JPH09149256A - Image reader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shorten photographing time and to appropriately reproduce a picture by controlling reproduction density through the use of a luminance detection result which is immediately before without detecting luminance when an original is judged to be the same and the change of height is judged to be within a prescribed value. SOLUTION: When a start key 8 is turned on, the lamp of an illumination part 3 is turned on and a read operation is started. Then, a flag is checked whether base luminance data at the time of previous photographing is in a memory or not. Then, the flag is checked whether height data at the time of previous photographing is in the memory or not. Then, whether the original is changed or not is judged by checking the output of an original change detection sensor 9. When that the original is the same and the change of height is within the prescribed value is judged as the result of checking, scanning is executed with base luminance data at the time previous photographing as data for density correction. Thus. an operation for detecting base luminance is required to be the least as possible.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading apparatus for photographing a book original or the like, and more particularly to an image reading apparatus for automatically correcting the density reproduced according to the background density of the original.

[0002]

2. Description of the Related Art Conventionally, in an image reading apparatus, the background density distribution of an original is detected using a luminance histogram, and when the image is reproduced, the γ conversion coefficient is controlled based on this background density distribution to determine the image density. A technique for optimizing the above is known. Further, the present applicant has previously filed a patent application for a technique for detecting an abnormality in the background luminance data and correcting the abnormality using the correlation between the background luminance information and the height information of the document. Further, a patent application has been filed for a technique for detecting an abnormality in height data and correcting the abnormality by using the correlation with the height information of the document detected immediately before (all are unknown).

[0003]

However, in the apparatus for optimizing the image density as described above, the background density distribution cannot be measured correctly when a photographic region or the like exists in a part of the page to be photographed, There is a problem that the image density cannot be controlled correctly. Further, in the technique of correcting data using the correlation with the height information according to the above-mentioned patent application, since the correlation coefficient changes depending on the glossiness of the document surface, the accuracy of the correction is improved. It was difficult to exceed a certain level. Further, in the technology for detecting an abnormality in the latest data and correcting the same by using the same data detected immediately before, which is based on the above-mentioned previous patent application, since the detection operation is repeated for each shooting, it takes a long time to shoot. Had a problem.

The present invention has been made in order to solve the above-mentioned problems, and when it is determined that the originals are the same and the change in height is within a certain range, the brightness is detected. Instead, it is an object of the present invention to provide an image reading apparatus capable of shortening the photographing time and controlling the reproduction density by controlling the reproduction density using the immediately preceding brightness detection result.

[0005]

In order to achieve the above object, the present invention reads an original such as a book or the like opened facing upward placed on an original table and detects the background brightness of the original. In an image reading apparatus that controls the density based on the background brightness, the original table on which the original is placed is read,
A reading unit for outputting image data; a document change detecting unit for detecting a change of a document placed on the document table;
Background luminance detection means for detecting the background luminance of the document, storage means for storing the background luminance data detected by the background luminance detection means, and image density of the image density based on the background luminance data stored in the storage means. A density control means for controlling and an updating means for updating the background luminance data stored in the storage means when a document change is detected by the document change detecting means. In the above configuration, when reading the originals continuously, if it is determined that the original read this time is not replaced with the original read immediately before, the operation of the brightness detection unit is stopped, The reproduction density is controlled using the immediately preceding background luminance detection result. Further, when the change of the document is detected, the brightness data is updated. As a result, the frequency of background luminance detection is reduced, and as a result, the time required for reading is shortened. Further, the original change detecting means for detecting the change of the original may detect the page amount of the original that has been turned.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows the overall structure of the image reading apparatus, and FIG. 2 shows a state in which a book, which is a subject, is placed on a document table of the apparatus. A document 10 such as a book or a file, which is a subject (hereinafter referred to as a book document), is placed upward on the document table 1 in a state of being opened, and a book document 10 is opened by optical scanning above the document. An image pickup device 2 having a line sensor for reading a surface is provided. The original placing surface of the original table 1 is colored darker than the background color of a general original, and when the book original 10 is read with the original placing surface as the background, the original surface and the original placing surface are different from each other. It can be identified. In this apparatus, a book document 10 placed on the document table 1 is arranged above the document table 1.
An illumination unit 3 for illuminating the document, an operation panel 4 for setting image reading conditions, and a mirror 5 for obliquely arranging the document table 1 on the back side and for projecting the side surface of the book document 10 and detecting the document height. And a control unit (not shown) that controls the imaging operation such as the preliminary scan operation and the main scan operation of the imaging device 2. The book document 10 is positioned by pressing the book document 10 against the lower end of the mirror 5. Therefore, the boundary between the document table 1 and the mirror 5 becomes the reference position of the document.

