JPH0247069A - Optical beam scanner - Google Patents

Abstract

PURPOSE:To easily correct the gradation of an image by so determining a relative position between an acoustic optical light modulator and scanning means as to mainly scan an optical beam emitted form the modulator on a matter to be scanned in a direction that the diameter of the beam is most expanded, and particularly employing an analog filter as correcting means. CONSTITUTION:A radiation image stored and recorded on a storing fluorescent sheet 9 is read by an optical beam scanner for so determining the relative position between an acoustic optical light modulator 3 and a main scanning optical system 5 that the expansion of the diameter of the optical beam 2' from the modulator 3 is in a main scanning direction, and an analog image signal obtained through an optical guide 10 and a photomultiplier 11 is input to an analog filter 22. When the beam diameter of the beam 2' is expanded in the main scanning direction, since the filter 22 has a frequency characteristic to correct a gradation due to the expansion, an imaging for improving the gradation can be omitted in image processing means 25, thereby improving the speed of imaging process.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a light source that generates a light beam, and an acousto-optic light modulator that adjusts or modulates the intensity of the light beam and emits the light beam.
Hereinafter, it will be referred to as AOM. ) and a scanning means for two-dimensionally scanning an object to be scanned with a beam emitted from the AOM.

(Prior Art) Reading a recorded radiation image, converting the image signal into blue, subjecting the image signal to appropriate image processing, and then reproducing and recording the image is carried out in various fields. For example, an X-ray image is recorded using an X-ray film with a low gamma value designed to be compatible with later image processing, and the X-ray image is read from the film on which it is recorded and converted into an electrical signal. By performing image processing on this electrical signal (image signal) and then reproducing it as a visible image in a copy photograph, etc., it is possible to obtain a +Ij raw image with good image quality performance such as contrast, sharpness, and graininess. A system that can do this has been developed (see Japanese Patent Publication No. 61-5193, see 2).

The applicant has also proposed radiation (X-rays, α-rays).

When irradiated with β rays, γ rays, electron beams, ultraviolet rays, etc.9.1, a part of this radiation energy is accumulated, and then when excitation light such as a photoreceptor is irradiated, stimulated luminescence occurs according to the accumulated energy. Using a stimulable phosphor (stimulable phosphor),
A radiation image of a subject such as a human body is photographed and recorded on a 1μ sheet of stimulable phosphor, and this stimulable phosphor sheet is scanned with excitation light such as a laser beam to generate stimulated luminescence. A radiation image recording IIg raw system has already been proposed, which photoelectrically reads the stimulated luminescence light to obtain image data, and based on this image data, outputs the radiation image of the subject as a developable image onto recording materials such as photographic light-sensitive materials, CRTs, etc. (Japanese Patent Application Laid-open No. 55-12429, 5B-11395,
No. 55-163472, No. 56-104 [i45,
55-II6340, etc.).

This system has the practical advantage of recording images over a much wider range of radiation exposure compared to conventional radiographic systems using silver halide photography. That is, in a stimulable phosphor, it is recognized that the amount of emitted light that is stimulated to emit light due to excitation after accumulation is proportional to radiation exposure over a very wide range.
Therefore, even if the amount of radiation exposure varies considerably due to various imaging conditions, the amount of stimulated luminescence emitted from the stimulable phosphor sheet can be read by the photoelectric conversion means by setting the reading gain to an appropriate value. By converting the radiation image into an electric signal and using this electric signal to output the radiation image as a visible image to a recording material such as a photographic light-sensitive material or a display device such as a CRT, a radiation image that is not affected by fluctuations in radiation exposure amount can be obtained. be able to.

An image reading device that obtains an image signal by reading an image such as a radiation image recorded on a recording sheet such as the above-mentioned X-ray film or stimulable phosphor sheet, and modulates a light beam based on the image signal obtained by reading the image. However, an image recording device that reproduces and records images on a recording sheet such as a photosensitive film using a modulated light beam usually includes a light source that generates a light beam, and a light source that generates a light beam.
A O that adjusts or modulates the intensity of the light beam and emits it.
A light beam scanning device comprising a scanning means for main scanning Fvl and a recording sheet, which is a scanning object, with a light beam emitted from the AOM and sub-scanning in a direction substantially perpendicular to the main scanning direction. is included.

In the above-mentioned image reading device, the above-mentioned light beam scanning device scans the recording track with a light beam having a substantially constant amount of light, and ζ5. [It reads the light representing the image obtained from the scanning point (stimulated luminescence light emitted from a stimulable phosphor sheet, light transmitted through an X-ray film, or reflected on an X-ray film, etc.) and converts it into an image signal.] It is composed of

Further, in the above-mentioned image recording device, using the above-mentioned light beam scanning device, a light beam is modulated by an AOM based on the image signal scanned by the above-mentioned image reading device, and the modulated light beam is applied onto a recording sheet. is configured to scan and reproduce and record an image on the recording sheet.

