JPH04326854A - Binary image forming device - Google Patents

Abstract

PURPOSE:To form a not-crushed image by reducing the diameter of a dot in the case of the image having a narrow dot interval, to form a thick and clear image by enlarging the dot diameter in respect to the image having the wide dot interval and to obtain the satisfactory reproducibility of the half tone image. CONSTITUTION:Binarizing attention pixel data and binarizing peripheral pixel data adjacent to the binarizing attention pixel data are stored in a binary signal storage circuit 41, and a distance from the binarizing attention pixel data to preceding/following printing bits is counted by a front counter 42 and a rear counter 43. A dot size judgement circuit 44 decides a beam diameter based on the distance information, and a pulse generating circuit 45 variably controls the pulse width of an ON signal so as to variably controls the beam diameter.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a binary image forming apparatus such as a laser printer that expresses characters or halftone images based on binary signals of print bits or non-print bits.

0002

[Prior Art] A laser printer charges the surface of a photoreceptor drum and controls the on/off state of a laser diode based on a binary signal consisting of print bits and non-print bits. A laser beam is reflected by a rotating optical system polygon mirror to sequentially scan the charged surface of the photoreceptor drum to form an electrostatic image by exposure, which is developed with toner and then transferred to paper. For binary image data as shown in (a) of FIG. 1 (hatched areas are pixels of print bits, unhatched areas are pixels of non-print bits), an actual printed image as shown in (b) of the same figure is obtained. In other words, the actual print size of one dot is made larger than the size of one pixel in order to prevent white streaks from occurring between pixels of consecutive print bits due to tilting of the polygon mirror in the optical system or jitter in the paper transport system. The laser beam diameter was increased so that

However, binary image forming apparatuses having such output characteristics have the disadvantage that good gradation reproducibility cannot be obtained when forming pseudo-halftone images such as photographic images. .

FIG. 12 shows the output characteristics of a binary image obtained by dithering using a well-known Bayer dithering matrix to obtain pseudo-halftones. In other words, the image was binarized using a 16-gradation Bayer dithering matrix. At gradation levels higher than the 8th gradation, the density of the output image is saturated and becomes an almost solid black image, resulting in a dark image with poor gradation reproducibility.

Therefore, conventionally, the binarized pixel data of interest and the
By referring to a plurality of binarized surrounding pixel data located around the binarized pixel data of interest, one dot for the binarized pixel data of interest is determined based on the arrangement pattern of print bits and non-printing bits of the binarized surrounding pixel data. A technique is known that improves the gradation reproducibility of a binary image by varying the actual print size of the image. (Refer to Japanese Unexamined Patent Publication No. 124667/1983)

[0006]

However, in this prior art, a memory is required to hold the binary signal of one line of binarized target pixel data as well as the binary signals of several lines before and after it, and the memory capacity is large. There was a problem that the size and cost would increase. In addition, 1 for the binarized pixel data of interest.
There was also the problem that the conditions for determining the actual print size of the dots were complicated, making it difficult to increase the processing speed.

Accordingly, the present invention makes it possible to variably control the actual print size of one dot for binary data of interest using a small memory capacity and through simple determination processing, thereby making it possible to easily obtain a binary image with excellent gradation reproducibility. The present invention aims to provide a binary image forming apparatus.

[0008]

[Means for Solving the Problems] The present invention refers to binary pixel data of interest and a plurality of binary peripheral pixel data adjacent to the binarized pixel data of interest on the same line. 2. Expressing a halftone image by varying the actual print dot size for the pixel data of interest depending on the data state.
In the value image forming apparatus, 2
A distance detection means for detecting the distance to a print bit of the digitized peripheral pixel data, and a dot for variably controlling the actual print size of one dot of the binarized target pixel data based on the distance information detected by the detection means. and size variable control means.

Further, dot position variable control variably controls the output position of one dot of binarized target pixel data based on the distance information detected by the distance detection means and the dot size information determined by the dot size variable control means. It is an additional means.