The image data taken by the image pickup device 2 is subjected to various kinds of processing by the control section and output to a desired output device (printer, computer, etc.). Further, the document table 1 is embedded with a start key 8 for causing the apparatus to start reading and a document change detection sensor 9 for detecting that the document has been changed. The document change detection sensor 9 is composed of a pair of a light emitting element and a light receiving element. When the book document 10 is placed on the document table 1, the light from the light emitting element is emitted from the book document 10.
The light is reflected on the back surface of and is incident on the light receiving element. The presence or absence of a document is determined by whether or not the light-receiving element detects light, and the document change detection is to detect that the light detection of the light-receiving element has been interrupted between the previous shooting and the current imaging. Done by

Start key 8 and document change detection sensor 9
Are provided on the right side of the document table 1 and one on the left side. The document change detection sensor 9 is not limited to this configuration, and the document may be inserted between the light emitting element and the light receiving element. For example, the light emitting element is provided in the image pickup apparatus 2, and the light receiving element is provided at a position where the light of the light emitting element of the document table 1 is incident. In this case, when the light receiving element detects light, it is determined that the document is not placed, and when the document is placed, the light to the light receiving element is blocked, so the light receiving element does not emit the light. When not detected, it is determined that the original is placed. In addition, a mechanical micro switch or an ultrasonic sensor may be used to detect the document change. The original table 1 is placed on the original base 1a, and the right side plate and the left side plate of the original table 1 are independently movable up and down. Here, the names of the respective parts of the book document 10 placed on the document table 1 are defined. A surface of the opened book document 10 on both right and left pages, which is read by the imaging device 2, is referred to as a document surface 10a, and a side surface of the book document 10 on the back side of the placed book document is a document side surface 10b. Called.

FIG. 3 and FIG. 4 show schematic configurations of the present apparatus as viewed from the front and the sides, respectively. The image pickup apparatus 2 includes a CCD line sensor 7 in which a plurality of image pickup elements are arranged on a line from the front side to the back side (main scanning direction), and a document surface 10a.
And an optical system having an imaging lens 6 for projecting the image on the line sensor 7. The line sensor 7 has a document surface 10a.
The image on the original surface 10a is read by moving in the sub-scanning direction (the direction of the arrow in FIG. 3) orthogonal to the main scanning direction on the image forming surface on which the image is formed. In addition, the imaging lens 6
Is provided so as to be movable in the optical axis direction by a driving device of a lens driving circuit 23 (see FIG. 8), and is moved according to the height of the book original 10 obtained by height detection described later, and the line sensor Document surface 1 always in focus on 7
The image of 0a is formed. The height detecting mirror 5 is provided on the document table 1.
It extends in the sub-scanning direction at the back side of the document table, and is installed at an angle of 45 ° with respect to the document placement surface of the document table 1.
The side surface 10b of the document placed on is reflected. The side surface 10b of the original image reflected on the mirror 5 is, together with the original surface 10a, a lens 6
Projected by. The line sensor 7 has a length sufficient to read the projected image of the document surface 10a and the side surface, and simultaneously reads the image of the document surface 10a and the side surface by scanning movement. Although the line sensor is used in this embodiment, an area sensor may be used instead of the line sensor.

