JP2000354166A - Image reader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To apply proper density correction to an image in the case that a density difference is in existence on an original face due to a curved face or the presence of a photograph. SOLUTION: A peak luminance value BP is detected on the basis of luminance distribution data DN for each line from a line sensor 31 and a valid underground density allowable to an object is set on the basis thereof. In the case that the peak luminance value BP exceeds this allowable range, a change in a density information quantity is referenced and when the density change is large, it is regarded to be a density increase detected around a joint of a book, a background setting value BS is decided without correcting the detected peak luminance value data to correct the density. Furthermore, when the density change is small, it is regarded to be a high density area such as a photographing area, the peak luminance value data are corrected, the corrected background setting value BS is set to correct the density.

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 reading an image of a subject such as a book original, and more particularly to a technique for performing density correction when there is a density difference in the original surface.

[0002]

2. Description of the Related Art In a conventional image reading apparatus of this type, a plurality of sample images are read in advance, a frequency distribution (luminance histogram) of luminance is obtained, a luminance having a maximum frequency is detected as a peak luminance, and correction is performed. Calculated based on the frequency distribution, and stored these as sample data, and then, when reading an unspecified image, determine the frequency distribution of the luminance to detect the peak luminance. An apparatus that performs image density correction using a threshold value of sample data is known (for example, Japanese Patent Application Laid-Open No. 10-25 / 1998).
No. 7323).

[0003] Further, the type of image (text, photo, etc.) is determined, and the image data is determined based on the background density for a character image and the height information of the original for a halftone image according to the type of image. A device for controlling the density of an original, and determining the shape of the original surface, based on background density when the original surface is flat, and image density control based on height information of the original when the original surface is curved. (See, for example, JP-A-8-237485).

Further, noise levels of both the height information of the original and the luminance distribution of the original obtained by imaging the original surface are detected.
If the values exceed the allowable range, the data is corrected by interpolating the data using the other data, and image distortion or density correction is performed according to the corrected height information of the original or the background luminance. An apparatus for performing this is known (for example, see Japanese Patent Application Laid-Open No. 8-307688).

[0005]

However, in the apparatus disclosed in the first publication, a luminance threshold for density correction is determined from the peak luminance of the luminance histogram in the presence of a photographic area (high density area) or the like. Since the value is determined, if there is a wide-area photograph area (high-density area) in the document, the luminance of the photograph or the like is detected as the peak luminance, so that there is a problem that appropriate density correction cannot be performed. Was. In the apparatus disclosed in the second and third publications, when the detected background density of a document is low, it is determined whether the detected background density is caused by a change in height or a high density area such as a photographic area. Since the determination is not made, the density correction may not be properly performed as described above.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problem and to provide an image reading apparatus capable of performing appropriate density correction even on a document surface having a high density area such as a wide photographic area in the document. And

[0007]

According to a first aspect of the present invention, there is provided an image reading apparatus for reading a subject, comprising: an imaging means for reading the subject; and a density detecting means for detecting a background density of the subject. A height detecting means for detecting the height of the subject; and a corresponding portion of the height information detected by the height detecting means when the background density detected by the density detecting means exceeds an allowable range. Depending on the magnitude of the height change, the density change due to the height change,
Determining means for determining whether the area is a high or low density area in a subject,
When the result of the determination by the determination unit is a high or low density area in the subject, a data correction unit that corrects the background density data of the subject, and an image corresponding to the background density of the subject corrected by the data correction unit. And a density control means for correcting the density.

In the above arrangement, if the background density (peak luminance) of the subject detected by the density detecting means exceeds an allowable range, the determining means refers to the amount of change in the height information detected by the height detecting means. , If the height change is large,
For example, it is regarded as a density increase detected near the binding portion of a book, and the detection data is used as it is. That is, a brightness threshold value for density correction is determined using the detected low brightness peak, and density correction is performed. When the height change amount is small, it is regarded as a high density area such as a photograph area, and data correction is performed. That is, a brightness threshold value for density correction is determined from the corrected data, and density correction is performed.

According to a second aspect of the present invention, there is provided an image reading apparatus for reading a subject, comprising: an imaging unit for reading the subject; a density detecting unit for detecting a background density of the subject; and a detecting unit for detecting the height of the subject. A density control unit for correcting the density of an image according to the background density detected by the density detection unit; and a density control unit configured to correct the density information when the amount of change in the height information detected by the height detection unit is small. Control means for making the correction a fixed amount.

