JP3687339B2 - Image reading device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image reading apparatus for photographing a book document or the like from above, and an image reading apparatus provided with a mechanism for detecting the height of the document and automatically performing focusing.
[0002]
[Prior art]
In the field of this type of conventional image reading apparatus, that is, a face-up scanner, for example, as shown in Japanese Patent Laid-Open No. 5-316302, the subject image is focused on the line sensor by the moving line sensor. A lens that adjusts the focus at regular intervals, or a lens based on the output of the height detection means for every line (one line or several lines) of scanning of the line sensor, as disclosed in Japanese Patent Laid-Open No. 7-254970. Some have been proposed to control the movement speed.
[0003]
[Problems to be solved by the invention]
However, in the conventional face-up scanner described above, if the document reading speed (line sensor movement speed) is increased, the height of the document changes rapidly, and the motor cannot follow the focus for each line. there were . In addition, in order to cope with the above-described problem, when focusing is performed every several lines, there is a problem that the accuracy of focusing is lowered.
The object of the present invention is to focus properly within the range of the performance of the drive motor for adjusting the focus when the reading speed is high and the height change of the document is abrupt. In the case where the image quality is moderate, an object of the present invention is to provide an image reading apparatus capable of performing proper focusing with high resolution.
[0004]
[Means for Solving the Problems]
To achieve the above object, an image reading apparatus of the present invention, the in the image reading apparatus for photographing an object by scanning the image pickup sensor, a height detecting means for detecting the height of the subject, the subject An imaging optical system that forms an image on an imaging sensor, a moving unit that moves the imaging sensor relative to the subject, a focus adjustment unit that drives the imaging optical system to perform focus adjustment, and the moving unit Control means for dividing the moving distance of the imaging sensor into a plurality of sections and controlling the focus adjustment by the focus adjustment means based on height information obtained by the height detection means. The means is based on the height information obtained by the height detection means, when the change in the height of the subject is gradual, compared with the case where the change in the height of the subject is abrupt. It is to set shorter the distance between.
[0005]
In the present invention , for example, when the change in height of a document is gentle as a subject , a focusing operation is performed with fine resolution (minimum pitch of height information, for example, every 1 mm pitch), the reading speed is high, and the document is If the height variation of the steep, that is, if the focus adjusting motor that can not follow the original height, it is possible to perform focusing in coarse resolution (e.g., a minimum pitch × every n of the height) . “N” that determines the resolution is set to an appropriate value based on the gradient of the height change of the document and the performance of the focus adjustment motor.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a perspective view showing an external appearance of an image reading apparatus (book scanner) 1, and FIG. 2 is a view showing an example of a usage state of the book scanner 1. The book scanner 1 includes a main body housing 10 that stores an electric circuit, a dark original platen 20 that supports an original, an imaging unit 30 that converts an original image into an electric signal, and a lamp unit 40 that illuminates the original. . The document table 20 is disposed on the front side of the main body housing 10. The imaging unit 30 is disposed above the document table 20 and is supported in a cantilever manner by a column 12 extending upward from the upper surface of the main body housing 10. The lamp unit 40 is disposed on the lower surface side of the imaging unit 30 and is fixed to the support column 12. A space 80 between the document table 20 and the imaging unit 30 is open to a free space outside the apparatus, and has a sufficient area for setting a book document. The distance between the document table 20 and the imaging unit 30 is 30 cm or more.
[0007]
An operation panel OP is provided on the upper end side of the front surface of the main body housing 10, and a distance measuring plate 16 (height detection means) for detecting the height of the document surface is fixed on the lower end side. The surface of the distance measuring plate 16 on the front side is a glossy flat surface and is inclined at 45 ° with respect to the upper surface of the document table 20. The upper end surface of the distance measuring plate 16 functions as a white plate 18 for shading correction. A main switch 51 is provided on the right side surface of the main body housing 10 toward the operation panel OP. One start key 52 is provided on each side of the platen 20 in the left-right direction for the user to instruct the start of reading. An armrest 25 is provided on the front side of the document table 20.
