JP2003195262A - Correction data preparation device for liquid crystal optical shutter and optical printer suing the device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lookup table in which opening time correction data are gathered for completely compensating the deviation of gradations of images expressed by a photosensitive body to a light quantity passing through a liquid crystal optical shutter by light transmission characteristics of the liquid crystal optical shutter. <P>SOLUTION: The liquid crystal optical shutter is opened and closed by a control means by using opening time data selected from an image gradation table storing a plurality of the opening time data in which the opening time of the liquid crystal optical shutter is different stepwise with equal intervals. An exposure amount corresponding to the opening time is measured by a photoelectric conversion element which receives light transmitted through the liquid crystal optical shutter by the opening and closing of the liquid crystal optical shutter. A plurality of the opening time correction data corresponding to the respective exposure amount are prepared such that the exposure amount becomes stepwise with the equal intervals by using output for which the exposure amount is measured, the plurality of the opening time correction data are gathered and the lookup table for obtaining the accurate gradation of the images is prepared. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a correction data creating apparatus for creating correction data for correcting a drive signal for driving a liquid crystal optical shutter based on a plurality of gradation data in accordance with the characteristics of liquid crystal. , And to an optical printer using the device.

[0002]

2. Description of the Related Art Conventionally, while exposing an optical head having a light source and a liquid crystal optical shutter relative to a photoconductor, exposure light emitted from the light source is appropriately changed by a liquid crystal optical shutter.
2. Description of the Related Art There is known an optical printer in which the exposure light is applied to a predetermined position on a photoconductor by a predetermined amount by blocking and transmitting the light to form an image on the photoconductor. Known liquid crystal optical shutters used in such optical printers are a reflective liquid crystal optical shutter that controls the amount of reflected light and a transmissive liquid crystal optical shutter that controls the amount of transmitted light. Furthermore, the liquid crystal optical shutter has a normally white type that does not reflect or transmit light when a voltage is applied, and a normally white type that does not reflect or transmits light when a voltage is not applied. There is a black type. Usually, an optical printer employs a transmissive and normally white liquid crystal optical shutter.

The formation of a gradation image on the photoconductor by such an optical printer is performed by controlling the opening time of the liquid crystal optical shutter, that is, the light transmission time, based on the given image data. Since the response is delayed with respect to the application of voltage, the irradiation time must be controlled in consideration of the response delay characteristic. Furthermore, since the response characteristics of the liquid crystal to the applied voltage differ depending on the temperature and the color (wavelength) of the transmitted light,
In order to perform accurate gradation display, it is necessary to perform correction in consideration of the response characteristics of the liquid crystal for each color and each temperature.

The response characteristics of the liquid crystal to the applied voltage will be described in more detail. FIG. 9 shows a case where a normally white transmissive liquid crystal optical shutter is used, and among the gradation data from 0 gradation to n gradation, 1st gradation, 2nd gradation, 3rd gradation, and n gradations.
It shows changes in the amount of transmitted light of a liquid crystal optical shutter when a liquid crystal drive voltage corresponding to a gray scale is applied. The color of light used and the ambient temperature are constant. The vertical axis represents the amount of transmitted light, the horizontal axis represents time, T1 is the first gradation, T2 is the second gradation, T3 is the third gradation, and Tn is the voltage to the liquid crystal optical shutter of the fourth gradation. The control time (since it is a normally white type, it is the time when no voltage is applied) is shown. 1
00 shows the light intensity change waveform of the first gradation, and 110 shows the voltage waveform applied to the liquid crystal at that time. Similarly, 200, 3
Reference numerals 00 and 400 denote light intensity change waveforms at the second, third, and nth gradations, and 210, 310, and 410 denote applied voltage waveforms at that time.

Here, for example, focusing on the light quantity change waveform 400 of the nth gradation (maximum gradation), when the applied voltage 410 becomes zero at time 0, the transmitted light quantity gradually increases and then changes to a constant value. When the voltage is applied again at time Tn, the amount of transmitted light sharply decreases. The first gentle change in the light amount change is called the rising response of the liquid crystal, and the subsequent sharp change is called the falling response. The difference between the rising response and the falling response is based on the characteristic peculiar to the liquid crystal material, and a technique for changing this characteristic is not known at this stage.

