JPH04152751A - Image forming device - Google Patents

Abstract

PURPOSE:To always obtain a picture with high picture quality by writing a prescribed test pattern on a photosensitive body, measuring the reproduction state of a test pattern developed by a toner, feeding back the measured value to an anti-aliasing processing section, in which the anti-aliasing processing is executed. CONSTITUTION:A test pattern written on a photosensitive drum is toner- developed by a multi-value color laser printer 500 and the reproduction state of the test pattern subject to toner development is measured through a toner adhesion concentration measurement equipment (toner adhesion state measuring means). Then the measured value of the toner adhesion concentration measurement equipment is fed back to an anti-aliasing processing section (PDL controller 200), and the S/N of the test pattern re-development of the test pattern subject to toner development is calculated from the measured value and the gradation after the anti-aliasing processing is corrected so that the gradation with deteriorated S/N is not in use.

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 (Fig. 20 0))
It is used to smooth the surface 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 by N*M (N,
After decomposing the image into sub-vixels (M is a natural number) and performing rask calculation at high resolution, the luminance of each pixel is determined by taking the average of N*M sub-pixels. Figure 21(a)
, ■), 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 Figure (a), The brightness kid of this pixel is the maximum brightness of the gradation that can be displayed (
For example, for 256 gradations, kid=255) is assigned. When performing anti-aliasing processing on this pixel using the uniform averaging method with N=M=7,
), a pixel is divided into 7*7 subpixels, and the number of subpixels covered by the image is counted. The count number (28) is divided by the total number of subpixels in one pixel (49 in this case) and normalized (averaged)
The brightness of that pixel is calculated by multiplying the brightness by the maximum brightness (255). 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 FIG. 22(a), [present]), 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. Figure 0))
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. In addition, as a filter, Fig. 23 (a), (
Filters shown in b), (C), and (d) are known.

■Convolution Integration Method The convolution integration 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
The 'XN' pixel is considered to correspond to the pixel of the equal-averaging method or the weighted averaging method. 24th
The figure shows a convolution method with 3×3 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 that print vector images, such as those used in computer graphics, have become widely used. There is a system using Post Script. Post Script is a page description language (Page Des
criptionLanguage: Hereafter, PDL
It belongs to a language genre called ``Japanese language'', and describes the form of the contents of a single document, including the text (letter part), graphics, and their arrangement and appearance. It is a programming language for systems such as this, and vector fonts are used as character fonts in such systems. Therefore, even if the characters are scaled, the print quality can be significantly improved compared to systems using bitmap fonts (for example, conventional word processors).
Another advantage is that character fonts, graphics, and images can be mixed and printed.

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 displays for computer graphics, there is a problem in that aliasing occurs due to the low resolution. For this reason, even in image forming apparatuses that print using laser printers, anti-aliasing processing is being applied to improve the quality of printed images.

[Problem to be solved by the invention]

However, with image forming apparatuses that apply 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. The sensitivity of the photoreceptor may decrease due to fatigue of the photoreceptor material and temperature changes, the dot area of the latent image formed on the photoreceptor may change, and the development characteristics (characteristics of the developer) may change over time or due to environmental changes. Since the state of toner adhesion to the latent image changes depending on the change in , there is a problem that the gradation characteristics of the reproduced image deteriorate and the image quality deteriorates.

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

[Means to solve the problem]

In order to achieve the above object, the present invention provides an image forming apparatus in which an electrostatic latent image on a photoreceptor is visualized by toner development through a developing means, and an image is obtained through a transfer/fixing means.
A writing device writes a predetermined test pattern on the photoconductor, a toner adhesion state measuring device measures the reproduction state of the test pattern developed with toner by the developing device, and the measured values of the toner adhesion state measuring device are inputted, and a predetermined test pattern is inputted. The present invention provides an image forming apparatus including an anti-aliasing processing means that performs anti-aliasing processing by feeding back to the processing of the image forming apparatus.

Further, in the above-described configuration, the anti-aliasing processing means calculates the SN of the toner-developed test pattern reproduction image based on the measured value, and does not use the gradation value with a bad SN for the anti-aliasing process. It is desirable to feedback the value.

[Effect]

In the image forming apparatus of the present invention, the antialiasing processing means inputs the measurement value of the toner adhesion state measuring means and feeds it back to a predetermined process to perform antialiasing processing. As a result, for example, the SN of the toner-developed test pattern reproduction image can be determined based on the measured value.
By calculating gradation values with poor SN and not using them for anti-aliasing processing, anti-aliasing processing can be performed effectively using only effective half-tone levels.

