JP2822072B2 - Gradation recording control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] The present invention relates to a tone recording control device having a tone density output unit for each pixel that outputs tone density data representing tone density for each pixel, and a light emitting unit that emits light according to an instruction. An object of the present invention is to provide a gradation recording control device such as an electrophotographic printer device capable of multi-leveling the density level of each element without deteriorating the stability of the density of each element. For each element forming a density pattern determined based on data, a light emission time / light emission number instruction unit for instructing the light emission unit to emit light at the light emission number and light emission time corresponding to the gradation density of the element is provided. Configuration.

[Industrial applications]

The present invention relates to a gradation recording control device that controls gradation recording, such as an electrophotographic printer device that performs recording using a laser or an LED array, etc., and particularly to a gradation density data representing a gradation density for each pixel. The present invention relates to a gradation recording control device having a pixel-by-pixel gradation density output unit and a light-emitting unit that emits light according to an instruction.

One of the recording methods of the electrophotographic printer device is an area gradation type recording method.

In this method, as shown in FIG.
(4 × 4 16 dots in this case) are collectively formed into a pixel matrix 120, and the gradation (halftone density) is changed by changing the number of recording dots 121 in the pixel matrix 120. In the image to be recorded, the density of the image is expressed by increasing or decreasing the number of recording dots 121 in the pixel matrix 120 based on the density of the portion corresponding to the pixel matrix 120. In this case, the area of each recording dot 121 is constant, and the number of dots is increased when the density is high, and reduced when the density is low, according to the density level.

By the way, in order to record a natural image with high quality, the number of gradations needs to be about 50, and the pixel density needs to be at least 4 dots / mm or more.

In the area gradation type recording method described above, if the matrix size of pixels is N × N (N is a natural number), N is 7 or more in order to set the number of gradations to 49 or more in natural image recording. Must be done.

As a result, the density of pixels capable of expressing shades is 1/7 or less of the dot density. Usually, since the dot density of an electrophotographic printer is 16 dots / mm or less, the pixel density is reduced to 2.3 dots / mm or less, and it is difficult to achieve both the number of gradations and the pixel density.

In order to solve this problem, attempts have been made to multi-value the recording density level of each dot to 3 to 5 levels. By combining the multi-valued formation of each dot and the area gradation method, it is possible to achieve both the number of gradations and the pixel density. FIG. 4 shows an example of a threshold matrix in a case where the number of levels of each dot is 4 and the pixel matrix is 4 × 4, and FIG. 5 shows a recording dot pattern.

In this example, the number of gradations is 49 and the pixel density is 4 pixels / mm, so that a high-quality natural image can be recorded.

[Conventional technology]

Conventionally, there has been a gradation recording control device of an electrophotographic printer device using an LED array for controlling the density level of each dot in several steps as shown in FIG.

As shown in FIG. 1, the apparatus according to the conventional example includes a pixel-based gray-scale density output unit 111 that outputs gray-scale density data representing the shading of each pixel obtained from the original image, and a gray-scale density data of each pixel. Dots (elements) that form a density pattern determined by
A light emission number instructing unit 112 for instructing light emission for each dot of the number of light emission times corresponding to the gradation density, and a light emitting unit 113 for emitting light for the specified light emission number for each of the elements. is there.

 The device according to the conventional example operates as follows.

The pixel-by-pixel tone density output unit 111 outputs tone density data for each pixel obtained from the original image.

Then, the light emission number instructing unit 112 instructs light emission of the number of light emission times corresponding to the gradation density of each dot forming the density pattern determined based on the gradation density data. Will emit light for a fixed light emission time.

As is apparent from the above description, the electrophotographic printer using the LED array according to the conventional example records the gradation density by changing the number of times of light emission.

[Problems to be solved by the invention]

By the way, in the electrophotographic printer device using the LED array according to the conventional example, the exposure time (light emission time) used for each single light emission is fixed without changing,
The gradation recording is performed by changing the number of times of light emission.

As described above, in order to change the dot area, the seventh
As shown in the figure, if the pulse width is kept constant and the number of pulses is changed, if the recording dot area is small, the dot area will change greatly with a slight change in the recording process conditions, and the dot area will be stable. Control becomes practically impossible.