In the above configuration, when the amount of change in height information is small in the entire area of the image reading target, the change in luminance due to the change in height is small, so that density correction for each area (each sub-scanning position) is not performed, and detection is performed. Density correction is performed uniformly over the entire area according to the background density.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments embodying the present invention will be described below with reference to the drawings. FIG. 1 is a perspective view showing the external appearance of the book scanner according to the present embodiment, and FIG. 2 is a diagram showing an example of the use state of the book scanner. The book scanner 1 is a main body housing 1 for housing electric circuits and the like.
0, dark platen 2 where document setting is performed
0, an imaging unit 30 that converts a document image into an electric signal,
And a lamp unit 40 for illuminating the original. The document table 20 is arranged on the front side of the main body housing 10. 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 image pickup unit 30 and is fixed to the 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 size for setting a book document (hereinafter referred to as a book document) BD. . The distance between the document table 20 and the imaging unit 30 is 30 cm or more.

An operation panel OP is provided on the upper end of the front surface of the main body housing 10, and a distance measuring plate 16 (height detecting means) for detecting the height of the document surface is fixed to the lower end. The front surface of the distance measuring plate 16 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 functions as a white plate 18 for shading correction. Body housing 10
A main switch 51 is provided on the right side of the operation panel OP.

A start key 52 is provided on each side of the document table 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.

As shown in FIG. 1, the imaging unit 30 has a line sensor 31 (imaging means) composed of a CCD 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. Imaging lens 32
Is provided so as to be movable in the front-rear direction.
It is positioned by the F mechanism. The line sensor 31 is attached to a movable body of a scanning mechanism (not shown),
While the arrangement direction of the D elements is kept up and down, parallel movement is performed along the left-right direction (sub-scanning direction) M2. By this parallel movement, a two-dimensional document image is captured.

The book scanner 1 having the above-described configuration is an image input means suitable for reading an object such as a book original or a three-dimensional object. By combining the book scanner 1 of the present invention with a digital copying machine, various types of originals can be read. A compatible overall copying system can be constructed.

When using the book scanner 1, the user places the book document BD upward on the document table 20 in an open state as shown in FIG. At this time, the book document BD is pressed against the lower end of the distance measuring plate 16 to perform positioning. That is, the boundary between the distance measuring plate 16 and the platen 20 is the book document BD.
It is the reference line for setting other manuscripts. The center of the reference line is the reference position PO (see FIG. 3A). The document table 20 is configured to be vertically movable independently of left and right. Thereby, the heights of the left and right pages when the pages are opened can be made substantially the same.

When reading a book document BD by the book scanner 1, a book mode is selected by a mode select switch (not shown). In the selected book mode, 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. For this reason, the curved state, the luminance frequency distribution under various conditions, and the like are detected in the first scan (hereinafter, referred to as a preliminary scan), and necessary in the second scan (hereinafter, referred to as a main scan) based on the detection results. Processing is performed. Image output to an external device (not shown) is performed during the main scan.

FIG. 3 is a plan view showing an example of reading the book document BD. The book document BD is set in a state where the book document BD is set on the document table 20 as shown in FIG. And the read image G0 after scanning
Is a book original B as shown in FIG.
D, an image G1 of the reading target surface, an image G20 of the document table 20,
And an image G18 reflected on the distance measuring plate 16.

The image G18 is a book document B in an opened state.
The image G is composed of images G181 and G182 showing the shape of the end face (a part called “heaven” in the book) in D and a background image G183 shown on the distance measuring plate 16. Image G18
Since the boundary between the image 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 (the number of pixels) between the boundary and the outline of the images G181 and G182. 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 is a block diagram of a main part of the signal processing system 100, FIG. 5 is a diagram showing an example of a luminance frequency distribution, and FIG. 6 is a diagram showing input characteristics of the density correction section 103C. Signal processing system 1
00 is a CPU that detects a peak luminance BP from the luminance frequency distribution data DN transmitted from the luminance detecting unit 104 described later.
101, an A / D converter 102 for converting a photoelectric conversion signal output from the line sensor 31 into an 8-bit signal,
An image processing circuit 103 that receives the converted 8-bit signal from the converter 102 and performs processing for improving image quality, receives the converted 8-bit signal from the A / D converter 102, and generates luminance frequency distribution data DN. Brightness detector 104, CPU
RAM 1 for storing peak luminance BP calculated in 101
The nonvolatile memory 106 stores the peak luminance BP calculated by the CPU 101 and the background setting value BS.

