JPH0789243B2 - Copy density control method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a copy density control method, and more particularly to a copy density control method for controlling the copy density of a film original.

[Conventional technology]

Conventionally, when copying a film original, etc., based on the detected value of the density of the background portion of the image (minimum value for negative image, maximum value for positive image), the exposure amount to the original or the development bias etc. Is controlled to control the density of the copied image.

Further, the maximum value and the minimum value of the image density, that is, the densities of both the background portion and the image portion of the document are detected, and the copy density is controlled based on the detected value.

[Problems to be solved by the invention]

In either method, since only the maximum or minimum density detection value is observed, if the maximum or minimum density shifts due to noise, etc., the image density will change as it is, so the appropriate density for each copy is stable. There were drawbacks such as not being able to obtain it.

Furthermore, if the original is smaller than the copy paper size to some extent, it is good if only the background portion of the image is detected.
When the image area is detected, the density of the frame part is detected outside the original, that is, when the image is copied,
The set density may be off. This can be prevented to some extent by changing the photometric area depending on the size of the copy paper, or by measuring the area near the center of the copy paper with a high probability of an image, but it is not perfect.

Furthermore, especially when detecting the background part of an image,
In the case of microfilm, the part of the platen of the flatbed camera may be imprinted on the part outside the original, and that part is detected as the density of the background part of the original,
In some cases, the concentration did not reach the proper level.

However, in the case of a photographic original or a newspaper original, if the density is partly dark or thin, there is a problem that the maximum or minimum value of the image density is pulled and the density does not become appropriate.

[Means for solving problems]

The present invention has been made to solve such a problem, and by using the frequency distribution of detected densities, malfunctions caused by noise are reduced, and the influence of partial image areas and original areas where densities are extremely different. It is possible to reduce
By detecting whether or not there is a frame on the document, and if there is a frame, the image density can be detected in the part excluding this frame, so that the copy density can be controlled stably and accurately. It is an object of the present invention to provide a copy density control method that can be performed.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.
FIG. 1 is a block diagram showing a control circuit configuration of an electrophotographic copying machine to which the present invention is applicable, and FIG. 2 is a basic configuration diagram of a reader printer used in the same embodiment.

In the figure, 1 is a microfilm original (hereinafter referred to as original), 2 is an illuminating lamp for irradiating the original 1, 3 is a spherical reflecting mirror for reflecting light rays from the illuminating lamp 2, 4
Is a condenser lens for condensing the light reflected by the spherical reflecting mirror 3,
The condenser lens 4, the spherical reflecting mirror 3 and the illuminating lamp 2 constitute an illuminating device.

5 is a projection lens on which the image light of the original 1 illuminated by this illuminating device is projected, 6 is a plane mirror which reflects the image light from this projection lens 5, and 7 is image light reflected by this mirror 6. Is a plane mirror that reflects light, 8 is a slit plate provided with a slit 9 through which the image light reflected by the mirror 7 passes, 10 is an exposure drum through which the image light is projected, and 11 is this exposure. It is a support body in which mirrors 6 and 7 for reflecting the image light projected on the drum 10 are crossed at a right angle and fixedly supported.

The support 11 is adapted to move integrally with the mirrors 6, 7 in the direction of arrow A. The mirrors 6 and 7 are normally at the home position, and they move forward when copying, and when moving forward,
The image of the original 1 is exposed on the photosensitive drum 10, and when the exposure of the image is completed, the document 1 is moved back to the home position.

The photosensitive drum 10 rotates in the direction of arrow B at a constant speed, and
6, 7 move at half the peripheral speed of the photosensitive drum 10. A slit plate 8 having the slit 9 immediately in front of the photosensitive drum 10.
Are arranged. Reference numerals 12-1 to 12-8 are light receiving elements for receiving a part of the projected image reflected by the mirrors 6 and 7 supported by the support 11. These light receiving elements 12-1 to 12-
8 is provided on the slit plate 8.

With the above-described structure, the image of the original 1 is divided into slits, is imaged on the circumference of the photosensitive drum 10 through the slits 9, and the originals 1 are sequentially scanned by the scanning indicated by arrows A and B. The entire image is exposed to light and the peripheral surface of the drum 10. At that time, the light receiving elements 12-1 to 12- are provided near the slit 9 of the slit plate 8.
8 is arranged to receive a part of the projected image reflected by the mirrors 6, 7.

