JPH0127628B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image reproducing apparatus that optically reads and reproduces an original image.

[Conventional technology]

It is known to read an original image using a solid-state element such as a CCD and modulate a laser beam to form a copy image on a photoreceptor.

In this case, the read signal is binarized to facilitate processing such as modulation. Therefore, only two brightness levels can be obtained, making it difficult to reproduce halftones.

Furthermore, conventional methods read an original image, perform A/D conversion on the read signal, and then perform threshold processing to reproduce a halftone image. If the timing of the images deviates for some reason, an accurate halftone image cannot be reproduced, which is an inconvenience.

〔the purpose〕

The present invention has been made in view of the above points, and an object of the present invention is to provide an image reproducing apparatus that can obtain accurate and high-quality halftone images.

That is, the present invention provides an apparatus for optically reading an original and reproducing an image, including means for photoelectrically converting an original image, means for generating a transfer clock for sequentially transferring pixel signals from the photoelectric converter, and a means for generating a transfer clock for sequentially transferring pixel signals from the photoelectric converter. means for sequentially A/D converting the pixel signals transferred from the means, the A/D converting means A/D converting the pixel signals based on a predetermined clock signal synchronized with the transfer clock. further comprising means for dithering the pixel signal output from the A/D conversion means using a predetermined threshold matrix and outputting a reproduced signal; and an arbitrary threshold matrix used by the output means. and selecting means, and the output means performs a switching operation of each threshold value of the threshold value matrix selected by the selection means based on the predetermined clock signal. It is something.

〔Example〕

In this embodiment, a document image is read by a CCD, BBD, etc., the read signal is A/D converted, and a reproduced signal is output in accordance with both the converted signal and a predetermined threshold array signal. Further, A/D conversion converts the read signal into predetermined bits between both reference black and white levels. Further, the threshold values are arranged in time in synchronization with the original reading operation (charge transfer operation), and are arranged repeatedly in synchronization. Further, the threshold value array is set as desired or automatically by a mode key from the copying machine operation section.

Therefore, in this embodiment, when reproducing an original with a blue background, by changing the threshold value, the blue background can be made into a white background, and an easy-to-read image can be obtained.

It is also possible to make part or all of a white document gray.

Furthermore, even when dealing with half-tone originals such as photographs, if the contrast is too strong or too weak, by appropriately setting the threshold value, the gradation can be appropriately corrected and an easily viewable image can be obtained. Furthermore, it is possible to reproduce the same document with partially different gradations.

In addition, in order to automatically set the threshold value, the document is pre-scanned, monitored on a cathode ray tube as necessary, and stored in memory to determine the density distribution of the document data obtained there.
It is also possible to have a computer determine the degree of concentration at the intermediate level and perform optimal control to achieve optimal gradation and easy-to-see reproduction.

Examples will be described in detail below.

FIG. 1-1 is a schematic sectional view of an example of a copying machine according to the present invention, and FIG. 1-2 is a plan view of the operating section thereof.

In Figure 1-1, 1 is a platen on which the original is placed;
Reference numeral 2 denotes a lamp that irradiates the original with light, which is connected to the arrow 101 along with mirrors 3 and 4 to expose the original to slit light.
move in the direction. Reference numeral 9 denotes a lens system for forming an image of reflected light from the original onto an image sensor 6 composed of a CCD through a mirror, 7 a control unit for reading and processing image signals from the sensor 6, and 17 a laser beam source. 23 is its oscillation drive unit, 19 is a polygon mirror for deflecting and sweeping the beam from the laser source, 10 is an f-θ lens for peripherally correcting the deflected beam, 11 is a photosensitive drum, and 12 is a corona charger for positively charging the drum surface. , 13 is a corona charger that removes static electricity from the drum surface in accordance with the image pattern; 14 is a lamp that removes static electricity from the drum surface when the image is not exposed; 15
1 is a developing device for developing an electrostatic latent image; 16 is a lamp for uniformly exposing the drum to form an electrostatic latent image;
7 is a corona charger for transferring the developed image onto the transfer paper from the cassette 18, 29 is a roller for fixing the transferred image, 20 is a tray for discharging and storing the fixing misaligned sheet, and 21 is a cleaning unit for cleaning the drum surface after transfer. It's a blade. 22
is a first central control unit that controls the oscillation unit 23 of the reading unit;
CPU 24 is a second central control unit that controls copy process means such as a drum motor, charger, lamp, etc.

