JPH07307868A - Print picture element control circuit - Google Patents

Abstract

PURPOSE:To obtain a print picture element control circuit in which the reproducibility of a black level in a white background is enhanced. CONSTITUTION:Image data 100 are stored by a line memory 1 for N-lines (N is an odd number being 3 or over). A picture element data reference circuit 2 provides the output of a noted picture element signal 103 based on noted picture element data in a median of NXM sets of picture element data formed by M digits (M is an odd number being 3 or over) to be stored and a peripheral picture element signal 102 based on picture element data of plural picture elements adjacent to the noted picture element. A picture element shape conversion circuit 3 outputs a laser drive signal 107 based on the noted picture element signal 103 and the peripheral picture element signal 102. The laser drive signal 107 is changed by the white/black level or the contrast of data of the noted picture element and the peripheral picture elements. The drive time of a laser beam is extended when the content of the change indicates for example that the peripheral picture elements are all at white level and the noted picture element has a black level.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a print pixel control circuit, and more particularly to a print pixel control circuit used in a laser printer.

[0002]

2. Description of the Related Art Conventionally, a print pixel control circuit is generally used in a laser printer device or a computer device, and is a circuit for forming an image in accordance with pixel data developed by these devices. This image formation is electrophotographic image formation, and is performed by switching control of the current for driving the laser in the laser scanning unit.
The laser is switched by controlling the laser drive current output from this circuit, and the switched laser is
The photoreceptor is exposed by being scanned by a rotating mirror or the like. An image is printed on the printing paper through an electrophotographic image forming process such as development, transfer, and fixing, which is a subsequent process.

In principle, each pixel for image formation developed in this laser printer is treated as a square as shown in FIG. However, since the cross section of the actual laser beam is circular and switching is performed while scanning, the shape of the pixel formed in the laser printer is substantially elliptical. The difference between the theoretical shape and the realistic shape of the pixel causes deterioration of print quality.

Japanese Patent Laid-Open No. 4-165761 discloses an example of the prior art for compensating and improving the deterioration of the print quality due to this cause. This invention discloses a method of selecting a dot pattern to be applied to a pixel of interest from the situation of pixels surrounding the pixel of interest when one pixel is composed of a plurality of dots. Further, in another Japanese Patent Laid-Open No. 4-17282, based on a plurality of pixel data adjacent to a target pixel, one
A method for determining the size and print position of an actual print dot within a pixel is disclosed. In both cases, by changing the shape and size of the pixel of interest or the printing position within that pixel depending on the surrounding pixels, it is possible to prevent blackening of the pseudo-halftone image and realize printing with excellent gradation expression. Has an aim.

[0005]

However, in the above-mentioned prior art example, the shape, size and print position of the target pixel are controlled based on the state of the surrounding pixels, but this control is performed only within the corresponding pixel. Control. For this reason, even if the print dot size of the black pixel is maximized or the dot density is maximized, only the treatment within the range of the relevant pixel is required, and the obtained result is limited. For example, when black pixels are isolated and exist in a white background, development is not performed with good reproducibility, and it is difficult to print fine halftone dot images with good reproducibility. Therefore, there is a problem in that the characteristics of the electrophotographic image forming process cannot be compensated and the print quality of an image including a fine halftone image cannot be improved.

As a feature of the electrophotographic image forming process due to the above problems, when black pixels are isolated in a white background, the pixels may not be developed with good reproducibility. This is a problem caused by the characteristics of the electrophotographic image forming process. Black pixels in a white background become extremely smaller or disappear than the original pixel size, and a fine halftone dot image is reproduced. Due to poor sex. To compensate for this characteristic, if the black pixels of the entire image are set to be simply large, on the contrary, the reproducibility of white in the black background deteriorates, the contrast decreases, and the white image or gradation reproducibility decreases. Is a new problem.

It is an object of the present invention to provide a print pixel control circuit which can enhance the reproducibility of black in a white background.

[0008]

In order to achieve such an object, the print pixel control circuit of the present invention uses an N line (however, N
Is a line storage means for storing pixel data of an odd number of 3 or more) and N × M pixel data composed of M digits (where M is an odd number of 3 or more) stored by the line storage means. Pixel data for outputting a target pixel signal based on a predetermined one target pixel data out of N × M input and a peripheral pixel signal based on pixel data of a plurality of pixels adjacent to the target pixel It has a reference means and a pixel shape conversion means for inputting a pixel signal of interest and a peripheral pixel signal to form a drive signal of a laser beam, and the drive signal of the laser beam is composed of respective data of the pixel of interest and the peripheral pixel. The feature is that it changes based on the content.

