JPH04152757A - Image forming device - Google Patents

Abstract

PURPOSE:To reduce a picture element of a low density level stably by receiving the result of measurement for toner adhesion state, obtaining a valid minimum value in which an intermediate tone level is reproduced and correcting gradation obtained by anti-aliasing processing to have the valid minimum value or over. CONSTITUTION:A test pattern written on a photosensitive drum is subject to toner development by a multi-value color laser printer, the reproducing state of the test pattern subject to toner development is measured through a toner adhesion concentration measuring equipment and the result is fed back to a gamma discrimination section of a PDL controller 200 to obtain a valid minimum value at which an intermediate tone level is reproduced and a valid maximum value at which an intermediate tone level is reproduced. Then the gradation obtained by the anti-aliasing processing is corrected in a range to be the valid minimum value or over and the valid maximum value or below in the intermediate tone correction processing based on the valid minimum value and the valid maximum value obtained by the gamma discrimination section.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image forming apparatus that performs anti-aliasing processing to remove jagged edges of an output image.
More specifically, the present invention relates to an image forming apparatus that can always produce stable and beautiful anti-aliased images.

[Conventional technology]

In the field of computer graphics, when displaying an image on a CRT, which is an output medium, a technique called anti-aliasing processing is used to make the displayed image more beautiful. This process is performed on the jagged parts (called aliases) on the stairs as shown in Figure 20(a).
Apply brightness modulation to visually display the image in Figure 20 O: 1
) as shown in the figure.

In conventional image forming apparatuses, (1) uniform averaging method, (2) weighted averaging method, (2) convolution integral method, etc. are generally applied as anti-aliasing processing methods.

■The uniform averaging method calculates each pixel (picture element) to N*M (N,
After decomposing the image into sub-pixels (M is a natural number) and performing rask calculation at high resolution, the brightness of each pixel is determined by taking the average of N*M sub-pixels. Figure 21(a)
, (b), anti-aliasing processing using the uniform averaging method will be specifically explained. If the edge of the image overlaps a certain pixel (here, it is assumed that the image is connected to the bottom right of the diagonal line), and when anti-aliasing processing is not performed, as shown in the same figure (aJ),
The brightness kid of this pixel is assigned the highest brightness of the displayable gradations (for example, kid·255 for 256 gradations). When performing anti-aliasing processing on this pixel using the uniform averaging method with N=M=7, the same figure (
As shown in b), decompose the pixel into 7*7 sub-pixels and count the number of sub-pixels covered by the image. The count number (28) is divided by the total number of subpixels in one pixel (49 in this case), normalized (averaged), and multiplied by the maximum brightness (255) to calculate the brightness of that pixel. In this way, in the uniform averaging method, the brightness of each pixel is determined by taking into consideration how the image covers each pixel.

■Weighting is an averaging method The weighting and averaging method is a partial modification of the uniform averaging method. In contrast, the weighted averaging method assigns a weight to each subpixel, and the brightness of that subpixel (kid) is determined depending on which subpixel the image covers. The effects are different. Note that the weight at this time is given using a filter.

With reference to FIGS. 22(a) and (b), FIG. 21(a)
An example is shown in which the same image data is weighted using the same dividing method (N=M=7) and the averaging method.

FIG. 22(a) shows a filter (here, conef
ilter), and the corresponding sub-pixel is given the same weight as this characteristic. For example, the weight of the upper right corner subpixel is 2. When an image is applied to each subpixel, the weight value given by the filter characteristics becomes the count value of that subpixel. Same figure (b)
This figure shows how the display pattern of the image is changed depending on the weight of the sub-pixels. In this case, if we count the weighted subpixels of the image, we get
It becomes 199. This value is divided by the sum of the filter values (336 in this case) corresponding to uniform averaging, averaged, and multiplied by the maximum brightness to calculate the brightness of this pixel. Incidentally, as filters, the filters shown in FIGS. 23(a), (g)), (c), and (d) are known.

■Convolution integral method The convolution integral method is a method that refers to the appearance of surrounding pixels when determining the brightness of one pixel. That is, the area around one pixel whose brightness is to be determined is N
'xN'' pixels are considered to correspond to pixels of the uniform averaging method or the weighted averaging method.
The figure shows a convolution method with 3x3 pixel references. In this figure, the pixel whose brightness we are trying to determine is 2401
Indicated by The image continues below and to the right of the diagonal line, and the subpixels painted black are the subpixels that are counted.

Each pixel is divided into 4*4. Therefore, in this case, a 12*12 filter will be used. This method has the effect of removing high frequency components contained in a vector image.

On the other hand, a publishing system using a personal computer,
With the spread of so-called DTP (desk top publishing), systems for printing vector images, such as those used in computer graphics, have become widely used. A typical example is a system using Adobe's Post Script. PostScript is a page description language (Page Des
criptionLanguage: Below 1, PD
It belongs to a language genre called ``L'', and describes the form of the contents of a document, including the text (letter part), graphics, and their arrangement and appearance. It is a programming language for such systems.
A vector font is used as the character font.

Therefore, even if characters are scaled, the print quality can be significantly improved compared to systems that use bitmap fonts (for example, conventional word processors), and character fonts, graphics, and images can be There is an advantage that printing can be performed in a mixed manner.

However, the resolution of the laser printer used in these systems is no more than 240 dpi.
Many of them have a resolution of ~400 dpi, and similar to CRT display of computer graphics, there is a problem that aliasing occurs due to the low resolution. For this reason, even in image forming apparatuses that print using laser blinking, anti-aliasing processing has come into use in order to improve the quality of printed images.

[Problem to be solved by the invention]

However, in image forming apparatuses that pass conventional anti-aliasing processing, the power of the laser beam irradiated onto the photoreceptor may change due to deterioration of the laser light source or dirt on optical components such as mirrors and lenses. In addition, the sensitivity of the photoreceptor decreases due to fatigue of the photoreceptor material and temperature changes, the dot area of the latent image formed on the photoreceptor changes, and furthermore, the development characteristics (characteristics of the developer) change over time or change. As the state of toner adhesion to the latent image changes due to changes in the environment, reproducibility at low density levels deteriorates, leading to problems such as white areas being ordered, and high density levels of midtones. There was a problem in that the dots were crushed and the result was a solid color. In particular, when using anti-aliasing processing to visually smooth out the jaggedness of edge pixels (pixels at the boundary between image and non-image areas) by using halftone recording, the deterioration of gradation characteristics becomes noticeable. Deterioration of image quality occurs.

