JPH04364668A - Scanner - Google Patents

Abstract

PURPOSE:To keep uniform resolution over the entire face of a picture without use of an expensive lens and to allow the scanner to cope with a secular change or dispersion between products. CONSTITUTION:A picture of an original is formed to a CCD 20 via a lens and converted into an electric signal, amplified by an amplifier 21 and converted into a digital data by an A/D converter 22 and the MTF is corrected for the lens by using a digital spatial filter 23. The MTF of the lens is corrected by varying the arithmetic operation constant of the digital spatial filter 23 according to the MTF of the lens with a center and a surrounding in the main scanning direction.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a scanner device, in particular, to convert image data into electrical signals while scanning the image surface of a document.
The present invention relates to a scanner device that converts this data into digital data and reads it.

0002

2. Description of the Related Art Conventional scanner devices include document reading devices such as facsimiles and digital copiers, and image scanner devices that are connected to a personal computer or the like to input image data of a document. An example of such a conventional scanner device is an image scanner 1 as shown in FIGS. 5(a) and 5(b). As shown in FIG. 5(a), this image scanner 1 has an automatic paper feeder (
Documents are taken into the device one by one using the ADF (ADF) 2, and images of the documents are read. The read document is discharged onto the paper discharge plate 3. The inside of image scanner 1 is shown in Figure 5.
As shown in (b), a fluorescent lamp 4 serving as a light source, mirrors 5, 6, 7, a lens 8, a photoelectric conversion unit 9, and the like are housed. The document conveyance path for conveying the document on the document table 10 includes a separation roller 11, conveyance rollers 12, 13,
It includes a document holding plate 14, discharge rollers 15, 16, and the like. The image scanner 1 transports a document set on a document table 10 by transport rollers 12 and 13 to a reading position where a document pressing plate 14 is provided, and transfers the document read at this reading position to ejection rollers 15 and 16. Paper discharge plate 3
Drain to the top.

The document conveyed to this reading position is illuminated by light from a fluorescent lamp 4, and the light reflected by the document is reflected by a mirror 5.
6 , 7 and a lens 8 into the photoelectric conversion section 9 . The photoelectric conversion unit 9 photoelectrically converts the incident light and outputs it as an image signal. In addition, the fluorescent lamp 4 and the mirrors 5, 6,
Reference numeral 7 is mounted on a traveling body (not shown), and reads and scans the original by sliding in the depth direction of the figure. Further, a document table 17 made of a transparent member such as glass is provided below the document table 10, and a book type document can be set on the document table 17. The original set on the original platen 17 is pressed onto the original platen 17 by the original platen 10, and the image of the original on the original platen 17 is read by moving the traveling body in the scanning direction.

Further, such a scanner device converts an analog image signal (analog image signal) read by an analog scanner such as an image sensor into a digital image signal (analog image signal).
It is quantized into a digital image signal), binarized, and read. For example, in a facsimile scanner device,
Since fine images such as characters are transmitted electronically, resolution characteristics are important. Regarding this resolution characteristic, in recent years MTF (Modulation), which discusses the entire spatial frequency domain, has been
The concept of transfer function has been introduced and is becoming popular as an example of objective evaluation of optical instruments in particular. That is, in order to improve the resolution of an image, conventional MTF correction configures a spatial filter based on multivalued data obtained by reading a document, and uses this to correct the resolution.

[0005] As the above-mentioned prior art, there is
No. 269183, JP-A-2-183382, JP-A-2
-190980 and those described in JP-A-3-1758.

[0006]

[Problems to be Solved by the Invention] As mentioned above, in a scanner device of the type that uses a lens, which is a reduction optical system, to form an image of reflected light from a document on a photoelectric conversion unit such as a CCD, converts it into an electrical signal, and reads it, Due to the optical MTF of the lens
will be lost to some extent. For this reason, conventionally, in order to prevent the basic resolution (the linear density on the document surface that is responsible for the sensor pitch) from becoming impossible to obtain, so-called electrical MT
F correction has been put into practical use. However, in the past, corrections were applied uniquely regardless of the part of the document, so
There were problems in that the resolution deteriorated closer to the left and right peripheries of the main scan, and it was also vulnerable to changes over time. This is because, as shown in Figures 6(a) and (b), the MTF of the lens is generally lower at the periphery than at the center due to aberrations, etc., and to improve this, it is expensive. This required the use of a different lens, which increased costs.

The present invention has been made in view of the above-mentioned conventional problems, and it is possible to maintain uniform resolution over the entire image without using expensive lenses, and also to prevent changes over time and variations between products. The purpose of the present invention is to provide a high-resolution scanner device that can handle various types of problems.

