JP3147959B2 - Image quality improvement method for image equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field 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, and an ink jet printer, that is, an image forming apparatus or an image display apparatus, and more particularly, to reduce jaggies of an image generated due to a low resolution recording method, that is, to reduce jaggies of an input image. The present invention relates to a method for improving image quality in an image forming apparatus or an image display apparatus for improving image quality.

[0002]

2. Description of the Related Art At present, a printer of 300 dpi is mainly used as an image forming apparatus. Therefore, the signal output from the electronic computer often corresponds to 300 dpi. However, for low resolution printers such as 300 dpi,
There is a disadvantage that the jaggy shown in FIG. 19 is conspicuous. In order to eliminate this disadvantage, the pixel density may be increased. However, when the pixel density is simply increased, the page buffer is increased, and the cost of the printer is increased due to the increase in the precision of the engine. Can not be used,
(2) There is a drawback that 300 dpi input devices (scanners, etc.) that are widely distributed cannot be used. By the way, in a laser printer, it is difficult to increase the pixel density in the sub-scanning direction, that is, it is difficult to increase the paper feed / drum feed pitch. On the other hand, in order to increase the pixel density in the main scanning direction, it is only necessary to increase the frequency for modulating the laser beam, and this can be realized relatively easily and at low cost. Therefore, there has been proposed a method of improving the image quality by increasing the positioning accuracy of the pixel in the main scanning direction by three times and changing the pixel size in 12 steps (US Pat. No. 4,847,641). In this method, pixels of an input image are cut out with a mask of a predetermined size, and R
This is a method of comparing the pattern written in the OM and correcting the position and size of the corresponding pixel when the pattern matches the pattern.

FIG. 20 is an explanatory diagram of this correction method. In FIG. 20, input data 1 is cut out by a sampling window 2 and compared with a template 3 on the right, and the position of a pixel corresponding to the case where the data match is determined. A change in size is made.

Further, in order to reduce jaggies at an angle close to a horizontal straight line as shown in FIG. 19, an image to be originally represented by one recording dot is divided into two dots in the sub-scanning direction to obtain image quality. There are ways to make improvements. The size of each of the two recording dots to be replaced has been determined by, for example, actually recording characters and figures and performing tuning so that jaggies are not noticeable in cut and try.

[0005]

However, FIG.
In the method described in the above section, it is necessary to have many mask patterns, so that the speed is slow, the amount of memory for storing the mask pattern is large, and the pixel arrangement that completely matches the limited mask pattern is considered. There was a problem that only the correction was made.

In the case of using a method in which one recording dot is divided into two dots in the sub-scanning direction and recorded, enormous manual labor is required for tuning.
When the dot diameter of the printer for recording changes, the tuning operation is repeated again, and if the tuning is insufficient, there is a problem that the effect of improving the image quality is small.

According to the present invention, by selecting one of the outputs of a plurality of shape determining means using different divided recording dot shape determination methods in accordance with the diameter of the recording dots and the dot interval, that is, the dot pitch, the sub-format is selected. The purpose is to determine the shape of the two divided recording dots in the scanning direction and improve the image quality.

[0008]

FIG. 1 is a block diagram showing the principle of the first invention. FIG. 1 is a principle block diagram of an image quality improvement method in an image forming apparatus as a recording apparatus for improving and outputting an input image.

In FIG. 1, the single dot diameter designating means 6
For example, it is a dot diameter register, which specifies the size of a single recording dot in the input image data, for example, the diameter, and the dot interval specifying means 7 is, for example, a dot interval register, which specifies the interval between single recording dots, that is, the dot pitch. .

[0010] The first recording dot shape determination unit _81, respectively a part of a single recording dot for jaggy reduction 2
When dividing into recording dots arranged in the sub-scanning direction,
Using the outputs of the single dot diameter specifying means 6 and the dot interval specifying means 7, the shapes of the two divided recording dots are determined. The second, third, ..., dividing the recorded dot shape determination unit ₈₂ of the n, 8 _3, ... 8 _n, by using the output of a single dot diameter specifying means 6, by different methods Vice The shape of the two divided recording dots in the scanning direction is determined.