The light receiving elements 12-1 to 12-8 detect the transmitted light of the original 1 to detect the image density of the original 1 and detect the exposure amount of the photosensitive drum 10 prior to the image exposure. In order to detect the image density by the light receiving elements 12-1 to 12-8, the originals 1 are scanned by prescanning the mirrors 6 and 7 before the regular exposure process, and the light receiving element 12 receives during the preliminary scanning. The brightness of the illumination lamp 2 is controlled on the basis of the light amount, and thereby the light amount on the photosensitive drum 10 is appropriately controlled, and a good copy of the original is obtained.

FIG. 1 is a block diagram showing a control circuit configuration of the electrophotographic copying machine, in which exposure adjustment is performed by digital signal processing using a microcomputer, which is a computer, to control copy density.

The image density signal obtained by photoelectric conversion by the light receiving elements 12-1 to 12-8 is switched by the multiplexer 21 by a signal from a one-chip microcomputer (hereinafter referred to as "CPU") 20 having a built-in I / O. The output amplifier circuit 22
Is input to the CPU 20, is amplified by the output amplifier circuit 22, and is then input to the CPU 20.

The CPU 20 performs arithmetic processing (described later) based on the image signals of the light receiving elements 12-1 to 12-8, and based on the arithmetic result,
The amount of lamp light and the developing bias are controlled. The lamp and developing bias 28 convert the digital signals output from the CPU 20 into analog signals by the D / A converters 24 and 25, respectively, and are controlled through the lamp regulator 26 and the high voltage unit 27.

Next, a calculation process inside the CPU 20 will be described.

FIG. 3 shows a frequency distribution chart based on the image information from the light receiving elements 12-1 to 12-8. This is
Although it is an example of a frequency distribution chart in the case of a negative image as shown in FIG. 4a, it can be seen that when the film density D becomes small, two peaks tend to approach each other as shown in the figure.

Further, when the image area portion, the background portion, and the frame portion are divided as shown in FIG. 4a, they can be divided into areas as shown in FIG. 5a on the frequency distribution chart. Also in the case of a positive film, it can be divided into regions as shown in FIGS. 4a and 4b. In both the negative image and the positive image, the frequency of the image area is low, the frequency is in the area between the background area and the frame area, the frequency of the background area is high, and the mountain is gentle. The frequency of the frame portion depends on the degree of the frame, but in general, an image with a frame has steep mountains. At this time, the information necessary for controlling to an appropriate image is that of the background portion, but in particular, here it is the peak value of the background portion of the frequency distribution chart.

However, if only the peaks on the frequency distribution chart are taken, it may not be clear whether they mean the background peaks or the frame peaks.

Therefore, a method of obtaining the peak S _{PK of the} background portion in the case of a negative film will be described below.

FIGS. 6a to 6c show the histogram when the frame area is increased, and the light receiving element output value S _PK when the peak value is shown.However, as shown in FIG. 6c, the peak value of the frame portion is If the peak value of the background part is exceeded, the peak value of the frame part will be regarded as the peak value of the entire frequency distribution chart, and if it is used as a parameter for proper image control, it will deviate significantly from the proper value. Become.

Therefore, as shown in FIGS. 6d to 6f, the light receiving elements 12-1 to 12-12
Output value S _max between the minimum value of the maximum output value S _max and the detected concentration is the maximum value of the detected concentration is output minimum value S _min from -8
From the threshold value S _SH, which is a value smaller than the constant value K to the maximum output value S _max , the peak value n _{PK2 of the} frequency which is the frequency of the detected concentration is detected, and this value is within a certain constant value n _SH . In this case, it is determined that there is no frame, and the light-receiving element output value S _PK when the peak value n _{PK of the} entire frequency distribution chart is indicated is taken.

Further, when the peak value n _PK2 exceeds n _SH , it is determined that there is a frame, and the light receiving element output value when the peak value n _PK is shown on the frequency distribution chart excluding the frequency distribution in the range (that is, Light-receiving element output 12-1 to 12-8 output minimum value S _min
From the above-mentioned constant value n _SH to the peak value n _{PK in} the frequency distribution diagram
The received light output value) is shown as S _PK . (FIG. 6f) FIG. 7 is a flow chart showing a control flow in one embodiment of the present invention, which uses a frequency distribution of detected densities at a plurality of portions of an original, and is shown in detail in this flow chart. A table showing the relationship between the peak value S _PK thus obtained, the lamp control data and the developing bias control data is stored in advance in the memory in the CPU 20, and the output data of the light receiving elements 12-1 to 12-8 is stored. The amount of lamp light and the developing bias are controlled by the calculated value of S _PK , and by these controls, the image is always controlled to be an appropriate image.

The above explanation is about the procedure for taking the peak value of the background portion in the case of a negative film and controlling the copy density based on the detected density value indicating this peak value.

