JPH07288657A - Detector for size of original - Google Patents

Abstract

PURPOSE:To detect a size of an original accurately even in the case of an original having a low green light reflection level by summing image signal data at a prescribed interval in both the main scanning and subscanning directions and comparing the sum with a prescribed threshold level so as to detect the size of the original. CONSTITUTION:A face of a platen cover is read at a prescribed interval in the main scanning and subscanning directions while no original is loaded. A read level L* is given to an accumulation counter 12a of an original size detection section, in which the level is sequentially summed and the sum is stored in a threshold level storage device 12b. Then an original is place on the platen and the face of the platen is similarly scanned and the levels are accumulated by the counter 12a and the sum is compared with a threshold level from the storage device 12b at a comparator 12c in each main scanning and sub scanning. When the sum is higher than the threshold level, a CPU 12d detects the size of the original based on the comparison result. Thus, the size of the original is accurately detected even when the ridges of the original is black.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a document size detecting device for detecting a document size in a copying machine or the like.

[0002]

2. Description of the Related Art As a document size detecting device, for example, as shown in Japanese Patent Application Laid-Open No. 2-277038, an inner surface of a platen cover is formed of a coloring member, and the platen cover is illuminated by an illuminating device and its reflected light There is known a device that detects the image with an image sensor and detects the boundary between the original and the platen cover based on the detection data of the image sensor.

In the document size detecting apparatus described in the publication, as shown in FIGS. 7 and 8, the difference between the image signal of pixel A and the image signal of pixel B 8 pixels before is taken, and the difference is obtained. When the threshold value is equal to or more than a certain threshold value N times in a row, it is determined that the boundary between the original and the platen cover. For example, in FIG.
The points B1 and A1, the points B2 and A2, ..., The pixel data of the points B8 and A8 are subtracted, and if the differences are larger than a set threshold value, the points B8 and A1 It is judged that it is the boundary between Haruaki and Platen Copper.

However, in the case of photographic originals and originals such as computer graphics, the image density around the originals is often high, for example, the inner surface of the platen cover is black,
When the edge of the document is black or dark green, the difference between the document and the platen cover is small, and it is difficult to accurately detect the size of the document. For example, if the threshold value is set higher, the detected original size will be smaller than the actual original size. In addition, if the threshold value is set to be low, or if there is dust or deterioration of the lamp, there is a problem in that erroneous detection may occur.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and it is possible to accurately copy an original having a low edge light reflection level, such as an original having a dark or dark edge. It is intended to detect size.

[0006]

SUMMARY OF THE INVENTION According to the present invention, an original placed on a platen glass is pressed by an original pressing member having a lower reflectance than the original, and an image of the original is imaged from below the platen glass. A document size detecting device in a document reading device for obtaining image signal data by scanning with a sensor, wherein the image signal data is input and means for accumulating image signal data at predetermined intervals in both the main scanning direction and the sub scanning direction. And a means for comparing the result accumulated by the accumulating means with a predetermined threshold value, and a means for detecting the document size based on the output of the comparing means. It is desirable that the image signal data obtained by reading only the pressing member be a cumulative value.

[0007]

When the image of the original is read by the image sensor, even if the difference between the pixel data of the dark portion of the original and the pixel data of the position corresponding to the platen cover is small, the difference is amplified by taking the cumulative total of the pixel data. be able to. Therefore, it is possible to detect the size of a document with a thick border.

Further, by setting the threshold value based on the cumulative value when only the platen cover is read, even when the reflectance of the platen cover changes due to dirt due to dust or deterioration of the lamp, the threshold value is set. Since it is automatically corrected, it does not affect the accuracy of size detection.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The features of the present invention will be specifically described below based on embodiments with reference to the drawings.

FIG. 1 is a block diagram showing the overall construction of a digital color copying machine to which the document size detecting device of the present invention is applied.