[0008]

[Means for solving the problem] The invention according to claim 1 includes:
An imaging device that forms an image of a document through a lens and converts it into an image signal, an A/D conversion device that converts the image signal into digital data, and corrects the resolution using the digital data. In a scanner device equipped with a digital spatial filter, when correcting the resolution by the digital spatial filter, the correction system of the digital spatial filter is changed between the center and peripheral areas of the main scan according to the resolution characteristics of the lens, and the image data is It is characterized by correcting.

According to a second aspect of the invention, in the scanner device according to the first aspect, a resolution characteristic detecting means for detecting the resolution characteristic over the entire main scanning area of the lens is provided in the device, and the resolution characteristic detecting means detects the resolution characteristic over the entire main scanning area of the lens. The correction system of the digital spatial filter is changed based on the resolution characteristics of the lens. According to a third aspect of the present invention, in the scanner device according to the first or second aspect, only the correction intensity in the main scanning direction is switched by the variable correction system.

0010

[Operation] According to the invention described in claim 1, when performing MTF correction using a digital spatial filter, the MTF of the lens is
In general, the quality is better at the center of the main scan, and it gets worse toward the periphery. Therefore, MTF correction is performed by changing the correction system of the digital spatial filter (hereinafter also referred to as a calculation constant, since spatial filter processing is performed by calculation in this specification) according to the MTF of this lens. This makes it possible to obtain uniform high resolution over the entire image.

According to the second aspect of the invention, the MTF of the lens actually provided in the apparatus is detected by the resolution detection means, and the calculation constant of the digital spatial filter is changed based on this lens MTF to correct the MTF. will be held. Therefore, even if the MTF changes due to variations in assembly or adjustment between products or changes over time, MTF correction is performed by always selecting appropriate calculation constants. This ensures stable product quality and high reliability.

According to the third aspect of the invention, the calculation constants of the digital spatial filter are switched only in the main scanning direction, and the sub-scanning direction, which is scanning perpendicular to the main scanning direction, is not affected. The constants are switched as follows. Therefore, since only the main scanning direction necessary for MTF correction of the lens is corrected, appropriate MTF correction is performed and a natural read image is obtained.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be explained below based on the drawings. FIG. 1 is a block diagram of a scanner device according to an embodiment of the invention. The external appearance and cross-sectional configuration of the scanner device itself are the same as those shown in FIGS. 5(a) and 5(b), so description thereof will be omitted.

As shown in FIG. 1, C
The original image formed on the light-receiving surface of the CD 20 is converted into an electrical analog image signal, amplified by an amplifier 21, and then digital data converted by an A/D converter 22 is converted into a digital signal via each buffer memory. It is input to the spatial filter 23. This digital spatial filter 23 has MTF
The correction intensity can be changed depending on the part of the image by changing the calculation constant of the matrix. Here, as shown in the calculation constant setting circuit 24, several types of calculation constants are set in advance so that they can be selected, and an instruction for switching the MTF correction strength according to the output value of the counter 26 is a constant switching instruction. The calculation is performed from the circuit 25 to the calculation constant setting circuit 24. The digital spatial filter 23 performs calculations according to the calculation constants from the calculation constant setting circuit 24, thereby making it possible to switch the correction strength depending on the location in the main scanning direction.

For example, as shown in FIG. 2, the MTF of a general lens is good at the center of the main scanning position, as indicated by the broken line in the figure, but becomes worse toward the left and right peripheries. Therefore, M due to the digital spatial filter 23
The switching of the correction strength of TF is as shown by the solid line in Fig. 2.
The peripheral areas are strongly corrected, and the center area is weakly corrected. As a result, MT by the digital spatial filter 23
Since the F correction is performed to cancel the resolution characteristics of the lens, it is possible to obtain a uniform and high-resolution image over the entire main scanning area. Therefore, sufficient resolution can be obtained without using an expensive lens with little aberration in the periphery of the lens, and the cost of the apparatus can be reduced.

FIG. 3 is a block diagram of a scanner device according to an embodiment of the invention. The MTF envelope detection circuit 27 shown in FIG. 3 is a resolution characteristic detection means that detects the MTF of the actually attached lens over the entire main scanning area. Here, as shown in FIG. 5(b), the Cable is placed in a place that does not interfere with the reading area for reading a sheet or book type original, for example, a part of the original platen 17.
A resolution chart of white/black stripes corresponding to the basic linear density of CD20 is attached over the entire main scanning area.

First, a traveling body for reading is moved to the position of the resolution chart, and the MTF over the entire main scanning area is measured. Next, the envelope data, which is the measurement result of the MTF, is stored in the one-line buffer 28 shown in FIG. If this operation is performed as part of the initialization operation when the scanner device is powered on, it is possible to always obtain appropriate resolution characteristics for each product.