〔Example〕

Hereinafter, an image forming system to which the image forming apparatus of the present invention is applied is taken as an example, and will be described as follows: ■ Outline of measured value feedback processing in antialiasing processing, ■ Block diagram of 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.

■Overview of measurement value feed pack 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 (toner adhesion state measuring means). The state of reproduction of the toner-developed test pattern is measured through the test pattern. Thereafter, the measured value of the toner adhesion density measuring device is fed back to the anti-aliasing processing unit (in this embodiment, the PDL controller 200 described later), and in the halftone threshold correction process, the measured value is used as a toner-developed test pattern. The SN of the reproduced image is calculated and the gradation values after anti-aliasing processing are corrected so that gradation values with poor SN are not used.

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
), 64(!6 levels are selected at moderate intervals, but any number may be used as long as the number is sufficient to monitor gamma and the intervals are sufficient. Also, the test pattern in Figure (a) The test patterns are arranged in descending order of level from top to bottom.
7) It is stored in the ROM 205 in advance, and is sent to the writing unit (multi-valued color laser printer 500 described later) once every several rotations of the photosensitive drum (for example, once every 10 times). Transferred and developed.

Furthermore, the six levels of the test pattern are made up of a plurality of basic units (here, four basic units are assumed for simplicity), each unit of which is composed of N*N 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. 1(C) shows the state of the toner adhesion density with respect 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). D11 to DI4, then sequentially in the sub-scanning direction I)
z+~D24, D31%D34, D41~D44,
DSI~D54, D0~D64.

The measurement value (toner adhesion density) measured by the toner adhesion density measuring device is fed back to an anti-aliasing processing section (PDL controller 200 described later).

In the halftone threshold correction process, the antialiasing processing section first calculates a density α with a poor standard deviation from the measured value in the following order.

(1) Input all the measured values of a certain level of the test pattern (four measured values in FIG. 1 (b)) (ii) Find the standard deviation σ of the four measured values.

(ij) Compare the standard deviation σ with a reference standard deviation Thr that is a preset standard of reproducibility.

(iv) The measured value where σ<Thr is defined as the concentration α with a bad standard deviation.

Next, assuming that the number of gradations of the printer is NP and the number of gradations specified in the vector image is KV, a threshold value Hs that satisfies Hs = αXKV /NP is determined for α described above.

After that, the gradation value for each color of the figure obtained by the overwriting process in the anti-aliasing process is compared with the threshold value Hs (red), (green), (blue), and if K1≦Hs, When Kr-hs K, ≦Hs, K,=hs When K, ≦Is, processing is performed to set Kb=hs (however, hs = Hs +1). In other words, a gradation value below the threshold Hs is a value with poor print reproduction on a multilevel printer, so the corresponding gradation value is not used, and the correction is made to a gradation value hs that is one gradation value higher than Hs. .

As a result, pixels whose density has been modulated by anti-aliasing processing can be
Printing will always be stable.

■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, an image reading device 3001, an image processing device 400. and a system control section 600 that controls the multivalued 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 bus 203, a RAM 204 that stores PDL language transferred from the receiving device 201 via the internal system bus 203, and a ROM 205 that stores anti-aliasing programs and the like.
, a page memory 206 that stores multivalued RGB 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 f400, 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 via the internal system bus 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 vector data, and as the name "page description language" indicates, image information is processed in units of pages. Further, one page is made up of at least one bus, each of which is 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 bus (processing 1).

Then, the linear elements of the work area registered in this bus 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 bus filling process shown in c), the scanning line yc to be processed (in this embodiment, the above-mentioned Yo, Y,
A scan line with a thickness of one pixel is described as a scan line, and a scan line that indicates a straight line with no thickness is described as a scan line), and the elements of the side that crosses that scan line. The real value of the X coordinate across yc (X shown in Figure 4, x2 x3 x4) is expressed as AET (A
active Edge Table: a table that records the X coordinates of edge portions that appear 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
The X coordinates crossing 11yc are not necessarily registered in descending order. For example, in process 1, if a straight line element passing through scanning lines yc and X3 in FIG. be registered. Therefore, after the AET is registered, the elements on each side within the AET are sorted in descending order of X coordinate. Then, pair the first two elements of AET and fill in the space between them. Anti-aliasing processing is achieved by adjusting the density and brightness of pixels in the edge portion in accordance with the approximate area ratio in this filling processing. Then remove the processed edge from the AET, update the scanline (update the Repeat the process.

