JP2002033919A - Reader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform density correction for reproducing the brightest area in white, and to correct the change of luminance generated due to change in the height (inclination) of an object in a reader. SOLUTION: Density correction quantity for image picked-up data is calculated for each reading position by using the maximum luminance detected from the output of an image pickup means, a read position having the maximum luminance value, and luminance distribution, based on the height (inclination) of an object as a reference. Thus, base blowing quantity can be corrected, and to appropriately reproduce a void area, when a void area whose area is small is present in a colored based original.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reading device (image scanner) for photographing various originals and three-dimensional objects to be read, converting the image into an electric signal, and outputting image data. The present invention relates to a technique for performing correction.

[0002]

2. Description of the Related Art In the field of a conventional scanner for reading a book document or the like, for example, as shown in Japanese Patent Application Laid-Open No. Hei 10-257323, a luminance having a maximum frequency of a luminance histogram (hereinafter referred to as a peak luminance) is detected. In addition, a technique has been proposed in which the density of an image is corrected using a brightness threshold value for correction associated with the brightness in advance. Further, even if the original has a uniform background luminance, the peak luminance of the histogram changes in accordance with a change in the height (angle) of the original surface in the case of a book original. ), A technique for performing density correction has been proposed.

[0003]

However, in the above-described conventional face-up scanner, density correction is performed for each area (each sub-scanning position) based on the peak luminance of the histogram (the luminance of the area having the largest area). In the case of a colored base document, if a white area (or a region brighter than the colored region) with a smaller area than the colored region exists in the document, the colored region is output in white, and naturally, a smaller area with a brighter area than the colored region is output. Since the area is also output in white, there is a problem that a blank area cannot be confirmed in the output image.

If there is a blank area (or a lighter area than the colored area) larger than the colored area,
The white area (or the area brighter than the colored area) is output in white only in the sub-scanning position, the colored area is reproduced with a certain density, and the colored area is reproduced in white at the other positions. There was also the problem of becoming.

The present invention has been made to solve the above-mentioned problem. By performing density correction for outputting the brightest area in white, a white background (or a white area having a smaller area than a colored area) is provided on a colored base document. A reading device that can reproduce the small area blank area even when there is a (bright) area and can also correct a luminance change caused by a change in height (a change in inclination) of the object. The purpose is to provide.

[0006]

In order to achieve the above object, the present invention comprises image pickup means for converting an optical image of an object to be read into electric signals in pixel units, and processes signals from this image pickup means. A reading device for outputting as image data, a maximum luminance detecting means for detecting a maximum luminance from the output of the imaging means, a maximum luminance position detecting means for detecting a reading position of the maximum luminance detected by the maximum luminance detecting means, A luminance distribution detecting means for detecting a luminance distribution generated by a change in height of the object, a maximum luminance detected by the maximum luminance detecting means, and a maximum luminance position detected by the maximum luminance position detecting means, Based on the luminance distribution detected by the luminance distribution detecting means, the imaging data output from the imaging means for each reading position by the imaging means. It is obtained by a density correction calculation means for calculating a density correction amount for data.

[0007] In this configuration, the maximum luminance detected from the output of the imaging means, the reading position having the maximum luminance value, and the luminance distribution due to the height (inclination) of the object are used as references.
A density correction amount (background removal amount) for the imaging data is calculated for each reading position. This makes it possible to correct the background removal amount. For example, when a small area white area exists in a colored base document, it is possible to prevent the white area from not being reproduced. In addition, uneven density due to a change in the height of the target object can be eliminated.

[0008]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of a reading apparatus according to an embodiment of the present invention. FIG. 1 shows an appearance of the book scanner 1, and FIG. 2 shows an example of a use state of the book scanner 1. Book Scanner 1
The apparatus includes a main body housing 10 that houses an electric circuit and the like, a dark document table 20 that supports a document, an imaging unit 30 that converts a document image into an electric signal, and a lamp unit 40 that illuminates the document. The platen 20 is the main body housing 1
0 is located on the front side. The imaging unit 30 is arranged above the document table 20 and is supported in a cantilever manner by a support column 12 extending upward from the upper surface of the main body housing 10. The lamp unit 40 is arranged on the lower surface side of the imaging unit 30 and is fixed to the column 12.

A space 80 between the document table 20 and the image pickup unit 30 is open to a free space outside the apparatus, and has a sufficient size for setting a book document. The distance between the document table 20 and the imaging unit 30 is 30 cm or more.