In the case of positive film, in comparison with the case of negative film, 1) the threshold value is set to a different value, and 2) the maximum output value S _max used to obtain the peak value S _PK of the background portion is the minimum output value. By using S _min and using the maximum output value S _max for the minimum output value S _min , the peak value S _SP of the background portion is obtained, the lamp light amount and the developing bias are controlled, and control is performed so as to obtain an appropriate image.

This can be understood from the fact that the lightness and darkness of an image are inversely related to each other in a negative film and a positive film.

According to the copy density control method of the embodiment, by using the frequency distribution of the detected density at a plurality of positions of the original, malfunctions due to noise and the like are reduced, and the influence of some image areas having extremely different densities is reduced. It detects whether the document has a frame, and if there is a frame, it detects the background image density by detecting the image density in the part excluding this frame part. By controlling the exposure lamp and the developing bias based on the value, there is an effect that a proper image can always be obtained accurately and stably.

Further, in the embodiment, the threshold value S _SH is determined at a fixed value K from the light receiving element output maximum value S _max , but it may be set to a constant value from the light receiving element output minimum value S _min , for example, K. Of course, the threshold value S _SH may be set to be (S _max + S _min ) / 2. In addition, with α as a coefficient, the calculation formula S _min + α (S _max −
S _min ). Further, the method of determining the threshold value S _SH is not particularly limited as long as S _min <S _SH <S _max . Furthermore, the values of K and α may be controlled so as to have different values in each case by providing means for determining whether the document is a negative image or a positive image. It goes without saying that the distribution of histograms may be represented by a histogram.

Although eight light receiving elements were used in the embodiment of the present invention,
It goes without saying that the number of light-receiving elements is not limited, and elements such as CCD arrays can be used.

〔The invention's effect〕

As described above, according to the present invention, by using the frequency distribution, malfunctions due to noise and the like are reduced, the influence of a partial image area having extremely different density is reduced, and the original has a frame. To detect if
If there is a frame, by detecting the image density in the part excluding this frame, the density of the background area can be reliably detected, and the exposure lamp and the developing bias can be controlled based on the detected value. Therefore, there is an effect that an appropriate image can always be obtained accurately and stably.

[Brief description of drawings]

FIG. 1 is a block diagram showing a control circuit configuration of an electrophotographic copying machine to which the present invention can be applied, FIG. 2 is a basic configuration diagram of a reader printer used in the embodiment, and FIG. Frequency distribution charts, Figures 4a and 4b
The figures show the image part, background part, and frame part in the negative image and the positive image, respectively.
Frequency distribution charts corresponding to Figures 4a and 4b, Figures 6a to 6f
The figure is a frequency distribution diagram for explaining one embodiment of the present invention,
FIG. 7 is a flow chart showing the control flow of the embodiment of the present invention. 1 ... Original 2 ... Illumination lamp 12-1 to 12-8 ... Light receiving element 20 ... CPU 21 ... Multiplexer In the drawings, the same reference numerals indicate the same or corresponding portions.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location G03G 15/08 501 Z

Claims (7)

[Claims] 1. A copy density control method in a copying apparatus having a density detecting means for detecting an image density of an original, said density detecting means detecting the density of a copying portion to obtain a frequency distribution of the detected density, A threshold value is provided between the maximum value and the minimum value, and when the peak value of the frequency distribution in the range from the threshold value to the maximum value or the minimum value of the detected concentration is a certain value or less, the distribution of the entire frequency is When the peak value is taken and exceeds the constant value, the peak value of the frequency distribution excluding the frequency distribution in the range is taken, and the copy density is adjusted based on the detected density value when the peak value is shown. Copy density control method. 2. The maximum value or the minimum value of the detected density is the maximum value of the detected density for a negative image original and the minimum value of the detected density for a blurred image original. The method for controlling copy density according to item 1. 3. The copy density control method according to claim 1, wherein the threshold value is a value calculated by a calculation formula S _min + K with a minimum value S _min of the detected density and a constant K. 4. The copy density control method according to claim 1, wherein said threshold value is a value calculated by a calculation formula S _max -K, where S _max is a maximum detected density. 5. The copy density control method according to claim 1, wherein the threshold value is a value calculated by a calculation formula (S _max + S _min ) / 2. 6. The calculation formula for the threshold value, where α is a coefficient S _min +
The copy density control method according to claim 1, wherein the method is a value calculated by α (S _max −S _min ). 7. The value of K or .alpha. Is different depending on whether the original is a negative image or a positive image, and any one of claims 3, 4, and 6 is claimed. The method for controlling copy density according to.