JP2004007191A - Image processing mechanism - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reconcile the increase of the number of tones and process stability in a highlight part. <P>SOLUTION: In a Pulse Width Modulation mechanism in which a pulse shifted to either left or right and in dither processing, the growth origination side of a pixel which secondly grows up is arranged so as to be adjacent to a first growth pixel. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a patent for an electrophotographic image output apparatus having a printing mechanism for performing n-level gradation expression in one pixel, and relates to an image conversion process of an n-fold process at the time of outputting a gradation image. is there.
[0002]
[Prior art]
With the spread of electronic devices in general, personal computers, and the like, the peripheral devices have also been spreading.
[0003]
Similarly, a printer that outputs a processing result, which is one of peripheral devices, has been widely used.
[0004]
Generally, a conventional image output printing device such as an ink jet printer or a laser printer has a built-in computer.
[0005]
It communicates with an external device such as a host computer, receives commands, print data, and the like from the host computer, draws and develops a print image on a bitmap memory, and prints out.
[0006]
Improvements in computer hardware have made it possible to handle more complex data, and have more commonly handled color images. Along with this, colorization has been progressing even in a print output device.
[0007]
For this reason, it is important how to perform smooth gradation expression in various printing mechanisms.
[0008]
The same applies to a monochrome printing device.
[0009]
When the original data is color gradation data, even if the color information is lost, a satisfactory output result cannot be obtained with a printing apparatus which cannot perform gradation expression sufficiently.
[0010]
In gradation printing, generally, a printing mechanism that individually holds and separates pigments of all densities is an unrealistic amount in consideration of natural image output.
[0011]
Normally, the gradation expression in the printing mechanism is expressed by the area ratio between the printed portion and the non-printed portion of the primary color pigment.
[0012]
In some printing methods such as the electrophotography method, the non-linearity of the boundary between the drawing part and the non-drawing part corresponding to the dot gain in the printed matter is large, and it is difficult to express a gradation with a single pixel. .
[0013]
In such a printing method, gradation is expressed by the number of dots in a unit area in units of a plurality of pixel groups.
[0014]
However, even in image processing for performing gradation expression with a plurality of pixel groups, gradation expression in pixels is not wasted.
[0015]
In image processing such as shading, it is necessary to reduce the unit area of shading to make it visually inconspicuous, and for a printing mechanism having a printing mechanism with a resolution of about 1000 dpi or less, a gradation expression within a unit area is required. Can not hold a sufficient number of pixels.
[0016]
Therefore, when there is a gradation expression mechanism in a pixel, it is necessary to secure a sufficient gradation by using the gradation expression based on the number of dots per unit area.
[0017]
[Problems to be solved by the invention]
There are several methods for expressing gradation in a pixel. One of the methods relatively easily adopted in a scanning printing mechanism is a method of performing a PWM process in a pixel.
[0018]
However, the intermediate value pixel on which the PWM modulation has been performed is an isolated pixel on drawing.
[0019]
As described above, the boundary region between the drawing unit and the non-drawing unit is widened, and an unstable print output lacking in stability and linearity is generated.
[0020]
In order to avoid this, it is only necessary to draw a saturated drawing pixel on an adjacent pixel, that is, a pixel that is drawn over the entire area of the pixel.
[0021]
The boundary region between the drawing part and the non-drawing part is reduced, and drawing with improved stability and linearity can be expected.
[0022]
Such continuous drawing over a plurality of pixels can be realized by adding a phase control unit to the PWM modulation unit.
[0023]
However, when controlling the phase information in the gradation expression in the pixel, it is naturally necessary to prepare the information for the phase control for each pixel.
[0024]
However, if the extra information amount for phase control is converted to the number of gradations, the number of logical gradations is increased by two to four times.
[0025]
The amount of information per pixel is exclusively limited by the implementation of the memory capacity of the print image in the image generator. In general, the unit cost per bit of a semiconductor memory tends to decrease, but the printing resolution of a printing mechanism is improved and the product unit price is decreasing so as to offset this.
[0026]
From the viewpoint of cost, it is not easy to measure both the stability of the printing process and the ability to express gradation with a limited amount of information per pixel.
[0027]
[Means for Solving the Problems]
Therefore, in the present invention, as the PWM phase that grows in the pixel, the pixel growth of the PWM, which was conventionally a fixed central growth type or the phase control type, is performed by fixing all the pixels at one of the scanning start and end positions. I do.