[0011] The selection means 9 is provided with the first, second,.
.One of the outputs of the n-th divided recording dot shape determining means is set to external,
For example, it is selected by a selection control signal input from an input panel, and is output as shape data of two divided recording dots to, for example, a laser control circuit that controls a laser optical system of a printer.

FIG. 2 is a block diagram showing the principle of the second invention. Comparing this figure with FIG. 1 showing the principle of the first invention,
The point that the output of the inclination detecting means 10 is used as a selection control signal for the selecting means 11 for selecting any one of the outputs of the first, second,... Is different. The inclination detecting means 10 detects the inclination formed by the straight line of the jaggy portion with the main scanning direction from the input image data, and outputs a selection control signal to the selection means 11 according to the detected inclination.

[0013]

According to the present invention, the first, second,..., N-th divided recording dot shape determining means 8 ₁ in FIGS.
In each of 8 ₂ ,..., 8 _n , the shape of the two divided recording dots in the sub-scanning direction is determined by a different shape determining method.

For example, if n = 4 and there are first to fourth divided recording dot shape determining means, different shape determining methods are used in the four divided recording dot shape determining means. For example, in the first recording dot shape determining means, the recording width of the divided recording dots in the two sub-scanning directions is set to be equal to the diameter of the single recording dot.
That is, the shape of the divided recording dots is determined so that the intervals between the envelopes of the two recording dots are equal. In the second divided recording dot shape determining means, for example, the two divided recording dot shape determining means are configured so that the sum of the diameters of the two divided recording dots becomes equal to the diameter of the single recording dot. The shapes of the two divided recording dots are determined so that the sum of the diameters of the divided recording dots becomes equal to a constant (> 1) times the diameter of the single recording dot. Further, in the fourth divided recording dot shape determining means, the shape of the divided recording dots is determined such that, for example, the sum of the areas of the two divided recording dots is equal to the area of the single recording dot.

In FIG. 1 showing the principle of the first invention,
For example, any one of the outputs of the four divided recording dot shape determining means determines the size and dot interval of a single recording dot,
That is, it is selected by a selection control signal input from outside according to the dot pitch, and is output to, for example, a laser control circuit for a laser optical system.

In FIG. 2 showing the principle of the second invention,
According to the output of the inclination detecting means 10, for example, one of the outputs of the four recording dot shape determining means is selected and output to the laser control circuit. For example, image data in a window of a certain size is cut out from the input image data in the bitmap memory by the inclination detecting means 10,
The data is compared with, for example, a template, and the inclination of the straight line in the jagged portion in the main scanning direction is detected. Then, one of the outputs of the four divided recording dot shape determining means is selected according to the inclination.

For example, in the first invention, the reason why one of the outputs of, for example, four divided recording dot shape determining means is selected according to the diameter and dot pitch of the single recording dot is as follows. According to the present invention, the density of an improved image after two recording dot divisions is equal to the density of a line formed by a single recording dot before the division. And can be made to be intuitively equal.

[0018]

FIG. 3 is a block diagram showing the overall arrangement of an image forming apparatus according to the first invention. In the drawing, as input image data, for example, a bitmap image of 300 dpi is stored in a line buffer of several lines or a page buffer 20, and the data is cut out by the image cutout unit 21 into a size of, for example, 7 dots vertically by 9 dots horizontally. It is. . The cut-out data of 63 dots is parallel to the jaggy detection unit 2
2, the jaggy detection unit 22 detects a jaggy generation unit by comparing it with, for example, a template (not shown).

The detected jaggy portion is simultaneously provided to a first improving section 23 ₁ , a second improving section 23 ₂ ,..., An n-th improving section 23 _n , and the image quality is improved by different methods. . The outputs of these improvement units are all input to the selector 24, one of the outputs of the improvement unit is selected according to the selection signal input from the input panel 25, and given to the laser control circuit 26 as an improved image output. It is used for controlling the laser optical system 27. Here the input panel 25
Is selected according to, for example, the size of a single recording dot for input image data, that is, the dot diameter and dot interval, that is, the dot pitch.