An operation panel OP is provided at the upper end of the front surface of the main body housing 10, and a distance measuring plate 16 for detecting the height of the document surface is fixed to the lower end. Distance measuring board 1
The front surface of 6 is a glossy flat surface and is a 45 ° inclined surface with respect to the upper surface of the document table 20. The upper end surface of the distance measuring plate 16 is a white plate 1 for shading correction.
Functions as 8. A main switch 5 is provided on a right side surface of the main body housing 10 toward the operation panel OP.
1 is provided. On both sides of the document table 20 in the left-right direction, one start key 52 for the user to instruct the start of reading is provided. The document table 20
An armrest 25 is provided on the front side of the.

In FIG. 1, an image pickup unit 30 has a CC
A line sensor 31 composed of a D array, an imaging lens 32,
And a mirror 33. The original screen is projected on 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 (not shown). The line sensor 31 is attached to a movable body of a scanning mechanism (not shown), and moves in parallel in the left-right direction (sub-scanning direction) M2 while keeping the arrangement direction of the CCD elements up and down. By this parallel movement, a two-dimensional document image is captured.

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, a comprehensive copying system suitable for various originals can be configured. When using Book Scanner 1,
The user places a book document B on the document table 20 as shown in FIG.
Place D upwards with D open. At that time, the distance measuring board 16
The book document BD is pressed against the lower end of the document to perform 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 vertically movable independently of left and right. This makes it possible to make the heights of the right and left pages when the spread is opened substantially the same.

In the book scanner 1, the same document is scanned twice (document reading). In the book document BD, the document surface is curved unlike the sheet document. Therefore, it is necessary to adjust the focus of imaging according to the curved state. Processing for compensating for the difference in luminance is also required. Therefore, 1
The curved state in the second scan (hereinafter, referred to as the preliminary scan)
A luminance distribution or the like is detected, and necessary processing is performed in a second scan (hereinafter, referred to as a main scan) based on the detection result. Image output to the external device is performed during the main scan.

FIG. 3 is a plan view showing an example of reading a book document BD. FIG. 3A shows a state in which a book document BD is set on the document table 20, and FIG.
Indicates a read image G0.

The read image G0 is composed of an image G1 of the surface to be read of the book document BD, an image G20 of the document table 20, and an image G18 reflected on the distance measuring plate 16. Image G1
The images G181 and G182 in 8 show the shape of the end face (the part called “heaven” in the book) of the book document BD in the open state. Image G18 of image G18
The portions other than 1, G182 are background images shown 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 boundary and the image G181, G18
The height of the document surface can be calculated from the distance (the number of pixels) from the second contour line. The boundary between the image G1 and the image G20 can be easily determined by utilizing the difference between the background color of the document surface and the color of the document table 20.

The upper and lower edges of the image G1 are curved because the height of the document surface is not constant.
That is, a subject near the imaging surface is imaged larger than a distant subject. At the time of 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 at the time of the preliminary scan.

FIG. 4 shows a block configuration of a main part of the signal processing system 100, FIG. 5 shows an example of a luminance frequency distribution, and FIG. 6 shows input / output characteristics of the density correction section 103C. Signal processing system 1
Reference numeral 00 includes a CPU 101, an AD converter 102, an image processing circuit 103, a luminance detection unit 104, and a RAM 105.

In the preliminary scan, the line sensor 31
The photoelectric conversion signal output from is converted by the AD converter 102 into, for example, 8-bit image data (luminance data) D1.
The values are converted to 0 and input to the luminance detection unit 104 in the order of pixel arrangement. The luminance detecting unit 104 includes a comparator and a counter, and generates luminance frequency distribution data DN of a read image by counting the imaging data D10 for one line for each value class.

Here, an example of the luminance frequency distribution data DN is shown. FIG. 5A shows an original in which an area having a density different from that of the base exists in the colored base, and FIG.
FIG. 5A shows luminance distribution data DN at position B (sub-scanning position mainly composed of characters) of FIG. 5A, and FIG. 5C shows position C of position C (sub-scanning position including an area darker than the background) of FIG. 5D shows the luminance distribution data DN, and FIG. 5D shows the luminance distribution data DN at a position D (a sub-scanning position including a region brighter than the background) in FIG. 5A. In the example of FIG. 5A, there are a high-luminance area f and a low-luminance area g in the book document.

The CPU 101 takes in the luminance frequency distribution data DN for one line, detects N data values of the peaks of the distribution from the high luminance side, and stores them in the RAM 105. In the present embodiment, N = 2 (pieces), which are referred to as peak luminance BP1 and peak luminance BP2 (see FIG. 5). However, the luminance range to be detected is the background possibility range. For example, if the imaging data D10 in FIG. 4 is an 8-bit 256 (0 to 255) gradation, a luminance value of about 70 to 255 is suitable as the background possibility range. ing.