The sensor 6 is a self-scanning image sensor in which the light receiving parts are arranged in the slit direction.
Two CCDs can be installed in series to increase the resolution of original reading. 36 is a semiconductor memory RAM that stores image data, and the first control unit 22 is a control unit that performs address scanning control of the image memory 36, and includes a CPU that controls input to and readout from the memory 36. 30 is a modulator that modulates the laser beam.

Explain the operation. The surface of the drum 11 is made of a three-layer photoconductor using a Cds photoconductor, is rotatably supported on a shaft, and starts rotating in the direction of the arrow when a copy command is issued by turning on the copy key 60. .

The original placed on the original platen glass 1 is illuminated by the illumination lamp 2 integrated with the first scanning mirror 3 by turning on the copy key or a dedicated memory key if necessary. scanning mirror 3
and is scanned by the second scanning mirror 4. By moving the first scanning mirror 3 and the second scanning mirror 4 at a speed ratio of 1:1/2, the original is scanned while the optical path length in front of the lens 9 is kept constant.

After passing through the lens 9, the reflected light image is formed on the light receiving section of the image sensor 6 (optical path 102).
The image is converted into electrical signals for each slit line by the self-scanning function of the CCD and stored in four buffer memories. Then, data for one slit line from this buffer memory is input as serial data to the image memory 36, and stored sequentially from the initial address of the memory 36.

In this case, the CCD output is processed by the circuit shown in FIG. 4 and stored in the memory 36 as a signal with halftones.

Data from the memory 36 is output in response to the copy start command, and is output to the laser oscillation source 17 via the buffer. The oscillation operation of the laser beam of the laser oscillator 17, its deflection, and modulation are started based on the data stored in the buffer.

The laser beam is swept in the horizontal direction by constant speed rotation of the polygon mirror 19, and is irradiated onto the photosensitive surface of the drum 11 in the horizontal direction via the f-θ lens 10.
The drum rotates at a constant speed to perform vertical scanning. This horizontal and vertical scanning is performed at a speed such that the electrostatic latent image formed on the drum matches the size of the original on the platen.

Simultaneously with the laser irradiation on the drum surface, AC or primary static charge removal with the opposite polarity (for example -) is performed using the static eliminator 13, and then the entire surface is exposed using the full exposure lamp 16 to form a high contrast electrostatic latent image on the drum 11. form. The electrostatic latent image on the photosensitive drum 11 is
Next, the toner image is visualized by the developer 15 as a toner image. The sheets in the cassette 18 are transferred to the paper feed roller 25.
The sheet is sent into the machine by the registration rollers 26, and the sheet is sent to the transfer section at a timing such that the leading edge of the sheet and the leading edge of the latent image match. A transfer charger transfers the toner image on the drum to a sheet, fixes it, and discharges it, completing one copy. For this one image, all pixel data related to the original stored in the memory 36 are reproduced.

In addition, the pixel data read by the CCD 6 is processed via a control circuit (see FIG. 4), which will be described later, and sent to the beam light modulator 3.
It is also possible to output directly to 0. It is also possible to output the signal from the control circuit to the buffer memory 30 depending on the laser beam scanning speed. In these cases, the start command is copy key 6.
Performed by 0.

In Fig. 1-2, 60 is a copy key, 62 is a numeric keypad for setting the number of repeated copies from the same original, 63 is a lever for adjusting the shading of the entire reproduced image, and 61 is for presetting the halftone mode. Key A is a key that focuses on halftone reproduction from white to gray, B is a key that focuses on halftone reproduction only in gray areas, C is a key that focuses on gray to black, and D is a standard key. It is a reproduction. OR
is a mode key for automatically presetting the halftone mode in order to perform a dummy scan of the original and reproduce the optimum gradation.

When the above mode key is turned on, predetermined data is set in a latch circuit, which will be described later, and the system waits. Thereafter, the copy key 60 is turned on to start scanning and print operation. During printing, input using the mode key and numeric keypad is prohibited to prevent malfunctions.

The halftone copying control will be described in detail below.

In this example, the gray level of a pixel in the original image is compared with the threshold value for that pixel to obtain a binary signal, but since a region is constructed by collecting several adjacent pixels,
Within this region, the threshold value takes a different value for each pixel. Therefore, if there are N pixels in this area, there are N threshold values. This allows 1 of the manuscript
Pixels can be input as N bits and output as 1 bit/1 pixel. As a result, the number of bits can be compressed to 1/N, but the image quality depends on how the threshold values are selected and arranged.

