JPH0456987B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a copying apparatus that identifies an original image and determines copying conditions.

(Prior Art) As one of this type of copying apparatus, one with the following control algorithm has been considered. That is, a document image is preliminarily scanned, and a density histogram is first created. Then, the minimum density is determined from this density histogram, and the developing bias voltage is determined based on the minimum density value. However, if the minimum density value is below a certain value, the developing bias voltage is determined based on the density width of the histogram.

However, in the case of copying machines using the control algorithm described above, since the background density is detected from the lowest density level, there is a problem that background fogging is likely to occur in the case of originals such as blueprints with uneven density on the background. be. Furthermore, in the case of the above-mentioned apparatus, there is a problem in that no consideration is given to gradation images.

(Object of the Invention) The present invention has been made in view of the above-mentioned problems, and its object is to realize a copying apparatus that can reproduce images satisfactorily regardless of whether they are line drawings or gradation drawings.

(Structure of the Invention) The present invention that achieves this object includes means for scanning an original image and photoelectrically converting the image information, quantizing the image information photoelectrically converted by the means, and creating a density histogram from the quantized data. , by focusing on a means for determining the low-density side peak level concentration and histogram concentration width from the density histogram, and a combination of the low-density side peak level concentration and histogram concentration width determined by the means, The developing condition determining means lowers the developing bias voltage when the histogram density width is narrow, and increases the developing bias voltage when the low density side peak level density is high and the histogram density width is wide. This method is characterized in that copying is performed according to determined developing conditions.

(Embodiments) Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention. In the figure, 10 is a main body of a copying machine, and 20 is an automatic document feeding device. First, in the copying apparatus main body 10, reference numeral 11 denotes an original glass (original table) on which the original 1 is set, and 12 irradiates light from a light source 12a of the original 1 on the original glass 11, and the reflected light is reflected onto a mirror 12b. and an exposure optical system that guides the light to the photoreceptor drum 13 via a lens 12c and the like. The photosensitive drum 13 is uniformly charged by the charging electrode 14,
The electrostatic latent image formed on the photoreceptor drum 13 by the exposure optical system 12 is developed in the developing section 15 .
16 is a condensing lens (not shown) that collects the reflected light from the original.
As the photoelectric conversion element 16, a solid-state imaging device such as a CCD or a photodiode array, a normal photo sensor, or a photo transistor is used. In this embodiment, these imaging devices are composed of a large number of elements, each element is arranged in a direction perpendicular to the plane of the paper in FIG. 1, and main scanning is performed by sequentially reading the output of each element. It's becoming like that. Note that the sub-scanning is performed by feeding the original 1. 17 is a signal processing unit which processes image signals photoelectrically converted by the photoelectric conversion element 16;
It receives Se and performs various signal processing for image identification.

A block diagram of the signal processing section 17 and its peripheral circuits is shown in FIG. In this figure 2,
16 converts the incident light amount signal into an electrical image signal Se
The above-mentioned photoelectric conversion element 171 is a sampling circuit for the image signal Se. The sampling circuit 171 uses peak sampling rather than peak sampling because it makes it easier to grasp the characteristics of the image in a global manner.
The apparatus is configured to perform equal time interval sampling. 172 is an A/D converter that converts the analog signal from the sampling circuit 171 into a digital signal. The output of the sampling 171 obtained when scanning the upper limit density (for example, effective reflection density 0.8) of the low density part of the original is at a level of 50 to 80% from the low level side of the input width of the A/D converter 172. The level has been adjusted to reach the target level. This is to enable even slight differences in background density to be detected on the density histogram by finely quantizing the low density portion. 173 is a central processing unit (hereinafter referred to as CPU) such as a microprocessor that creates a density histogram based on the output data of the A/D converter 172 and performs image identification from the density histogram; 174 receives data from the CPU 173; Memory (RAM) for recording, storing, and supplying the recorded data to the CPU 173, 1
A memory (ROM) 75 stores calculations and other programs for the CPU 173. Furthermore, 176
is a reference clock generator, which generates pulses and a sampling circuit 17 that control the light reception time of the photoelectric conversion element 16.
1 and A/D converter 172, and a clock signal that determines the timing of calculation, data sending or calling of CPU 173, etc. Above CPU17
The image identification in step 3 is performed based on the low-density side peak level density of the density histogram (the peak level density present at the lowest density side) and the histogram density width. For example, when a density histogram as shown in Fig. 3 (the horizontal axis of the figure shows the number of levels 0 to 64 corresponding to the effective reflection density) is obtained, based on the low density side peak level density d and the histogram density width Perform image identification. That is, the background density of the image is determined from the value of the low-density side peak level density d, and the density distribution of the image is determined from the size (width) of the histogram density width.
Specifically, as shown in Figure 3, the horizontal axis (effective reflection density)
Divide into multiple concentration sections (in the case of Fig. 3, there are two sections () and () separated by the number of levels 30, which will be explained below based on this example), and determine which section the low concentration peak level concentration d falls into. At the same time, find out what value the histogram density width (described below based on this example), and performs image identification. and,
The combination of (), () and , outputs an identification signal Sb for determining the development conditions. still,
Each of the sections 171 to 176 described above forms the signal processing section 17.

