JPS61277263A - Exposure method - Google Patents

Abstract

PURPOSE:To reproduce gradation, half-tone, and color well by scanning a laser beam plural times repeatedly with a data signal of one main scanning period to expose a picture to light. CONSTITUTION:A picture read in main scanning periods H1 and H2 is written by plural scannings as H1a-H1d of the data signal in the period H1 and H2a-H2b of the data signal in the period H2. Since the number of times of scanning for write in increased and the picture of one main scanning period which is written by one scanning normally is divided to plural scannings and is exposed to light, half tone and color of the obtained picture are reproduced well.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an exposure method for forming color images using electrophotographic technology, and specifically relates to a raster scan exposure method using a laser beam as a light source. It is about improvement.

[Summary of the invention]

In the present invention, when forming an image by exposing an electrophotographic photoreceptor to a laser beam using a re-raster scan, the laser beam is repeatedly scanned multiple times using a data signal for one main scanning period to perform image exposure. The aim is to achieve accurate gradation and color reproduction.

[Conventional technology]

In so-called laser printers, which perform image exposure by raster scanning a laser beam on an electrophotographic photoreceptor, writing is performed by changing the laser light intensity in an analog manner, or digitally by changing the laser light intensity. Conventionally, even when writing is performed by changing the scanning laser beam, the scanning laser beam is sequentially changed every scanning period. This method is similar to interlacing in television, and is an appropriate method for obtaining sufficient image information capacity.
Information capacity corresponding to the scanning density of the laser beam can be obtained.

However, in image formation by such raster scan exposure, the spot of the laser beam is not rectangular, and the intensity distribution of the beam has a so-called Gaussian distribution as shown in Figure 7. As a result, gradation reproduction and color reproduction in the case of color images are non-linear.

For example, when forming an image by supplying a signal whose intensity changes in an analog manner as shown in Fig. 8, it is desirable to obtain an image as shown in Fig. 9A, but in reality, the beam intensity Since the change in is also accompanied by a change in the effective spot diameter,
The result will be something like the one shown in FIG. 9B. Also, when forming an image by supplying digital signals, for example, in the same two-dot representation, the main scanning direction (H direction)
The substantial area will be different depending on whether it is continuous in the sub-scanning direction (V direction) or in the sub-scanning direction (V direction).

[Problem that the invention seeks to solve]

In this way, with the conventional exposure method in which the laser beam is scanned only once using a data signal every l main scanning period, it is difficult to reproduce tone and color as calculated (especially when performing color correction, etc.).
It has become extremely difficult to do so.

Therefore, the present invention was proposed in order to eliminate the drawbacks of conventional exposure methods, and provides good gradation reproduction, halftone reproduction, and color reproduction regardless of the characteristics of the intensity distribution of the laser beam. The purpose of this invention is to provide an exposure method that allows for

[Means for solving problems]

In order to achieve the above-mentioned object, the present invention, when forming an image by exposing an electrophotographic photoreceptor with a laser beam in a raster scan manner, repeatedly scans the laser beam a plurality of times using data signals for one main scanning period to form an image. It is characterized by performing exposure.

[Effect]

In this way, by repeatedly scanning the laser beam multiple times using the same data signal for one main scanning period, the laser beams with the same intensity act as if they were integrated, so for example, the laser beam has a Gaussian distribution. However, the actual effect is equivalent to having a rectangular distribution, and changes in shading due to changes in intensity and reproduction of intermediate tones due to area become close to ideal conditions.

〔Example〕

The present invention will be explained below using a laser printer as an example.

For example, when an image written on a manuscript is created using a laser printer using electrophotography, the information on the original manuscript is stored in the main scanning direction (H direction) and It is divided by scanning in the sub-scanning direction (■ direction) and sent to the printer as a data signal on the time axis.

Then, on the printer side, this data signal is sequentially reassembled (for example, by direct scanning, or via memory in the case of changing the time axis) and changed to the intensity of the laser light to scan and expose the electrophotographic photoreceptor. conduct.

In this case, in the conventional exposure method, the data signal that drives the laser beam changes one after another every main scanning period, and the number of scans that divide the document and the number of scans written by the printer are different. , are basically the same (not necessarily the same considering trimming etc., but 1:
There is no change in the fact that it corresponds to l. )become.

In contrast, in the present invention, data signals for one main scanning period are used to perform exposure with a laser beam multiple times using the same signal via a memory. Therefore, in the present invention, the number of scans during writing is several times the number of scans when reading the original.