In this example, as shown in FIG. 6B, a 2×2 dither matrix is compared for each pixel in one area and outputted for each pixel.

In FIG. 6, a is a pixel group in one area of the document, b is a 2×2 dither matrix, and c is a pattern of a reproduced image, and the larger the numbers a and b, the higher the gray level. First, the level 0 of the input pixel is compared with the level 1 of the dither matrix, and since it is lower than that level, 0 is output as a reproduction signal to make it white.

Next, level 1 of the pixel in the scan direction is compared with level 4 of the dither, and 0 is outputted to indicate white. In this way, scan to the right side of the diagram, and when one line is finished, the second line is scanned.
Moving to the line, pixels and matrix are similarly compared, and pixels 3 and 3 are matrix elements 2 and 3.
Since it is larger, output 1 to reproduce black.
In this way, halftones are reproduced.

In addition, in this example, the range of the number of levels of the read pixel is divided into more than the number of matrix elements as shown in Figs. I'm trying to make it reproducible.

In addition, in this example, when the pixel levels are divided into 1 to 8, the levels of the matrix elements are set to the levels 1, 2, and
1, 3, 5, 7 without changing the level order like 3, 4
It can be done. Also, element level is 3,
4, 5, and 6 to reproduce pixel levels 1 to 3 and levels 6 to 8 at each single level, and
6 is divided by the above threshold value and the output is controlled to obtain fine halftone gradations.

Note that it is also possible to change the arrangement at the element level, and it is also possible to find the optimal arrangement thereby.

Figure 2 shows an image reading element (Fairchild Co., Ltd.)
C ⁴ D) Block diagram of a CCD linear sensor. a is an exposure section that accumulates charges according to the level of received light through exposure, b is a transfer section using a shift register for serially transferring the charges, and c
d is a generator that generates clock pulses for transfer, and d is a circuit that sequentially samples and holds the transfer data. The process of data transfer will be explained with reference to the CCD signal timing diagram shown in FIG.

The photoelectrons accumulated in the exposure area of FIG. 2a for a certain period of time are simultaneously transferred to each cell of the exposure area a to the shift register of FIG. 2b by the pulse _φX of FIG. _φT in FIG. 3 is a transfer clock for shift register b, and the transferred information is sequentially sent to the hold circuit in FIG. 2 d and output. φ _R in FIG. 3 is a reset pulse for the hold circuit d. Figure 3
V _OUT is an image signal, and the image signal includes a reference black level signal BL-RF and a reference white level signal WT-RF in addition to the actual image signal. This reference signal is the right pulse of the read signal VDS in Figure 3,
Output from the CCD itself. FIG. 3V _EOS high level (EOS) is an end-of-scan signal output every time a scan ends. Due to the transfer scan for one line, the hold circuit d has a low level BL-
Output the RF signal, then output the read signal VDS,
Then, the BL-RF signal and finally the high-level reference white level signal WT-RF are output as V _OUT .
At the same time, the V _EOS port detects the high level and
Outputs the end signal EOS for the line. Note that the output V _OUT is the video input port of the control circuit in Figure 4.
Input to VIDEO.

FIG. 4 is an example of a data processing control circuit according to the present invention.

In the figure, 101 and 101' are input data V _OUT, respectively.
Reference black and white level signals from BL−RF, WT−
Sample and hold circuits G1 and G1' sample RF and hold it while reading the original, respectively sample circuits 101 and 101',
WT-A signal that becomes 1 only when the RF signal exists
Gate circuit that performs sampling operation based on the AND condition of BL, WT and sample timing φ _R ′, 102
is the image signal (black and white binary reference level signal from the sample hold circuit and read signal from the CCD)
and outputs 8 levels (8 levels) according to the input level.
A/D converter, 104, 10
4' is an amplifier, G2 is a gate circuit for enabling the A/D converter 102 to perform conversion according to an AND condition between the signal from the flip-flop 106 and φ _R ', and the flip-flop 106 is a line scan start signal START and a stop signal STOP. A conversion timing generator 103 that operates repeatedly in inversion under the conditions of transfer clock pulse φ _R inputs the 8 bits from the A/D converter 102, determines the selected output according to the threshold value, and forms a binary video signal. Data selector, G7-G9 are latch circuits 107-
Gate circuits and latch circuits 107 to 110 which set the threshold value of the data selector 103 using the 3-bit code from 110 latch the element data of the dither matrix shown in FIG. 6b or 6d as a set of 3-bit codes, and each The latch data corresponds to matrix element data 1, 4, 2, 3 or 1, 3, 4, 2, etc. (in the order of 107→110). 111 and 112 are latch circuits 107 to 1
10 is a preset means for sequentially inputting matrix element data, and keys A to D in Fig. 1-2 are used.
It operates when there is an input, selects a desired threshold value, and sets it in each latch circuit.