By the way, since the gradation in an optical printer is expressed by the density of light emitted from the photoconductor, the magnitude of the gradation is proportional to the amount of light irradiation to the photoconductor. The light irradiation amount is the product of the light intensity and the irradiation time, that is, the diagonal lines 120 and 2 in FIG.
Since it is equivalent to the areas indicated by 20, 320 and 420, the increase amount of the gradation data and the increase amount of the shaded area must be proportional. However, due to the rising response of the liquid crystal, if the opening time of the liquid crystal is made equal intervals as shown in the figure,
The amount of increase in area is not the same. Therefore, in order to display an image on the photoconductor so that the density change of the photoconductor is proportional to the gradation data, the exposure time is not increased at equal intervals so as to keep the area of the diagonal line constant, and Must be increased to.

As described above, in order to accurately draw a gradation image on the photoconductor, the photoconductor is exposed for a corrected exposure time in consideration of the rising response characteristic of the transmitted light amount of the liquid crystal optical shutter. Will be needed. Therefore, conventionally, for each temperature and each color, the exposure time for displaying each gradation is corrected in consideration of the response characteristics to the applied voltage of the liquid crystal, and this is a table regarding correction data summarized by temperature and color. That is, by creating a look-up table and storing it in the storage means such as the ROM of the optical printer, the liquid crystal optical shutter is driven by the corrected data for exposure.

[0008]

However, in the conventional correction data creating apparatus, a driving voltage in the case of the maximum gradation is applied to the liquid crystal optical shutter, the change in the intensity of the transmitted light at this time is detected by the sensor, and The values are integrated to obtain the integrated value at the maximum gradation (the total area of the diagonal line 430 in FIG. 9), and this area is divided by the number N of gradation displays so that the areas are equal, and the correction data is obtained. I was creating. Then, with respect to the fall response of the liquid crystal, the fall response of each gradation is predicted from the value at the maximum gradation and corrected by calculation. According to such a conventional correction method, since there is only one type of drive waveform of the liquid crystal optical shutter, there is an advantage that correction data can be easily created, but on the other hand, the influence of the liquid crystal falling response generated in each gradation display is affected. Could not be corrected accurately. Therefore, the corrected data becomes incomplete, and there is a problem that a faithful image based on the input image data cannot be reproduced.

An object of the present invention is to provide a correction data creating apparatus for a liquid crystal optical shutter, which is capable of creating correction data in consideration of not only the rising response characteristic of liquid crystal but also the falling response characteristic of liquid crystal. It is to provide an optical printer.

[0010]

In order to achieve the above object, a correction data generating apparatus according to the present invention is configured so that a light transmission time in arbitrary gradation data of a liquid crystal optical shutter driven based on a plurality of gradation data. In the correction data creating apparatus for correcting to a predetermined value, a sensor for detecting the intensity of light after passing through the liquid crystal optical shutter and outputting it as an electric signal, an integrating means for integrating the output of this sensor, And a temporary liquid crystal drive signal creating means for creating an uncorrected temporary liquid crystal drive signal corresponding to the gradation data for which correction data is to be created or the gradation data in the vicinity thereof, and the correction is performed by the temporary liquid crystal drive signal. The liquid crystal light shutter is driven based on the gradation data for which data is to be created, the transmitted light at this time is converted into an electric signal by the sensor, and the output thereof is the integrating means. Creating the correction data based on a more integrated value.

Further, in the above-mentioned correction data generating apparatus, during the period when the sensor detects light or the period when the integrating means performs integration, the image data for which the correction data is to be generated or the image data in the vicinity of the image data is generated. The period from the period including the rising response period of the liquid crystal optical shutter driven based on the period to the period including the falling response period.

Further, a predetermined image is formed on the photosensitive member by driving the liquid crystal optical shutter based on the correction data created by using the correction data creating device.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will now be described based on examples with reference to the drawings.

