Drawing showing a conceptual diagram of PWM The drawing which shows the example of a structure of the random number addition process part with respect to a grayscale signal Example of random number addition control Drawing showing a configuration example of a normal random number addition processing unit Drawing showing another configuration example of the random number addition processing unit

Explanation of symbols

100 Digital Color Image Printer Unit 300 Reader Unit 205 Operation Unit 207 Image Processing Unit 301 Jade Correction Unit 302 Input Color Processing Unit 304 LOG Processing Unit 305 Output Color Processing Unit 307 Color Separation Unit 308 Random Number Addition Processing Unit

Claims (8)

A plurality of image forming means for forming an image using at least one set of similar color shades and a plurality of image signal components composed of the color components of the dark color, and a plurality of shades of the same color. Color separation means for converting into image signal components of
Random number adding means for adding a random number to the color-separated image signal;
In an image processing apparatus comprising at least
The random number adding means receives an image signal corresponding to a light and dark color material, and the image signal corresponding to a dark color material is used to define an absolute amount of a random number to be added. An image processing apparatus that adds a random number to an image signal corresponding to a light color material.   The image processing apparatus according to claim 1, wherein the dark and light color material of the similar color is a dark and light color material of similar colors of cyan and magenta.   The image processing apparatus according to claim 1, wherein the color material having the same color and shades is a color material having the same color of cyan, magenta, and black. Image forming means for forming an image using at least one set of similar color shades;
In an image processing apparatus including a plurality of image signal components composed of color components of a dark color material, and a color separation unit that converts the plurality of image signal components that form dark and light color materials with the same color,
The color separation means includes a first conversion means for converting an input image signal into an image signal corresponding to a dark color material, and a second conversion means for converting into an image signal corresponding to a light color material. And random number adding means for adding a random number to the image signal,
In the random number adding means, the input image signal is used to specify an absolute amount of a random number to be added, and a random number having the specified absolute amount is added to an image signal corresponding to a light color material. An image processing apparatus.   The image processing apparatus according to claim 3, wherein the dark and light color material of the similar color is a dark and light color material of similar colors of cyan and magenta.   The image processing apparatus according to claim 3, wherein the dark and light color material of the similar color is a dark and light color material of the similar color of black.   The image processing apparatus according to claim 1, wherein the image forming unit is an electrophotographic printer.   The image processing apparatus according to claim 1, wherein the image forming unit is an ink jet printer.

Images