JPH0743464B2 - Image recorder - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an image recording apparatus that includes at least two laser light sources driven based on the same input image signal, and combines and records image information recorded by the laser light sources. It is a thing.

“Prior Art” Generally, a laser can be used as a light source, and an optical scanning method using a rotating polygon mirror or a vibrating mirror can have a large scanning angle.
Due to its low color dispersion, it is often used in facsimile machines, various display devices, printing devices and the like.
Particularly when a rotary polygon mirror is used, it is widely used as a high-speed scanning device. In a device using such a scanning method, a phenomenon occurs in which the scanning pitches produced by the surface tilt of the rotary polygonal mirror, the drum rotation unevenness, and the vibration are unevenly spaced (hereinafter referred to as pitch unevenness).

FIG. 10 shows a gray scale of gradation output, and this gradation output is performed by the dither method or the density pattern method. Although eight levels of output from a to h are shown in the figure, it has a level of about 64 levels of the recording device for outputting a high-quality image, and is thinned out and displayed. (For examples of Taiza method, density pattern method, etc. by electrophotography, see Kawamura, Kitajima, Kadowaki; 1st Non-Impact Printing Technology Symposium Proceedings, 1984, P.88) Pitch unevenness is noticeable in a portion where the image density is high, that is, in portions f to h in the figure.
The reason why it occurs in the portion where the image density is high will be described below.

FIG. 11A shows a 4 × 4 taser threshold matrix for the purpose of explanation. As described in the above-mentioned document, a dot concentration type (Fatting type) threshold value array is used, and a pseudo halftone dot pattern is formed as an output image. FIG. 11 (B) shows an output image when the uniform input data value D = 1. (That is, the state of the highlight portion of the image.)
If there is no pitch unevenness, vibration, etc., and it is ideally stored, the level 1 state of the threshold matrix becomes black as shown in FIG. 11B, and a uniform pattern is formed. (This square indicates the pixel position to be recorded.) Next, consider the case where there is uneven pitch. It is assumed that the upper dot in FIG. 11 (B) is displaced downward by one pixel and the lower dot is displaced upward by one pixel due to the pixel unevenness.

The highlight portion of the image is output as shown in FIG. 11C, and the density value of each dot is stored.

On the other hand, when the shadow portion, for example, the input image data is 3 and uniform, it becomes as shown in FIG. 11 (D), and the blackening dots are continuous. At this time, the image density is increased by making the image continuous. (Fig. 21
Part) FIGS. 12 (a) and 12 (b) are diagrams for explaining this. The light energy distribution in the section P-P 'in FIG. A ', B', B ". When the two dots are separated by a spatial distance, the light energy distributions of the two Gauss Bream sections are shown as A in Fig. 12 (a). When developed at t) in the figure, it becomes like A '.

On the other hand, when the two dots shown in FIG. 12 (b) come close to each other in a pitch irregularity, the light energy curve synthesized as in B of 30 rises. Therefore, the output becomes B ″ and the blackened area is increased as compared with the state where A ′ is simply approached like B ′.

From the above description, it can be seen that the unevenness in pitch is noticeable in the darker part of the image density than in the middle part.

Since the occurrence of this pitch unevenness has a very bad influence on the print quality, various methods for correcting it have been reported.
Each method uses a complicated optical system, which leads to cost reduction and deterioration of reliability due to a complicated structure.

"Purpose" The present invention aims to eliminate the above-mentioned drawbacks of the prior art, and provides an image recording apparatus capable of recording high-quality image information with a simple structure without causing density unevenness. is there.

[Example] Hereinafter, an example according to the present invention will be described in detail with reference to the drawings.

FIG. 1 is a schematic configuration diagram of an embodiment according to the present invention. In the figure, 1 is a light source composed of two semiconductor lasers, 7 is a collimator lens, 8 is an imaging lens, 11 is a photosensitive drum, and 12 is a rotating polyhedral surface. A mirror, 13 is a reflection mirror, and 14 is a light receiving element.

As shown in FIG. 2, the light source 2 is composed of a chip 2 made up of two semiconductor laser elements that can be driven independently and are formed on the same wafer.
Is emitted. The emitted light beam is collimated by the collimator lens 7 and is deflected by the rotating polygon mirror 12.
An imaging spot is connected on the surface of the photosensitive drum 11 by the imaging lens 8 to form an electrostatic latent image according to the degree of modulation.