The present invention has been made in view of the above, and even if there is fatigue of the photoreceptor or changes in the environment such as temperature, white spots etc. do not occur, and the present invention can stably produce low density levels. The first objective is to be able to reproduce the pixels of .

In addition, the present invention has a second feature that even if there is fatigue of the photoreceptor or changes in the environment such as temperature, pixels at a high density level can be stably reproduced without solid coloring in halftone areas.
The purpose of

Furthermore, a third object of the present invention is to always obtain high-quality images regardless of fatigue of the photoreceptor or changes in the environment such as temperature.

C Means for Solving the Problems] In order to achieve the above-mentioned first object, the present invention provides an image forming method that measures the toner adhesion state of a toner-developed test pattern and feeds back the measurement results to an anti-aliasing processing section. In the apparatus, an effective minimum value determining means inputs the measurement result of the toner adhesion state and determines a reproducible effective minimum value of the halftone level, and an anti-resistance control is performed based on the small active amount determined by the effective minimum value determining means. The present invention provides an image forming apparatus including a correction means for correcting a tone value obtained through aliasing processing so that it becomes equal to or greater than an effective minimum value.

In addition, in order to achieve the above-mentioned second object, the present invention provides an image forming apparatus that measures the toner adhesion state of a toner-developed test pattern and feeds back the measurement result to an anti-aliasing processing section. An effective maximum value determination means that inputs the measurement results and determines the reproducible maximum effective value of the halftone level, and a gradation value determined by anti-aliasing processing based on the effective maximum value determined by the effective maximum value determination means. The present invention provides an image forming apparatus including a correction means for correcting the value to be equal to or less than the effective maximum value.

Furthermore, in order to achieve the above-mentioned third object, the present invention measures the toner adhesion state of a toner-developed test pattern and feeds back the measurement result to the anti-aliasing processing section. An effective minimum value determining means for inputting measurement results to determine the minimum reproducible effective value of the halftone level, and an effective minimum value determining means for inputting the measurement results of the toner adhesion state and determining the reproducible maximum value of the intermediate tone level. Based on the effective minimum value determined by the maximum value determination means, the effective minimum value determined by the effective minimum value determination means, and the effective maximum value determined by the effective maximum value determination means, the gradation value determined by anti-aliasing processing is determined to be greater than or equal to the effective minimum value. , and a correction means for correcting so that the range is less than or equal to the effective maximum value.

[Effect]

In the image forming apparatus of the present invention as set forth in claim 1, the effective minimum value determining means inputs the measurement result of the toner adhesion state and determines the reproducible effective minimum value of the halftone level. Thereafter, the correction means corrects the gradation value obtained by anti-aliasing processing so that it is equal to or greater than the effective minimum value, based on the effective minimum value obtained by the effective minimum value determination means.

Further, in the image forming apparatus of the present invention as set forth in claim 2, the effective maximum value determining means inputs the measurement result of the toner adhesion state and determines the reproducible effective maximum value of the halftone level. Thereafter, the correction means corrects the gradation value obtained by the anti-aliasing process so that it is equal to or less than the effective maximum value, based on the effective maximum value obtained by the effective maximum value determination means.

Furthermore, in the image forming apparatus of the present invention as set forth in claim 2, the effective minimum value determining means inputs the measurement result of the toner adhesion state and determines the reproducible effective minimum value of the halftone level. The effective maximum value determining means inputs the measurement result of the toner adhesion state and determines the reproducible effective maximum value of the halftone level. Thereafter, in the correction means, based on the effective minimum value determined by the effective minimum value determining means and the effective maximum value determined by the effective maximum value determining means, the gradation value determined by anti-aliasing processing is adjusted to be greater than or equal to the effective minimum value. , and correct it so that it is within the range of the effective maximum value.

〔Example〕

Hereinafter, an image forming system to which the image forming apparatus of the present invention is applied will be described as an example. ■ Overview of measurement value feedback processing in anti-aliasing processing, Block diagram of 0 image forming system, ■ Configuration and operation of PDL controller, ■ Image processing A detailed explanation will be given in the following order: the configuration of the apparatus, (1) the configuration and operation of the multi-valued color laser printer, and (2) the multi-valued drive of the driver.

■Summary of measurement value feedback processing in anti-aliasing processing The image forming apparatus of this embodiment develops a test pattern written on a photoreceptor drum with toner, and uses a toner adhesion density measuring device (details will be described later) to develop the test pattern written on the photoreceptor drum. Measure the reproduction state of the toner-developed test pattern. Thereafter, the measured value of the toner adhesion concentration measuring device is fed back and inputted to the gamma determination section (which also serves as effective minimum value determining means and effective maximum value determining means) of PDL controller 2°00, which will be described later, to determine the toner adhesion state. Based on the measured values, a reproducible effective minimum value of the halftone level and a reproducible effective maximum value of the halftone level are determined. After that, in halftone correction processing, based on the effective minimum value obtained by the gamma determination section and the effective maximum value, the gradation value obtained in the unchealiasing processing is set to be equal to or greater than the effective minimum value and the effective maximum value. The correction is made so that it falls within the following range.

First, the test pattern will be explained with reference to FIGS. 1(a) to 1(d).

The test pattern is for a laser printer that writes one dot with 64 values, and as shown in Figure 1(a), six levels between 0 and 63 values are arranged in the sub-scanning direction, and in the main scanning direction. are all arranged with the same value. The same figure (a
), 6 levels are selected at regular intervals of 64 values, but any number may be used as long as the number is sufficient to monitor gamma and the interval is sufficient. Further, in the test pattern shown in FIG. 12A, the levels are arranged in descending order from the top. This test pattern is the R
It is stored in advance in the OM205, and occurs once every several rotations of the photoreceptor drum (for example, once every 10 times).
Writing unit (multivalued color laser printer 5 described later)
00) for toner development.