[0028]
Then, image processing is performed to select an arrangement where at least the first pixel that grows first and the second pixel that grows next within the unit area are drawn continuously.
[0029]
Although it depends on the size of the halftone processing and the printing resolution, the density range in which the first pixel and the second pixel grow is a light density area close to paper white.
[0030]
For example, when halftone processing of about 200 lines is performed in a printing mechanism of 600 dpi, the drawing area is about 20% when the second pixel has completely grown.
[0031]
In the present invention, image processing is performed with the above-described arrangement with emphasis placed on the stability of the characteristics of the light density portion.
[0032]
The first growth pixel and the second growth pixel when the halftone processing is performed grow continuously and are stable in process.
[0033]
This is the same stability as in the case where the phase control is performed, and the same number of gradations as when the phase control is not performed can be secured.
[0034]
By using only one growth direction, it is natural that the intermediate value pulse is arranged with a larger gap in comparison to the rigid pulse of the central growth.
[0035]
However, since an arrangement in which drawing is continuous in such a light-density expression is selected, the occurrence of such an unfavorable arrangement in the process surface exists in a medium-to-high-density region where the drawing region is wide. .
[0036]
In the medium to high density region, a plurality of pixels are already drawn in a saturated state, and the density contribution of such an intermediate pulse is relatively small as the area of the drawing region.
[0037]
In addition, the stability of the process from the medium density to the high density area in electrophotography is not a problem in image quality because factors other than such fine texture arrangement are greatly involved.
[0038]
BEST MODE FOR CARRYING OUT THE INVENTION
[First embodiment]
FIG. 1 shows a configuration example of the first embodiment of the present invention.
[0039]
100 is a printing mechanism.
[0040]
Reference numeral 200 denotes an image forming unit.
[0041]
110 is an optical modulator.
[0042]
Reference numeral 111 denotes a laser element as a light source for forming a latent image on the photoconductor.
[0043]
110 adjusts the pulse width of the drive signal of the light source for each pixel according to the input data.
[0044]
In the present embodiment, the input of the image modulating unit is 4 bits, and a 16-value pulse width including non-light emission and full lighting is output based on the control input, and given to 111.
[0045]
Reference numeral 112 denotes an optical scanning system.
[0046]
Optical scanning scans the optical axis.
[0047]
Since it is easier to change the trajectory of the optical axis than to physically move the light source itself, the light source that requires physical connection is fixed, and the optical axis moving means 112 is prepared, and the light irradiation position is adjusted. Scanning is performed by moving.
[0048]
The output paper itself is conveyed, and the corresponding photoconductor also rotates.
[0049]
Therefore, since it is sufficient to scan only in one axis direction, 112 may be constituted by a linear scanning mechanism such as a polygon mirror.
[0050]
Reference numeral 113 denotes an optical system.
[0051]
The scanning of the polygon mirror or the like is a straight line, but is not a uniform scanning.
[0052]
It is not technically ready to draw pixels of the same size at each scanning position in non-constant speed scanning.
[0053]
Therefore, a system for performing correction so as to scan at a constant speed is required.
[0054]
113 realizes constant-speed scanning.
[0055]
The output of 111 is scanned by 112, and the guidance and correction of the optical axis are performed by 113 so as to scan the photoconductor at a constant speed.
[0056]
Reference numeral 114 denotes a photoconductor.
[0057]
The latent image of the charge optically drawn on the photoreceptor is developed by toner in a developing system (not shown), transferred to a sheet, and output.
[0058]
In this figure, a schematic view of the optical system of the printing mechanism is shown, and a developing unit, a fixing unit, a control system, and the like are omitted.
[0059]
210 is a page memory.
[0060]
In physical mounting, it is secured in a partial area of the main memory.
[0061]
In the present embodiment, the page memory is assigned information of 4 bits per pixel. The information in the page memory is read in accordance with the timing signal generated by the printing mechanism, and the data is output to the printing mechanism 110.
[0062]
If the data of 210 cannot be output to 110 in accordance with the timing at which the printing mechanism occurs, buffering is performed by FIFO or the like as necessary.
[0063]
Further, in order to save the memory capacity, there is a case where the whole 210 is partially expanded without being expanded at the same time.
[0064]
Reference numeral 220 denotes a drawing mechanism.
[0065]
The image information is developed on 210 according to the control information from the external device.
[0066]
The actual physical configuration includes a CPU, a ROM, hardware, and the like.
