JP2000013599A - Shading correction method and device for image reader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To correct nonuniformity of a recording body, nonuniformity of light beams, efficiency nonuniformity until light which is carrying image information is inputted to a line sensor and the sensitivity nonuniformity of the line sensor, etc., and to provide reproducing images without gradation nonuniformity or structure noise in an image reader using the line sensor. SOLUTION: Reference image signals A are, obtained from a standard original 3 uniformly irradiated with radiation and the reference image signals A, include the sensitivity irregularities of the line sensor 14 or the like. Then, image signals S are obtained from a stimulable phosphor sheet 4 where radiation images are stored and recorded, the image signals S are normalized by the reference image signals A in an arithmetic means 18, and correction signals S1 from which shading is eliminated are obtained. For the correction signals S1, an image processing is executed in an image processing means 19, and processing completed image signals S' are obtained. The reproducing images of the processed image signals S' turn into ones of high image quality without variable density nonuniformity by the shading.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a recording medium on which image information is recorded, which is irradiated with a light beam to generate light containing the image information, and this light is detected photoelectrically to obtain an image signal. The present invention relates to a shading correction method and apparatus for correcting fluctuations in an image signal due to unevenness in irradiation of a light beam in an image reading apparatus.

[0002]

2. Description of the Related Art Conventionally, a recording medium on which image information is recorded is irradiated with a light beam, and image information is read by detecting reflected light, transmitted light or emitted light from the recording medium. The device is widely used in practice. Such image information reading devices include plate making scanners,
A radiation image information recording / reproducing system using a stimulable phosphor sheet proposed by the present applicant in addition to a computer and a facsimile input device (Japanese Patent Laid-Open No. 55-12429,
Nos. 56-11395 and 56-11397).

[0003] That is, radiation (X
Rays, α-rays, β-rays, γ-rays, electron beams, ultraviolet rays, etc.), a part of this radiation energy is accumulated in the phosphor, and when this phosphor is irradiated with excitation light such as visible light, it accumulates. It is known that a phosphor emits stimulated light emission according to the applied energy, and a phosphor exhibiting such properties is called a storage phosphor. The radiation image reading apparatus uses the stimulable phosphor to record radiation image information of a subject such as a human body on a stimulable phosphor sheet once, and irradiates the stimulable phosphor sheet with excitation light. It produces stimulating light,
The image signal is obtained by photoelectrically reading the obtained stimulated emission light.

In the above-described image reading apparatus, photoelectric reading means is used to detect light carrying image information, which is obtained from a recording body by irradiating the recording body with a light beam. The photoelectric reading means includes a relatively small-sized photomultiplier tube (photomultiplier) and an optical guide having one end arranged along the main scanning line and the other end joined to the photomultiplier. What
A long photomultiplier directly arranged along the main scanning line (see Japanese Patent Application Laid-Open No. 62-16666) is used.

However, in the above-described image reading apparatus,
Irregularity of the light guide in the main scanning direction of the light guide, detection unevenness of the photoelectric reading means due to unevenness of the sensitivity of the long photomultiplier in the main scanning direction, and irradiation unevenness of radiation when recording a radiation image on the stimulable phosphor sheet. The image signal obtained from the photoelectric reading unit may fluctuate due to uneven sensitivity of the stimulable phosphor sheet itself, uneven scanning of the light beam, or the like. If the light detection efficiency is partially reduced (shading) due to such unevenness, it is naturally impossible to correctly detect the image information recorded on the recording medium, and the obtained image signal is reproduced. In the reproduced image obtained by the above, shading is caused by shading.

Therefore, the applicant of the present invention detects the shading state in advance and corrects the sensitivity of an image signal or a photomultiplier according to the scanning position of the light beam to avoid the influence of the shading. A shading correction device has already been proposed (Japanese Patent Laid-Open No. 60-54571).
Nos. 62-47259 and 62-47261).