Book original 1 placed on original table 1
When 0 is placed facing upward in the open state, the document surface 10a has a shape that is spatially curved in the height direction.
Therefore, it is necessary to detect the height of the book document 10 at each position in the sub-scanning direction and adjust the distortion of the read image and the focus adjustment of the image formed on the line sensor 7 according to this height. There is.

FIG. 5 is a diagram showing the principle of height detection processing used in this embodiment. By placing the book document 10 at a predetermined position, an image 11 of the document side surface 10b is displayed on the mirror 5, and by reading the image 11 of the document side surface 10b displayed on the mirror 5 by the line sensor 7, the book is read. Manuscript 10
Find the height distribution of.

FIG. 6 shows a state of image data read by the image pickup apparatus 2 having the above structure. In the figure, a is the image of the document surface 10a, b is the image of the document table 1, c is the image of the background portion reflected on the mirror 5, d is the image of the side surface of the book document 10 reflected on the mirror 5, and e is the document. The alignment reference of is shown. The image a on the document surface and the image d on the document side surface are read as being curved in the main scanning direction due to the height change of the document. The document surface and the document side surface are generally white and are read as white. On the other hand, the image of the document table 1 and the background portion c reflected on the mirror 5 which are colored darker than the background of the document have a small amount of reflected light and are read in black.

FIG. 7 shows the output of one line in the main scanning direction read by the line sensor 7. In this example, the case where the image at the position indicated by the dotted line in FIG. 6 is read by the line sensor 7 is shown. The horizontal axis represents the address of the image sensor of the line sensor 7, and the vertical axis represents the output (image density) of each image element. In the figure, the image c of the background portion reflected on the mirror 5, the image d of the side surface of the document reflected on the mirror 5, the image a of the document surface 10a, and the image b of the document table 1 on the image pickup element. Area. Dth is a predetermined threshold for determining whether the image is a document image or another image. n1 is a minimum address value of the image sensor having an output exceeding the threshold value Dth, that is, a value indicating the position of the upper edge of the image 11 on the document side surface 10b. n2 is an address value of the image sensor corresponding to the alignment reference of the document, and is a fixed value. (N2
-N1) is the number of pixels corresponding to the document height used in the height detection processing. The height distribution data of the document is obtained from the (n2-n1) value of each line. From this height distribution data, the image pickup lens 6 is driven in the vertical direction so as to eliminate the image distortion correction coefficient for correcting the image distortion caused by the height change of the document and the defocus caused by the height change of the document. And automatic focus (AF) control data for calculating.

FIG. 8 is a block diagram of a control circuit of the image reading apparatus. In this embodiment, the line sensor 7 is
Scan operation for actual image reading (main scan operation)
Prior to this, a preliminary scan for sampling the image data for detecting the height of the document surface and controlling the density, which will be described later, is executed. Originals 1 collected by the taking lens 7
The reflected light from 0 is imaged on the line sensor 7, is converted into an electric signal according to the amount of received light by the image sensor of the line sensor 7, and is arranged in the A / D converter 12 in the order of arrangement of the image sensors. Is output. The electric signal input to the A / D converter 12 is converted into digital image data, which is output to the image memory 13 during the preliminary scan and to the trimming circuit 15 via the Log conversion circuit 14 during the main scan.
The image memory 13 has a capacity for storing the input image data for several lines, and sequentially stores the image data obtained by the preliminary scan for several lines.

The image data output from the A / D converter 12 indicates the level corresponding to the amount of light received by the image sensor of the line sensor 7, that is, the brightness level on the document surface, and is therefore Log converted. The circuit 14 converts the density level of the image. The conversion of the Log conversion circuit 14 is performed by the following equation. D = Iog1 / L However, D: density value, L: luminance value The trimming circuit 15 inputs the image data of the side surface of the book original 10 because the input image data also includes the image data of the side surface of the book original 10. The data is deleted, only the image data of the document surface 10a is extracted, and the density control circuit 16
Output to The density control circuit 16 adjusts the image density level by a density control process described later. The image data whose density level has been adjusted is subjected to γ correction and distortion correction by the γ correction circuit 17 and the distortion correction circuit 18, and is output to an external device such as a printer or a personal computer. Here, the distortion correction means, in the case of the book document 10, the document surface 10a.
Since the image is distorted due to the curvature of, it means to correct this. The γ correction will be described later.