Further, each of the six levels of the test pattern consists of a plurality of basic units (here, four basic units are assumed for simplicity), each unit consisting of NUN pixels. Therefore,
As shown in FIG. 1(b), the test pattern has a configuration in which four units lined up in the main scanning direction are all at the same level, and six different levels are arranged in each row in the sub-scanning direction.

Further, FIG. 1C shows the toner adhesion density relative to the writing level of the test pattern when measured by a toner adhesion density measuring device. Therefore, the six levels T1 to T6 in FIG. 1(a) become the toner adhesion densities R1 to R6, respectively, when measured by a toner adhesion density measuring device.

The toner adhesion density measuring device measures the toner adhesion density of the test pattern after development, uses the average value data within each basic unit as the measurement value, and sequentially measures it in the main scanning direction as shown in FIG. 1(d). DIl~D I4, then D in order in the sub-scanning direction
2+-'-D24, D31-D34, D4I-D44,
DSI to DS4 and D61 to D64.

The measurement value (toner adhesion density) measured by the toner adhesion density device is determined by the PDL controller 200 described later.
is fed back to the gamma determination section.

The gamma determination unit (which also serves as effective minimum value determining means and effective maximum value determining means) inputs the toner adhesion state measured by the toner adhesion concentration measuring device and determines the reproducible effective minimum value of the halftone level, and Find the maximum reproducible effective value of the halftone level.

The processing of the gamma determination section will be specifically explained below.

First, the toner adhesion state measured by the toner adhesion density measuring device is input, and the average value is determined by sequentially adding up four pieces of data. Here, the average value of the four data of D, ~D14 is calculated, and the average value of ,D,, ~Dzm is calculated as T2, D
The average value of 31 to D34 is Dn, the average value of D41 to D 44 is D4, D, ...the average value of DS4 is ■5, D 61 to
If the average value of D64 is 6, then Dn should correspond to Rn (n is 1 to 6) shown in FIG. 1(C). Therefore, the explanation will be continued using Rn as the average value from Dn-Rn.

The average value Rn obtained as above is compared in order from R1 with the minimum reproducible effective density 4aA of the halftone level obtained at that time, and when Rn>A, Rn is set to a new value. It is stored as a reproducible effective minimum density value A of the halftone level, and the writing level T corresponding to that Rn is stored.
The value of n (see FIG. 1C) is stored as the minimum reproducible effective value TL of the new halftone level.

Next, let m=
2, and when ΔR<D, it is determined that the density is saturated, and the writing level T corresponding to Rm at that time is determined.
The value of m is stored as the reproducible effective maximum value B of the halftone level.

However, which writing level corresponds to the toner adhesion density depends on the writing level stored as test pattern data and the value of n (or m) indicating which position of the test pattern is the data read. Can be matched.

The effective minimum value TL obtained by the gasomer determination section in this way
, and the effective maximum value TH in the halftone correction process,
It is used to correct the gradation value obtained by anti-aliasing processing so that it falls within a range of not less than the effective minimum value TL and not more than the effective maximum value TH.

The processing in the halftone correction process will be explained below.

After determining the gradation value K of each pixel using normal anti-aliasing processing, halftone correction processing uses the following formula to adjust the intermediate value so that the range is greater than or equal to the effective minimum value A and less than or equal to the effective maximum value B. A tone value Ks with the tone corrected is obtained.

The tone value Ks obtained in this way is determined as the final tone value to be output by anti-aliasing processing.

For example, in a multilevel printer with 64 gradations, the gradation value is 1.
If the result that only levels from 0 (minimum effective value TL) to 55 (maximum effective value TI() are effectively output) is fed back from the gamma judgment unit, the level calculated by normal antialiasing processing is By changing the adjustment value K, it is possible to generate a signal at a write level that is effectively output.

■Block diagram of the image forming system The image forming system of this embodiment uses the Page Description Language output from DTP (Desk Top Publishing).
e: hereinafter referred to as PDL language)) and image information read by an image reading device. The configuration of the image forming system of this embodiment will be described below with reference to FIG.

The image forming system includes a host computer 100 that creates a document written in PDL language (Postscript language is used in this embodiment);
The PDL controller 200, which applies anti-aliasing processing to the PDL language sent in pages from an image reading device 300 that reads image information via the PDL controller 20;
0. Alternatively, an image processing device 400 that inputs the image output from the image reading device 300 and performs image processing (details will be described later), and a multi-value color printer that prints the multi-value image data output from the image processing device 400. laser·
A printer 500, a PDL controller 2001 and an image reading device 300. Image processing device 400. and a system control section 600 that controls the multilevel color laser printer 500.

■Configuration and operation of PDL controller FIG. 3 shows the configuration of the PDL controller 200, which includes a receiving device 201 that receives the PDL language sent from the host computer 100, and storage control and control of the PDL language received by the receiving device 201. A CPU 202 that executes anti-aliasing processing, an internal system 203, a RAM 204 that stores the PDL language transferred from the receiving device 201 via the internal system 203, and a ROM 205 that stores anti-aliasing programs and the like.
, a page memory 206 that stores multivalued ROB image data subjected to anti-aliasing processing, a transmitting device 207 that transfers the RGB image data stored in the page memory 206 to the image processing device 400 , and a system control unit 600 . It is composed of an I10 device 208 that performs transmission and reception.

Here, the CPU 202 receives the P received by the receiving device 201.
The DL language is stored in the RAM 204 through the internal system hash 203 according to the program stored in the ROM 205. After that, you will receive one page of PDL language,
Once stored in the RAM 204, the graphic elements in the RAM 204 are subjected to anti-aliasing processing based on the flowchart described later, and the multivalued RGB image data is stored in the plain memory section of the page memory 206. , B, and a feature information memory section).

The data in the page memory 206 is then transferred to the transmitter 2
07 to the image processing device 400.