On the other hand, in the above-described image reading apparatus, an image reading apparatus using a line sensor in which a plurality of solid-state photoelectric conversion elements are linearly arranged has been proposed as a means for photoelectrically reading light carrying image information. (For example,
JP-A-60-111568 and JP-A-60-236354). The image reading devices described in these publications use an array light source in which LEDs or semiconductor lasers are linearly connected and emit light simultaneously, or a non-directional light source such as a fluorescent lamp or a Xe lamp and a row of slits or small holes. In combination with an aperture or the like, the recording medium is irradiated with a linear light beam, and light carrying image information emitted from a location where the light beam is checked is photoelectrically read by a line sensor.

[0008]

By the way, the image signal obtained by the above-described image reading apparatus using the line sensor also has the same radiation irradiation unevenness and stimulable phosphor as the apparatus using the photomultiplier. The unevenness in sensitivity of the sheet itself, the unevenness in irradiation with excitation light, the unevenness in efficiency until the stimulated emission light emitted from the sheet is input to the line sensor, the unevenness in sensitivity in the line sensor, and the like occur. In particular, in the case of a line sensor, since the size of each sensor represents one pixel, the sensitivity unevenness of the line sensor is visually recognized as noise in an image or structural noise such as poor granularity rather than shading unevenness. It will be. In the case of an image reading apparatus using a line sensor, the excitation light is irradiated linearly in the width direction of the sheet, but it is very difficult to make the concentration of the linear excitation light uniform. In addition, the influence of the unevenness of excitation light irradiation is great.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a shading correction method and apparatus for an image reading apparatus that can reduce the above-described influence of shading in an image reading apparatus using a line sensor. Is what you do.

[0010]

According to a shading correction method for an image reading apparatus according to the present invention, a recording medium on which image information is recorded is two-dimensionally scanned by a linear light beam, and the image information is scanned by the scanning. The carried light is arranged to face the portion of the recording body irradiated with the light beam, and the image information is read by a line sensor including a large number of solid-state photoelectric conversion elements that receive the light and perform photoelectric conversion. A shading correction method for an image reading apparatus for obtaining an image signal representing the image signal, wherein the image signal is corrected based on a two-dimensional reference image signal obtained in advance by scanning a standard original having a uniform density as a reference. It is.

Here, the standard original may be any pattern as long as it has a uniform density. Also,
In the present invention, the density in the case of the uniform density does not necessarily mean the optical density. For example, when a stimulable phosphor sheet is used as a standard document, the radiation accumulated and recorded on the stimulable phosphor sheet is used. This means the energy level, and when the light beam is ideally and uniformly irradiated, the image original in which the amount of reflected light, transmitted light or emitted light from each part of the recording medium is uniform is uniform. Is a standard manuscript having The reference signal obtained by scanning the standard original is an analog signal having intensity unevenness corresponding to the shading generated in the reproduced image.

Further, correcting an image signal based on a reference image signal means subtracting the reference image signal from the image signal and normalizing the image signal by the reference image signal.

[0013] The shading correction device according to the present invention comprises:
In the above-described shading correction device of the image reading device using the line sensor, a storage unit that stores a two-dimensional reference image signal obtained in advance by scanning a standard original having a uniform density as a reference, based on the reference image signal And correction means for correcting the image signal.

[0014]

According to the present invention, since an image signal is corrected using a reference image signal obtained in advance by scanning a standard original having a uniform density as a reference, radiation irradiation unevenness is reduced.
It is possible to reduce the influence of shading caused by unevenness in sensitivity of the recording body itself, unevenness of light beam irradiation, efficiency unevenness until light carrying image information is input to the line sensor, unevenness in sensitivity of the line sensor, and the like. Therefore, by reproducing the image signal obtained by the present invention, it is possible to reproduce a clear image free from shading unevenness and structural noise caused by shading.

[0015]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic diagram showing a configuration of an image reading apparatus according to an embodiment of the present invention. As shown in FIG. 1, there are provided endless belts 9a and 9b rotated by a motor (not shown) for transporting a standard document 3 and a stimulable phosphor sheet 4 described later in the arrow Y direction. Above the endless belts 9a and 9b, an array light source 10 in which LEDs are linearly arranged so as to emit linear excitation light 11 is provided. In the present embodiment, the array light source 10 is disposed at a position away from the sheet 4 for convenience, but it is preferable to provide the array light source 10 and the sheet 4 close to each other. Further, below the position where the excitation light 11 is scanned, a line sensor 14 that receives the stimulating light 13 from below is arranged perpendicularly to the transport direction of the standard original 3 and the sheet 4. The line sensor 14 is connected to an A / D converter 17, and the A / D converter 17 is connected to arithmetic means 18, and the arithmetic means 18 is connected to image processing means 19. Further, the image reading apparatus of the present embodiment includes a first memory 20 for storing a reference image signal A obtained from a standard original 3 made of a stimulable phosphor sheet uniformly irradiated with radiation as described later. And a second memory 21 for storing an image signal S obtained from the stimulable phosphor sheet 4 on which a radiation image is accumulated and recorded.

The line sensor 14 is configured by linearly arranging solid-state photoelectric conversion elements such as a photoconductor or a photodiode, and a signal obtained by photoelectrically converting stimulated emission light by each element is used as a signal of an image signal. It represents a signal of one pixel. The light receiving surface of the line sensor 14 is provided with a filter that cuts the excitation light 11 and transmits only the stimulated emission light.

The stimulable phosphor sheet 4 and the standard original 3 are formed with two notches 3A and 4A as shown in FIG. 1, and the positions of the notches 3A and 4A are provided in the line sensor 14. The position is detected by the detected position sensor 25. The positions of the notches 3A and 4A detected by the position sensor 25 are used as reference positions for performing shading correction as described later.

Next, the operation of the present embodiment will be described.

First, a standard original 3 made of a stimulable phosphor sheet uniformly irradiated with radiation is placed on an endless belt 9a,
Set on 9b. The standard document 3 set at this predetermined position is conveyed (sub-scan) in the direction of arrow Y by the endless belts 9a and 9b. On the other hand, the linear excitation light 11 emitted from the array light source 10 irradiates the standard original 3 in an arrow X direction substantially perpendicular to the sub-scanning direction (arrow Y direction).
From the location of the standard document 3 irradiated with the excitation light 11, the stimulated emission light 13 of a light amount corresponding to the accumulated and recorded radiation image information is emitted. This stimulated emission light 13 is a line sensor
The solid-state photoelectric conversion elements constituting the line sensor 14 convert the amount of stimulated emission light 13 received by the solid-state imaging device 14 into a reference image signal A0. On the other hand, the notch 3A of the standard document 3 is detected by the position sensor 25,
The detected position signal P is input to the calculating means 18.

The analog reference image signal A0 output from each element of the line sensor 14 is input to an A / D converter 17,
Here, it is converted into a digital reference image signal A and stored in the first memory 20. The reference image signal A includes irradiation unevenness (two-dimensional unevenness) of the radiation to the stimulable phosphor sheet, sensitivity unevenness (two-dimensional unevenness) of the stimulable phosphor sheet, irradiation unevenness (one-dimensional unevenness) of the excitation light 11, Stimulated light 13 is a line sensor
A signal waveform (shading waveform) having an intensity distribution as shown in FIG. 2 due to efficiency unevenness (one-dimensional unevenness) until input to the input terminal 14 and sensitivity unevenness (one-dimensional unevenness) of the line sensor 14. . Although the shading waveform is shown two-dimensionally for convenience in FIG. 2, the shading waveform is actually a three-dimensional signal waveform on the surface of the standard document 3.

Next, the stimulable phosphor sheet 4 on which the radiation image is accumulated and recorded in the same manner as described above is placed on the endless belt 9.
The radiation image information is read by being set on a and 9b and scanned by the excitation light 11. The stimulated emission light 13 emitted from the stimulable phosphor sheet 4 by the scanning of the excitation light 11 is
Detected by the line sensor 14 in the same manner as in the case of the standard document 3, converted into an analog image signal S0 and input to the A / D converter 17, where it is converted into a digital image signal S and stored in the second memory Stored in 21. This image signal S has a waveform in which an image signal to be read by scanning the stimulable phosphor sheet 4 is superimposed on the waveform of the reference image signal A shown in FIG.

Next, the reference image signal A and the image signal S stored in the first and second memories 20 and 21 are used by the arithmetic means.
The following equation (1) is input to each pixel and
Is performed to obtain a correction signal S1 subjected to shading correction.