FIG. 4 is a block diagram showing the overall configuration of the image forming apparatus according to the second invention. 3, data in the window clipped by the image clipping unit 21 is input to the jaggy detection and angle detection unit 28 as parallel data as in FIG. The jaggy detection and angle detection unit 28 detects a jaggy generation unit and detects an angle formed by a straight line of the jaggy portion with the main scanning direction of the printer. The image of the jagged portion is given to each improvement unit as in FIG. 3, and the selector 29 outputs a selection signal from the jaggy detection and angle detection unit 28 according to the angle between the straight line of the jaggy portion and the main scanning direction. , One of the outputs of the plurality of improvement units is output to the laser control circuit 26 as an improved image output.

FIG. 5 is an explanatory diagram of a first divided recording dot shape determining method. FIG. 11A shows an example of a straight upper right jaggy. Figure (b) shows the result of jaggy correction.
By dividing a part of the single recording dot in (a) into two dots in the sub-scanning direction, jaggy is reduced. The division into the two recording dots is performed so that the interval between straight envelopes as a correction result is constant. Further, the two divided recording dots are recorded such that the center is located on a certain main scanning line and the main scanning line one line above.

FIG. 5C is an explanatory diagram of a method for 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 assumed to be equal.

In FIG. 5C, r _{n, m} indicates 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, 2} and r _{1, 2} of the recording dots is obtained by dividing the uncorrected single recording dots to two, each of the center is in the main scanning line.

In FIG. 5C, the radii r ₀ , ₀ of the single recording dot and the radii r ₁ , ₂ and r ₀ , 2 of the two divided recording dots are shown.
The relationship with ₂ is given by the following equation. 2 × r ₀ , ₀ = r ₀ , ₂ + r ₁ , ₂ + pitch (1) where “pitch” is a paper feed pitch in the sub-scanning direction.
In equation (1), by using the angle θ between the straight line having a jaggy and the main scanning direction, the radii r ₀ , ₂ and r ₁ , ₂
Is given by the following equation.

[0025]

(Equation 1)

Here, it is assumed that "pitch" is the same in both main scanning and sub-scanning directions as described above. FIG. 6 is a detailed explanatory diagram of the dot size determining method in the first method, and explains equations (2) and (3). Figure (a)
In, AB = 2pitch × tan θ is _{established, r 0, 0 = r 0} , 2 + 2pitch · tan from theta (2) expression is derived.

Similarly, in FIG. 6B, CD = 2 pitch
× tan theta is _{established, r 0, 0 = r 1} , 2 + pitch -2pitch · tan from theta (3) expression is derived.

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

[0029]

(Equation 2)

Here, r is the radius of a single recording dot (= r ₀ ,
₀ ), and when m is 4 or more, the operations of equations (4) and (5) are repeatedly performed. FIG. 7 is an explanatory diagram of the second divided recording dot shape determination method. FIG. 3A shows the jaggy occurrence point, and the jaggy occurrence point is located at the center of the window. By comparing this pattern with a template pattern prepared in advance, a jaggy occurrence point can be detected. When the horizontal window size is 9, it is possible to improve four dots on the right side and four dots on the left side from the jaggy occurrence point. That is, a maximum of 8 dots is improved.

FIG. 7B is an explanatory diagram of the improvement rule. Consider fixing the dot just outside the window. This 2
A straight line connecting the centers of the two dots is drawn, the dot pitch is set to 1, and the distance between the center of the dot on the lower main scanning line and the straight line is used as a weight for the dot on the upper main scanning line. The distance between the dot center on the line and the straight line is assigned as a weight to the dot on the lower main scanning line. As a result, the weights for the eight dots on the upper main scanning line are 1/9, 2/9, 3/9, ..., 8/9 from the left, and the weights for the dots on the lower main scanning line are 8 / 9, 7/9, 6/9, ・ ・
・ It becomes 1/9.