0010

[Operation] With the present invention having such a configuration, the binarized pixel data of interest and the binarized peripheral pixel data adjacent to the binarized pixel data of interest on the same line are extracted, and the binarized pixel data is The distance from the pixel data of interest to the print bit of the binarized peripheral pixel data is detected. Then, based on the distance information, the actual print size of one dot of the binarized target pixel data or the actual print size and print position are variably controlled.

[0011]

Embodiments Hereinafter, embodiments in which the present invention is applied to a laser printer will be described with reference to the drawings.

FIG. 1 is a block diagram of a laser printer, in which a drum unit 2 is provided approximately in the center of a housing 1. As shown in FIG. The drum unit 2 includes a photoreceptor drum 3 whose surface is formed of a photoreceptor. This photoreceptor drum 3 is driven to rotate in one direction clockwise in the figure, and around this photoreceptor drum 3 there is a charger 4 that charges the surface of the photoreceptor drum 3 according to an electrophotographic process. A laser scanner unit 5 that irradiates the surface of the photoreceptor drum 3 charged by the charger 4 with a laser beam to record information by exposure, and the exposed photoreceptor drum 3
A developing device 6 that attaches toner as a developer to the surface of the photoreceptor drum 2, a transfer charger 7 that transfers the toner image formed on the surface of the photoreceptor drum 2 to the conveyed paper, and a cleaning device 8 that removes toner from the photoreceptor drum 3. , photosensitive drum 3
A drum unit is constructed by sequentially arranging static elimination lamps 9 for eliminating static electricity.

The transfer charger 7 is located below the photosensitive drum 3, and a pickup roller 11 moves paper toward the transfer charger 7 from a paper feed cassette 10 attached to one side of the housing 1. are transported one by one at a predetermined timing.

The toner image on the photoreceptor drum 2 is transferred to the conveyed paper by the transfer charger 7, and the toner image is thermally fixed by the fixing device 12.
It is designed to be discharged outside.

Here, a drive motor 14 is provided in the housing 1 as a common drive source for the paper transport mechanism and the rotation mechanism for the photosensitive drum 3. Further, inside the housing 1, a fan 15 for discharging internal heat to the outside,
An interlock switch 16, a power supply device 17, and the like are provided to detect the opening of the casing 1 and turn off the power.

FIG. 2 is a block diagram showing the main circuit configuration.
21 is a processor constituting the main body of the control unit; 22 is a communication interface that receives binary signals of image data sent from the host device via the transmission line 23; and 24 is a binary signal received by the communication interface 22. 25 is the video RAM for storing 1 page in units of pages.
A video signal output circuit reads the binary signal stored in M24 and sends it to the laser scanner unit 5, and these are connected by a bus line 26.

The laser scanner unit 5 includes a laser oscillator 27 that emits a laser beam, and a laser oscillator 2 that emits a laser beam.
a laser control circuit 28 that controls on/off and the beam diameter of the laser beam from 7; a start sensor 29 consisting of a PIN diode, etc. that detects the start position of the laser beam; and a polygon motor drive circuit that rotationally drives the polygon mirror 30. 31 and a PLL control circuit 32 that controls the motor rotation speed by this drive circuit 31.

The laser control circuit 28 stores the binarized target pixel data in the central area X as shown in FIG. A binary signal storage circuit 41 that stores peripheral pixel data in corresponding peripheral areas X1, X2, X3 and Y1, Y2, Y3, and this binary signal storage circuit 4.
When the binarized pixel data of interest stored in the central area 2 stored in the central area X of the binary signal storage circuit 41
When the digitized target pixel data is a print bit, a backward counter 43 counts the number of bits to the closest print bit in the binary peripheral pixel data behind the binarized target pixel data, and both counters 42 , 43, a dot size determination circuit 44 that determines the actual print size of one dot of the binarized target pixel data based on each count value of 43;
A pulse generation circuit 45 that variably controls the laser beam diameter by modulating the pulse width of the ON signal to the laser oscillator 27 according to the determination result of the dot size determination circuit 44
and is provided.

