JP2001281574A - Scanning optical system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance sharpness while maintaining the continuity of gradation. SOLUTION: In order to obtain the necessary light quantity of one pixel, a modulating signal corresponding to the one pixel is set in the range of duty 50% and in the center of the range of the one pixel. About the shortage of the light quantity corresponding to a part set as duty 50%, the necessary light quantity can be held and the beam diameter can be thinned by doubling the intensity. Thereby, sharpness can be enhanced. In addition, the continuity of density by a dot can be maintained by setting one predetermined pulse width (width narrower than a full pulse width) rather than applying a plurality of pulse widths as conventional.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention comprises a plurality of light sources each emitting light having a different wavelength, and records a plurality of light beams emitted from the plurality of light sources and modulated in accordance with image density by an optical system. The present invention relates to a scanning optical system that focuses and scans a material.

[0002]

2. Description of the Related Art In recent years, for writing an image in a digital lab system or the like for recording an image recorded on a photographic film on a photographic paper, an image exposure apparatus which scans and exposes the photographic paper using a light source that generates a laser beam has been used. Widely used.

[0003] Such an image exposure apparatus is composed of R (red), G
A light source that generates laser light of each color of (green) and B (blue), modulates the laser light for each of R, G, and B based on the color image data, and converts the laser light into a beam expander; It passes through an optical system such as a cylindrical lens, is deflected in the main scanning direction by a deflector, conveys the photographic paper in the sub-scanning direction, and scans and exposes the photographic paper through a scanning lens system such as an fθ lens and a cylindrical lens. And a color image was recorded.

Here, the light beam output from the light source is modulated based on the image density. For example, when an SHG laser is applied, modulation is performed by an external modulator such as an AOM.

When the light beam performs main scanning, signals modulated by a plurality of modulation signals are continuous within a time corresponding to one pixel. A locus connecting the peaks of these modulation signals is a pulse waveform. Therefore, duty 0-100%
Is controlled by changing the pulse width while keeping the intensity constant (pulse width modulation). However, in the case of the above-described pulse width modulation, the control time interval becomes narrower as the number of gradations increases, and the pixel clock becomes 2 pixels.
In order to obtain an 8-bit gray scale (256 gray scales) at 0 MHz, control must be performed at a time interval of about 0.2 nsec.

In order to solve this problem, it has been proposed to reduce the time step by using both pulse width modulation and intensity modulation (for example, see Japanese Patent Application Laid-Open No. 4-230778).

In this prior art, a plurality of pulse widths are prepared in advance, an optimum pulse width is selected according to the image density, and the intensity at the selected pulse width is controlled. Thereby, since the gradation expression is shared by both the pulse width and the intensity, the control time unit can be increased.

[0008]

However, in the above prior art, it is necessary to prepare a plurality of pulse widths in advance. Further, there is a possibility that the continuity of the gradation corresponding to the switching of the pulse width is lost. In other words, when scanning is performed with different pulse widths despite having substantially the same gradation, the dot sizes become inconsistent, and image quality may be degraded.

In the pulse width control, if the pulse width is large, there is a problem that the surface potential of the recording material (photosensitive material) does not have a steep distribution in a low density portion, and the dot reproducibility is reduced. .

An object of the present invention is to provide a scanning optical system capable of improving sharpness while maintaining continuity of gradation in consideration of the above fact.

[0011]

According to the first aspect of the present invention, there are provided a plurality of light sources each of which emits light having a different wavelength.
A scanning optical system that converges a plurality of light beams emitted from the plurality of light sources and modulated on the basis of an image density on a recording material by an optical system, and scans the light beam. Using an applied pulse width of a predetermined ratio with respect to a full pulse width corresponding to one pixel, and controlling the intensity so as to perform modulation in accordance with the image density within a range of the applied pulse width. Features.

According to the first aspect of the present invention, in order to obtain a light amount corresponding to the image density for each pixel, the applied pulse width is set to a predetermined ratio to the full pulse width corresponding to one pixel. The intensity is controlled in order to obtain a required light amount in the pulse width.

Accordingly, the locus connecting the peaks of the modulated signal becomes narrower than the full pulse width, and the sharpness can be improved.

