JPH06311364A - Background elimination device for digital copying machine provided with automatic document feeding device - Google Patents

Abstract

PURPOSE:To detect and eliminate background density without preliminary scanning by reading an original when it is set onto a platen glass and deciding a threshold level used for eliminating background and using the threshold level for a picture signal read in copying so as to eliminate the background. CONSTITUTION:A picture area of an original is divided into blocks when an original is set under the control of a control means 9 and a comparator 1 detects a density of a picture element of each area and a minimum density of a picture element of each area is stored in a density storage means 3. Then a histogram generating means 6 reads a minimum density stored in the means 3, counts it and generates a histogram by the usual method to decide a threshold level. Then a background elimination means 8 enters the copying and uses a decided threshold level for picture data through original read to eliminate background. Thus, background is eliminated without using preliminary scanning.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic document feeder for pulling a document onto a platen glass, an image input device for reading a document on the platen glass and taking out a digital image signal, and an image processing device for processing the digital image signal. The present invention relates to a background removal device for a digital copying machine equipped with an automatic document feeder including an image output device that outputs a processed image signal.

[0002]

2. Description of the Related Art In image recording devices such as copying machines and fax machines,
In addition to the usual manuscripts using white paper, manuscripts using various papers such as newspaper, straw paper, recycled paper, and colored paper are read. In this way, since an original without using ordinary paper has a high background density, if the original is read by an original reading unit such as a CCD sensor and the image data is output as it is, the reproduced original has a rough background and is dirty. Will be.

For an original having such a background having a certain density, a certain area such as near the center of the original is read, and the average light amount is detected to perform the developing bias to obtain the background. It is processed so that the highlight part of is saturated and the density of the background becomes thin.

However, since the conventional background removal method as described above only detects the average amount of light in a certain area, the detection level changes depending on the image density of the document, and the document has a dark background. There is a problem that it is not possible to correctly judge whether the original is bright. Moreover, if the processing for shifting the conversion curve of the input and the output to saturate the highlight side is performed as the background removal, the density is lowered as a whole.

Further, when copying a document such as a newspaper or magazine that has been cut out on a blank paper and edited, a plurality of background densities are mixed, so that the background having a relatively high density is to be removed. Then, the low contrast part such as handwritten characters written on a white background is also erased, and it is impossible to remove the background of high density and leave the handwritten characters on a white background at the same time.

Therefore, the original information is read in the pre-scan and the image data is recorded in the main scan. The density detecting means detects the density of each pixel of the original, and the histogram is obtained by counting the number of pixels for each density. And a threshold value determining means for detecting a peak from the histogram to determine a threshold value for removing the background, and creating a histogram of the density distribution from the read information of the entire surface of the original by prescanning to determine the peak. A background removal device that detects and determines a threshold value for background removal is proposed (for example, Japanese Patent Application No. 2-
145100). With this background removal device,
In the density detecting means and the histogram creating means, the density is divided into a plurality of areas only in a low density area where the background density can be detected, and the density is detected and the number of pixels is counted by sampling at a predetermined interval for each area. There is.

As another background processing method, a CCD is used.
In some cases, the background is removed by returning the signal before reading and shading correction by the sensor to the reference voltage of the A / D converter.

[0008]

However, in the conventional method in which the density histogram is created, the peak is detected, and the threshold value for the background removal is determined, the prescan is always required, and therefore the original must be read twice. However, there is a problem that processing takes time. In particular, in a digital copying machine equipped with an automatic document feeder, it is necessary to carry out a prescan every time a document is replaced, which is a factor that reduces productivity.

Further, in the method of returning to the reference voltage of the A / D converter, the maximum value is searched for in the data before the shading correction, but since this data contains unevenness of the optical system, it is substantially effective. In addition, the maximum value can be searched only around the center of the manuscript. Therefore, there is a problem that if the center of the original has a high density image quality, the process of skipping too much is performed.

An object of the present invention is to solve the above problems and to provide a background removing apparatus capable of detecting and removing background density in consideration of the entire area of a document without performing prescan. To do. Another object of the present invention is to enable highly accurate background density detection and accurate background removal in a copying machine equipped with an automatic document feeder, without lowering productivity.

[0011]

To this end, the present invention is directed to an automatic document feeder for pulling a document onto a platen glass, an image input device for reading a document on the platen glass, and a digital image signal for processing the digital image signal. In a digital copier equipped with an automatic document feeder consisting of an image processing device that outputs a processed image signal and an image output device that outputs a processed image signal, when the document is pulled onto the platen glass, the document is read and the image signal is captured to detect the background density. A background density detecting / threshold determining means for determining a threshold to be used for background removal, and a background removing means for performing background removal using a threshold for an image signal obtained by reading an original on a platen glass in a copy operation. It is characterized by. Further, the background density detection / threshold value determination unit divides the document into a plurality of areas and detects the background density for each block, and further, at that time, obtains the minimum density value for each block, and a histogram of the minimum density value. To determine the threshold.

[0012]

In the background removal device of the digital copying machine equipped with the automatic document feeder of the present invention, when the document is pulled onto the platen glass, the document is read, an image signal is taken in, the background density is detected, and a threshold value used for background removal. Since the background density detection / threshold value determining means and the background removing means for removing the background using the threshold value for the image signal obtained by reading the original on the platen glass in the copy operation are provided without pre-scanning. It is possible to detect the density level of the background of the document for removing the background in synchronization with the document pull-in timing of the automatic document feeder.

Further, the background density detecting / threshold determining means divides the original into a plurality of areas and detects the background density for each block, and at that time, obtains the minimum density value for each block, and the minimum density is calculated. Since the threshold value is determined by creating a histogram of the values, it is possible to reduce the memory capacity for detecting the background density, detect the background density with high accuracy, and perform the accurate background removal.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing an embodiment of a background removal method of a digital copying machine equipped with an automatic document feeder of the present invention, FIG. 2 is a diagram for explaining a background detection block, and FIG. 3 is an example of background removal processing. FIG. 4 is a diagram for explaining, FIG. 4 is a diagram showing an example of a threshold value and an image signal after the background removal, and FIG. 5 is a diagram for explaining an example of background removal processing in a density region around the threshold value. In FIG. 1, as the image data, data obtained by reading the original when the original is pulled onto the platen glass from the automatic original feeding device and during the subsequent copying operation is input. When the original is pulled in, the image area of the original is divided into blocks B ₁₁ , ..., B _ij , ... As shown in FIG. 2, and the minimum density value of the pixel density values of the respective areas is set. The density is stored in the density storage unit 3, a histogram is created, and a threshold value used for background removal is determined.

That is, the density storage means 3 stores the minimum density value of the pixels of the blocks B ₁₁ , ..., B _ij , .. The writing unit 2 writes the density value data, and the reading unit 3 reads the density value data. The switching means 5 uses the read-out means 3 and the concentration storage means 3
The output destination of the density value data read from is switched, and the original is read while the original is pulled onto the platen glass from the automatic document feeder, and when the image data is stored in the density storage means 3, it is output to the comparator 1. After the reading of the entire area of the document is completed, the histogram is output to the histogram creating means 6 when the histogram is created and the threshold value used for the background removal is determined. The comparator 1 compares the image data when the document is read while pulling the document onto the platen glass from the automatic document feeder with the density value data read from the density storage means 3, and outputs the smaller one to the writing means 2. To do.

When the minimum density value of each block of the original is stored in the density storing means 3, the histogram creating means 6 passes through the reading means 4 and the switching means 5 to the density storing means 3
The histogram is created by reading out the minimum density value stored in and counting the number of blocks in each density area with a counter. The threshold value determining unit 7 determines a threshold value used for background removal from the created histogram, and the creation of the histogram and the determination of the threshold value based on the histogram are the same as the conventional processing described above. The background removing means 8 removes the background by using a threshold value for the image data that has entered the copy operation and read the document. For example, as shown in FIG. 3, the threshold value is included _in the input image signal D _in. The background is removed by setting all the signals smaller than Dh to 0 and outputting. By performing this background removal processing, the density signal (broken line) of the background portion of the image signal does not become 0 as shown in FIG. 4, and the signal of the image portion remains with its density stored.

The control means 9 controls the mode signal indicating whether the document is pulled in or copied and the position signal x of the document of the input image data.
Based on y, the writing / reading address of the density storing means 3 is instructed to the writing means 2 and the reading means 4, and the switching control of the switching means 5 and the operation control of the histogram creating means 6 are performed.

Further, in the background removal processing of the background removal means 8, if the density signal of the background portion is simply set to 0 by comparing with the threshold value, there is a problem that the density range around the threshold value becomes uncomfortable. Therefore, the discomfort can be reduced by not only simply removing the image data below the threshold as the background, but also by changing the density gradient near the threshold. FIG. 5 shows the relationship between the input image data and the output image data when this processing is performed for the density area around the threshold value. As is apparent from the figure, this process does not output the input image data that exceeds the threshold Th as it is, but performs a process for smoothing the input image data that is 1.5 times the threshold Th. When the input pixel value is less than or equal to the threshold Th, the output pixel value is set to 0, and when the input pixel value is greater than or equal to 1.5 times the threshold Th, the output pixel value is set as it is. The output pixel value is multiplied by three. That is, if the input pixel value D _in and the output pixel value D _out are set, then D _out = (D _in −Th) × 3. By performing the processing in this way, it is possible to suppress graininess in the image portion in the density region around the threshold value.

FIG. 6 is a diagram showing an overall configuration outline of a digital copying machine equipped with the automatic document feeder of the present invention, and FIG. 7 is an operation and threshold value determination process of the digital copying machine equipped with the automatic document feeder of the present invention. It is a figure for explaining the flow of.

In a digital copying machine equipped with an automatic document feeder, the automatic document feeder 15 is attached to the image input device 11 as shown in FIG. The original is read, and the background removal device 12 determines a threshold value from the image signal to remove the background. The image input device 11 reads an original with a CCD sensor and inputs the image as an electric signal to input an A / D signal.
The converter converts the digital image signal to perform shading correction processing. The automatic document feeder 15 automatically pulls a document on the platen glass of the image input device 11.
Not only the original on the platen glass is read by the copy operation, but also when the original is automatically pulled in, the original reading device with the CCD sensor mounted on the carriage is moved to the original taking side (the tip of the platen glass) to remove the background. The original is read to determine the threshold used for the. The background processing device 12 detects the background density using a threshold value from the image signal sent from the image input unit 11 during the copy operation,
The background removal processing is performed by the threshold value determination unit 16 (see FIG. 1).
Therefore, the automatic document feeder 15
The threshold value is determined from the image signal sent from the image input unit 11 when the document is pulled in by. The image processing device 13 performs edit processing such as color conversion, sharpening processing, smoothing processing, and color tone correction processing. The image output device 14 receives the processed image signal, forms an image with an output device such as an electrophotographic system, and outputs the image.

In the digital copying machine, when the copy start button is pressed as shown in FIG. 7A, first, the original reading device having the CCD sensor mounted on the carriage is moved to the front end of the platen glass (step S1), and the automatic original is read. The document pulling operation is started from the feeding device (step S2).
At this time, the document is read, and the threshold value used for the background removal is determined from the read document image (step S3).

Thereafter, the document reading device is moved to the home position (step S4), the normal copying operation is started, and the reading scanning is performed by the document reading device (step S5). The background is removed from this image signal by using the previously determined threshold value (step S6).

In the threshold value determining process, as shown in FIG. 7B, the start of document reading is awaited (step S11). When the original reading is started, it is checked whether or not the reading is in the original drawing mode (step S12). In the case of the original pull-in mode, it is determined which original area the image data is a block of (step S13), the density is read from the storage area of the corresponding register, and the storage density is compared with the image data (step S14). Then, the stored content of the register is updated with the smaller one of the image data and the stored density (step S15). This is repeated until all lines are completed (step S16).

Through the above processing, the minimum density value is stored in the register for each block of the one-page original divided into blocks. Therefore, next, the density value of the register is read to create a histogram (step S16), and the threshold value used for background removal is determined (step S18). Then, the background removal is executed by starting the next document reading (step S
18 → S11 → S12 NO).

The present invention is not limited to the above embodiment, but various modifications can be made. For example, in the above-described embodiment, the threshold value is determined for each page of the document to remove the background, but one page of the document may be divided into a plurality of regions to determine the threshold value.

[0026]

As is apparent from the above description, according to the present invention, in a digital copying machine equipped with an automatic document feeder, when a document is pulled onto a platen glass, the document is read and an image signal is taken in to obtain a background density. To determine the threshold to be used for removing the background, and to remove the background using the threshold for the image signal of the original read on the platen glass in the copy operation, so without using prescan,
It is possible to detect the density level of the background portion of the original for removing the background in synchronization with the original drawing timing of the original feeding device. Therefore, it is possible to remove the background without lowering the productivity. Also, the original is divided into a plurality of areas and the background density is detected for each block, and at that time, the minimum density value is obtained for each block,
Since the histogram of the minimum density value is created and the threshold value is determined, it is possible to reduce the memory capacity for detecting the background density, and to detect the background density with high accuracy and perform the accurate background removal. .

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of a background removal method of a digital copying machine equipped with an automatic document feeder according to the present invention.

FIG. 2 is a diagram for explaining a background detection block.

FIG. 3 is a diagram for explaining an example of background removal processing.

FIG. 4 is a diagram showing an example of a threshold value and an image signal after background removal.

FIG. 5 is a diagram for explaining an example of background removal processing in a density area around a threshold value.

FIG. 6 is a diagram showing an overall configuration outline of a digital copying machine provided with the automatic document feeder of the present invention.

FIG. 7 is a diagram for explaining the operation of a digital copying machine equipped with the automatic document feeder of the present invention and the flow of threshold value determination processing.

[Explanation of symbols]

1 ... Comparator, 2 ... Writing means, 3 ... Concentration storage means, 4
... reading means, 5 ... switching means, 6 ... histogram creating means, 7 ... threshold determining means, 8 ... background removing means, 9 ...
Control means

Claims (3)

[Claims] 1. An automatic document feeder for pulling a document onto a platen glass, an image input device for reading a document on the platen glass and extracting a digital image signal, an image processing device for processing the digital image signal, and a processed image signal. In a digital copying machine equipped with an automatic document feeder including an image output device for outputting, when a document is pulled onto a platen glass, the document is read, an image signal is taken in, the background density is detected, and a threshold value used for background removal is determined. An automatic document feeder including a background density detecting / threshold value determining means and a background removing means for removing the background using a threshold value for an image signal obtained by reading an original on a platen glass by a copy operation. Background removal device for digital copiers. 2. A digital apparatus having an automatic document feeder according to claim 1, wherein the background density detection / threshold value determining means divides the original into a plurality of areas and detects the background density for each block. Background removal device for copiers. 3. The automatic document feeding according to claim 1, wherein the background density detecting / threshold value determining means determines a minimum density value for each block, creates a histogram of the minimum density value, and determines the threshold value. Background removal device of digital copier equipped with device.