The CPU 21 is a microcomputer and controls the operation of the reading device. The CPU 21 sequentially reads the image data stored in the image memory 13 line by line, detects the height of the document surface 10a at each reading position based on the image data, and detects the height of the document surface of each line on the background portion. The brightness level of the corresponding image data is detected and stored in the memory 22. Further, during the main scan, the CPU 21 supplies the height data or the density level data stored in the memory 17 to the density control circuit 16 to control the density level adjustment of the image data executed by the density control circuit 16. Further, the CPU 21 controls the lens drive circuit 2
A control signal is output to 3, and the lens is moved according to the reading position of the line sensor 7 so that the image of the document surface 10a is always focused on the line sensor 7. The CPU 21 also outputs a control signal to the scanning drive circuit 24 and the lamp drive circuit 25 to control the scan movement of the line sensor 7 and the lighting of the lamp of the illumination unit 3.

Further, the CPU 21 is connected with a document change sensor 9 and a document table pressure sensor 31, and further with an interface 28 for communicating with the external control device 27, from the external control device 27. It is possible to receive various commands and information through the CPU 21 and to send the operation status and the like from the CPU 21 to the external control device 27. The interface 28 uses an interface capable of two-way communication, and may be a serial communication system so-called RS422, or may be connectable to a LAN such as parallel communication or the Internet.

Further, in the present apparatus, the density level of the read image data is adjusted according to the density of the image portion of the document surface 10a and the density level of the background portion (automatic density control). The image density control will be described below.

FIG. 9 is a diagram for explaining changes in the amount of light received by the line sensor 7 due to the bending of the book original 10. The book document 10 placed on the document table 2 generally has a shape in which the binding portions are valleys and the central portions of both pages are mountains. Here, if the document surface 10a has a high gloss and is close to a mirror surface, the light emitted from the illumination unit 3 to the document surface 10a is specularly reflected by the document surface 10a, and at the binding portion, the center of the image reading device. Toward the outside of the device at both ends. Since the imaging device 2 is located above the center of the device, the amount of light received by the line sensor 7 is large at the binding portion of the document and small at both end portions. This phenomenon does not occur in documents with high diffusion such that the light incident on the document is uniformly reflected in all directions, but documents such as books and files with images drawn on the surface of the document have some glossiness. Because of this, a difference in the amount of received light occurs depending on the shape.

FIG. 10 shows the background luminance distribution for one page of the book document 10 in the sub-scanning direction. Since the central portion of the document is low in height, the distance from the illumination unit 3 and the image pickup device 2 is long, and the surface is inclined, so that the background luminance is low. In addition to the reason for the central portion, the left and right end portions of the document also have a large decrease in luminance due to fading and the like, and thus the background luminance also has a low value. Thus, with respect to the background luminance changing in the sub-scanning direction, density correction is performed in units of several lines to make the background luminance level uniform. This makes it possible to reproduce a uniform image in all parts of the document.

FIG. 11 is a histogram showing the distribution of the brightness level of the image data for one line in the image data stored in the memory 22. In the figure, the horizontal axis represents the brightness level of the image data, and the vertical axis represents the number of pixels (frequency) of each brightness level. In a document of a character image, the luminance distribution has a normal distribution pattern having peaks in the luminance level corresponding to the character portion and the luminance level corresponding to the background portion. Therefore, based on this distribution, it is possible to detect the brightness levels of the character part (image part) and the background part of the document. In the present embodiment, the luminance of the character portion has a frequency of ½ of the peak value in the luminance distribution of the background portion of the distribution, and a luminance level LB lower than the luminance level of the peak is detected and set as the background luminance level. . The above-described brightness level detection processing is performed by the CPU 21 for the image data at each reading position in the sub-scanning direction.
The CPU 21 converts the brightness level LB into the density level DB and stores it in the memory 22. The conversion from the brightness level to the density level is executed based on the conversion formula described in the Log conversion circuit 14 described above.