Referring to FIG. 1, the configuration of a correction data creating apparatus for a liquid crystal optical shutter according to the present invention will be described. In FIG. 1, the correction data creation device 1 is a normally white type,
Then, the liquid crystal optical shutter 2 having a shutter element color-coded by the three color filters of RGB, the light source 3 for emitting the exposure light, and the light source 3 after passing through the liquid crystal optical shutter 2
Is attached to the liquid crystal optical shutter to detect the temperature of the liquid crystal optical shutter, and the photoelectric conversion element 4 (for example, a phototransistor) that detects the exposure light from the device and outputs the intensity change of the light as an electric signal. The temperature detecting means 5 (for example, a thermocouple), the heating means 6 attached to the liquid crystal optical shutter to heat the liquid crystal optical shutter (for example, a thin film resistor heater), and the liquid crystal optical shutter are corrected. A liquid crystal optical shutter drive unit 7 driven by a previous drive signal (uncorrected liquid crystal drive data), a heater driver 8 for supplying a current for heating the heating unit 6, and a light source control unit 9 for supplying electric power to the light source 3. An integrating means 10 (for example, a capacitor) for integrating the electric output of the photoelectric conversion element 4 and a correction for storing the temporary liquid crystal drive data before the correction. Data storage means (e.g., ROM
And other semiconductor memory elements. ) And the corrected data storage means 12 (for example,
It is composed of a semiconductor memory element such as a RAM. ), Display means 13 (for example, composed of a liquid crystal display element) capable of displaying the corrected liquid crystal drive data, display drive means 14 for driving the liquid crystal display means 13, and image data from an external control circuit 15. And a control circuit 16 for processing.

Next, the operation of the liquid crystal optical shutter 1 according to the present invention and the basic function of each component will be described. First, the external control means 15 is composed of a computer or the like and creates image data having gradation and sends it to the control means 16. When the gradation data to be corrected is input to the control unit 16 from the external control unit 15, the control unit 16 calls the pre-correction liquid crystal drive data stored in the pre-correction data storage unit 11. The pre-correction liquid crystal drive data is the time during which no voltage is applied to the liquid crystal shutter corresponding to each gradation (the liquid crystal optical shutter is a normally white type, which means light transmission time, that is, exposure time). Represented by length. More specifically, the uncorrected liquid crystal drive data, that is, the no-voltage application time to the liquid crystal optical shutter for each gradation has a value that increases at equal intervals in proportion to the gradation data. Then, the liquid crystal optical shutter drive means 7 drives the liquid crystal optical shutter based on the retrieved uncorrected liquid crystal drive data. Further, the control means 16 controls the liquid crystal optical shutter driving means 7 to drive the liquid crystal,
Alternatively, prior to that, a command is issued to the light source driving means 9,
The light source 3 is caused to emit light. Further, the control means 16 monitors the signal from the temperature detection means 5, and the liquid crystal optical shutter 2
In order to prevent the above temperature from falling below a predetermined temperature, a command is issued to the heater driving means 8 so that the heating means 6 is controlled to be heated when the temperature falls below the predetermined temperature. There is.

When the liquid crystal optical shutter is driven by the uncorrected liquid crystal drive data corresponding to arbitrary gradation data, the light source 3 is driven.
The light from passes through the liquid crystal optical shutter and reaches the photoelectric conversion element 4. The photoelectric conversion element 4 outputs a voltage proportional to the intensity of the received light, and this output is input to the integrating means 10. The control means 16 creates the corrected liquid crystal drive data based on the output of the integration means 10, and the corrected data storage means 12
To enter. The display means 13 can be driven by the display drive means 14 to display the data in the corrected data storage means 12, so that the operator can confirm the contents of the corrected data storage means 12 and perform processing such as correction. It's easy to do.

Next, a procedure for the control means 16 to create corrected liquid crystal drive data using the output of the integrating means 10 will be described. In the following embodiments, the gradation data will be shown in the case of 0 gradation (no exposure) to 64 gradations (all exposure). FIG. 2 is a flow chart showing an operation procedure of the correction data creating apparatus for the liquid crystal optical printer according to the present invention.

In step S1, the control means 16 receives the gradation data from the external control means 15 and defines the variable i for executing the program as i = 1.

In step S2, the control means 16 selects one of the gradations 0 to 64 input by the external control means 15.
60 gradations selected every 0 gradations are set as representative gradations, and pre-correction liquid crystal drive data corresponding to the 10th gradation is read out from the pre-correction data storage means 11 to drive the liquid crystal optical shutter. The liquid crystal optical shutter driving means 7 drives the liquid crystal optical shutter 7 based on the pre-correction liquid crystal driving data. The representative gradation C is C = 10 × i
And then selected. Then, i is redefined as i = i + 1 and the process moves to the next step.

