JPH03254269A - Picture forming method - Google Patents

Abstract

PURPOSE:To reduce the processing quantity of a picture data and to obtain a uniform picture output by forming gradation higher toward a larger picture element diameter when a basic picture element diameter is small and forming gradation lower toward a smaller picture element diameter when the basic picture element diameter is larger. CONSTITUTION:In the picture forming in which a picture element whose picture element diameter is equal to a basic picture element diameter, or over or less is formed in 1 dot, the picture element is formed symmetrically horizontally around a position equivalent roughly to 1/2 delay of a time from the picture element forming data reception till a time requiring to form a maximum picture element. When the basic picture element diameter is small, the gradation is formed higher toward a smaller picture element diameter and when the basic picture element diameter is larger, the gradation is formed lower. Thus, the processing quantity of the picture data is reduced and a uniform picture output is obtained by placing the dot to the center of the basic pitch.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to image formation in image forming apparatuses such as laser printers, which expresses gradations by changing the size of the 1-dot basic pixel diameter corresponding to the basic pixel density. Regarding the method.

(Prior art) Conventionally, as a method of changing the size of the one-dot basic pixel diameter corresponding to the basic pixel density, gradation is achieved by forming pixels with a pixel diameter that is the same as or smaller than the basic pixel diameter. As a result, the pixels are spread out based on the center position of the pixel pitch (see FIG. 8 of Japanese Patent Application Laid-Open No. 156070/1989).

On the other hand, no method has been found so far to create gradation by forming pixels larger than the basic pixel diameter in units of one dot.

(Problem to be Solved by the Invention) In the case of the above-mentioned method of creating gradation by forming pixels with a pixel diameter that is the same as or smaller than the basic pixel diameter, 5. If the basic pixel density increases, the pixel diameter must be further reduced. However, due to the relationship with the diameter of the toner particles, it becomes difficult for the toner to form a toner image on the surface of the photoreceptor (drum), making it meaningless to reduce the pixel diameter.

(Object of the Invention) The present invention solves the above-mentioned problems and provides a VSS (Variable 5Po
An object of the present invention is to provide an image forming method in which a uniform image with gradation can be obtained even when forming images with various basic pixel densities.

(Structure and operation) In order to achieve the above object, the present invention provides an image that can be formed with one dot having a pixel diameter larger than or equal to the basic pixel diameter corresponding to the basic pixel density. During formation, the pixel formation position for one dot is approximately 1/1 of the time required for maximum pixel formation from the time of receiving pixel formation data.
It is characterized by forming pixels symmetrically centering on the position delayed by 2.

In the present invention, when the basic pixel diameter is small, the gradation is produced in the larger direction, and on the other hand, when the basic pixel diameter is large, the gradation is produced in the smaller direction. As a result, the amount of image data to be processed can be reduced, and by placing the dots at the center of the basic pitch, a uniform image output can be obtained.

(Embodiment) FIG. 8 is a schematic perspective view showing an example of an optical writing retracting section of a laser beam scanning type image forming apparatus in which the present invention is implemented.

To summarize the operation of this optical writing section, a laser beam emitted from a semiconductor laser diode (LD) 1 is formed into parallel light by a collimating lens 2. Next, an aperture 3 having a slit portion corresponding to the size of the dot to be formed cuts off the excess laser beam.

A laser beam in the main scanning direction is focused by a cylinder lens (#, ) 4 onto a photoreceptor (drum-shaped) 5 in a predetermined shape and size, and a polygon mirror 6 focuses the laser beam in the main scanning direction (in the longitudinal direction of the photoreceptor). )X is scanned. Also, a pair of Fθ
The lens 7 converts isometric motion into uniform motion and also corrects field curvature. Then, the angle of the light is changed by a mirror (#2) 8, and the light is focused in the sub-scanning direction (photoconductor rotation direction) y by a cylinder lens (#2) 9 and irradiated onto the photoconductor 5.

In addition, the laser beam from the polygon mirror 6 is captured by the mirror (#,) 10, and the cylinder lens (#,) 1
1 to the light receiving element 12 for synchronization in the main scanning direction.

FIG. 1 shows a block configuration diagram of an embodiment of the present invention, in which 13 is a data conversion circuit that distributes image data 14 into PM (power modulation) data 15 and PWM (pulse width modulation) data 16; The PM circuit is a power modulation circuit that varies the exposure energy per unit area and unit time, and has the effect of mainly enlarging the dot diameter in the sub-scanning direction y.