In this way, by the preliminary scan, the memory 2
When the background density level DB at each reading position is stored in No. 2, the CPU 21 is
This density level is read out and the density control circuit 1 is sequentially read.
Give to 6. The density control circuit 16 executes density adjustment of image data according to these density levels.

FIG. 12 is a diagram for explaining the density adjustment of the image data executed by the density control circuit 16. In the figure, the second quadrant represents a linear function used for the density adjustment executed by the density control circuit 16. The vertical axis in the second quadrant represents the density level of the image data input to the density control circuit 16, and the horizontal axis represents the density level after density adjustment, that is, the density level of the image data output from the density control circuit 16. Is shown.

The density control circuit 16 sets a linear function based on the background density level DB supplied from the CPU 21 so that the background density level DB is an intercept, and the trimming circuit is set by this set linear function. The image data input from 15 is converted and output. Therefore, by this density adjustment, the background portion of the document surface 10a is output as white (density 0) image data, and the character portion is output as black image data. As a result, even if the original surface has a gray background, such as newspaper, the image data of the background area is converted to a white level and is reproduced on the background of the print paper on the print image. Become. Further, since the image density adjustment is executed at each reading position in the sub-scanning direction, the background of the document surface 10a is unified to the white level at each reading position, and the book document 10 as shown in FIG. It is possible to correct the variation in luminance due to the curvature of the original surface.

The first quadrant in FIG. 12 is the γ correction circuit 1
7 shows a state of density conversion of image data used for the γ correction executed by No. 7. The horizontal axis in the first quadrant represents the density level of image data input to the γ correction circuit 17, that is, the density level of image data output from the density control circuit 16, and the vertical axis represents the density after γ correction. The level, that is, the level of the image data output from the γ correction circuit 17 is shown. In the γ correction, non-linear conversion is performed according to the characteristics of the output destination printer or the like. In this embodiment,
In order to improve the reproducibility of light characters, the slope of the conversion function in the low density range is set, and in order to improve the reproducibility of photographs, the slope of the output density is moderate in the intermediate density range.

FIG. 13 shows a state in which the document table 1 of the image reading apparatus shown in FIG. 1 is removed. In the figure,
A column 32 that supports the document table 1 is provided on the base 1a, and a document table pressure sensor 31 that measures the pressure received by the column 1a from the column 32 is provided at the base of the column 32. The platen 1 placed on the column 32 is composed of left and right plates, and the pressure of each plate can be measured by the platen pressure sensor 31. If the number of pages of the document placed on the plate is large, the weight of the document becomes large and the pressure received by the base 1a also becomes large. Therefore, the approximate number of original pages on each plate can be obtained from the pressure exerted by the left and right plates on the base 1a. At the end of the previous shooting and at the start of the next shooting (when the start key 8 is ON)
In addition, the CPU 21 checks the sensor 31 to detect the amount of change in the number of original pages on each of the left and right pages.

14A, 14B, and 14C show the CPU 21 at the time of photographing in the image reading apparatus configured as described above.
6 is a flowchart showing the processing procedure of FIG. When the power of the image reading device is turned on (# 1), the image reading device is initialized (# 2), and first, a flag "no previous background luminance data" is set (# 3). This flag is set to "1" when the background luminance data is stored in the memory 22 in the reading device, and is set to "0" when the background luminance data is not set in the memory 22. It is something. Next, the flag "no previous height data" is set (# 4). This height data is used to correct image distortion caused by the height of the book document. Next, start key 8 is ON
When the start key 8 is turned on, the lamp of the illumination unit 3 for illuminating the original to start the reading operation is turned on (# 6).

