JPS6186721A - Correcting coefficient determining method in scanning speed variation correcting method - Google Patents

Abstract

PURPOSE:To always select the optimum value,, by successively changing the value of an optical coefficient and observing the degree of correction while reading operations are performed by means of an optical beam whose speed is forcedly changed by using a correcting coefficient determining sheet and using the value when the correction is the best as the value of the correcting coefficient. CONSTITUTION:A correcting coefficient determining sheet 4 is scanned with an optical beam 2 to which scanning speed variation is forcedly given and a correcting signal, h1=k.h, is formed by multiplying the optical beam scanning speed signal (h) by an optional coefficient (k). Then a corrected reading signal s1 is found by calculating the correcting signal h1 and a reading signal obtained as a result of the scanning the sheet 4 and a signal part s2 of only noise component caused by the forcedly given speed variation is extracted from the signal s1. Thereafter, the value of the (k) when the value of the signal s2 becomes the smallest is found by means of a feedback system in which the value of the (k) is successively changed in accordance with the value of the extracted signal s2 and the value is determined as a prescribed correcting coefficient K. Therefore, the optimum value can be determined always.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to scanning of a light beam based on a read signal S obtained by scanning a light beam on a reading object via a scanning means such as a galvanometer mirror. The present invention relates to a method for determining the value of a correction coefficient used when removing noise components caused by speed fluctuations.

More specifically, the corrected read signal 81 is calculated by calculating the read signal S and a correction signal H1=K-H formed by multiplying the signal H regarding the scanning speed of the light beam by a predetermined correction coefficient K. The present invention relates to a method for determining the value of the predetermined correction coefficient in a scanning speed fluctuation correction method to be sought, and in particular, to a method that can be suitably applied to a reading operation of a stimulable phosphor sheet in a radiation image information recording and reproducing system. .

(Technical Background of the Invention and Prior Art) When a certain kind of phosphor is irradiated with radiation (X-rays, α-rays, β-rays, γ-rays, electron beams, ultraviolet rays, etc.), a part of this radiation energy is emitted into fluorescent light. It is known that when this phosphor accumulates in the body and is irradiated with excitation light such as visible light, the phosphor exhibits stimulated luminescence in response to the accumulated energy. The fluorescer that shows this is called a storage fluorophore.

Using this stimulable phosphor, radiation image information of a subject such as a human body is recorded on a -H sheet-shaped stimulable phosphor, and this stimulable phosphor sheet is scanned with excitation light such as a laser beam. to generate stimulated luminescent light, and photoelectrically convert the obtained stimulated luminescent light into
The applicant has already proposed a radiation image information recording and reproducing system that reads an image signal to obtain an image signal, and outputs the radiation image of the subject as a visible image to a recording material such as a photographic light-sensitive material, a CRT, etc. based on this image signal. . (JP-A-55-12429, JP-A-56-11395, etc.) In such a radiation image information recording and reproducing system, as described above, a stimulable phosphor sheet on which radiation image information is accumulated and recorded is exposed to light. A reading operation is performed in which an image signal (read signal) is obtained by scanning with a beam, and the light beam scanning in the reading operation is performed by deflecting the light beam by a scanning means such as a galvanometer mirror.

However, when scanning by deflecting a light beam using a scanning means such as a galvanometer mirror, the scanning of the light beam may be affected due to fluctuations in the movement speed of the scanning means, for example, fluctuations in the oscillation speed of the galvanometer mirror. The speed (the speed at which the light beam travels over the object to be read) may vary. If the scanning speed fluctuates in this way, the scanning light energy per unit area will change, and the read image signal obtained by the scanning will include an adverse effect due to the fluctuation, making it impossible to perform highly accurate reading operations. .

One method for eliminating such inconveniences due to scanning speed fluctuations is to scan a light beam such as a laser beam that is deflected by a scanning means such as a galvanometer mirror and scanned over a reading target such as a stimulable phosphor sheet. The speed is detected and a signal H related to the scanning speed is obtained, and this speed signal H
is multiplied by a predetermined correction coefficient K to form a correction signal H1,
Scanning that removes noise components caused by fluctuations in the light beam scanning speed in the read signal S by calculating this correction signal H1 and the read signal S obtained by scanning the read target with the light beam. There is a speed fluctuation correction method, which was developed in 1982 by the applicant with Nobutaka Fukai as the inventor.
A patent application was filed on September 12th.

In this method, there is a certain correspondence between fluctuations in the scanning speed of the light beam and noise in the read signal S caused by this fluctuation, and therefore a correction coefficient corresponding to this correspondence is prepared. Then, the signal H related to the scanning speed is multiplied by this correction coefficient K to form a correction signal H1, and this correction signal Hs is applied to the read signal S, for example, by multiplying or adding both signals S and Hl. This is based on the viewpoint that noise components caused by fluctuations in the set meal speed can be removed from the read signal S by performing calculations such as the following.