Incidentally, the shape of the density histogram changes depending on the size of the unit imaging area (area of the reading spot on the document, hereinafter referred to as spot) by the photoelectric conversion element 16. For example, in the case of a line drawing, the time-series pattern of the light intensity signal (effective reflection density) corresponding to the image density obtained when a document image (area to be determined) is scanned with a small-area spot is one of the most low-density signals. In the case of a gradation image, the pattern is a pattern in which one or a small number of high density signals are scattered, and in the case of a gradation image, high, medium or low density signals are relatively mixed and distributed. On the other hand, the time-series pattern of the image density light intensity signal (effective reflection density) obtained when the spot area is relatively wide is that the high density signal increases rapidly in the case of line drawings compared to that of the spot with a small area. However, in the case of gradation images, it does not show much change. Next, the difference in the effective density histogram depending on the size of the spot will be specifically explained. Fourth
The figure and Figure 5 are character image parts (line drawings) of a certain newspaper.
Histogram obtained by scanning the photographic image area (gradation image) at equal intervals of 1 mm using a 0.1 mm square (0.01 mm ² ) spot and a 2 mmφ (3.14 mm ² ) spot, respectively (density 0.1 is used as the density interval). The histogram shown by the solid line is obtained from the character image part (line drawing), and the histogram shown by the broken line is obtained from the photographic image part (gradation drawing). As is clear from a comparison of the two figures, in the line drawing, the maximum peak of the histogram for a 2 mm diameter spot is significantly shifted to the lower density side than the maximum peak for a 0.1 mm square spot. On the other hand, in a gradation image, there is not much movement.
This situation changes the sampling interval to 0.3mm, 0.9mm,
Since there is almost no difference even if the difference is changed to 1.0 mm or 1.5 mm, this is caused by the size of the spot. Further, although the concentration interval of the histogram can be arbitrarily set, the movement phenomenon of the maximum peak can be observed in the same way. Therefore, how to choose the area of the spot is a problem, especially in the case of line drawings, but it is important to select a steep spot so that the low density peak level density can be clearly determined even when the low density side is finely quantized. It is necessary to select a spot area where a peak can be obtained. From this point of view, it is preferable to select the spot size to be 0.1 mm ² or more.

A process control section 18 receives the identification signal Sb from the signal processing section 17, and sets development conditions based on the identification signal Sb. In addition to this, the process control unit 18 also includes an automatic document feeder 2.
It performs various controls such as controlling the feeding operation of zeros and controlling the movement of the reading optical system 12. This control of the development conditions by the process control section 18 is achieved by controlling the development bias voltage. Figure 6 shows the image identification signal Sb
This figure shows an example of the developing bias voltage V _B selected by the process control unit 18 according to the combination of (), (), and , which are instructed by .
indicates that the developing bias voltage is low, N indicates that the developing bias voltage is an intermediate value, and H indicates that the developing bias voltage is high. The table shown in FIG. 6 may be written in the ROM 175, for example, and the CPU 173 may output the above-mentioned values as set values to the process control section 18, or the table shown in FIG. A ROM in which the table is written may be provided separately, and the CPU 173 may output a signal indicating a combination of (), (), and so on. The description herein is
The latter configuration is assumed.

