JPH0568153A - Image processor - Google Patents

Abstract

PURPOSE:To attain both the quality of character void and the uniformity mediate gradation by forming exposure area data and exposure intensity data to be increased reversely proportionally and correspondingly to the density of image data in each pixel and forming a laser drive signal based upon both data. CONSTITUTION:An LUT 3 outputs exposure area pulse forming exposure area data Y1 reversely proportional to the density of image data (1) outputted from an image data storing part 1. On the other hand, an LUT 5 outputs exposure intensity data Y2 to be increased correspondingly to the density value of the data (1) and a PWM circuit 4 outputs an exposure area pulse (4) obtained by modulating the pulse width of a pixel clock period in accordance with the data Y1. A data register 6 outputs the data Y2 only for the output period of the pulse (4) and a DAC 7 D/A converts the output of the register 6 and outputs the converted result to an optical power modulator such as an AOM to control laser power. Consequently the quality of character void and the uniformity of intermediate gradation can be attained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing apparatus for generating a laser drive signal for a laser imager according to each pixel of image data.

[0002]

2. Description of the Related Art In a laser imager such as a laser printer, in order to improve the uniformity of image quality (obtain an image without a feeling of roughness due to dots), pixels are arranged so that each pixel looks continuous due to overlapping of adjacent pixels. It is desirable that the diameter be large to some extent. Such a pixel state is shown in FIG.

However, in this state, the white spots surrounded by black appear small due to the spread of the bottom of the laser beam spot. Therefore, a white character on a black background becomes thin. In order to thicken such white characters, the pixel diameter may be reduced as shown in FIG. Then, the discontinuity of pixels causes the black background to appear rough.
In particular, the roughness becomes more noticeable when the gradation is intermediate than that of solid black.

[0004]

As described above, there is a trade-off relationship between roughness and missing characters.
Therefore, conventionally, an appropriate compromise has been found, or FIG.
As shown in (c), the laser output time is extended so that the pixel has directivity. Each pixel appears as a point independently in FIG. 6B, but as a horizontal line in FIG. 6C. In this case, the method of FIG. 6C is preferred because of the anisotropy of the human eye (the property that vertical lines are more visible than horizontal lines) and the familiarity with scanning lines of CRT monitors.

However, even the method of FIG. 6 (c) has the drawback that the vertical lines of white characters are thinner than the horizontal lines.
The present invention has been made to solve the above problems, and an object of the present invention is to provide an image processing apparatus capable of achieving both missing characters and uniformity of halftone.

[0006]

In an image processing apparatus for generating a laser drive signal of a laser imager according to each pixel of image data, the exposure area data which is inversely proportional to the density of the image data of each pixel is generated. One processing means, second processing means for generating exposure intensity data that increases according to the density of image data of each pixel, exposure area data generated by the first processing means, and exposure generated by the second processing means Data generating means for generating a laser drive signal based on the intensity data is provided.

[0007]

The exposure area data is determined by the first processing means in inverse proportion to the density of each pixel, and the exposure intensity data is determined by the second processing means according to the density of each pixel. Therefore, when the density value of the image data is large, the laser intensity is large and the pixel diameter is small. On the other hand, when the density value of the image data is small, the laser intensity is low and the pixel diameter is large.

[0008]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 is a configuration diagram showing the principle configuration of an embodiment of the present invention. Here, a general medical laser printer will be described. In this figure, 1 is an image data storage unit in which medical image data is stored, 2 is an image processing circuit which is a characteristic part of this embodiment, and 3 is a pulse width of a laser beam for each pixel. A look-up table (hereinafter referred to as LUT) constituting the first processing means, 4 is a PWM circuit for generating exposure area data based on the output of the LUT 3, and 5 is exposure intensity for determining the pulse intensity of the laser beam of each pixel. An LUT constituting second processing means for generating data, 6 is a data register for generating digital data for laser power modulation from exposure area data and exposure intensity data, and 7 is D / A for digital data for laser power setting. It is a D / A converter for conversion.

FIG. 2 is an explanatory view showing a usage state of the apparatus of this embodiment, and FIGS. 3, 4 and 5 are explanatory views showing signal waveforms and pixel shapes of respective parts. The operation of the apparatus of this embodiment thus configured is as follows.

The image data read from the image data storage unit 1 is supplied to LUT3 and LUT5. LUT
In 3, the exposure area data Y1 for generating the exposure area pulse inversely proportional to the density value of the image data is output. On the other hand, the LUT4 outputs the exposure intensity data Y2 that increases according to the density value of the image data. This LUT 3,5
Y1 = 3200-0.6X (1) Y2 = 743X / (3200-0.6X) (2) when the density value of the image data is X. It is assumed that X1, Y1, Y2 = [0.4095].

