JP2004354986A - Method and apparatus for forming image - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and an apparatus for forming an image by which the reproducibility of small dots and thin lines can be improved and the picture quality can be improved. <P>SOLUTION: In the process of forming an image by exposing an image forming material to a plurality of light beams, the method includes steps of: setting a first light quantity level and a second light quantity level higher than the first quantity level, controlling the pixel recording time of the pixel signal to record the pixels for forming an image on the image forming material, and generating a first signal to drive the first light quantity level based on the pixel signal; and generating a second signal to drive the second light quantity level based on the pixel signal. The pixel recording time of the pixel signal is controlled in accordance with the combination of the first signal and the second signal. The pixel is recorded in the image forming material by exposing with light beams in the first quantity level and the second quantity level by the combination of the first signal and the second signal. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an image forming method and apparatus, and more particularly to an exposure control technique during image formation of an exposure optical apparatus that forms an image with a plurality of exposure optical systems.

  In recent years, computer-to-plate (CTP) has been used in which a computer creates a digital image and directly records an image on a printing plate without interposing a film at the time of plate making. As an image forming apparatus used in such a CTP or the like, a laser beam is generated according to a digital image signal while holding an image forming material such as a photosensitive thermosensitive recording material, a heat mode recording material or a photosensitive material on the surface of a rotating drum. An image forming apparatus that performs exposure and forms an image is used.

In this technique, the lighting state of the light beam emitted from the exposure light source is controlled by a binarized image signal generated based on the image data of the original image to be recorded. By moving the exposure light source relatively, the light beam is scanned two-dimensionally on the image forming material, and a desired image is formed on the image forming material.
The image for plate making is a halftone dot image using so-called halftone dots, and each halftone dot is formed by a set of a large number of dots formed by scanning exposure using a light beam having a predetermined size determined according to the resolution. To be recorded.

Conventionally, in an image forming apparatus for a thermal plate for printing, in order to improve the reproducibility of small dots and fine lines, the beam diameter is reduced to increase the amount of light.
However, if the amount of light is increased too much, the balance between the white line and the black line is lost, ablation occurs, defects on the image occur, and the laser life is shortened. In particular, when the beam diameter is not reduced, the balance between the white line and the black line is noticeably lost. For this reason, it has been difficult to set the optimal light amount.

As a countermeasure against this, for example, in order to increase the luminance of the light source when exposing the contour portion of the image recorded on the image forming material and sharpen the density edge in the contour portion, the binary signal is differentiated. Thus, a method for enhancing an edge has been proposed (see, for example, Patent Document 1).
JP-A-8-23422

However, according to the method described in Patent Document 1, the edge is emphasized in proportion to the magnitude of the set light amount. However, when the laser characteristic is not linear, the ratio of edge enhancement cannot be adjusted. There is a problem that it is difficult to set the light intensity.
Further, the beam shape changes at the time of defocusing. For this reason, the recording line width determined by the threshold value of the image forming material varies. Furthermore, when the sensitivity fluctuation occurs, the threshold value of the image forming material changes, and the recording line width fluctuates. In such a case, there is a problem that the reproducibility of small dots and fine lines is deteriorated, and image quality deterioration such as fluctuations and unevenness of halftone percentage occurs.

  An object of the present invention is to provide an image forming method and apparatus capable of solving the above-described problems of the prior art, improving the reproducibility of small dots and fine lines, and improving the image quality.

  In order to solve the above-mentioned problems, a first aspect of the present invention is an image forming method for forming an image by exposing an image forming material with a plurality of light beams. A step of setting a second light amount level that is greater than the light amount level or a predetermined light amount level of the difference between the second level and the first light amount level, and forming an image on the image forming material. Adjusting a pixel recording time of a pixel signal to record a pixel, generating a first signal for driving the first light amount level based on the pixel signal, and based on the pixel signal Generating a second signal for driving the second light quantity level or the predetermined light quantity level, and the pixel recording time of the pixel signal is the first signal and the second signal level. Pair with signal The pixel is exposed to the image forming material by exposure with a light beam of the first light amount level and the second light amount level from a combination of the first signal and the second signal. The present invention provides an image forming method characterized by recording the above.

  Further, the first signal is the pixel signal that drives the first light amount level, and the second signal is an edge signal of the pixel signal that drives the predetermined light amount level, The first light amount level and the predetermined light amount level are added to obtain the second light amount level, or the predetermined light amount level is subtracted from the second light amount level to obtain the first light amount level. Is preferred.

  The second signal is an edge signal of the pixel signal, the first signal is a remaining signal obtained by removing the edge signal from the pixel signal, and the first light amount level is set to the remaining signal. It is preferable that the second light quantity level is driven by the edge signal.

  In addition, the rising edge and the falling edge of the pixel signal are detected, a first timing delayed by an edge signal time from the rising edge of the pixel signal is generated, and the delayed pixel signal is set at the first timing. Generating a delayed pixel signal by generating a second timing delayed by the edge signal time from a falling portion of the pixel signal, and resetting the delayed pixel signal at the second timing; A third timing delayed from the rising portion of the delayed pixel signal by the edge signal time is generated, and the first edge signal at the rising portion of the delayed pixel signal is generated by the first timing and the third timing. And a second portion at the falling portion of the delayed pixel signal according to the second timing and the falling portion of the pixel signal. Preferably, it was to generate an edge signal.