This semiconductor laser chip (hereinafter referred to as array laser) 2
Is slightly inclined with respect to the scanning direction, and the light beams A1a and A'1
It is adjusted so that b approaches and scans on the photosensitive drum 11. FIG. 4 shows the state of the image forming spots on the scanning surface, and the interval D between the scanning lines by the two spots is set so that D <P. However, P is the scanning pitch width.

A method for correcting pitch unevenness by such two imaging spots will be described below with reference to the block diagram of the signal processing unit in FIG.

In this embodiment, only the highlight portion with low image density is used. However, since the image density does not increase as it is, the exposure is performed twice by two laser beams, and the latent image is overwritten.

The input image data 31 indicates image data from, for example, an image input device (reader) or an image file (disk memory), and is composed of density data (or brightness data) of about 8 bits per pixel. The added data is converted by the γ conversion circuit 32 into a linear γ having a gradient of ½ so that the maximum density becomes about ½ of the normal density. An example of the input data 36 and the output data 37 by the γ conversion circuit 32 is shown in FIG. As shown,
An γ-converted output data signal 37 indicated by a chain line having a slope of 1/2 with respect to the input data signal 36 is output. This is a lookup table ROM (or RAM) with the characteristics shown in FIG.
It is realized by.

One of the density-converted output data signals 37 is input to the line memory 33, where it is delayed by a delay corresponding to one line of the array laser 2 and the dither circuit B34b.
Entered in. One output data signal 37 is directly input to the other dither circuit A34a. The signal (8-bit density data) input to the dither circuit is compressed into binary data of 1 bit or multi-valued data of about 2 bits. In this compression processing, it is compressed to an optimum value according to the characteristics of the printer. The output data of the dither circuit A34a and the dither circuit B34b are input to the respective laser driver circuits 35a and 35b, and the array laser 2 is driven with the strength according to the input data.

Overlapping recording by these two lasers requires that the registration ratio be adjusted to high brightness. Otherwise, the resolution will be degraded. One of the measures for improving the registration resolution is to make the number of lines in the line memory 33 variable. As a result, the adjustment can be performed with accuracy for one line. Furthermore, it is possible to mechanically adjust the inclination of the array laser 2 shown in FIG. This allows even finer adjustment (thinner than one line width). Improving the registration ratio in the main scanning direction is easy, and a cue signal is generated via the reflecting mirror 13 and the light receiving element 14 shown in FIG. In the case of the array laser 4, as many cue signals as the number of arrays in the case of the array laser 4 are generated (in this case, two signals), and the corresponding outputs may be generated as horizontal synchronizing signals.

Next, the binarization circuit, that is, the dither circuits 34a, 34 shown in FIG.
The b will be described in detail. Dither circuit A (34a) and B
If (34b) and (34b) consist of exactly the same threshold matrix, the superposition of both output images produces a kind of beat called the moire phenomenon. In order to prevent this, each threshold matrix can be arranged so as to have a screen angle, and the beat frequency due to superposition can be driven to the high frequency side.

As shown in FIG. 7, by arranging the basic halftone dots (which will be referred to as basic cells) made up of a × a pixels by appropriately shifting them, a halftone dot dot having a screen angle is formed. be able to. The portion of the gap C generated at this time may be appropriately attached to some cell. If the shift value (displacement vector) is = (a, b), the obtained screen angle θ is Get more. Using the displacement vector values a and b, the square threshold matrix size N corresponding to one cycle of the halftone dot is Becomes However, LCM (a, b) represents the least common multiple of a and b. In the case of various matrix sizes N, screen angle θ, halftone dot pitch ||, and the number of pixels N ₀ = a ² + b ² included in the basic cell in the case of this basic cell size from 2 × 2 to 5 × 5, It is shown in FIG.

In FIG. 8, it is desirable to use a matrix that is as small as possible in order to reduce the load on the hardware. For this reason, in the present embodiment, the number of pixels (N ₀ ) in the basic cell can be large, and the matrix size is a = 4 and b = 2 so that N = 10.

