JPH0612400B2 - Automatic image density adjustment device - Google Patents

Description

The present invention relates to an automatic image density adjusting device for use in a copying apparatus, which detects the density of a document to be copied and determines the density distribution according to the situation of the density distribution. The present invention relates to an improvement of an automatic image density adjusting device that automatically adjusts image density.

[Prior art]

In a copying apparatus such as an electrophotographic copying machine, an operator selects a dial or a plurality of buttons suitable for image quality according to the characteristics of a document to be copied, so that the exposure amount to the photoconductor and the developing device A good copy image is obtained by adjusting the bias voltage value and the like. However, in this type of copying apparatus, it is very troublesome to adjust the dial or select a plurality of buttons according to the density of the original document in addition to simply pressing the copy start button. Moreover, since it depends on human intuition to make adjustments and selections, there is a drawback that copying is likely to fail.

From such a point, recently, an automatic image density adjusting device has appeared which detects the density state of a document to be copied by some method and automatically controls the exposure amount or the developing bias voltage value accordingly. It was

In a detection system that can detect not only the density of the background part of the document (background density) but also the density of the character part (character density) to some extent, the document density detection can detect the background density part and the character density part of the density histogram. Taking the range of extreme values,
As a result, in the line image area, there is an example in which the gradation image is discriminated, and the spatial frequency is discriminated from high and low. For example, the proposals of JP-A-53-134437 and JP-A-56-89751 relate to this. Cost is increased due to the need for an imaging optical system of a system that raises the resolution so that the original density detection can also detect the character density, and the SN ratio is kept high because toner adheres to the imaging optical system. It is difficult to do so, and the reliability is lowered.

On the other hand, the exposure lamp which is lit by AC is also used as a light source for detecting the original density, and the original density detection is made into a system in which the resolution is lowered to the background density of the original, and the original density detected by scanning the original surface is detected. There has been no example of performing so-called batch processing in which all the obtained data are processed and judged at once after sampling a plurality of times.

In the case of text originals, even if you look at a train's timetable where letters are mixed, the ratio of the text portion to the original surface is 10% or less, so the image density detected by the original density detection system with the sensor resolution reduced. In the case of a text original, the effect of the character density is small, and is close to the background density.

By using an exposure lamp as a light source for detecting the original density and reducing the resolution of the original density detection so that the detection range is only the background density, the drawbacks of the above method are eliminated, but the line image or gradation image Judgment becomes difficult. In this case, when the image density is determined by the same processing method for a character original in which characters are written on the background having a certain background density and an original without a background such as a photographic image, inconvenience occurs.

FIG. 5 shows a density histogram when original density detection with reduced resolution is performed using an exposure lamp that is lit by AC, and FIG. 5 (a) shows a density histogram for a line drawing. b) shows a density histogram for a gradation image. Regarding the line drawing original shown in FIG. 5A, the histogram has a spread because the exposure lamp light amount A
This is due to the C component (flicker). For such an original, an appropriate copy can be obtained by determining the density based on the average value of the histogram. Further, for a document having gradation as shown in FIG. 5B, the actual density change is added in addition to the above flicker component, and the histogram is expanded. At this time, when the average value of the histogram is obtained, it is judged that the density is actually darker than the lightest density, and as a result, the selected density is biased to be slightly lighter. That is, if the density is selected in the same manner for the line drawing and the original having gradation, a problem occurs.

[Problems to be Solved by the Invention]

The present invention uses an exposure lamp of AC lighting as a light source for detecting the original density, and when the detection range is limited to the background density of the original, an automatic image density is provided so as to obtain a proper copy even for a line image and a gradation image. It is an object to provide an adjusting device.

