JPH07336537A - Printed picture element control circuit - Google Patents

Abstract

PURPOSE:To improve the reproducibility of an isolated black level point. CONSTITUTION:Picture element data by M-picture elements X N-lines are stored in an N-line memory 1. A picture element data reference circuit 2 receives data from the memory and latches data by, e.g. N picture element x N picture element. When only data of a noted picture element is '1' (black level) and other data are all '0' (white level), a level '1' is outputted to a line memory 3 as sub-picture element data. Then an LED head exposes twice a photosensing body at the same position based on original picture element data and the sub-picture element data. Thus, an isolated black level point is exposed twice and the reproducibility is improved.

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 used in an electrophotographic LED printer or the like.

[0002]

2. Description of the Related Art A print pixel control circuit used in, for example, an electrophotographic LED printer generates synchronizing signals such as a latch signal and an enable signal, transfers image data to an LED head in synchronization with a video clock, This is a circuit for controlling the head so that the photoconductor is exposed.

In electrophotographic LED printers, LE
After the photoconductor is exposed by the D head, development, transfer,
An image is printed on the printing paper through an electrophotographic image forming process such as fixing.

Conventionally, in a print pixel control circuit used in an LED printer or a laser printer, various measures for image signal processing have been made in order to compensate and improve the deterioration of print quality due to the characteristics of the electrophotographic image forming process. .

For example, Japanese Patent Publication No. 4-165761 discloses the following method. That is, when one pixel is composed of a plurality of dots, the print quality is improved by selecting the dot pattern to be applied to the pixel of interest from the situation of the pixels surrounding the pixel of interest. Also,
According to the method disclosed in Japanese Patent Publication No. 4-172872, the print quality is determined by determining the size and print position of the actual print dot in one pixel of the pixel of interest based on a plurality of pixel data adjacent to the pixel of interest. Is improving. In the electrophotographic image forming process, the print dots are circular and are larger than the theoretical pixel size, so blackening of the pseudo-halftone pixels occurs. By changing the shape, size, or print position of a pixel within the pixel, the above blackening is prevented, and printing with excellent gradation expression characteristics is realized.

[0006]

On the other hand, as another undesirable characteristic of the electrophotographic image forming process, when a black pixel is isolated in a white background, the pixel is not reproducibly developed. There is that. Therefore, black pixels in the white background become extremely smaller than the original pixel size or disappear, making it difficult to print fine halftone images with good reproducibility.

In order to compensate for this characteristic, it is possible to set the condition so that the black pixel of the entire image becomes large, but in that case, the reproducibility of the white pixel in the black background becomes poor and the white pixel becomes white. The extracted image is deteriorated and the gradation reproducibility is deteriorated.

In the conventional print pixel control circuit described above, the shape, size and print position of the pixel of interest are controlled based on the state of the surrounding pixels, but the control is performed only within the corresponding pixel. Therefore, even if the print dot size is set to the maximum or the dot density is set to the maximum, the control can be stopped within the range of the relevant pixel, and development can be performed with good reproducibility to print fine halftone images faithfully. Have difficulty.

It is an object of the present invention to solve the above problems and to develop a reproducible image even with isolated black dots in a white background, and to improve the print quality of a fine halftone dot image. To provide a circuit.

[0010]

According to the print pixel control circuit of the present invention, a print pixel control circuit that supplies pixel data to a print head that exposes a photosensitive member based on the pixel data detects a predetermined number of adjacent pixels. Based on the memory for accumulating data and the pixel data accumulated in this memory, sub-pixel data for exposing the photoconductor at the same position as the exposure position of the photoconductor by the corresponding original pixel data is stored. A feature is that it is provided with an arithmetic circuit for generating.

[0011]

The operation circuit generates the sub-pixel data for exposing the photoconductor at the same position as the exposure position of the photoconductor by the corresponding original pixel data based on the predetermined number of pixel data stored in the memory. To do. Therefore, in the case where all the pixels adjacent to a certain black pixel are white pixels, if the data of the black pixel is generated as the sub-pixel data by the arithmetic circuit, the position on the photoconductor corresponding to the black pixel is The original black pixel data and the subpixel data are exposed twice. Therefore, even an isolated black dot in a white background can be developed with good reproducibility, and the printing quality of a fine halftone dot image can be improved.

