JP2007055250A - Semiconductor laser drive control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor laser drive control device capable of improving gradation characteristics from a highlight region to a high-density region in an image forming device. <P>SOLUTION: First, a correction processing part receives image data, and an image attribute discrimination part judges whether the data are related to a character/thin line or others on the basis of attribute information on a pixel of interest. If it is judged that the data are related to a character/thin line, a pattern matching to data stored in a line buffer is performed to obtain a pixel distance, and in accordance with the pixel distance, a correction amount is determined on the basis of an LUT set in a correction amount determination part. Subsequently, on the basis of the determined correction amount, corrected image data are generated and output to the following step. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a semiconductor laser drive control device that drives a semiconductor laser based on input image data.

  2. Description of the Related Art Conventionally, copying machines and laser beam printers that employ an electrophotographic method are known as high-speed, high-quality image forming apparatuses. In recent years, as digital contents have become common in offices and homes, the demand for higher image quality of image forming apparatuses has further increased, and the recording resolution has increased to 1200 dpi, 2400 dpi, and 3600 dpi. It is out.

  In such an electrophotographic image forming apparatus, binary or multi-value data is converted into the amount of light applied to the image carrier. Then, the surface of the image carrier is scanned with, for example, laser light having the obtained irradiation light quantity. Through the above process, an image is formed, and any image from a binary image such as a character to an image including a halftone such as a photograph can be formed.

  Examples of methods for reproducing halftones include a dither method, an error diffusion method, and a density pattern method. By using these methods, multi-value output can be performed for each pixel, and a good output image can be obtained.

  As a method for converting the output multi-value data into an irradiation light amount, a pulse width modulation method (PWM / Pulse Width Modulation) and a power modulation method (PM / Power Modulation) have been proposed. In addition, a light quantity control system combining these has been proposed.

  There is a demand for higher recording resolution and higher image quality for recent image forming apparatuses. Along with this, it has been a challenge to achieve good dot reproducibility in the highlight area and to reproduce high density dots and high density lines such as white letters and white lines.

  In order to meet the demand for higher recording resolution, it is essential to increase the speed of the laser driving device. However, the increase in speed has the following disadvantages. That is, the amount of light decreases due to a poor rise of laser emission in the highlight area, and the amount of light increases due to a fall of laser emission in the high density area, thereby reducing the linearity of laser emission, thereby improving the image quality. Is damaged.

  Accordingly, it has been proposed to realize good dot reproducibility in the highlight region. These techniques are disclosed in Japanese Patent No. 2698099, Japanese Patent Laid-Open No. 9-116750, Japanese Patent Laid-Open No. 2001-130050, and the like. Techniques described in Japanese Patent Application Laid-Open No. 2002-361922, Japanese Patent Application Laid-Open No. 2002-361925, Japanese Patent Application Laid-Open No. 2003-266763, Japanese Patent Application Laid-Open No. 2004-288000, Japanese Patent Application Laid-Open No. 2000-177171, Japanese Patent Application Laid-Open No. 06-155800, and Japanese Patent Application Laid-Open No. 2004-122587 are known. .

  Alternatively, a correction technique using a LUT (look-up table) in an engine capable of outputting multiple values within one pixel is widely known.

  However, it was not possible to correct the collapse due to the falling failure in the high density region where the laser light signal changes from intermittent to continuous.

  When correction is applied only to a highlight area or a specific area with only high density, appropriate correction cannot be made for all gradations, and the gradation becomes discontinuous in the correction application area and the correction non-application area, and tone jumping occurs. It was easy to occur.

  Also, if the same correction amount is corrected for all gradations, the correction is efficiently performed from the highlight area where the laser emission delay becomes a problem to the high density area where the laser extinction delay becomes a problem. I couldn't.

  On the other hand, in an engine capable of multi-value output within one pixel, with regard to correction technology using an LUT, when the resolution is increased as in recent years and the number of bits per pixel is reduced, sufficient correction is performed. could not. Specifically, it is difficult to perform sufficient correction under the output conditions of 1 to 4 bits at a resolution of 1200 dpi and 2400 dpi.

  Further, the LUT used for the correction depends on the pixel condition around the correction target pixel, specifically, the pixel interval from the falling edge of the previous pixel to the rising edge of the correction pixel in the scanning direction of the correction target pixel. Is done. For this reason, sufficient correction cannot be performed by simple LUT correction within one pixel, which causes a problem in tone reproducibility.