FIG. 7C shows an output example of divided recording dots using this weighting. In the figure, the weight described in (b) is used so that the sum of the diameters of the two divided recording dots is determined to be equal to the diameter of the single recording dot. As a result, the diagonal jaggies are clearly reduced.

However, according to the second shape determination method described with reference to FIG. 7, when the dot diameter is not so large (140 μm or less) as compared with the dot pitch, the density near the jaggy generation point decreases, and the density of the line is reduced. There is a problem that is noticeable. Thus, the result of improving the density change to be small is the third divided recording dot shape determination method shown in FIG. FIG. 7A shows the jaggy occurrence points as in FIG. 7A.

In the third method shown in FIG. 8, the weight for each dot position on the upper and lower main scanning lines is determined as in the second method. To make the dot diameter larger than in FIG. 7, a factor a greater than 1 is multiplied.
FIG. 8C shows an output example of an improved image when a = 1.2.
In this case, since the sum of the diameters of the divided recording dots is 1.2 times the diameter of the single recording dot, the dot size of the divided recording dots is increased as a whole, and the density change is more conspicuous as compared with FIG. Is gone.

FIG. 9 is an explanatory diagram of the image quality improving effect by the third method. The figure shows the result of a subjective evaluation experiment on jaggies of a laser printer. Image quality is ultimately determined by human subjective judgment,
Subjective evaluation experiments were performed on 10 printer researchers using a single oblique line having a width of one dot recorded in an 80 mm frame as an evaluation image. Dot pitch is 80
The micron and dot diameter ranged from 80 to 240 microns.

The evaluation criteria for the image quality are as follows: 5: The difference is not known 4: The user understands but does not care 3: The user is not disturbed 2: The user is disturbed 1: The difference is very disturbing Is the reference image (a 150 micron wide line created by the same device as the evaluation image)
The evaluation image was compared with the evaluation image at a clear visual distance, and the image quality of the evaluation image was evaluated based on the reference image and the above-described five levels. Each image was randomly presented so as not to be in the order of image quality, for example, and the average value of the evaluation points of the subject was calculated for each evaluation target image. Inappropriate evaluation values whose evaluation points were reversed were excluded.

In FIG. 9, "no improvement" is an evaluation of the input image before jaggy improvement shown in FIG. Further, “improved” is an evaluation result for an image after the image quality has been improved using the third divided recording dot shape determination method described with reference to FIG. The angle in the figure indicates the angle formed by the oblique line with the main scanning direction. When moving 16 dots in the horizontal direction, the angle at which one dot moves up is 3.6 °, the angle at which the dot moves up by 8 dots, the angle at which one dot moves up is 7.1 °, the angle at which one dot moves up is four dots, and the angle at which one dot moves up is 14 ° Becomes

FIG. 9 shows that the image quality can be improved under any of the conditions by using the third method shown in FIG. 8, but the greatest improvement effect is obtained when the dot diameter is 110 to 150 microns. Have been. When the dot diameter is 200 microns or more, the density of the improved portion is lower than before the improvement, and the improvement effect is reduced.

FIG. 10 is an explanatory diagram of the fourth divided recording dot shape determination method. FIG. 7A shows a jaggy occurrence point in the input image. FIG. 10B is an explanatory diagram of a shape determination rule in the fourth method. In the fourth method, the square root of the weight determined by the second method described with reference to FIG. 7 is used as a new weight. As a result, in the fourth method, the image quality is improved so that the sum of the areas of the two divided recording dots becomes equal to the area of the original single recording dot, as shown in FIG. In this case, when the dot diameter is large, an improvement result that can be compared with the third method is obtained. However, when the dot diameter is small, the density of the improved portion increases, and the improvement effect is lower than in the third method. .