The contents of the data to be changed are the degree of black and white or light and shade in the image formation of each pixel, and the change of the drive signal is preferably the drive time of the laser light or the magnitude of the drive current of the laser light. .

[0010]

Therefore, according to the print pixel control circuit of the present invention, the pixel data of N lines is stored, and from the stored N × M pixel data composed of M digits, a predetermined number out of N × M is stored. The target pixel signal based on the target pixel data of 1 pixel and the peripheral pixel signal based on the pixel data of a plurality of pixels adjacent to the predetermined 1 pixel, and the drive signal of the laser light based on the configuration content of each data. Change. Therefore, it is possible to change the drive signal according to the difference between the lightness and darkness of the target pixel and the lightness and darkness of the peripheral pixels, and to emphasize the lightness and darkness of the obtained image.

[0011]

Embodiments of the print pixel control circuit according to the present invention will now be described in detail with reference to the accompanying drawings. 1 to 6, there is shown an embodiment of the print pixel control circuit of the present invention.

FIG. 1 is a block diagram showing a first embodiment. The print pixel control circuit is composed of an N line memory 1, a pixel data reference circuit 2 and a pixel shape conversion circuit 3 as shown in FIG. The pixel shape conversion circuit 3 is composed of a black dot extension circuit 4 and a laser drive circuit 5.

The N-line memory 1 is a memory configured by a FIFO memory for accumulating pixel data for N lines. The number N of lines is an odd number of 3 or more, and the corresponding columns of each line are output side by side. FIG. 6 is a diagram showing the state of the pixel column 601 output from the N-line memory 1 when N = 3. For each of the X, Y and Z lines, the K columns are transferred side by side.

The pixel data reference circuit 2 is a circuit configured to latch N.times.M image data 100 in M digits centering on the target pixel, and calculates pixels around the target pixel, When the surrounding pixels meet the specified condition, the black dot extension signal 102 which is a peripheral pixel signal is output.
Here, M is an odd number of 3 or more. In FIG. 3, N = 3 and M =
6 is a circuit diagram showing an example of a pixel data reference circuit 2 in the case of 3. FIG. The pixel data reference circuit 2 shown in FIG.
6 pixels (3 lines × 2 =) by the individual latches 10a to 10f
6 pixels) and 3 of the input image data at the current time
The circuit configuration is such that a total of 9 pixels can be simultaneously referred by combining pixels (3 lines × 1 pixel). The 9 pixels are classified into one target pixel and peripheral pixels composed of eight pixels around the target pixel, and pixel data of the eight pixels is calculated by the pixel calculation circuit 11
Entered in.

The pixel calculation circuit 11 calculates a pixel to select a pixel combination that meets the specified conditions. When the combinations satisfy the conditions, the pixel switching signal 101, which is the output signal of the pixel arithmetic circuit 11, is turned on. In order to use it as an output signal to the black dot extension circuit 4,
Further, it is extended by the time of one pixel through the latch 10g of one stage and is output as the black dot extension signal 102. In the embodiment of the pixel data reference circuit 2 shown in FIG. 3, the pixel calculation circuit 11 is composed of a NOR gate which receives as input signals the data of the eight pixels around the pixel except the pixel data of interest (Yk in FIG. 6).

In the pixel row 601 in the area surrounded by the broken line shown in FIG. 6, the surrounding pixels Xk- with Yk as the target pixel.
1, Xk, Xk + 1, Yk-1, Yk + 1, Zk-1, Zk, Zk + 1,
Eight pixels are used as reference pixels. The above-mentioned prescribed condition is a case where all of these reference pixels are white (0), and the pixel switching signal 101 becomes 1 only under this condition, which is a signal for processing the pixel of interest. Also, the target pixel Yk
Is output as the pixel-of-interest signal 103 from the pixel data reference circuit 2.