18 is a PWM circuit, which is a pulse width modulation circuit that makes the laser beam irradiation time variable, and is mainly used in the main scanning direction
This is effective in enlarging the dot diameter.

Here, the main scanning direction is the scanning direction X of the laser beam, as shown in FIG. . 19 is an LD drive circuit, which connects the PM circuit 17 and PWM
Based on the surface output from circuit 18, set LDI to 0N10.
FF control. 20 is a photodiode (PD) that detects the optical output (#2) of LDl, and after converting the detected current into voltage,
This is fed back to the LD drive circuit 19 to stabilize the light emission intensity of the LDI. Note that optical output #1 indicates the laser beam irradiated onto the photoreceptor 5 described above.

Next, to explain the operation, for example, the image data 14 sent from the host machine is sent to the data conversion circuit 13 in order to smoothly produce one-dot gradation (degree of spread of dots).
Then, the data is distributed to the PM circuit 17 and PWM circuit 18 as PM data 15 and PWM data 16, respectively.

A power modulated output based on the PM data is input from the PM circuit 17, and a pulse width modulated output based on the PWM data is input from the PWM circuit 18 to the LD drive circuit 19. This LD drive circuit 19 controls the drive current of the LDl in order to obtain an optical output (#,) corresponding to the output level of the PM circuit 17, and supplies the drive current for a time corresponding to the pulse width of the PwM circuit 18. do. Inside the LD unit, there is a photodiode (PD) that detects the amount of light emitted by the LDI.
)20, the light output (#, ) is proportional to the light output (#, ).
2) is fed back to the LD drive circuit 19 to stabilize the relationship between the output of the PM circuit 17 and the optical output (#□).

The method of the present invention drives and controls the LDI shown in FIG. 1 to form uniform images and pixels with good gradation in image formation of various basic pixel densities (DPI), which will be described below.

Figures 2 (1) and (2) show how pixels are formed by the method of the present invention, (1) is 600DPI, (2) is 200DPI.
This is the case for the basic pixel density (DPI). This is based on the image data 14, with the center of the pitch P at the maximum pixel as the reference pixel i, (n=1, 2.3...
) is formed (at a position delayed by approximately 1/2 of the time required to form the maximum pixel). This basic pixel is indicated by 10,
The maximum pixel is i in case (1). In case (2) i. and
This is called the center method.

In addition, in FIG. 3, at the same time as the image data 14 is input, the pixel if
Since it begins to form an i, it is called the tip method. Compared to the leading edge method, the center type described above is superior in terms of image quality because the pixel i is formed based on the center of the pitch at the maximum pixel, but it requires some circuitry to determine the center of the pitch based on the image data 14. It gets complicated.

Also, in Figure 2 (1) above, the basic pixel density is high density 60
0DPI, and the pixel diameter at this time is 1/200 in
That is, in the case of vSS, which is expanded to a pixel diameter (io to 14) up to 200 DPI.

In addition, Fig. 2 (2) shows 200D with a low standard pixel density.
This is a case of VSS in which the pixel diameter at this time is reduced to 1/600 in (from 10 to 14).

Expansion of the basic pixel diameter shown in FIGS. 2 (1) and (2) above.

FIG. 4 shows a concrete block configuration diagram for performing the reduction.

This is a detailed block diagram of FIG. 1, and FIG. 5 is a waveform diagram showing the time chart of FIG. 4.

In FIG. 4, reference numeral 21 denotes a timing control circuit that operates with the image writing clock signal WCLK (see FIG. 5), and clock signals A to D for transferring image information at the rising edge of this WCLK. against IWCLK
Clock signal A' for image information transfer with a delay of 3 WCLK
~D' is output.

Reference numerals 22 to 25 denote latch circuits (1), (2), (3), and (4) formed of flip-flop circuits F/F, and image information signals that are timed with the clock signals A to D and form image data 14. Latch WDATA. 13-
1 to 13-4 are data conversion circuits (corresponding to 13 in FIG. 1), which convert WDATA latched by the latch circuits 22 to 25.
Convert the data into PMD□~ corresponding to PM data 15
PMD and PWMD engineering equivalent to PWM data 16
Obtain PWMD4. 18-1 to 18-4 are PWM circuits (
18 in FIG. 1), the timing is taken using the clock CLK for performing pulse width modulation and the clock signals A' to D', and pulse width modulation signals PWMS, to PWM are
Generate S4. 26 to 29 are gates (1) to (4) constituted by AND circuits, which are connected to the PMD□ to PMD and PMD, respectively.
WMS, .about.PWM S, are input, and power modulation signals PMS1 to PMS4 (PM data 15) are outputted only during the periods of pulse width modulation signals PWMS, .about.PWMS4, respectively. 30 is a circuit that selects the maximum value of the power modulation signals PMS, ~PMS, from the gates (1) to (4), and 13 is a digital (D)/analog (A) converter that controls the light emission power of the LDI. Output voltage (LDPCV)
Output.

