JPS59197032A - Controller for copy density - Google Patents

Abstract

PURPOSE:To control a copy density in accordance with an obtained frequency distribution by sampling the outut waveform of a density detector, which scans an original, to accumulate its frequency. CONSTITUTION:Densities of the texture color and the picture on an original 4 which s sent to an original placing face 7 by an ADF device 6 are detected by a detector 8, and density values which are outputted in succession to a maximum value and minimum value of the output signal of a sampling circuit 10 are selected, and density divisions to which these density values belong are discriminated by a density discriminating circuit 11, and a histogram based on density divisions is formed in a counting circuit 12. A developing part 3 is controlled in accordance with the state of this histogram by a bias adjusting device 14 to adjust the copy density. Consequently, an accurate character density is obtained by sampling of a peak value, and an accurate texture density is detected even for the texture part of less level variance, and the copy density is controlled accurately.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a copy density control device that detects the density of a document and controls copy density.

(Prior Art) Generally, it is desirable that the background color of a copy made by a copying machine or the like is the same as the background color of the copy paper (generally white), regardless of the background color of the original. However, for example, if you adjust the copy depth so that the background color of the copy of A is white for an original with a relatively dark background color, 1)) when copying an original with a pale image such as brush writing, the Image quality deteriorates.

Many of today's copying machines are equipped with manual density control devices, and in cases such as the one described above, the operator can make trial copies and adjust the density to the optimum level, or rely on empirical Nr to make adjustments. However, it was not possible to prevent unnecessary copying.

In addition, in recent years, copying machines equipped with automatic document transfer devices (ADF devices) have rapidly become popular in order to speed up and improve the efficiency of copying operations. In this case, it is necessary to operate the mI reward control device quickly and frequently every time the density pot fl of the original changes. but,
Such an operation is nearly impossible in reality.

Therefore, various copy opening control devices have been proposed that detect the density of the original and automatically adjust the copy density (Japanese Patent Laid-Open No. 53-93834, etc.). Because the density conditions are controlled from the minimum value, for documents with darker images than the most necessary image density, such as pencil documents with printed lines, the density conditions may be adjusted for the printed lines. There were many inconveniences.

Furthermore, as an improved LC method, (1) the density distribution of the original is sampled at regular intervals, and the maximum and minimum values of the density are also sampled, and the frequency distribution for density values is obtained by mixing the two; A method for determining concentration conditions by utilizing the statistical properties of its distribution (Japanese Patent Laid-Open No. 1983-
No. 45564) or (ff) The density distribution of the original is sampled at regular intervals, the frequency distribution function corresponding to the density value is determined, and the maximum value in this distribution is smoothed, thereby contributing to the determination of density conditions. (Japanese Unexamined Patent Publication No. 1983-
No. 89751) has been proposed.

In both of these cases (:r>, (II), a sampling method with a fixed period is used, so in order to obtain accurate character/ground density, it is necessary to increase the sampling frequency. However, the sampling As the frequency increases, the overall frequency increases, which necessitates an increase in the capacity of the data memory that stores the frequency.In addition, sampling the intermediate portions of the rising and falling edges of the output waveform increases the appearance. , there is a drawback that the intermediate density portion increases.In addition, in the method shown in (I) using In1 of constant period sampling and peak value sampling, the sampling frequency for sampling the peak value must be changed. Although sampling at a frequency of 1/N (N is an integer of 2 or more, for example) prevents the increase in frequency obtained from a flat output (detected m degree signal) waveform like the background, The disadvantage is that there is a possibility of sampling the middle part of the rising edge or falling edge.

(Objective of the Invention) The present invention eliminates such drawbacks, saves data memory for storing frequencies for S degree values without increasing the sampling frequency, and obtains accurate background and character densities. An object of the present invention is to provide a copy density control device that controls the copy density based on the present invention.

(Structure of the Invention) The present invention achieves this object in a copy density control device that detects the density of an original and controls the copy density. If it changes, sample the maximum or minimum value and accumulate the frequency, and if the output waveform does not change,
The present invention is characterized in that the frequencies obtained by sampling at a constant period are compressed and accumulated, and the copy density is controlled according to the frequency distribution obtained based on these accumulations.

(Example) Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention, and shows its application to a copying machine (the developing device is of a magnetic brush type) equipped with a F00F device. Therefore, this figure also shows components other than the copy density control device. In the figure, Ex is a part other than the copying density control device I, that is, a copying machine part. In this EX, 1 is a photoreceptor drum, and the electrostatic The latent image is developed in the developing section 3. Note that the copy density is adjusted by switching the bias voltage applied to the developing section 3. Further, the originals 4 in the original stock section 5 are sent onto the original placing surface 7 one by one by the ADF device 6.

Reference numeral 8 denotes an original density detector for detecting the density of the original 4. The original density detector 8 is moved by the original density detector driving device 9 in a direction perpendicular to the transport direction (main scanning direction) of the original 4.
Detects the background color and reflectance of the image. Original density detector 8
The output of the document density detector 8 is the average value of the amount of reflected light in the irradiation spot area. The average value of the density shows a higher reflectance than the image area, making it impossible to faithfully capture the density distribution of the original. Therefore, it is necessary to reduce the detection spot diameter. Further, it is desirable that the output of the document density detector 8 changes linearly within the range of the seismic intensity distribution of the document. The document density detector 8 used for this purpose is preferably a photodiode, but other types of document density detectors may be used for ease of handling.AD
When F is not used, the original density detector 8 may be provided in the optical system, for example, in a part of the first mirror to be scanned, and read the density of the original while it is stationary or moving at a predetermined position.