  On the other hand, there is a problem in the technique for correcting non-linearity of electrophotography. In recent years, an electrophotographic image recording apparatus is a so-called digital system in which an image pattern is formed by blinking of a laser and a halftone area is expressed by an area ratio to be blinked. However, a similar problem exists with respect to the development characteristics for the analog method, which is a conventional technology. In other words, the toner density does not adhere in the highlight area and the image density is low, and in the high density area, the toner density is saturated and exhibits an S-characteristic. This is generally known as a principle non-linearity generated in the latent image to developing process of electrophotography.

  In order to correct such basic characteristics of electrophotography, it is possible to perform a correction opposite to the S-characteristic such that the light quantity in the highlight area is increased and the light quantity in the high density area is reduced. As such a technique, Japanese Patent Application Laid-Open No. 2000-177171 and Japanese Patent Application Laid-Open No. 06-155800 disclose techniques for realizing good gradation characteristics from highlight to high density regions. However, the disclosed technique is a technique for performing correction for increasing the amount of light and correction for reducing the amount of light with respect to the one-dot one-space and one-line one-space images. Therefore, an image area where a laser turn-off delay occurs cannot be a correction target.

  Therefore, an object of the present invention is to provide a semiconductor laser drive control device that can solve the above-described problems and can further improve the gradation characteristics from the highlight region to the high concentration region. In order to achieve this object, the present invention has the following features.

  A semiconductor laser drive control device provided by the present invention is a semiconductor laser drive control device that controls the drive of a semiconductor laser based on image data, and increases the amount of light emitted from the semiconductor laser in a highlight region, so that it can be used in a high-concentration region. And a drive control means for driving and controlling the semiconductor laser based on the pixels corrected by the correction means. The correction means scans the laser light emitted from the semiconductor laser. In this case, the correction amount is sequentially changed according to the time interval from the time when the laser light emission is finished to the time when the laser light emission is started.

  The correction means of the semiconductor laser drive control device described above performs different corrections on the light emission characteristics of the semiconductor laser for the highlight region and the high concentration region.

  The correction means of the semiconductor laser drive control device described above is configured such that when scanning the laser light emitted from the semiconductor laser, the time interval from the end of the laser emission to the start of the laser emission, and the time interval On the other hand, the correction amount is sequentially changed according to the time interval with reference to a look-up table in which correction amounts that sequentially change are associated with each other.

  The correction of the pixel of interest with reference to the lookup table is performed using a lookup table that is switched according to the presence or absence of pixels around the pixel of interest.

  The above semiconductor laser drive control device simultaneously performs correction for correcting the delay due to the light emission characteristics of the semiconductor laser in the highlight region and the high concentration region and correction due to the basic characteristics of the electrophotography scanned with the laser light. It is characterized by that.

  The correction means performs correction on the image data.

  The correction means corrects the laser driving pulse width signal.

  The correction means performs correction on the laser power.

  The present invention has a major purpose of correcting the light emission delay at the rising edge of the PWM signal and the turn-off delay at the falling edge. However, it is also possible to correct the nonlinearity inherent in the electrophotography at the same time. . For example, in the highlight area, correction can be performed so that laser driving is appropriate, and it is also possible to obtain appropriate gradation by increasing the exposure amount in the highlight area, which is inherently difficult to reproduce dots. is there.

  According to the present invention, since it is configured as described above, when performing image recording at high speed and high density, the gradation characteristics from the highlight area to the high density area are further improved, and the line width reproducibility is also ideal. A laser driving device can be realized.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
<First Embodiment>
FIG. 1 shows a first embodiment of the present invention. This is an example of a laser beam printer, and its structure is shown in FIG.

  In FIG. 1, reference numeral 1 denotes a laser beam printer, which employs a pulse width modulation (PWM) method as a method for converting multi-value data into irradiation light quantity, and includes an image processing unit 100, a laser drive control unit 120, and the like. Have The image processing unit 100 performs color conversion processing and halftone processing based on input data from the host computer 2 connected to the laser beam printer 1, and performs correction processing by the correction processing unit. The laser drive control unit 120 performs PWM control based on the data processed by the image processing unit 100 to drive and control the semiconductor laser.