[0012]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 shows an electrophotographic type L including an embodiment of the present invention.
It is a block diagram showing an ED printer. The print pixel control circuit of the present invention comprises an N line memory 1, a pixel data reference circuit 2, a line memory 3, a selector 4, and a sync signal generation circuit 5.

The N-line memory 1 is a FIFO memory for storing data of M adjacent pixels (M is an integer of 3 or more) connected for N lines (N is an odd number of 3 or more). The output of the FIFO memory is the FIFO of the next line.
It is connected to the input of the O memory, and at the same time, connected to the input of the pixel data reference circuit 2. FIG. 4 shows a pixel column output from the N-line memory 1 for N = 3. Input of pixel data to the N-line memory 1 is performed in synchronization with the clock supplied from the oscillator 6, and is sequentially shifted.

The pixel data reference circuit 2 includes L pixels × N lines centering on the pixel of interest (L is an odd number of 3 or more,
It has a circuit for latching pixel data of L ≦ M).
Then, the pixels around the target pixel are logically operated, and when the surrounding pixels satisfy a predetermined condition, data (“1”) representing black is output as a sub-pixel. In other cases, data ("0") representing white is output.

FIG. 2 is a circuit diagram showing a concrete example of the pixel data reference circuit 2 when N = L = 3. As shown in the figure, data of 2 pixels × 3 lines = 6 pixels is latched by the six latches 20. Therefore, the data of 9 pixels can be referred to at the same time by combining the input data (for 3 pixels) of each line of X, Y, Z currently input to the circuit 2.

Pixel data for these 9 pixels is input to the pixel calculation circuit 21. The pixel calculation circuit 21 outputs data (“1”) representing black as a subpixel when the input data for 9 pixels satisfies a predetermined condition. Specifically, the circuit 21 receives the data of the surrounding 8 pixels as NO.
It is composed of an R gate 22 and an AND gate 23 which receives the pixel of interest and the output of this NOR gate.

Assuming that the pixel data in the area surrounded by the dotted line shown in FIG.
_k is the pixel of interest, and X _k-1 , X _k , X _{k + 1} , Y _k-1 ,
The data of 8 pixels of Y _{k + 1} , Z _k-1 , Z _k , and Z _{k + 1} are input to the NOR gate 22 as reference pixel data. When all the reference pixel data represents white (“0”) and the data of the target pixel Y _k represents black (“1”), data (“1”) representing black is output as the sub-pixel data.

In the example of FIG. 2, six latches 20 are used for N = L = 3, but the number of reference pixels can be increased by increasing the number of latches 20. It is possible to selectively process black pixels in a wider white background. In addition, the pixel calculation circuit 21
Although a combination of an 8-input NOR gate and an AND gate is shown as above, various conditions that the surrounding pixel and the target pixel should satisfy can be set variously by combining various gate circuits.

Returning to FIG. 1, the line memory 3 is composed of a FIFO memory that stores data for M pixels. The sub-pixel data output from the reference circuit 2 is input to this memory and is sequentially shifted based on the video clock from the oscillator 2. As will be described later, by using such a line memory, the positional relationship between the sub pixel and the corresponding main pixel is maintained. That is, the sub-pixel is
It is exposed and printed at the same position in the horizontal direction as the corresponding main pixel.

The synchronizing signal generating circuit 5 generates a latch signal and an enable signal for controlling the LED head by counting the video clock from the oscillator 6, and further generates a data switching signal to be supplied to the selector 4. To do.

Generation of a control signal in the sync signal generating circuit 5, transfer of video data supplied to the LED head 7, and exposure printing will be described below with reference to FIG. In the following, the original pixel data input to the print pixel control circuit is referred to as main pixel data, and the subpixel data generated by the pixel data reference circuit 2 is referred to as subpixel data.

The sync signal generation circuit 5 counts the video clocks to generate the latch signal, the enable signal, and the data switching signal shown in FIG. The one-line cycle is a time assigned to one line in printing exposure and can be obtained as an inverse number of (printing paper conveyance speed) × (linear density). Conventionally, the video data is input to the shift register 8 of the LED head 7 in synchronization with the video clock, and after the video data for one line is aligned, the latch signal is turned on once in one line cycle to the latch 9. LEDs are latched and based on their data while the enable signal is on.
A drive current has been designed to flow to the LED element 11 through the drive circuit 10.