The operation of the PDL controller 200 will be described below with reference to FIGS. 4(a) and 4(b).

FIG. 4(a) shows a flowchart of processing performed by the CPU 202. As described above, the PDL controller 200 performs anti-aliasing processing on the PDL language sent page by page from the host computer 100, and converts it to red (R).

It is developed into three-color images: green (G) and blue (B).

In the PDL language, graphics and characters are all described using hector data, and as the name "page description language" indicates, image information is processed in units of pages. Furthermore, one page is made up of a small number of paths (one or more paths), with each path being made up of one or more elements (graphic elements and character elements).

First, when PDL language is input, it is determined whether the element is a curved vector, and if it is a curved vector, it is approximated to a straight line vector and registered as a straight line element (line) in the work area. This is performed for all graphic and character elements within one path, and linear elements are registered in the work area for each path (processing 1).

Then, the linear elements of the work area registered in this path unit are sorted by the starting X coordinate of the straight line (Processing 2
).

Next, in process 3, while updating the X coordinate one by one,
Performs filling processing using scanning lines. For example, in Figure 4 (
When performing the path filling process shown in b), the elements of the side across which the scanning line yc to be processed and the real value of the X coordinate across the scanning line yc (XI
3 X4) and AET (Active Edge Ta)
ble: Register in the table (table for recording the X coordinate of the edge portion appearing on the scanning line). Here, the order of the elements registered in the work area is the order in which they were registered in process 1, so they are not necessarily registered in order of decreasing X coordinate across the scanning line yc. For example, in process 1, if a straight line element passing through scanning lines yc and x3 in FIG. 4 is processed first, x3 is first registered in AET as the be done. Therefore, after registering AET, the elements of each side in AET are
Sort in ascending order of coordinates. Then, pair the first two elements of AET and fill in the space between them. Anti-aliasing processing is achieved in this filling processing by adjusting the density and brightness of the pixels in the edge portion according to the approximate area ratio. Then remove the processed edge from AET and update the scan line (update the X coordinate)
In other words, 1 until all edges in AET are processed.
The same process is repeated until all elements in one path are processed.

Above processing 1. Processing 2. The work in process 3 is executed pass by pass and repeated until all passes for one page are completed.

Next, FIGS. 4(C) and 4(d) will explain the anti-aliasing process and halftone darkness value correction process that are executed during the scan line filling process of process 3 described above.
) will be explained in detail with reference to the flowchart.

Here, for example, in process 1 of FIG. 4(a),
), this figure has the following elements.

(a) Line vectors of 5 trees AB, BC, C'D, DE, EA (represented by real numbers) (a) Color and brightness values inside the figure This figure is shown in Figure 5 (b) by the above-mentioned operation. It is divided into seven straight line vectors (expressed as real numbers) extending in the main scanning direction. At this time, in this embodiment, the following information is added to the starting points and ending points of the seven straight line vectors. That is, (c) Starting point coordinate values (real number expression) of vector elements ((a) above) that constitute the starting point and ending point of the straight line vector (d) Information on the vector elements that constitute the starting point and ending point of the straight line vector ( f) Characteristic information of the starting point and end point of a straight line vector (right edge, left edge, end point of a figure, line of 1 dot or less, intersection of straight lines, etc.) When an edge pixel is detected in the scan line filling process, Antialiasing processing shown in the flowchart of FIG. 4(C) is executed.

First, in subpixel filling processing, a filling area for each subpixel is calculated using a 3*3 subpixel division method (S401). This process is repeated for all vectors that cross the scanning line (S402).

Next, in the density determination process, the approximate area ratio of each pixel is calculated in order from the first pixel of the target scanning line using a uniform averaging method (anti-aliasing processing method) filter (S403). The fifth value obtained in this way
The approximate area ratio of the figure in FIG. 6(a) has a value as shown in FIG.

Next, each color (BK, R
, G, and B) are calculated (5404). Here, for example, the fifth
Assuming that the figure in figure (a) is drawn in red (maximum brightness: 255) on a white background (maximum brightness: 255), the area ratio of the area below the area k (see Figure 6) Therefore, the brightness values of each color of the figure (red) + (green) and Kb (blue) are determined based on the following formula.

)C, -KR+×k + K*z×(1k)K9=
KGIXk + KG2X(1-k)Kb =
K,, xk + KBZX (1k) However, K *
＋ ＋ K G
□ indicates the brightness value of each previously painted color. In addition, KFIZ
, Kcm, and KB□ refer to data in each plane memory section corresponding to RGB of the page memory 206.

Next, in the halftone correction process, the gamma determination section (see FIG. 4(d)) reproduces the halftone level obtained by adding , , , to the gradation values obtained in the above overwriting process. Using the minimum possible effective value A and the maximum reproducible effective value B of the halftone level, the edge pixels (halftone pixels) subjected to antialiasing processing are corrected using the following formula, and the final value is A gradation value Ks is obtained. For example, the effective minimum value TL
If only the effective maximum value TH (55) level is effectively output from (10), the tone value K calculated by normal anti-aliasing processing is corrected to obtain the tone value Ks (5405) .

After that, the gradation value of each color is written to the plain memory section 206a of the page memory 206 in page memory drawing processing (
S406).

Furthermore, the processes from 5403 to 5406 described above are repeatedly executed for all pixels of one line (S407).

The CPU 202 repeats the above processing up to the last pixel of the scanning line (y coordinate), and at the same time updates the contents of (c) above with the information of (d) above.

Next, the operation of the gamma determination section will be explained with reference to the flowchart in FIG. 4(d). In this example, gamma
Although the determination section is configured by a program, it is not particularly limited to this, and may be configured by hardware using a comparator or the like.

First, the toner adhesion state measured by the toner adhesion density measuring device is input, and the average value is determined by sequentially adding up four pieces of data. Here, the average value of the four data DIl to D, 4 is πI, and the average value of D21 to D24 is Dz, D
The average value of 31 to D34 is -D3, the average value of D41 to D44 is , D3. ～The average value of DS4 is ■5, D61
If the average value of %D64 is ■6, then Zn is as shown in Figure 1 (C)
It should correspond to Rn (n is 1 to 6) shown in . Below, the explanation will be continued assuming that the average value is Rn from Dn = Rn (
5408).