According to a second aspect of the present invention, in the first aspect of the present invention, the controlled intensity is the intensity at full pulse width × (applied pulse width / reciprocal of full pulse width).
Is a constant value calculated by:

According to the second aspect of the present invention, the control of the intensity is fixed within one pixel, and the arithmetic expression for the intensity is expressed as: intensity at full pulse width × (applied pulse width / reciprocal of full pulse width). . The intensity is calculated based on this equation, and the intensity of each modulated signal is adjusted. Since the intensity is constant, control becomes easy.

According to a third aspect of the present invention, in the first aspect of the present invention, the controlled intensity is a plurality of different values for each modulation unit, and a locus connecting the peak values of each modulated signal is sharp. It is characterized by being shaped.

According to the third aspect of the present invention, the trajectory connecting the modulated signals is further sharpened. That is, the locus connecting the peaks of the modulation signal becomes a triangular wave, and the sharpness can be further improved. According to the third aspect, in order to obtain the intensity of each modulated signal, the maximum peak (apex) is determined in terms of area, and the peak of each modulated signal is placed on a line connecting each of the apex and both ends of the base. I just need.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 1, a lab system 10 includes a line CCD scanner 14, an image processing unit 1
6, a laser printer unit 18 and a processor unit 20. The line CCD scanner 14 and the image processing unit 16 are provided in the input unit 26 shown in FIG. Reference numeral 20 is provided in the output unit 28 shown in FIG.

The line CCD scanner 14 is for reading a film image recorded on a photographic film such as a negative film or a reversal film.

The line CCD scanner 14 reads the film image by a line CCD and outputs image data. In addition, instead of the line CCD scanner 14 described above,
Area C where film image is read by area CCD
A CD scanner may be provided.

The image processing section 16 stores image data (scanned image data) output from the line CCD scanner 14.
Is input, and image data obtained by photographing with a digital camera, image data obtained by reading a document other than a film image (for example, a reflection document, etc.) with a scanner, image data generated by a computer, etc. Hereinafter, these are collectively referred to as file image data.) It is also possible to externally input (for example, input via a storage medium such as a memory card, or input from another information processing device via a communication line). It is configured as follows.

The image processing section 16 performs image processing such as various corrections on the input image data and outputs the image data to the laser printer section 18 as recording image data. Also,
The image processing unit 16 outputs image data on which image processing has been performed to an external device as an image file (for example, outputs the image data to a storage medium such as a memory card, or transmits the image data to another information processing device via a communication line). Is also possible.

The laser printer unit 18 includes a laser light source that oscillates R, G, and B laser beams.
The printing paper is irradiated with laser light modulated in accordance with the image data for recording input from 6, and an image is recorded on the printing paper by scanning exposure. Further, the processor unit 20 performs each process of color development, bleach-fix, washing, and drying on the photographic paper on which the image is recorded by the scanning exposure by the laser printer unit 18. Thus, an image is formed on the printing paper.

FIG. 3 shows the configuration of the optical system of the laser printer unit 18. The laser printer unit 18 includes laser light sources 210R, 210G, 21 as light sources of the present invention.
0B of three laser light sources. Laser light source 21
0R is a semiconductor laser (L) that emits a laser beam of R wavelength (for example, 680 nm) (hereinafter referred to as R laser beam).
D). The laser light source 210G is
An LD and a wavelength conversion element (SHG) that converts the laser light emitted from the LD into a laser light having a half wavelength, and has a wavelength from SHG to G (for example, 532n).
The oscillation wavelength of the LD is determined so that the laser light of m) (hereinafter referred to as G laser light) is emitted. Similarly,
The laser light source 210B also includes an LD and an SHG, and the oscillation wavelength of the LD is determined so that the SHG emits a laser beam having a wavelength of B (for example, 475 nm) (hereinafter, referred to as a B laser beam). .

Laser light sources 210R, 210G, 210B
The condenser lens 212 and the acousto-optic modulator (AOM) 214 are sequentially arranged on the laser light emission side of the optical disc. A
The OM 214 is arranged so that the incident laser light passes through the acousto-optic medium, and is connected to an AOM driver (not shown). When a high-frequency signal is input from the AOM driver, the OM 214 is acousto-optic. Ultrasonic waves according to the high-frequency signal propagate in the medium, diffraction occurs due to the acousto-optic effect acting on the laser light transmitted through the acousto-optic medium,
The laser light having the intensity corresponding to the amplitude of the high-frequency signal is AOM
It is emitted from 214 as diffracted light.