For example, when scanning a stimulable phosphor sheet, as shown in Figure 2, the laser beam energy (hereinafter simply referred to as energy or laser beam energy) per unit irradiation area when stimulating luminescent light is generated by laser beam irradiation. ) and the amount of stimulated luminescence (energy x time),
Therefore, assuming that the residual energy is constant, the energy is inversely proportional to the speed, and the amount of stimulated luminescence is determined by the read signal S.
Therefore, the relationship between this laser beam energy and the amount of stimulated luminescence corresponds to the relationship between the above-mentioned scanning speed fluctuation and the noise component in the read signal S caused by this fluctuation). .

The relationship is as shown in B and C (Songs A, B, and C each represent the case of different types of stimulable phosphors).

For example, when scanning a stimulable phosphor sheet having the characteristics shown by curve A using a laser beam with energy E1, when the scanning speed of the laser beam changes, the laser beam energy changes in inverse proportion to the scanning speed of the laser beam. The amount of stimulated luminescence light changes by the amount obtained by multiplying the slope α at point P, which is the energy El, by the amount of change in energy. Note that the energy change based on this laser beam speed change is within an extremely narrow range centered on El in the graph of Figure 2, so the energy change can be calculated by multiplying the slope α at point P, which is the center of the change, by the amount of change. It is possible to almost accurately calculate the amount of change in the amount of emitted light.

Therefore, a correction coefficient K corresponding to this inclination α is prepared, and the scanning speed signal H of the laser beam is multiplied by the correction coefficient H.
1 and calculate the read signal S and this correction signal H1 appropriately. Therefore, for example, when the scanning speed changes in the increasing direction, the scanning speed signal H also increases, and the laser beam energy decreases and the read signal Since the amount of stimulated light emission also decreases, the noise component caused by laser noise can be removed from the read signal S by adding or multiplying both signals to compensate and correct this decrease. It is.

The value of the above correction coefficient indicates the correspondence between the scanning speed fluctuation and the resulting reading signal fluctuation, so it generally takes a different value depending on the reading target, scanning conditions, etc. For example, when the object to be read is a stimulable phosphor sheet, as shown in FIG. Since the values are different, the value of the correction coefficient K is also different accordingly.

However, in order to implement the above method, it is first necessary to set a value for the correction coefficient, and the degree of correction (removal of noise components) depends on whether the value of K is set optimally. The value of K needs to be set as optimally as possible. Furthermore, if the scanning reading device used to determine the correction coefficient K using the above method is one that is not prone to accidental scanning speed fluctuations, there is a problem in that a long period of experimentation is required to determine the correction coefficient. Ta.

(Object of the Invention) In view of the above circumstances, an object of the present invention is to provide a correction coefficient determination method that can efficiently determine the optimum value for the correction coefficient in the above-described traveling speed fluctuation correction method. .

(Structure of the Invention) In order to achieve the above object, the method according to the present invention first inputs a noise signal that causes a light beam scanning speed fluctuation to the scanning means in the scanning speed fluctuation correction using the correction coefficient K as described above. By this, the short tube speed of the light beam is forcibly varied, the scanning target for determining the correction coefficient is scanned with the light beam whose scanning speed has been forcibly varied, and the scanning speed of the light beam of this scanner is detected. Find the speed signal, multiply this signal by an arbitrary coefficient k, and get the correction signal h = k, h
A read signal S obtained by scanning the read target for determining the correction coefficient with the original beam and this correction signal h1 are calculated to obtain a corrected read signal S1, and from this corrected read signal S1 the above The above-mentioned signal S2 is extracted by a feedback method in which a signal portion containing only noise components due to the forcibly applied light beam scanning speed variation is extracted, and the value of the above-mentioned constant is sequentially changed according to the extracted value of the signal S2. The present invention is characterized in that the value of k at which the value of k is the smallest is determined, and that value is determined as the value of the predetermined correction coefficient.

(Embodiments) Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of the method according to the present invention, which is embodied as a method applied when scanning and reading a stimulable phosphor sheet in the radiation image information recording and reproducing system described above. This is what I did.

First, an embodiment of a scanning speed fluctuation correction method, which is a premise of the method according to the present invention, will be described with reference to FIG.