The dot size determination circuit 44 has a condition table 50 shown in FIG. 4, and determines the actual print size of one dot of the binarized target pixel data according to the contents of the condition table 50. There is. That is, when the count value of at least one of the front counter 42 and the rear counter 43 is "2", the small dot size is determined to be approximately equal to the size of one pixel, and in other cases, it is determined to be larger than the size of one pixel. Decide on a large dot size.

On the other hand, when the pulse width of the ON signal when the beam diameter is determined to be a large dot size is 1, the pulse generating circuit 45 generates the same pulse width when the beam diameter is determined to be a small dot size. For example, the laser beam diameter is variably controlled by modulating it to 3/5.

Here, the front counter 42 and the rear counter 43 constitute distance detecting means for detecting the distance from the binarized target pixel data to the print bit of the binarized surrounding pixel data. Further, the dot size determination circuit 44 and the pulse generation circuit 45 constitute dot size variable control means for variably controlling the actual print size of one dot of the binarized target pixel data based on the distance information detected by the distance detection means. do.

In the present embodiment having such a configuration, a binary signal corresponding to one page of image data stored in the video RAM 24 is sequentially read out from the first bit under the control of the processor 21, and is sent to the video signal output circuit 25. The signal is supplied to the laser control circuit 28 of the laser scanner unit 5 through the laser scanner unit 5. In the laser control circuit 28, an on-pulse is output to the laser oscillator 27 every time the print bit (1) is supplied, and a laser beam is generated from the laser oscillator 27 while this on-pulse is being input. The laser beam thus generated is incident on the polygon mirror 30 and reflected, and reaches the surface of the photoreceptor drum 3, which is charged by the charger 4, and the area where the beam reaches is exposed. Here, the beam diameter of the laser beam generated from the laser oscillator 27 is variably controlled by the laser control circuit 28.

Specifically, each time a print bit is supplied to the laser control circuit 28 via the video signal output circuit 25, the print bit is converted into binarized pixel data of interest, and the bit is converted into binarized pixel data of interest. Three bits before and after the same line are stored in the binary signal storage circuit 41 as binary peripheral pixel data. Then, the forward counter 42 counts the number of bits to the nearest print bit among the binary peripheral pixel data located ahead of the binary pixel data of interest, and the backward counter 43 counts the number of bits up to the nearest print bit. The number of bits up to the nearest print bit in the binary peripheral pixel data located after the pixel data is counted.

As a result, if at least one of the number of bits counted by the front counter 42 and the number of bits counted by the rear counter 43 is "2", the beam diameter is determined to be small dot size; In this case, the beam diameter is determined to be a large dot size.

In the case of a large dot size, the pulse width of the ON signal to the laser oscillator 27 is modulated long, and in the case of a small dot size, the same pulse width is modulated short,
The laser beam diameter is variably controlled.

For example, in the case of FIG. 5(a), the count value of the front counter 42 is "1" and the count value of the rear counter 43 is also "1", so the large dot size is determined as the laser beam diameter, and as shown in the figure. A black dot larger than the size of one pixel is drawn on the paper. In addition, in the case of FIG. 5(b), since the count value of the rear counter 43 is "2", a small dot size is determined as the laser beam diameter, and a black dot approximately equal to the size of one pixel is drawn on the paper as shown in the figure. be done. In the cases of FIGS. 5(c) and 5(d), the count value of the front counter 42 is "2" (in the case of FIG. 5(d), the count value of the rear counter 43 is also "2").
''), a small dot size is also determined as the laser beam diameter, and a black dot approximately equal to the size of one pixel is drawn on the paper as shown in the figure.

Now, suppose that the binary signal shown in A in FIG. 3 is supplied to the laser beam control circuit 28 via the video signal output circuit 25 as part of one line of image data.
The beam diameter of the laser beam generated by the laser oscillator 27 is variably controlled as shown in FIG.

