JP3099341B2 - Image recording method and apparatus - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image recording method and apparatus used in an electrophotographic copying machine, a printer, a facsimile, and the like, and more particularly, to a method using a solid-scanning optical writing head. The present invention relates to an image recording method and an apparatus for performing halftone image recording.

[Conventional technology]

Conventionally, as the image recording apparatus, a light emitting diode array (hereinafter, referred to as an LED array) is used as an image exposure unit.
And light from a light source to a liquid crystal shutter array (hereinafter, LCS).
There is a type using a so-called solid scanning type optical writing head which controls light transmission or light shielding by an array. Then, the image recording apparatus forms an electrostatic latent image by performing exposure according to image data on a photosensitive drum by a solid-scanning optical writing head, develops the electrostatic latent image, and records an image. Is configured to do so.

This type of image recording apparatus mainly records a line image such as a character or a figure by binary recording as to whether or not the image is exposed by a solid-scanning optical writing head.

However, with the recent diversification and advanced information required for image information, not only line images such as characters and figures,
There is an increasing demand for recording a so-called halftone image that expresses gradation in a recorded image such as a photographic image.

On the other hand, an image recording apparatus employing the above-described binary recording method can also perform halftone image recording by employing a dither method, a density pattern method, or the like.

However, these dither methods and density pattern methods have a problem that high resolution cannot be obtained because the intermediate density is expressed using a plurality of pixels. In particular, in a so-called digital copying machine in which an image reading device, an image processing device, and an image recording device are combined, a device capable of recording halftone images without lowering the resolution is required in order to obtain high-quality image reproducibility. ing. For this reason, there has been a problem that an image recording apparatus using a conventional solid-scanning optical writing head cannot be used in a digital copying machine.

On the other hand, multi-valued fonts aiming at improving image quality have appeared in printers in which a data processing device and an image recording device are combined, and the demand for recording a halftone image is also increasing.

Therefore, as a device capable of meeting these demands, Japanese Patent Application Laid-Open No. 63-87078 and Japanese Patent Application Laid-Open No. 63-87078 describe a prior art that enables recording of a halftone image in an image recording device using a solid-scanning optical writing head. This is disclosed in Japanese Unexamined Patent Publication No. Hei 1-1115633.

These techniques record halftone image data of 2 ⁿ grayscale levels consisting of n bits per pixel by dividing it into n times per line and printing, and weighting the recording for each time by the exposure time width. ^0, 2 ^1, 2 ² ... a 2 ^n, and is configured to obtain a halftone image of the 2 ⁿ levels.

[Problems to be solved by the invention]

However, the prior art has the following problems. That is, the image recording apparatus according to the above proposal is a technique developed for an X-ray tomography camera, and is directly exposed on a film as a photoconductor by a solid-scanning optical writing head such as an LED array. This is for recording images. Therefore, with respect to the gradation good film, 2 ⁰ by exposure time width weights recorded each time,
By setting 2 ¹ , 2 ² ... 2 ⁿ , a halftone image corresponding to the exposure time can be obtained, which is an effective means. However, the spatial frequency characteristics in the high frequency band are poor, and the development characteristics of the high gain are poor. However, there is a problem that it is difficult to apply the present invention to an electrophotographic image recording apparatus using a photosensitive drum.

In other words, the recording is divided into 1 line per n times as described above, ⁰ 2 by the weight of the exposure time width of the recording of each time, 2 ^1, 2 Any ² ... 2 as a ^n, a long exposure time width On the side, the recorded image density is saturated, and even if the exposure time width is changed, no change in the density of the recorded image can be obtained. There was a problem.

[Means for solving the problem]

Therefore, the present invention has been made to solve the above-mentioned problems of the prior art, and an object of the present invention is to provide an image recording apparatus using a solid-scanning optical writing head, in which only character images and line images are used. Another object of the present invention is to provide an image recording method and apparatus capable of obtaining good reproducibility even for a halftone image such as a photographic image.