The above operation may be performed at the start of each reading, or may be performed at intervals of about once every several months. FIG. 4 is a block diagram of a scanner device according to an embodiment of the invention. A characteristic configuration in claim 3 is that the digital spatial filter 23 in FIG. 1 is divided into a main scanning direction correction filter circuit 23a and a sub-scanning filter circuit 23b, as shown in FIG. By changing the calculation constant of the scanning direction correction filter circuit 23a, only the correction strength in the main scanning direction can be changed.

The digital spatial filter 23 generally used for correction is a two-dimensional filter that includes not only the main scanning direction but also the sub-scanning direction. This is because the MTF correction performed in scanner devices such as facsimiles not only restores the resolution caused by the lens system, but also uses a two-dimensional filter to relieve image deterioration caused by mechanical scanning unevenness in the sub-scanning system. It is from. However, when switching the calculation constants of the digital spatial filter 23 midway in the main scanning direction as in the present invention, if the calculation constants for main scanning and sub-scanning are switched symmetrically as in the conventional case, Since the MTF correction performed using different calculation constants for the center and periphery of the lens extends to the sub-scanning direction, unnaturalness may appear in the read image depending on the document.

[0020] Therefore, in the invention according to claim 3,
The digital spatial filter is divided into those for the peripheral scanning direction and the sub-scanning direction, and only the calculation constant of the main scanning direction correction filter circuit 23a is switched by the calculation constant setting circuit 24, so that the influence of correction on the main scanning direction is reduced. This can be prevented from affecting the sub-scanning direction. Thereby, the level difference in resolution between the central part and the peripheral part in the main scanning direction due to the lens system is appropriately corrected, and uniform high resolution can be obtained over the entire main scanning direction.

[0021]

As described above, according to the invention described in claim 1, the correction system of the digital spatial filter 23 is switched according to the MTF in the main scanning direction of the lens, and by performing MTF correction, an expensive lens can be used. High resolution can be maintained over the entire image without using
A high resolution scanner device can be provided at low cost.

According to the second aspect of the invention, the resolution characteristic detection means detects the resolution characteristic of the lens actually attached over the entire main scanning area, and based on this, the correction coefficient of the digital spatial filter 23 is determined. By switching, it is possible to correct changes in the scanner device over time and variations in assembly or adjustment between devices, thereby stabilizing the quality of the scanner device and contributing to improved reliability.

Further, according to the third aspect of the invention, by changing the correction system of the digital spatial filter 23 and switching only the correction intensity in the main scanning direction, the resolution characteristics in the main scanning direction can be corrected in the sub-scanning direction. It is possible to prevent this from spreading, and it is possible to appropriately correct only the resolution characteristics in the main scanning direction by the lens system.

[Brief explanation of drawings]

FIG. 1 is a block configuration diagram of a scanner device according to an embodiment of the invention.

FIG. 2 is a diagram showing the relationship between the MTF of a lens and the correction strength of the MTF that corrects it.

FIG. 3 is a block configuration diagram of a scanner device according to an embodiment of the invention as set forth in claim 2;

FIG. 4 is a block configuration diagram of a scanner device according to an embodiment of the invention recited in claim 3;

FIG. 5 is a configuration diagram of a general scanner device,
(a) is a perspective view, and (b) is a sectional view.

[Fig. 6] Fig. 6 is a characteristic diagram of a general lens, in which (a) is a diagram showing the MTF between the center and peripheral parts of the lens, and (b) is a diagram showing the usage range of the lens. It is a line diagram.

[Explanation of symbols]

1 Image scanner (scanner device) 8
Lens 9 Photoelectric conversion section (imaging means) 20 CCD (imaging means) 21 Amplifier 22 A/D converter (A/D conversion means) 23
Digital spatial filter 23a Main scanning direction correction filter circuit 23b
Sub-scanning filter circuit 24 Arithmetic constant setting circuit 25 Constant switching instruction circuit 26 Counter 27 MTF envelope detection circuit (resolution characteristic detection means) 28 1-line buffer 29 Comparator

Claims (3)

[Claims] Claim 1: An imaging device that forms an image of a document through a lens and converts it into an image signal, an A/D conversion device that converts the image signal into digital data, and an image pickup device that uses the digital data. a digital spatial filter that corrects resolution; when correcting the resolution by the digital spatial filter, a correction system of the digital spatial filter is applied at the center and peripheral areas of the main scan according to the resolution characteristics of the lens; A scanner device that corrects image data by changing the image data. 2. The scanner device according to claim 1, wherein resolution characteristic detection means for detecting the resolution characteristic of the lens over the entire main scanning area is provided in the device, and the resolution characteristic of the lens detected by the resolution characteristic detection means is provided within the device. A scanner device characterized in that the correction system of the digital spatial filter is changed based on. 3. The scanner device according to claim 1, wherein only the correction intensity in the main scanning direction is switched by the variable correction system.