Referring again to FIG. 1, the automatic document feeder 20
1, a paper feed unit 22 that takes in the originals 1 placed on a paper feed tray 21 one by one, and a conveyor belt 2 that holds the originals 1 on the outer surface of the original glass 11 side and sends them to the left in FIG.
3. A drive roller 24 and a driven roller 25 ensure the above-mentioned movement of the conveyor belt 23. In order to send the document 1 taken in by the paper feed section 22 to the conveyance start position by the conveyor belt 23, the document 1 is transferred to the conveyor belt 23.
Pressure rollers 26 and 27 that press the belt (the part that wraps around the drive roller 24), guide rollers 28 and 29 that regulate the main transport path of the transport belt 23, and between the guide rollers 28 and 29, the transport belt 23 is Presser rollers 30 and 3 that press against the 11 side
1. In cooperation with the stopper roller 32, the original glass 1
A stopper 33 that stops the original 1 on the document 1 at an appropriate setting position, a paper discharge tray 34 on which the original 1 discharged after reading is accumulated, and a sensor that detects that the original 1 is set at the appropriate position on the original glass 11. It is composed of 35 mag.

The operation of the copying apparatus configured as above will be explained next.

First, when the original 1 is set on the paper feed tray 21 and a copy start button (not shown) is activated, the process control unit 18 moves the reading optical system 12 to the initial position (first position).
(The leftmost position in the figure is the exposure scanning start position)
At the same time, the paper feed section 22 and the conveyor belt 23 are rotated to convey the document 1, and the document glass 1 is
After stopping the document 1 at the proper position at the upper end of the stopper 33 protruding from the upper surface of the document 1, the conveyor belt 2
Also stop the rotation of 3. During this feeding, the image of the original 1 is identified by the photoelectric conversion element 16 and the signal processing section 17. That is, first, the light intensity signal is converted into an electrical image signal Se by the photoelectric conversion element 16,
A sampling circuit 171 samples this image signal Se. Next, the analog signal Se is converted into a digital signal by the A/D converter 172. This digitized image signal Se is
read by the CPU 173;
The above-described density histogram creation and image identification are performed with the help of the memories 174 and 175, and an image identification signal Sb is output from the CPU 173. This image identification signal Sb is input to the process control section 18. On the other hand, the sensor 35 also sets the original 1 in the proper position, and a signal to that effect is also input to the process control section 18. Above 2
When the signal is input to the process control unit 18, the process control unit 18 controls a predetermined charging current (surface potential).
The light source 12a irradiates the original 1 with light of a predetermined intensity (it may have been irradiated before then), and the reflected light is transmitted to the mirror 12b and the lens 12.
c, etc., to the photoreceptor drum 13, and an electrostatic latent image is formed there. Then, development is performed while applying a developing bias voltage based on the identification result to the developing section 15, and then the toner image is transferred to a transfer paper (not shown), the transfer paper is separated from the photoreceptor drum 13, and the toner image is transferred to the transfer paper. After going through the process of fixing the toner image, etc.
One copy process is completed. On the other hand, in parallel with these developing, separating, and fixing operations, after the exposure is completed, the process control section 18 moves the upper end of the stopper 33 below the upper surface of the original glass 11, and then moves the conveyor belt 3 again.
3 to send the copied original 1 to the paper discharge tray 34. At the same time, conveyance of a new original 1 is started, and the original is set at an appropriate position on the original glass 11.
Thereafter, the same copying operation is repeated, and the paper feed tray 21
All original documents 1 placed on the computer will be copied.