[0067]
However, the CPU and the ROM are shared for uses other than the drawing mechanism.
[0068]
Reference numeral 221 denotes a halftone cell for expressing gradation.
[0069]
When the image information is developed on 210, the halftone cell is referred to.
[0070]
The group to be referred to in the halftone cell is selected according to the coordinates of the pixel to be written on 210, the density information is converted into pulse width information, and written on 210.
[0071]
The holding groups in the halftone cell have different values, and if uniform density information is developed in a wide area, a repeated texture of the halftone cell cycle is developed as pixel information on the page memory.
[0072]
In FIG. 1, there is only one 221. However, in the case of a multi-color printer or a configuration having a plurality of print modes, a plurality of halftone cells are selectively used.
[0073]
FIG. 2 shows the correspondence between the input value and the pulse width in the light modulation unit.
[0074]
The optical modulator performs pulse modulation corresponding to the input value and the pulse width having the relationship shown in FIG.
[0075]
That is, in the present embodiment, the pulse waveform extends from the pixel start side to the pixel end side.
[0076]
The pulse width increases as the input value increases.
[0077]
Depending on the configuration of the laser element and the drive circuit, the drive time and the laser emission time do not always correspond linearly, and the width of each pulse does not necessarily increase at equal intervals in order to perform correction, but at least for the input value. In other words, the pulse width is designed to increase monotonically.
[0078]
Reference numeral 231 denotes an interface with an external device.
[0079]
Reference numeral 232 denotes a printing language interpreting unit that interprets a command group from an external device and calculates an image to be generated.
[0080]
In an actual physical configuration, similarly to 220, it is configured by a CPU, a ROM, hardware, and the like.
[0081]
FIG. 3 shows the order of pixel growth in the halftone cell.
[0082]
In the present embodiment, the size of the halftone cell is shown as 4 × 4.
[0083]
As the input density value increases, the values are sequentially drawn in numerical order.
[0084]
The gradation information of the image is assumed to handle 256 values from 0 to 255.
[0085]
The number of gradations that can be represented by each pixel is 16 values.
[0086]
In order to make the input data correspond to 16 units, 15 events are required per pixel.
[0087]
FIG. 4 shows a table of halftone cells which indicates how many individual pulse widths of individual pixels are selected for more than one input value.
[0088]
As is clear from FIG. 4, in the order shown in FIG. 3, a value is set at which the growth of the next pixel does not start until the previous pixel is saturated.
[0089]
Thus, when the same density is given in the halftone cell, the first growth pixel and the second growth pixel are always drawn continuously, and the process stability of electrophotography is ensured.
[0090]
When the modulation shown in FIG. 2 is performed according to the correspondence between the density and the output value in the fourth box, the drawing texture grows as shown in FIG.
[0091]
Here, the values when the density input values are 14 to 18 are shown. This is a density range in which all the first growth pixels are turned on when the conversion as shown in FIG. 4 is performed and the start of the second growth pixels starts.
[0092]
As shown in FIG. 5, the second growth pixel is arranged so that the growth start side is adjacent to the first growth pixel.
[0093]
The texture for the density expression continuously spreads as the expression density increases.
[0094]
In the case of the conventional method in which the growth start of the pulse of the PWM modulation is at the center, the drawing regions are separated as shown in the center growth of FIG.
[0095]
Further, in the printing mechanism in which the pulse growth start point starts from any end, when the arrangement as in the present invention is not adopted, the drawing area is separated from the light density area as shown in FIG.
[0096]
The laser beam actually has a Gaussian distribution spread with respect to the optical axis. In such a small area drawing, an image is unstable in fixing because the photosensitive member is not charged sufficiently enough to stably adhere the toner.
[0097]
FIG. 4 shows a correspondence table between the input density and the output pattern for easy understanding. However, in actual circuit processing or a program system, processing numerical values in a range becomes complicated. -1) is set, and the output value is determined depending on whether it is more than twice or less.
[0098]
The texture pattern that can be represented is determined by the size of the halftone cell and the number of gradation representations of each pixel.
[0099]
Even with the size of the halftone cell and the number of gradation representations of each pixel in the present embodiment, the texture pattern itself that can be represented is enormous.
[0100]
However, as the textures to be assigned to specific densities, select a pattern that causes the movement of the texture such that when the density increases, the area that was drawn at a certain low density is not drawn when drawn at a higher density. In such a case, the movement of halftone dots, the phenomenon of density inversion, and the like are likely to occur, which causes deterioration of print quality.