In other words, when the light emitting time per light emitting circuit is short, and when the density level of the tone density of each dot is low and the number of times of light emitting is small, the change in density with respect to the change in exposure (light emitting) time is not significant. There is a problem that the recording density becomes extremely large, the recording at a low density becomes unstable, and the pixel density tends to shift in a low density portion, or the image becomes rough due to an increase in the density variation.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a gradation recording control device such as an electrophotographic printer device capable of multi-leveling the density level without deteriorating the stability of the density of each element. .

[Means for solving the problem]

In order to solve the above technical problems, the gradation recording control device according to the first invention calculates a gradation level for each element forming a pixel matrix of each pixel in order to represent a gradation density for each pixel. An instruction to emit light at the number of times of light emission and light emission time corresponding to each density level of each element forming a density pattern determined based on the tone density data from the pixel tone density output unit 1 output as tone density data As the concentration level decreases, the number of times of light emission is reduced to increase the light emission time, and as the concentration level increases, the number of light emission times is increased to shorten the light emission time.
It has a number-of-emissions instruction unit 2.

As shown in FIG. 1, an image forming apparatus according to a second aspect of the present invention includes the gradation recording control apparatus according to the first aspect of the invention and a pixel matrix of each pixel for representing the gradation density of each pixel. It has a tone density output unit for each pixel that outputs the density level of each element to be formed as tone density data, and a light emitting unit that emits light in accordance with an instruction from the tone recording control device.

[Action]

The pixel-by-pixel gradation density output unit 1 detects the gradation density for each pixel of the original image.

Here, the “gradation density” refers to the density of each stage when the density of an image is expressed in several stages.

When the gradation density is detected for each pixel and the gradation density data is output, the light emission time / light emission number instruction unit 2 is the gradation density for each element forming a density pattern determined based on the data. Determine the concentration level.

Here, the “density pattern” is, for example, a pattern predetermined for each gradation density as shown in FIG. 5, and is also called a recording dot pattern.

An “element” is one area obtained by dividing each density pattern, and corresponds to, for example, a dot of a unit in which the light emitting unit 3 emits light.

Further, the light-emission time / light-emission number instructing unit 2 gives an instruction of the light-emission number, which is also determined according to the gradation density, based on the light-emission time determined according to the gradation density of each element.

Generally, when the gradation density of an element is high (dark), the number of times of light emission is increased to increase the dot area corresponding to each element, and when the gradation density of the element is low (light), the number of times of light emission is determined. Is determined to be less.

In the present invention, in addition to the number of times of light emission, the light emission time is determined according to the gradation density of the element for the following reason.

When the gradation density is low, the number of times of light emission is reduced as described above. At this time, if the light emission time is short, the amount of energy for light emission is necessary for stable light emission. This is because the recording density becomes lower than a certain threshold value, recording becomes unstable, the density of the pixels easily shifts, and the variation in the density increases due to the increase in the variation in the density.
In addition, when the gradation density is high, the number of times of light emission is increased. At that time, if the light emission time is long, the energy amount for light emission increases and the light emission becomes too dark.

Therefore, when the number of times of light emission is small, each light emission time is increased, and in order to prevent the energy amount of light emission from falling below the threshold value, the light emission time is increased to some extent. The light emission time is made variable in accordance with the number of light emission so as to shorten the time to some extent.

FIG. 9 shows the relationship between the number of times of light emission required for stable light emission and the light emission time obtained by experiments.

The light emitting section 3 emits light in the designated number of times in the designated time.

Examples Next, examples of the present invention will be described.

FIG. 2 shows the entire LED array printer according to the present embodiment.

This device, as shown in FIG.
An optical modulation signal generator 23 for generating an optical modulation signal to be turned on / off in accordance with recording data; and the optical modulation signal generator 23
Each of which emits an ON / OFF modulated light beam according to the output of
An LED array 21 in which LED elements are arranged, and the LED array 21
And a photoconductor drum 22 that rotates in the direction of a vertical arrow that is the longitudinal direction of the photoconductor drum 22 and that exposes a recording pattern of dots, wherein data serially output from the light modulation signal generator 23 is parallel. Then, the LED array 21 instructs the LED array 21 to emit light, and a dot pattern can be recorded on plain paper or an OHP film by an electrophotographic process.