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

Next, FIGS. 4(C) and 4(d) will explain anti-aliasing processing 1 and halftone threshold correction processing that are executed during the scan line filling processing of processing 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) Five line vectors AB, BC, CD, DE, and EA (represented by real numbers) (b) Color and brightness values inside the figure This figure is created by the above-mentioned operation as shown in Figure 5 (b). , 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 value (real number expression) of the vector element ((a) above) that constitutes the starting point and ending point of the straight line vector (=) Inclination information (dip) of the vector element that constitutes the starting point and ending point of the straight line vector Characteristic information of the start 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, the fourth The anti-aliasing process shown in the flowchart of FIG. 3(C) is executed.

First, in subpixel filling processing, a filling area for each subpixel is calculated using a 3*3 subpixel division method (s, 1o1). 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, B) gradation values (luminance values) are calculated (S4
04). For example, if the figure in Figure 5(a) is drawn in red (maximum brightness: 255) on a white background (maximum brightness = 255), then the approximate area ratio k(
(see Figure 6), the brightness values for each color of the figure are (red),
(green) and Kb (blue) are obtained based on the following formula.

K, = Kx+Xk + Ki+gX(1k)Kv
=KGIXk + KGzX(1k)Kb = K
□Xk +KmzX(1k) However, K m r , K
e I and K m I respectively indicate the brightness values of the colors (red, green, and blue, respectively) of the figure given by [0 above, and KR□, KG2. KB□ represent the brightness values of each previously painted color. Note that KR□, , , , 2 refer to data in each plane memory section corresponding to the ROB of the page memory 206.

Next, in the halftone dark value correction process described later, among the tone values obtained in the overwriting process described above, tone values that can print well the tone values with poor printing reproduction (gradation values below Hs) are determined. (
hs) (S405).

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 (
5406).

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.

FIG. 4(d) shows a flowchart of the halftone darkness value correction process.

First, a density α having a poor standard deviation is determined in the following order from the toner adhesion density (measured value) of the test pattern measured by the toner adhesion density measuring device (toner adhesion state measuring means) (8408).

(i) Input all the measured values of a certain level of the test pattern (four measured values in FIG. 1(b)) (ii) Find the standard deviation σ of the four measured values.

(ij) Compare the standard deviation σ with a reference standard deviation Thr that is a preset standard of reproducibility.

(iv) The value of the measured value where σ<Thr is defined as the concentration α with a bad standard deviation.

Next, if the number of gradations of the printer is NP and the number of gradations specified in the vector image is KV, then for the above α, Hs =
A threshold value Hs that is αXKV/NP is determined (S409).

After that, the gradation value for each color of the figure obtained by the overwriting process of 5404 is compared with the threshold value Hs (red), ):, (green), Kb (blue), and if K, ≦Hs, then K ,=hs If K,≦Hs, then K,=hs If K,≦Hs, then set K,=hs (however, hs=Hs+1). In other words, since a gradation value below the threshold 'fi Hs is a value that has poor print reproduction on a multilevel printer, the corresponding gradation value is not used, and instead a gradation value hs that is one gradation value higher than Hs is used. Correct (5410).

(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 W300.
The three color image signals read by D7r, 7g, and 7b are converted into blank (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).
, into yellow (Y), magenta (M), and cyan (C) recording signals. Here, the mode in which image signals are input from the image reading device 300 is called a copying machine mode, and the mode in which RGB image data is input from the PDL controller 200 is called a graphinx mode.

The image processing device E400 includes CCDs 7r, 7g, and 7
Input the color gradation data obtained by A/D converting the output signal of
A shading correction circuit 401 that performs correction for sensitivity variations in internal terminal elements of D7r, 7g, and 7b, and color gradation data output from the shading correction circuit 401 or color gradation data (RGB) output from the PDL controller 200. The multiplexer 402 selectively outputs one of the image data) according to the above-mentioned mode, and the 8-bit data (color gradation data) output from the multiplexer 402 is input, and the gradation is changed according to the characteristics of the photoreceptor. γ correction circuit 4 that outputs as 6-bit data
03, and red (R) and green (G) output from the γ correction circuit 403.