That is, according to the first aspect of the present invention, a large number of recording elements are arranged corresponding to the recording width of the latent image carrier,
A solid-scanning optical writing head that performs exposure or non-exposure scanning according to image data for each pixel recorded by each recording element, and divides one pixel into a plurality of sub-pixels by the solid-scanning optical writing head In this state, one line along the main scanning direction is scanned a plurality of times by the number of times corresponding to the number of sub-pixels, thereby performing image exposure on the latent image carrier to form an electrostatic latent image. An image recording method for developing an electro-latent image and recording an image, wherein the multi-gradation input image data input to the solid-state scanning optical writing head corresponding to each pixel is classified by a predetermined threshold value. In addition to converting the density information of the input image data into exposure image data of a number corresponding to the number of sub-pixels, and in a reproduction mode of a halftone image, the solid-state scanning optical writing head scans one line at a time. In addition, the direction in which the number of sub-pixels to be exposed increases along the sub-scanning direction as the input image data becomes higher in density is switched so that the lower density side is connected between adjacent images.

Further, according to the second aspect of the present invention, as shown in FIG. 1, a large number of recording elements are arranged corresponding to the recording width of the latent image carrier 1, and the recording is performed by each recording element. A solid-scanning optical writing head 3 that performs exposure or non-exposure scanning according to image data 34 for each pixel, and in which one pixel is divided into a plurality of sub-pixels by the solid-scanning optical writing head 3, By scanning one line along the main scanning direction a number of times corresponding to the number of sub-pixels, image exposure is performed on the latent image carrier 1 to form an electrostatic latent image. An image recording apparatus for developing an image and recording an image by dividing the multi-tone input image data 34 input to the solid-state scanning optical writing head 3 corresponding to each pixel by a predetermined threshold value. Density information of input image data is converted to the number of sub-pixels Pattern conversion means for pattern-converting the image data into a corresponding number of exposure image data. In addition, the direction in which the number of sub-pixels to be recorded increases along the sub-scanning direction as the input image data becomes higher in density is mutually different. The first and second pattern conversion means 32 and 33 are opposite to each other. In the reproduction mode of the halftone image, the first pattern conversion is performed every time one line is scanned by the solid-scanning optical writing head 3. Means 32 and the second pattern conversion means 33 to switch the multi-gradation input image data 34 to the exposure image data 35,
This is converted into 36 and recorded, so that the low density side is connected between adjacent pixels.

In the present invention, in the case of the character mode, the second
As shown in the figure, there is always one pattern conversion means (for example,
33) converts the multi-tone input image data 34 to the exposure image data 35
Convert to

As the latent image carrier, for example, a photoconductor drum is used, but the present invention is not limited to this, and it goes without saying that a belt-shaped photoconductor may be used.

As the solid-state scanning optical writing head, for example, an LED array is used.However, the present invention is not limited to this. For example, an LCS array or the like that controls transmission or blocking of light from a light source according to image data is used. May be used.

Further, as the pattern conversion means, for example, TTL
-A ROM is used, and the density information of the input image data is converted into a pattern corresponding to the number of sub-pixels by pattern-dividing the multi-tone input image data by a predetermined threshold by referring to a table. Things are used.

For example, in the character mode, the pattern conversion circuit sequentially exposes the input image data such that the bit number increases sequentially from the low bit number side to the high bit number side as the density of the input image data increases, and remains in the same direction until the image data ends. Is used, but the invention is not limited to this, and as the input image data becomes higher in density, the exposure is performed in such a manner that the bit number is sequentially increased from the high bit number side to the low bit number side. May be used.

On the other hand, in the reproduction mode of the halftone image such as the photograph mode,
For example, the image exposure is performed by sequentially switching the first pattern conversion means and the second pattern conversion means in which the number of sub-pixels to be recorded increases in opposite directions as the input image data becomes higher in density for each line. Is used.

Further, in the present invention, the exposure time of the optical writing head during each sub-scan may be constant, but is not limited to this. The exposure time of each sub-scan is changed according to the development characteristics. May be.

[Action]

According to the first aspect of the present invention, the operation as described in the configuration is achieved.

Further, in the invention according to claim 2 of the present invention, the multi-gradation input image data input to the solid-state scanning optical writing head corresponding to each pixel is divided by a predetermined threshold value, so that the input image data is divided. Pattern conversion means for pattern-converting the density information into the number of exposure image data corresponding to the number of sub-pixels, and the pattern conversion means increases the number of sub-pixels to be recorded as the input image data becomes higher in density. In the halftone image reproduction mode, the first pattern conversion means and the second pattern conversion means are provided for each scanning of one line by the solid-state scanning optical writing head. The multi-tone input image data is converted into the exposure image data by switching between the two pattern conversion means.