  FIG. 2 will be described. The image carrier 11 can be a functionally separated type having a two-layer structure, such as a charge generation layer and a charge transport layer, or a single layer type with a conductive support substrate as the lowermost layer. As the charging unit 12, a corona charging method using a corona charger composed of a wire and an electric field control grid can be used. Further, as the charging unit 12, a roller charging method in which direct current or a superimposed bias of direct current and alternating current is applied to a charging roller brought into contact with the image carrier 11 can be used. As the image exposure unit, a scanner type using a semiconductor laser, or another optical system such as a condenser for the LED can be used.

  The developing unit 19 is a magnetic one-component non-contact developing method in which magnetic toner is conveyed by magnetic force and is developed in a non-contact manner on the image carrier at the development nip, and development processing is performed by contacting the image carrier at the development nip. A magnetic contact development method can be used. Further, as the developing unit 19, a non-magnetic one-component non-contact phenomenon method can be used. In this method, non-magnetic toner is regulated and charged by a blade, carried on a developing sleeve and conveyed, and the toner is fly-developed in a non-contact manner in a developing nip. Further, as the developing unit 19, a non-magnetic one-component contact developing method for performing a developing process in contact with the image carrier at the developing nip can be used. Alternatively, the developing unit 19 may be a two-component developing system in which non-magnetic toner is mixed with a carrier that is magnetic powder and conveyed to the developing nip with the developing sleeve, and development processing is performed.

  As the transfer unit 14, a transfer method using an electric force or a mechanical force can be used. As a method for performing transfer using an electric force, a corona transfer method in which transfer is performed by applying a DC bias having a polarity opposite to the charging polarity of the toner using a corona wire can be used. Further, as a method for performing transfer using an electric force, a roller transfer system in which a roller is brought into contact and a bias having a polarity opposite to that of the toner can be applied.

  As the fixing unit 15, the recording paper is passed through the abutting portion of the two opposing rollers, and the toner is fixed to the recording material by heat or pressure, or the toner is heated and fixed using a non-contact heater or lamp. Can be used. It is also possible to use a belt-like unit as a unit for sandwiching the recording material and fix it by applying heat or pressure.

  Next, the operation will be described. The image carrier 11 is charged by the charging unit 12, and the image carrier 11 is exposed by laser light, and an electrostatic latent image is formed on the image carrier 11. The toner layer on the toner carrier 13 of the developing unit 19 is brought into contact with the surface of the image carrier 11, the electrostatic latent image on the image carrier 11 is developed by the reverse development method, and the toner image is formed on the image carrier 11. Is formed. The toner image on the image carrier 11 is transferred by the transfer unit 14 onto the recording paper fed at a predetermined timing. Then, the toner image transferred onto the recording paper is heated and pressed by a fixing unit 15 having a heating roller and a pressure roller and fixed.

  The residual toner on the image carrier 11 after the transfer process is scraped off by a blade-like cleaning member 16 brought into contact with the surface of the image carrier 11 and collected by a cleaner. Thereafter, the above steps are repeated for each image formation.

  FIG. 3 is a diagram showing elements of the scanning optical system 17 of FIG. The scanning optical system 17 includes a semiconductor laser 21, a collimator lens 22, a cylindrical lens 23, a polygon mirror 24 that rotates at high speed, and an f-θ lens 25. Then, the semiconductor laser 21 blinks the laser beam based on the image data from the image processing unit 100 and based on the laser drive signal from the laser drive control unit 120. The laser beam emitted from the semiconductor laser 21 is made into substantially parallel light by the collimator lens 22 and guided to the polygon mirror 24 by the cylindrical lens 23. The laser light is reflected and deflected by a polygon mirror 24 that rotates at a constant speed. Then, the light passes through the f-θ lens 25, is deflected again at the folding mirror position 26, forms a spot image on the image surface 27 of the image carrier 11, and is scanned in the scanning direction 28 at a constant speed.

  FIG. 4 shows a procedure of correction processing in the correction processing unit of the image processing unit 100 of FIG. By these procedures, pixel intervals, rising and falling intervals are detected from the uncorrected image data and PWM signal, and the image data and PWM signal are corrected based on the correction amount corresponding to the obtained detection amount.