FIG. 11 is a comparison diagram of the improvement effect of the shape determination method. In the figure, the first method, that is, the method of making the width of the envelope of two divided recording dots constant, and the third method, that is, the method of making the sum of the diameters of two dots 1.2 times the diameter of a single recording dot And the fourth method, ie, a method in which the sum of the areas of two dots becomes equal to the area of a single recording dot, and a comparison between “no improvement”, ie, the case of the input image as it is.

In FIG. 11, the dot pitch is constant at 80 μm. From this result, when the dot diameter is generally 1.7 times or more the dot pitch, the first method or the fourth method can be used.
Below that, the use of the third method increases the improvement effect.

FIG. 12 is a system configuration block diagram of an embodiment of the image forming apparatus. This embodiment corresponds to an embodiment of the second invention for detecting the angle formed by the straight line of the jaggy portion with the main scanning direction.

In the figure, an image forming apparatus includes a bitmap memory 31 for storing input bitmap image data,
Line buffer memories 32a to 32m as a group of registers for temporarily holding data read serially from the bitmap memory 31, a register 33 for holding data cut out from these line buffer memories, and a register 33 Angle detector 34 for detecting the inclination of a jagged straight line from the bitmap image data obtained, a first dot diameter register 35 for holding the radius of a single recording dot manually designated, and the size of a laser beam of an exposure optical system to be described later. Diameter detector 36 for detecting the size of the laser beam, and an alarm detector 3 for sending an alarm signal when the size of the laser beam detected by the dot diameter detector 36 becomes, for example, equal to or smaller than a prescribed size.
7. Second radius indicating the radius of a single recording dot according to the size of the laser beam as the output of dot diameter detector 36
Dot diameter register 38, first dot diameter register 35
And a switch 39 for switching the output of the second dot diameter register 38, a dot interval register 40 for instructing the dot interval, that is, a dot pitch, a single recording dot radius, a dot interval, and a slope of a straight line including jaggies. The radius of the two recording dots was calculated from the equations (4) and (5) so that the diameter of the recording dot and the recording width in the sub-scanning direction of the two divided recording dots were equal. Dot shape calculation lookup table (LUT) 41 in which results are tabulated, dot shape calculation LUT 4
The laser drive driver 42 drives the laser in accordance with the output of No. 1 and an exposure optical system 43 for creating a latent image on an electrophotographic process.

The dot shape calculation LUT 41 is the same as that shown in FIG.
First divided recording dot shape determining means 8₁Equivalent to
In the second invention, other shape determining means
Step 8 _Two~ 8_nLUTs corresponding to are provided, respectively.
The output of the first or second dot diameter register is stored in the LUT.
Given one of the outputs of the n LUTs, the angle detection
Is output as dot diameter data in accordance with the output of the
You. Here, the dot shape calculation LUT 41 is the first dot.
Diameter register 35 or second dot diameter register 38
And the output of the dot interval register 40 and the output of the angle detector.
An address signal is formed from the output and the address signal.
It is configured to output the corresponding dot diameter data
It is a look-up table (LUT).

In FIG. 12, when image data is transferred from a printer external interface (not shown) to the bitmap memory 31 and a print command is output from the external interface, the bitmap data is sent to the line buffer memories 32a to 32m from the top of the page. Is done. The line buffer memories 32a to 32m are serial input registers. When bitmap data is taken into these registers (M), N bitmap data are taken out of each serial input register in parallel,
The data of the image area of the bitmap of N × M pixels is stored in the register 33.

The bitmap image data of N × M pixels cut out in the register 33 is input to the angle detector 34, and the inclination of the straight line is detected. When the first method is used, the detected angle, the dot diameter of the printer, and the dot interval determine the size of the dot to be divided in order to improve the linear jaggies as described above. Here, the dot interval of the printer is normally set in the dot interval register 40 at the time of factory shipment. The dot diameter of the printer is set in the first dot diameter register 35 at the time of shipment from the factory, or is set in the second dot diameter register 38 as a detection result of the dot diameter detector 36.

