JPS61189762A - Shading correction method for picture information reader - Google Patents

Abstract

PURPOSE:To eliminate the streaky shading by obtaining the shading characteristics of a condenser prior to the reading of light out of a recording medium and with resolution higher than a digital read signal and giving the correction to an analog read signal before its digitization in accordance with its shading characteristics in a light reading mode. CONSTITUTION:The radiant rays such as X rays, etc. of even intensity are irradiated on a storage type fluorescent sheet 10 before the radiation picture information is read. Then the sheet 10 is loaded to a picture reader. Here a reference output signal SO delivered from a photomultiplier 17 is supplied to an A/D converter 30 with changeover of a switch 22 and converted into a digital signal with the bit resolution sufficiently higher than a digital read signal Sd. This digital signal is supplied to a correction value arithmetic circuit 31 and the difference is obtained for each picture element between said digital signal and a reference output signal SdO of the direction along an incident end surface 16a. When the radiation picture information is read, a shading correction circuit 23 reads the correction value out of a memory 32 for execution of correction. In this case, the signal Sd has no variation more than the proper correction value owing to the shortage of resolution. This prevents the generation of the streaky shading.

Description

Detailed Description of the Invention (Field of the Invention) The present invention relates to an image information reading device in which light containing image information is photoelectrically detected by a photodetector. The present invention relates to a method for correcting a change in the output of the photodetector.

(Technical Background and Prior Art of the Invention) Image information is read by scanning a recording medium on which image information is recorded with a light beam and detecting reflected light, transmitted light, or emitted light from the recording medium. 2. Description of the Related Art Image information reading devices have conventionally been used in, for example, image input units of computers, image reading units of facsimiles, and the like. In such an image information reading device, as shown in Japanese Patent Laid-open Nos. 56-11395@ and 56-11397, in order to efficiently detect light, a photodetector is placed on a light condenser. It is often used continuously.

That is, one end of a light condenser made of a light-guiding material is used as a light incident end face, while the other end is used as an output end face, a photodetector such as a photomultiplier tube is connected to this output end face, and the light condenser is If the incident end face is arranged so as to extend along the light beam scanning line on the recording medium, the light transmitted from each scanning point will enter the condenser from the above incident end face, and will be efficiently focused. It will be guided to the detector.

However, when detecting light through a light condenser as described above, the shading of the light condenser (i.e., the occurrence of areas with poor light guiding efficiency at the ends of the light condenser, for example) causes problems with the photodetector. The output may change. Naturally, when such shading occurs, it becomes impossible to correctly detect light from the recording medium.

In order to solve the above problem, the shading characteristics across the beam scanning direction of the condenser are determined before reading the light from the recording medium, and when reading the light, the shading characteristics obtained from the photodetector are calculated. It has been considered to correct the read signal according to the shading characteristics so as to eliminate changes in the output of the photodetector due to shading. However, in this case, streak-like unevenness may occur in the reproduced image formed based on the read signal that has undergone shading correction. That is, the above shading correction is usually performed by digitally converting an analog read signal output from a photodetector such as a photomultiplier tube, and adding or subtracting a digital correction value according to the shading characteristics to this digital read signal. However, if the bit resolution in this digital correction is low, points where the correction value is more or less than the appropriate value will occur regularly in the beam scanning direction (concentrator width direction), so in the reproduced image, the High or low density points occur, and these points are connected in the sub-scanning direction (direction substantially perpendicular to the beam scanning direction), resulting in streak-like unevenness.

It is possible to eliminate the above problems by sufficiently increasing the bit resolution of the digital correction and the bit resolution of the reproduced image output, but doing so would require a computing device with a large capacity of memory. , another problem arises in that the speed of the correction processing and image processing described above is reduced.

(Objective of the Invention) Therefore, it is an object of the present invention to provide a shading correction method that does not cause the above-mentioned streak-like unevenness in a reproduced image.