Therefore, in the halftone image reproduction mode, the first scanning is performed every one line by the solid-state scanning optical writing head.
The multi-tone input image data is converted into image density data by switching between the pattern conversion means and the second pattern conversion means, so that the exposure of the scanning of two adjacent lines is performed in a concentrated manner. The number of lines of the electrostatic latent image per unit length is halved. Thus, the number of lines in the sub-scanning direction is 1/2
Therefore, it is possible to form an image corresponding to the spatial frequency characteristic of the electrophotographic process, to perform image recording with good reproducibility of gradation, and to improve the reproducibility of a halftone image.

〔Example〕

 Hereinafter, the present invention will be described based on the illustrated embodiment.

FIG. 3 shows an embodiment of the device configuration of the image recording apparatus according to the present invention. In FIG. 1, reference numeral 1 denotes a photosensitive drum. As the photosensitive drum 1, for example, a photosensitive drum using an organic photoconductor (OPC) having a negative charge polarity is used. The photosensitive drum 1 is disposed so as to be rotatable at a predetermined process speed (for example, 130 mm / s) in a direction indicated by an arrow by a drive mechanism (not shown). Further, the surface of the photosensitive drum 1 is uniformly charged to a predetermined potential (for example, about -600 V) by a primary charger 2 composed of a corotron prior to image exposure described below. .

On the outer periphery of the photosensitive drum 1, an LED head 3 as a solid-scanning optical writing head for exposing the drum surface in accordance with image data is disposed adjacent to the downstream side of the primary charger 2 in the drum rotation direction. ing.

As shown in FIG. 4, this LED head 3 has an LE in which a large number of recording elements fixed on a substrate 4 made of Al or the like are arranged.
A D array 5 is provided, and the LED arrays 5 are linearly arranged in a direction perpendicular to the drawing. Also LED
Driver ICs 6 and 6 'for driving the array 5 are fixed to both sides of the array 5, respectively. The LED array 5 and the driver ICs 6 and 6' are electrically connected to each other by bonding wires 7. ing. Further, a selfoc lens 8 (trade name of Nippon Sheet Glass Co., Ltd.) is fixedly arranged above the substrate 4 so as to face the LED array 5 at a predetermined distance. Reference numeral 8 denotes an image formed on the photosensitive drum 1 by an image formed by the LED array 5 that emits light in accordance with image data.

The LED head 3 configured as described above performs image exposure on the uniformly charged photosensitive drum 1 by so-called image writing, exposing only the image portion and not exposing the background portion. Body drum 1
An electrostatic latent image corresponding to the input image data is formed as shown in FIG. At this time, by scanning one line a plurality of times corresponding to the number of sub-pixels in a state where one pixel is divided into a plurality of sub-pixels by the LED head 3,
Image exposure is performed on the photosensitive drum 1 to form an electrostatic latent image.

In the drawing, reference numeral 9 denotes a heat sink for releasing heat of the substrate 4.

The electrostatic latent image formed on the photosensitive drum 1 is
As shown in the figure, the toner image is developed by the developing device 10 and becomes a toner image. As the developing device 10, for example, a two-component developer consisting of a carrier and a toner is used, and
A reversal developing device which applies a 0 V developing bias VB (see FIG. 5) to perform reversal developing is used. As the carrier, for example, a polymer carrier having a diameter of about 100 μm is used. As the toner, for example, a diameter of 10 μm
A black toner having a negative polarity of the order of magnitude is used.

As shown in FIG. 3, the toner image formed on the photosensitive drum 1 is supplied from a paper cassette 11 by a paper feed roller 12, and is supplied to a drum surface by a registration roller 13 in synchronization with the rotation of the photosensitive drum 1. Is transferred by the charging of the transfer charger 15 onto the supplied recording paper 14. afterwards,
The recording paper 14 onto which the toner image has been transferred is subjected to fixing processing by heat and pressure by a fixing device 16 and is discharged onto a paper stacker 17 to complete a series of image recording steps.

The photosensitive drum 1 after the toner image transfer process is completed
The surface of the is removed residual toner and paper dust and the like by a cleaner 18 having a fur brush, and is uniformly exposed to light by an erase lamp 19 composed of an LED array having an emission wavelength of, for example, 630 nm. Prepare for the next image recording step.