In other words, when the interval between the adjacent print bits for the binarized pixel data of interest is narrow, the laser beam diameter for the binarized pixel data of interest becomes small, and the white areas between black dots become large. Become. As a result, an image without distortion can be obtained even in areas where black dots are densely packed.

On the other hand, if the interval between the print bits adjacent to the binarized pixel data of interest is wide or there is no interval, the laser beam diameter for the binarized pixel data of interest becomes large. As a result, for an image such as a line drawing in the sub-scanning direction or the main scanning direction, a clear image that is thick and free of white streaks etc. can be obtained.

FIG. 6 shows an example of gradation characteristics when an image obtained by dithering to obtain pseudo halftones is processed using the well-known Bayer type dither matrix in the binary image forming apparatus of this embodiment.
Shown below. As is clear from the figure, the density of the output image is not saturated even at a relatively high gradation level, and it has good gradation reproducibility.

As described above, according to this embodiment, by simply providing a small storage area for storing the binarized pixel data of interest and the 3 bits of binarized peripheral pixel data before and after it, the binarized pixel data of interest can be stored. The actual print size of one dot can be variably controlled, and a binary image with excellent gradation reproducibility can be easily obtained. Moreover, the actual print dot size can be determined by a simple process of counting the number of bits from the binarized target pixel data to the print bit in the neighboring binarized peripheral pixel data, enabling high-speed processing. become,
Printing speed can be increased.

Although this embodiment shows an example in which the dot size of actual printing is variably controlled by modulating the pulse width of the ON signal to the laser oscillator 27, the present invention is not limited to this. The dot size of actual printing may be variably controlled by adjusting the intensity of the dot. Further, in this embodiment, the laser beam diameter is variably controlled into two types, large and small, but it is also possible to variably control it into three or more types.

FIGS. 7 and 8 show the laser beam diameters of large, medium, and
This shows a modification of the above-mentioned embodiment in which three types of dot sizes are used; that is, a condition table 51 shown in FIG. 7 is set in the dot size determination circuit 43. Further, the pulse generating circuit 45 sets the pulse width to 1 when the beam diameter is determined to be a large dot size, and increases the pulse width to 3/5 when the beam diameter is determined to be a small dot size, for example, to a medium dot size. When the beam diameter is determined to be, for example, the beam diameter is configured to be modulated to 4/5.

By doing this, the front counter 4
Number of bits counted by 2 and backward counter 43
At least one of the number of bits counted by
”, the beam diameter is determined to be small dot size, and 1
A black dot approximately equal to the size of the pixel is drawn on the paper ((b) in FIG. 8 corresponds to this). In addition, both counters 42,
At least one of the 43 bit numbers is “3” and the other is “2”.
'', the beam diameter is determined to be a medium dot size, and a black dot slightly larger than the size of one pixel is drawn on the paper ((c) in FIG. 8 corresponds to this). On the other hand, in other cases, the beam diameter is determined to be a large dot size, and a black dot larger than the size of one pixel is drawn on the paper (
(a) in FIG. 8 corresponds to this). Next, other embodiments of the present invention will be described.

Note that this other embodiment differs from the previous embodiment in that a part of the function of the laser control circuit 28 is changed. Therefore, the same parts as in the previous embodiment are given the same reference numerals, and detailed explanation thereof will be omitted.

FIG. 9 is a functional block diagram of the laser control circuit 28 in another embodiment. That is, in this other embodiment, the laser control circuit 28 includes the same binary signal storage circuit 41, front counter 42, rear counter 43, and dot size determination circuit 44 as in the previous embodiment, and the front counter 42 and rear counter 43. a dot position determination circuit 46 that determines the output position of one dot of the binarized target pixel data based on each count value and the dot size information determined by the dot size determination circuit 44, and the dot size determination circuit 44 and A pulse generation circuit 45A is provided which modulates the pulse width of the ON signal to the laser oscillator 27 according to the determination result of the dot position determination circuit 46, and variably controls the laser beam diameter and its output position by shifting the pulse rising position. There is.