  The edge signal of the pixel signal is preferably a logical product of the first edge signal and the second edge signal and the delayed pixel signal.

  Further, the first signal drives the first light quantity level, and the second signal drives the second light quantity level, and drives the first light quantity level. The first light quantity level is set at the start timing of the first signal, and the second light quantity level is set at the start timing of the second signal that drives the second light quantity level. preferable.

  In addition, the rising edge and the falling edge of the pixel signal are detected, a first timing delayed by an edge signal time from the rising edge of the pixel signal is generated, and the second light quantity level is determined by the first timing. Is generated, a second timing further delayed from the first timing by the edge signal time is generated, the first light quantity level is set by the second timing, and the falling portion sets the first timing. A second light amount level is set, a third timing delayed from the falling portion by the edge signal time is generated, and the second light amount level is reset by the third timing to be an original light amount level. Is preferred.

  Similarly, in order to solve the above-described problem, a second aspect of the present invention is an image forming apparatus that forms an image by exposing an image forming material with a plurality of light beams. Means for adjusting a pixel recording time of a pixel signal to record a pixel for forming an image; means for setting a first light quantity level; and a second light quantity level greater than the first light quantity level, or A means for setting a predetermined light amount level as a difference between a second level and the first light amount level, and a first signal for driving the first light amount level are generated based on the pixel signal. Means for generating a second signal for driving the second light quantity level or the predetermined light quantity level based on the pixel signal, and the adjusting means comprises pixel recording of the pixel signal. Time, said first It adjusts according to the combination of the signal and the second signal, and exposure is performed with the light beam having the first light amount level and the second light amount level based on the combination of the first signal and the second signal. Thus, an image forming apparatus is provided that records the pixels on the image forming material.

  In the image forming apparatus according to the second aspect, the first signal is the pixel signal that drives the first light amount level, and the second signal has the predetermined light amount level. The edge signal of the pixel signal to be driven, and means for obtaining the second light amount level by adding the first light amount level and the predetermined light amount level or the predetermined light amount from the second light amount level It is preferable to include means for subtracting the light quantity level to obtain the first light quantity level.

  The second signal is an edge signal of the pixel signal, the first signal is a remaining signal obtained by removing the edge signal from the pixel signal, and the first light amount level is set to the remaining signal. It is preferable that the second light quantity level is driven by the edge signal.

  Further, in each of the above image forming apparatuses, further, a means for detecting a rising portion and a falling portion of the pixel signal and a first timing delayed by an edge signal time from the rising portion of the pixel signal are generated. A delayed pixel signal is set at the first timing, a second timing delayed by the edge signal time from a falling portion of the pixel signal is generated, and the delayed pixel signal is generated at the second timing. Generating the delayed pixel signal by resetting, and generating a third timing delayed by the edge signal time from a rising portion of the delayed pixel signal, and generating the first timing and the third timing Means for generating a first edge signal at the rising portion of the delayed pixel signal, and the falling portion of the pixel signal and the second The timing preferably comprises means for generating a second edge signal at the falling portion of the delayed pixel signal.

  The edge signal of the pixel signal is preferably a logical product of the first edge signal and the second edge signal and the delayed pixel signal.

  In each of the image forming apparatuses, the first signal drives the first light amount level, the second signal drives the second light amount level, and Means for setting the first light amount level at the start timing of the first signal for driving the first light amount level; and at the start timing of the second signal for driving the second light amount level. And a means for setting the second light quantity level.

  Further, in each of the above image forming apparatuses, further, a means for detecting a rising portion and a falling portion of the pixel signal and a first timing delayed by an edge signal time from the rising portion of the pixel signal are generated. Generating a second timing that is further delayed by the edge signal time from the first timing, and setting the second light quantity level at the first timing. A means for setting the first light quantity level; and setting the second light quantity level by the falling part and generating a third timing delayed from the falling part by the edge signal time, And a means for resetting the second light quantity level to the original light quantity level at the timing of 3.

  According to the first and second aspects of the present invention, the amount of light is increased only at the edge portion, thereby eliminating the deterioration of the reproducibility of small dots and fine lines, the image quality deterioration such as fluctuations and unevenness of halftone dots, and the like. It is possible to improve the image quality by preventing the line width of the vertical and horizontal thin lines that are generated by increasing the amount of light at the edge part from being adjusted by adjusting the pixel recording time, for example by combining shortening or extension. It becomes.

Hereinafter, an image forming method and apparatus according to first and second aspects of the present invention will be described in detail based on preferred embodiments shown in the accompanying drawings.
In this embodiment, the light level of the rising and falling edges of a pixel for exposing an image forming material, for example, a pixel dot, is relatively compared to the light level of other portions. In order to cope with the difference in the line width between the vertical thin line and the horizontal thin line that may be generated by increasing the light amount of the edge portion and the deterioration of the image quality caused by the line width, In combination with adjustment of pixel recording time for recording, for example, shortening or extending, the rise and fall of the laser beam (start and end of the laser beam, for example, rise and fall of the binary signal for driving the laser) A lower light amount level is given to the (down) edge portion than in a portion other than the edge portion.