In the signal processing system 100 having the above configuration, the photoelectric conversion signal output from the line sensor 31 during the pre-scanning operation is output to the
Bit image data (luminance data) D10,
The pixels are input to the luminance detecting unit 104 in the order of pixel arrangement scanned from top to bottom along the arrangement direction of the CCD elements. The luminance detection unit 104 includes a comparator and a counter, and counts the imaging data D10 for one line for each gradation of value to generate luminance frequency distribution data DN of a read image. Here, in the case of a typical book original BD and a book mainly composed of characters, the luminance frequency distribution has local maximum values in the character range and the background range as shown in FIG.

The CPU 101 fetches the luminance frequency distribution data DN, detects the data value of the gradation having the highest frequency as the peak luminance value BP, and stores the data value in the table T1 in the memory 106.
And calculate the ground setting value BS in the manner described below to calculate RA
It is stored in M105. This series of operations is performed for each line. Further, the frequency of each gradation 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. After the completion of the preliminary scan, the CPU 101 calculates a background setting value BS from the stored data and the above-described height data in a manner described later. Density correction unit 10
3C performs the density correction of the background density based on the background setting value BS during the main scan.

At the time of the main scan operation, the imaging data D10
Are input to the image processing circuit 103 (CPU) in the order of pixel arrangement. The image processing circuit 103 is a correction process that enhances a high-frequency component in the image signal after photoelectric conversion obtained from the line sensor 31 to enhance the contour to improve image quality.
Processing such as F correction (sharpening processing), density correction, and image distortion correction is performed. The image processing circuit 103 includes an external device (not shown).
Is output.

The density correction is a data processing for correcting the image data, which has been subjected to the brightness / density conversion in accordance with the following equation (1), as shown by the solid line in FIG. Accordingly, the imaging data value of a pixel having a density lower than the background setting value BS is replaced with a white background data value. The density correction unit 103 is provided with a base setting value BS in line units from the CPU 101 in accordance with the progress of sub-scanning.

D = log ₁₀ (1 / R) (1) D: density value R: luminance value

Here, a method of calculating the base setting value BS will be described. FIG. 7 is a diagram showing height data of a book document. In the book document BD, the binding portion becomes a valley, and the height gradient of the document becomes steep near the valley. In other words, the scanning surface of the line sensor 31 forms a large angle with respect to the reflected light perpendicular to the document surface, and the height changes gently in other portions, and is parallel to the scanning surface of the line sensor 31,
Or at a small angle. Lamp unit 40
Is reflected on the original surface and is reflected by the line sensor 31.
At this time, the light receiving amount is smaller near the binding portion where the angle difference between the document surface and the scanning surface of the line sensor 31 is large than in other portions. FIG. 8 is a diagram showing a distribution of peak luminance values BP when a book document mainly composed of characters is read. As described above, near the binding part (= steep height change)
, It can be seen that the peak luminance value is greatly reduced.

FIG. 9 shows a distribution of a book document including a high-density (low-brightness) region such as a photographic region in the document. That is, there is a portion where the peak luminance value is greatly reduced other than the binding portion, and the height data of the portion (see FIG. 7)
Since the height change is small, it can be inferred that this is not a luminance decrease depending on the book shape, that is, a high density (low luminance) area in the document. By utilizing the amount of change in height data and the peak luminance value in this manner, it is possible to perform optimal density correction for reading a book document.

Specifically, first, as shown in FIG. 10, from the luminance frequency distribution data of the entire reading range, the data value of the class having the highest frequency is detected as the overall peak luminance value. ± α is the effective background luminance range. α is desirably an amount capable of setting a luminance change due to a gentle height change of the book document as an effective range. For example, if the luminance frequency distribution data DN has 8 bits and 256 gradations, α is preferably about 20.

Data of the peak luminance value exceeding the effective background luminance range refers to the height data corresponding to the position. If the amount of change in the height is large, the luminance is decreased by the binding portion. Normal. If the height change amount is small, it is determined as a high-density (low-brightness) area in the document, and is determined as abnormal data.

The abnormal data is interpolated by connecting the preceding and succeeding normal data with a straight line (FIG. 11), and after the interpolation of the abnormal data, the peak luminance value is smoothed (FIG. 12). Then, a background setting value BS for luminance change correction associated in advance with the smoothed peak luminance value is obtained (FIG. 13). Note that the interpolation of abnormal data is not limited to the method according to the present embodiment. For example, a method as disclosed in JP-A-8-307688 may be used.

In a document having a small height change, the density change depending on the shape of the document is very small. Therefore, in that case, the peak luminance value BP at each sub-scanning position is replaced with the entire peak luminance value. By doing so, natural density correction not affected by the original image can be performed.