The average value Rn obtained in the above manner is compared in order from R1 with the reproducible effective minimum value A of the halftone level obtained at that time, and when Rn > A, Rn
is stored as the reproducible effective minimum density value A of the new halftone level, and the write level TnO value (see FIG. 1(C)) corresponding to that Rn is stored as the effective minimum density value TL (here, TL=10). ) (5409).

Next, let m=
2, and when ΔR<D, it is determined that the density is saturated, and the value of the writing level Tm corresponding to Rrrl at that time is set as the reproducible effective maximum value TH of the halftone level.
(Here, TH=55) (S4
10).

(2) Configuration of Image Processing Apparatus The configuration of the image processing apparatus 400 will be explained with reference to FIG.

The image processing device 400 is a CC in the image reading device 300.
The three-color image signals read by D7r, 7g, and 7b are converted into black (BK), yellow (Y), magenta (M), and cyan (C) recording signals necessary for recording. Additionally, the RGB image data given from the PDL controller 200 described above is similarly blanked (BK).
Yellow (Y), magenta (M), and cyan (
C) into each recording signal. Here, the mode for inputting an image signal from the image reading device 300 is a copying machine mode,
The mode in which RGB image data is input from the PDL controller 200 is called a graphics mode.

The image processing device 400 includes CCDs 7r, 7g, and 7b.
The color gradation data obtained by A/D converting the output signal of
a shading correction circuit 401 that performs correction for sensitivity variations, etc. of internal terminal elements of 7r, 7g, and 7b;
a multiplexer 402 that selectively outputs either the color gradation data output from the shading correction circuit 401 or the color gradation data (RGB image data) output from the PDL controller 200 according to the above-described mode;
A γ correction circuit 403 inputs the 8-bit, 7) data (color gradation data) output from the multiplexer 402, changes the dot tonality according to the characteristics of the photoreceptor, and outputs it as 6-bit data; and a γ correction circuit. Red (R) output from 403,
Green (G).

A complementary color generation circuit that converts 6-bit gradation data indicating the gradation of blue (B) into 8-level data (6 digits) of each complementary color, cyan (C), magenta (M), and yellow (Y). 405 and Y output from the complementary color generation circuit 405
A masking processing circuit 406 performs predetermined masking processing on each gradation data of , M, and C, and a masking processing circuit 406 that performs predetermined masking processing on each gradation data of Y,
A UCR processing/black generation circuit 407 that inputs M and C gradation data and executes UCR processing and black generation processing;
The 6-bit YM, C, and BK gradation data output from the R processing/black generation circuit 407 are converted into 3-bit gradation data Y1. M1. A gradation processing circuit 408 that converts CI and BKI and outputs it to the laser drive processing unit 502 inside the multivalued color laser printer 500, and a synchronization control circuit that synchronizes each circuit of the image processing device 400. 409.

Although details will be omitted, the γ correction circuit 403 has a configuration in which the gradation can be arbitrarily changed using an operation button on the console 700.

Further, as an algorithm used in the gradation processing circuit 408, a multi-value dither method, a multi-value error diffusion method, etc. can be applied. For example, a dither matrix of the multi-value dither method is
x3, multilevel color laser printer 500
The number of gradations is the product of 3×3 area gradations and 3 focus (that is, 8 levels) multilevel levels, and is 3×3×8=72 (gradations).

Next, the processing of the masking processing circuit 406 and the UCR processing/black generation circuit 407 will be explained.

Generally, the arithmetic expression for the masking process of the masking process circuit 406 is as follows: Y,,M,,C,: Data before masking process Y,,M,
,C,: Data after masking processing Also, the arithmetic expression for [JCR processing of UCR processing/black generation circuit 4 O7 is also generally expressed as follows.

Therefore, In this example, both Using the coefficient C product, I am trying to find new coefficients.

In this embodiment, a new coefficient (all°, etc.) that performs the masking process and the T'CR process simultaneously is calculated and determined, and the new coefficient is used to determine the scheduled input of the masking process circuit 406. Value Y,,M,.

Output value corresponding to Ci (6 bits each) (yo', etc.: value that is the calculation result of the UCR processing/black generation circuit 407)
is calculated and stored in a predetermined memory in advance.

Therefore, in this embodiment, the masking processing circuit 406 and U
The CR processing/black generation circuit 407 is composed of a set of ROMs, and the data at the address specified by the inputs Y, M, and C of the masking processing circuit 406 is given as the output of the UCR processing/black generation circuit 407.

In addition, for fishing on a boat, the masking processing circuit 406 performs Y,
The UCR processing/black generation circuit 407 corrects the M and C signals, and the UCR processing/black generation circuit 407 performs correction for color balance in overlapping toners of each color. After passing through the tJcR processing/black generation circuit 407, black component data BK is generated by combining the manually input three color data of Y, M, and C, and the output YM and C color component data are black component data. The value is corrected by subtracting BK.

In the above configuration, the γ correction circuit 403 executes processing based on the T correction conversion graph shown in FIG. 8, and the complementary color generation circuit 405 generates complementary colors shown in FIGS. 9(a), (b), and (C). After that, the masking processing circuit 406 and the UCR processing/black generation circuit 4
07 executes processing based on the following formula, page memory 20
The RGB image data of No. 6 is processed by a γ correction circuit 403, a complementary color generation circuit 405. Masking processing circuit 406. and U
After passing through the CR processing/black generation circuit 407, FIG. 10(a),
(b), (cl, (d)). Here, from the effective minimum value TLIO to the effective maximum value TH5
The case where only level 5 is effectively output is taken as an example.

Furthermore, if the gradation processing circuit 408 uses the Heyer type 3×3 multivalued dither matrix shown in FIG. 11, Y in FIGS. 10(a), m), (c), and (a) M.

The CBK data is shown in Figure 12 (a), (b), and
(C) Converted to the data shown in (d).

