JPH0678146A - Image input device - Google Patents

Abstract

(57) [Abstract] [Purpose] To realize highly accurate shading correction at low cost. According to this device, a standard white plate 102 for shading correction, a first standard white plate 102 having a relatively short length that reproduces a predetermined reflectance with high accuracy, and an image sensor 1 are provided.
The first standard white plate 103 having a sufficient length having a uniform reflectance in the image forming area 01. The first and second standard white boards 101, 102 are read at the same predetermined amplification factor α ₁ , and the output value W ₂ of the second standard white board 102 is corrected according to the output ratio W ₁ / W ₂ of both. Shading data as white level reference data is obtained, or the amplification factor α is set again according to the output ratio W ₁ / W ₂ of the both, and the second standard white board 102 is read again with the amplification factor α. To get the shading data.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image input device such as a digital copying machine, a facsimile or an image scanner, and more particularly to generation of reference white level data for shading correction.

[0002]

2. Description of the Related Art A reading technique of a conventional image input device will be described by taking a reader unit of a digital copying machine or a general-purpose image scanner as an example. The basic principle is common to other image input devices such as facsimiles.

FIG. 1 shows an example of the configuration of a conventional image input device. In this example, a one-dimensional CCD line sensor is used as an image sensor. 1A is a side view of the image input device, and FIG. 1B is a bottom view of the same device.

In the figure, reference numeral 200 is a body of the image input apparatus. Image original 202 placed on original platen glass 204
Is fixedly installed by a pressure plate 201 and is illuminated by a document illumination lamp 205. The light reflected from the image original 202 is reflected by the image forming lens 206 to the CCD line sensor 2.
It is imaged on 07. In order to determine the white level reference before reading the image original 202, the standard white plate 203 is read using the optical components of the original illumination lamp 205, the imaging lens 206, and the CCD line sensor 207, and the read data is the image processing unit 208. Is temporarily stored in a shading data storage unit (not shown).

After reading the white level data in this way, the optical components 205 to 207 scan the original image in the direction of the arrow in the figure to read the image data. This image data is subjected to shading correction by referring to the above white level data.

Usually, shading correction follows the following equation (1).

[0007]

[Equation 1]

Here, S _i is image data, S _w is white level data, S _k is black level data, and N is a normalization constant. Further, S is image data after shading correction.

[0009]

In the conventional sampling of the white level data for the shading correction, the white level data shown in FIG.
Like the standard white plate 203 shown in (B), the white level data was read using a standard white plate having a length that covers all the pixels of the photoelectric conversion element (one line of the CCD line sensor). Usually, it is made by applying a pigment on a metal substrate, and the entire surface of the size of the standard white plate as described above (usually a length of 210 mm which corresponds to the short side of A4 size) is predetermined reflection. It was extremely difficult to make it uniformly at a high rate (high brightness of about 90%). Further, the production of the standard white board under such severe conditions lowers the yield and raises the cost.

On the other hand, a color chart in which a pigment is applied to a paper as a substrate as a relatively inexpensive standard white plate is conceivable, but the reproducibility and uniformity of reflectance are relatively good, but the light resistance is poor and the standard. It cannot be used as a white plate due to a problem of fading.

Further, although a white plate made of ceramics or the like is excellent in reproducibility of reflectance, uniformity, and fading property, it is practically difficult to use this reference white plate because it is very expensive.

In view of the above points, it is an object of the present invention to provide an image input device which is inexpensive and can realize highly accurate shading correction.

[0013]

To achieve the above object, a first aspect of the present invention is to form an image by forming an image of reflected light or transmitted light from a document image on an image sensor and scanning the document image. In an image input device for obtaining a read signal, a first standard white plate having a relatively short length that reproduces a predetermined reflectance with high precision, and shading having a uniform reflectance within the image forming area of the image sensor. A second standard white plate having a length sufficient for correction, an amplifier circuit for amplifying a read signal of the second standard white plate, a read signal of the first standard white plate and the second standard white plate The read signal of the second standard white board 2 is amplified by the determined amplification factor of the amplification circuit from the read signal and the read data thus obtained is converted into a white image for shading correction. Characterized by comprising a control means for a bell reference data.

In one aspect of the present invention, preferably, the determined amplification factor of the amplifier circuit is a read signal of the second standard white plate read by a photoelectric conversion element of the same pixel forming the image sensor. The first amplified signal is read by the photoelectric conversion element of the same pixel.
The amplification factor is determined so as to be equal to the read signal of the standard white board.

As another aspect of the present invention, the determined amplification factor of the amplifier circuit is an average value of read signals of the second standard white board read by the image sensor, and the average value is read by the image sensor. The amplification factor is determined so as to be equal to the average value of the read signals of the first standard white plate.

Furthermore, as another aspect of the present invention, as for the determined amplification factor of the amplifier circuit, the maximum value of the read signal of the second standard white plate read by the image sensor is read by the image sensor. It can be characterized in that the amplification factor is determined so as to be equal to the maximum value of the read signal of the obtained first standard white plate.

In order to achieve the above object, the second aspect of the present invention forms an image reading signal by forming an image of reflected light or transmitted light from a document image on an image sensor and scanning the document image. In the image input device, the first reflector having a relatively short length that reproduces the predetermined reflectance with high accuracy.
Standard white plate, a second standard white plate having a uniform reflectance in the image forming area of the image sensor and having a sufficient length for shading correction, and an average value of read signals of the first standard white plate. A control means for multiplying the ratio of the read signal of the second standard circuit to the average value of the read signal of the second standard circuit to the read signal of the second standard white board and using the value thus obtained as white level reference data for shading correction. It is characterized by having.

Further, the present invention is preferably characterized in that the portion of the first standard white plate and the portion of the second standard white plate are integrally formed as one standard white plate.

[0019]

According to the present invention, the first standard white plate, which is a minute white plate piece that reproduces the predetermined reflectance with high accuracy, and the reflectance lower than that of the first standard white plate, The standard white plate is composed of two second standard white plates of a normal size which are excellent in uniformity, and the white level for shading correction is obtained from the read signals of the first standard white plate and the second standard white plate. Create the data. As a result, inexpensive and highly accurate shading correction can be realized.

[0020]

Embodiments of the present invention will now be described in detail with reference to the drawings.

(First Embodiment) FIG. 2 shows the arrangement of standard white plates for reading shading correction data in the image input apparatus of the first embodiment of the present invention, which is shown in FIG. It is a figure which looked up at the image input device from below. In the figure, 100 is the body of the image input device, 101 is a CCD line sensor, and this sensor is located at the home position in this figure. Reference numeral 102 denotes a first standard white plate, the material of which is made of a material having relatively excellent light resistance and weather resistance such as ceramics, and its reflectance is a predetermined reference white (for example, a reflectance of 90%. The high reflectance of 1) is reproduced with high accuracy within an error, for example, within several percent. However, as described above, since this white plate is extremely expensive in a large area, in this embodiment, it is made up of minute slices (for example, a few millimeters square) in order to sample several pixels of the CCD line sensor 101, and the cost can be reduced. I am trying.

Reference numeral 103 denotes a second standard white plate, and the material thereof is made of a material having relatively excellent light resistance and weather resistance such as ceramics like the first standard white plate 102.
The second standard white plate 103 only needs to have a constant reflectance over the entire white plate, and has a wide allowable range with respect to variations in the absolute value of the reflectance. In this sense, the second standard white board 1
No. 03 eliminates the need to apply white pigment by selecting the material, eliminates uneven coating (unevenness of reflectance) that occurs when applying white pigment, and realizes highly accurate uniformity, and the allowable range of absolute reflectance. By increasing the size of the white plate, the white board can be easily manufactured.
Although it is a large white board having the length of the line sensor 101, it is inexpensive.

With the above arrangement of the CCD line sensor 101, the first standard white plate 102, and the second standard white plate 103, the shading data fetching operation when reading the image original 104 will be described below.

When the shading data fetching operation is started, the CCD line sensor 101 arranged at the home position scans to read the first standard white board 102. FIG. 3 is a circuit diagram showing the flow of signals up to creation of shading data according to the first embodiment of the present invention. As shown in FIG. 3, the read signal of the first standard white plate 102 read by the CCD line sensor 101 is analog-amplified by the amplifier circuit 302, and the amplified analog signal is sample-held by the sample-hold circuit 303. After that, it is converted into a digital signal by an A / D (analog / digital) conversion circuit 304. This digital signal (read data) is stored in a memory (a random access memory) that stores shading data, particularly a memory 306 called a shading RAM, via a shading correction circuit 305.