FIG. 14 is a flowchart of the reading operation. In response to the start key 52 being turned on (# 21), the book scanner 1 turns on the light source of the lamp unit 40 (# 22) and starts the preliminary scan (# 23). During the preliminary scan, the luminance frequency distribution data DN is created for each line to detect the peak luminance BP, and also detect the document height (# 24). When the preliminary scan is completed (# 2
5) As described above, the background setting value BS is calculated (# 2)
6). Subsequently, the main scan is started (# 27), and during the main scan, the density correction is performed for each line using the background setting value BS as a threshold (# 28). When the main scan is completed (# 2
9) Turn off the light source of the lamp unit 40 (# 30),
Wait for a new start instruction.

As is apparent from the above description, in the present embodiment, the CPU 101 determines whether the lowering of the background density is caused by a change in height based on the signals detected by the density detecting means and the height detecting means. And a data correction unit.

Further, the present invention is not limited to the configuration of the above-described embodiment, and various modifications are possible. For example, in addition to a book original as an object, image reading of various three-dimensional objects, specifically, parts for automobiles, etc. It can be applied to shape / dimension inspection such as presence or absence of burrs, and foreign matter / flaw inspection of wafers and machine parts.

[0036]

As described above, according to the first aspect of the present invention, when the background density (peak luminance) of the subject detected by the density detecting means exceeds the allowable range, the discriminating means uses the height detecting means. Referring to the detected height information change amount,
Since the density correction is performed according to the magnitude of the height change amount, optimal density correction can be performed even when the subject is a book document or the like and a high density region such as a photographic region exists in the document surface. .

According to the second aspect of the present invention, when the amount of change in the height information from the detected height data is small in the entire area of the image to be read, the luminance change due to the height change is small. Density correction is not performed, and the entire area is uniformly corrected for density in accordance with the detected background density, thereby enabling optimum density correction.

[Brief description of the drawings]

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

FIG. 2 is a diagram illustrating an example of a use state of the book scanner.

3A is an example of reading a book document, and FIG. 3A is a plan view showing a state where the book document is set on a platen;
FIG. 3B is a diagram illustrating a read image.

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

FIG. 5 is a diagram illustrating an example of a luminance frequency distribution.

FIG. 6 is a diagram illustrating input / output characteristics of a density correction unit.

FIG. 7 is a diagram illustrating an example of height data.

FIG. 8 is a diagram illustrating an example of a distribution of a peak luminance value BP.

FIG. 9 is a diagram illustrating an example of a distribution of a peak luminance value BP.

FIG. 10 is a diagram showing a valid data range.

FIG. 11 is a diagram showing a distribution of peak luminance values BP after data interpolation.

FIG. 12 is a diagram showing a distribution of a peak luminance value BP after smoothing.

FIG. 13 is a diagram showing a distribution of a base setting value BS.

FIG. 14 is a diagram illustrating a flowchart of a reading operation.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Book scanner 16 Distance measuring board (height detection means) 18 White plate 20 Original table 30 Imaging unit 31 Line sensor (Imaging means) 101 CPU (Density detection means, discrimination means, data correction means) 103C Density correction part (Density control) Means) 104 brightness detection unit BD book manuscript

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5B057 AA11 BA02 BA11 BA19 BA30 CA08 CA12 CA16 CB08 CB12 CB16 CC03 CE11 DA06 DC22 DC36 5C077 LL04 MM20 NN03 NP01 PP15 PP42 PP43 PP44 PP52 RR14 TT06 TT10

Claims (2)

[Claims] 1. An image reading apparatus for reading a subject, comprising: imaging means for reading the subject; density detecting means for detecting the background density of the subject; height detecting means for detecting the height of the subject; If the detected background density exceeds the allowable range, the density change due to the height change or the change in the subject according to the magnitude of the height change of the corresponding portion of the height information detected by the height detecting means is detected. Discriminating means for discriminating a high or low density area of the object, and when the result of the discrimination by the discriminating means is a high or low density area in the subject, data correcting means for correcting background density data of the subject; An image reading apparatus, comprising: density control means for correcting the density of an image according to the background density of a subject corrected by data correction means. 2. An image reading apparatus for reading a subject, comprising: an imaging unit for reading the subject; a density detecting unit for detecting a background density of the subject; a detecting unit for detecting the height of the subject; Density control means for correcting the density of the image according to the background density; and control means for setting the density correction by the density control means to a constant amount when the amount of change in the height information detected by the height detection means is small. An image reading device, comprising: