JPH0524253A - Image forming device - Google Patents

Abstract

(57) [Abstract] [Object] A printer as an image forming apparatus is intended to improve the image quality of an input image in accordance with the result of detection of the inclination of a straight line in a jaggy portion. Structure: means 7 for detecting the inclination formed by the above-mentioned straight line with the main scanning direction, means 8 and 9 for designating the size of a single recording dot and its interval, respectively, and outputs of means 7, 8 and 9 By using the divided recording dot shape determining means 9 for equalizing the diameter of the single recording dot and the recording width of the two divided recording dots in the sub-scanning direction, and dividing each of the single recording dots into two. Reduce jaggies.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a laser printer and an LED.
The present invention relates to a printer such as a printer, a liquid crystal printer, a thermal transfer printer, an inkjet printer, or the like, that is, an image forming apparatus. The present invention relates to an image forming apparatus to improve.

[0002]

2. Description of the Related Art Currently, printers used as image forming apparatuses are mainly 300 dpi. Therefore, many of the signals output from electronic computers are compatible with 300 dpi. However, a low resolution printer such as 300 dpi has a drawback that the jaggies shown in FIG. 9 are conspicuous. In order to eliminate this defect, the pixel density should be increased. However, if the pixel density is increased very simply, in addition to an increase in the page buffer and an increase in the printer cost due to the high accuracy of the engine, (1) the bitmap font for 300 dpi that has been distributed to the public It cannot be used (2) There is a drawback that the widely distributed 300 dpi input device (scanner, etc.) cannot be used. By the way, in the laser printer, it is difficult to increase the pixel density in the sub-scanning direction, that is, to increase the pitch of paper feed / drum feed, and even if it is possible, the cost will be high. On the other hand, in order to increase the pixel density in the main scanning direction, it suffices to increase the frequency for modulating the laser light, which can be realized relatively easily and at low cost. Therefore, there has been proposed a method for improving the image quality by triple the pixel positioning accuracy in the main scanning direction and changing the pixel size in 12 steps (USP 4,847,641). In this method, the pixels of the input image are cut out with a mask of a predetermined size, compared with a pattern written in ROM in advance, and if they match the pattern, the position and size of the corresponding pixel are determined. How to fix it.

FIG. 10 is an explanatory diagram of this correction method. In the figure, input data 1 is converted into sampling window 2
Then, the position and the size of the corresponding pixel are changed when the data match, as compared with the template 3 on the right.

Further, in order to reduce jaggies at an angle close to a straight line in the horizontal direction as shown in FIG. 9, what should be originally expressed by one recording dot is divided into two dots in the sub-scanning direction and the image quality is divided. There are ways to make improvements. 2 replaced
The size of each recording dot was determined by actually recording characters and figures and performing tuning so that jaggies would not be noticeable in cut and try.

[0005]

When using a method of recording one recording dot by dividing it into two dots in the sub-scanning direction, enormous labor is required for tuning, When the dot diameter of the printer is changed, the tuning work is repeated again, and if the tuning is insufficient, the image quality improving effect is small.

According to the present invention, the angle of the horizontal straight line of the jaggy portion with respect to the main scanning direction is detected, and the size of the two divided recording dots in the sub-scanning direction is determined according to the angle to improve the image quality. To improve.

[0007]

FIG. 1 is a block diagram showing the principle of the present invention. This figure is a principle block diagram of an image forming apparatus that records a high-quality straight line with little jaggies and improves the image quality of an input image while using a low-resolution recording method.

In FIG. 1, the inclination detecting means 6 detects the inclination in the main scanning direction of the straight line of the jaggy portion from the input image data in the bit map memory, for example. This inclination detection is performed by comparison with a template, for example. The individual dot diameter designating means 7 is, for example, a dot diameter register, and designates the size, for example, the diameter, of a single recording dot in the input image data, and the dot interval designating means 8 is
For example, it is a dot interval register, and specifies the interval of single recording dots, that is, the dot pitch.