(Structure of the Invention) The shading correction method in the image information reading device of the present invention detects light from a recording medium using a light condenser and a photodetector as described above, and converts the analog read signal output from the photodetector into a digital signal. In an image information reading device that converts the light to obtain a digital read signal, the shading characteristics of the condenser are determined at a higher resolution than the digital read signal before reading the light from the recording medium, and when the light is read, the The present invention is characterized in that the analog read signal before conversion is corrected in accordance with the shading characteristics so as to eliminate changes in the output of the photodetector due to shading.

As mentioned above, if the analog read signal before digital conversion is corrected according to the shading characteristics obtained with a higher resolution than the digital read signal, the correction value will not be too large or too small than the appropriate value. , the above-mentioned streak-like unevenness is prevented from occurring. In this way, only the shading correction is performed at high resolution, and the digital read signal is created at a lower resolution, which reduces the speed of image processing and requires a large memory capacity for the image processing arithmetic unit. I don't even need my mother's things.

(Embodiments) Hereinafter, the present invention will be described in detail based on embodiments shown in the drawings.

FIG. 1 shows an image information reading device that performs shading correction according to an embodiment of the present invention. As an example, this image information reading device can be used in a radiation image information recording and reproducing system using a stimulable phosphor sheet, which the present applicant has already proposed in JP-A-55-12429 and JP-A-56-11395. This is a radiation image information reading device that reads stimulated luminescence light emitted from a phosphor sheet. The stimulable phosphor sheet 10 on which radiation image information has been accumulated and recorded is conveyed in the direction of arrow Y for sub-scanning by a sheet conveying means 11 such as an endless belt.

Further, the laser beam 13 as excitation light emitted from the laser light source 12 is directed to an optical deflector 1 such as a galvanometer mirror.
4, the stimulable phosphor sheet 10 is main-scanned in a direction X substantially perpendicular to the sub-scanning direction Y. From the part of the sheet 10 irradiated with the laser beam 13 in this way,
Stimulated luminescent light 15 is emitted in an amount corresponding to the accumulated and recorded radiographic image information, and this stimulated luminescent light 15 is transmitted to the light condenser 1.
The light is collected by the photodetector 6 and detected in a charged manner by a photomultiplier tube 17 as a photodetector.

The light condenser 16 is formed by molding a light guiding material such as an acrylic plate, and has a linear incident end face 16a that extends along the beam scanning line on the stimulable phosphor sheet 10. The protruding DA end face 16b is arranged as shown in FIG.
The light-receiving surface of the photomultiplier 17 is coupled to the photomultiplier 17. The stimulated luminescent light 15 entering the light condenser 16 from the incident end surface 16a travels through the light condensing body 16 through repeated total reflection, exits from the output end surface 16b, is received by the photomultiple 17, and is then received by the photomultiple 17. The photomultiplier 17 detects the amount of stimulated luminescence light 15 carrying radiation image information. Regarding the preferable shape, material, and manufacturing method of the light condensing body 16,
For example, it is described in detail in US Pat. No. 4,346,295.

The analog output signal (read signal) S of the Photomaru 17 is amplified by the log amplifier 20, and the recording scale factor setting device 21 sets the recording scale factor? The latitude L is determined and sent to the shading correction circuit 23 via the switch 22, where it undergoes shading correction to be described later, and then digitized by the A/D converter 24. Digital read signal 3 obtained in this way
After being subjected to processing such as gradation processing and frequency processing in the image processing circuit 25, the signal d is input to an image reproducing device 26 such as a CRT or an optical scanning recording device. Since the read signal Sd carries the light intensity of the stimulated luminescence light 15, if this read signal Sd is used, the copper wire image stored and recorded on the stimulable phosphor sheet 10 can be reproduced. device 26
is reproduced as a visible image.

In addition to inputting the read signal Sd immediately to the image reproducing device 26 as described above, the read signal Sd may be temporarily recorded on a recording medium such as a magnetic disk or a magnetic tape.