The above series of operations are performed for each line.
In addition, the frequency of each class of the luminance frequency distribution data DN for each line is accumulated, and the luminance frequency distribution data of the entire reading range is created and stored in the RAM 105. After the completion of the preliminary scan, the CPU 101 calculates a background setting value BS from the stored data in a manner described later. Density correction unit 103
C performs density correction based on the background setting value BS during the main scan.

In the main scan, the image data D10
Are input to the image processing circuit 103 in the order of pixel arrangement. The image processing circuit 103 performs processing such as MTF correction, density correction, and image distortion correction for improving image quality. Image data D20 that has passed through the image processing circuit 103 is output to the external device. The density correction is data processing for correcting the image data that has been subjected to the luminance / density conversion in accordance with the following equation (1) using the characteristics shown in FIG. 6, and is performed by the density correction unit 103C. D = log ₁₀ (1 / R) (1) Expression D: Density value R: Luminance value Here, the background setting value BS is a threshold value, and when the input data is equal to or less than the background setting value BS, it is replaced with white background data. .

By passing through the density correction section 103C, the photographing data value of the pixel having a density lower than the background setting value BS is replaced with a white background data value. In the density correction unit 103C, the base setting value BS in line units is set to
Provided from the PU 101.

Here, a method of calculating the base setting value BS will be described with reference to FIGS. First, a relative luminance distribution in the sub-scanning direction caused by a change in the height (inclination) of the document is obtained. First, from the luminance frequency distribution data of the entire read range stored in the RAM 105, the data value of the class having the highest frequency (this is the total peak luminance value B)
PA). Since the overall peak luminance value BPA is the luminance value with the highest frequency, it is often widely distributed over the entire document. Therefore, in the luminance frequency distribution data DN at each sub-scanning position, the luminance value in the vicinity thereof has a peak (peak).
Often exist, and the peak luminance value BP of each line
1, and BP2 are often detected.

FIG. 7 shows the peak luminance values BP1 and BP2 at each sub-scanning position and the overall peak luminance value BPA. In the figure, when BP1 or BP2 is not detected, the brightness value is represented as 0. In FIG. 7, the portion a where the luminance is prominently high corresponds to a blank character or the like, and the portion b where the luminance is low at the center in the sub-scanning direction is high at the binding portion of the book document. Corresponds to the region where the height is low. As described above, the total rest peak luminance value B
Near the PA, the peak brightness of each line BP1 or B
It can be seen that P2 exists.

Therefore, the peak luminance value BP at each sub-scanning position
1 and BP2, ± α of the entire peak luminance value BPA is defined as the effective background luminance range, and the one within this range and closer to the all-rest peak luminance value BPA is selected as the luminance change distribution data, so that the document height is determined. It is possible to obtain the relative luminance distribution of the original background in the sub-scanning direction caused by the change in (slope). FIG. 8 shows the luminance distribution data selected as described above.

In FIG. 7, α is desirably set to an amount that can make the luminance change due to a gradual change in the height of the book document an effective range.
For (0-255) gradation, about 20 is preferable. However, since the luminance greatly decreases at the binding portion of the book document, this is dealt with by shifting the effective range to the lower luminance side as shown in FIG.

If neither of the peak luminance values BP1 and BP2 is detected as luminance change distribution data, the sub-scanning position is regarded as abnormal data, and normal data before and after the sub-scanning position are connected by a straight line and complemented. After complementing the abnormal data, a smoothing process is performed, and the result is luminance distribution data in the sub-scanning direction generated by a change in document height (inclination). In FIG. 8, the data after the smoothing process is indicated by a thick line.

Next, the maximum luminance area (sub-scanning position) of the read document is detected. This is performed by detecting the maximum value of the peak luminance value BP1 (the peak on the high luminance side) at each sub-scanning position. As shown in FIG. 8, the sub-scanning position where the maximum value is detected is S, and the peak luminance value BP1 at the sub-scanning position S is the maximum peak luminance value SBP1 (the maximum value of BP1 in FIG. 7 corresponds to this). ). This maximum peak luminance value SBP1 serves as a reference for density correction.

The base setting value BS at each sub-scanning position is calculated as follows. The difference between the maximum peak luminance SBP1 and the luminance distribution data in the sub-scanning direction at the sub-scanning position S is calculated as a shift amount (see FIG. 8), and this shift amount is added to the luminance distribution data in the sub-scanning direction. Then, the base set values associated with these values in advance are set as BS.