As described above, the reading operation of the first standard white board 102 is completed, and then the reading of the second standard white board 103 is started. Actually, the CCD line sensor 101 scans as shown by an arrow in FIG. 2, and the second standard white plate 103 is continuously read from the first standard white plate 102. The second standard white board 103 is read in the same manner as the reading of the first standard white board 102, but the amplification factor of the amplifier circuit 302 uses the same value as that determined by the first standard white board 102, and the sample hold circuit 303. The read data is stored in the shading RAM 306 via the A / D conversion circuit 304 and the shading correction circuit 305.

Next, a CPU (Central Processing Unit) 307
The read data of the first standard white board 102 and the read data of the second standard white board 103 are respectively input from the shading RAM 306, and the second standard white board 103 is read.
The gain value (amplification factor) such that the read data of 1 becomes equal to the read data of the first standard white board 103 is obtained as follows.

For example, assume that the value of the read signal of the first standard white plate 102 is W ₁ and the amplification factor at that time is α ₁ . In addition, the gain α ₁ remains unchanged and the second standard white board 1
The value of the read signal when reading 03 is W ₂ .
The first and second standard white plates 102, 10 are added to the current amplification factor α ₁ .
Amplification factor W ₁ / W _{2 obtained} by multiplying the output ratio W ₁ / W ₂ of ₃
* Α ₁ is set again in the amplifier circuit 302 and the second standard white board 103 is read again, whereby the first standard white board 101 is read.
The shading data that gives the same output value as the output value (shading data) of is obtained.

In practice, the amplification factor α ₁ is the A / D conversion circuit 3
08 digitize and read by CPU307, CPU
Α = W ₁ / W ₂ * α ₁ is calculated in 307, and the calculated value is analogized by the D / A (digital / analog) conversion circuit 308, and the amplification factor α = W ₁ / W ₂ * α ₁ is amplified. Circuit 30
The value is set to 2 again, and the shading data is read again by the second standard white board 103.

When the reading of the shading data is completed and the original image is read, the amplifier circuit 302 is read again.
Is set to the first amplification factor α ₁ and image reading is performed.

FIG. 4 is a flow chart of the processing procedure of the above-described first embodiment of the present invention.

(Second Embodiment) In the first embodiment of the present invention described above, the second standard white plate 102 is read after the reading of the first standard white plate 102 and is amplified again according to the respective output ratios. The ratio α is calculated, the amplification factor is set in the amplification circuit 302, the shading data is read by the second standard white board 103, and the amplification factor of the amplification circuit 302 is changed to α after the reading of the shading data is completed.
I returned to ₁ and scanned the original image. On the other hand, in the second embodiment of the present invention, FIG.
As shown in. That is, in this example, as shown in FIG. 5, assuming that the value obtained by reading the entire second standard white plate 103 at the amplification factor α ₁ is W _i (i represents all pixels of the CCD sensor), the first standard white plate 103 The ratio ω = W ₁ / W ₂ of the read signal W ₁ read by 102 and the read signal W ₂ read by the second standard white plate 103 in the shading RAM 306.
The value of W = ω * W _i obtained by multiplying _i by the CPU 307 is newly set as shading data, and this is rewritten in the shading RAM 306. As a result, the second standard white board 103 only needs to be read once, and the same effects as those of the first embodiment can be obtained.

FIG. 6 is a flow chart of the processing procedure of the second embodiment of the present invention described above.

(Third Embodiment) In the above-described first and second embodiments of the present invention, as shown in FIG. 2, the first standard white board and the second standard white board are different from each other. Although the configuration is composed of a single white plate, it may be configured as shown in FIG. FIG. 7 shows a third embodiment of the present invention. As shown in FIG. 7, a first standard white plate portion 502 is formed by partially coating a pigment or the like on a second standard white plate 503. Thus, the same effect as in the first and second embodiments can be obtained also by integrating the standard white plate 501.

At this time, the amplification factor α of the amplifier circuit 302 of FIG.
Is determined by the first standard whiteboard portion 502. Figure 8
Represents the read output of the CCD line sensor 101 of the first standard white plate portion 502 and the second standard white plate portion 503. That is, as shown in FIG. 8B, the output data for each pixel read by the shading RAM 306 with the amplification factor α is the first standard white plate portion 502 (average value S
₁ ) and the second standard white plate portion 503 (average value S ₂ ). The CPU 307 fetches this output data from the shading RAM 306 and outputs the average value S ₁ and the average value S _2.
And the respective output ratio β = S ₁ based on S ₁ and S ₂
By multiplying / S ₂ by the read signal of the second standard white board portion 503, shading data at the time of reading the first standard white board portion 502 is obtained over the entire area as shown in FIG. 8C.