Actually, the angle of a straight line including a jaggy, the dot diameter of the printer, and the dot interval are determined by the dot shape calculation unit LUT.
41, and corresponding to them, the dot shape calculation LU
The dot diameter data of the divided recording dots stored in T41 is stored in the laser drive driver 42, read out in synchronization with the recording process of the exposure optical system 43 of the recording device, and read at a predetermined position with a predetermined dot diameter. Is used for modulation of the laser light source of the exposure optical system.

In FIG. 12, an angle detector 34 determines whether or not there is a straight line in a bitmap image of N × M pixels cut out to a register 33, and detects the angle if there is. Summarizing this detection method, U.
As is evident from the description of SP 4,847,641, the pixels of the input image are cut out with a mask of a predetermined size, compared with the angle detection pattern written in the ROM in advance, and the corresponding pattern is determined from the matched pattern. The angle is determined. That is, the angle detector 34 shown in FIG.
In the block diagram shown in FIG. 14, the angle detection ROM 341 stores angle detection patterns (a) to (f) as shown in FIG.
And the angle corresponding to each detection pattern is stored in the angle output ROM 342. When an N × M cutout image is input, the ENOR circuit of the pattern comparing unit 343 detects a match between the cutout image and the detection pattern. When this match is established, the pattern comparing unit 343 outputs a detection signal via an AND circuit. Output. The angle output ROM 342 outputs an angle corresponding to the detection pattern that matches the cut-out image. It should be noted that the counter 344 has an angle detection RO
This is an address counter for sequentially incrementing the corresponding address of M341 and the angle output ROM 342.

Next, the change in dot diameter by the laser driver 42 will be described. FIG. 15 is an example of the relationship between the light emission time and the dot diameter. The figure plots the 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. 16 shows an example of the relationship between the change in the light emission time, the exposure amount, and the dot shape. In the figure, it can be seen that the exposure amount changes according to the light emission time, and the dot diameter determined by the exposure amount required for development changes.

FIG. 17 is a block diagram showing the configuration of an embodiment of the laser driving driver. 12, a laser driving driver stores a dot diameter data memory 47 for storing dot diameter data output from the dot shape calculation LUT 41 in FIG. 12 in units of pixels, and a dot diameter data / for converting dot diameter data into laser emission time data. A shift register group 49 and a latch 50 for controlling the laser emission time based on the output of the emission time converter 48, the dot diameter data / emission time converter 48, a print clock 51 for instructing dot printing timing, and a shift register group 49. And a driver 54 for driving the laser 53.

FIG. 18 is a timing chart of the exposure control in FIG. Radius r on the main scanning line on the horizontal axis in FIG.
_The operation of hitting a dot diameter of ₀ , ₀ ,..., _R0 , _n will be described with reference to FIGS.

In FIG. 18, the print clocks C ₁ ,
In order to record dots of radii r ₀ , ₀ , r ₀ , ₁ , r ₀ , ₂ at C ₂ , C ₃ , first, the dot diameter data r ₀ , ₀ is stored in the dot diameter data memory 47 at print clock timing C _0. , And is converted by the dot diameter data / emission time converter 48 into emission time data. For dot diameter data r _{0, 0} is the largest dot diameter, as the emission time data is converted into level 7. In the case of the emission time at level 7, the dot diameter data / emission time converter 48 outputs "1" to all the shift registers 49a to 49g. Such correspondence between the light emission time data and the dot diameter data can be arbitrarily set by configuring the dot diameter data / light emission time converter 48 with a P-ROM or a ROM.

[0054] The output signal of the shift register 49a~49g is, depending on the timing P ₁ of the parallel load signal,
It is set in each shift register. After that,
In synchronization with the sub-clocks S ₁ , ₁ , S ₁ , ₂ ,..., The contents are vertically transferred in the direction from 49 g to 49 a in each shift register, and the contents of 49 a are sequentially output to the latch 50. Is done. The contents stored in the latch 50 are stored in the driver 54.
Is used for light emission of the laser 53.