The divided recording dot shape determining means 9 is, for example, a look-up table, and the inclination of the straight line of the output jaggy portion of the inclination detecting means 6 in the main scanning direction and the diameter of the individual recording dot designated by the individual dot diameter designating means 7. , And the dot pitch designated by the dot spacing designating means 8,
The shape of the two divided recording dots is specified so that the recording width of the two dots in the sub-scanning direction becomes equal to the diameter of the single recording dot.

[0010]

According to the present invention, when a single recording dot is divided into two recording dots in the sub-scanning direction, the recording width is made equal to the diameter of the single recording dot so that the width of the straight line can be increased at any portion. That is, the image quality is improved so that the intervals of the envelopes become equal.

In order to equalize the widths of the envelopes, the diameter of a single recording dot is divided into two so that the recording width in the sub-scanning direction of the two recording dots divided and recorded becomes equal. The radius of each recording dot is determined. The recording dots divided into two are a part of the recording dots,
Other recording dots are not divided and are recorded as individual recording dots.

The centers of the respective recording dots divided into two must naturally be on the main scanning line. Therefore, the interval between the centers of the two recording dots divided in the sub-scanning direction is the dot pitch in the sub-scanning direction. Matches For example, in order to reduce the jaggies of a straight line rising to the right, the divided recording dots are arranged so that the center of two divided recording dots is on a certain main scanning line and the main scanning line one above it. The shape is determined.

In FIG. 1, the divided recording dot shape determining means 9 uses the inclination of the straight line of the jaggy portion in the main scanning direction, the size of the individual recording dots, and the interval between the individual recording dots to form two recording dots. The shape is determined according to the calculation formula of the radius of. The shape of the two divided recording dots can be determined by providing a look-up table that stores the relationship between them instead of actually performing the calculation.

As described above, in the present invention, the straight line of the jaggy portion can be corrected to a straight line having no envelope and having envelopes with equal intervals.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 2 is an explanatory diagram of the jaggy correction system of the present invention. FIG. 7A shows an example of a straight up jaggie. FIG. 16B shows a jaggy correction result, in which a part of the single recording dots in FIG.
Jagging is reduced by dividing into individual dots. The division into the two recording dots is performed so that the interval between the straight line envelopes as the correction result becomes constant. Further, the two divided recording dots are recorded so that the center is located on a main scanning line and a main scanning line one above the main scanning line.

FIG. 2C is an explanatory diagram of a method of determining two divided recording dots. In the figure, the scale on the horizontal axis indicates the dot interval in the main scanning direction, and the unit interval corresponds to the dot pitch in the main scanning direction. The scale on the vertical axis indicates the sub-scanning dot interval, and the unit interval corresponds to the paper feed pitch in the sub-scanning direction. In this embodiment, these pitches are the same.

In FIG. 2C, r _n and _m indicate the dot radius of the m-th recording dot in the sub-scanning direction (vertical direction) on the n-th line in the main scanning direction. Radius r ₀ of the recording dots at the origin, ₀ is the radius of a single recording dots which do not change under the corrected and uncorrected image. For example, the radius r ₀ ,
The recording dots of ₂ and r ₁ , ₂ are obtained by dividing the individual recording dot before correction into two, and the centers of the individual recording dots are on the main scanning line.

[0018] In FIG. 2 (c), the relationship between the radius r _{1, 2} and r _{0, 2} of radius r _{0, 0} and two divided recording dots alone recording dot is given by the following equation. 2 × r ₀ , ₀ = r ₀ , ₂ + r ₁ , ₂ + pitch (1) where “pitch” is the paper feed pitch in the sub-scanning direction.
In the equation (1), the radius r ₀ , ₂ and r ₁ , ₂ are given by the following equation by using the angle θ between the straight line with jaggies and the main scanning direction.

[0019]

[Equation 1]

Here, "pitch" is the main scan as described above,
It is assumed to be the same in both sub-scanning directions. FIG. 3 is an explanatory diagram for determining the size of the recording dots to be divided,
The equations (2) and (3) will be described. In the figure (a), AB = 2pitch × tan θ holds, and the equation (2) is derived from r ₀ , ₀ = r ₀ , ₂ + 2pitch · tan θ.