In the figure, 1 indicates an image input section. The image input unit 1 includes a platen glass on which a document is placed, a light source that illuminates the document placed on the platen glass from below the platen glass, and an image sensor that forms reflected light from the document ( (Not shown). Further, a platen cover that covers the back surface of the document in an openable and closable manner is provided. The inner surface of the platen cover is formed of a coloring member colored with black, silver or the like so that the optical reflectance including the infrared region is lower than that of the original.
The reason why the reflectance of the inner surface of the platen cover is lowered is to increase the difference between documents having a high reflectance in general and facilitate the detection of the position of the edge of the document.

The image sensor is, for example, a CCD (charge coupled device) sensor, and electrically reads an image in the main scanning direction. Further, by moving the reading position in a direction orthogonal to the main scanning direction, image reading in the sub scanning direction is performed.

The image input section 1 reads the original image as described above and outputs 8-bit red, green and blue color signals RG.
Generate B. This RGB signal is supplied to the color signal conversion unit 3 through the input gradation correction unit 2 to be converted into an L ^* a ^* b ^* signal and supplied to the image editing unit 4. The L ^* a ^* b ^* signal from the image editing unit 4 is converted into the YMC signals of yellow, magenta and cyan by the second color signal conversion unit 5, and the black signal K is converted through the under color removal (UCR) processing unit 6. While being generated, an amount proportional to the black signal K is removed from the YMC signal. The YMCK signal from the undercolor removal processing unit 6 is passed through the image switching unit 7, the spatial filter unit 8 and the output gradation correction unit 9 to obtain a YMCK signal that matches the characteristics of the image output device 10.
It is converted into a K signal.

On the other hand, the L ^* a ^* b ^* signal from the image editing unit 4 is input to the character / photograph separating unit 11 so that the characters in the original image and the halftone image are separated, and the image switching unit 7 outputs the space. The filter unit 8 and the output gradation correction unit 9 are controlled to reproduce the original with high quality.

Further, in this embodiment, the color conversion section 3
A document size detecting unit 12 is provided to which the L ^* signal is supplied. This is a document size detection unit 12, the preliminary scan to detect the document size to, L ^* signal is supplied from the color conversion section 3, the size of the document from the L ^* signal is detected. For example, the size of the recording paper in the image output unit 10 is switched according to the detected document size. The L ^* signal corresponds to the reflectance of the document or platen cover, and the darker the document is, the smaller the value of the L ^* signal is.

FIG. 2 is a block diagram showing a configuration example of the document size detecting section 12. The L ^* signal from the color conversion unit 3 is supplied to the cumulative counter 12a, and the output of the cumulative counter 12a is supplied to the threshold storage unit 12b. Cumulative counter 12
The output of a and the output of the threshold storage 12b are supplied to the comparator 12c, and the output of the cumulative counter 12a is output to the threshold storage 12b.
When it becomes larger than the output of, the comparator 12c outputs "1", for example. The output of the comparator 12c is the CPU 1
Read by 2d. Also, this CPU 12d
The operations of the cumulative counter 12a and the threshold storage 12b are controlled.

Next, the operation of the above-mentioned digital color copying machine will be described focusing on the operation of the document size detecting section.

First, in the image input unit 1, when the platen cover is closed and the power is turned on with no document placed, the image input unit 1 starts operation, and the surface of the platen cover is in the main scanning direction and the sub scanning direction. At regular intervals,
For example, the main scanning direction is read for each pixel, and the sub scanning direction is read at 1 mm intervals. Since the accuracy of detecting the document size is sufficient in the unit of mm, reading may be performed at intervals of 1 mm in the main scanning direction. The RGB signal from the image input unit 1 is passed through the input gradation correction unit 2 and the color signal conversion unit 3 to L ^*.
It is converted into an a ^* b ^* signal, and the L ^* signal therein is supplied to the document size detecting section 12. The reading level of the image signal obtained by reading the surface of the platen cover, that is, the platen cover reflection level is sequentially added by the cumulative counter 12a and accumulated, and the cumulative result is stored in the threshold storage 12b as a threshold for document size detection. To be done.

Next, in the image input section 1, a document is placed, the platen cover is closed, and a copy start button (not shown) provided on the operation panel is pressed. First, the size of the document is detected. Pre-scanning for is started. Figure 3
3 is an explanatory diagram showing a relationship between a platen cover 1a and a document P in the image input unit 1. FIG. When reading the document P,
An image is electrically read by the image sensor in the main scanning direction, and an image is read in the sub-scanning direction by moving the reading position in a direction orthogonal to the main scanning direction.

Prior to the preliminary scanning, first, the CPU 12d
This resets the contents of the cumulative counter 12a. Next, the reading level of the image signal obtained by reading the surface of the platen cover or the document is sequentially added in the main scanning direction and the sub-scanning direction by the cumulative counter 12a, and is cumulatively added. The accumulated result is stored in the threshold storage unit 12 in the comparator 12c every time one main scanning is completed and every one sub-scan is completed.
compared to the threshold from b. As described below, when the cumulative result is larger than the threshold value, it means that the original is included in the scanning position.
d detects the document size based on the comparison result.

In the present embodiment, another value L converted by the conversion table of FIG. 4 is used instead of L ^* for the convenience of internal processing.
p is used. That is, the larger the converted value Lp, the smaller the lightness value L ^* .

Here, assuming that the inner surface of the platen cover is black and the image input section 1 reads an image with 256 gradations, when the platen cover is read by the image sensor, it corresponds to the L ^* signal from the color signal conversion section 3. When the average value of the values to be set is Lp, the average value Lp shows a high value of 200 or more. That is, the lightness L ^* is 25. However, the average value Lp is 190 depending on the dirt condition of the platen cover.
It may fall below. When the resolution of the image sensor in the image input unit 1 is 16 pixels / mm, A3 size (2
(97 mm x 420 mm)
It requires 297 × 16 pixels in the main scanning direction and 420 × 16 pixels in the sub scanning direction. Therefore, the threshold Sm in the main scanning direction is Sm = 297 × 16 × s, and the threshold Ss in the sub scanning direction is Ss = 420 × 16 × s. Note that s is a threshold value set slightly lower than the average value Lp. Here, the threshold value is set to 195.

When scanning an original, the image reading levels are sequentially accumulated independently for each of the main scanning method and the sub-scanning direction, and these accumulated values are used as the threshold value S.
The size of the document can be detected by comparing m and Ss.

Assuming that the relationship between the original and the platen cover is as shown in FIG. 3A, the cumulative value of the cumulative values is the threshold value S on the line Lm (n + 1) in the main scanning direction.
It is larger than m, and the accumulated value is smaller than the threshold value Sm in the line Lm (n). Similarly, in the sub-scanning direction, the cumulative value of the line Ls (n + 1) in the sub-scanning direction is larger than the threshold value Ss, and the line Ls
In (n), the cumulative value becomes smaller than the threshold value Sm. FIG. 3B is an explanatory diagram showing the relationship between the cumulative values Am and As and the threshold values Sm and Ss in the main scanning direction and the sub scanning direction.

Here, at least one total counter in the main scanning direction may be used, and it may be reset for each line. In the sub-scanning direction, the presence or absence of a document cannot be determined unless scanning is performed up to the end of the platen cover, so a counter for the number of pixels is required. However, the precision of the document size detection need not be so fine, and here, one counter per 1 mm is sufficient.

FIG. 5 shows an example of the structure of a cumulative counter in the main scanning direction. The total counter 13 in the main scanning direction is 2
It is composed of an input adder 13a and a latch circuit 13b which receives the output of the adder 13a as an input, is reset by a line synchronization signal, and is enabled by a clock signal. The lightness L ^* and the output of the latch circuit 13b are the adder 13a.
Are added together, and the added output is latched for each clock signal.
Latched in 3b. Therefore, the lightness L ^* is accumulated for one line in the latch circuit 13b.

