JPH1035020A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve a quality characteristic, particularly a granular characteristic of an output image without increasing a video rate of an image signal by a constitution wherein writing positions of small pixels are arranged so as to form a lattice pattern of equilateral triangles. SOLUTION: A laser beam emitted from a laser light source is allowed to be incident on a scanning start signal generator and is scanned on a surface of a photosensitive drum. Dots of an image formed on the photosensitive drum by the scanning of the laser beam are arranged to form equilateral triangles such that each of the interval (a) in the scanning direction of the dots 15 is a pitch 14 and each of the interval (h) in the sub-scanning direction thereof is a pitch 12. When the equilateral triangle lattice having a side (a) formed from dots 15 is subjected to Fourier transform, it becomes a condition that the original equilateral triangle lattice is rotated by 90.degree. and the side (a) becomes a basic frequency (f) of the image so that the space frequency of the image indicates preciseness of the cyclic structure. As a result, it is possible to improve a granular characteristic of the output image without increasing a video rate of the image signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus which improves the quality of a recorded image by arranging light beams written on an image forming body in accordance with image data in a regular triangular lattice pattern. Related to the device.

[0002]

2. Description of the Related Art In recent years, image forming apparatuses such as copiers, printers, and facsimile machines have been required to operate at higher speeds and to improve image quality. Has been put to practical use.

In the digital tone reproduction method, an image is decomposed into pixels, the data of the individual pixels is processed by an image processing device, and the image output device forms dots on a recording medium such as recording paper. To form a recorded image. In such an image output apparatus, a density gradation method and an area gradation method are widely known as methods for reproducing gradation information of an image.

The density gradation method has a multi-value gradation reproducibility even at the most microscopic pixel level of an image output device, and is realized by, for example, a sublimation-type heat-sensitive method. In addition, when properly managed, there is an advantage that high image quality can be easily realized, but there is a problem in that plain paper characteristics, high speed, stability and the like are lacking. For these reasons,
The area gradation method is widely used for printers.

The area gradation method is limited to two states, that is, whether ink is applied or not when viewed at the most microscopic pixel level of an image output device. One of the methods is to reproduce the tones, and one of the methods is to decompose each pixel of the input image into finer fine pixels and make the density of each pixel correspond to the area ratio of the fine pixels. A representative example of this method is a density pattern method.

[0006] The resolution is the same as that of the input image. The average density of the input image in a region having a predetermined size is made to correspond to the average area ratio of the output image, and a predetermined number of dots are arranged according to the change in density. There is a way to do that. A typical example of this method is an error diffusion method.

[0007]

However, according to the conventional image forming apparatus, in the density pattern method, in order to increase the number of reproducible gradations, the resolution of fine pixels must be increased. There is a problem that the rate increases and the cost increases. In the error diffusion method, when the resolution of the input image is low, the frequency of each output dot, that is, the fundamental frequency of the image becomes low, and noise such as a feeling of roughness recognized by human eyes is reduced. Since the intensity is increased, there is a problem that the quality characteristics of an image are deteriorated. SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide an image forming apparatus which is excellent in quality characteristics of an output image, particularly, granularity characteristics without increasing a video rate of an image signal.

[0008]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides an image forming apparatus which reproduces a density change of a recorded image by a change in the area of a fine pixel in a predetermined area. Provided is an image forming apparatus in which writing positions are arranged so as to form a substantially regular triangular lattice pattern.

According to another aspect of the present invention, there is provided an image forming apparatus comprising a light beam modulating means, a light beam scanning means, and a recording means for recording an image by the light beam. Provided is an image forming apparatus having delay means for delaying a beam scanning start position by a predetermined amount every other line.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an image forming apparatus according to the present invention will be described with reference to the drawings.