Complementary color generation circuit 405 converts 6-bit gradation data indicating the gradation of blue (B) into gradation data (6 bits) of cyan (C), magenta (M), and yellow (Y), which are respective complementary colors. and Y, M output from the complementary color generation circuit 405
, C, and a masking processing circuit 406 that performs predetermined masking processing on each gradation data of Y, M,
A UCR processing/black generation circuit 407 inputs each gradation data of C and executes UCR processing and black generation processing, and Y outputted from the UCR processing/black generation circuit 407.

Convert each 6-bit gradation data of M, C, and BK to 3-bit gradation data YLMI, CL, and BKI,
It is composed of a gradation processing circuit 408 that outputs output to the laser drive processing section 502 inside the multivalued color laser printer 500, and a synchronization control circuit 409 for synchronizing each circuit of the image processing apparatus 400.

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-bit (that is, 8 steps) multivalue level, 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 UCR processing of the UCR processing/black generation circuit 407 is generally expressed as follows.

Therefore, in this embodiment, new coefficients are obtained using the product of both coefficients.

In this embodiment, a new coefficient (such as "all") that performs this masking processing and UCR processing at the same time is calculated in advance, and
Furthermore, using the new coefficients, the masking processing circuit 40
6 scheduled input values Y,,M,.

Output value (Y0゛, etc.: U) corresponding to C, (6 bits each)
A value that is the calculation result of the CR processing/black generation circuit 407 is obtained 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 boat fishing, the masking processing circuit 406 performs Y and M according to the characteristics of the spectral reflection wavelength of the toner for forming a recorded image.
, C signals, and the tJcR processing/black generation circuit 407 performs correction for color balance in overlapping toners of each color. After passing through the UCR processing/black generation circuit 407, black component data BK is generated by combining the input three color data of Y, M, and C, and the output Y
, M, and C are corrected to values obtained by subtracting the black component data 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 executes processing as shown in FIGS. 9(a) and (b).

Assuming that processing is executed based on the complementary color generation conversion graph shown in (C), and then the masking processing circuit 406 and the UCR processing/black generation circuit 407 execute processing based on the following equation,
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), (c), (d) (7).

Furthermore, if the gradation processing circuit 408 uses the Heyer type 3×3 multilevel dither matrix shown in FIG. 11, Y in FIGS. 10(a), ff1), (C), and (d),
The data for MC and BK are shown in Figure 12 (a) and (
b), (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 block diagram 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 outputs a laser beam by inputting the 3-bit data of Y, M, q, and BK output from 00 (in this case, image density data). Input buffer memory 503)', 503
m, 503c, and a laser diode 504y that outputs laser beams corresponding to Y, M, C, and BK, respectively.
, 504m, 504c, and 504bk, and drivers 505y, 505m, and 505c that drive the laser diodes 504y, 504m, 504c, and 504bk, respectively.
505bk.

In addition, the black 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 black 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, driver 50
5m and a buffer memory 503m are combined into a magenta recording unit MU (see Figure 14), a yellow developing unit, and a buffer memory 503m.
Transfer part 5oly, laser diode 504y,
Driver 505y, and.

The combination of buffer memories 503y is called a yellow recording unit YU (see FIG. 14). As shown in the figure, each of these recording units is connected to a conveyor belt 506 that conveys the recording paper.
Black recording unit B from the recording paper conveyance direction
KU, cyan recording unit 7) Cut, magenta recording unit MU, and yellow recording unit YU are arranged in this order.

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)
The laser drive processing unit 502 includes the aforementioned 3M buffer memories 503y, 503m, and 503c.
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.
and a registration roller 509 that aligns the recording paper sent out from the paper feed cassettes 50'7a and 507b.
The recording units BKU, CU,
It is composed of a fixing roller 510 that sequentially transports MU and YU and fixes the transferred image on the recording paper, and a paper discharge roller 511 that discharges the recording paper to a predetermined discharge section (not shown). Here, each recording unit YU, MU, CU, BKU
are photosensitive drums 512y, 512m, 512c, 51
2bk, and photoreceptor drums 512y and 512m, respectively.