  Referring to FIG. 4 in detail, the correction processing unit receives the image data, and the image attribute determination unit determines whether it is a character / thin line or the other based on the attribute information of the target pixel. If the character / thin line is determined, pattern matching is performed on the data stored in the line buffer. Then, the pixel interval is obtained, and the correction amount is determined based on the LUT set by the correction amount determination unit according to the pixel interval at this time.

  As a method for obtaining the pixel interval at this time, it is also possible to obtain the pixel interval by conditional branching in addition to pattern matching. The method based on conditional branching will be described in detail. When the target pixel i is a rising pixel (the target pixel is a black pixel and the preceding pixel is a white pixel), the i-kth pixel is verified from k = 0 to n. Then, the value of k when a black pixel appears can be set as the pixel interval. The value of n at this time can be limited to the pixel interval range handled by the LUT when performing correction. It is also possible to calculate a desired value by detecting a falling pixel in advance and counting the number of pixels until the rising pixel appears after this pixel. Image data corrected based on the correction amount determined in this way is generated, and the data is output to the next step.

  Although an example of a binary image has been described here, the same concept can be applied to a multi-value image.

  At this time, as shown in FIG. 4, correction processing is performed at the stage of image data. Accordingly, it is more preferable that processing can be switched on / off and the correction amount can be optimized based on image attribute information, that is, image characteristics such as characters / thin lines and natural images.

Here, various methods can be used as a method for performing halftone processing on an input image. The most commonly used image processing methods are a dither method and a density pattern method. In the dither method, when one pixel of a read input signal is output in correspondence with one pixel for binary recording, one pixel is turned on or off based on m × m threshold data.

  The pulse width of the laser light signal at this time is controlled by the gradation, but the light emission position at this time is “center”, “left”, “right” in the pixel, the pixel position in the matrix pattern, and the peripheral pixels. Can be set in consideration of the influence of

  Furthermore, using an error diffusion method or an image forming method using a blue noise mask is also suitable for high-definition image output realized in this embodiment.

  The engine resolution can be applied to any engine resolution such as 400 dpi, 600 dpi, 1200 dpi, 2400 dpi, 3600 dpi, and the like. However, when the resolution becomes high such as 1200 dpi, 2400 dpi, 3600 dpi, etc., correction within one pixel is difficult as described above. Since the image clock becomes high and the necessity for correction increases because of the high resolution, the application of this embodiment in a high resolution engine is more preferable.

  The laser emission characteristics with respect to the laser drive pulse signal input to the semiconductor laser 21 of FIG. 3 are shown in FIG. As shown in FIG. 5, the ON level laser emission width (pulse width) is narrowed in the highlight portion, the ON level laser emission width is widened in the high concentration portion, and the linearity of laser emission is lowered.

  That is, the following problems occur when the ON level pulse width of the laser drive pulse signal (PWM signal, see FIG. 5A) is not corrected. The laser light signal emitted from the laser light emitting element based on the laser driving pulse signal has an actual laser light emission width narrower in the highlight portion than the desired laser light emission width due to the characteristics of the laser light emitting element. . And it becomes wide in the high concentration part. This reduces the linearity of laser emission.

  Here, in FIG. 5, the arrow indicates the scanning direction of the laser beam. In the present embodiment, for the sake of simplicity, a decrease in linearity of laser driving is handled as a laser emission characteristic. However, as is well known, a reduction in linearity that occurs when a pulse width signal is generated from a data signal is also subject to correction.

  Therefore, by correcting the pulse width with respect to the rising position of the laser emission, as shown in FIG. 6, it is set wider than the pulse width based on the input data, and as a result, a desired laser emission width can be obtained. it can. As the correction means, known correction means can be used, such as adding binary data or multi-value data in the image data generation unit, or directly changing the pulse width.

  In this example, since all the rising positions of the laser emission are corrected, the highlight linearity is improved as shown in FIG. 8 with respect to the characteristics of LaserPower with respect to the data before correction (FIG. 7). However, the linearity at the high density portion is worse than before the correction. Here, the horizontal axis Data is an input data value when the pulse width is driven at the engine resolution, and the vertical axis LaserPower is an integrated light amount emitted from the laser.