■Configuration of multivalued color laser printer First, the 13th
The schematic configuration of the multivalued color laser printer 500 will be described with reference to the control blocks shown in the figure.

A photoreceptor development processing unit 501 uniformly charges the surface of a photoreceptor drum (described later), exposes the charged surface to a laser beam to form a latent image, develops the latent image with toner, and transfers it to recording paper. The details will be explained later, but the development and development of BK data is
A black developing/transfer section 501bk that performs transfer, a cyan developing/transfer section 501c that develops and transfers C data,
A magenta developing/transfer section 50 that develops/transfers M data.
1m, and a yellow developing/transfer section 501y that develops and transfers Y data.

The laser drive processing unit 502 includes the image processing device 4 described above.
It inputs the 3-bit data of Y, M, C, and BK (here, image density data) output from 00, and outputs a laser beam.
a buffer memory 503y for inputting 3-bit data;
Laser diode 5 that outputs laser beams corresponding to 503m, 503c, Y, M, C, and BK, respectively.
04y, 504m 504c, 504bk and laser diode 504y, 504m, 504c, 504b
Tribars 505y, 505m, and 5 drive k, respectively.
It consists of 05c and 505bk.

Note that the blank developing/transfer section 5 of the photoreceptor development processing section 501
01bk, the laser drive processing unit 502, the laser diode 504bk, and the driver 505bk are called a blank recording unit BKU (see FIG. 14). Similarly, a cyan developing/transfer section 501c, a laser diode 504c, a driver 505c, and
The buffer memory 503c is combined with a cyan recording unit CU (see FIG. 14) and a magenta developing/transfer section 501m.
, Laser diode 504m, Tribar 505m
, and a combination of buffer memory 503m, magenta recording unit MU (see FIG. 14), yellow developing/transfer section 501y, laser diode 504y,
The combination of the driver 505y and the buffer memory 503y is a yellow recording unit) YU (see Figure 14).
It is called. As shown in the figure, these recording units are arranged around a conveyor belt 506 that conveys the recording paper in the following order from the conveyance direction of the recording paper: a blank recording unit BKU, a cyan recording unit CU, a magenta recording unit MU, and a yellow recording unit YU. has been done.

Due to this arrangement of each recording unit, the laser diode 5 for black exposure starts exposure first.
04bk, and the laser diode 504y for yellow exposure starts exposure last. Therefore,
There is a time difference in the order of exposure start between each laser diode,
Data recorded during the time difference (output of the image processing device 400)
In order to hold the data, the laser drive processing unit 502 includes the three sets of buffer memories 503y, 503m, and 503c described above.
is provided.

Next, the configuration of the multivalued color laser printer 500 will be specifically explained with reference to FIG.

The multilevel color laser printer 500 includes a conveyor belt 506 that conveys recording paper, and recording units YU, MU, and YU arranged around the conveyor belt 506 as described above.
Paper cassette 507 containing CU, BKU, and recording paper
a, 507b, and paper feed rollers 508a, 508b that feed recording paper from paper feed cassettes) 507a, 507b, respectively.
The recording units BKU, CU, M
A fixing roller 510 that sequentially conveys U and YU and fixes the transferred image on the recording paper, and a fixing roller 510 that fixes the transferred image on the recording paper, and the recording paper is transferred to a predetermined ejection section (
(not shown). Here, each recording unit YU MU, CU, BKU
are photosensitive drums 512y, 512m, 512c, 51
2bk and photoconductor tram 512y, 512m5 respectively
a charger 513y that uniformly charges 12c and 512bk;
513m, 513c, 513bk and photosensitive drum 51
Polygon mirrors 514y, 514m, 5 for guiding laser beams to 2y, 512m, 512c, 512bk
14c 514bk and motor 515y, 515m,
515c, 515bk, and photosensitive drums 512y, 51
2m Toner developing devices 516y, 516m, 516c, and 516bk that develop the electrostatic latent images formed on 512c and 512bk using toners of corresponding colors, and a transfer charger that transfers the developed toner images to recording paper. 51
7y, 517m, 517c, 517bk, and photosensitive drums 512y, 512m, 512c, 512b after transfer.
A cleaning device 51 that removes toner remaining on k
It consists of 8y, 518m, 518c, and 518bk.

Note that 519y, 519m, 519c, and 519bk are photosensitive drums 512y, 512m, 512c, and 51, respectively.
This figure shows a toner adhesion density measuring device for reading the test pattern provided on the 2bk, and is composed of a CCD line sensor and an LED light source arranged in the thrust direction.

In the above configuration, the operations of the yellow recording unit YU will be explained using exposure, development, and transfer as examples.

Figures 15 (a) and (b) are yellow record uniforms 7) YU
The configuration of the exposure system is shown. In the same figure, a laser beam emitted from a laser diode 504y is reflected by a polygon mirror 514y, passes through an f-theta lens 520y, and further passes through a mirror 521y.

522y and is irradiated onto the photosensitive drum 512y through the dustproof glass 523y. At this time, since the polygon mirror 514y is rotated at a constant speed by the motor 515y, the laser beam moves in a direction along the axis of the photosensitive drum 512y (main scanning direction). Furthermore, in this embodiment, a photosensor 524y is provided to detect the base point for tracking the scanning position of the main scan, so that the laser beam at the non-exposed position is detected. The laser diode 504y outputs recording data (
Since the photoreceptor drum 504y is activated to emit light based on the 3-bit data from the image processing device 400, multivalue exposure corresponding to the recording data is performed on the surface of the photoreceptor drum 504y. The surface of the photosensitive drum 504y is uniformly charged in advance by the charger 513y as described above, and an electrostatic latent image corresponding to the original image is formed by the exposure. The electrostatic latent image is developed by a yellow developing device 516y to become a yellow toner image. This toner image is transferred from the cassette 507a (or 507b) to the paper feed roller 50, as shown in FIG.
8a (or 508b), and is transferred by a registration roller 509 onto a recording sheet conveyed by a conveyor belt 506 in synchronization with the formation of a toner image of the black recording unit (BKU).