In the embodiment of the pixel data reference circuit 2 shown in FIG. 3, six latches 10a to 10a are provided for N = 3 and M = 3.
The case where 10f is used is shown. This latch 10a ~
If the number of 10f is increased, the number of reference pixels (N × M−1) can be increased, and black pixels in a wide white background can be selectively processed. Further, in the example of FIG. 3, an example in which an 8-input NOR gate is used as the pixel arithmetic circuit 11 is shown. Although detailed illustration is omitted in FIG. 3, it is possible to set conditions for combination of arbitrary surrounding pixels by combining inverter gates, AND gates or OR gates.

FIG. 4 is a circuit diagram showing an embodiment of the black dot extension circuit 4. The black dot extension circuit 4 of the embodiment includes a counter 21, an extension dot generation circuit 22, an AND gate 24 and an OR gate 25. Counter 21 is 1
It is a clock counter having a period of 1/8 of the pixel printing time. The count output signal of the counter 21 obtained by counting up the 1/8 dot clock 104 is input to the extension dot generation circuit 22. The extended dot generation circuit 22
Based on the count output signal output from the counter 21, a pulse signal having a pitch of 1/8 pixel and a time width corresponding to a maximum of 1/2 pixel is generated, and the generated pulse signal is used as an extension dot pulse signal 111. Output. In the case of the embodiment of FIG. 4, the pulse width of the extended dot pulse signal 111 can be variably extended at a pitch of a time width corresponding to 1/8 pixel.

In the AND gate 24, the above-mentioned extended dot pulse signal 111 is gated by the black dot extension signal 102. That is, when the pixel of interest meets the specified condition, the black dot extension signal 102 is turned ON (1) at the print timing of the next pixel, and the extension dot pulse signal 111 from the extension dot generation circuit 22 is supplied to the OR gate 25. Sent. In the OR gate 25, when the pixel signal 103 of interest and the extended dot pulse signal 111 are sent from the AND gate 24, a signal extended by that amount is output as the laser drive circuit input signal 106.

The above laser drive circuit input signal 106 is input to the laser drive circuit 5, and a laser drive signal 107 is generated. The laser light driven by the laser drive signal 107 is lit for a time longer than the time width of the normal pixel by the time width of the extended dot pulse signal 111. Therefore, the target pixel is exposed in a wider range than the normal pixel. Due to this wide range of exposure, even if the pixel of interest is in a white background, it becomes easier to develop than normal pixels, and the reproducibility of black pixels is improved.

Next, a second embodiment of the present invention will be described with reference to FIG. FIG. 2 is a block diagram showing the second embodiment. The print pixel control circuit of the second embodiment comprises an N line memory 1, a pixel data reference circuit 2 and a drive level variable laser drive circuit 6. First of the present embodiment
The difference from the second embodiment is that the pixel shape conversion circuit 3 of the first embodiment is constituted by a drive level variable laser drive circuit 6 in the second embodiment. However, the configurations and operations of the N-line memory 1 and the pixel data reference circuit 2 are the same as in the case of FIG. 1, and the duplicated description of these circuit portions will be avoided. The same parts as those in the first embodiment that do not need to be identified are designated by the same reference numerals.

FIG. 5 is a circuit diagram showing an embodiment of the drive level variable laser drive circuit 6. The drive level variable laser drive circuit 6 in FIG.
1a, 31b, NPN transistor 32, analog switches 33a, 33b, inverters 34a, 34b, and resistors.

In the NPN transistor 32 of the output stage, the collector terminal is connected to the driving power source Vcc via a resistor, the base terminal is linked to the pixel switching signal 101 and the target pixel signal 103 which are peripheral pixel signals, and the emitter terminal is the laser. The drive signal 207 is output. One of the image switching signals 101 for controlling this output signal raises the drive power supply Vcc of the circuit to high / low.
The voltage is divided into two low-level reference level voltages VH / VL, and the divided two-stage voltage VH / VL is converted into analog switches 33a and 33b.
It is selected by the on / off switching operation of. The switched voltage signal is coupled to the base terminal through PNP transistors 31a and 31b that are cascade coupled. The other target pixel signal 103 is coupled to the base terminal of the NPN transistor 32 at the output stage via the inverter 34b.