Charger 513) that uniformly charges 512c and 512bk
', 513m, 513c, 513bk, and polygon mirrors 514y, 514m for guiding the laser beam to the photosensitive drums 512y, 512m, 512c, 512bk.
, 514c, 514bk and motor 515y, 515m
, 515c, 515bk, and photosensitive drums 512y, 5
Toner developing devices 516y, 516m, 516c, and 516bk that develop the electrostatic latent images formed on 12m, 512c, and 512bk using toners of corresponding colors, and a transfer charging device that transfers the developed toner images to recording paper. Vessel 51
7y, 517m, 517c, 517bk and photosensitive drums 512y, 512m 512c, 512b after transfer
A cleaning device 51 that removes toner remaining on k
8y, 518m.

518c and 518bk.

Note that 519y, 519m, 519c, and 519bk are photosensitive drums 512)', 512m, 512c, and 519bk, respectively.
This figure shows a toner adhesion density measuring device for reading a test pattern provided on the 12bk, and is composed of a CCD line sensor and an LED light source arranged in the thrust direction, and a calculation section.

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 15(b) show yellow recording unit YU.
The configuration of the exposure system is shown. In the 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 then 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 in a 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 C
The unit U is equipped with a cyan toner developing device Wif 516c and forms and transfers a cyan toner image, and the mayant recording unit (MU) includes a magenta toner developing device 516m and forms and transfers a magenta 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.

■ Multi-value drive drivers 505y, 505m, 505c, and 505bk drive Y, M, C, and B signals sent from the image processing device 400.
Based on the 3-bit data of K, the corresponding laser diodes 504y and 504m.

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 multi-level drive by power modulation applied in this embodiment will be explained in detail with reference to FIGS. 16(a), (b), (C), (→).
.

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

As shown in FIG. 16(a), the driver 505y includes a laser diode on10ff circuit 550 that turns on and off the laser diode 504y based on a predetermined speed and the D drive clock, and a laser diode on10ff circuit 550 that turns on and off the laser diode 504y based on the D drive clock, and 3-focus image density data (here, Y data). ) to an analog signal D
/A converter 551 and a current (LD drive current) I that drives the laser diode 504y by inputting an analog signal based on the image density value from the D/A converter 551.
d Laser diode On/uf f circuit 550
The constant current circuit 552 supplies the current to the constant current circuit 552.

Here, the LD drive clock is "'1" and on "0"
As shown in FIG. 16(b), 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 Id 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 (Yes), when the image density data value is "4" (data N-1 in the same figure), the corresponding LD drive current Id is supplied by the constant current circuit 552. , the laser beam power of the laser diode 504y is level 4. Also, the image density data value is
7′” (data N in the figure), the constant current circuit 5
The corresponding LD drive current 1d is supplied by the laser diode 504y, 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 on10ff circuit 550 includes TTL inverters 553 and 554, differential switching circuits 555 and 556 that perform an onloff toggle operation, and a VC,
1>V'G2, the differential switching circuit 555
n, differential switching circuit 556 is off, VGI<
When VC2, differential switching circuit 555 is off.
.

Resistors RZ and 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 3. Therefore, when the LD drive clock is '1'', the output of the inverter 554 generates vcl, the above condition (VGI>VO2) 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.

Conversely, when the LD drive clock is "0", there is no output from the inverter 554, so the above condition (VGI<
VO2), and the differential switching circuit 555
ff, the differential switching circuit 556 turns on and turns off the laser diode 504y.

The D/A converter 551 has a latch 5 that latches the input image density data while the LD drive clock is "1".
57 and a V ref generator 5 that provides the maximum output value V□.
58, and a 3-pin D/A converter 559 that outputs analog data Vd based on image density data and maximum output value Vr*f. Note that the relationship between Vd, image density data, and maximum output value Vr,t 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 R4 and Rs. D/A converter 551 Rano output Vd is applied to the base 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(b) shows the output of the lunch 557 mentioned above.

5 is a timing chart showing the relationship between VGI, Vd, and Id. Here, Vd is V□,
Values are taken in 8 steps from O/7 to 7/7, and Id is this V
Based on the dO value, 1. -I, shows 8 levels. The laser diode 504y is placed on the photoreceptor drum 512y at the 17th level according to the 8 levels of this Id (■o-level O1■1-rehert..., ■, =rehelebe).
A latent image as shown in the figure is formed.

In the image forming system to which the anti-aliasing processing and the apparatus of the present invention are applied, the toner image shown in FIG. 18 is finally created for the pentagon ABCDH shown in FIG. 5(a) by the above-described configuration and operation. Formed on recording paper. FIG. 19 shows a toner image of a pentagon ABCDH 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 the tone value, a stable image can be created.