By the way, in this embodiment, as shown in FIG. 1, the multi-gradation input image data 34 input to the solid-state scanning type optical writing head 3 corresponding to each pixel is divided by a predetermined threshold value, thereby Pattern conversion means for pattern-converting the density information of the image data into exposure image data 35, 36 corresponding to the number of sub-pixels; The first and second pattern converters 32 and 33 are arranged such that the directions in which the number of pixels increases are opposite to each other. In the halftone image reproduction mode, the solid-state scanning optical writing head scans one line at a time. First pattern conversion means 32
And the second pattern conversion means 33 are switched to convert the multi-gradation input image data 34 into exposure image data 35 and 36.

That is, the control circuit of the image recording apparatus according to this embodiment is configured as shown in FIG. 6 to FIG.

FIG. 6 shows an equivalent circuit of the LED head. In the figure, reference numeral 20 denotes each LED chip as a recording element for recording each pixel, and these LED chips 20, 20
Are linearly arranged in a large number (4763 in this embodiment) to constitute the LED array 5. The material of the LED array 5 is, for example, GaAlAs, and its emission wavelength is, for example, 720 nm. Furthermore, L
The recording width of the ED array 5 is set to, for example, 300 mm, and the recording density is set to, for example, 400 dpi. Furthermore, the average light output of the LED array 5 is 2.6 μW / dot, the variation of the light output is ± 5%, and the size of the light emitting section is 44 × 30 μm.
m. The operating frequency of the driver ICs 6 and 6 'of the LED head 3 is, for example, 5 MHz.
The number of data inputs of C6 and 6 'is set to, for example, 16 parallel inputs.

These LED chips 20, 20... Are alternately driven one by one by a drive circuit (driver ICs 6, 6 '). In the illustrated embodiment, the odd-numbered LED chips 20 counted from the left are used. , 20... Are driven by the upper drive circuit, and the even-numbered LED chips 20, 20,. LED chip 2 above
Are connected to a power supply circuit 22 through a power supply line 21, and a predetermined voltage (for example, + 5V) is applied to one end of each of the LED chips 20, 20,. Is applied to

The gate circuits 23, 23,... Are connected to the other ends of the LED chips 20, 20,.
Are connected to the ground via the ground line 24 and light up when the gate circuits 23 are open. Therefore, each of the LED chips 20, 20 ...
Are driven to be turned on or off by opening and closing the gate circuits 23, 23.

On the other hand, in the figure, 25 and 25 'are shift register circuits,
These shift register circuits 25 and 25 'have image data (DATA) 26 and driver strobe (D
ST) 27, start pulse (EI) 28, clock pulse (CL
K) 29 signals are input. The odd-numbered (D1 to D15) image data of the 16-bit image data (DATA) 26 input to one shift register circuit 25, and the other shift register circuit 25 , The even-numbered (D2 to D16) image data of the image data (DATA) 26 to be input.

Reference numerals 30, 30 'denote latch circuits for latching image data (DATA) 26 sent from the shift register circuits 25, 25', respectively. Latch strobe (LST) 31 is input. The outputs of the latch circuits 30, 30 'are input to one ends of the gate circuits 23, 23,..., And the other ends of the gate circuits 23, 23,.
7 has entered. Therefore, the gate circuits 23, 23... Are connected to the output from the latch circuits 30, 30 'and the driver strobe (DS
T) Opened and closed by AND with 27, LED chip 2 as described above
Control of turning on or off 0, 20,...

Next, FIG. 7 shows a block diagram of a data processing circuit.

In the figure, reference numerals 32 and 33 denote first and second pattern conversion circuits, respectively.
Reference numerals 2 and 33 denote density information of the input image data 34 by dividing input image data (DATA) 34 input from an image input device or a host computer (not shown) at, for example, 256 gradations of 8 bits using a predetermined threshold. This is a circuit for performing pattern conversion into exposure image data of a number corresponding to the number of sub-pixels (eight in this embodiment).

As shown in Table 1 below, the first pattern conversion circuit 32 receives input image data (DATA) 3 input at 256 gradations, for example.
4 is divided by threshold values of 0 to 27, 28 to 56, 56 to 84,..., And the density information of 256 gradations of the input image data (DATA) 34 is exposed to an exposure image composed of 8-bit bit patterns D1 to D8. This is a circuit for pattern conversion into data 35.
For example, when the gradation number of the input image data (DATA) 34 is “100”, the pattern is converted into 8-bit exposure image data 35 consisting of “11100000”.