That is, matrix size 10x10 when a = 4 and b = 2
If is selected, a halftone dot pattern having a screen angle of 26.6 ° is created. On the other hand, if a threshold matrix of the left and right mirror images (corresponding to a = 4 and b = -2) is created, a screen angle of −26.6 ° is possible, but the present invention is not limited to this and other screen angles are possible. You can also choose one.

In any case, by choosing different screen angles,
Moire phenomenon is unlikely to occur in the composition of two images. Moreover, since the overlapping of individual dots is random, the density of the combined image is uniform.

As described above, high-quality image recording can be performed by stopping the exposure at a high density where the image unevenness is likely to occur and the exposure at a low density where the image unevenness is less likely to occur.

Also, in the above description, two sets of semiconductor lasers (array lasers) were used as means for generating two laser beams, but as shown in FIG. 9, the light beams from the two single lasers 41 and 42 are polarized. The beam splitter 40 may be configured to combine the beams. Further, although the diamatrix is performed by a pseudo halftone dot method, this can also be performed by a one-dimensional line screen (line screen) method. At this time, it is necessary to change the direction (angle) of the line so that moire fringes do not occur. Therefore, 45 ° and -45 ° (135 °)
The threshold matrix may be set by the line angle of.

Also, the output device is a storage device by electrophotography, and the method of superimposing in the state of a latent image has been described, but it is also possible to superimpose in the state of a developed toner image.

As described above, according to the present embodiment, by combining the outputs from the plurality of laser light sources driven based on the same input image signal, it is possible to perform recording at high density where pitch unevenness occurs during recording. With each light source, the required recording density can be achieved by recording at a relatively low density with no noticeable pitch unevenness, and high-quality image recording is possible with a simple configuration.

[Effect] As described above, according to the present invention, image processing is performed on an input image, a plurality of data for a plurality of laser light sources are formed from the same input image signal, and the plurality of data are output at the time of recording output. Since image information from a plurality of laser light sources that is output based on the above data is combined and output, it is possible to perform high-quality image recording while suppressing the occurrence of pitch unevenness.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an image recording apparatus of one embodiment according to the present invention, FIG. 2 is a diagram showing a structure of an array laser as a light source of this embodiment, and FIG. 3 is an array laser shown in FIG. FIG. 4 is a diagram showing a mounting state, FIG. 4 is a diagram showing a light beam from the array laser of this embodiment, FIG. 5 is a block diagram of an image data recording processing section of this embodiment, and FIG. FIGS. 7 and 8 are diagrams showing γ conversion of the conversion circuit, FIGS. 7 and 8 are diagrams showing dither processing examples of the dither circuit of this embodiment, and FIG. 9 is a diagram showing the structure of a light source of another embodiment according to the present invention. FIG. 10 is a diagram showing a gray scale of gradation output, FIG. 11 (A) is a diagram showing a 4 × 4 dither frame matrix, and FIGS. 11 (B) to (D) are shown in FIG. 11 (A). The figure which shows the output image of the threshold matrix which shows, FIG.12 (a), (b) is the light energy distribution of PP 'cross section of FIG.11 (B), and It is a diagram illustrating a reduction toner distribution. In the figure, 1 ... Light source, 1a, 1b ... Light beam, 2 ... Array laser, 7 ... Collimator lens, 11 ... Photosensitive drum,
12 …… Rotating polygon mirror, 13 …… Reflecting mirror, 14 …… Light receiving element, 20 …… Pitch unevenness, 31 …… Recorded image data, 32 ……
γ conversion circuit, 33 ... Line memory, 34a, 34b ... Dither circuit, 35a, 35b ... Laser driver, 41, 42 ... Single semiconductor laser.

Claims (1)

[Claims] 1. An image recording apparatus comprising a plurality of laser light sources, wherein input means for inputting an image signal, image processing is performed on the input image signal input by the input means, and the same input image signal is used for the image processing. Image processing means for forming a plurality of data for a plurality of laser light sources, based on the plurality of data formed by the image processing means, the main means for outputting image information with the plurality of laser light sources, Image information from the plurality of laser light sources output from the plurality of laser light sources so that a line interval D of scanning by two spots is D <P with respect to a scanning pitch width P. An image recording apparatus comprising: a synthesizing unit for synthesizing.