At the timing C ₂ of the print clock, the dot diameter data memory 27 at the timing C ₁
Radius r _{0, 1} dot diameter data read from is converted into light emission time data, the result is a shift register 49a
Is parallel loaded in accordance with the timing P ₂ to ~49g. At this time, the dot diameter data r _{0, 1} is 1 level smaller as the light emitting time for a little less than the maximum dot diameter, the exposure time is 6/7 of the maximum exposure time.

Dot diameter data / light emission time converter 48
, Six shift registers 49a to 49f excluding 49g.
Is output to the sub clock S._Two,
₁, S _Two,_Two, ..., one after another in the vertical direction
And used for emission of the laser 53 through the latch 50.
You.

As an application of this embodiment, the dot diameter detector 36 shown in FIG. 12 always detects the size of the laser beam of the exposure optical system 43, and uses the dot diameter as the size of the above-mentioned single recording dot. Determine the shape of
The shape can be made to follow the fluctuation of the laser beam diameter.

In FIG. 12, this is realized by switching the switch 39 from the first dot diameter register 35 to the second dot diameter register 38. The dot diameter detector 36 is disposed at one end of the exposure optical system 43 in the main scanning direction of the laser beam, and measures the diameter of the laser beam each time the laser beam starts scanning one line. The measured laser beam diameter is held in the second dot diameter register 38 as a single dot diameter for one line scanning period,
It is used to output dot diameter data by the dot shape calculation LUT 41 via the switch 39.

At this time, the alarm detector 37 compares the laser beam diameter detected by the dot diameter detector 36 with the size of the laser beam diameter determined by the dot diameter data output from the dot shape calculation LUT 41 to obtain an actual value. An alarm signal is output when the laser beam diameter deviates from a predetermined value.

In the above description, the size of the dot is changed by controlling the laser emission time. However, the same effect can be obtained by controlling the laser drive voltage or drive current while keeping the emission time constant. Obviously you can get it. The present invention can be applied not only to the image forming apparatus but also to an image display apparatus such as a display.

[0061]

As described in detail above, according to the present invention, even if a low-resolution printer is used, an optimum image quality improving method can be applied according to, for example, the dot diameter and the dot pitch. Good image quality improvement comparable to that obtained by drawing a straight line with a printer having a high resolution can be realized.

[Brief description of the drawings]

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

FIG. 2 is a principle block diagram of the second invention.

FIG. 3 is a block diagram illustrating an overall configuration of the image forming apparatus according to the first invention.

FIG. 4 is a block diagram illustrating an overall configuration of an image forming apparatus according to a second invention.

FIG. 5 is an explanatory diagram of a first divided recording dot shape determination method.

FIG. 6 is a diagram for explaining in detail the dot size determination in the first method.

FIG. 7 is a diagram illustrating a second divided recording dot shape determination method.

FIG. 8 is a diagram illustrating a third divided recording dot shape determination method.

FIG. 9 is a diagram illustrating an image quality improvement effect obtained by a third shape determination method.

FIG. 10 is a diagram illustrating a fourth divided recording dot shape determination method.

FIG. 11 is a diagram showing a comparison of image quality improvement effects by each method.

FIG. 12 is a block diagram illustrating a system configuration of an embodiment of the image forming apparatus.

FIG. 13 is a block diagram of an angle detector.

FIG. 14 is a diagram showing an angle detector pattern.

FIG. 15 is a diagram showing a change in dot diameter according to a light emission time.

FIG. 16 is a diagram showing a change in an exposure amount and a dot shape according to a change in light emission time.

FIG. 17 is a block diagram illustrating a configuration of an embodiment of a laser driving driver.

18 is a timing chart of the exposure control in FIG.

FIG. 19 is a diagram illustrating an example of jaggies in an input image.

FIG. 20 is a diagram illustrating a conventional example of an image quality improving method.