The other recording units BKU, CU, and MU have similar configurations and perform similar operations, but the black recording unit BKU is equipped with a black toner developing device 516bk and forms and transfers a black toner image, and the cyan recording unit The CU is equipped with a cyan toner developing device 516c, which forms and transfers a cyan toner image.
MtJ is equipped with a magenta toner developing device 516m, and forms and transfers one Zenk toner image.

In addition, the test pattern is written once every several rotations of the photoreceptor drum (for example, once every 10 times).
A test pattern stored in advance in the ROM 205 from the DL controller 200 is transferred to the laser drive processing unit 50.
This is carried out by transferring the information to 2.

■Driver multi-value drive driver 505y, 505m 505c 505b
k is sent from the image processing device 400 (Y, M, C
, BK, the laser diodes 504y and 504m are used daily.

It performs control for multi-value driving of 504c and 504bk, and power modulation, pulse width modulation, etc. are generally used as the driving method.

Hereinafter, the multivalue drive by power modulation applied in this embodiment will be explained in detail with reference to FIGS. 16(a), (b), (C), and (d). In addition, Triba 505y, 505m
.

505c, 505bk, and laser diode 50
4y, 504m, 504c, and 504bk have the same configuration, so here, the driver 505y and laser diode 504y will be explained as examples.

As shown in FIG. 16(a), the driver 505y turns on and off the laser diode 504y based on a predetermined LD drive clock.
n10ff circuit 550 and a D/D converter that converts 3-bit image density data (here, Y data) into an analog signal.
An analog signal based on the image density value is input from the A converter 551 and the D/A converter 551, and a current (LD drive current) Jc is used to drive the laser diode 504y.
1 and a constant current circuit 552 that supplies the current to the diode on10ff circuit 550.

Here, the LD drive clock is defined as on at 1'' and off at 0'', as shown in Figure 16 (bl).
The laser diode on10ff circuit 550 turns off the laser diode 504y accordingly.

Furthermore, since there is a proportional relationship between the LD drive current 1d and the laser beam power, by generating the LD drive current 1d based on the image density data value, the laser beam power output corresponding to the image density data value can be obtained. become. For example, as shown in FIG. 16(b), when the image density data value is "'4"' (data N-1 in the figure), the constant current circuit 552 supplies the corresponding LD drive current Id. The laser beam power of the laser diode 504y becomes level 4. Also, the image density data value is “7”.
'' (data N in the figure), the constant current circuit 55
2, the corresponding LD drive current 1d is supplied, and the laser beam power of the laser diode 504y becomes level 7.

Next, referring to FIG. 16(C), laser diode on10ff circuit 550. A specific circuit configuration of the D/A converter 551 and the constant current circuit 552 is shown. The laser diode F on/off circuit 550 includes TTL inverters 553 and 554 and differential switching circuits 555 and 55 that perform on/off toggle operation.
6 and VC; When 1>VC2, the differential switching circuit 555 is on and the differential switching circuit 556 is off.
, when VGl<VC2, the differential switching circuit 555
is off.

Resistors R, , R form a voltage dividing circuit that generates VC2 that satisfies the conditions for the differential switching circuit 556 to be turned on.
It consists of , and. Therefore, when the LD drive clock is "1P", the output of the inverter 554 generates VGI, the above condition (VGI>VC2) is satisfied, the differential switching circuit 555 is turned on, and the differential switching circuit 555 is turned on.
6 is turned off and the laser diode 504y is turned on.

On the other hand, when the LD drive clock is 0°,
Since there is no output from the inverter 554, the above condition (vcl
<vc2), the differential switching circuit 555 is turned off, the differential switching circuit 556 is turned on, and the laser diode 504y is turned off.

The D/A converter 551 has a latch 55 that latches manually input image density data while the LD drive clock is 1".
7 and ■r□ generator 55 which gives the maximum output value V ref
8, and a 3-bit D/A converter 559 that outputs analog data Vd based on image density data and maximum output value Vraf. Note that the relationship between Vd, image density data, and maximum output value V ref is expressed by the following equation.

The constant current circuit 552 includes the laser diode 504 in the laser diode ON10ff circuit 550 as described above.
y current, and the transistor 560
and resistors R, , R5. The output Vd from D/A converter 551 is applied to the gate of transistor 560 to determine the voltage applied to resistor R4.

In other words, the current flowing through the resistor R4 is the current flowing through the transistor 5.
60, the current 1d flowing through the laser diode 504y is controlled by Vd.

FIG. 16(d) shows the output VGI of the chip 557 mentioned above.
, Vd, and Id. Here, Vd is image density data (3-bit data:
Based on 8 gradation data from 0 to 7), Lef
Values are taken in 8 stages from 7 to 7/7, and Id indicates 8 levels of L-1, based on this VdO value. The laser diode 504y has 8 levels of this Id (1,
- Level 01, = Levelt..., I7 = Level 7), a latent image as shown in FIG. 17 is formed on the photosensitive drum 512y.

In the image forming system to which the anti-aliasing process of the present invention and its official guests are applied, the toner image shown in FIG. 18 is finally created for the pentagon ABCDE shown in FIG. is formed on the recording paper. FIG. 19 shows a toner image of pentagon ABCDE when the feedback processing of the present invention is not performed, and as is clear from comparing FIG. 18 (toner image of the present invention) and FIG. By correcting tone values with poor reproducibility, such as saturated dots, a stable image can be created.

Further, in this embodiment, multi-value drive using power modulation is applied, but it goes without saying that the same effect can be obtained by using multi-value drive using mid-pulse modulation.

〔Effect of the invention〕

As explained above, the image forming apparatus of the present invention measures the toner adhesion state of the toner-developed test pattern,
In an image forming apparatus that feeds the measurement result to an anti-aliasing processing section, an effective minimum value determining means inputs the measurement result of the toner adhesion state and determines a reproducible effective minimum value of the halftone level, and an effective minimum value determining means Since it is equipped with a correction means that corrects the gradation value obtained by anti-aliasing processing so that it is equal to or greater than the effective minimum value based on the effective minimum value obtained by Even if there is a problem, pixels at a low density level can be stably reproduced without white spots or the like occurring.