On the other hand, in the present invention, the period of one line period is divided into two, and the first half is a period for handling main pixel data,
The latter half is the period for handling subpixel data. That is, the main pixel data is transferred to the shift register 8 in the first period T1 of one line cycle. Thereafter, the LED element 11 is driven based on the latched data by the latch signal which is turned on during the period of t1 and is latched by the latch 9 in the period of E1 when the enable signal is turned on, and printing exposure is performed. On the other hand, the sub-pixel data is transferred to the shift register 8 during the period T2, and the latch signal is transmitted during the period t2.
When it is turned on, it is latched by the latch 9. Then, during the period E2 when the enable signal is turned on, the LED element 11 is driven based on the latched data, and printing exposure is performed.

The image data input to the shift register 8 of the LED head 7 is switched in the selector 4 based on the data switching signal, and the main pixel data in the period S1 and the subpixel data in the period S2 are respectively transferred to the shift register 8. Supplied.

Since the sub-pixel data are aligned in the line memory 3 and then given to the LED head 7, the horizontal positional relationship with the main pixel data is the same, and the sub-pixel data and the main pixel data correspond to each other. , The same position on the photoreceptor is exposed.

Then, as described above, when the surrounding pixels and the target pixel satisfy a predetermined condition, the sub-pixel data becomes data representing black ("1"), and the normal exposure is performed by the main pixel data. After that, the same position, that is, the same pixel is exposed again by the subpixel data. Therefore,
Since a wider area is exposed than a normal pixel, even if the pixel is in a white background, it is more easily developed than usual, and the reproducibility of a black pixel is improved.

[0027]

As described above, in the print pixel control circuit of the present invention, the arithmetic circuit determines the exposure position of the photoconductor by the corresponding original pixel data based on the predetermined number of pixel data accumulated in the memory. Sub-pixel data for exposing the photoconductor is generated at the same position. Therefore, in the case where all the pixels adjacent to a certain black pixel are white pixels, if the data of the black pixel is generated as the sub-pixel data by the arithmetic circuit, the position on the photoconductor corresponding to the black pixel is The original black pixel data and the subpixel data are exposed twice. Therefore, even an isolated black dot in a white background can be developed with good reproducibility, and the printing quality of a fine halftone dot image can be improved.

[Brief description of drawings]

FIG. 1 is a block diagram showing an electrophotographic LED printer including an example of a print pixel control circuit according to the present invention.

FIG. 2 is a circuit diagram showing in detail a pixel data reference circuit which constitutes the print pixel control circuit of FIG.

FIG. 3 is a timing chart showing signals related to a sync signal generating circuit that constitutes the electrophotographic LED printer of FIG.

FIG. 4 is an explanatory diagram showing a main pixel column of an N-line memory that constitutes the print pixel control circuit of FIG.

[Explanation of symbols]

 1 N Line Memory 2 Pixel Data Reference Circuit 3 Line Memory 4 Selector 5 Synchronization Signal Generation Circuit 6 Oscillator 7 LED Head 8 Shift Register 9, 20 Latch 10 LED Drive Circuit 11 LED Element 21 Pixel Operation Circuit 22 NOR Gate 23 AND Gate

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location B41J 2/455

Claims (6)

[Claims] 1. A print pixel control circuit that supplies pixel data to a print head that exposes a photosensitive member based on pixel data, and a memory that stores data of a predetermined number of adjacent pixels and a memory that stores the data in the memory. Based on the pixel data,
A print pixel control circuit, comprising: an arithmetic circuit that generates sub-pixel data for exposing the photoconductor at the same position as the exposure position of the photoconductor by the corresponding original pixel data. 2. The memory is configured such that M is an integer of 3 or more and N is 3.
2. The print pixel control circuit according to claim 1, wherein when the above odd number is set, data of adjacent pixels for M pixels × N lines are accumulated. 3. The arithmetic circuit, when the data of a specific pixel which is not a peripheral pixel among the data accumulated in the memory represents black and the other data represent all white, the sub-pixel data is black. 2. The print pixel control circuit according to claim 1, wherein the print pixel control circuit generates data representing 4. The print pixel control circuit according to claim 1, wherein M and N are both 3. 5. The print pixel control circuit according to claim 1, wherein the print head is composed of an LED. 6. The print pixel control circuit according to claim 1, wherein the print head is a print head of an electrophotographic LED printer.