On the diffracted light emission side of the AOM 214,
A plane mirror 215 is provided, and the plane mirror 215 is provided.
A beam expander 21 as a first optical system that converts incident laser light into parallel light
6. A cylindrical lens 217 as a second optical system that linearly images parallel light incident from the beam expander 216, and a polygon mirror 2 as a main scanning unit
18 are arranged in order, and the R laser light, the G laser light, and the B laser light emitted from each of the AOMs 214 as diffracted light.
After the laser light is reflected by the plane mirror 215,
Beam expander 216 and cylindrical lens 2
The light is applied to substantially the same position on the deflecting / reflecting surface of the polygon mirror 218 via the light source 17, and is reflected by the polygon mirror 218.

On the laser beam emitting side of the polygon mirror 218, an fθ lens 220 for correcting the scanning speed on the exposure surface, a cylindrical lens 221 for correcting surface tilt having a lens power in the sub-scanning direction, and a cylindrical mirror 222 are sequentially arranged. And a cylindrical mirror 222
A folding mirror 223 is disposed on the side of emitting a laser beam.

The three laser beams reflected by the polygon mirror 218 are transmitted to the fθ lens 220 and the cylindrical lens 2
21 in order, is reflected by the cylindrical mirror 222, is reflected by the folding mirror 223 in a substantially vertical downward direction, and passes through the aperture 226 to form the photographic paper 224.
Is irradiated.

In the scanning optical system having the above structure, the AOM2
14, the AOM 214 has a predetermined applied modulation pulse width (applied pulse width). The applied pulse width determined in this embodiment is
The width is 50% of the full pulse width (scan width for one pixel), and is the center position of the scan width for one pixel.

When the pulse width becomes 50%, the intensity is increased in order to maintain the light amount at the full pulse width.

That is, FIGS. 4A and 4B are peak characteristic diagrams of a modulation signal for obtaining the same light amount, respectively. As shown in FIG. 4A, in order to obtain the same light amount as the full pulse width (duty 100%), FIG.
Applicable pulse width (duty 50%) as shown in
It can be seen that the peak value of each modulated signal in the above can be set to twice the full pulse width.

By halving the duty and doubling the intensity, the trajectory connecting the peak points of the modulation signal in one pixel becomes an elongated pulse waveform, and the required light amount is transferred to the photographic paper 224 in a short time. Can be given. That is, since the dot diameter can be reduced, the sharpness can be improved.

The operation of the present embodiment will be described below.

When an image is recorded on the photographic paper 224, the required light quantity for each pixel is calculated based on the image density data.

Since the light amount for one pixel is constituted by a group of a plurality of modulation signals, a required light amount is obtained from the number of modulation signals and the intensity of each modulation signal.

Here, in the present embodiment, the pulse width (applied pulse width) used as one pixel is set to 50% of the full pulse width and set at the center of one pixel range.

In order to obtain a required light amount with the pulse width of 50%, the intensity is doubled (see FIG. 4B). As a result, the required amount of light can be applied to the photographic paper 224 in a short time, so that the dot diameter can be reduced and the sharpness can be improved.

In this embodiment, the balance between colors is also positively affected. That is, when the beam spot diameter in the main scanning direction must be larger than other colors due to the design of the optical system, by reducing the modulation pulse duty of the color of the thick beam, one pixel by beam scanning can be obtained. The thickness of the integral amount profile per hit can be made equal to other colors.

In the case where the diameter of the main scanning beam is adjusted by providing an aperture in the main scanning direction, a profile having side lobes on both sides on the image forming surface is obtained due to the effect of beam shading. Even if the spot diameter is the same, compared to a beam having a spot file having a clean Gaussian distribution, this component causes deterioration in image quality especially in a high-frequency image region. In order to offset the degradation, the pixel duty is made smaller than the color of the Gaussian distribution beam, whereby the MTF degradation on the high frequency side can be offset.

In this embodiment, the duty 50
%, The applied pulse width is set, and the intensity of each modulation signal within one pixel is set to a constant value. As shown in FIG. 5B, the duty is set to 100%, and the center modulation signal has the maximum peak. (FIG. 5A is the same as FIG. 4A).

In this case, the peak value of the other modulation signal can be determined by connecting the maximum peak position (apex) and the bottom of the modulation signal with a straight line. In other words, the area of the triangle formed by the trajectory connecting the peaks of the respective modulation signals may be equal to the area of the original rectangular pulse.

FIG. 6 shows an MTF value characteristic diagram with respect to a spatial frequency. FIG. 7 shows a one-pixel scanning integrated light amount distribution characteristic diagram in the above three modes (duty 100%, duty 50%, triangular wave). It is shown. 6 and 7, the thin line is conventional (duty 100%)
The dashed line is the characteristic of the present embodiment (duty 50%), and the thick line is the characteristic of the modified example (triangular wave).

As can be seen from FIG. 6, even if the beam spot diameter is the same, the MTF can be improved by reducing the diameter of the integrated light amount profile of one pixel scanned by changing the duty and shape of the modulation pulse. .

As described above, in the present embodiment, in order to obtain a necessary light amount of one pixel, the modulation signal corresponding to the one pixel is set to the range of 50% duty and the center of the range of one pixel, By doubling the intensity of the light quantity shortage equivalent to the percentage, the required light quantity can be maintained and the beam diameter can be reduced.
Sharpness can be improved. Note that, instead of applying a plurality of pulse widths as in the related art, by setting a predetermined pulse width (a width smaller than the full pulse width), it is possible to maintain the continuity of the density of dots.

The applicable pulse width is not limited to the duty of 50%, but rather the nature of the image (character, image, DT).
P, etc.).

[0046]

As described above, the scanning optical system according to the present invention has an excellent effect that sharpness can be improved while maintaining continuity of gradation.

[Brief description of the drawings]

FIG. 1 is a schematic block diagram of a digital laboratory system according to an embodiment.

FIG. 2 is an external view of a digital laboratory system.

FIG. 3 is a schematic configuration diagram of an optical system of a laser printer unit.

FIGS. 4A and 4B are characteristic diagrams for obtaining a required light amount according to a set duty and intensity for one pixel, wherein FIG. 4A is a conventional diagram and FIG. 4B is a characteristic diagram of the present embodiment.

FIGS. 5A and 5B are characteristic diagrams for obtaining a required amount of light according to a set duty and intensity for one pixel. FIG. 5A is a characteristic diagram of a related art, and FIG.

FIG. 6 shows a spatial frequency for indicating a pixel duty difference.
FIG. 4 is an MTF characteristic diagram.

FIG. 7 is a graph showing a one-pixel scanning integrated light amount distribution characteristic.

[Explanation of symbols]

18 Laser printer section 210R, 210G, 210B Laser light source (light source) 216 Beam expander 217 Cylindrical lens 218 Polygon mirror 220 fθ lens 221 Cylindrical lens 224 Printing paper

Continued on front page F term (reference) 2C362 CA09 CA11 CA40 2H045 AA01 BA02 BA24 5C072 AA03 BA15 HA02 HA06 HA13 HA16 HB04 HB06 XA05 5C074 AA05 AA08 BB03 BB26 CC26 DD05 DD11 EE06 FF05 FF15 HH02

Claims (3)

[Claims] 1. A light source for emitting light having different wavelengths, wherein a plurality of light beams emitted from the plurality of light sources and modulated in accordance with image density are condensed on a recording material by an optical system. A scanning optical system for scanning, wherein at the time of modulation according to the image density, an application pulse width of a predetermined ratio is used for a full pulse width corresponding to one pixel, and a range of the application pulse width Wherein the intensity is controlled so as to perform modulation according to the image density. 2. The scanning optical system according to claim 1, wherein the controlled intensity is a constant value calculated by (intensity at full pulse width × (applied pulse width / reciprocal of full pulse width)). 3. The scanning optical system according to claim 1, wherein the intensity to be controlled is a plurality of different values for each modulation unit, and a locus connecting peak values of the respective modulation signals has a sharp shape. system.