  In order to prevent such a decrease in linearity in the high density part, for example, it is conceivable to correct the pulse width only for the highlight isolated dots without correcting the pulse width in the high density part. An example of this is shown in FIG. However, when such correction is performed, the linearity in the high density portion is not deteriorated, but as shown in FIG. 10, a gradation step occurs at the switching portion between the gradation region to be corrected and the gradation region not to be corrected. End up.

  Therefore, in the present embodiment, only the correction for increasing the pulse width (hereinafter referred to as “plus correction”) is performed in the highlight region where the laser emission width decreases. On the other hand, in a high concentration region where the laser emission width increases, correction for narrowing the pulse width (hereinafter referred to as “minus correction”) is performed. This improves the linearity of laser emission.

  Specifically, as shown in FIG. 11, it is possible to improve the linearity of the high density part as shown in FIG. 12 by performing a minus correction to reduce the pulse width in the high density part. An example of the correction pulse width switching method at this time is shown in FIG. The horizontal axis in the figure is the laser pulse falling to rising interval obtained from the pixel information or the laser pulse information, and the width becomes shorter toward the right.

  In the present embodiment, plus correction is performed in a highlight region where the laser emission width decreases. Then, the correction width is sequentially changed according to the time interval from the time when the laser light emission ends to the time when the laser light emission starts. Thus, it is one of the features of this embodiment that the linearity of laser emission is improved and the discontinuity of gradation characteristics is eliminated.

  Specifically, as shown in FIG. 14, the correction amount is switched stepwise from the highlight area to the high density area. Thereby, as shown in FIG. 15, laser driving with high linearity from the highlight area to the high density area is possible. An example of the pulse width switching method at this time is shown in FIG. The horizontal axis in FIG. 16 is the falling edge to the rising edge of the laser pulse obtained from the pixel information or the laser pulse information, and the interval becomes narrower toward the right.

  Further, in the present embodiment, plus correction is performed in the highlight region where the laser emission width decreases, and the correction width is set according to the time interval from the time when the laser emission ends to the time when the laser emission starts. Change it sequentially.

  Further, in the high density region where the laser emission increases, the minus correction is sequentially changed according to the time interval from the time when the laser emission is finished to the time when the laser emission is started.

  As a result, the linearity of the laser emission can be greatly improved and the discontinuity of the gradation characteristics can be eliminated.

  Specifically, as shown in FIG. 17, by changing the correction amount stepwise from the highlight area to the high density area, the linearity is high from the highlight area to the high density area as shown in FIG. Laser drive is possible. An example of the pulse width switching method at this time is shown in FIG. The horizontal axis Data in the figure is the input data value when the pulse width drive is performed at the engine resolution, and the vertical axis LaserPower is the integrated light amount emitted from the laser.

  As a means of switching the correction amount at this time, correction is performed using numerical calculation or a look-up table according to the blank time from the position where the laser emission ended before the rise of the laser emission to be noticed. The amount can be determined in stages.

  As a monitoring method of the blank time at this time, a method of detecting a position where the laser light emission has ended before the rising position of the laser light emission from the falling edge and the rising edge of the pulse electric signal, the time point of the image data Thus, various methods such as a method of detecting by referring to a value a few pixels before the target pixel or a method of detecting by pattern matching at the time of image data can be applied.

  In addition, according to the present embodiment, even when sufficient laser emission response is obtained with respect to input image data, it is possible to realize further highlight area reproducibility of the final toner image. Alternatively, it is possible to realize reproducibility at a higher concentration part.

  Incidentally, the recent electrophotographic image recording apparatus is a so-called digital system in which an image pattern is formed by blinking of a laser and a halftone area is expressed by an area ratio to be blinked. However, a problem similar to the development characteristics (FIG. 23) of the conventional analog method occurs. The horizontal axis of FIG. 23 shows the development contrast representing the potential difference from the DC component of the development bias to the latent image potential. As can be seen from FIG. 23, the toner density does not adhere in the highlight area and the image density is low, and in the high density area, the toner density is saturated and exhibits S-characteristics. This is generally known as a principle non-linearity generated in the latent image to developing process of electrophotography.

  In this embodiment, in order to correct such basic characteristics of electrophotography, correction opposite to the S-characteristic is performed so as to increase the amount of light in the highlight area and reduce the amount of light in the high density area. Thereby, favorable gradation characteristics can be realized from highlight to high density region. Therefore, according to the present embodiment, it is possible to obtain appropriate gradation even in an image region in which a laser extinguishing delay occurs at the same time as elimination of nonlinearity due to the basic characteristics of electrophotography.