In addition, when the first pattern conversion circuit 32 classifies the input image data 34 with thresholds of 0 to 27, 28 to 55, 56 to 84,... The number of bits is set to increase on the side.

On the other hand, the second pattern conversion circuit 33, as shown in the following Table 2, inputs image data (DATA) 34 input at 256 gradations.
Are divided by threshold values of 0 to 27, 28 to 55, 56 to 84..., And the density information of 256 gradations of the input image data (DATA) 34 is exposed image data consisting of 8-bit bit patterns D1 to D8. This is a circuit for pattern conversion to 36. In addition, the second pattern conversion circuit 33 divides the input image data (DATA) 34 with threshold values of 0 to 27, 28 to 55, 56 to 84,. The number of bits is set so as to sequentially increase from the higher bit number to the lower bit number.

In the bit patterns of Tables 1 and 2, "1" data indicates that exposure is performed in the sub-scan, and "0"
Indicates that no exposure is performed in the sub-scan.

As the first and second pattern conversion circuits 32 and 33, for example, a circuit composed of a TLL-ROM is used. By dividing the multi-tone input image data by a predetermined threshold with reference to a table, the input image data Is used to pattern-convert the density information of (1) into exposure image data of a number corresponding to the number of sub-pixels.

Reference numeral 37 denotes a data selector for switching images output from the pattern conversion circuits 32 and 33 according to a mode selection signal 39 sent from the timing generation circuit 38. The timing generation circuit 38 outputs a mode selection signal 39 including, for example, a character mode and a photograph mode. The switching between the character mode and the photograph mode is provided, for example, on an operation panel of the image recording apparatus. This is performed by operating a switching button (not shown).

In this embodiment, when the character mode is selected by the mode selection signal 39, the signal 35 from the first pattern conversion circuit 32 is always selected, and when the photo mode is selected by the mode selection signal 39, the pattern Output signal of conversion circuit 32
The configuration is such that the output signal 35 and the output signal 36 of the pattern conversion circuit 33 are alternately switched and selected for each scanning of one line.

Reference numerals 40 and 41 denote line buffer memories which alternately store the exposure image data 35 and 36 converted by the pattern conversion circuits 32 and 33 line by line, and alternately output the stored exposure image data 35 and 36. Is what you do. A memory control signal 42 is input to the line buffer memories 40 and 41.

43 is the output image data 4 of the line buffer memories 40 and 41
A data selector for selecting sub-scanning image data corresponding to each sub-scanning from 4 and 45. This data selector
The sub-operation data selection signal 47 is input to 43.

Reference numeral 48 denotes a serial-parallel conversion circuit for converting the 8-bit sub-image data 49 from the data selector 43 into image data (DATA) 26 of 16 bits of the LED head 3 and is constituted by a latch circuit. Then, as shown in FIG. 6, the image data (DATA) 26 converted by the serial-parallel
Output to D head 3.

The driver strobe (DST) 2 in FIG.
7, Start pulse (EI) 28, Clock pulse (CLK) 2
9. Each signal of latch strobe (LST) 31 is LE
These are drive timing signals for the D head 3, and these signals 2
7 to 29 and 31 are output from the timing generation circuit 38.
Further, from the timing generation circuit 38, an input data control signal 50 is output to an image input device or the like (not shown).
The input data control signal 50 includes a clock pulse line sync signal and a page sync signal for inputting input image data from an image input device or the like.

FIG. 8 is a block diagram showing the circuit configuration of the line buffer memory in detail.

Line buffer memory 40 and line buffer memory 41
Has a similar configuration. These line buffer memories 40 and 41 store the shift register 5 as shown in FIG.
1, 51, 51 ..., 3-state buffers 52, 52, 52 ...
Static RAM 53, 53, 53 ... and 3-state buffer 5
8, 54, 54,...

Each of the shift registers 51, 51, 51,... Receives image data 49 of a corresponding bit from the data selector circuit 43. That is, the first bit data D1 of the 8-bit image data 49 input to the first shift register 51 is stored in the second shift register 51.
The data D2 of the second bit among the image data 49 input in bits are input respectively. Also, a shift register clock 55 is input to these shift registers 51, 51, 51,.

