JPH0520028B2 - - Google Patents

Description

Detailed Description of the Invention (Field of the Invention) The present invention relates to an image information reading device that photoelectrically detects light containing image information using a photodetector.
The present invention relates to a method for correcting a change in the output of a photodetector due to shading of a light condenser connected to 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, for example,
As shown in Nos. 11395 and 56-11397,
In order to efficiently detect light, a photodetector is often connected to a light condenser. In other words, one end of a light collector made of a light-guiding material is used as an incident end face for light, while the other end is used as an output end face, a photodetector such as a photomultiplier tube is connected to this exit end face, and the light collector is used as an input end face for light. If the end face is arranged so that it extends along the light beam scanning line on the recording medium, the light emitted from each scanning point will enter the light condenser from the incident end face, and will be efficiently focused and sent to the photodetector. You will be guided to this point.

However, when detecting light through a light condenser as described above, shading of the light condenser (i.e., the formation 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 the light from the recording medium.

In order to solve the above-mentioned problem, the shedding 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 shedding characteristics obtained from the photodetector are determined. It has been considered to correct the read signal according to the above-mentioned shading characteristics so as to eliminate the change 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 the shading correction. In other words, the above-mentioned shedding correction is usually performed by adding or subtracting a digital correction value to the digitized read signal according to the shedding characteristics, but if the bit resolution in this digital correction is low, the correction value may not be the appropriate value. In the reproduced image, there will be points with higher or lower density than the surrounding areas, and these points will appear in the sub-scanning direction. (in a 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, an object of the present invention is to provide a shading correction method that does not cause the above-mentioned streak-like unevenness in a reproduced image.

(Structure of the Invention) A shedding correction method in an image information reading device of the present invention is a method for correcting shedding in an image information reading device that detects light from a recording medium using a light condenser and a photodetector as described above. of,
The present invention is characterized in that digital correction is performed as described above in accordance with the shading characteristics of the light condenser, and a random component is further added to the corrected read signal.

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

FIG. 1 shows an image information reading apparatus that performs shading correction according to an embodiment of the present invention. This image information reading device, for example,
The applicant has already filed JP-A-55-12429 and JP-A-56-11395.
This is a radiation image information reading device that reads stimulated luminescence light emitted from the stimulable phosphor sheet in a radiation image information recording and reproducing system using a stimulable phosphor sheet proposed in No. 1, etc. A stimulable phosphor sheet 10 on which radiographic image information has been accumulated and recorded is transported by a sheet conveying means 1 such as an endless belt.
1, the paper is transported in the direction of arrow Y for sub-scanning. Further, the laser beam 13 as excitation light emitted from the laser light source 12 is deflected by an optical deflector 14 such as a galvanometer mirror, and the stimulable phosphor sheet 10 is directed in a direction X substantially perpendicular to the sub-scanning direction Y. Main scan. Stimulated luminescent light 15 is emitted from the portion of the sheet 10 irradiated with the laser beam 13 in an amount corresponding to the radiographic image information stored and recorded. The light is collected and photoelectrically detected by a photomultiplier tube 17 serving as a photodetector.

The light condenser 16 is formed by molding a light guide material such as an acrylic plate, and has a linear incident end surface 16a extending along the beam scanning line on the stimulable phosphor sheet 10. The photo mark 17 is arranged on the output end surface 16b formed in an annular shape.
The light-receiving surfaces of the two are combined. The above-mentioned entrance end surface 16a
The stimulated luminescent light 15 that entered the condenser 16 from
Proceeds through the interior of the light condensing body 16 by repeating total reflection,
It is emitted from the emission end face 16b and received by the photoprint 17, and the amount of the stimulated luminescent light 15 carrying the radiation image information is detected by the photoprint 17. The preferable shape, material, and manufacturing method of the light condensing body 16 are described in, for example, U.S. Patent No.
It is described in detail in No. 4346295.

The output signal S of the photomal 17 is the log lamp 20
A recording scale factor (latitude) L is determined by a recording scale factor setting device 21, and digitized by an A/D converter 22. The digital read signal Sd obtained in this way is input to the shading correction circuit 24 via the switch 23, and this correction circuit 2
4, the image is subjected to shading correction (this point will be explained in detail later), and after being subjected to processing such as gradation processing and frequency processing in the image processing circuit 25,
For example, the image 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 luminescent light 15, by using this read signal Sd, the radiation image stored and recorded on the stimulable phosphor sheet 10 can be reproduced by the image reproducing device 26. It 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, since the light condensing body 16 is sometimes formed in a complicated shape, the above-mentioned shading may occur. When this shedding occurs, the output signal S of the photomultiplier 17
varies depending on the beam scanning position even for the same amount of stimulated luminescent light 15.
cannot be detected correctly. Hereinafter, the point of correcting this shading will be explained in detail.

Before reading the radiation image information as described above, the stimulable phosphor sheet 10 is irradiated with radiation such as X-rays of uniform intensity. The stimulable phosphor sheet 10 subjected to so-called solid exposure in this way is
The image is read in the same manner as above. From the sheet 10 scanned by the laser beam 13,
Stimulated luminescent light 15 with uniform intensity is emitted, and this stimulated luminescent light 15 passes through a light condenser 16 to a photoluminescent light 17.
detected by. At this time, the reference output signal S ₀ outputted from the photomultiplier 17 is sent to the A/D converter 22 through the log amplifier 20 and recording scale factor setter 21 and digitized in the same manner as described above. Digitized reference output signal
Sd ₀ is input to the correction value calculation circuit 30 by switching the switch 23 . This correction value calculation circuit 30
calculates the difference in the reference output signal Sd ₀ in the direction along the incident end face 16a (this is caused by the shading and indicates the shading characteristic) for each pixel. That is, as shown in FIG. 2, X ₁ , X ₂ , X ₃ along the main scanning direction
...Assuming that the pixels in the _j column of
Let it be Rn. The correction value calculation circuit 30 operates from 1 to
Find the difference Un=Rn− _R0 between the average value _R0 of all representative signal values _R1 , _R2 ...Rj of column j and each representative signal value Rn, and calculate these values _U1 , _U2 ,... ...Uj is stored in the memory 31 as a correction value.