The imaging unit 30 includes a line sensor 31 (imaging sensor) made of a CCD array, an imaging lens 32 (imaging optical system), and a mirror 33. The document screen is projected onto the light receiving surface of the line sensor 31 by the mirror 33 and the imaging lens 32. The imaging lens 32 is provided so as to be movable in the front-rear direction, and is positioned by an AF mechanism (focus adjustment means) (not shown). The line sensor 31 is attached to a movable body of a scanning mechanism (not shown), and translates along the left-right direction (sub-scanning direction) M2 while keeping the arrangement direction of the CCD elements up and down. A two-dimensional document image is picked up by this parallel movement.
[0008]
The book scanner 1 having the above configuration is an image input unit suitable for reading a book document. By combining the book scanner 1 and the digital copying machine, it is possible to configure a comprehensive copying system suitable for various kinds of documents.
When the book scanner 1 is used, the user places the book document BD upward on the document table 20 as shown in FIG. At that time, the book original BD is pressed against the lower end of the distance measuring plate 16 for positioning. That is, the boundary between the distance measuring plate 16 and the document table 20 is a reference line for setting the document. The center of the reference line is the reference position P0 (see FIG. 3). The document table 20 is configured to be movable up and down independently on the left and right. Thereby, the height of the left and right pages when the pages are opened can be made substantially the same.
[0009]
In the book scanner 1, the same original is scanned twice (original reading). In the book original BD, unlike the sheet original, the original surface is curved. Therefore, it is necessary to adjust the imaging focus according to the curved state. Processing to compensate for the difference in luminance is also necessary. Therefore, the curved state is detected in the first scan (hereinafter referred to as preliminary scan), and necessary processing is performed in the second scan (hereinafter referred to as main scan) based on the detection result. Image output to an external device is performed during the main scan. The reading mode includes a mode for reading both the left and right pages at once (scanning form similar to that of a sheet document) and a mode for separately reading the left and right pages. In either mode, a preliminary scan and a main scan are performed for each page.
[0010]
FIG. 3 is a plan view showing an example of reading a book document BD. 3A shows a state where the book original BD is set on the original table 20, and FIG. 3B shows the read image G0. The read image G0 includes an image G1 of the reading target surface of the book document BD, an image G20 of the document table 20, and an image G18 reflected on the distance measuring plate 16. Images G181 and G182 in the image G18 indicate the shape of the end surface (portion called “heaven” in the book) of the book document BD in a spread state. The part of the image G18 other than the images G181 and 182 is a background image reflected on the distance measuring plate 16. Since the boundary between the image G18 and the image G20 corresponds to the above-mentioned reference line and is known, the height of the document surface can be calculated from the distance (number of pixels) between the boundary and the contour lines of the images G181 and 182. . The boundary between the image G1 and the image 20 can be easily determined using the difference between the background color of the document surface and the color of the document table 20.
Note that the upper edge and the lower edge of the image G1 are curved because the height of the document surface is not constant. That is, a subject close to the imaging surface is imaged larger than a distant subject. During the main scan, image processing for correcting the curved image G1 to an image when the height of the document surface is constant is performed based on the height information of the document surface obtained during the preliminary scan.
[0011]
FIG. 4 is a block diagram of the signal processing system 100 of the book scanner 1. The output of the line sensor 31 is converted into, for example, 8-bit image data D102 by the AD converter 102. During the preliminary scan, the image data D102 is temporarily stored in the temporary memory 104 and transferred to the luminance detection unit 112 via the CPU 101 (control means). The luminance detection unit 112 aggregates the luminance of each pixel for each predetermined line in the sub-scanning direction to create a luminance histogram, and calculates a threshold for determining the background luminance and the presence / absence of an image. The counting unit 113 counts the number of pixels whose luminance is not more than a threshold value based on the luminance histogram. The position detection unit 114 indicates the scanning position on the imaging surface. The CPU 101 calculates the height of the document surface based on three pieces of information: background luminance, the number of pixels corresponding to the image, and the scanning position. Further, the CPU 101 generates data for AF control based on the height data. An AF motor 36 that is a driving source of the AF mechanism drives the imaging lens 32 based on the generated data to perform focus adjustment.