S1 (x, y) = S (x, y) / A (x, y) (1) (x, y): coordinates of a pixel A position signal P indicating the positions of the notches 3A, 4A of the phosphor sheet 4 is input, and the reference image signal A and the image signal S are aligned with reference to the position signal P, and the above equation (1) is obtained. Is performed.

The correction signal S1 is input to the image processing means 19 and subjected to image processing to obtain a processed image signal S '. The processed image signal S 'is input to a reproducing unit (not shown) and reproduced as a visible image, or stored in a storage unit (not shown). The image obtained by reproducing the processed image signal S ′ obtained in this manner has the above-described unevenness of radiation irradiation, the unevenness of sensitivity of the sheet 4, the unevenness of irradiation of the excitation light 11, Efficiency unevenness until emission light 13 reaches line sensor 14, line sensor
This is a clear image in which the shading unevenness caused by the sensitivity unevenness of No. 14 has been eliminated, and the diagnostic performance is remarkably improved.

In the above embodiment, the radiation image stored in the stimulable phosphor sheet 4 is read to obtain an image signal S, and the image signal S is temporarily stored in the second memory 21.
Although the shading correction is performed by the calculating means 18 after the storage, the radiographic image stored and recorded on the stimulable phosphor sheet 4 is read, and the reference image signal A is obtained in real time with respect to the obtained image signal S. The calculation shown in the above equation (1) may be performed between pixels corresponding to the above. At this time, the calculation according to the above equation (1) may be performed for each pixel, or may be performed for each line of scanning. By obtaining the correction signal S1 in this manner, the second memory 21 becomes unnecessary, and the configuration of the apparatus can be simplified. Further, since it is not necessary to store the image signal S in the second memory 21, the correction signal S1 can be quickly obtained.

In the above embodiment, the image reading apparatus for reading the radiation image information stored and recorded on the stimulable phosphor sheet has been described. However, the present invention is not limited to this. The present invention can be applied to any image reading device such as a device that reads a radiation image.

Further, in the above embodiment, the linear excitation light 11 is irradiated on the standard original 3 and the sheet 4 by the array light source 10, but the invention is not limited to this.
Other light sources may be used, such as a linear excitation light by a combination of a diffusion light source and a slit.

In the above embodiment, notches 3A and 4A are provided in the standard original 3 and the stimulable phosphor sheet 4 to align the pixels of the reference image signal A and the image signal S. Instead of 3A and 4A, holes, optical markers and the like are provided in the standard manuscript 3 and the stimulable phosphor sheet 4.
, So that the positioning of the reference image signal A and the image signal S may be performed.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a configuration of an image reading apparatus according to an embodiment of the present invention.

FIG. 2 is a graph showing a signal waveform of a reference image signal.

[Explanation of symbols]

 10 Array light source 11 Excitation light 13 Stimulated emission light 14 Line sensor 17 A / D converter 18 Operation means 19 Image processing means 20 First memory 21 Second memory 25 Position sensor

Claims (2)

[Claims] 1. A recording medium on which image information is recorded is two-dimensionally scanned by a linear light beam, and the light carrying the image information is scanned by the scanning to a portion of the recording medium irradiated with the light beam. In a shading correction method of an image reading apparatus which is arranged to face and is read by a line sensor including a large number of solid-state photoelectric conversion elements that receive the light and perform photoelectric conversion to obtain an image signal representing the image information, A shading correction method for an image reading apparatus, wherein the image signal is corrected based on a two-dimensional reference image signal obtained in advance by scanning a standard document having a uniform density. 2. A recording medium on which image information is recorded is two-dimensionally scanned by a linear light beam, and the light carrying the image information is scanned by the scanning to a portion of the recording medium irradiated with the light beam. In a shading correction device of an image reading device which is arranged to face and is read by a line sensor composed of a large number of solid-state photoelectric conversion elements for receiving the light and performing photoelectric conversion to obtain an image signal representing the image information, Storage means for storing a two-dimensional reference image signal obtained in advance by scanning a standard document having a uniform density, and correction means for correcting the image signal based on the reference image signal. Shading correction device for image reading device.