FIG. 6 shows an example of the structure of a cumulative counter in the sub-scanning direction. The sub-scanning direction cumulative counter 14 includes an address calculator 14a that counts clock signals and is reset by a line synchronization signal, a line memory 14b that stores the lightness L ^* at an address specified by the address calculator 14a, and a line memory. Adder 14c with the output of 14b as one input
And the output of the adder 14c is stored in the address specified by the address calculator 14a, reset by the page synchronization signal, and a part of the output is added from the addition memory 16d which is the other input of the adder 14c. It is configured. In the addition memory 14d, the values of the brightness L ^{* at} the same horizontal position are accumulated vertically for one page.

In the above description, the threshold values Sm and Ss are fixed values for the sake of simplicity, but in reality, as shown in FIG.
Since m and Ss are set according to the cumulative value when the platen cover is actually read, even if the reflectance of the platen cover changes due to dirt due to dust or deterioration of the lamp, the threshold value is Since it is automatically corrected, it does not affect the accuracy of size detection.

In this embodiment, the L ^* signal is used for detecting the original size, but it goes without saying that it may be judged from the RGB signal.

[0030]

As described above, according to the present invention, the reading levels are accumulated in the main scanning direction and the sub-scanning direction and compared with the cumulative value of the reading levels of only the platen cover. Even if the difference between the level of the platen cover and the level of the platen cover is small, this difference is accumulated, so the level difference becomes large at the end of scanning, and it is necessary to accurately detect the size of a document with dark or dark edges. You can Even if the platen cover has stains, the threshold for size detection is automatically corrected according to the stains, so that the size of the original can be accurately detected without being affected by stains. You can

[Brief description of drawings]

FIG. 1 is a block diagram showing an overall configuration of a digital color copying machine to which a document size detecting device of the present invention is applied.

FIG. 2 is a block diagram showing a configuration example of a document size detection unit.

FIG. 3 is an explanatory diagram showing a relationship between a platen cover and a document in an image input unit.

FIG. 4 is a conversion table of lightness L ^* .

FIG. 5 is a block diagram showing a configuration example of a cumulative counter in the main scanning direction.

FIG. 6 is a block diagram showing a configuration example of a cumulative counter in the sub-scanning direction.

FIG. 7 is an explanatory diagram of a conventional document size detection operation.

FIG. 8 is a principle explanatory diagram of a pixel determination operation in the conventional example shown in FIG. 7.

[Explanation of symbols]

1 ... Image input unit, 2 ... Input tone correction unit, 3 ... Color signal conversion unit, 4 ... Image editing unit, 5 ... Color signal conversion unit, 6 ... Undercolor removal processing unit, 7 ... Image switching unit, 8 ... Spatial filter, 9 ...
Output gradation correction unit, 10 ... Image output unit, 11 ... Character / photograph separation unit, 12 ... Original size detection unit, 12a ... Cumulative counter, 12b ... Threshold value storage unit, 12c ... Comparator, 12d ... C
PU

Claims (2)

[Claims] 1. A document placed on a platen glass,
A document size detecting device in a document reading device which obtains image signal data by pressing an image of a document with a document pressing member having a lower reflectance than that of the document and scanning the image of the document from below the platen glass with an image sensor. Means for accumulating the image signal data at predetermined intervals in both the main scanning direction and the sub-scanning direction using the signal data as input; a comparing means for comparing the results accumulated by the accumulating means with a predetermined threshold; and the comparing means. A document size detecting apparatus comprising means for detecting a document size based on the output of the document size. A document size detecting device characterized by the above. 2. The document size detecting apparatus according to claim 1, wherein the threshold value is a value obtained by accumulating image signal data obtained by reading only the document pressing member.