In step S3, the integrating means 10 causes the light source 3
The output of the photoelectric conversion element 4 which detects the light emitted from the liquid crystal and transmitted through the liquid crystal optical shutter 2 and outputs it as an electric signal is integrated in a predetermined inspection period and sent to the control means 16. The predetermined inspection period may be changed depending on each liquid crystal drive voltage, or may be longer than the time of the liquid crystal drive voltage of the maximum gradation and may be constant. In the inspection period, the integration may be made sufficiently long to control the input and output of the photoelectric conversion element.

In step S4, the control means 16 temporarily stores the integrated value based on the data of the tenth gradation sent from the integrating means 10.

In step S5, it is determined whether the representative gradation is the last value, that is, the 60th gradation, and 6
If it is not the 0th gradation, i = i + 1 is set and the process returns to S2. Then, S2 to S5 are repeated until the 60th gradation is reached, and then the process proceeds to S6.

In step S6, the control means 16 performs mathematical optimization based on the integrated value of the representative gradations (10th, 20th, 30th, 60th gradations) to correct the gradations other than the representative gradations. The integrated value of the liquid crystal drive data is predicted and temporarily stored as integrated value curve data.

In step S7, the control means 16 converts the pre-correction liquid crystal drive data corresponding to all the gradations (0 to 64 gradations) based on the integrated value curve data according to a predetermined rule. Then, the corrected liquid crystal drive data is created.

In step S8, the control means 16 stores the corrected liquid crystal drive data in the corrected data storage means 12.

The step S6 will be described in more detail. 3 to 5 show the output value of the integrating means in the representative gradation. The vertical axis represents the integrated value of the voltage, which is equivalent to the amount of transmitted light of the liquid crystal optical shutter. The horizontal axis is
Although the gradation is shown, it is equivalent to the time when no voltage is applied to the liquid crystal optical shutter. The difference between FIG. 3, FIG. 4 and FIG. 5 is that each of the drawings shows the case where light that has passed through a color filter and is converted into R, G and B colors is used.
R light, FIG. 4 shows G light, and FIG. 5 shows B light. Point P1
0, P20, P30 ... P60 are respectively 10, 20,
The measured value of the integrated value at 30 ... 60 gradations is shown. The curve Lopt connecting these points is created by mathematical optimization. The control unit 16 controls the representative gradation (1
Integrated values (values on the curve Lopt at each gradation) for all gradations other than 0, 20, 30, ... 60 gradations
Is obtained by mathematical optimization and temporarily stored.

The step S7 will be described in more detail. In S7, the control means 16 converts the uncorrected liquid crystal drive data into the corrected liquid crystal drive data based on a predetermined rule. The basic idea of this conversion is as follows. Originally
In an optical printer that forms an image by exposing a photoconductor using a liquid crystal optical shutter, the rate of increase in the numerical value of gradation data and the amount of transmitted light of the liquid crystal must match. More specifically, the exposure amount when the gradation data of the 20th gradation is exposed must be 10 times the exposure amount when the gradation data of the 10th gradation is exposed. If it is desired that the gradation data be proportional to the exposure amount, the image formed after exposure is represented as an incorrect gradation display. Since the exposure amount, that is, the transmitted light amount of the liquid crystal optical shutter is equivalent to the output value of the integrating means 10, for example, in the case of FIG. 3, the position of each point P is a straight line where the gradation data and the integral value are in a proportional relationship. Ideally, it should be on Ladp. Therefore, in the above conversion, each point on the curve Lopt is positioned on the straight line Ladp. The conversion method will be described with reference to FIG. First, assuming that the gradation data to be converted is, for example, the 10th gradation, the straight line Lad whose X-axis value is the same as the 10th gradation
Find the point Pa on p. Next, a point Pb on the curve Lopt having the same Y-axis value as the point Pa is obtained. Then, finally, a point Pc where the value on the X axis is the same as Pb and the value on the Y axis is 0 is obtained. The corrected liquid crystal drive data is obtained when no voltage is applied to the liquid crystal optical shutter corresponding to the value of the point Pc at the gradation 10. In the same manner, correction data can be calculated for all the gradations for which it is desired.