That is, by turning on keys A to D, the threshold values of the numbers circled in FIG. 8 a to d are selected, and each latch circuit 107 is
~110. Key on (e.g. key A
is turned on, the matrix arrangement shown in FIG. 6b is selected and set).
1 outputs C1 to turn on the latch circuit 107, further generates element data 1 from the preset means 112 and causes the latch circuit 107 to latch on, and then outputs C2 from the preset means 111 to turn on the latch circuit 108. Further, element data 4 is generated from the preset means 112 and latched in the latch circuit 108, and element data 2 and 3 are similarly generated in the latch circuit 109,
Latch it to 110. The circuit for this purpose is omitted because it can be done with a normal matrix circuit. In this way, a desired threshold value is preset into each latch circuit as a 3-bit code. In the case of FIG. 8a, the bright areas are divided into four levels and the output is selected, so that the intermediate tones in the bright areas can be reproduced more finely than the intermediate tones in the dark areas.

G3 to G6 are for synchronizing the output of the latch circuits 107 to 110, and the latch circuits 107 to 108 or the latch circuits 109 and 110 are alternately activated depending on the even number or odd number of pixels to be read,
This gate alternately selects and switches between latch circuits 107 and 108 and latch circuits 109 and 110 depending on the odd number, and in combination with flip-flop 105 constitutes a quaternary counter. The flip-flop 105 is composed of two flip-flops, and the two flip-flops are repeatedly inverted and controlled by a signal φ _R ' corresponding to a pixel scan in the line direction and a signal end-of-scan EOS corresponding to a line change. The situation of latch circuit selection is shown in FIGS. This allows the threshold values to correspond to the elements of the matrix pattern depending on the reading (transfer) scan.

Note that φ _R ' is the transfer clock φ _R as shown in Figure 5 d and k.
The line scan start signal START and stop signal STOP, which are delayed by half a bit, are obtained at the timings f and g in FIG.

The operation will be explained with reference to the time chart shown in FIG.

The V _OUT signal in Figure 3 is input to the VIDEO input port in Figure 4.

Before starting scanning the original, perform dummy scanning for one line of the most cut CCD. Port output during this scan
A reference black level signal BL-RF and a reference white level signal WT-RF from VIDEO are held in sample and hold circuits 101 and 101', respectively. As shown in Fig. 5 i, j, k, l, the reference black level signal is determined by the BL signal and the sample timing signal φ _R '.
Similarly, the reference white level signal WT-RF is inputted and held at BL-RF using the WT signal (not shown in FIG. 5) and the sample timing signal φ _R '.

In addition, in FIG. 5, i is the BL signal which becomes 1 only during the period when the reference black level signal BL-RF is present, j is the image signal transfer clock φ _R , and k is the reference black level signal BL-RF.
A sample timing signal representing the RF sample timing, 1, indicates the input image signal to be sampled.

The reference output of each sample and hold circuit is supplied to the A/D converter 1 via amplifiers 104 and 104'.
It is input to the reference voltage port of 02. When document scanning is started, the read data VDS is input to the A/D converter port. During this scanning, the reference black and white levels are input to the port and held, so the A/D converter performs A/D conversion to convert the input data to the port between these black and white levels into 8-bit levels.
The conversion level is shown in FIG. Therefore, the intermediate tones of pixels are divided into nine level ranges.

By the way, the port of the A/D converter 102,
On the other hand, since the enable signal LE is applied only during the image area as shown in FIG. 5h, the video signal input to the port is A/D converted only during that period as described above. The timing of this enable signal is obtained by the flip-flop 106 and φ _R ', which are operated by the START signal (FIG. 5f), STOP signal (FIG. 5g), and φ _R signal (FIG. 5a). This produces the waveform shown in Figure 5e.

Further, the A/D converter 102 has eight comparators (not shown), whose reference inputs are from ports to
The output of the comparator is output as is. for example
This is possible with the ADC-HU3BGC type.