Next, the flag is checked to determine whether or not the background luminance data at the previous photographing is in the memory 22 (# 7). If the background luminance data is in the memory 22, that is, the flag is determined. If is "1"(# 7, YE
S) Next, the flag is checked to determine whether or not the height data at the previous shooting is in the memory 22 (#
8), if height data is in memory 22, ie,
If the flag is "1"(# 8, YES), then it is determined whether the document is changed by checking the output of the document change detection sensor 9 (# 9), and the document is changed. If not (# 9, NO), the change amount of the page of the document is determined by checking the output of the pressure sensor 31 (# 10),
If the amount of change does not exceed the predetermined value (# 10, NO),
The main scan is performed by using the background luminance data at the previous shooting as the data for density correction (# 12). If there is no previous background luminance data, that is, if the flag is "0"(#
7, NO), if there is no previous height data, that is,
When the flag is "0"(# 8, NO), when the document on the document table 1 is replaced (# 9, YES), or
When the pages of the manuscript are turned over more than the specified value (# 1
For 0, YES, a preliminary scan is performed (# 11), and then a main scan is performed (# 12). When the main scan is completed, the lamp of the illumination unit 3 is turned off (# 13).

The operation of the preliminary scan (# 11) will be described below. In the preliminary scan, (#
111), a histogram is created (# 112), and the background luminance LBn of the line is calculated from the histogram (# 113). Further, every time one line is read, height data for correcting the image distortion due to the height of the document is detected by counting the number of pixels corresponding to the image on the side surface of the document (# 114). Such an operation is executed for all the lines for which the preliminary scan is performed (# 11
5). After the sampling is completed for all the lines, the detected data is used as the data for density correction to update the data in the memory 22 (# 116), and the setting “with background luminance data” is set (# 117). Next, the detected height data is used as image distortion correction data in the memory 2
The data in 2 is updated (# 118), and "height data exists" is set (# 119).

In the main scan (# 12), after reading one line (# 121), density correction (# 122) and image distortion are performed based on the background luminance distribution data and height data stored in the memory 22. Correction (# 123) is performed. This correction process is performed for all lines (# 124).

In the above embodiment, whether or not the number of manuscript pages has changed greatly is judged by checking the manuscript table pressure sensor 31, but the manuscript pages are changed from right to left or from left to right. It is also possible to recognize the change in the number of original pages by counting how many pages have been turned over, and to update the height distribution data when the number of pages has been turned over by a predetermined number of pages. The method will be described with reference to FIGS. FIG. 15 is a front view of the image reading device. The page-turning count sensors 50 and 51 (hereinafter, referred to as page-turning sensors) are provided in the image pickup device 2 at positions facing left and right pages of the book document 10 placed on the document table 1. These page-turning sensors 50, 51 are connected to the document surface 10a of the book document 10 and the page-turning sensors 50, 51.
It is to measure the distance between and.

The page turning detection method will be described with reference to FIG. FIG. 16 is a diagram showing how distance measurement is performed on the right page. In order to make the measurement principle easy to understand, the configuration of the page turning sensor 50 is shown in an enlarged manner, and the distance between the document surface 10a and the imaging device 2 is also shown short. Further, the distance measurement of the left page is performed symmetrically with the right page, and the description thereof will be omitted. The page turning sensor 50 includes a light emitting element 52, a lens 53, and a line sensor 54 (the same applies to 51). The light emitting element 5 that irradiates the document surface 10a with the page not floating
The optical path of 2 is 1, and is shown by a solid line. Further, the original surface 10a 'in which the page is floating while the page is being turned
Is indicated by a dashed line, and the original surface 10a in the floating state is shown.
The optical path of the light emitting element 52 that is irradiated with ‘′ is represented by l ′ and is indicated by a broken line.