That is, in the present invention, as shown in 211aA, for example, an image read at the main scanning period HI+HX,
As shown in FIG. 2B, H, , due to the H1 data signal,
, H, , , H, , , H, and H 2+1+' Hzb+ H2e+ Hta are written by scanning multiple times (four times in this example).

In this way, by increasing the number of scans during writing, images for l main scanning periods, which are normally written in one scan, can be written.
By dividing the exposure into a plurality of scans, the resulting image has good halftone reproduction and color reproduction.

For example, according to the plurality of scans, when viewed in the sub-scanning direction (V direction), the laser beams act as if a number of laser beams having the same intensity were integrated. Therefore, as shown in FIG. 3A, even if each laser beam has a Gaussian distribution g, the actual effect is equivalent to having a rectangular distribution S. This also applies when the intensity of the laser beam is low, as shown in FIG. 3B.

Therefore, although the same data signal is actually scanned and exposed many times, the actual optical effect is as if writing was done once with a laser beam with a roughly rectangular intensity distribution. It will have a similar effect.

By doing this, for example, when analog writing is performed, the change in shading due to the change in the intensity of the laser beam will be caused by the fourth r.
As shown in XJ, halftones are reproduced in a state close to the ideal state.

In addition, when writing digitally, when expressing halftones by area, such as with the dither method or density pattern method, the area of 0N10 F F can be determined as calculated, making it possible to reproduce halftones according to theory. becomes.

As mentioned above, in order to repeatedly expose with a signal for one main scanning period, at least a line memory is required.
The circuit configuration of the laser printer may be as follows.

For example, to print a video signal, as shown in FIG. frame memory (through
3), and the synchronization signal is stored in the system controller (4).
supply to. Then, the video signals stored in the frame memory (3) are sequentially recalled by the clock signal of the system controller (4) and output to the printer via the D/A converter (5).
The video signals for l main scanning periods stored in are repeatedly output in synchronization with each synchronization signal.

Alternatively, when printing general serial input, as shown in FIG. 6, the serial input is stored in the page memory (12) via the shift register (11), and the control signal is input to the system controller (13). The signal in the page memory (12) is output to the printer via the switcher (14).

With such a circuit configuration, the laser beam can be scanned multiple times using the same signal.

Furthermore, the effect on information capacity caused by writing the same data signal multiple times can be sufficiently resolved by reducing the beam diameter of the laser beam so that the writing density is greater than the number of pixels used to read the document. be.

[Effects of the Invention] As is clear from the above explanation, in the present invention,
Since a signal for one main scanning period is repeatedly applied to the laser beam that exposes the electrophotographic photoreceptor, and the image for one main scanning period is exposed by multiple scans, the intensity distribution of the laser beam can be made into a rectangular distribution. This makes it possible to form images with excellent gradation reproduction, color reproduction, etc.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing a scanning method during image reading, FIG. 2 A is a schematic diagram showing how an image is divided during reading scanning, and FIG. 2 B is a schematic diagram showing how an image is divided during writing scanning. It is a schematic diagram. FIG. 3 is a characteristic diagram showing the substantial intensity distribution of the laser beam when the same data signal is repeatedly exposed.
Figure A shows the case where the beam intensity is strong, and Figure 3B shows the case where the beam intensity is weak. FIG. 4 is a schematic diagram showing how halftones of an image are reproduced when exposed by the method of the present invention. FIG. 5 is a block diagram showing an example of the circuit structure of a laser printer when printing a video signal, and FIG. 6 is a block diagram showing an example of the circuit structure of a laser printer when printing serial manually. Ru. FIG. 7 is a characteristic diagram showing the intensity distribution of a general laser beam. FIG. 8 is a characteristic diagram showing an example of a data signal applied to a laser beam, and FIG. 9A is a schematic diagram showing an ideal halftone reproduction state of an image obtained by the data signal shown in FIG. FIG. 9B is a schematic diagram showing the halftone reproduction state of an image obtained when the data signal shown in FIG. 8 is exposed with a laser beam having an intensity distribution as shown in FIG. 7.

Claims (1)

[Claims] When forming an image by exposing an electrophotographic photoreceptor to raster scan with a laser beam, the image exposure is performed by repeatedly scanning the laser beam a plurality of times using a data signal for one main scanning period. exposure method.