Next, the 8-bit parallel output of the A/D converter 102 is input to each input port of the data selector 103, and the output data is selectively controlled by the 3-bit control signal input to ports _A0 to _A2 . In this case, the threshold value for selection control can be changed depending on the content of the 3-bit code to ports _A1 to _A2 . Also, in this example, the dither matrix shown in FIG. 6b is used, so the threshold values are arranged periodically.
The selection of the threshold value is controlled depending on whether the corresponding pixel along the line is an even number or an odd number, or whether it is an even number line or an odd number line.

As a result, the data selector 103 applies level weighting to the pixel data by threshold control, and outputs the pixel data as a temporally serial binary signal to a beam modulator or memory. Thereby, copying can be performed at the desired gradation and optimum gradation.

To explain the operation of the threshold selection control, the flip-flop 105 is inverted by the φ _R ' corresponding to the pixel and the EOS signal corresponding to the line, and its four outputs are decoded by gates G3 to G6 to form a quaternary counter. , outputs signals o to r in FIG. This signal is input to the terminals of the latch circuits 107-110 as a select signal. Therefore, the latch circuits 107 to 110 output 3-bit data corresponding to the selected and latched matrix elements in synchronization with the pixel timing, depending on whether the pixels on one line are even or odd, or whether the pixels are even or odd on the line. The 3-bit data is sent to the data selector 103 via gates G7 to G9.
It is input to the A ₀ to A ₂ terminals and the threshold values are sequentially switched.

By the way, the control circuit 11 sets data by signals to the terminals, , and terminals of the latch circuit.
2, 111 is a latch circuit 1 which processes and outputs a signal obtained from the scanning by pre-scanning the original before image scanning for printing is started.
The optimum threshold control data can be latched from 07 to 110.

Note that the reference black level signal BL-RF and reference white level signal WT-RF input to the sample and hold circuits 101 and 101' are not specific to CCDs,
It is also possible to read and use black and white marks etc. provided at specific positions on the document platen glass.

In addition, the document is pre-scanned, and the black peak and white peak of the document are read and determined, and the sample and hold circuit presets and holds them as a reference black level signal BL-RF and a reference white level signal WT-RF. be able to.

In this way, the image signal can express light and shade using a black and white binary signal by sequentially changing the four threshold values. However, for diazo originals or originals with colored backgrounds, it is preferable to erase the color of the background before playing. The control circuit is not shown, but if you use a program control method like a microcomputer, you can easily set the dither threshold by preparing programs for diazo originals, colored originals, etc. . Furthermore, it is often the case that a part of a white original is not reproduced with shading, but in this case, the threshold value only needs to be changed when reading a desired location. In this way, important parts of a document can be marked by using different shading. The above control can be easily performed by creating a general-purpose program and inputting the data necessary for the control circuit using a numeric keypad or a keyboard switch. In addition, it is also easy to read the image signal into the control circuit during the first dummy scan, calculate the optimal dither threshold value, and automatically set it. or,
The optimal dither matrix can also be determined by storing the image signal on a CRT monitor without sending it to the reproducing device, and by manually setting the threshold value while looking at the monitor. Although a 2×2 dither matrix is set in this embodiment, higher quality image processing can be performed by controlling not only the threshold value but also the size of the dither matrix.

〔effect〕

As explained above, according to the present invention, a high-quality halftone image can be accurately reproduced.

[Brief explanation of drawings]

1-1 and 1-2 are a sectional view and a plan view of the operating section of a copying machine to which the present invention can be applied, FIG. 2 is a block diagram of the reading section in FIG. 1, and FIG. 3 is a block diagram of the reading section in FIG. 4 is a processing control circuit diagram of this embodiment, FIG. 5 is an operation time chart of FIG. 4, and FIGS. 6, 7, and 8 are explanatory diagrams of the operation in FIG. 4. In the figure, 6 is CCD, 1
7 is a laser oscillator, 101 and 101' are sample and hold circuits, and 102 is an A/D converter.

Claims (1)

[Scope of Claims] 1. An apparatus for optically reading an original and reproducing an image, comprising: means for photoelectrically converting the original image; means for generating a transfer clock for sequentially transferring pixel signals from the photoelectric converter; means for sequentially A/D converting the pixel signals transferred from the photoelectric conversion means; the A/D conversion means converts the pixel signals into A/D based on a predetermined clock signal synchronized with the transfer clock; The pixel signal is configured to perform D conversion, and further includes means for dithering the pixel signal output from the A/D conversion means using a predetermined threshold value matrix and outputting a reproduced signal, and a threshold value matrix used by the output means. An image reproducing apparatus characterized in that the output means performs a switching operation of each threshold value of the threshold value matrix selected by the selection means based on the predetermined clock signal. .