Here, the dot size determination circuit 44 has a condition table 51 shown in FIG. 7, and according to the contents of this condition table 51, the actual print size (large, large, (middle, small).

On the other hand, if the dot size determined by the dot size determination circuit 44 is a large dot size, the dot position determination circuit 46 changes the output position of one dot to 1 regardless of the count values of both counters 42 and 43. Determine the center of the pixel. Furthermore, if the dot size determined by the dot size determination circuit 44 is a medium dot size, both count values are compared, and if both are "3", the output position of one dot is determined to be the center of one pixel. , if only the count value of the front counter 42 is "3", it is determined that the position is one pixel to the right, and only the count value of the rear counter 43 is "3".
”, it is determined to be one pixel to the left. Furthermore, if the dot size determined by the dot size determination circuit 44 is a small dot size, both count values are compared, and if both are "2", the output position of one dot is determined to be the center of one pixel. , only the count value of the front counter 42 is "
If it is "2", it is determined to be one pixel to the right, and if only the count value of the rear counter 43 is "2", it is determined to be one pixel to the left.

Further, the pulse generating circuit 45A determines that the beam diameter is determined to be a small dot size when the pulse width of the ON signal is 1 when the dot size determination circuit 44 determines the beam diameter to be a large dot size. The same pulse width when the beam diameter is determined to be a medium dot size is modulated to, for example, 2/5, and the same pulse width when the beam diameter is determined to be a medium dot size is modulated to, for example, 3/5 to variably control the laser beam diameter. When the determination circuit 46 determines that the output position of one dot is the center position, the pulse of the on signal is raised so that the center of the pulse coincides with the center when the pulse width = 1, and when the output position of one dot is determined to be on the right side, the pulse is increased. The pulse of the ON signal is raised so that the falling edge of the signal matches the falling edge of the pulse when the pulse width is 1, and when the left position is determined, the rising edge of the pulse is made to match the rising edge of the pulse when the pulse width is 1. The output position of the laser beam is variably controlled by raising the ON signal pulse.

Here, the dot position determination circuit 46 and the pulse generation circuit 45A determine the position of one dot of the binarized target pixel data based on the distance information detected by the distance detection means (front counter 42 and rear counter 43). A dot position variable control means for variably controlling the output position is configured.

In another embodiment of such a configuration,
The dot size determination circuit 44 determines the actual printing size of one dot for the binarized target pixel data, and the dot position determination circuit 46 determines the output position of the dot, and the pulse generation circuit 45A outputs the laser according to the determined information. An on-pulse is supplied to the oscillator 27 to generate a laser beam.

For example, FIGS. 10(a), (d), (m), (
In the case of p), since the count values of the front counter 42 and the rear counter 43 are both other than "2" or "3", it is a large dot pulse and the output position is at the center, and the paper has one pixel as shown in the figure. A black dot larger than one pixel is drawn at the center position.

In the case of FIGS. 10(b), (j), and (m), the count value of the rear counter 43 is "2" and the count value of the front counter 42 is other than "2", so it is a small dot pulse and The output position is shifted to the left, and a black dot smaller than the size of one pixel is drawn on the paper to the left of one pixel as shown.

In the case of FIGS. 10(c) and 10(o), the count value of the rear counter 43 is "3" and the count value of the front counter 42 is other than "2" and "3", so it is a medium dot pulse and The output position is shifted to the left, and a black dot approximately equal in size to one pixel is drawn on the paper to the left of one pixel, as shown in the figure.

In the case of FIGS. 10(e), (g), and (h), the count value of the front counter 42 is "2" and the count value of the rear counter 43 is other than "2", so it is a small dot pulse and The output position is shifted to the right, and a black dot smaller than the size of one pixel is drawn on the paper to the right of one pixel as shown.