The original surface 10a with the page not floating
The light from the light emitting element 52 reflected by the
4 is incident on add1. The light reflected by the original surface 10a 'with the page floating is a of the line sensor 54.
It is incident on dd2. Thus, if the distance between the document surface and the page turning sensor 50 is long, the light from the light emitting element 52 is incident on the right side of the line sensor 54, and if the distance is short, it is incident on the left side (in the case of 51). Is left and right reversed). Therefore, the distance between the document surface and the page turning sensor 50 can be obtained from the position of the light incident on the line sensor 54.

FIG. 17 is a diagram showing how pages of book document 10 are turned. When the pages of the book manuscript 10 are turned from right to left, (1)-(2)-
The order is (3)-(4)-(5)-(6). When turning from left to right, (6)-(5)-(4)-
The order is (3)-(2)-(1).

FIG. 18A shows a page turning sensor 5 when the pages of the book document 10 are turned from right to left.
Outputs of 0 and 51 are shown. The output of the page turning sensor 50 for the right page is shown by a solid line, and the output of the page turning sensor 51 for the left page is shown by a broken line. This output is obtained by replacing the position of the light incident on the line sensor 54 with the distance between the document surface and the sensor. As the document surface 10a is turned over and displaced from the state (1) to the state (2),
The distance between the document surface and the sensor 50 becomes shorter, and the output of the right page page turning sensor 50 becomes gradually smaller.
In (3), until then, the light of the light-emitting element 52 was reflected to the page being turned over to detect the distance. Since the reflective surface is switched, the output value suddenly increases (the distance between the sensor 50 and the document surface increases). Between (3) and (4), the page turning sensor 5
There is no change in output for both 0 and 51. When the turned page is in the state of (4), the page turning sensor 51 for the left page has detected the distance by reflecting the light of the light emitting element 52 to the page below until then. Since the light reflection surface is switched to the turned page, the output value of the page turning sensor 51 for the left page suddenly decreases. Then, the distance between the document surface and the sensor 51 becomes longer as the state is changed from (4) to (5),
The output value of the page turning sensor 51 for the left page becomes large. When the page is turned over to the state (6), the output of both the page turn sensors 50 and 51 does not change.

FIG. 18B shows the page turning sensor 5 when the pages of the book original 10 are turned from left to right.
Outputs of 0 and 51 are shown. The output of the page turning sensor 50 for the right page is shown by a solid line, and the output of the page turning sensor 51 for the left page is shown by a broken line. As the document surface 10a is turned over and displaced from (6) to (5), the distance between the document surface and the sensor 50 becomes shorter, and the output of the page turning sensor 51 for the left page gradually becomes smaller. .
In (4), until then, the light of the light-emitting element 52 was reflected on the turned page to detect the distance. However, the light is off the turned page and the next page below. Since the reflective surface is switched, the output value suddenly increases (the distance between the sensor 50 and the document surface increases). Between (4) and (3), the page turning sensor 5
There is no change in output for both 0 and 51. When the turned page becomes the state of (3), until then, the right page turning sensor 50 reflects the light of the light emitting element 52 to the page below and detects the distance. Since the reflection surface of the light is switched to the turned page, the output value of the page turning sensor 50 for the right page suddenly decreases. Then, as the displacement from (3) to (2) occurs, the distance between the document surface and the sensor 50 increases,
The output value of the page turning sensor 50 for the right page increases. When the page is turned over to the state (1), the output of both the page turn sensors 50 and 51 is not changed. Sensors 50 and 51 are used to count page turning.
If the change in the output of 1 is in the order of the sensor 50 and the sensor 51, it is counted as +1. That is, +1 is counted when the page is turned from right to left, and -1 is counted when the page is turned from left to right. The total page change amount is the absolute value of the sum of these count values.

The total page change amount obtained by this method is
The method using the platen pressure sensor 31 described above (see FIG.
4, # 9, # 10) can be replaced with the page change amount detected. If these methods are used together,
When a plurality of pages can be turned together at once, it is possible to detect a large amount of change by the method using the platen pressure sensor 31, and when the pages are turned one page at a time and the output of the pressure sensor 31 gradually changes little by little. In addition, the magnitude of the change amount can be detected by the page change amount detected by the page turning sensors 50 and 51.