[0012]
During the main scan, the image data D102 is sent from the AD conversion unit 102 to the image processing unit 103. The image processing unit 103 performs processing such as correction of image distortion caused by the curvature of the document surface, density correction, and masking for erasing the image of the user's hand holding the document. Image data that has undergone predetermined image processing is output to an external device such as a copying machine or a printer. The CPU 101 controls the drive system including the lamp control unit 45 and the sensor drive unit 35 (moving means) according to the program in the memory. The sensor driving unit 35 supplies a predetermined clock signal to the line sensor 31.
[0013]
FIG. 5 is a flowchart of the image reading operation.
In response to the start key 52 being turned on (# 1, YES), the book scanner 1 turns on the light source of the lamp unit 40 (# 2) and starts a preliminary scan (# 3). In the preliminary scan, the height of the document surface as described above is measured (# 4). After the preliminary scan is completed (# 5 YES), AF control information is created (# 6), and then the main scan is started (# 7). In the main scan, predetermined image processing and AF operation in accordance with scanning of the line sensor 31 described later are performed (# 8), and the processed image data is sequentially output to an external device. When the main scan is finished (# 9, YES), the light source of the lamp unit 40 is turned off (# 10), and a new start instruction is awaited.
[0014]
Next, an AF operation control method by the AF motor 36 will be described with reference to FIGS. First, document height information will be described with reference to FIG. The height information of the document is sampled at a constant cycle (for example, every 1 mm pitch) during preliminary scanning. For the sake of explanation, the interval of the height information (here, 1 mm pitch) is set as a section “H”, and the i-th section is set as H [i]. Further, P (H [i]) is a value obtained by converting the height change at H [i] into the number of pulses. Further, t is a time for reading the section H by the line sensor (hereinafter referred to as a reference pitch reading time) . t is obtained from the reading speed determined by the reading magnification and the reading density, and is constant during scanning. The AF motor 36 uses a stepping motor.
[0015]
The AF motor 36 is controlled during the main scan. After the height information is obtained in the preliminary scan, the drive pattern in the main scan is calculated in advance, and the AF motor 36 is driven and controlled using this data during the main scan. . Here, an interval for focusing is K, and a j-th interval is K [j]. Also, let P (K [j]) be the number of pulses output in the interval K [j].
The data used during the main scan consists of the focusing interval (number of sections H in K [j], which is n (K [j])) and the section (n (K [j]) The number of pulses P (k [j]) to be output in the H section) and the pulse rate of each pulse.
The AF motor 36 is driven by acceleration / deceleration. For example, assume that acceleration / deceleration is performed in 11 steps as follows.
[0016]
[Table 1]
1) 230 pps (4.3479 msec)
2) 463 pps (6.5062 msec)
3) 600 pps (8.1716 msec)
4) 710 pps (9.5787 msec)
5) 805 pps (10.8199 msec)
6) 890 pps (11.9430 msec)
7) 967 pps (12.9763 msec)
8) 1039 pps (13.9385 msec)
9) 1106 pps (14.8425 msec)
10) 1169 pps (15.6977 msec)
11) 1200 pps (16.5310 msec)
[0017]
The acceleration / deceleration driving of the AF motor 36 is performed by sequentially outputting the above pulse rate one pulse at a time. The time between the stop state and the speed (pulse rate) is shown in parentheses. For example, when accelerating to 1200 pps, 11 pulses are required, which takes 16.5310 msec. In the present embodiment, the above acceleration / deceleration is performed in 11 steps, but the acceleration / deceleration pattern may be another pattern.