Further, the image forming apparatus of the present invention measures the toner adhesion state of a toner-developed test pattern and feeds the measurement result to an anti-aliasing processing section. Then, based on the effective maximum value determining means for determining the reproducible maximum value of the halftone level, and the effective maximum value determined by the effective maximum value determining means, the gradation value determined by anti-aliasing processing is determined to be less than or equal to the effective maximum value. Since it is equipped with a correction means that corrects the image so that it becomes opaque, even if there is fatigue of the photoreceptor or changes in the environment such as temperature, there will be no uneven coating in the halftone area.
High-density level pixels can be stably reproduced.

Furthermore, the image forming apparatus of the present invention measures the toner adhesion state of the toner-developed test pattern and feeds the measurement result to the anti-aliasing processing section. an effective minimum value determining means for determining a reproducible effective minimum value of the halftone level; and an effective maximum value determining means for inputting the measurement result of the toner adhesion state and determining a reproducible maximum value of the halftone level. , based on the effective minimum value determined by the effective minimum value determination means and the effective maximum value determined by the effective maximum value determination means, the gradation value determined by anti-aliasing processing is set to be equal to or greater than the effective minimum value, and is equal to or greater than the effective maximum value. Since the present invention is equipped with a correction means for correcting the value to be within the range below, it is possible to always obtain high-quality images without being affected by fatigue of the photoreceptor or changes in the environment such as temperature.

[Brief explanation of drawings]

FIGS. 1(a) to (d) are explanatory diagrams showing test patterns,
FIG. 2 is an explanatory diagram showing the configuration of the image forming system of this embodiment, FIG. 3 is an explanatory diagram showing the configuration of the PDL controller,
FIG. 4(a) is a flowchart showing the operation of the PDL controller, FIG. 4(a) is an explanatory diagram showing path filling processing, FIG. 4(C) is a flowchart showing anti-aliasing processing, 5 is a flowchart of halftone darkness value correction processing, FIGS. 5(a) and 5(b) are explanatory diagrams showing linear hetator division of a figure, and FIG. 6 is an explanatory diagram showing near-near area ratio after performing anti-aliasing processing. , FIG. 7 is an explanatory diagram showing the configuration of the image processing device, FIG. 8 is an explanatory diagram showing the T correction conversion graph of the T correction circuit, FIG. 9 (a),
(b) and (C) are explanatory diagrams showing conversion graphs for complementary color generation used in the complementary color generation circuit, and Figures 10 (a) and (b)
, (c), (d) are explanatory diagrams showing the state in which the RGB image data shown in Figures 7 (a) et al.) and (C) are output from the UCR processing/black generation circuit, and Figure 11 is a Heyer Explanatory diagram showing a 3×3 multivalued dither matrix of type 1.
Figures 2 (a), (b), (c), and (d) are Y, M, C, and B in Figure 1O (aL (b), (c), and (d)).
An explanatory diagram showing a state in which K data is converted by a gradation processing circuit, Fig. 13 is a control block diagram showing a multi-value color laser printer, and Fig. 14 is an explanation showing the configuration of a multi-value color laser printer. 15(a), (g)) are explanatory diagrams showing the configuration of the exposure system of the yellow recording unit, and FIGS. 16(a), (b), (c), (d) are Fig. 17 is an explanatory diagram showing the value drive, and Fig. 17 is an explanatory diagram showing the state of the latent image depending on the level of power modulation.
8 is an explanatory diagram showing the final toner image of pentagon ABCDH shown in FIG. 5(a), FIG. 19 is an explanatory diagram showing the toner image of pentagon ABCDE when no feedback processing is performed, and FIG. 21(a) and 21(b) are explanatory diagrams showing antialiasing processing using the uniform averaging method; FIG. 22(a) is an explanatory diagram showing conventional antialiasing processing. 23 (a), (b), (C
1, (d) is an explanatory diagram showing an example of a filter used in the weighted averaging method, and FIG. 24 is an explanatory diagram showing a convolution integral method with 3×3 pixel reference. Explanation of symbols 100 ---- Host computer 200 ---- PDL controller 201 ----
---Receiving device 202---CP TJ400/519 y. Internal system lot RAM 205~---ROM Page memory 207-=Transmitting device I10 device Image reading device Image processing device Multivalued color laser printer 519m, 519c, 519bk Toner adhesion density measuring device Laser drive processing unit System control unit

Claims (3)

[Claims] (1) In an image forming apparatus that measures the toner adhesion state of a toner-developed test pattern and feeds the measurement result back to the anti-aliasing processing section, the measurement result of the toner adhesion state is input and halftone levels are reproduced. effective minimum value determining means for determining a possible effective minimum value; and based on the effective minimum value determined by the effective minimum value determining means, correcting the gradation value determined by anti-aliasing processing so that it is equal to or greater than the effective minimum value. An image forming apparatus comprising: a correction means. (2) In an image forming apparatus that measures the toner adhesion state of a toner-developed test pattern and feeds the measurement result back to the anti-aliasing processing section, the measurement result of the toner adhesion state is inputted and halftone levels are reproduced. effective maximum value determining means for determining a possible effective maximum value; and based on the effective maximum value determined by the effective maximum value determining means, correcting the gradation value determined by anti-aliasing processing so that it is equal to or less than the effective maximum value. An image forming apparatus comprising: a correction means. (3) In an image forming apparatus that measures the toner adhesion state of a toner-developed test pattern and feeds the measurement result back to the anti-aliasing processing section, the measurement result of the toner adhesion state is input and halftone levels are reproduced. effective minimum value determining means for determining a possible effective minimum value; effective maximum value determining means for inputting the measurement result of the toner adhesion state and determining a reproducible maximum effective value of the halftone level; and the effective minimum value determining means. Based on the effective minimum value determined by the means and the effective maximum value determined by the effective maximum value determining means,
An image forming apparatus comprising: a correction means for correcting a gradation value obtained by anti-aliasing processing so that it falls within a range of not less than an effective minimum value and not more than an effective maximum value.