In the case of FIG. 10(f), since the count values of the front counter 42 and the rear counter 43 are both "2", it is a small dot pulse and the output position is the center position, and as shown in the figure, there are 1 A black dot smaller than the size of one pixel is drawn at the center of the pixel.

In the case of FIGS. 10(i) and (l), the count value of the front counter 42 is "3" and the count value of the rear counter 43 is other than "2" and "3", so it is a medium dot pulse and The output position is shifted to the right, and a black dot approximately equal in size to one pixel is drawn on the paper to the right of one pixel, as shown in the figure.

In the case of FIG. 10(k), since the count values of the front counter 42 and the rear counter 43 are both "3", it is a medium dot pulse and the output position is the center position, and as shown in the figure, there are 1 dots on the paper. A black dot approximately equal in size to one pixel is drawn at the center of the pixel.

Now, suppose that the binary signal shown in A in FIG. 9 is supplied to the laser beam control circuit 28 via the video signal output circuit 25 as part of one line of image data.
The beam diameter of the laser beam generated by the laser oscillator 27 is variably controlled as shown in FIG. In this way, the same effects as in the above embodiment can be achieved in other embodiments as well.

Note that in other embodiments as well, it is possible to variably control the laser beam diameter and output position by adjusting the intensity of the ON signal to the laser oscillator 27.

Furthermore, the present invention is not limited to laser printers, but can of course be applied to thermal printers, inkjet printers, etc. that reproduce halftone images such as characters and photographs based on binary signals. .

[0052]

Effects of the Invention As detailed above, according to the present invention, the actual print size of one dot for binarized data of interest can be variably controlled with a small memory capacity and simple determination processing, resulting in excellent gradation reproducibility. Easy to obtain binary images2
A value image forming device can be provided.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a laser printer that is an embodiment of the present invention.

FIG. 2 is a block diagram showing the main circuit configuration of the same embodiment.

FIG. 3 is a functional block diagram of a laser control circuit in the same embodiment.

FIG. 4 is a diagram showing a condition table in the same embodiment.

FIG. 5 is a diagram used to explain the operation of the same embodiment.

FIG. 6 is a gradation characteristic diagram of an output image in the same example.

FIG. 7 is a diagram showing a condition table in a modification of the same embodiment.

FIG. 8 is a diagram used to explain the operation of the above modification.

FIG. 9 is a functional block diagram of a laser control circuit in another embodiment of the present invention.

FIG. 10 is a diagram used to explain the operation of the same embodiment.

FIG. 11 is a diagram showing conventional laser beam output characteristics.

FIG. 12 is a gradation characteristic diagram of a conventional output image.

[Explanation of symbols]

5... Laser scanner unit, 21... Processor, 24
...Video RAM, 25...Video signal output circuit, 27...Laser oscillator, 28...Laser control circuit, 30...Polygon mirror, 41...Binary signal storage circuit, 42...Front counter,
43...Backward counter, 44...Dot size determination circuit, 4
5, 45A... Pulse generation circuit, 46... Dot position determination circuit, 50, 51... Condition table.

Claims (2)

[Claims] 1. Referring to the binary pixel data of interest and a plurality of binary peripheral pixel data on the same line as the binary pixel data of interest, the state of the pixel data is used to determine the actual printing dots for the pixel data of interest. In a binary image forming apparatus that expresses a halftone image by variably adjusting the size, the two
distance detection means for detecting a distance from the digitized target pixel data to the print bit of the binarized peripheral pixel data;
A binary image forming apparatus comprising: a dot size variable control means for variably controlling the actual print size of one dot of the binary pixel data of interest based on the distance information detected by the detection means. 2. A dot that variably controls the output position of one dot of the binarized target pixel data based on the distance information detected by the distance detection means and the dot size information determined by the dot size variable control means. 2-2 of claim 1, characterized in that a position variable control means is added.
Value image forming device.