Therefore, the present embodiment has the following configuration in order to increase the amount of light only at the rising and falling edge portions of the laser beam.
First, voltage setting means for setting a voltage corresponding to the first light amount level (target light amount) and the up light amount level (additional light amount) or the second light amount level (target light amount + additional light amount) is provided. For example, values corresponding to the first light amount level (target light amount) and the up light amount level (additional light amount) or the second light amount level (target light amount + additional light amount) are set as the target light amount DAC (digital / analog converter) and additional light amount, respectively. The DAC is set to the sum light amount DAC of the target light amount and the additional light amount.
Then, in accordance with the pixel signal (pixel modulation signal), the up light amount level is added to the first light amount level, or the up light amount level is subtracted from the second light amount level, or the second light amount from the first light amount level. Switch to level. For example, the image modulation signal and the additional signal that enable the output of each DAC described above are controlled, and each DAC output is added or subtracted or switched.

In addition, there is a timing control means for making the addition / subtraction or switching timing rise or fall of the pixel modulation signal.
As a result, when forming an image in a plurality of exposure optical systems using a plurality of light beams, even if the drawing position timing of the light beam of each exposure optical system is different, this timing control means causes the rise of the laser beam, The light level can be added / subtracted or switched so that the light level is increased at the falling edge.
In addition, even if only the edge portion is used, the line width between the vertical thin line and the horizontal thin line will be different by increasing the amount of light, and there is a concern about the deterioration of the image quality. In order to cope with this, in order to record pixels The light quantity level is increased at the rising and falling edge portions of the laser beam, that is, the light quantity level is added / subtracted or switched by the timing control means combined with the adjustment (shortening or extension) of the pixel recording time.
In this way, for example, the timing for applying the additional signal can be controlled to rise or fall of the image modulation signal whose pixel recording time is adjusted, thereby improving the reproducibility of small dots and fine lines and improving the image quality.

FIG. 1 is a block diagram showing a schematic configuration of an embodiment of an image forming apparatus according to the second aspect of the present invention for carrying out the image forming method according to the first aspect of the present invention.
As shown in FIG. 1, the image forming apparatus 10 includes a rotating drum 14 that holds an image forming material 12 on which an image is exposed and formed around an outer peripheral surface, a light source unit 16, and a rotation axis direction of the rotating drum 14. A sub-scanning unit 18 that can move along the light source unit 20, a light source driving circuit 20 that outputs a control signal for driving the light source unit 16, a main scanning position detector 22 that detects the rotational angular position of the rotating drum 14, and the rotating shaft of the rotating drum 14. A sub-scanning position detector 24 for detecting a directional position, a rising / falling edge detector 26 for detecting a rising edge and a falling edge of a pixel signal (input modulation signal), and an edge light amount increase in the image forming method of the present invention; In addition to controlling the adjustment of the pixel recording time, the main control circuit 28 that performs various controls of the entire apparatus including the light source driving circuit 20 is included.

Here, the image forming apparatus 10 shown in FIG. 1 performs sub-scanning on the image forming material 12 such as a printing plate mounted on the outer surface of the rotating drum 14 rotated in the main scanning direction by a driving source such as a motor (not shown). A plurality of light beams such as a plurality of laser beams modulated (on / off control) are respectively emitted from the sub-scanning unit 18 that moves in the direction based on the binarized image signal, and the plurality of emitted light beams This is for exposing and recording a plurality of pixels (pixel dots) to form a halftone image composed of a plurality of pixel dots, and includes a so-called outer drum type printing plate automatic exposure apparatus. Although not shown, the sub-scanning unit 18 is moved in the axial direction of the rotary drum 14 by a known moving mechanism using a linear guide, a ball screw mechanism, or the like. In the present invention, the type of the exposure apparatus is not limited to the outer drum system, and may be an inner drum system or a flat bed system.
The image forming material 12 used in the present invention is not particularly limited as long as an image can be formed by a light beam emitted from a light source such as a laser. For example, it may be a so-called photosensitive thermosensitive recording material or heat mode recording material that forms an image (latent image) corresponding to the energy of the light beam, or an image (latent image) is formed by exposure to the light beam. A so-called photosensitive material may also be used. In addition, the image forming material 12 may form a multi-tone image, but in particular, a hydrophobic (ink-philic) portion and a hydrophilic (ink-phobic) portion such as a printing plate used for CTP or the like. It is preferable to form a binarized image consisting of parts.

  In the image forming apparatus 10 of the illustrated example, the light source unit 16 may be a plurality of LDs (on / off control individually) as long as the light source unit 16 can emit a plurality of light beams that are independently modulated (on / off control). A laser diode), a combination of a light source that emits continuous light and a modulator, a combination of a light source such as a broad area array type LD and a spatial modulation element, or the like. In the illustrated example, the light source unit 16 is built in the sub-scanning unit 18, but the present invention is not limited to this, and a plurality of light beams for exposing the sub-scanning unit 18 to the image forming material 12. Of course, it is possible to use an exposure head composed of an imaging optical system for forming an image on the top, and the light source unit 16 may be fixed to the outside of the sub-scanning unit 18 and connected between them by an optical fiber cable array. .