With the above configuration, when the pixel switching signal 101 is ON (1), the higher level reference voltage VH is selected by the analog switch 33a, the base current of the transistor 32 increases, and the pixel signal 103 of interest is selected. The current value of the laser drive signal 207 when black (1) increases. When the pixel switching signal 101 is OFF (0), the lower level reference voltage VL is selected by the signal via the inverter 34a. When the pixel signal 103 of interest is "0", the signal is inverted by the inverter 34b, the base voltage of the NPN transistor 32 becomes high level, and the laser drive current value 207 becomes large.

Therefore, when the reference pixels around the pixel of interest satisfy the specified condition, the pixel is exposed with a stronger laser than usual. Also in this case, since a wider range than the exposure range of the normal pixel is exposed, even if the pixel is in the background of white background, it is more easily developed than usual and the reproducibility of the black pixel is improved.

Therefore, by configuring as described above,
Even isolated black pixels in a white background can be printed with good reproducibility.

As described above, the present invention comprises an N line memory, a pixel data reference circuit, and a pixel shape conversion circuit, and the pixel shape conversion circuit includes a black dot extension circuit or a drive level variable laser drive circuit. Therefore, even when black pixels are isolated in a white background, there is an effect that development can be performed with good reproducibility and fine halftone dot images can be printed with good reproducibility to improve print quality.

Although the above-described embodiment is a preferred embodiment of the present invention, the present invention is not limited to this and various modifications can be made without departing from the gist of the present invention. For example, the case of forming a monochrome image has been described in the above embodiment, but the present invention can also be applied to the shading of a color image. Also, although the case where all the peripheral pixels are white has been described, depending on the composition ratio of the white dots,
The extension time or the magnitude of the current may be variable.

[0029]

As is apparent from the above description, the print pixel control circuit of the present invention has N lines stored in the N line storage means.
A target pixel signal based on the target pixel data of a predetermined one pixel and a peripheral pixel signal based on the pixel data of a plurality of pixels adjacent to the predetermined one pixel from xM pixel data;
The drive signal is changed according to the difference between the lightness and darkness of the target pixel and the lightness and darkness of the peripheral pixels. Therefore, it is possible to emphasize the contrast of the obtained image based on the configuration of the shade of the target pixel and the shade of the peripheral pixel.

[Brief description of drawings]

FIG. 1 is a circuit configuration block diagram showing a first embodiment of a print pixel control circuit of the present invention.

FIG. 2 is a circuit configuration block diagram showing a second embodiment of the print pixel control circuit of the present invention.

FIG. 3 is used in the first and second embodiments, N = 3, M
6 is a circuit configuration diagram showing an embodiment of a pixel data reference circuit in the case of = 3. FIG.

FIG. 4 is a circuit configuration diagram showing an embodiment of a black dot extension circuit.

FIG. 5 is a circuit configuration diagram showing an embodiment of a drive level variable laser drive circuit used in the second embodiment.

FIG. 6 is a conceptual diagram showing a configuration example of a reference pixel row from a 3-line memory.

[Explanation of symbols]

 1 N line memory 2 Pixel data reference circuit 3 Pixel shape conversion circuit 4 Black dot extension circuit 5 Laser drive circuit 6 Variable drive level laser drive circuit 10 Latch 11 Pixel operation circuit 21 Counter 22 Extended dot generation circuit 23 Inverter 101 Pixel switching signal (Peripheral pixel signal) 102 Black dot extension signal (Peripheral pixel signal) 103 Target pixel signal

Claims (4)

[Claims] 1. A line storage means for storing pixel data of N lines (where N is an odd number of 3 or more) and M digits stored in the line storage means (where M is an odd number of 3 or more). Pixel data of N × M pixels that are input, and a pixel signal of a plurality of pixels adjacent to the pixel of interest based on a pixel signal of interest based on a predetermined one pixel of pixel data of the input N × M A pixel data reference unit that outputs a peripheral pixel signal based on data; and a pixel shape conversion unit that inputs the pixel signal of interest and the peripheral pixel signal to form a drive signal of laser light. The print pixel control circuit is characterized in that the drive signal is changed based on the content of the data of each of the target pixel and the peripheral pixel. 2. The print pixel control circuit according to claim 1, wherein the configuration content of the data to be changed is a degree of black and white or shading in image formation of each of the pixels. 3. The print pixel control circuit according to claim 1, wherein the change of the drive signal is a drive time of the laser light. 4. The print pixel control circuit according to claim 1, wherein the change of the drive signal is a magnitude of a drive current of the laser light.