In the system shown in FIG. 1, a laser beam 2 emitted from a light source 1 is deflected by a scanning means 3 consisting of an optical deflector such as a galvanometer mirror to scan a stimulable phosphor sheet 4 to be read. The scanning speed is forcibly changed, and the stimulated luminescence light emitted from the sheet 4 is photoelectrically read by a photodetector 5 such as a photomultiplier, and the read signal S (in this embodiment, a photodetector) is obtained. This is a method of removing noise components caused by fluctuations in the scanning speed of the laser beam 2 used for the above scanning from the read signal S, which is a signal obtained by logarithmically converting the signal SO output from the detector 5 using a logarithmic converter 6. First, in order to detect the scanning speed of the laser beam 2 while scanning the sheet 4 and obtain a signal 1-1 related to the speed, a part of the light beam 2 is taken out by the half mirror 7, and this is reflected by the reflection mirror 8. The synchronous light 9 is reflected by the scanning means 3 and emitted as a synchronous light 9.
is incident on the grid 10, the grid 10
outputs a light pulse from the photodetector 11.
Based on this electric pulse, the frequency (period)-voltage converter 12 outputs a signal H (in this embodiment, the frequency-voltage converter 12 outputs a signal H regarding the scanning speed). Then, in order to multiply this speed signal H by a predetermined correction coefficient K to form a correction signal ratio = H, the speed signal H is outputted by the variable amplifier 13. The read signal is amplified by an amplification factor to output a correction signal 1-11=K-H, and further, the above read signal S and this correction signal H1 are calculated to obtain a corrected read signal S1. S
= log So + the above correction signal H1 to obtain the corrected read signal S 1 = S + H1 = log So +
It is constructed so that H can be found.

The manner of calculation for obtaining the corrected read signal S1 is not necessarily limited to the above-mentioned manner, and may be obtained by calculating, for example, in the manner described below.

One aspect is an operation that does not use the logarithmic converter 6 in FIG.
The corrected read signal S1= So +Ht =
This is to calculate So + KH.

Another aspect is an operation in which a logarithmic converter (not shown) is added to logarithmically convert the output signal HO from the frequency-voltage converter 12 in FIG.
is H=log H.

Therefore, the corrected read signal 81 is 5t=S+H1
It is calculated as = 7ogSo + Klogl-1o.

Yet another embodiment is to add the signal H1 from the signal S without using the logarithmic converter 6 in FIG.
The signal S and the signal H1 are multiplied, and in this embodiment, the correction method read signal Sl is 5t=SXHt=+
It is calculated as 5oxKH.

Here, if the scanning speed fluctuation is set to about 1 to 2 inches, the calculation formulas for calculating the correction method read signal S1 in each of the above modes become mutually approximate formulas, and therefore, almost the same S1 is obtained no matter which mode is used. be able to.

Next, an embodiment of the method for determining the value of the correction coefficient in the scanning speed fluctuation correction method as described above will be described with reference to FIG. 1 as well.

Let us now calculate the correction coefficient K for an arbitrary combination of stimulable phosphor and laser beam energy.

First, a sheet (y-t for determining a correction coefficient) 4 comprising a stimulable phosphor of the same type as the stimulable phosphor described above is prepared,
This sheet 4 is read by scanning a laser beam with the same energy as the laser beam energy described above. In this case, scanning speed fluctuations are forcibly applied to the laser beam 2 that performs scanning. In this embodiment, a driver 15 drives a galvanometer mirror 3 that scans a laser beam 2.
A noise signal 17 having a frequency sufficiently higher than that of the drive signal 16 is input together with a normal galvanometer drive signal 16, and the noise signal 17 is configured to forcefully apply a scanning speed variation.

Laser beam 2 with forced velocity fluctuations in this way
The correction coefficient determination sheet 4 is scanned, and the read signal S is calculated in the same manner as the scanning speed fluctuation correction method described above to obtain a correction method read signal S1. For example, the signal So output from the photodetector 5 is logarithmically converted to S-5-1O.

On the other hand, the synchronizing light 9 emitted from the galvanometer mirror 3 given the speed fluctuation is transmitted to the converter 1 via the grid 10, the photodetector 11, and the frequency-voltage converter 12.
Let the signal ho output from 2 be a signal related to the traveling speed, and multiply this signal by an arbitrary coefficient k to obtain a correction signal, =
*h is formed in =, and both signals S and hl are added to obtain a correction method read signal Sl = s -1 - hl.

Next, a signal portion S2 containing only noise components caused by the forcibly applied scanning speed fluctuation is extracted from this correction method read signal Sl. Here, the signal portion containing only the noise component caused by the scanning speed fluctuation is not limited to a signal containing only the noise component truly caused by the scanning speed fluctuation, but also includes the sheet 4 that has been read in addition to the noise component. However, this latter information component is a signal component that hardly changes, in other words, the fluctuation is extremely small compared to the fluctuation of the noise component, and therefore the It also includes a signal portion where it is possible to determine from the characteristic value of the signal whether or not the extracted signal contains a noise component.