Here, the light condensing body 16 may be formed in a complicated shape, so that shading as described above may occur. When this shading occurs, the output signal S of the photomultiplier 11 becomes the stimulated luminescent light 15 with the same amount of light.
This also changes depending on the beam scanning position, making it impossible to correctly detect the stimulated luminescence light 15. Hereinafter, the point of correcting this shading will be explained in detail.

Before reading the radiation image information as described above,
The volumetric phosphor sheet 10 is irradiated with radiation such as X-rays of uniform intensity. The stimulable phosphor sheet 10 thus subjected to so-called solid exposure is subjected to image reading in the same manner as described above. Stimulated luminescent light 15 of uniform intensity is emitted from the sheet 10 scanned by the laser beam 13, and this stimulated luminescent light 15 is transmitted through the condenser 16 to the photomultiplier 17.
detected by. At this time, the reference output signal S0 outputted from the photomultiple 17 is amplified by the log amplifier 20 in the same manner as described above, set to the recording scale factor Lo in the recording scale factor setting device 21, and the switch 22 is switched to /D converter 30. The reference output signal So is digitized in this A/D converter 30 with a sufficiently higher bit resolution than the digital read signal Sd, and the digitized reference output signal Sdo is input to the correction value calculation circuit 31. This correction value calculation circuit 31 outputs a reference output signal Sd in the direction along the incident end face 16a.

(This is caused by the shading and indicates the shading characteristics) is determined for each pixel. That is, if one row of pixels XI, X2, X3...Xj are lined up along the main scanning direction X as shown in FIG. The average value of the output signal Sdo is determined, and this is set as the representative signal value Rn of the nth column. Then, the correction value calculation circuit 31 calculates all the representative signal values R+, Rz of columns 1 to j.
・・・・・・Find the difference jJn = Rn − Ro between the average value Ro of Rj and each representative signal value Rn, and calculate these 1 series Ut
, Uz, . . . Uj are stored in the memory 32 as correction values for the recording scale factor Lof, :. As described above, when reading the radiation image information stored and recorded on the stimulable phosphor sheet 10, the analog read signal S is outputted through the shading correction circuit 23. This shading correction circuit 23 uses the correction value U+
, Uz...Uj are read from the memory 32 and converted into a continuous analog signal (Ja) by the D/A converter 33, and then a correction is made to subtract this analog signal jla from the analog read signal S. At this time, the correction values Ul, Uz,
...The timing of reading Uj is determined by using a clock signal CL synchronized with the scanning of the laser beam 13.
Correction value Un from the read signal S for the n-th 11th pixel
is controlled so that it is reduced. If the analog read signal S is corrected by subtracting the correction value Un, the change in the output of the photomultiplier 17 due to the shading of the condenser 16 is compensated, and the stimulated luminescence light 15 can be read correctly. By using the read signal Sd obtained by digitizing the subsequent signal S', the radiation image information stored and recorded on the stimulable phosphor sheet 10 can be correctly reproduced.

The above shading correction is performed using the digital read signal 3.
Correction values U1, Uz with sufficiently larger pitch resolution than d
・・・・・・Find Uj and use this correction value UisU2...
Since this is done by correcting the analog read signal S based on Uj, the digital read signal Sd will not fluctuate beyond the appropriate correction value due to insufficient resolution of shading correction.

Therefore, in the reproduced image reproduced based on this digital read signal Sd, as described above, there are no points where the density is higher or lower than the surroundings, and the occurrence of streak-like unevenness is prevented.

Note that if the recording scale factor of the read signal S when reading image information and the recording scale factor of the reference output signal So for determining the correction values Ur, Uz...Uj are different from LlLo, shading correction These values are applied to the circuit 23, L.

is input, and the shading correction circuit 23 converts the correction values U1, Uz・old−・tJj into analog signals jl in order to compensate for the difference in recording scale factors.
A signal obtained by multiplying a by Lo/L is used as a correction signal.