Are converted into 8-bit signals by the shift registers 51, 51, 51, and are input to the 3-state buffers 52, 52, 52,. The three-state buffers 52, 52, 52,... Hold the input signal in three states of “H” level, “L” level, and “Z” level (high impedance level), as is well known. is there.
Are input to the three-state buffers 52, 52, 52,...

The output signals from the three-state buffers 52, 52, 52,.
Are input to and stored in the static RAMs 53, 53, 53,. Further, a memory address signal 59 is input to the static RAMs 53, 53, 53,.

And output signals 6 from the static RAMs 53, 53, 53,.
Are input to the three-state buffers 54, 54, 54,. The read / write selection signal 61 is input to the three-state buffers 54, 54, 54,.

The read and write select signals 57 and 61 are configured to alternately repeat read and write for each line scan. Also, the memory address signal 59 is the static RAM5
, 53, 53,..., A chip select signal CS, a write enable signal WE, and an output enable signal OE.

The following is a summary of the timing data of this embodiment.

One line scanning period 488.46 (μs) One sub scanning period 61.06 (μs) Input image data clock 10 (MHz) LED head clock 5 (MHz) With the above configuration, the image recording apparatus according to this embodiment The image is recorded in this manner. That is, as shown in FIG. 1, the surface of the photoreceptor drum 1 has a predetermined potential (-) by a primary charger 2 prior to image exposure.
600V). Thereafter, the surface of the photosensitive drum 1 is exposed by the LED head 3 in accordance with the input image data, and an electrostatic latent image is formed.

In this embodiment, the following processing is performed on the input image data (DATA) 34 of 8 bits and 256 gradations, and the image is exposed by the LED head 3 described above.

First, as shown in FIG. 9, input image data (DATA) is sent from an image processing device (not shown), a host computer, or the like.
34, the input image data (DATA) 34
Is input for each page scan according to the start pulse (EI) 28. As shown in FIG. 7, the input image data (DATA) 34 includes first and second pattern conversion circuits 32 and 33.
Is input to The input image data (DATA) input to the first and second pattern conversion circuits 32, 33
34 is divided by a predetermined threshold value according to Table 1 or Table 2, and is subjected to pattern conversion into exposure image data 35 and 36 of a number corresponding to the number of sub-pixels (8 in this embodiment).

Thereafter, the exposure image data (DATA) 35, 36 converted into a predetermined pattern by the pattern conversion circuits 32, 33.
Are input to the data selector 37, respectively. The data selector 37 selects the signal 35 or 36 from the first pattern conversion circuit 32 or the second pattern conversion circuit 33 based on the mode selection signal 39 from the timing generation circuit 38.

In this embodiment, the signal 35 from the pattern conversion circuit 32 is always selected when the character mode is selected, and the output 35 from the pattern conversion circuit 32 and the pattern conversion circuit 33 when the photo mode is selected. , 36 are alternately switched line by line.

That is, in the above example, when the input image data (DATA) 34 having the number of gradations of “100” is continuously input, the first pattern conversion circuit 32 always operates in the character mode. The exposure image data 35 of “11100000” after the pattern conversion is selected.

On the other hand, in the photograph mode, the exposure image data 35 of “11100000” subjected to pattern conversion by the first pattern conversion circuit 32 and the exposure image data of “00000111” subjected to pattern conversion by the second pattern conversion circuit 33 36 is alternately selected.

The pattern conversion image data 35 and 36 selected by the data selector 37 are alternately input to the line buffer memories 40 and 41 for one line of input image data (DATA) 34. As shown in FIG. 8, the 8-bit pattern-converted image data 35 and 36 input to the line buffer memories 40 and 41 are such that the data of the first bit D1 is stored in the first shift register 51, The data of bit D2 of the second
Are input to the shift registers 51, 51,... Corresponding to each bit, and each bit D1, D2
... is 8-bit data corresponding to 8 sub-pixels
Are converted to D11 to D18, D21 to D28,.

For example, if the exposure image data 35 subjected to pattern conversion by the first pattern conversion circuit 32 is "11100000" and the exposure image data 35 for one line is all "11100000", as shown in FIG. 8-bit data D of “11111111” by the first to third shift registers 51
Are converted to 11 to D18 ... and the fourth and subsequent shift registers 51
8-bit data D41 to D48, which become "00000000"
Respectively.