[0101]
Also, the algorithm for converting the input density into the output value becomes complicated.
[0102]
To prevent this, a condition is usually imposed that the texture corresponding to a certain density step includes all textures of lower density.
[0103]
This makes it difficult for process instability such as halftone dot movement and gradation inversion to occur, but drastically reduces the number of usable textures.
[0104]
In the present embodiment, a growth pattern with such restrictions is selected.
[0105]
When such constraints are set, the number of texture patterns determined by the gradation expression power per pixel and the halftone cell in the present embodiment is 241 patterns, which is less than 256. The same texture.
[0106]
Although the linear assignment is performed in the table of FIG. 4, the number of textures that can be used to correct the non-linearity due to various factors in the printing process actually decreases further.
[0107]
This is, of course, the case when the same density value is given to all the halftone cells, and since the halftone cell processing is performed pixel-independently, when the density is changed in the halftone cell, it differs. Texture will result.
[0108]
The image is developed on the page memory. The holding table of the halftone cell is selected according to the coordinates of the pixel.
[0109]
The pulse width information is written on the memory by comparison with the event.
[0110]
Up to this point, the 256-level gradation information is converted into 16-level pulse width information on which halftone processing has been performed.
[0111]
When the drawing is completed, the developed pulse width information is sequentially transmitted to the printing mechanism.
[0112]
The transmitted pulse width information modulates the optical output, resulting in an optical output that matches the pulse width information.
[0113]
The latent image drawn on the photoconductor by the optical system is developed, transferred and fixed on output paper, and discharged as a print output.
[0114]
In the configuration of the present embodiment, the simplest single-color printing mechanism is taken as an example, but it is of course possible to realize a multi-color printing mechanism.
[0115]
[Second embodiment]
The second embodiment shows the arrangement of halftone cells in the LED array electrophotographic system.
[0116]
The scanning direction of the array head system coincides with the paper conveyance.
[0117]
Therefore, the lighting waveform of each pixel is, for example, as shown in FIG.
[0118]
In the present embodiment, the pulse grows from below.
[0119]
In the printing mechanism having such a pulse waveform, when the size of the halftone cell is 4 × 4, a growth order as shown in FIG. 8 is selected.
[0120]
By setting the growth order of FIG. 8 and a value such that the growth pixel before the start of each growth pixel is saturated and the growth is started, when the same density is supplied into the halftone cell, As in the case of the first embodiment, the drawing of the first growth pixel and the drawing of the second growth pixel are always continuous.
[0121]
【The invention's effect】
According to the present invention, it is possible to increase the printing stability of a light color area without reducing the amount of information allocated to the number of logical gradations, and to improve the image quality of a printing output.
[Brief description of the drawings]
FIG. 1 is a configuration example of a first embodiment of the present invention.
FIG. 2 shows a correspondence between an input value and a pulse width in an optical modulation unit.
FIG. 3 shows a pixel growth order in a halftone cell.
FIG. 4 is an output conversion table of a density and a halftone cell.
FIG. 5 is an example of a texture growth pattern of a first growth pixel and a second growth pixel.
FIG. 6 is an example of a conventional texture growth pattern.
FIG. 7 is an example of FWM drawing in an array type printing mechanism.
FIG. 8 shows a pixel growth order in a halftone cell according to the second embodiment.
[Explanation of symbols]
100 printing mechanism.
Reference numeral 200 denotes an image forming unit.
Reference numeral 110 denotes a light modulation unit.
111 is a laser element of a light source for forming a latent image on the photoconductor.
112 Optical scanning system.
113 optical system.
114 photoconductor.
210 page memory.
220 Drawing mechanism.
221 A halftone cell for gradation expression.
231 is an interface with an external device.
232 Language interpreter.

Claims (1)

In a configuration including a printing mechanism that performs a plurality of gradation expressions in one pixel,
In image processing corresponding to a printing mechanism having a control means for performing by changing the light emission amount of the individual pixel by changing the light emission time,
In a printing mechanism, wherein a pixel growth start point starts from one of a scan start end and a scan end end,
Image processing for expressing gradation by combining multiple pixels.
An image processing apparatus having image processing, wherein an arrangement of a second growth pixel adjacent to a first growth pixel is made adjacent to the first growth pixel at a growth start position in the pixel.

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