6 to 8 show the relationship between the gradation display value and the integrated value when driven by the corrected liquid crystal drive data created by the above method. It can be seen that the gradation display value and the integral value are in a substantially proportional relationship.

In the embodiment shown in FIG. 1, after the corrected liquid crystal drive data is created, the light source 3 and the liquid crystal optical shutter 2 are moved relative to the photoconductor based on this data to expose the photoconductor. Thus, an optical printer using the correction data creation device of the present invention can be provided. The means for moving the light source 3 and the liquid crystal optical shutter 2 relative to the photoconductor is a well-known and commonly used technique, and therefore its illustration is omitted.

As described above, according to the present invention,
Since it is possible to create liquid crystal drive correction data that also takes into account the liquid crystal falling response characteristics, a liquid crystal optical shutter correction data creation device for an optical printer that is capable of more accurate gradation display than before is provided. can do.

[Brief description of drawings]

FIG. 1 is a block diagram of a correction data creation device for a liquid crystal optical shutter according to the present invention.

FIG. 2 is a flowchart showing the operation of the correction data creation device for a liquid crystal optical shutter according to the present invention.

FIG. 3 is a diagram showing a relationship between a gradation and an integral value when a liquid crystal is driven by liquid crystal drive data before correction for R light.

FIG. 4 is a diagram showing a relationship between a gradation and an integrated value when a liquid crystal is driven by liquid crystal drive data before correction for G light.

FIG. 5 is a diagram showing a relationship between a gradation and an integrated value when a liquid crystal is driven by liquid crystal drive data before correction for B light.

FIG. 6 is a diagram showing a relationship between a gradation and an integral value when a liquid crystal is driven by corrected liquid crystal drive data for R light.

FIG. 7 is a diagram showing a relationship between a gradation and an integral value when a liquid crystal is driven by corrected liquid crystal drive data for G light.

FIG. 8 is a diagram showing a relationship between a gradation and an integral value when a liquid crystal is driven by corrected liquid crystal drive data for B light.

FIG. 9 is a diagram for explaining the reason why correction of liquid crystal drive data is necessary in the conventional technique.

[Explanation of symbols]

1 Correction data creation device 2 Liquid crystal optical shutter 3 light sources 4 Photoelectric conversion element 5 Temperature detection means 6 heating means 7 Liquid crystal optical shutter drive means 8 heater driver 9 Light source driving means 10 integration means 11 Pre-correction data storage means 12 Corrected data storage means 13 Display means 14 Display drive means

Continued front page    F-term (reference) 2C162 AE13 AE23 AE28 AE47 FA08                       FA36                 2H088 EA33 FA12 HA06 HA12 HA28                       MA04 MA13 MA20                 2H093 NA56 NB03 NC13 NC28 NC47                       NC50 NC54 NC57 NC63 NC65                       NC66 NC76 ND02 ND06 ND09                       ND17 ND32 ND33 ND45 ND56                       ND58 NE05 NE06 NG12

Claims (3)

[Claims] 1. An apparatus for creating correction data for correcting a light transmission time of a liquid crystal optical shutter corresponding to each of a plurality of gradation data to a predetermined value, the intensity of light after passing through the liquid crystal optical shutter. For detecting and outputting as an electric signal, an integrating means for integrating the output of the sensor, and a temporary liquid crystal for creating a temporary liquid crystal drive signal before correction corresponding to a plurality of gradation data for which the correction data is to be created. A drive signal generating means, and drives the liquid crystal optical shutter based on gradation data for which the correction data is to be generated by the temporary liquid crystal drive signal, and the transmitted light at this time is converted into an electric signal by the sensor. A correction data creating device for a liquid crystal optical shutter, which is characterized in that the correction data is created based on a value obtained by converting the output and integrating the output by the integrating means. 2. The liquid crystal light driven based on the gradation data for which the correction data is to be created or the gradation data in the vicinity thereof during the period when the sensor detects light or the period when the integrating means performs integration. The correction data creation device for a liquid crystal optical shutter according to claim 1, comprising a rising response period and a falling response period of the shutter. 3. A correction data generating device according to claim 1 is used to generate correction data, and the liquid crystal optical shutter is driven based on the correction data to set a predetermined value on the photoconductor. An optical printer that forms images.