Next, the operation will be described. The image data 14 consists of an image information signal WDATA that defines a pixel and an image writing clock signal WCLK that takes in this WDATA. Then, as shown in FIG. 5, the timing control circuit 21 cyclically generates clock signals A to D for image information transfer at the rising edge of WCLK. At this time W
Up to 4 data of WDATA are taken into each latch circuit 22 to 25 at the rising edge of CLK, and each latched data is transferred to PMD1 to PMD by data conversion circuits 13-1 to 13-4.
4 and PWMD, ~PWMD.

On the other hand, clock signals A' to D' are generated by the timing control circuit 21 with a delay of IWCLK relative to clock signals A to D, each having a width of 3 WCLK. This means that the PWM width is maximum upper in/upper 1n=3. That is, it corresponds to 200 600 3 WCLK. And each PWM circuit 18-1
In ~18-4, pulse width modulation signals PWMS and ~PWMS4 corresponding to PWMD1 to PWMD4 are generated, but this PWMS ~PWMS4 (PM data 15) is output only during the period of pulse width modulation signals PWMS1 to PWMS. Then, the selection circuit 30 selects the maximum value of PMS to PtS from the gates 26 to 29 (the maximum value of PM values), and the LDPCV converted into an analog value by the D/A converter 31 is sent to the LD drive circuit 19. Output.

FIG. 6 shows the PWM circuit 18 (18) shown in FIGS. 1 and 4.
-1 to 18-4) 6 shows a circuit configuration diagram of an embodiment of the invention. In the same figure, 180 is a counter, 181.182 is a delay line that delays the output clock (CLK200) of the counter 180, and 181 to L8n are input to the delay line. Figure 7 shows the AND circuit that synthesizes the clocks.
Combined outputs P1 to Pn for LK200 are shown.

186 is the desired P by the PWM data (PWMD) 16.
With the selector that selects fi, the pulse width modulation signal PWMS
is obtained.

That is, the maximum PWM width data is first set in the initial value setting 187, and the counter 180 outputs CLK200 while counting CLK until the set value is reached. CLK20
0 is input to the delay lines 181 and 182, and when each output is combined, pl, p2, etc. in Fig. 7 are obtained.
pn is output, and the desired P, by PWMD.

is selected by the selector 186 and output as PWMS.

(Effects of the Invention) As explained above, the present invention produces gradation in the larger direction when the basic pixel diameter is small, and conversely, produces gradation in the smaller direction when the basic pixel diameter is large. The amount of data processed can be reduced. and.

A uniform image output can be obtained in the VSS method by setting the dots at the center of the pitch at the basic pixel.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is a diagram showing how pixels are formed by the center method according to the method of the present invention, FIG. 3 is a diagram showing how pixels are formed by the tip method, and FIG. 4 is a specific block configuration diagram of FIG. 1, FIG. 5 is a time chart of FIG. 4, FIG. 6 is a circuit configuration diagram of an embodiment of the PWM circuit shown in FIGS. 1 and 4, and FIG. Figure 7 is the 6th
FIG. 8 is a schematic perspective view showing an example of an optical writing retreat section of a laser beam scanning image forming apparatus in which the present invention is implemented. 1... Semiconductor laser diode (LD), 13
, 13-1 to 13-4... data conversion circuit, 14-...
・Image data, 15...PM data, 16...P
WM data, 17... PM circuit, 18, 18-1
~18-4... PWM circuit, 19... LD drive circuit, 20... Photodiode (PD), 21... Timing control circuit, 22-25... Latch circuit (1)
~(4), 26~29...Gate (1)~(4), 3
0... Selection circuit, 31... D/A converter,
180...Counter, 181.182...Delay line, 183-18n-A N D circuit, 18
6...Selector. Figure 1 Light output (#1)

Claims (1)

[Claims] For the 1 dot basic pixel diameter corresponding to the basic pixel density,
In image formation in which one dot can be formed with a pixel diameter larger than or equal to the basic pixel diameter, the pixel formation position of one dot is delayed by approximately 1/2 of the time required for maximum pixel formation from the time when pixel formation data is received. An image forming method characterized by forming pixels symmetrically with respect to a position centered on the image.