Here, the PWM circuit 4 which receives Y1 outputs an exposure area pulse in which the pixel clock period is pulse width modulated according to the exposure area data Y1. Then, the data register 6 outputs the exposure intensity data Y2 in the pulse period of the exposure area pulse. This is equivalent to the exposure intensity data Y2 being pulse width modulated according to the exposure area data Y1. Then, the DAC 7 outputs the output of the data register 6 to D
/ A-converts and supplies to the optical power modulator 9 such as AOM.

In this way, the final exposure amount (Y1
-Y2) is proportional to the density value X. FIG. 3 shows the relationship between the exposure area pulse (FIG. 1) and the pixel shape. As shown in this figure and the equation (1), the larger the density value, the smaller the pixel shape, and the smaller the density value, the longer the pixel shape becomes. Then, in such a pixel shape, the laser power is controlled by the exposure intensity data Y2.

FIG. 4 is an explanatory diagram showing a signal state and a printing result when a white dot is drawn on a black background and when a gray solid paint is drawn. The pixel clock is in the state shown in FIG.
It is assumed that the density value of the image data is the value shown in FIG. At this time, the output of LUT1 is determined by the table based on the above equation (1) and becomes as shown in FIG. 4 (c). Then, based on the output of this LUT 3, the PWM circuit 4 outputs the exposure area pulse as shown in FIG. On the other hand, the output of the LUT 5 is determined by the table based on the equation (2), and is as shown in FIG. Therefore, in the data register 6, the PWM circuit 4
The exposure area pulse output from 1 determines the exposure area of one pixel, and the laser intensity within this range is determined by the exposure intensity data Y2. The DAC 7 receiving the output of the data register 6 outputs a pulse according to the exposure area and the exposure intensity as shown in FIG. In this waveform, the height direction indicates the laser intensity and the width direction indicates the laser pulse width. Therefore, the print result is
It becomes like (g).

FIG. 5 shows an example of the printing result shown in FIG. 4 (g). In FIG. 5A, the case where white dots are formed on a black background is shown. In this case, since the area of the black spot is small, the phenomenon that the white spot becomes small is suppressed. Therefore, even when forming a white line on a black background,
The phenomenon that the white line becomes thin is suppressed.

On the other hand, in the case of FIG. 5B in the case where a gray solid (halftone) is formed, the laser pulse becomes horizontally long, so that dots adjacent in the horizontal direction overlap each other. As a result, a white line can be seen in the lateral direction, but the roughness is reduced. Dots formed by the conventional device (Fig. 5)
Compared with (c)), since there was no overlap in the past,
White lines were visible in the vertical and horizontal directions (because one black dot can be visually recognized), and the graininess was very large. Therefore, according to the apparatus of this embodiment, it is understood that the rough feeling in the halftone is greatly improved.

As described in detail above, the laser power based on the exposure intensity data proportional to the density for obtaining the density gradation and the laser pulse width based on the exposure area data having a reciprocal relationship with the density. Since the laser exposure is performed in, it is possible to achieve both good character missing and uniformity of intermediate gradation.

[0017]

As described in detail above, according to the present invention, the laser power based on the exposure intensity data proportional to the density for obtaining the density gradation and the exposure area data having a reciprocal relationship with the density are obtained. Since the laser exposure is performed with the laser pulse width based on the above, it is possible to realize an image processing apparatus capable of achieving both good character omission and uniformity of halftone.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a configuration of a first embodiment of the present invention.

FIG. 2 is an explanatory diagram showing the entire laser printer.

FIG. 3 is a waveform diagram showing a signal waveform of each part.

FIG. 4 is a waveform diagram showing a signal waveform of each part.

FIG. 5 is an explanatory diagram showing an example of a pixel shape.

FIG. 6 is an explanatory diagram showing an example of a pixel shape in a conventional device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Image data 2 Image processing device 3 Look-up table 4 PWM circuit 5 Look-up table 6 Data register 7 DAC

Claims (1)

[Claims] 1. An image processing apparatus for generating a laser drive signal for a laser imager according to each pixel of image data, comprising first processing means for generating exposure area data which is inversely proportional to the density of the image data of each pixel. A second processing unit that generates exposure intensity data that increases according to the density of the image data of each pixel, based on the exposure area data generated by the first processing unit and the exposure intensity data generated by the second processing unit And a data generating unit for generating a laser driving signal.