[Means for Solving the Problems]

The present invention is intended to achieve the above-mentioned object, and the present invention uses an exposure lamp for image formation which is AC-lit as a light source,
When the detected density is a text original, a sensor with reduced resolution that becomes the background density is used, and after sampling the detected original density multiple times while performing optical scanning, a batch processing method that processes and judges all data at once An automatic image density adjusting device, which is a document having the same density as the spread value of a density histogram created by a plurality of times of detected sampling and the average density detected in a uniform density as a light source with AC lighting stored in advance in a memory. When the spread value is equal to or larger than the reference spread value, the density is selected based on the lowest density value of the density histogram detected as described above, and the spread If the value is less than or equal to the reference spread value, the density is selected based on the average value of the density histogram by the above detection. It is intended to provide an automatic image density adjustment apparatus according to claim.

〔Example〕

FIG. 1 is a cross-sectional view of essential parts of a copying apparatus showing an embodiment of the present invention. On the upper part of the copying machine main body 1, there are arranged an original placing table 2 made of transparent glass on which the original D is placed, and a platen cover 3 covering the original D after placing the original D on the original placing table 2.

A first mirror unit 6 provided with an exposure lamp 4 and a first mirror 5 is provided below the document table 2 and inside the copying machine main body 1. The first mirror unit 6 is parallel to the document table 2 and in the left-right direction in the drawing. It is attached so as to be linearly movable, and optically scans the entire surface of the document D. Reference numerals 7 and 8 denote a second mirror and a third mirror, respectively. The second mirror unit 9 in which these are integrated has a left-right direction at a speed half that of the first mirror unit 6 so as to maintain a predetermined optical path length. Move straight to. Of course, the movement of the second mirror unit 9 is parallel to the document placing table 2 as in the case of the first mirror unit 6. The reflected light from the document D on the document table 2 is reflected by the first mirror 5,
The light is reflected by the second mirror 7 and the third mirror 8, and further enters the photosensitive drum 20 as an image support through the main lens 10 and the fourth mirror 11 through the slit S provided near the document surface. It has become.

In this optical system copying machine, the exposure lamp 4 is used as a projector.
Also, the sensor A is provided on the side of the main lens 10. Therefore, the sensor A detects the average ability of the document seen through the slit S.

In such a configuration, the density of the original is optically detected by the sensor A using a part of the image forming optical system by the preliminary scanning of the optical system, and the density histogram is created.

FIG. 2 shows an example of a specific circuit configuration for detecting the document density. The portion surrounded by the dotted line in FIG. 2 is the sensor A in FIG. The photodiode PD receives the reflected light on the document surface, and the photocurrent I obtained by the photodiode PD is IV converted by the amplifier A1. Here, the output of the amplifier A1 becomes IR ₁ , which is a value proportional to the document density. Then, the voltage is amplified by the amplifier A2, and the output is Becomes The output from the sensor A is input to the A / D converter, and after being A / D converted, is taken into the CPU. This work is performed at a certain sampling period to create a density histogram.

FIG. 3 illustrates a process of creating a density histogram from the output of the sensor A described above. The fourth is the algorithm for determining the original density from the density histogram.
It is a figure. In this embodiment, 5 from density 1 to density 5
A case is shown in which one of the two densities is selected as the original density.

J1 to J4 in the flow are judgment data that should be called thresholds for selecting the respective concentrations. As is clear from the flow of FIG. 4, the processing is changed when the spread of the detected original density histogram is the same as the original density and is uniform, and the reference spread is larger or smaller than the data. That is, when the original spread is larger than the reference spread data, the original is judged to be other than the line drawing and the density is determined according to the lightest level of the histogram.When the detected spread of the density of the original is less than the reference spread data, it is judged as the line drawing and the average level is determined. Determine the concentration. According to the flow of density selection according to the present invention shown in FIG. 4 as described above, proper copies can be obtained for both the line drawing and the gradation plane.

The above-mentioned reference spread data corresponds to the spread of the histogram of only the flicker of the AC light source. Since this differs depending on the background density of the original, for example, the reference spread data for the density is obtained in advance and written in the ROM of the CPU. Then, the reference spread data corresponding to the average density at that time is read out, and the spread of the histograms as shown in FIG. 4 * is compared.