FIG. 9 shows the shifted data and the background setting value BS. This makes it possible to correct a luminance change caused by a change in the height (inclination) of the document and to perform a density correction based on the brightest area of the document in which white characters or the like exist. That is, in the case of a color document, the current brightest region, such as an outline character, is reproduced in white, and the background portion of the color document can be reproduced as it is.

The method of obtaining the relative luminance distribution in the sub-scanning direction caused by a change in the height (inclination) of the document is not limited to the method of this embodiment. For example, the height information may be used as it is as the luminance distribution data, and any method may be used as long as the relative luminance distribution in the sub-scanning direction caused by a change in the height (inclination) of the document can be determined. It is possible. In the present embodiment, the reading target is described as a book document, but other target objects (organs, excavated items, etc.) may be used.

FIG. 10 is a flowchart of the reading operation. The book scanner 1 turns on the light source of the lamp unit 40 in response to the start key 52 being turned on, and starts the preliminary scan (# 21 to # 23). During the preliminary scan, the luminance frequency distribution data DN is created for each line, and peak luminance values BP1 and BP2 are detected. The document height is also detected (# 24). When the preliminary scan is completed, the background setting value BS is calculated as described above (# 25, # 2).
6). Subsequently, the main scan is started, and during the main scan, density correction is performed for each line with the base set value BS as a threshold (# 27, # 28). When the main scan is completed, the light source of the lamp unit 40 is turned off and a new start instruction is waited (# 29, # 30).

[0034]

As described above, according to the present invention, the sub-scanning position having the maximum luminance value is detected, and the density correction amount (background removal amount) at each reading position is read with the maximum luminance value. Since the luminance at the position is determined based on the luminance, it is possible to perform density correction appropriate for reading a color original. In addition, if the maximum luminance position and the relative luminance distribution in the sub-scanning direction caused by the change in height or inclination of the object are detected and the density correction amount is calculated in consideration of these, the three-dimensional Optimal density correction can be performed on objects (book documents) and the like.

[Brief description of the drawings]

FIG. 1 is an exemplary perspective view showing the appearance of a book scanner according to an embodiment of the present invention.

FIG. 2 is an exemplary perspective view showing an example of a use state of the book scanner;

3A is a diagram illustrating a state where a book document is set on a document table, and FIG. 3B is a diagram illustrating a read image;

FIG. 4 is a block diagram of a signal processing system in the book scanner.

FIG. 5 is a diagram showing an example of a luminance distribution.

FIG. 6 is an input / output endurance diagram of a density correction unit.

FIG. 7 is a diagram showing an example of a distribution of peak luminance.

FIG. 8 is a view showing an example of a luminance distribution caused by a change in the document height and smoothed data thereof.

FIG. 9 is a diagram showing an example of a distribution of a background luminance and a distribution of a background setting value BS.

FIG. 10 is a flowchart of a reading operation.

[Explanation of symbols]

1: book scanner 30: imaging unit 16: distance measuring plate 31: line sensor BD: book original BP1: luminance value of the peak of the histogram for one line (high luminance side) BP2: luminance value of the peak of the histogram for one line (Low luminance side) BS: Base setting value BPA: Frequency maximum luminance value of histogram of entire reading area S: Sub-scanning position amount at which BP1 becomes maximum value SBP1: Maximum value of BP1

 ────────────────────────────────────────────────── ─── Continued on the front page F term (reference) 5B047 AA01 BB02 CB05 CB09 CB22 CB23 5B057 AA11 CA08 CA12 CB08 CB12 CE11 CH08 DB02 DB09 5C077 LL04 LL19 MM03 PP15 PP25 PP43 PP58 PQ19 SS01

Claims (1)

[Claims] 1. A reading device, comprising: an imaging unit that converts an optical image of an object to be read into an electric signal on a pixel basis, processes a signal from the imaging unit and outputs the image signal as image data. A maximum luminance detecting means for detecting a maximum luminance from the object; a maximum luminance position detecting means for detecting a reading position of the maximum luminance detected by the maximum luminance detecting means; and detecting a luminance distribution generated by a change in height of the object. Luminance distribution detecting means, based on the maximum luminance detected by the maximum luminance detecting means, the maximum luminance position detected by the maximum luminance position detecting means, and the luminance distribution detected by the luminance distribution detecting means. A density correction calculating method for calculating a density correction amount for image data output from the image capturing means for each reading position by the image capturing means; Reading apparatus characterized by comprising and.