Similarly, in FIG. 3B, CD = 2 pitc
h × tan θ holds, and equation (3) is derived from r ₀ , ₀ = r ₁ , ₂ + pitch−2pitch · tan θ.

Similarly, the radius of the divided recording dots is generally given by the following equation.

[0023]

[Equation 2]

Here, r is the radius of the single recording dot (=
r ₀ , ₀ ), and when m is 4 or more, (4),
The calculation of equation (5) is repeated. FIG. 4 is a system configuration block diagram of an embodiment of the image forming apparatus. In the figure, the image forming apparatus includes a bit map memory 11 and a bit map memory 1 for storing input bit map image data.
The line buffer memory 12a as a register group for temporarily holding the data serially read from 1
.About.12 m, a register 13 for holding the data cut out from these line buffer memories, an angle detector 14 for detecting the inclination of a straight line with jaggies from the bitmap image data cut out in the register 13, a single recording manually instructed. The first dot diameter register 15 for holding the radius of the dot, the dot diameter detector 16 for detecting the size of the laser beam of the exposure optical system, which will be described later, and the size of the laser beam detected by the dot diameter detector 16 are defined, for example. Alarm detector 17 that outputs an alarm signal when the size becomes less than or equal to the second size, and the second dot diameter register 1 that indicates the radius of the single recording dot by the size of the laser beam as the output of the dot diameter detector 16.
8, a switch 19 for switching the output of the first dot diameter register 15 and the output of the second dot diameter register 18, a dot interval register 20, which indicates a dot interval, that is, a dot pitch, a radius of a single recording dot, a dot interval, and From the inclination of a straight line including jaggies, the radius of two recording dots is set to (4) so that the diameter of a single recording dot is equal to the recording width of two recording dots divided and recorded in the sub-scanning direction. ) And (5), the dot shape calculation lookup table (LU
T) 21, a laser drive driver 22 that drives a laser according to the output of the dot shape calculation LUT 21, and an exposure optical system 23 that creates a latent image on the electrophotographic process.

In FIG. 4, when image data is transferred from the printer external interface (not shown) to the bit map memory 11 and a print command is output from the external interface, the bit map data is sent to the line buffer memories 12a to 12m from the top of the page. To be done. The line buffer memories 12a to 12m are serial input registers, and when the bit map data is taken in these registers (M), N bit map data are taken out in parallel from the respective serial input registers,
The data of the matrix map image area of N × M pixels is stored in the register 13.

Bit map image data for N × M pixels cut out in the register 13 is input to the angle detector 14, and the inclination of the straight line is detected. The detected angle, the dot diameter of the printer, and the dot spacing determine the size of the divided dots to improve straight line jaggies as described above. Here, the dot interval of the printer is usually determined in the dot interval register 20 at the time of factory shipment. The dot diameter of the printer is set in the first dot diameter register 15 at the time of factory shipment, or is set in the second dot diameter register 18 'as the detection result of the dot diameter detector 16.

Actually, the angle of the straight line including jaggies, the dot diameter of the printer, and the dot interval are the dot shape calculation unit LUT.
21 and the dot shape calculation LU corresponding to them is input.
The dot diameter data of the divided recording dots stored in T21 is stored in the laser driving driver 22 for one scanning of the exposure optical system, read out in synchronization with the recording processing of the exposure optical system 23 of the recording apparatus, and is read at a predetermined position. It is used for modulation of the laser light source of the exposure optical system in order to record dots with a predetermined dot diameter.

In FIG. 4, the angle detector 14 determines whether or not there is a straight line in the N × M pixel bitmap image cut out in the register 13 and detects the angle if there is a straight line. This detection method can be easily inferred from the method described in the above-mentioned USP 4,847,641. In summary, the pixels of the input image are cut out with a mask of a predetermined size and compared with an angle detection pattern written in ROM in advance, and the corresponding angle is determined from the matched pattern.