[Explanation of symbols]

6 Single dot diameter specifying means 7 Dot interval specifying means 8 ₁ , 8 ₂ First, second,... Divided recording dot shape determining means 9, 11 Selecting means 10 Tilt detecting means 20 Page buffer or line buffer 21 Image cutout Unit 22 jaggy detection unit 23 ₁ , 23 ₂ , first, second,... Improvement unit 24, 29 selector 25 input panel 26 laser control circuit 27 laser optical system 28 jaggy detection and angle detection unit

Continuing on the front page (72) Inventor Jun Juno, Fujitsu Limited (1015, Uedanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture) (72) Inventor Tomohisa Mikami, 1015, Uedanaka, Nakahara-ku, Nakahara-ku, Kawasaki City, Kanagawa Prefecture (56) References JP-A-5-147261 (JP, A) JP-A-4-320862 (JP, A) JP-A-4-216077 (JP, A) JP-A-2-178067 (JP, A) JP-A Sho 61-263363 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H04N 1/409 B41J 2/435-2/52 H04N 1/23-1/29

Claims (6)

(57) [Claims] An apparatus for improving and outputting an input image, comprising: a single dot diameter specifying means (6) for specifying a size of a single dot in input image data; and a dot interval specification for specifying an interval between the single dots. Means (7), and a part of the single dot is reduced to 2
When dividing into dots arranged in the sub-scanning direction, the single dot diameter specifying means (6) and the dot interval specifying means (7)
Using the output of the first divided dot shape determining means (81) which determines the shape of the two divided dots using the output of ( ₁ ) and the output of the single dot diameter specifying means (6), The second,..., N-th divided dot shape determining means (8 ₂ ,...) For determining the shape of the two divided dots
.. 8 _n ) and any of the outputs of the first, second,..., N-th divided dot shape determining means (8 ₁ , 8 ₂ ..., 8 _n ) Image quality improvement in an image apparatus, comprising: selection means (9) for selecting according to a selection control signal input from the outside according to the size and interval of the image data and outputting the data as shape data of two divided dots. method. 2. An apparatus for improving and outputting an input image, comprising: a single dot diameter specifying means (6) for specifying the size of a single dot in the input image data; and a dot interval specification for specifying an interval between the single dots. Means (7), and a part of the single dot is reduced to 2
When dividing into dots arranged in the sub-scanning direction, the single dot diameter specifying means (6) and the dot interval specifying means (7)
Using the output of the first divided dot shape determining means (81) which determines the shape of the two divided dots using the output of ( ₁ ) and the output of the single dot diameter specifying means (6), The second,..., N-th divided dot shape determining means (8 ₂ ,...) For determining the shape of the two divided dots
.. 8n), an inclination detecting means (10) for detecting an inclination formed by the straight line of the jaggy portion with the main scanning direction from the input image data, and the first control signal outputted by the inclination detecting means (10). , The second,..., N-th divided dot shape determining means (8 ₁ , 8 _2, ..., 8 _n ), and outputs the data as the shape data of the two divided dots. An image quality improving method in an image apparatus, comprising: 3. The first divided dot shape determining means (8)
₁ ) determining the shape of the two divided dots such that the width of the two divided dots in the sub-scanning direction is equal to the diameter of the single dot. An image quality improvement method in the image device described in the above. 4. The second divided dot shape determining means (8)
₂ ) determining the shape of the two divided dots such that the sum of the diameters of the two divided dots in the sub-scanning direction is equal to the diameter of the single dot. Or an image quality improvement method in the image device according to 2. 5. The third divided dot shape determining means (8)
₃ ) determining the shape of the two divided dots such that the sum of the diameters of the two divided dots in the sub-scanning direction is equal to a constant (1) times the diameter of the single dot. 3. An image quality improving method in an image apparatus according to claim 1, wherein 6. The fourth divided dot shape determining means (8)
₄ ) determining the shape of the two divided dots such that the sum of the areas of the two divided dots in the sub-scanning direction is equal to the area of the single dot. Or an image quality improvement method in the image device according to 2.