For example, if a stimulable phosphor sheet whose entire surface is uniformly irradiated with radiation (solid exposure) is used as a correction coefficient determination sheet, the signal related to the information recorded on this sheet will be uniform, and therefore the read signal Any part of S can be treated as a signal containing only noise components due to scanning speed fluctuations.

In this embodiment, the above solid exposure sheet is used as the correction coefficient determination sheet, and therefore the correction method read signal S1
If only the frequency band of the noise signal 170 inputted to the galvanometer mirror 3 is extracted, the extracted signal S2 is a signal portion containing only noise components caused by the forced scanning speed fluctuation, In order to do this, a bandpass filter 20 is used that passes only the frequency band of the noise signal input to the galvanometer mirror 3. Once the signal S2 containing substantially only noise components is extracted in this way, this A characteristic value representing the magnitude of the noise component of the signal S2, for example, the root mean square value of the signal S2 (
The value of k when the characteristic value of the signal S2 is the smallest is determined by the feedback equation in which the value of the predetermined fik is sequentially changed according to the magnitude of the RMS), and this value is used as the value for the predetermined correction coefficient. Once determined, it is stored and recalled for use the next time with the same stimulable phosphor and laser beam energy combination.

In this embodiment, the extracted signal S2 is rectified by a rectifier 21, A/D converted by an A/D converter 22 to obtain a digital signal DI, and k is adjusted so that this digital signal D1 becomes smaller. Correction amount determining means 23 to change the value
outputs a digital signal D2, and converts this signal D2 into D/
Any value of k initially set after A conversion (for example, =
0) and repeats feedback to perform the same control under a new k to find k at which Dl becomes the smallest, determine it as a value for a predetermined correction coefficient, and store it. ing.

(Effects of the Invention) As described above, the method according to the present invention multiplies the scanning speed signal H by a predetermined correction coefficient K to form a correction signal H1=K@H, and combines this correction signal H1 and the read signal S. In the method of removing noise components caused by scanning speed fluctuations from the read signal S by calculating
This light beam scanning speed signal is multiplied by an arbitrary coefficient k to form a correction signal hl==k@h, and this correction signal h
A corrected read signal S1 is obtained by calculating the read signal S read by scanning the correction coefficient determination sheet, and from this signal S1, only the noise component caused by the forcibly applied speed fluctuation is calculated. The value of k when the value of the signal S2 becomes the smallest is determined by a feedback method in which the signal portion S2 is extracted and the value of the signal S2 is sequentially changed according to the value of the extracted signal S2, and that value is set to the above-mentioned predetermined value. The correction coefficient is determined as the value of .

That is, the method according to the present invention actually uses a sample (sheet for determining correction coefficients) and performs a reading operation with a light beam to which a clear velocity change is forcibly applied, and sequentially changes the values to perform correction. Since the value of k at which the best correction is made is determined as the value of the correction coefficient by observing the 8 average, it is possible to always determine the optimum value.

In particular, in the method according to the present invention, since a large noise component is included in the read signal S1 or S2 by forcibly changing the scanning speed of the light beam, this noise component can be reduced by changing k. can be clearly understood in a short time, and therefore the optimum value for the correction coefficient can be determined extremely efficiently.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the method according to the present invention, and FIG. 2 is a diagram showing the relationship between the laser beam energy per unit irradiation area and the amount of stimulated luminescence in a stimulable phosphor sheet. .

Claims (1)

[Claims] Detecting the scanning speed of a light beam scanned over the reading object by the scanning means, obtaining a signal H related to the scanning speed, and multiplying this speed signal H by a predetermined correction coefficient K. A correction signal H_1 is formed, and this correction signal H_1
and a read signal S obtained by scanning an object to be read with the light beam, thereby removing a noise component caused by the light beam scanning speed fluctuation in the read signal S. In the speed fluctuation correction method, a reading target for determining a correction coefficient is scanned by a light beam whose scanning speed is forcibly changed by inputting a signal that causes a scanning speed fluctuation to the scanning means, and this scanning The scanning speed of the light beam in the center is detected to obtain a signal h related to the scanning speed, and this signal h is multiplied by an arbitrary coefficient k to obtain a correction signal h_1.
A read signal s obtained by scanning the read target for determining the correction coefficient with the light beam and this correction signal h_1 are calculated to obtain a corrected read signal s_1, and from this corrected read signal s_1 the above The above-mentioned signal s_2 is extracted by a feedback method in which a signal portion containing only noise components caused by forcibly applied light beam scanning speed fluctuations is extracted, and the value of the above-mentioned constant k is sequentially changed according to the value of the extracted signal s_2. A correction coefficient determining method characterized in that the value of k at which the value of k is the smallest is determined, and that value is determined as the value of the predetermined correction coefficient K.