By the way, FIG. 7 is a diagram showing the relationship between original density and copy density when the developing bias voltage is changed.
FIG. 8 is a diagram showing, for reference, the relationship between the document density of the surface potential and the amount of light. The solid line in FIG. 7 shows the characteristics when the amount of light is large, and the broken line shows the characteristics when the amount of light is small. For reference, ● indicates the case where the developing bias voltage is high, ◯ indicates the case where the developing bias voltage is intermediate, and △ indicates the case where the developing bias voltage is low. On the other hand, the solid line and broken line in Fig. 8 indicate the specification under two different settings, where ○ indicates a large amount of light, ● indicates an intermediate amount of light, and ×
indicates a case where there are few. It can be seen from FIG. 7 that the higher the developing bias voltage is, the more the development starts in the high density area, and the greater the amount of light, the more noticeable the image skipping in the low density area. Also, from Figure 8,
It can be seen that when the black paper potential is increased, a rapid potential change occurs in the low density area, and this tendency becomes stronger as the amount of light increases.

According to the above-mentioned copying apparatus, for example, when the low-density side peak level density d is low and the histogram density width When the width X is wide, the developing bias voltage becomes high due to the combination of (), and in other cases, it becomes intermediate. Since this distinction is made using the low-density side peak level density d as one discrimination criterion, background fogging can be reliably avoided. In particular, the concentration classification is 3 instead of 2 () and ().
If you choose the above, you can increase the number of developing bias voltage levels, so you can avoid background fogging and
The density of the line parts can also be maintained in a good state. Furthermore, since the histogram density width X is also used as a discrimination criterion, the reproduction of gradation images is also improved. This histogram density width X can be divided into 3 or more divisions.

Note that as the histogram density width in the above description, a width obtained by cutting at a constant frequency may be used.

Furthermore, although the above description has been made regarding a case in which the photoelectric conversion element 16 does not move during reading for document image identification (a case in which the elements of the imaging device are arranged in an array), the present invention is not limited to this. for example,
Main scanning is performed by running a laser beam over the original 1, and the reflected light from the original 1 is guided to an optical sensor having a single light-receiving surface via a light guiding member such as an optical fiber or a condensing member. It may be configured as follows.

Furthermore, although the above embodiments relate to a copying machine that has an automatic document feeder, it is possible to use a general copying machine that does not have an automatic document feeder, and even if the type is a movable document table type, it is not a fixed type. It is possible to implement even if there is. Also, there is no need to limit the copying process to the normal cursoron method.

(Effects of the Invention) As explained above, according to the present invention, since the peak level density on the low density side can be precisely determined by fine quantization, it is possible to accurately identify what level of background density the original has. Therefore, images can be reproduced without causing background fog. Furthermore, since consideration is given to gradation images, it is possible to obtain an image that is easy to see and of high quality.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the main parts of an embodiment of the present invention, FIG. 2 is a block diagram of the signal processing section in FIG. 4 and 5 are explanatory diagrams of the histogram waveform. FIG. 6 is an explanatory diagram showing a value selection table for density control. FIG. 8 is a diagram showing the relationship between original density and copy density, and FIG. 8 is a diagram showing the relationship between original density and surface potential. 10...Copying device main body, 11...Original glass,
12...Exposure optical system, 12a...Light source, 13...
Photosensitive drum, 14...Charging electrode, 15...Developing section, 16...Photoelectric conversion element, 17...Signal processing section, 171...Sampling circuit, 172...
A/D converter, 173...CPU, 174...Memory (RAM), 175...Memory (ROM), 1
76... Reference clock generator, 18... Process control unit, 20... Automatic document feeder.

Claims (1)

[Claims] 1. A means for scanning an original image and photoelectrically converting the image information, quantizing the image information photoelectrically converted by the means, creating a density histogram from the quantized data, and calculating a low-density side peak level density and a histogram from the density histogram. Paying attention to the means for determining the density width and the combination of the low-density side peak level density and histogram density width determined by the means, if the low-density side peak level density is low and the histogram density width is narrow, the developing bias voltage is lowered. , further comprising a developing condition determining means for increasing the developing bias voltage when the low density side peak level density is high and the histogram density width is wide, and copying is performed according to the developing condition determined by the developing condition determining means. A copying device that uses