Next, the change in dot diameter by the laser drive driver 22 will be described. FIG. 5 shows an example of the relationship between the light emission time and the dot diameter. The figure is a plot of the actual measurement results, and it can be seen that the dot diameter changes significantly when the light emission time is shorter than 0.6 μs.

FIG. 6 shows an example of the relationship between the change in light emission time, the exposure amount, and the dot shape. In the same figure, it can be seen that the exposure amount changes depending on the light emission time, and the dot diameter determined by the exposure amount changes for development.

FIG. 7 is a block diagram showing the configuration of an embodiment of the laser drive driver. In the figure, the laser driver is a dot diameter data memory 27 for storing the dot diameter data output in pixel units from the dot shape calculation LUT 21 of FIG. 4, and the dot diameter data / for converting the dot diameter data into the laser emission time data. The shift register group 29 and the latch 3 for controlling the laser emission time by the outputs of the emission time converter 28 and the dot diameter data / emission time converter 28
0, print clock 3 to indicate dot print timing
1. Sub clock 32 for instructing shift timing of stored contents of shift register group 29, laser 33, laser 3
It is composed of a driver 34 for driving the device 3.

FIG. 8 is a timing chart of the exposure control in FIG. A radius r ₀ on the main scanning line on the horizontal axis of FIG.
_The operation of setting the dot diameters of ₀ , ..., R ₀ , _n will be described with reference to FIGS. 7 and 8.

In FIG. 8, the print clock C₁, C₂，
C₃With radius r₀，₀, R₀，₁, R ₀，₂Mark the dot
To record, first print clock timing C₀De
Diameter data r₀，₀From the dot diameter data memory 27
It is read out and read by the dot diameter data / light emission time converter 28.
Is converted into light emission time data. Dot diameter data r₀，
₀Is the maximum dot diameter.
Is converted to level 7. For level 7 emission time
From the dot diameter data / light emission time converter 28,
'1' is output to the shift registers 29a to 29g of
It Correspondence between such emission time data and dot diameter data
The relationship is that the dot diameter data / light emission time converter 28 is PR
Arbitrary by configuring with OM or ROM
Can be set to.

The output signals to the shift registers 29a to 29g are changed according to the timing P ₁ of the parallel load signal.
It is set in each shift register. After that setting,
In synchronization with the sub clocks S ₁ , ₁ , S ₁ , ₂ , ...
The contents are vertically transferred in the direction from 29g to 29a in each shift register, and the contents of 29a are latched one after another.
It is output to 0. The contents stored in the latch 30 are used by the driver 34 to emit the laser 33.

At the timing C ₂ of the print clock, at the timing C ₁ , the dot diameter data memory 2
The dot diameter data of radius r ₀ , ₁ read from 7 is converted into light emission time data, and the result is converted to the shift register 2
9a to 29g are loaded in parallel according to the timing P ₂ . At this time, since the dot diameter data r ₀ , ₁ is slightly smaller than the maximum dot diameter, the light emission time is reduced by one level, and the exposure time is 6/7 of the maximum exposure time.

Six shift registers 29a to 29f excluding 29g from the dot diameter data / light emission time converter 28.
'1' is output, and the stored contents are transferred in the vertical direction one after another in synchronization with the sub clocks S ₂ , ₁ , S ₂ , ₂ , ... And used for the emission of the laser 33 via the latch 30. To be

As an application of this embodiment, the size of the laser beam of the constant exposure optical system 23 is detected by the dot diameter detector 16 of FIG. 4, and the dot diameter is divided as the size of the above-mentioned single recording dot. It is also possible to determine the shape of and to make the shape follow the fluctuation of the laser beam diameter.

In FIG. 4, this is the first switch 19
Dot diameter register 15 to second dot diameter register 1
It is realized by switching to the 8 side. The dot diameter detector 16 is arranged at one end of the exposure optical system 23 in the main scanning direction of the laser beam, and measures the diameter of the laser beam every time the laser beam starts scanning one line. The measured laser beam diameter is held in the second dot diameter register 18 as a single dot diameter for one line scanning period, and is used for outputting dot diameter data by the dot shape calculation LUT 21 via the switch 19.