The present invention is not limited to the configuration of the above embodiment, but various modifications can be made without departing from the spirit of the invention.

[0039]

As described above, according to the image reading apparatus of the present invention, when it is determined that the original has not been replaced by detecting that the original has been changed, the operation of the luminance detecting means is performed. Since the reproduction density is controlled by using the immediately preceding brightness detection result after stopping, and the brightness data is updated when a change in the document is detected, the background brightness detection operation is minimized. In addition, the time required for reading can be shortened. Further, the document change detection may be such that the page turning of the document is detected, the brightness data is detected when the page amount exceeds a predetermined value, and the brightness data is updated. The same effect as above can be obtained.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an overall configuration of an image reading apparatus according to an embodiment of the present invention.

FIG. 2 is a perspective view showing how a book is placed on a document table of the apparatus.

FIG. 3 is a diagram showing a schematic configuration of the present device when viewed from the front.

FIG. 4 is a diagram showing a schematic configuration of the apparatus when viewed from the side.

FIG. 5 is a diagram showing the principle of height detection processing used in this embodiment.

FIG. 6 is a diagram showing a state of image data read by an imaging device.

FIG. 7 is a diagram showing an output state of one line in the main scanning direction read by a line sensor.

FIG. 8 is a block diagram of a control circuit of the image reading apparatus.

FIG. 9 is a diagram illustrating a change in the amount of light received by a line sensor due to the bending of a book document.

FIG. 10 is a diagram showing a background luminance distribution in the sub-scanning direction for one page of a book document.

FIG. 11 is a histogram diagram showing a distribution of brightness levels of image data for one line in the image data stored in the memory.

FIG. 12 is a diagram for explaining density adjustment of image data executed by a density control circuit.

FIG. 13 is a perspective view showing a state in which a document table of the image reading apparatus is removed.

14A, 14B, and 14C are flowcharts showing a processing procedure of the CPU at the time of photographing in the image reading apparatus.

FIG. 15 is a front view of an image reading apparatus including a page turning count sensor.

FIG. 16 is a diagram for explaining a page turning detection method.

FIG. 17 is a diagram showing how pages of a book document are turned.

FIG. 18A is a diagram showing an output of a page turning sensor when pages of a book document are turned from right to left;
(B) is a diagram showing the output of the page turning sensor when the pages of the book document are turned from left to right.

[Explanation of symbols]

 1 Original Plate 2 Image Pickup Device 5 Height Detection Mirror (Height Detection Unit) 7 CCD Line Sensor (Imaging Unit) 9 Original Change Detection Sensor (Replacement Presence / Absence Detection Unit) 10 Original Document 21 CPU (Brightness Detection Unit)

Claims (2)

[Claims] 1. An image reading apparatus for reading an original such as a book or the like, which is placed on a platen and opened upward, detects the background luminance of the original, and controls the density based on the background luminance. A reading unit that reads the document table on which the document is placed and outputs image data, a document change detection unit that detects a change in the document placed on the document table, and a background that detects the background brightness of the document. Luminance detecting means, storage means for storing the background luminance data detected by the background luminance detecting means, density control means for controlling the image density based on the background luminance data stored in the storing means, An image reading apparatus comprising: an updating unit that updates the background luminance data stored in the storage unit when a document change is detected by the document change detecting unit. 2. An image reading device for reading an original such as a book or the like, which is placed on a platen and opened upward, detects the background brightness of the original, and controls the density based on the background brightness. A reading unit that reads the document table on which the document is placed and outputs image data; a page amount detection unit that detects the amount of pages of the document that is placed on the document table; and a background brightness of the document. Background luminance detecting means for detecting the background luminance, storage means for storing the background luminance data detected by the background luminance detecting means, and density control for controlling the image density based on the background luminance data stored in the storing means. And an updating unit that updates the background luminance data stored in the storage unit when a page amount of a predetermined value or more is detected by the page amount detecting unit. Reader.