Next, a concrete example of the reference spread data will be described.

Now, set OD0.0 (reflectance 100) to 0 level and set OD∞
The reference spread data will be described below when (reflectance 0) is set to 63 levels. Here, the reference spread data is the flicker component for each density, as described above,
The flicker component corresponding to each density is constant. For example, if 15% of the signal component, which is the average density value, is used as the flicker component, the flicker component for a certain document is represented by the density component x0.15, which is the average density value for that document.

The signal component of OD0.0 is 64, the signal component of OD0.1 is 50, OD
Since the signal component of 0.2 is 40 ……, the reference spread data for OD0.0 64 × 0.15 ≒ 10 OD0.1 〃 〃 50 × 0.15 ≒ 8 OD0.2 〃 〃 40 × 0.15 ≒ 6 OD0.3 〃 〃 32 × 0.15≈5. Therefore, for example, the reference spread data for each average density can be determined as follows with some margin added to the above calculated values.

Average density Reference spread data 64 to 58 13 57 to 51 12 12 50 to 44 11 43 to 37 10 36 to 30 9 29 to 23 8 22 to 15 7 14 to 0 6 The present invention uses, for example, the above data and is as follows. Concentration can be selected. That is, an image forming exposure lamp lit by AC is used as a light source, and when a detected density is a character original, a sensor having a reduced resolution which becomes a background density is used, and the detected original density is sampled plural times while performing optical scanning. After that, all the data are processed at once to calculate the spread value, the average density, and the lowest density value, and then the standard spread data for the average density (for example, when the average density is 40, the standard spread data is 10 ) Is read from the ROM, and the calculated spread value is compared with the reference spread value. When the calculated spread value is equal to or larger than the reference spread value, the judgment data J1 is based on the lowest density value.
.About.J4 and the density is selected to determine which of density 1 to density 5 is applicable. If the calculated spread value is greater than or equal to the reference density value, the calculated average density value is used as a reference for comparison with the judgment data J1 to J4, and density 1 to density 5
The concentration is selected to determine which one of the above.

〔The invention's effect〕

As described above, according to the present invention, the batch processing is performed as a system in which the exposure lamp which is lit by AC is also used as the light source for detecting the original density, and the original density detection is performed with the dividing ability lowered to the original background density. As a result, an automatic image density adjusting device is provided which enables cost reduction and is capable of highly reliable automatic image density detection.

[Brief description of drawings]

FIG. 1 is a sectional view of a main part of a copying machine showing an embodiment of the present invention. FIG. 2 is an embodiment of a circuit configuration diagram of the present invention. FIG. 3 shows the operation according to FIG. FIG. 4 is a flow chart showing an embodiment of the present invention. FIG. 5 shows a density histogram of a line drawing and a gradation image. 1 ... Copier main body, 2 ... Original table 4 ... Exposure lamp, 10 ... Main lens A ... Sensor, PD ... Photodiode A1, A2 ... Amplifier J1, J2 ... Judgment data

Claims (1)

[Claims] 1. An image forming exposure lamp lit by AC is used as a light source, and when a detected density is a character original, a sensor having a reduced resolution which becomes a background density is used to detect a plurality of original densities while performing optical scanning. An automatic image density adjustment device of batch processing method that processes and judges all the data at once after sampling once. The spread value of the density histogram created by the detected multiple times of sampling and the AC stored in the memory in advance.
Compare the average density detected at a uniform density with a light source that is lit and the reference spread value of the density histogram when an original of the same density is exposed, and if the spread value is equal to or greater than the reference spread value, the above detection is performed. The density is selected with reference to the lowest density value of the density histogram according to, and when the spread value is less than or equal to the reference spread value, the density is selected based on the average value of the density histogram by the detection. Automatic image density adjustment device.