FIG. 3 shows the light modulation signal generator 23 and the LED array 21.
3 shows a portion related to the gradation recording control device according to the present embodiment.

The present apparatus mainly includes a pixel-by-pixel tone density output unit 11 that outputs tone-density data for each pixel, and a tone for each element that forms a density pattern (recording dot pattern) determined based on the tone-density data. A light emission time / light emission number instruction unit 12 for giving an instruction of light emission at the light emission number and light emission time corresponding to the density as a light modulation signal, and at the light emission number designated for each dot, during the designated light emission time, And a light-emitting unit 21 such as an LED array that emits light. Although the present embodiment is generally applied to an electrophotographic printer in which the emission intensity cannot be changed, such as an LED printer using an LED array, a laser capable of changing the emission intensity is used. It is also possible to apply to a type printer.

The pixel-by-pixel tone-density output unit 11 reads a reading diagram (not shown) for reading the tone density of each pixel from the original image, and a data clock signal generating unit 11b that generates a clock signal at the predetermined timing. And a latch section 11a for temporarily holding the gradation density data and outputting the gradation density in synchronization with the data clock signal input timing.

For example, in the case where the pixel matrix of each pixel is 4 × 4 (= 16 dots) and the number of density levels of each dot is 4, the number of gradation densities in this embodiment is as follows.
As shown in FIGS. 4 and 5, there are 49 pieces, and the data width of the gradation density data requires 6 bits.

The light emission time / light emission number instructing unit 12 generates an X address signal for designating an X coordinate indicating a position of a dot as the element forming each pixel (pixel matrix). And a Y address signal generator 12b for similarly generating a Y address signal.
And the dot level as each element that forms a density pattern (recording dot pattern) at the address position specified by the tone density data, the X address, and the Y address and determined based on the tone density data of each pixel. A ROM 12c that outputs wave number data Pw corresponding to the number of times of light emission K and light emission time corresponding to the data representing the modulated density, and a light modulation signal to the LED array 21 based on the number of times of light emission K and wave width data Pw. A programmable pulse generator 12d that outputs a time signal representing a corresponding light emission time the number of times of light emission.

Subsequently, the operation of the gradation recording control device according to the present embodiment will be described.

The light modulation signal generator 23 of the electrophotographic printer device
The 6-bit data, which is the gradation density data for each pixel to be recorded, is stored in the latch section 11a of the pixel-by-pixel gradation density output section 11 of the gradation recording device in the data clock signal generation section 11b. Input and held at the rising edge of the timing pulse signal.

When there is an instruction signal from the data clock signal generation unit 11b of the pixel-by-pixel gradation density output unit 11, the latch unit 11a sends the gradation density data to the ROM 12c.

The gradation density data is obtained by using the X address signal generated by the X address generation unit 12a and the Y address generation unit 12a.
Input to the ROM 12c together with the Y address signal (2 bits each) generated by b.

Then, the ROM 12c sets the number of times of light emission corresponding to the gradation density of the element specified by the X address (horizontal direction) and the Y address (vertical direction) forming a density pattern determined based on the gradation density data of each pixel. The corresponding pulse number (number of light emission) K and wave width data Pw corresponding to the light emission time are output.

Here, the relationship between the pulse number K and the wave width data Pw is shown in FIG. 6, and when the pulse number is large, the pulse width Pw is narrowed and the pulse number is small as shown in FIG. In this case, as shown in FIG.
By widening Pw, stable recording can be obtained regardless of the recording dot area.

For this reason, the ROM 12c outputs pulse width data Pw such that the change in the exposure energy becomes small at the same time as the number of pulses K.

At this time, when the number of pulses is increased, the number of printed dots is large, and when the number of pulses is small, the printed dots are small.

In this way, LE corresponds to the recording density level of each dot.
The number of pulses and the pulse width for driving the D array 21 increase and decrease, and the size of the recorded dot changes.

The pulse number signal K and the pulse width signal Pw output from the ROM 12c are input to a programmable pulse generator 12d that generates an LED drive signal, and correspondingly, K pulses having a pulse width Pw as shown in FIG. An LED head drive bit string corresponding to the pulse is generated. In FIG. 10, the length of the LED head drive bit string is 16 bits. Currently available LED arrays adopt a control method of transferring On / Off data to each LED element and exposing all LED elements to a common enable signal for a predetermined time.