Reference numeral 10 denotes a sampling circuit that samples the output of the document density detector 8 at time intervals that are sufficient to approximately capture the maximum and minimum levels thereof. Reference numeral 11 denotes a concentration discriminator circuit which receives the output of the sampling circuit 10, and selects local maximum values, local minimum values, and concentration values that have been continuously output a predetermined number of times (for example, N times) from among the signals output from the sampling circuit 10. It discriminates which of the predetermined concentration categories these belong to and sends an output indicating which concentration category they belong to to the counting circuit 12.

The frequency circuit 12 receives the output of the density discrimination circuit 11, calculates the frequency of density values in each density division, and constructs a density histogram based on the density divisions. This histogram shows the characteristics of the document, that is, the characteristics corresponding to the differences between a form document with dark writing on a white background, a document with pencil writing on a relatively dark background, etc. Reference numeral 13 controls the bias voltage of the magnetic brush bias adjuster 14 according to the aspect of the hiss 1 to gram obtained in this way, and in the case of colored originals, the copying density is lowered to bring the background color closer to white. ,
In the case of a light image original on a white background, the developing section 3 is controlled so as to increase the degree of copying and further emphasize the image.

The operation of the apparatus of the present invention having the above structure will be clear from the above description of the structure, and in particular, the operations of the concentration discrimination circuit 11 and the counting circuit 12 are shown in the flowchart of FIG. The meaning of each character in FIG. 4 is as follows.

Xk: Current sampling value Xk-1: One previous sampling value Xk -2: Two previous sampling value n; Number of repetitions of the same level N: Upper limit of the number of repetitions of the same level Cmax: Saturation value of frequency Operation shown in this flowchart Then, the sampling value
After reading k, if Xk-1 is an extreme value or if it is the same density value that has been output N times in a row, these are adopted as accumulation targets to create a histogram. That is, when the output of the original density detector 8 changes (the sampling value Xk changes), only the extreme values (8i maximum and minimum values) are sampled; state where does not change (Xk = Xk-
In 1), the frequency (consecutive number of times of the same value) obtained by sampling at a fixed period is compressed to 1/N and added to the frequency of that level.

When sampling is performed in this manner, the sample values counted by the counting circuit 12 become, for example, the values indicated by the O marks (extreme values) and the X marks (continuous values) as shown in FIG. Based on these values, a histogram like the solid line Δ in FIG. 4 is constructed.

Note that if the output of the document density detector 8 is sampled at a constant period as in the conventional method, the intermediate density portion of His 1 to Gram will apparently increase due to sampling at the intermediate portion between the rise and fall of the output. Therefore, the frequency of extreme values also appears to increase, resulting in a distribution as shown by dotted line B in the histogram in FIG. On the other hand, even in a method in which fixed-period sampling and peak rimbling are performed together, the upper intermediate density value appears to be mixed into the Hiss 1 gram, resulting in a result as shown by the dotted line C in FIG.

In this way, the 1q and 1C histograms show characteristic patterns depending on the type of copy document. As described above, the image quality control circuit 13 adjusts the copy density by applying a preset bias voltage to the magnetic brush according to such a characteristic pattern.

When grasping the characteristics of this histogram, it may be done after removing the frequency 1-(n due to noise etc. from the histogram. In that case, as is clear from Fig. 4, the maximum m degree value is less than Dl. Although it is shown decreased in D2,
In actual purchases, the difference can be ignored.

In the above embodiment, the bias voltage of the magnetic brush is adjusted as the m degree adjustment means, but by adjusting the lamp light amount, exposure aperture amount, photoreceptor drum charge amount, etc., il!
It is also possible to perform v control.

Furthermore, although the above embodiment was applied to a copying machine having a ΔDF device, it can also be applied to a general copying machine, whether the type is a movable document table type or a fixed type. It is. Further, in the above embodiment, both the maximum value and the minimum value are accumulated as extreme values, but when only documents of a certain size are handled, only one of them may be used. Further, the judgment corresponding to FIG. 2 may be processed using a microcomputer in rough 1 to wear.

(Effects of the Invention) As explained above, according to the present invention, the following effects can be obtained.

(I) Accurate character density, etc. can be obtained by sampling peak values, and copy density control can be performed accurately.

(II) Since the background portion where the level change is small is treated as the background density, it is possible to accurately detect the background density and perform accurate copying density control.

(III) In (II) above, based on the fact that the frequency of the background level is originally high, if the same level continues N times, it is stored as one, so the memory can be saved without degrading the detection performance.

[Brief explanation of the drawing]

Fig. 1 is a conceptual diagram showing an embodiment of the present invention, Fig. 2 is a flowchart showing the procedure of signal processing and judgment, Fig. 3 is an explanatory diagram of sampling, and Fig. 4 is an explanatory diagram showing an example of a histogram. be. 1... Photosensitive drum 2... Exposure optical system 3...
Developing section 4... Original 5... Original stocking section 6... ADF device 7... Original placement surface 8...
Original density detector 9... Original density detector drive device 10... Sampling circuit 11... Density discrimination circuit 12... Counting circuit 13...
・Image quality control circuit 14...Bias adjuster patent applicant Konishiroku Photo Industry Co., Ltd.

Claims (1)

[Claims] In a copy density control device that detects the density of the original and controls the copy density, when the output waveform of the original temperature detector obtained by reading and scanning the original changes, the maximum value or minimum value is sampled. If the output waveform does not change, the frequencies obtained by sampling at a certain period are compressed and accumulated, and the copy density is controlled according to the frequency distribution obtained based on these accumulations. A copying 11if 1 degree control device.