[0018]
In data generation for AF control, first, height information (at a pitch of 1 mm) at each sub-scanning position of a document is converted into a lens movement amount, which is further converted into the number of pulses of the AF motor 36. Next, n (K [j]) of each section K [j], the number of output pulses P (K [j]), and the pulse rate of each pulse are obtained.
[0019]
The procedure will be described below with reference to FIGS. 6A, 6B and 6C and the flowchart of FIG. 6A, 6B, and 6C are diagrams showing a method for obtaining the number of pulses for AF control corresponding to the height of the document with respect to the sub-scanning position, and FIG. 6A is a reference pitch (1 mm pitch). (B) shows the case where acceleration / deceleration in the sections K [j] and K [j + 1] is possible. (C) is a diagram in the case where the number of output pulses P (K [j]) is finally determined.
1) Taking n (K [j]) as 1, P (K [j]) is obtained (# 11- # 13). Since n (k [j]) = 1, P (K [j]) = P (H [i]) (see FIG. 6A).
[0020]
2) Find n (K [j + 1]) and P (K [j + 1]).
First, n (K [j + 1]) = 1 is set (not determined), and P (K [j + 1]) is obtained (# 14, # 15). Here, since n (K [j + 1]) = 1, P (K [j + 1]) = P (H [i + 1]) (see FIG. 6A).
At this time, it is determined whether the time required to output the P (K [j + 1]) pulse from the stop state is longer than t × n (K [j + 1]) (# 16) (t is the reference (Pitch reading time) If this determination is YES, P (K [j + 1]) pulses can be output from the stop state within n (K [j + 1]) interval, so within interval K [j] Is set (# 18). However, if the determination of # 16 is NO, that is, if the P (K [j + 1]) pulse cannot be output from the stop state within the n (K [j + 1]) section, n (K [j + 1]) is increased by 1 (# 20), and a new P (K [j + 1]) is obtained (# 15). This time, n (K [j + 1]) = 2, so P (K [j + 1]) = P (H [i + 1]) + P (H [i + 2]) ( See FIG. 6 (B)). In this way, n (K [j + 1]) is incremented by 1 from the stop state until P (K [j + 1]) pulse output is possible.
[0021]
3) The output pattern (pulse rate of each pulse) of P (K [j]) is determined (see # 17, FIGS. 6B and 6C). Here, in the present embodiment, the start pulse rate in each section is set to the end pulse rate in the previous section K [j-1] in order to facilitate the operation and to ensure the stop operation. The end pulse rate is set to the pulse rate of P (K [j + 1]) + 1 step or less obtained in 2) above. The P (K [j + 1]) + 1 step is, for example, the sixth pulse rate (890 pps) of the above acceleration / deceleration step when P (K [j + 1]) = 5. This is because the next (j + 2) th output pulse P (K [j + 2]) becomes zero, that is, stops in the interval K [j + 1], in other words, the interval K [j + 1] Since there is a possibility of termination at the minimum pulse rate (230 pps in this embodiment), P (K [j + 1) is set in the output pattern setting of P (K [j]) so that it is possible to cope with such a case. ]) It shall be finished in +1 step or less. Therefore, if it ends in P (K [j + 1]) + 1 steps or less, K [j + 1] can be decelerated to the lowest pulse rate (230 pps) with P (K [j + 1]) pulses. It is possible to stop reliably in the next section.
[0022]
In the output pattern (pulse rate) setting of P (K [j]) as described above, even if the determination of # 16 is YES, P (K [j] ) Is large and pulse output cannot be performed within t × n (K [j]) (# 18 · NO), n (K [j]) is increased by 1 (# 21), and the process returns to # 13. A new P (K [j]) is obtained, and the processes from 2) onward are repeated until pulse output can be performed (setting OK).