Therefore, it is necessary to convert the pulse waveform into a bit string as shown in FIG. 10, and the output of the programmable pulse generator 12d for generating the LED drive signal is output from the LED array.
Then, the desired exposure is performed.

LED array 2 with the most stable recording dot area
The relationship between the number of driving pulses and the pulse width of the LED array 21 and the area of the recording dots is such that the number of driving pulses and the pulse width of 1 and the area of the recording dots are most stable. Although it differs depending on the type of the body, the developing toner, and the like, the characteristics are substantially as shown in FIG. The pulse number is less than K _min, not recording dot area on the output of the pulse number is constant, since the stable recording dots can not be obtained, the pulse number smaller than K _min is not used. When the number of pulses is K _min , the area ratio of the recording dots is
Becomes 100%, without increasing the dot area rate increases the pulse number more is because, K _max or more pulse number not be used only unnecessarily increase the energy for printing. When the number of pulses is from _Kmin to _Kmax , the dot area recorded increases monotonously with an increase in the number of pulses. Therefore, as shown in FIG. 9, the number of recording pulses and the recording pulse width characteristics that minimize the variation in density recorded within this range are determined, and the optimum recording pulse width is determined.

The pulse width data Pw representing the pulse width is determined with respect to the number K of pulses for realizing the gradation density corresponding to each element (dot) of the density pattern so as to have the relationship shown in FIG. The 4-bit data is input to the programmable pulse generator 12d, and a corresponding signal is transmitted to the LED array 21.

Thus, each LED element emits a light beam on / off-modulated according to the output of the light modulation signal generator 23 and condenses on the photoconductor drum 22. Is rotated in the direction of the arrow Y, which is perpendicular to the longitudinal direction, so that the recording pattern by dots is exposed on the photoconductor drum 22, and the dot pattern can be recorded on plain paper or OHP film by an electrophotographic process. Become.

〔The invention's effect〕

As described above, according to the recording control device of the present invention, not only the number of times of light emission, but also the time of light emission in each time, according to the tone density of each element forming a density pattern corresponding to the tone density of each pixel. Is also changed.

Therefore, the gradation recording control device according to the present invention can perform recording with high quality image quality without deteriorating the stability of each density by the optimal light emission time according to each light emission frequency.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the principle of the present invention, FIG. 2 is a diagram showing an LED array printer according to an embodiment, FIG. 3 is a block diagram according to the embodiment, and FIG. FIG. 5 shows an example of a recording dot pattern according to the embodiment, FIG. 6 shows an embodiment in which the number of pulses and the pulse width are simultaneously changed, and FIG. 7 shows a pulse with a constant pulse width. FIG. 8 is a diagram showing a conventional example in which the number is changed, FIG. 8 is a diagram showing the relationship between the number of recording pulses and the recording dot area ratio, FIG. 9 is a diagram showing the relationship between the number of recording pulses and the recording pulse width, and FIG. FIG. 11 is a diagram showing a pulse waveform and a bit string corresponding to the embodiment, and FIG. 11 is a block diagram and FIG.
The figure shows a pixel matrix and recording dots. 1, 11: tone density output unit for each pixel 2, 12: light emission time / number of light emission instruction unit 3, 13: light emission unit

Continuation of front page (58) Field surveyed (Int.Cl. ⁶ , DB name) B41J 2/52

Claims (2)

(57) [Claims] An output unit for outputting a density level of each element forming a pixel matrix of each pixel as gradation density data in order to represent a gradation density of each pixel; An instruction for light emission at the light emission frequency and light emission time corresponding to each density level of each element forming a density pattern determined based on the gradation density data is given as the light emission frequency decreases as the density level decreases. Having a light emission time / light emission number instruction section (2) for increasing the number of light emission and shortening the light emission time as the concentration level increases. Recording control device. 2. The gradation recording control device according to claim 1, wherein a gradation level of each element forming a pixel matrix of each pixel is represented as gradation density data in order to represent a gradation density of each pixel. An image forming apparatus, comprising: a pixel-by-pixel tone density output unit; and a light-emitting unit (3) that emits light in accordance with an instruction from the tone recording control device.