The 8-bit data D11 to D18, D21 to D28 ...
Are written into the static RAMs 53, 53... Bit by bit through the three-state buffers 52, 52.

As a result, one line of the pattern conversion pixel data 35 or the pattern conversion image data 36 corresponding to the sub-pixel is written into each static RAM 53, 53. That is,
The first static RAM 53 has the first bit data D1 of the pattern conversion image data 35 and 36, and the second static RAM 53 has the second bit data D1 of the pattern conversion image data 35 and 36. Are written respectively.

The pattern conversion image data 35, 36 written in the static RAMs 53, 53 are written in the other line buffer memory 40 or 41 for line scanning of the next line. Meanwhile, the data is output to the data selector 43 through the three-state buffers 54, 54,. Control of writing or output of these pattern conversion image data 35, 36 is performed by read / write selection signals 57, 61.
Done by

The data selector 43 alternately selects bit data from the line buffer memory 40 and the line buffer memory 41 line by line. If the bit data from the line buffer memory 40 is currently selected, as shown in FIG.
Bit data written bit by bit into the static RAMs 53, 53..., The data of each pixel to be recorded in the first sub-scan, that is, the signal corresponding to the first shift register 51 is sequentially transmitted from the first static RAM 53. Eight are selected and output to the serial-parallel conversion circuit 48. In this serial-parallel conversion circuit 48, a signal of 16 bits is formed by combining two of the eight signals output from the data selector 43, as shown in FIG.
Output to This is because the LED head 3 has 16 input terminals.

Accordingly, the data selector 43 sequentially selects 8 bits from one side of the 4736 bit data to be recorded in the first sub-pixel of one line of the LED head 3 and outputs the data to the serial-parallel conversion circuit 48. Then, the image data 26 for each bit output to the serial-parallel conversion circuit 48 is written to the shift register circuits 25, 25 'of the LED head 3, as shown in FIG. The writing of image data 26 in the shift register circuit is performed in synchronization with a clock pulse (CLK) 29 input to the shift register circuits 25 and 25 'as shown in FIG.

In this embodiment, since the LED head 3 has 16 input terminals and 4736 LED chips 20, 20,..., The data set in one line of sub-scan is 4736 ÷ 16 = Finish with 296 clocks.

In this way, as shown in FIG.
4736 parallel data written in the shift register circuits 25 and 25 'are latched by the latch circuits 30 and 30' by a latch strobe (LST) 31, and the output signals from the latch circuits 30 and 30 ' , 23,... Are driven by a logical product with a driver strobe (DST) 27.

The above steps are repeated according to the eight sub-pixels, and the image exposure for one line is completed.

Next, bit data from the other line buffer memory 40 or 41 is selected by the selector 43, and image exposure for the second and subsequent lines is performed in the same manner.

Then, image exposure corresponding to the input image data is performed on the photoreceptor ram 1 by the LED head 3 to form an electrostatic latent image. This electrostatic latent image is developed by the developing device 10, and an image is recorded.

At that time, as described above, in the character mode, since the exposure image data 35 from the first pattern conversion circuit 32 is always selected, the bit growth direction in the exposure of the sub-pixel of each line is as shown in FIG. As shown in FIG.

On the other hand, in the photograph mode, the exposure image data 35 and 36 from the first pattern conversion circuit 32 and the second pattern conversion circuit 33 are alternately selected line by line.
As shown in FIG. 12, the bit growth direction in the exposure of the sub-pixel of each line is opposite for each line. As a result, adjacent two lines of sub-pixels are connected, so that the number of lines to be recorded is 1/2 of the original number. Therefore, since the image is recorded in a state where the number of lines of the recorded image is halved, it is possible to perform the image recording that matches the spatial frequency characteristics of the electrophotographic process, and the gradation in the high density image portion is Reproducibility is improved.

FIG. 13 shows the image recording characteristics in the character mode, and FIG.
The figure shows the results of actually measuring the recording characteristics of the image in the photograph mode. As is apparent from these figures, in the photograph mode, the output image density linearly changes in accordance with the 256 gradations of the input image data (DATA) 34.