[0035]

As described above, according to the present invention,
The first standard white plate, which is a relatively small piece that accurately reproduces the predetermined reflectance of the standard white plate for shading correction, and has a sufficient length that has a uniform reflectance within the image sensor reading area. Since it is composed of the second standard white plate, it is possible to solve the technical difficulty of producing a highly accurate uniform reflecting surface on the entire surface of the standard white plate having a large area, and it is possible to obtain the effects of increasing the manufacturing yield rate and reducing the manufacturing cost. . Further, according to the present invention, since it is possible to easily create a highly accurate standard white board, the accuracy of the image reading signal is also improved, and higher quality image reading can be realized at low cost.

[Brief description of drawings]

FIG. 1 is a vertical sectional view (A) showing an internal configuration of a conventional image input device and a plan view (B) seen from below.

FIG. 2 is a plan view showing an arrangement configuration of first and second standard white plates and a CCD line sensor below a document table surface in the image input apparatus according to the first embodiment of the present invention.

FIG. 3 is a block diagram showing a circuit configuration of an image read signal processing system in the image input apparatus according to the first embodiment of the present invention.

FIG. 4 is a flowchart showing a processing procedure of the first embodiment of the present invention.

FIG. 5 is an explanatory diagram showing a relationship between respective standard whiteboards and shading data ranges according to the second embodiment of the present invention.

FIG. 6 is a flowchart showing a processing procedure of a second embodiment of the present invention.

FIG. 7 is a plan view (A) showing an arrangement configuration of a standard white plate and a CCD line sensor under a document table surface in an image input apparatus of a third embodiment of the present invention and an enlarged view (B) of the standard white plate.

FIG. 8 is a graph showing an output value (B) when the standard white board (A) of the third embodiment of the present invention is read and shading data (C) after correction.

[Explanation of symbols]

 101 CCD line sensor 102 First standard white board 103 Second standard white board 104 Original document 302 Amplifying circuit 303 Sample hold circuit 304 A / D conversion circuit 305 Shading correction circuit 306 Shading RAM 307 CPU 308 A / D / D / A conversion circuit 502 First standard white plate part 503 Second standard white plate part

Claims (6)

[Claims] 1. An image input device which obtains an image reading signal by forming an image of reflected light or transmitted light from an original image on an image sensor and scanning the original image with a highly accurate predetermined reflectance. A first standard white plate having a relatively short length, which has a relatively short length, and a second standard white plate having a sufficient reflectance for shading correction, which has a uniform reflectance in the image forming area of the image sensor; An amplification circuit for amplifying the read signal of the second standard white board; and an amplification factor of the amplification circuit determined from the read signal of the first standard white board and the read signal of the second standard white board. And a control unit that amplifies the read signal of the second standard white board 2 with an amplification factor and uses the read data obtained thereby as white level reference data for shading correction. Image input device. 2. The determined amplification factor of the amplifier circuit is
A signal obtained by amplifying the read signal of the second standard white plate read by the photoelectric conversion element of the same pixel that constitutes the image sensor and a read signal of the first standard white plate read by the photoelectric conversion element of the same pixel The image input device according to claim 1, wherein the amplification factors are determined to be equal to each other. 3. The determined amplification factor of the amplifier circuit is
The amplification factor is determined so that the average value of the read signals of the second standard white plate read by the image sensor is equal to the average value of the read signals of the first standard white plate read by the image sensor. The image input device according to claim 1, wherein the image input device is provided. 4. The determined amplification factor of the amplifier circuit is
The amplification factor is determined so that the maximum value of the read signal of the second standard white plate read by the image sensor is equal to the maximum value of the read signal of the first standard white plate read by the image sensor. The image input device according to claim 1, wherein: 5. An image input device which obtains an image reading signal by forming an image of reflected light or transmitted light from an original image on an image sensor and scanning the original image to obtain a predetermined reflectance with high accuracy. A first standard white plate having a relatively short length, which has a relatively short length, and a second standard white plate having a sufficient reflectance for shading correction, which has a uniform reflectance in the image forming area of the image sensor; The average value of the read signals of the standard white board of No. 1 and the second
Control means for multiplying the read signal of the second standard white board by the ratio to the average value of the read signal of the standard circuit, and using the value thus obtained as white level reference data for shading correction. An image input device characterized by. 6. The first standard white plate portion and the second standard white plate portion are integrally formed as a single standard white plate as claimed in claim 1. Image input device.