  The light source drive circuit 20 drives (on / off drive) light sources such as a plurality of LDs of the light source unit 16 based on a plurality of light source drive signals generated by the drive signal generator 30 of the main control circuit 28, respectively. A light source driver such as an LD driver. The details of the function of the light source driving circuit 20 will be described later.

The main control circuit 28 is supplied with a pixel signal representing image data indicating an image to be recorded on the image forming material 12 from an image supply source (not shown) or resolution data indicating the resolution of image recording. ing. The main control circuit 28 has a drive signal generator 30 and outputs various signals for controlling the light source drive circuit 20. Based on various detection signals, the main control circuit 28 has an edge portion of a halftone dot constituting an image. An instruction is given to increase the amount of light by a predetermined length (width), that is, to increase the emission intensity. That is, the main control circuit 28 provides the drive signal generator 30 with a reference pixel clock and a reference pixel clock for obtaining a pixel signal used for light source drive and image recording based on the image data and a synchronization timing of the pixel signal. An N-times pixel clock having a frequency N times as high as N is supplied.
The drive signal generator 30 uses the supplied pixel signal, the reference pixel clock, and the N-times pixel clock to change the pixel according to fluctuations in reproducibility of small dots and fine lines due to an increase in the amount of edge light, or fluctuations in resolution (net%). Recording time is shortened or extended, that is, an adjusted adjustment pixel signal and an edge signal generated by generating an adjusted adjustment pixel signal and an edge signal for increasing the amount of light for the edge portion of the pixel dot of the halftone dot constituting the image, Alternatively, these combined signals are output to the light source driving circuit 20.

  The main control circuit 28 outputs a light source drive signal for controlling the drive timing and light amount level of each light source of the light source unit 16 that controls the light source drive circuit 20, the light amount increase timing of the edge portion, the light amount level to be increased, and the like. However, the drive signal generator 30 has a drive timing signal having an adjusted (shortened or extended) pixel recording time and a timing for increasing the amount of light at the edge portion of the halftone pixel dots constituting the image. A signal is generated, and the main control circuit 28 outputs, together with these timing signals, a parameter indicating the target light amount level to be output by the pixel signal and the edge light amount level to be increased at the edge portion to the light source driving circuit 20. In the light source driving circuit 20, parameters of each light quantity level are set to, for example, each DAC (digital / Na log converter) (set by not illustrated), set value, for example, a current value may be one that drives the light source LD, etc. according to the respective timing signals. That is, the main control circuit 28 performs digital signal processing by the drive signal generator 30 to generate each timing signal, and performs analog signal processing by the light source drive circuit 20 to increase the edge light amount at the target adjustment pixel recording time. It may be controlled to emit a light beam.

  Alternatively, the main control circuit 28 uses the drive signal generator 30 to indicate the light source drive signal that can represent the drive timing and the light amount level, and the additional drive signal that can represent the light amount increase timing of the edge portion and the light amount level to be increased. And the generated both drive signals are output from the drive signal generator 30 to the light source drive circuit 20, and the light source drive circuit 20 is controlled to drive a light source such as an LD according to the drive signals. The drive signal generator 30 may generate a combined drive signal of the light source drive signal and the additional drive signal, and the generated combined drive signal may be output from the drive signal generator 30 to the light source drive circuit 20, The light source drive circuit 20 may drive a light source such as an LD in accordance with the combined drive signal. In these cases, the target light amount level parameter and the edge light amount level parameter are set in the target light amount DAC and the edge light amount DAC (not shown) in the main control circuit 28, respectively.

  FIG. 2 shows an example of a specific circuit configuration of the drive signal generation circuit 30 used in the main control circuit 28. As shown in FIG. 2, the drive signal generation circuit 30 includes a clock phase control unit 32 and an output signal generation unit 34. Here, in the clock phase control unit 32, when the recorded pixel is large with respect to the resolution, for example, when the reproducibility of small dots and fine lines is deteriorated and becomes thicker due to an increase in the amount of edge light, A configuration for shortening the pixel recording time for each pixel signal for exposing pixels, for example, pixel dots, for forming an image on the image forming material 12 will be described as an example.

The clock phase controller 32 receives the reference pixel clock and the N-times pixel clock supplied from the main control circuit 28, and generates and outputs a plurality of reference clocks obtained by delaying the phase of the reference pixel clock by a predetermined amount. It is.
Further, FIG. 3 shows the state of signals in each part of the schematic configuration of the clock phase control unit 32 and the output signal generation unit 34. Hereinafter, the schematic configuration of the clock phase control unit 32 and the output signal generation unit 34 and the pixel recording time reduction will be described with reference to FIGS. 2 and 3.

The clock phase control unit 32 includes a delay element 36, a selection unit A38, and a shift register 40.
First, in the drive signal generator 30 of the main control circuit 28, an N-times pixel clock having a frequency N times that of the reference pixel clock is created and input to the delay element 36. The delay element 36 generates a signal (delayed signal) delayed by the input N-times pixel clock and inputs the signal to the selection unit (selector) A38. The selection unit A38 generates a delay signal selected by the set value A. This delayed signal is set as a signal (delayed N-times pixel clock) obtained by delaying the N-times pixel clock by a unit equal to or lower than the reference pixel clock, that is, a unit shorter than the period of the reference pixel clock (delay time T in FIG. 3). And used as a strobe signal for the shift register 40. A reference pixel clock is input to the shift register 40 as an input signal. From the shift register 40, reference clock 1, reference clock 2,... Are output as output signals. This output signal becomes a reference clock signal obtained by delaying the reference pixel clock.

The output signal generation unit 34 includes a first selection unit 42, a selection unit B44, D-FFs (D-type flip-flops) 46 and 48, AND circuits 50 and 52, and a selection unit C54.
The first selection unit 42 selects the reference clock 1 (a) as a reference clock including a delay equal to or less than the reference pixel clock and uses it as a strobe signal for the D-FF 46.
In the illustrated example, the selection unit B44 selects the reference clock 2 (b) by the setting value B as the reference clock including the delay of the reference pixel clock, and uses it as the strobe signal of the D-FF 48.

The D-FF 46 outputs a signal (c) for synchronizing the pixel signal synchronized with the reference pixel clock with the reference clock 1 (a) selected by the first selection unit 42. This is for synchronizing with a signal including a delay by the selection unit B44. The signal (c) is input to the D-FF 48 and the AND circuit 52.
The D-FF 48 is for synchronizing the signal (c) with the reference clock 2 (b) selected by the selection unit B44, and when the signal (c) is input to the D-FF 48, The signal (d) is output from the FF 48. The signal (d) is a signal for synchronizing the signal (c) with the reference clocks 1 (a) and 2 (b) selected by the selection unit B44, and is input to the AND circuits 50 and 52. The
When the value set in the selection unit B44 is, for example, 0, that is, when it is not shortened, the signal (c) and the signal (d) are shifted by one reference pixel clock, and the output signal of the D-FF 46 is LOW The trouble that it will remain is generated. In this case, if the signal (e) is created as a preset signal to the D-FF 46, a signal without shortening can be created for the output signal.

The AND circuit 50 is for creating a signal (f) in which the front part of the pixel signal is shortened by the pixel signal and the signal (d). This signal (f) is a signal including a delay equal to or less than the reference pixel clock and a delay of the reference pixel clock.
The AND circuit 52 is for creating a signal (g) in which the front part of the pixel signal is shortened by the signals (c) and (d). This signal (g) is a signal including a delay of the reference pixel clock.

  When the signal (f) and the signal (g) are input to the selection unit C54 and there is no delay equal to or less than the reference pixel clock, that is, when the set value C is 0, the signal (g) is selected and the delay is In some cases, a selection signal (h) for selecting the signal (f) is input. An output signal is generated and output from the signal (f) and the signal (g) as a signal obtained by shortening the front part of the pixel signal by an AND circuit. In this way, the pixel recording time is shortened.

The above description has been made on the case of shortening the pixel recording time. However, the pixel recording time is extended by making the AND circuit an OR circuit. In this way, when the recording pixels of the exposure optical system are thin relative to the resolution, for example, there is an increase in the relative edge light amount, but the reproducibility (dot%) of small dots and thin lines deteriorates due to a decrease in the overall light amount. When the image becomes thinner, the pixel recording time is extended, and the main scanning width can be extended.
Further, if the signal (e) is created as a reset signal for the D-FF 48, it is possible to create a signal that is not extended with respect to the output signal.

Next, in the main control circuit 28 and the light source driving circuit 20, the pixels for forming an image on the image forming material 12, for example, the rising and falling edge portions of the laser beam for exposing the pixel dots are large. A method of increasing the light amount only at the edge portion by giving the light amount level will be described.
In the following description, as shown in FIGS. 5 to 8, the light amount level when the non-edge portion of one pixel (pixel dot) is exposed is referred to as a first light amount level, which is referred to as a target light amount, The light amount level at the time of exposure is set to the second light amount level. The second light amount level is larger than the first light amount level, and the light amount is increased by this amount at the edge portion, and this increased amount (up amount) is referred to as the edge light amount.
Eventually, the second exposure level = target light quantity (first exposure level) + edge light quantity.

There are various methods of performing exposure by increasing the light amount only at the edge portion depending on the first light amount level and the second light amount level. First, as shown in FIG. 5, with respect to the target light amount (first light amount level). A method of creating the second light quantity level by adding the edge light quantity will be described.
First, the first light amount level (target light amount) and the value corresponding to the edge light amount that is increased at the edge portion are set in the target light amount DAC and the edge light amount DAC in the main control circuit 28 or the light source drive circuit 20, respectively. To do. The pixel signals (image modulation signals) and edge signals that enable these DAC outputs are controlled to perform respective DAC outputs.

The present invention controls the timing for applying the edge signal to the rise and fall of the image modulation signal, and adjusts (shortens or extends) the pixel recording time between the rise and fall of the image modulation signal. The image quality is improved by improving the reproducibility of the lines and fine lines.
Next, a method of generating an edge signal for increasing the amount of edge light for the image modulation signal (pixel signal) whose pixel recording time has been adjusted (shortened or extended) in the main control circuit 28 (drive signal generator 30) will be described. .
FIG. 4 simply shows an example of an edge signal generation method performed in the drive signal generator 30 of the main control circuit 28 of the image forming apparatus 10 of the present invention. In the example shown in FIG. 4, the image modulation signal (input modulation signal) is for three pixels and the edge signal is for one clock, as can be seen by comparison with the N-times pixel clock shown at the top in FIG. It is. Needless to say, the pixel recording time of the image modulation signal is adjusted (shortened or extended).

First, the input modulation signal (image modulation signal) shown second from the top in FIG. 4 is set at a timing delayed by an edge signal time (in this case, one clock) using an N-times pixel clock. A signal is generated, and then the input modulation signal is delayed by an edge signal time (one clock) from the falling portion of the input modulation signal to reflect that the pixel recording time is adjusted (shortened or delayed). The timing is generated using an N-times pixel clock, and the set signal is reset at this timing.
The rising part and the falling part are detected by the rising part / falling part detector 26.
As a result, the delay modulation signal (image modulation signal) shown third from the top in FIG. 4 is created.

Next, a timing delayed by the edge signal time (one pixel) from the rising portion of the delay modulation signal thus created is generated by an N-times pixel clock, and the rising edge signal (4) from the top in FIG. Rising edge signal).
Further, the timing delayed by the edge signal time (one clock) from the falling portion of the original image modulation signal (input modulation signal) is created by the N-times pixel clock, and the fifth falling from the top in FIG. Part edge signal (falling edge signal) is created.
Finally, the edge signal shown at the bottom of FIG. 4 is created by ORing these rising edge and falling edge signals.

Further, since the edge signal time may be longer than the delay modulation signal (image modulation signal), the edge signal needs to be ANDed with the delay image modulation signal.
Furthermore, since the delay modulation signal has a drawing timing delayed from that of the original image modulation signal (input modulation signal), the system needs to shift the drawing timing in accordance with the edge signal time.

As described above, in the main control circuit 28 or the light source drive circuit 20, the rising edge and the falling edge of the rising edge and the falling edge are generated by the edge signal created by the drive signal generator 30 using the initially set target light quantity and edge light quantity. Control is performed to increase the amount of light at the edge portion.
FIG. 5 shows how the light quantity is controlled. As shown in FIG. 5, in the non-edge portion, exposure is performed with a target light amount (first light amount level), and at the rising edge portion and the falling edge portion, the edge light amount is equal to the first light amount level. The exposure is performed at the second light quantity level obtained by adding (adding).

The method of creating the waveform with the light amount increased only at the edge portion is not limited to the method of adding the edge light amount to the first (target) light amount level to create the second light amount level. There are several ways.
For example, as shown in FIG. 6, the first (target) light amount level may be created by subtracting the edge light amount from the second light amount level at which the edge portion is exposed.
Alternatively, as shown in FIG. 7, the first (target) light amount level and the second light amount level are held separately, and the light amount level is switched between the non-edge portion and the edge portion, so that the non-edge portion and the edge are switched. May be driven so as to be exposed at each light quantity level. In other words, the first light amount level may be driven by the edge signal other than the edge signal of the modulation signal (modulation signal XOR (exclusive OR) edge signal), and the second light amount level may be driven by the edge signal.

  Alternatively, as shown in FIG. 8, a value corresponding to the first light amount level (target light amount) and the second light amount level (target light amount + edge light amount) is set at an appropriate timing for one DAC. Thus, the DAC output may be changed to increase the light amount level only at the edge portion.

Also, examples of edge signals are not limited to those shown in FIG. 4 but may be those shown in FIGS. 9 and 10.
FIG. 9 shows a case where the modulation signal is for two clocks and the edge signal is also for two clocks, and FIG. 10 shows a case where the modulation signal is for one clock and the edge signal is for three clocks.
Thus, when the edge signal time to be added is the same as the pixel recording time (modulation signal time) of the modulation signal or longer than the pixel recording time of the modulation signal, the edge signal to be added is set as follows. That's fine.
First, the first timing delayed by the edge signal time from the rising portion of the modulation signal is generated, and the light amount level is reset at the generated first timing. Next, after the first timing, if the modulation signal time is the same as or shorter than the edge signal time, the next light amount level is not set.
The generation circuit for generating each signal shown in the time charts of FIGS. 4, 9, and 10 is not shown, but is not particularly limited. Japanese Patent Application No. 2002 relating to the application of the present applicant. The timing circuit of the exposure circuit proposed in the specification of -301951 is applicable, and any circuit may be used as long as it can generate each signal shown in the above-described time chart.

  As described above, according to the present embodiment, the light amount level is increased only at the edge portion of the light beam for exposing pixels (pixel dots) for forming an image, and the pixel recording time is adjusted (shortened or extended). Since they are combined, even if the amount of light is increased, the line widths of the vertical thin line and the horizontal thin line are different, so that the image quality is not deteriorated due to the deterioration of the reproducibility of the small dots or the fine lines, and the image quality can be improved.

  In addition, the beam shape changes at the time of defocusing, and therefore the recording line width determined by the image forming material threshold fluctuates. Also, when the sensitivity fluctuation occurs, the image forming material threshold also changes and the recording line width changes. Fluctuates. In such a case, the reproducibility of small dots and fine lines deteriorates, and there is a concern about image quality deterioration such as fluctuations and unevenness of halftone dots. However, the pixel recording time is adjusted and / or the amount of light is increased only at the edge portion. As a result, the reproducibility of the small dots and fine lines can be improved, and further, the fluctuation and unevenness of the halftone can be eliminated and the image quality can be improved.

Also, by increasing the amount of light only at the edge, the balance between white and black lines is lost when the total amount of light is increased (particularly when the beam diameter is not narrowed) or an image caused by ablation. It is possible to prevent defects such as the above defects or shortening of the laser life.
In addition, as described above, by increasing the amount of light even in the edge portion, the line width of the vertical thin line and the horizontal thin line may be different and the image quality may be deteriorated. To prevent this, adjustment of the pixel recording time (shortening or Even if (extension) is applied, it is possible to increase the amount of light only at the target rising or falling edge portion, and the image quality can be improved.

  In the embodiment described above, the drive signal generator 30 of the main control circuit 28 generates a pixel signal (image modulation signal) in which the pixel recording time is adjusted (shortened or extended), and the main control circuit 28 or the light source drive circuit. 20, the edge signal used to increase the amount of edge light with respect to the adjustment pixel signal is generated, or the combined signal of both is generated, but the present invention is not limited to these embodiments. For example, the main control circuit 28 or the light source driving circuit 20 may generate a composite signal of the pixel signal and the edge signal, and adjust (shorten or extend) the pixel recording time of the composite signal. In addition, the edge light intensity can be increased by the edge signal for the pixel signal (image modulation signal) whose pixel recording time has been adjusted (shortened or extended). If the reproducibility of the thin line is improved, and as a result, the image quality can be improved, the adjustment pixel signal may be generated, the edge signal may be generated, or the combined signal of both may be generated. good. The adjustment pixel signal and the edge signal or a composite signal of both may be generated anywhere in the main control circuit 28, the drive signal generator 30, and the light source drive circuit 20, or generated across a plurality of circuits. Also good.

  The image forming method and apparatus of the present invention have been described in detail with reference to various embodiments and examples. However, the present invention is not limited to the above embodiments and examples. It goes without saying that various improvements and changes may be made without departing from the gist of the invention.

1 is a block diagram illustrating a schematic configuration of an embodiment of an image forming apparatus that performs an image forming method according to the present invention. FIG. 2 is a circuit diagram showing a specific configuration example of a clock phase controller and an output signal generator in the drive signal generator of the main control circuit shown in FIG. 1. 3 is a timing chart showing the state of signals in each part of the schematic configuration of a clock phase control unit and an output signal generation unit shown in FIG. 2. 6 is a timing chart illustrating an example of an edge signal creation method in the image forming method according to the present invention. It is a diagram which shows the example of the waveform which increased the light quantity only in the edge part. It is a diagram which shows the other example of the waveform which similarly increased the light quantity only in the edge part. It is a diagram which shows the other example of the waveform which similarly increased the light quantity only in the edge part. It is a diagram which shows the other example of the waveform which similarly increased the light quantity only in the edge part. It is a diagram showing another example of how to make an edge signal in the image forming method according to the present invention. FIG. 6 is a diagram showing another example of how to generate edge signals in the image forming method according to the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Image forming apparatus 12 Image forming material 14 Rotating drum 16 Light source unit 18 Sub scanning unit 20 Light source drive circuit 22 Main scanning position detector 24 Sub scanning position detector 26 Rising part / falling part detector 28 Main control circuit 30 Drive signal Generator 32 Clock phase controller 34 Output signal generator 36 Delay element 38 Selector A
40 shift register 42 first selection unit 44 selection unit B
46, 48 D-FF (D-type flip-flop)
50, 52 AND circuit 54 selector C

Claims (14)

An image forming method for forming an image by exposing an image forming material with a plurality of light beams,
Setting a first light amount level and a second light amount level greater than the first light amount level or a predetermined light amount level of the difference between the second level and the first light amount level;
Adjusting a pixel recording time of a pixel signal to record pixels for forming an image on the image forming material;
Generating a first signal for driving the first light level based on the pixel signal;
Generating a second signal for driving the second light level or the predetermined light level based on the pixel signal;
The pixel recording time of the pixel signal is adjusted according to the combination of the first signal and the second signal,
According to a combination of the first signal and the second signal, the pixel is recorded on the image forming material by exposure with a light beam having the first light amount level and the second light amount level. Image forming method. The first signal is the pixel signal that drives the first light amount level, and the second signal is an edge signal of the pixel signal that drives the predetermined light amount level,
The first light quantity level and the predetermined light quantity level are added to obtain the second light quantity level, or the predetermined light quantity level is subtracted from the second light quantity level to obtain the first light quantity level. The image forming method according to claim 1. The second signal is an edge signal of the pixel signal, and the first signal is a remaining signal obtained by removing the edge signal from the pixel signal,
The image forming method according to claim 1, wherein the first light quantity level is driven by the remaining signal and the second light quantity level is driven by the edge signal. Detecting a rising portion and a falling portion of the pixel signal, generating a first timing delayed by an edge signal time from the rising portion of the pixel signal, and setting a delayed pixel signal at the first timing, Generating a second timing delayed by the edge signal time from the falling portion of the pixel signal, and generating the delayed pixel signal so as to reset the delayed pixel signal at the second timing;
A third timing delayed from the rising portion of the delayed pixel signal by the edge signal time is generated, and the first edge signal at the rising portion of the delayed pixel signal is generated by the first timing and the third timing. 4. The image forming method according to claim 2, wherein a second edge signal is generated at a falling portion of the pixel signal and at a falling portion of the delayed pixel signal at the second timing.   The image forming method according to claim 4, wherein the edge signal of the pixel signal is a logical product of the first edge signal and the second edge signal and the delayed pixel signal. The first signal is for driving the first light quantity level, and the second signal is for driving the second light quantity level,
The first light quantity level is set at the start timing of the first signal for driving the first light quantity level, and the second signal is set at the start timing of the second signal for driving the second light quantity level. The image forming method according to claim 1, wherein the light amount level is set.   A rising edge and a falling edge of the pixel signal are detected, a first timing delayed by an edge signal time from the rising edge of the pixel signal is generated, and the second light quantity level is set by the first timing. Then, a second timing further delayed by the edge signal time from the first timing is generated, the first light quantity level is set by the first timing, and the second light level is set by the falling portion. The light quantity level is set, a third timing delayed by the edge signal time from the falling portion is generated, and the second light quantity level is reset at the third timing to obtain the original light quantity level. The image forming method described in 1. An image forming apparatus that forms an image by exposing an image forming material with a plurality of light beams,
Means for adjusting a pixel recording time of a pixel signal to record pixels for forming an image on the image forming material;
Means for setting a first light level;
Means for setting a second light amount level greater than the first light amount level or a predetermined light amount level of the difference between the second level and the first light amount level;
Means for generating a first signal for driving the first light quantity level based on the pixel signal;
Means for generating a second signal for driving the second light level or the predetermined light level based on the pixel signal;
The adjusting unit adjusts a pixel recording time of the pixel signal according to a combination of the first signal and the second signal;
According to a combination of the first signal and the second signal, the pixel is recorded on the image forming material by exposure with a light beam having the first light amount level and the second light amount level. Image forming apparatus. The image forming apparatus according to claim 8, wherein
The first signal is the pixel signal that drives the first light amount level, and the second signal is an edge signal of the pixel signal that drives the predetermined light amount level,
Further, the first light quantity level is obtained by adding the first light quantity level and the predetermined light quantity level to obtain the second light quantity level or subtracting the predetermined light quantity level from the second light quantity level. An image forming apparatus comprising means for obtaining a level. The second signal is an edge signal of the pixel signal, and the first signal is a remaining signal obtained by removing the edge signal from the pixel signal,
The image forming apparatus according to claim 8, wherein the first light amount level is driven by the remaining signal, and the second light amount level is driven by the edge signal. The image forming apparatus according to claim 9 or 10,
And means for detecting rising and falling portions of the pixel signal;
A first timing delayed from the rising edge of the pixel signal by an edge signal time is generated, a delayed pixel signal is set at the first timing, and the edge signal time is delayed from the falling edge of the pixel signal Means for generating the delayed pixel signal by generating the delayed second signal and resetting the delayed pixel signal at the second timing;
A third timing delayed from the rising portion of the delayed pixel signal by the edge signal time is generated, and a first timing at the rising portion of the delayed pixel signal is generated based on the first timing and the third timing. Means for generating an edge signal;
An image forming apparatus including: a second edge signal at a falling portion of the delayed pixel signal based on the falling portion of the pixel signal and the second timing;   The image forming apparatus according to claim 11, wherein the edge signal of the pixel signal is a logical product of the first edge signal and the second edge signal and the delayed pixel signal. The image forming apparatus according to claim 8, wherein
The first signal is for driving the first light quantity level, and the second signal is for driving the second light quantity level,
Means for setting the first light amount level at a start timing of the first signal for driving the first light amount level;
An image forming apparatus comprising: means for setting the second light quantity level at a start timing of the second signal for driving the second light quantity level. The image forming apparatus according to claim 13, further comprising:
Means for detecting rising and falling portions of the pixel signal;
Means for generating a first timing delayed by an edge signal time from a rising portion of the pixel signal, and setting the second light amount level according to the first timing;
Means for generating a second timing further delayed by the edge signal time from the first timing, and setting the first light amount level according to the second timing;
The second light amount level is set by the falling portion, a third timing delayed from the falling portion by the edge signal time is generated, and the second light amount level is reset by the third timing. And an original light amount level means.

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