<Second Embodiment>
The second embodiment of the present invention will be described below.

  First, a technique for correcting the light emission characteristics of the semiconductor laser according to this embodiment will be described. As shown in FIG. 20, the amount of emitted light (LaserPower) for each input data from 00h to FFh (index specifying the density of a pixel with h added to the hexadecimal number) obtained by PWM driving each pixel with the same signal value. Measure. FIG. 21 shows the result of plotting the amount of emitted light against the input data. It can be said that a in this case is ideal because the light emission quantity with respect to the input data has a linear relationship. As shown in FIG. 22, when the pulse width to be emitted and the pulse width to be turned off are short, the response is poor and the optical waveform is distorted. Then, as shown in FIG. 21b, the laser does not emit light in the highlight region and the laser does not turn off in the high concentration region, so that the linearity of the laser deviates greatly from the ideal.

  In order to correct such laser driving, it is possible to apply a technique for performing correction using an LUT in one pixel. However, in the LUT correction for correcting the pulse width within one pixel, a problem related to the reproducibility of gradation occurs.

  First, this point will be described from the viewpoint of normal image formation. For example, when a 200-line screen is formed at 600 dpi, as shown in FIG. 24, an image pattern is formed using three pixels as one block (sub-matrix). For example, FIG. 24A shows a pattern formed sequentially from the center pixel to both ends, forming from the right end (R), forming from the center (C), and forming from the left end (L), respectively. The starting point of PWM formation is different. FIG. 24B shows a pattern in which the left pixel to the right pixel are sequentially formed, and all the pixels are formed with the left end (L) as a base point.

  On the premise of such an image forming method, a problem when an image is output using an LUT for each pixel will be described with reference to FIG. FIG. 25A shows an image pattern. FIG. 25B shows a PWM pattern. Then, when output is performed using a semiconductor laser having a light emission characteristic as shown in FIG. 21B, the inverse gamma characteristic is corrected using an LUT as shown in FIG. In such a case, a correction signal as shown in FIG. 25 (d) is formed. When this is output by a semiconductor laser having a light emission characteristic as shown in FIG. 21B, an optical waveform as shown in FIG. 25E is output.

  Here, the light emission characteristic of FIG. 21 is the output light amount when the same signal is input to all the pixels as shown in FIG. In the case where an image is formed by collectively combining a plurality of pixels as shown in FIG. 25, the influence of the peripheral pixels is different even for pixels having the same 10h information as in B and G of FIG. Specifically, G in FIG. 25 is an isolated pixel, and A in FIG. 25 is a condition having an adjacent pixel on the left side. In both cases B and G in FIG. 25, the conditions of peripheral pixels contributing to laser emission are different from those in FIG. 20 in which the same image signal is input to all pixels. That is, although the same semiconductor laser is used, B and G in FIG. 25 do not show gradation characteristics as in FIG.

  FIG. 26 shows the gradation characteristics by classifying the influence of the left and right pixels of the pixel of interest (the pixel being classified) into four categories. 26A to 26D, the vertical axis represents the density of the target pixel, and the horizontal axis represents the duty ratio of the pulse width. FIG. 26A shows a case where there is no signal in the left and right pixels, FIG. 26B shows a case where only the right pixel has a signal, and FIG. 26C shows a signal only in the left pixel. FIG. 26 (d) shows a case where there are signals in the left and right pixels. It can be understood that FIGS. 26A to 26D show different light emission characteristics. Specifically, B and G in FIG. 25 correspond to FIG. 26A and FIG. 26B, respectively, and the final output waveform is FIG. 25E. Looking at FIG. 25 (e), G is a desired value, D is a small value, and A + B is a desired value with respect to FIG. 25 (b), which is the target PWM signal.

  Here, a problem arises when the highlight pixel lights up adjacent to the formed pixel such as A + B. That is, as shown in FIG. 25 (e), due to excessive correction, a large output difference is generated between the gradation of the sub-matrix indicated by D + E + F and the gradation of the sub-matrix indicated by A + B + C. Therefore, a tone jump occurs at a gradation in which the highlight pixel is adjacent to the formed pixel. Accordingly, sufficient matching cannot be achieved unless the LUT is switched according to the four types of patterns in FIG.

  In this embodiment, the rise and fall points of the PWM signal used for laser driving are detected, and the time interval from the rise point of the PWM signal to the extinction point is monitored. Then, the correction amount is changed stepwise based on the time interval at that time. The laser emission characteristics to be mainly corrected in the present embodiment are strongly influenced by peripheral pixels as shown in FIG. Therefore, in order to perform proper correction, correction in units of one pixel is not effective. For this reason, attention is paid to the relationship between rise and fall, specifically the turn-off time interval, in which the light emission characteristics in question are governed, and correction is performed according to the time interval. Alternatively, in consideration of the influence of surrounding pixels as shown in FIG. 26, the correction amount is optimized according to the four types of patterns shown in FIG. That is, in the present embodiment, the LUT is selected according to the presence / absence of a signal of a pixel adjacent to the target pixel. Therefore, the LUT is switched according to the four types of patterns in FIG. By doing so, it is possible to perform appropriate image correction without a tone jump.

<Third Embodiment>
FIG. 27 shows a third embodiment of the present invention. This embodiment is different from the first embodiment and the second embodiment in that correction processing is performed by the host computer 2.

  The correction processing in the present embodiment is not essentially different from the correction processing procedure in the correction processing unit of FIG. 4 according to the first embodiment. The pixel interval, rise and fall intervals are detected from the image data before correction and the PWM signal, the correction amount suitable for the obtained detection amount is corrected to the image data and PWM signal, and the subsequent processing is continued. .

<Fourth Embodiment>
FIG. 28 shows a fourth embodiment of the present invention. The present embodiment is different from the first embodiment and the second embodiment in that correction processing is performed by the laser drive control unit 320.

  FIG. 29 shows a procedure of correction processing by the correction processing unit of the laser drive control unit 320 of FIG. The pixel interval, rise and fall intervals are detected from the image data before correction and the PWM signal, the correction amount suitable for the obtained detection amount is corrected to the image data and PWM signal, and the subsequent processing is continued. .

  Referring to FIG. 29 in detail, the rise and fall interval detector of the PWM signal detects the rise and fall of the signal, obtains their time interval from the reference clock, and calculates the correction amount based on the LUT of the correction amount determination unit. The determined and corrected PWM signal is generated and output. In FIG. 29, the method for detecting the rise and fall after the PWM waveform has been described has been described. However, it is of course possible to perform correction processing for digital data in the laser drive control unit.

(Other embodiments)
The present invention can be applied to a system having a plurality of devices (for example, a host computer, an interface device, a league, a printer, etc.). Further, the present invention may be applied to an apparatus (for example, a copying machine, a facsimile apparatus, etc.) comprising a single device.

  Needless to say, the object of the present invention can also be achieved as follows. That is, a recording medium that records a program code of software that realizes the functions of the above-described embodiments is supplied to the system or apparatus. Then, the computer (CPU or MPU) of the system or apparatus reads and executes the program code stored in the recording medium.

  In this case, the program code itself output from the recording medium realizes the functions of the above-described embodiment. And this invention has a recording medium which memorize | stored the program code.

  As a recording medium for supplying the program code, for example, the following can be used. That is, a floppy (registered trademark) disk, hard disk, optical disk, magneto-optical disk, CD-ROM, CD-R, magnetic tape, nonvolatile memory card, and ROM.

  It goes without saying that the execution of the program code explained by the computer not only realizes the functions of the above-described embodiments, but also enables the following. That is, based on an instruction of the program code, an OS (operating system) running on the computer performs part or all of the actual processing. And the function of embodiment mentioned above is implement | achieved by the process.

  Further, the program code read from the recording medium is written in a memory provided in a function expansion board inserted into the computer or a function expansion unit connected to the computer. Thereafter, based on the instruction of the program code, the CPU or the like provided in the function expansion board or function expansion unit performs part or all of the actual processing. Needless to say, the process includes the case where the functions of the above-described embodiments are realized.