As described above, when reading the radiation image information stored and recorded on the stimulable phosphor sheet 10, the digital read signal Sd is outputted through the shading correction circuit 24. This shading correction circuit 24 stores the correction values U ₁ , U ₂ , . . . Uj in a memory 31.
The correction value Un is subtracted from the digital read signal Sd for the pixel in the n-th column, and the random component F created by the random component creation circuit 32 is added for each pixel. Correction is performed for the read signal Sd of all pixels. . If the above-mentioned correction value Un is corrected, the change in the output of the photoprint 17 due to the shading of the condenser 16 is compensated, and the stimulated luminescence light 15 can be read correctly, so the corrected read signal Sd' can be used. For example, radiation image information stored and recorded on the stimulable phosphor sheet 10 can be correctly reproduced.

In addition to performing the above correction, the read signal Sd
Since a random component F is added to each pixel,
Even when the bit resolution of the digital correction for subtracting the correction value Un is low, the above-mentioned streak-like unevenness does not occur in the reproduced image. In other words, even if the correction value Un is more or less than the appropriate value due to the lack of bit resolution, since the random component F is added, this difference will not occur regularly in the beam main scanning direction. ,
Therefore, density unevenness extending in the sub-scanning direction does not occur in the reproduced image. Of course, the magnitude of the random component F is set to an extent that does not significantly change the digital read signal Sd.

In addition, if the recording scale factor of the output signal S when reading image information and the recording scale factor of the reference output signal S ₀ for calculating the above correction values U ₁ , U ₂ . . . Uj are different from L and L ₀ , respectively. In this case, these values L and L ₀ are input to the shading correction circuit 24.
is input, and the shading correction circuit 24 applies L ₀ / to the correction values U ₁ , U _{2 .} . . Uj, respectively, in order to compensate for the difference in these recording scale factors.
The value multiplied by L is used as the correction value.

Furthermore, in the above embodiment, the random component F
However, as the random component F, it is possible to use a random component F that is randomized within a pixel column in the main scanning direction or sub-scanning direction and is common to each image column. good. In addition, when the high voltage applied to the photomultiplier 17 is changed, the correction values U ₁ , U ₂ . The correction value may be read out from the memory 31 according to the high voltage to be set and used for the shading correction. And photomaru 1
If the high voltage applied to 7 is changed steplessly or in very small steps, correction values for several high voltages close to the set high voltage.
U ₁ , U _{2 . .} . Uj may be read out from the memory 31 in several ways, and these correction values may be interpolated in the shading correction circuit 24 to obtain a correction value corresponding to the set high voltage. In this way, the number of correction values stored in the memory 31 can be reduced. In addition, in order to reduce the number of correction values stored in the memory 31 _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 31 in the correction circuit 24, as described above.

Furthermore, in the embodiment described above, the stimulated luminescent light 15 emitted from the stimulable phosphor sheet 10 that has been exposed solidly to radiation is used as the reference light that is incident on the condenser 16 in order to obtain the correction value. However, the reference light 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. In some cases, the stimulated luminescent light emitted from the stimulable phosphor sheet can also be used as reference light. In this case, in order to remove the image remaining on the stimulable phosphor sheet 10 that has already been read, an erasing light source (which emits visible light as erasing light) that is normally built into the reading device is used to determine the correction value. It is possible and convenient. Furthermore, the shedding correction method of the present invention is applicable not only to a device that reads the stimulated luminescence light emitted from the stimulable phosphor sheet 10 described above, but also to a device that reads reflected light, transmitted light, etc. emitted from a recording medium carrying image information. It 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 light condenser and correctly read the light carrying image information, thereby making it possible to correctly read the light carrying image information. It becomes possible to accurately reproduce the image information recorded in the .
Further, 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 the drawing]

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 the shading correction according to the method of the present invention. DESCRIPTION OF SYMBOLS 10... Stimulative phosphor sheet, 13... Laser beam, 14... Optical deflector, 15... Stimulated luminescent light, 16... Light collector, 16a... Incident end face of light collector, 16b... ...Emission end face of light condenser, 17...Photometer, 20...Log amplifier, 22...A/D converter, 24...Shading correction circuit, 30...
. . . Correction value calculation circuit, 31 . . . Memory, ₃₂ . . . Random component creation circuit, S .

Claims (1)

[Claims] 1. Scanning a recording medium on which image information is recorded with a light beam to obtain light containing the image information, and condensing this light by a condenser having an incident end face extending along the beam scanning direction, In an image information reading device that uses a photodetector connected to an output end face of the light condenser to detect and obtain a digital read signal, prior to reading the light, shading of the light condenser in the beam scanning direction is performed. The characteristics are determined in advance, and when reading the light, the read signal is digitally corrected according to the shading characteristics so as to eliminate changes in the output of the photodetector due to shading, and the corrected read signal is further randomly corrected. A shading correction method in an image information reading device characterized by adding a component.