In addition, when the high voltage applied to the photomultiplier 17 is changed, the correction values U+, Uz, . , reads a correction value from the memory 32 according to the high voltage set at the time of image reading,
It may be used for shading correction. When the high voltage applied to the photomultiplier 17 is changed steplessly or in very small steps, correction values IJ+ for several high voltages close to the set high voltage are set.
Uz...Uj may be read from the memory 32 in several ways and these correction values may be interpolated using a known interpolation method to obtain a correction value corresponding to the set high voltage. In this way, the number of correction values stored in the memory 32 can be reduced. In addition, in order to reduce the number of correction values stored in the memory 32 in this way,
Among the j-column pixel columns up to The correction value may be obtained by interpolating the correction value read from the memory 32, as described above.

Furthermore, correction values Lh, Uz... are calculated from the reference output signal So.
(When determining Jn, if it is difficult to obtain these correction values with high precision due to the influence of noise, etc.,
The correction values Ul, Uz, . . . , lJn may be obtained from a signal obtained by smoothing the reference output signal So.

Furthermore, in the embodiment described above, the A/D converter 3
The bit resolution of the shading characteristic is increased by digitizing the reference output signal So using 0 at a bit resolution higher than that of the digital read signal Sd.
This A/D conversion may be performed with the same bit resolution as the digital read signal Sd, and the bit resolution may be increased at the stage of calculating the average values Rn and Ro.

In the embodiment roughly described above, the reference light incident on the condenser 16 for determining the correction value is the reference light emitted from the stimulable phosphor sheet 10 that has been solidly exposed to radiation such as X-rays. Although the emitted light 15 is used, the reference destination for determining the correction value is not limited to this.

For example, a stimulable phosphor sheet formed to the same size as the stimulable phosphor sheet 10 and capable of storing visible light energy is uniformly irradiated with visible light, and then the stimulable phosphor sheet is irradiated with a laser beam 13. However, the stimulated luminescent light emitted from the stimulable phosphor sheet can also be used as reference light. In this case, in order to obtain the correction value, an erasing light source (which emits visible light as erasing light), which is usually built into the reading device, is used to remove the image remaining on the stimulable phosphor sheet 10 that has been read. It is available and convenient.

Furthermore, the shading correction method of the present invention is applicable not only to the device that reads the stimulated luminescence light emitted from the stimulable phosphor sheet 10 described above, but also to the device that reads the reflected light, transmitted light, etc. that is emitted from the recording medium and carries image information. The present invention can also be applied to other image information reading devices.

(Effects of the Invention) As explained in detail above, according to the shading correction method of the present invention, it is possible to automatically compensate for the shading of the condenser, correctly read the light carrying image information, and It becomes possible to accurately reproduce the image information recorded in the .

Furthermore, according to the method of the present invention, the occurrence of streak-like unevenness in the reproduced image due to the shading correction is also prevented, and the image quality of the reproduced image formed based on the read signal is greatly improved.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing a radiation image information reading apparatus that performs shading correction according to an embodiment method of the present invention, and FIG. 2 is an explanatory diagram for explaining shading correction according to the method of the present invention. DESCRIPTION OF SYMBOLS 10... Luminescent phosphor sheet 13... Laser beam 14... Optical deflector 15... Stimulated luminescent light 1G... Light collector 16a... Incident end surface 16b of the light collector ...Emission end face of condenser 17...Photomulti 20...Log amplifier 23...Shading correction circuit 24.30...A/D converter 31...Correction value calculation circuit 32... Memory 33...D/A
Converter S...analog read signal So...reference output signal Sd...digital read signal

Claims (1)

[Claims] Scanning a recording medium on which image information is recorded with a light beam to obtain light containing the image information, condensing the light with a condenser having an incident end face extending along the beam scanning direction, and condensing the condensing light. In an image information reading device that detects an analog read signal using a photodetector connected to an output end face of the body, and then converts the analog read signal into a digital read signal, the The shading characteristics of the condenser are determined with a higher resolution than the digital read signal, and when reading the light, the analog read signal before digital conversion is subjected to the shading so as to eliminate changes in the output of the photodetector due to shading. A shading correction method in an image information reading device, characterized in that correction is performed according to characteristics.