[0023]
If the above setting is possible (# 18, YES), it is checked whether the processing of all sections is finished (# 19). If all sections are not finished, j = j + 1 is set (# 22) and # 12 is reached. Returning, the above processing is repeated, and the processing is ended when the processing of all sections is completed.
[0024]
In this way, all the sections are processed, and “number of sections n (K [j])”, “number of output pulses in section P (K [j])”, and “pulse rate of each output pulse” are obtained as AF control information ( j = 1 to last section) (see FIG. 6C). At the time of the main scan, in synchronization with the reading of the line sensor, AF control is performed by sequentially outputting pulses based on the above AF control information. In FIG. 6C, when n (K [j]) = 3 and n (K [j + 1]) = 2, the pulse rate of the section K [j] can be set and P (K [j] the indicates that the present decision. Subsequently, as start section the H [i + 3] interval, repeating the same process returns to FIG. 6 (a), create an AF control information for all sections 6C, the pulse P (K [j + 1]) in the section K [j + 1] is set to the minimum pulse rate , so that it must be stopped in the next section. Even if something happens, it can be stopped reliably.
[0025]
FIG. 8 shows the number of pulses of the AF motor 36 for each section created as described above. In the j-th section K [j], n (K [j]) = 3, and n ( P (K [j]) pulse is output within K [j]) × t time. In this embodiment, since the operation is performed as described above, when the change in the height of the document is gentle, a focusing operation is performed with a fine resolution (minimum pitch of height information, for example, every reference 1 mm pitch). If the reading speed is high and the document height changes suddenly and the AF motor 36 cannot follow the document height change, focusing can be performed with coarse resolution (reference pitch x every n). it can. That is, the unit of the focusing operation is variable, and an appropriate focus adjustment operation can be obtained according to the gradient of the height change of the document and the performance of the AF motor 36.
[0026]
【The invention's effect】
As described above, according to the present invention, since the resolution of the focus adjustment control (focusing) is made variable, it is possible to always perform proper focusing on a document having various gradients and is also suitable for high-speed reading. AF control compatible with is possible.
[Brief description of the drawings]
FIG. 1 is a perspective view showing an external appearance of a book scanner according to an embodiment of the present invention.
FIG. 2 is a diagram illustrating an example of a usage state of a book scanner.
FIGS. 3A and 3B show an example of reading a book document, where FIG. 3A is a plan view of a book document set on a document table, and FIG. 3B is a diagram showing a scanned image.
FIG. 4 is a block diagram of a signal processing system of a book scanner.
FIG. 5 is a flowchart of a reading operation.
6A, 6B, and 6C are diagrams for explaining a method for setting an AF control section. FIG.
FIG. 7 is a flowchart for creating AF control information.
FIG. 8 is a schematic diagram of height information and AF control sections.
[Explanation of symbols]
1 Book scanner
16 Distance plate (height detection means)
20 Document table
30 Imaging unit
31 Line sensor (imaging sensor)
32 Imaging lens (imaging optics)
35 Sensor drive (moving means)
36 AF motor (focus adjustment means)
101 CPU (control means)

Claims (2)

In an image reading apparatus for photographing a subject by scanning an image sensor,
A height detecting means for detecting the height of the object,
An imaging optical system for forming the object onto the image sensor,
Moving means for moving the image sensor relative to the subject;
Focus adjusting means for adjusting the focus by driving the imaging optical system;
Control means for controlling the focus adjustment by the focus adjustment means based on the height information obtained by dividing the movement distance of the imaging sensor by the movement means into a plurality of sections; and With
The control means, based on the height information obtained by the height detection means, when the change in the height of the subject is gradual, compared with the case where the change in the height of the subject is abrupt. The image reading apparatus is characterized in that the distance is set short .   The image reading apparatus according to claim 1, wherein the subject is a document having a curved document surface.

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