FIG. 1 shows an image forming apparatus according to an embodiment of the present invention. The laser light source 1 emits a laser beam corresponding to image data at a predetermined timing by a laser light source driving unit 14, and the laser light source 1 emits a laser beam. A collimator lens 2 for converting the laser beam into parallel light, and a motor 3
A polygon mirror 4 driven at a predetermined speed to deflect the laser beam incident through the collimator lens 2 and fθ lenses 5 and 6 for correcting the laser beam so that the scanning speed is constant on a predetermined main scanning line. And a photosensitive drum 7 that forms an electrostatic latent image by being scanned by a laser beam corrected by the fθ lenses 5 and 6
A charger 8 for charging the photosensitive drum 7 to a predetermined potential before scanning with a laser beam;
A developing device 9 for developing the electrostatic latent image formed on the recording medium with toner, a transfer device 11 for transferring the toner image developed by the developing device 9 to a recording sheet 10, and receiving a scanning start signal emitted from the laser light source 1 A scan start signal generator 12 for outputting a scan start signal, a write timing delay circuit 13 for generating a delay signal for delaying the write timing of the main scanning line based on the input of the scan start signal, an image data and a delay signal And a laser light source driving unit 14 for supplying a predetermined driving voltage to the laser light source 1 by inputting the same.

The laser light source drive unit 14 receives as input image data 0 and 1 halftone images generated by a halftone image generation unit (not shown). In this case, an existing algorithm such as a dither method or an error diffusion method can be used for the halftone image generation unit.

The laser light source 1 emits a laser beam based on a driving voltage supplied from a laser light source driving unit 14. This laser beam enters the polygon mirror 4 via the collimator lens 2. The laser beam deflected by the polygon mirror 4 is focused to a predetermined beam diameter by the fθ lenses 5 and 6 and scans the photosensitive drum 7. At this time, when the exposure pitch of the polygon mirror 4 in the main scanning direction of the photoconductor drum 7 is Px, and the exposure pitch of the photoconductor drum 7 in the sub-scanning direction is Py,

(Equation 1) The rotational speeds of the polygon mirror 4 and the photosensitive drum 7 are set such that

The write timing delay circuit 13
The scan start signal input from the scan start signal generator 12 is configured to generate a delay corresponding to Px / 2 at the even-numbered main scan line.

The operation of the image forming apparatus according to the present invention will be described below.

When a driving voltage corresponding to image data is supplied from the laser light source 14, a laser beam is emitted from the laser light source 1. After the laser beam enters the scanning start signal generator 12, it scans the surface of the photosensitive drum 7.

The scanning start signal generator 12 outputs a scanning start signal to the write timing delay circuit 13 based on the incidence of the laser beam. The write timing delay circuit 13 outputs the scan start signal to the laser light source drive section 14 without delay for the odd-numbered input of the scan start signal, and outputs Px / 2 equivalent for the even-numbered input. Generates a delay and outputs it. Due to this delay, the dots formed on the photosensitive drum 7 are shifted from the dots written in the immediately preceding line by P in the main scanning direction.
x / 2.

FIG. 2 shows a dot arrangement of an image formed on the photosensitive drum 7 based on the scanning of the laser beam. The dots 15 have a pitch a of 14 in the main scanning direction and a pitch h of the sub scanning direction. They are arranged in a grid pattern of a regular equilateral triangle with a pitch of 12.

Further, when a regular triangular lattice composed of the dots 15 and having a side of length a is subjected to Fourier transformation, one side of the regular triangular lattice is rotated by 90 degrees.

(Equation 2) , And this becomes the fundamental frequency f _{0 of the} image.

FIG. 3 shows the image shown in FIG.
This shows a state in which only two pixels have been cut out and two-dimensional discrete Fourier transform processing has been performed. The equilateral triangular lattice formed by dots 15 is rotated by 90 degrees with respect to the original image, and the pitch a between dots 15 is Is formed by about 42.5 pixels. The spatial frequency of this image is 42.5 / 512 = 0.0830 (3). The spatial frequency indicates the fineness of the periodic structure forming the image.

FIG. 4 shows a dot arrangement of an image formed on the photosensitive drum 7 as a comparative example. The dots 15 are arranged in a square lattice with a pitch b of 14 in the main scanning direction and the sub-scanning direction. I have.