At this time, the alarm detector 17 compares the laser beam diameter detected by the dot diameter detector 16 with the size of the laser beam diameter determined by the dot diameter data output from the dot shape calculation LUT 21 to obtain an actual value. An alarm signal is output when the laser beam diameter deviates from a predetermined value.

Although the dot size is changed by controlling the laser emission time in the above description, the same effect can be obtained by controlling the laser drive voltage or drive current with the emission time kept constant. Of course, you can get it.

[0041]

As described in detail above, according to the present invention, even if a low-resolution printer is used, a straight line having no envelope and having envelopes with equal intervals can be obtained.
It is possible to achieve a good image quality comparable to that of a straight line drawn with a high-resolution printer.

[Brief description of drawings]

FIG. 1 is a principle block diagram of the present invention.

FIG. 2 is a diagram illustrating a jaggy correction method of the present invention.

FIG. 3 is a diagram illustrating how to determine the size of recording dots to be divided.

FIG. 4 is a block diagram showing a system configuration of an embodiment of the image forming apparatus.

FIG. 5 is a diagram showing changes in dot diameter depending on light emission time.

FIG. 6 is a diagram showing changes in the amount of exposure and dot shape due to changes in light emission time.

FIG. 7 is a block diagram showing a configuration of an embodiment of a laser drive driver.

8 is a timing chart of exposure control in FIG.

FIG. 9 is a diagram showing an example of jaggies in an input image.

FIG. 10 is a diagram illustrating a conventional example of an image quality improving method.

[Explanation of symbols]

6 Tilt detection means 7 Single dot diameter designating means 8 dot interval specification means 9 divided recording dot shape determining means 14 Angle detector 15 First dot diameter register 16 dot diameter detector 17 Alarm detector 18 Second dot diameter register 20 dot interval register 21 Dot shape calculation lookup table (LUT) 22 Laser drive driver

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Internal reference number FI Technical display location G06F 15/72 350 9192-5L // G09G 5/36 8121-5G (72) Inventor Jun Shio 1015 Kamiodanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture, Fujitsu Limited (72) Inventor Tomohisa Mikami 1015, Kamiodanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture, Fujitsu Limited

Claims (5)

[Claims] 1. An inclination detecting means (6) for detecting an inclination formed by a straight line of a jaggy portion with respect to a main scanning direction from input image data.
A single dot diameter designating means (7) for designating a size of a single recording dot in the input image data, a dot interval designating means (8) for designating a space between the individual recording dots, and Outputs of the tilt detecting means (6), the individual dot diameter designating means (7), and the dot interval designating means (8) when dividing each part of the individual recording dots into two recording dots arranged in the sub-scanning direction. Divided recording dot shape determining means (9) for determining the shape of the two divided recording dots so that the recording width of the two divided recording dots in the sub-scanning direction becomes equal to the diameter of the single recording dot. And an image forming apparatus characterized by recording a high-quality straight line with low resolution and little jaggies to improve image quality. 2. The divided recording dot shape determining means (9)
Is configured by a look-up table in which the shapes of the divided recording dots are stored in association with the inclination of the straight line of the jaggy portion in the main scanning direction, the size of the individual recording dots, and the interval between the individual recording dots. The image forming apparatus according to claim 1, wherein: 3. The specified value of the individual dot diameter specifying means (7) can be manually changed.
The image forming apparatus described. 4. The image forming apparatus further comprises a dot diameter detector for detecting an actual recording diameter of a single recording dot diameter, and the detection result of the actual recording diameter and the divided recording dot shape determining means (9). The image forming apparatus according to claim 1, wherein an alarm signal is output when the recording widths of the divided recording dots corresponding to the outputs are not equal. 5. The image forming apparatus further comprises a dot diameter detector for detecting an actual recording diameter of an individual recording dot, and a detection result of the actual recording diameter is designated by the individual dot diameter designating means (7). 2. The image forming apparatus according to claim 1, wherein the recording width of the two divided recording dots in the sub-scanning direction is automatically controlled.