In this embodiment, as shown in FIG. 9, the ratio of the exposure time t during each sub-scan in the sub-scan time T is approximately
Although it is fixed at 0.2, it may be changed according to each sub-pixel.

In this embodiment, as shown in Tables 1 and 2, the first and second pattern conversion circuits 32 and 33 convert the image data into image density data 35 and 36 with the same threshold value. As a result, a case where nine gradations are set has been described, but the present invention is not limited to this.
Of course, the number of thresholds may be increased or decreased.

At this time, as shown in the following Tables 3 and 4, the threshold values used in the first and second pattern conversion circuits 32 and 33 are different from each other, so that each of the first and second pattern conversion circuits 32 and 33 can be used. The number of thresholds to be converted by 33 plus 1; in this example, 17
It is possible to express gradation.

[Effects of the Invention] The present invention has the above configuration and operation. In an image recording method and apparatus using a solid-scanning optical writing head, not only character images and line images, but also intermediate Good reproducibility can be obtained even for toned images.

[Brief description of the drawings]

1 and 2 are block diagrams each showing a schematic configuration of an image recording apparatus according to the present invention, FIG. 3 is a configuration diagram showing an embodiment of the image recording apparatus according to the present invention, and FIG.
FIG. 5 is a cross-sectional view showing the structure of the head, FIG. 5 is a graph showing the potential of the photosensitive drum, FIG. 6 is a block diagram showing the LED head, FIG. 7 is a block diagram showing a signal processing circuit, and FIG. 9 (a) to 9 (f) are waveform diagrams respectively showing signals input to the LED array, FIG. 10 is an explanatory diagram showing bit data signals, FIG. 11 and FIG. Is an explanatory diagram showing the recording state of the image, respectively, and FIGS. 13 and 14 are graphs showing the recording state of the image, respectively. [Explanation of Symbols] 1 ... Photoreceptor drum 3 ... LED array 32 ... First pattern conversion circuit 33 ... Second pattern conversion circuit 34 ... Input image data 35, 36 ... Exposure image data

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) H04N 1/40-1/409 H04N 1/46 H04N 1/60

Claims (2)

(57) [Claims] 1. A solid-state scanning device in which a large number of recording elements are arranged in accordance with the recording width of a latent image carrier, and exposure or non-exposure scanning according to image data is performed for each pixel recorded by each recording element. In the state where one pixel is divided into a plurality of sub-pixels by the solid-state scanning type optical writing head, one line along the main scanning direction is scanned a plurality of times corresponding to the number of sub-pixels. An image recording method for forming an electrostatic latent image by performing image exposure on the latent image carrier, and developing the electrostatic latent image to record an image, comprising: By dividing the multi-tone input image data input corresponding to each pixel by a predetermined threshold value, the density information of the input image data is converted into exposure image data of a number corresponding to the number of sub-pixels, and Image reproduction mode In the scanning mode, the direction in which the number of sub-pixels to be exposed increases along the sub-scanning direction as the input image data becomes higher in density in each scanning of one line by the solid-state scanning type An image recording method wherein switching is performed such that the low density side is connected. 2. A solid-state scan in which a large number of recording elements are arranged corresponding to the recording width of a latent image carrier, and exposure or non-exposure scanning is performed for each pixel recorded by each recording element in accordance with image data. In the state where one pixel is divided into a plurality of sub-pixels by the solid-state scanning type optical writing head, one line along the main scanning direction is scanned a plurality of times corresponding to the number of sub-pixels. An image recording method for forming an electrostatic latent image by performing image exposure on the latent image carrier, and developing the electrostatic latent image to record an image, comprising: Pattern conversion means for pattern-converting the density information of the input image data into exposure image data of a number corresponding to the number of sub-pixels by dividing the multi-tone input image data input corresponding to each pixel by a predetermined threshold value Be prepared In addition, the pattern conversion means comprises first and second pattern conversion means in which the direction in which the number of sub-pixels to be recorded increases along the sub-scanning direction as the input image data becomes higher in density is opposite to each other. In the halftone image reproduction mode, the multi-gradation input image data is switched by switching between the first pattern conversion means and the second pattern conversion means every time one line is scanned by the solid-scanning optical writing head. An image recording apparatus, wherein the recording is performed by converting the data into exposure image data, and the low density side is connected between adjacent pixels.