When a square lattice formed by the dots 16 and having a side of b whose length is b is subjected to Fourier transform, one side becomes a square lattice of 1 / b, which is the fundamental frequency f _{0 of the} image.

FIG. 5 shows the image shown in FIG.
This shows a state in which only two pixels have been cut out and two-dimensional discrete Fourier transform processing has been performed. A square lattice formed by dots 16 is formed at a pitch b ′ of about 36.5 pixels.
The spatial frequency of this image is 36.5 / 512 = 0.0713- (4).

Thus, when one side a of the regular triangular lattice is equal to one side b of the square lattice, the fundamental frequency f _{0 of the} image composed of the dot arrangement of the regular triangular lattice is constituted by the dot arrangement of the square lattice. About 1 from the fundamental frequency f _{0 of the} image
5% higher. Therefore, it is effective in a circuit configuration in which a slight change in resolution in the sub-scanning direction does not affect the hardware cost, and only the resolution in the main scanning direction is a problem.

In the images of the above-mentioned regular triangular lattice and square lattice, the dots 15 and 16 before the Fourier transform are used.
Have a pitch of 14. From this, the theoretical value of the spatial frequency of the equilateral triangular lattice is

(Equation 3) Further, since the theoretical value of the spatial frequency of the square lattice is 1/14 = 0.0714 (6), it substantially matches the theoretical value of the spatial frequency of the regular triangular lattice and the square lattice. The pitch of the dots forming each grid is a value selected so that the equilateral triangular grid takes nearly integer coordinates, and other values may be set.

On the other hand, in order to compare the regular triangular lattice and the square lattice with the same average video rate, the relationship between a and b where the number of lattice points in a predetermined area becomes equal is obtained.

(Equation 4) Becomes Substituting b at this time into equation (4) of the fundamental frequency of the equilateral triangular lattice gives

(Equation 5) , And an improvement in the fundamental frequency of 7.5% is recognized.

Based on this theoretical formula, two-dimensional discrete Fourier transform processing was similarly performed on an image having a pitch a of 15 in the main scanning direction of an equilateral triangular lattice in a state where the average video rates were equal. Obtained an equilateral triangular lattice of about 39.5 pixels. The spatial frequency of this image is 39.5 / 512 = 0.0771 --- (9), which substantially matches the theoretical value of 1.075 × (1/14) = 0.0768 --- (10). I have.

As described above, the fundamental frequency of an image can be increased without increasing the video rate by changing the grid configuration for arranging dots from a square grid to a regular triangular grid. The granularity characteristics of an image can be improved by reducing the luminous intensity of a noise component that causes a sense or the like.

[0029]

As described above, according to the image forming apparatus of the present invention, the arrangement of dots written on the photosensitive drum is arranged in a regular triangular lattice pattern.
The granularity characteristics of the output image can be improved without increasing the video rate of the image signal.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram illustrating an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a metric space of dots arranged in a regular triangular lattice.

FIG. 3 is an explanatory diagram showing a frequency space after Fourier transform of dots arranged in an equilateral triangular lattice.

FIG. 4 is an explanatory diagram showing a metric space of dots arranged in a square lattice.

FIG. 5 is an explanatory diagram showing a frequency space after Fourier transform of dots arranged in a square lattice.

[Explanation of symbols]

 Reference Signs List 1, laser light source 2, collimator lens 3, motor 4, polygon mirror 5, 6, fθ lens 7, photosensitive drum 8, charging device 9, developing device 10, recording paper 11, transfer device 12, scanning start signal generator 13 , Write timing delay circuit 14, laser light source driver 15, dot 16, dot

Claims (2)

[Claims] 1. An image forming apparatus which reproduces a density change of a recorded image by a change in the area of a fine pixel within a predetermined area, wherein the writing positions of the individual fine pixels are arranged so as to form a substantially regular triangular lattice pattern. An image forming apparatus. 2. An image forming apparatus comprising a light beam modulating means, a light beam scanning means, and a recording means for recording an image by the light beam, wherein the light beam scanning start position is set at every other line. An image forming apparatus comprising a delay means for delaying a fixed amount.