Further, in this embodiment, multi-value driving using power modulation is applied, but it goes without saying that similar effects can be obtained by using multi-value driving using pulse width modulation.

[Effects of the Invention] As explained above, the image forming apparatus of the present invention visualizes the electrostatic latent image on the photoreceptor by toner development through the developing means, and obtains an image through the transfer/fixing means. In an image forming apparatus, a writing means writes a predetermined test pattern on a photoreceptor, a toner adhesion state measuring means measures the reproduction state of the test pattern developed with toner by a developing means, and a measured value of the toner adhesion state measuring means Since it is equipped with an anti-aliasing processing means that performs anti-aliasing processing by inputting and feeding back to predetermined processing, high-quality images can always be obtained regardless of fatigue of the photoreceptor or changes in the environment such as temperature. be able to.

Further, in the above-described configuration, the anti-aliasing processing means calculates the SN of the toner-developed test pattern reproduction image based on the measured value, and does not use the gradation value with a bad SN for the anti-aliasing process. Since the value is fed back, high-quality images can always be obtained without being affected by fatigue of the photoreceptor or changes in the environment such as temperature.

[Brief explanation of the drawing]

FIGS. 1(a) to (c) 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(C) is a flowchart showing the path filling process, FIG. d) is a flowchart of halftone threshold correction processing, FIGS. 5(a) and 5(b) are explanatory diagrams showing linear vector division of figures, and FIG. 6 is an explanatory diagram showing approximate area ratio after performing anti-aliasing processing. , 7th
The figure is an explanatory diagram showing the configuration of the image processing device, FIG. 8 is an explanatory diagram showing the γ correction conversion graph of the T correction circuit, and FIG. 9 (a)
, (b), (C) are explanatory diagrams showing conversion graphs for complementary color generation used in the complementary color generation circuit, and Figures 1O (a), (b)
), (C), (d) are shown in Figure 7(a). The RGB image data shown in (b) and (C) is OC
An explanatory diagram showing the state output from the R processing/black generation circuit,
FIG. 11 is an explanatory diagram showing a Bayer type 3×3 multilevel dither matrix, and FIG. 12 (a), (b), (C),
(d) is shown in Figure 10 (a), (b), (C), (
d) is an explanatory diagram showing the state in which the Y, M, C, BK data is converted by the gradation processing circuit.
A control block diagram showing a laser printer, FIG. 14 is an explanatory diagram showing the configuration of a multivalued color laser printer,
15(a) and 15(b) are explanatory diagrams showing the configuration of the exposure system of the yellow recording unit, and FIGS. 16(a) and 16(b),
(c) and (d) are explanatory diagrams showing multi-level driving by power modulation, Figure 17 is an explanatory diagram showing the state of latent images depending on the level of power modulation, and Figure 18 is the diagram shown in Figure 5 (a). Explanatory diagram showing the final toner image of pentagon ABCDE, No. 19
The figure shows pentagon ABC without feedback processing.
Explanatory diagrams showing toner images of DE, FIGS. 20(a) and 2(b)
is an explanatory diagram showing conventional anti-aliasing processing, the second
1(a) and 1(b) are explanatory diagrams showing antialiasing processing using the uniform averaging method, and FIG. 22(a). ■) is an explanatory diagram showing anti-aliasing processing using the weighting averaging method, Part 23 (a), [Yes]), (C)
, (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--m--PDL controller 201--
---One receiving device 202-------- CPU U2
03------Internal system bus 204----
・-RAM 205------ROM206--
--- Page memory 207 --- Transmitting device 208.--11 --- I/O device 300 ---
- Image reading device 400 --- Image processing device

Claims (2)

[Claims] (1) In an image forming apparatus in which an electrostatic latent image on a photoreceptor is visualized by toner development through a developing means and an image is obtained through a transfer/fixing means, a predetermined test pattern is written on the photoreceptor. a writing means; a toner adhesion state measuring means for measuring a reproduction state of a test pattern developed with toner by the developing means; a measured value of the toner adhesion state measuring means is inputted and fed back to a predetermined process to perform anti-aliasing. An image forming apparatus comprising an anti-aliasing processing means for performing processing. (2) In the first aspect, the anti-aliasing processing means determines the SN of the toner-developed test pattern reproduction image based on the measured value.
An image forming apparatus characterized in that the measured value is fed back by calculating the gradation value and not using the gradation value with poor SN for antialiasing processing.