It is a block diagram which shows the 1st Embodiment of this invention. It is sectional drawing which shows the structure of the laser beam printer of FIG. It is a figure which shows the element of the scanning optical system of FIG. It is a figure which shows the procedure of the correction process in the correction process part of FIG. It is explanatory drawing for demonstrating the characteristic of the semiconductor laser of FIG. It is explanatory drawing for demonstrating an example of pulse width correction | amendment. It is a figure which shows the characteristic of LaserPower with respect to Data before correction | amendment. It is a figure which shows the characteristic of LaserPower with respect to Data after correction | amendment. It is explanatory drawing for demonstrating the pulse width correction | amendment performed only about the isolated dot of highlight. It is a figure which shows the characteristic of LaserPower with respect to Data after correction | amendment. It is explanatory drawing for demonstrating an example of the pulse width correction | amendment in 1st Embodiment. It is a figure which shows the characteristic of LaserPower with respect to Data after correction | amendment. It is a figure which shows an example of the correction width | variety with respect to a pixel space | interval. It is explanatory drawing for demonstrating the example which switches correction amount in steps from a highlight area | region to a high density area | region. It is a figure which shows the characteristic of LaserPower with respect to Data after correction | amendment. It is explanatory drawing for demonstrating the example which switches correction amount in steps from a highlight area | region to a high density area | region. It is explanatory drawing for demonstrating plus correction | amendment and minus correction | amendment. It is a figure which shows the characteristic of LaserPower with respect to Data after correction | amendment. It is explanatory drawing for demonstrating the example which switches correction amount in steps from a highlight area | region to a high density area | region. It is a figure which shows the light-emission light quantity with respect to each input data from 00h to FFh which made each pixel PWM drive with the same signal value. It is a figure which shows the result of having plotted the emitted light quantity of FIG. 18 with respect to input data. It is explanatory drawing for demonstrating the characteristic of the semiconductor laser of FIG. It is a figure which shows the characteristic of the development with respect to an analog system. It is a figure which shows formation of the pattern of an image. It is explanatory drawing for demonstrating the subject when image output is performed using LUT for every pixel. It is a figure which shows a gradation characteristic. It is a block diagram which shows the 3rd Embodiment of this invention. It is a block diagram which shows the 4th Embodiment of this invention. It is a block diagram which shows the element of the laser drive control part 320 of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Laser beam printer 2 Host computer 11 Image carrier 12 Charging unit 13 Toner carrier 14 Transfer unit 15 Fixing unit 16 Cleaning member 17 Scanning optical system 19 Development unit 21 Semiconductor laser 22 Collimator lens 23 Cylindrical lens 24 Polygon mirror 25 f-θ Lens 26 Folding mirror position 27 Image plane 28 Scanning direction 100 Image processing unit 120 Laser drive control unit 320 Laser drive control unit

Claims (8)

A semiconductor laser drive control device for driving and controlling a semiconductor laser based on image data,
Correction means for increasing the light emission amount of the semiconductor laser in a highlight region and reducing the light emission amount of the semiconductor laser in a high concentration region;
Drive control means for driving and controlling the semiconductor laser based on the pixels corrected by the correction means,
The correction means sequentially changes the correction amount according to the time interval from the time when the laser emission is finished to the time when the laser emission is started when scanning the laser beam emitted from the semiconductor laser. A semiconductor laser drive control device.   2. The semiconductor laser drive control device according to claim 1, wherein the correction unit performs different corrections on light emission characteristics of the semiconductor laser with respect to a highlight region and a high concentration region.   2. The correction means according to claim 1, wherein the correction means scans the laser light emitted from the semiconductor laser, the time interval from the time when the laser light emission is finished to the time when the laser light emission is started, and the time interval. The semiconductor laser drive control apparatus is characterized in that the correction amount is sequentially changed according to the time interval with reference to a lookup table in which correction amounts that change sequentially are correlated.   4. The semiconductor laser according to claim 3, wherein the correction of the target pixel with reference to the look-up table of the correction means is performed using a look-up table switched according to the presence or absence of pixels around the target pixel. Drive control device.   2. The correction according to claim 1, wherein the correction due to the light emission characteristics of the semiconductor laser in the highlight region and the high concentration region is corrected simultaneously with the correction due to the basic characteristics of the electrophotography scanned by the laser light. A semiconductor laser drive control device.   2. The semiconductor laser drive control device according to claim 1, wherein the correction unit corrects the image data.   2. The semiconductor laser drive control device according to claim 1, wherein the correction unit corrects the laser drive pulse width signal. 2. The semiconductor laser drive control device according to claim 1, wherein the correction unit corrects the laser power.

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