(Problem to be Solved by the Invention) When an image based on an image signal obtained from a recording sheet is displayed in the above-mentioned image reading device on, for example, a CRT display device, or when an image is reproduced on a recording sheet in the above-mentioned recording device There has been a problem in that when recording, etc., blurring (decrease in image sharpness and contrast) may occur in a predetermined direction in the displayed or recorded image.Up until now, this degree of blurring has not occurred. However, if blurring occurs in the direction of a predetermined corner, the image becomes difficult to see, and there is also the risk of misjudgment when observing the details of the image.

Therefore, when the inventors pursued the cause of this problem, A.
It turned out that OM was the cause.

A OM divides the light beam into a 0-order beam and a 1st-order beam by interfering a sound wave (usually an ultrasonic wave) with an incident light beam. By changing the intensity of the sound wave, the 0-order beam and the 1st-order beam are separated. The purpose is to adjust or modulate the intensity of the light irradiated onto the recording sheet so that the intensity of the light irradiated onto the recording sheet remains constant, or to temporally modulate the intensity of the light irradiated onto the recording sheet. used in

When sound waves propagate within the AOM, the AOM generates heat. Moreover, the heat is not generated uniformly, but the temperature varies within the AOM.
+i also occurs. 1'11 of this temperature is the structure of AOM, A
Determined by the OM installation method etc. Further, the temperature gradient differs depending on the power (average power over a predetermined period of time) that drives the AOM.

When the temperature inside the AOM changes and a temperature gradient occurs, the 1g degree change directly causes the 'IA IW change,
The temperature gradient causes mechanical strain in the AOM, and this strain causes sufficient refraction of light ([i) inside the AOM, and the AOM also takes on birefringence, so that the AOM
It has been found that the cross section of the light beam emitted from the light beam becomes a substantially oval shape extending in a predetermined direction, and that the image is blurred in the direction of the long sleeve of the oval. Additionally, as a result of experiments, it was found that the fact that the AOM has birefringence is the main reason why the cross section becomes approximately oval.

However, as long as the AOM is used, the occurrence of temperature gradients, distortions, etc. inside the AOM is unavoidable.

The present invention provides the above-mentioned '1 (in view of the circumstances), even if the diameter of the light beam emitted from the AOM spreads in a predetermined direction, the blurring of the image due to the spread in the predetermined direction can be prevented by using an image reading device, an image recording device, etc. [1] It is an object of the present invention to provide a light beam scanning device that can be easily corrected.

(Means for Solving the Problems) The light beam scanning device of the present invention includes a light source that generates a light beam, an acousto-optic sensor (AOM) that adjusts or modulates the intensity of the light beam, and emits the light beam. and an optical beam scanning device comprising scanning means for main-scanning a scanned object with a light beam emitted from the modulator and sub-scanning in a direction substantially perpendicular to the main-scanning direction. The modulator is characterized in that the relative arrangement of the modulator and the scanning means is determined so that the main scanning object is scanned in the direction in which the diameter of the tip beam emitted from the scanning device is widest.

Here, as mentioned above, the direction in which the diameter of the light beam is the widest is the long direction of the beam cross section when the cross-sectional shape of the light beam emitted from the AOM is wide in a specific direction due to heat generation inside the AOM, etc. means. Further, the light beam emitted from AO~1 may be either a zero-order beam or a first-order beam.

The 15 main scanning directions mentioned above refer to Jj directions in which the object to be scanned is temporally continuously scanned.

(Function) In the light beam scanning device of the present invention, the relative arrangement of the AOM and the scanning means is determined so that the main scanning target is scanned in the direction in which the diameter of the destination beam emitted from the AOM is widest. Therefore, the direction in which the diameter of the previous beam was wide is the direction of main scanning, which is scanned continuously in time. Therefore, in the image reading device using this light beam scanning device, continuous analog image signals are obtained in the main scanning direction, so by using an analog filter with appropriate frequency characteristics, the beam diameter can be adjusted. The blur caused by widening in the main scanning direction can be easily captured and IFed in real time.

In addition, in an image recording device using this light beam scanning device, since each pixel arranged in the main scanning direction is recorded continuously in time, the light beam emitted from the AOM is aligned in the main scanning direction. By emphasizing the high frequency components of the analog image signal that drives the AOM using analog filters 9- and 9- before driving the AOM with the intention of widening the image to The image is recorded.

(Example) Examples of the present invention will be described below with reference to the drawings.

FIG. 1 is a perspective view showing an embodiment of a light beam scanning device of the present invention.

This light beam scanning device consists of a laser light source 1 that generates a light beam 2, an AOM 3 that modulates the light beam 2 mounted on a mount 3', and a light beam 2' (0-order beam) emitted from the AOM 3. A scanning optical system 5 (here, only the rotary polygon vL5a is shown) main-scans the recording sheet 4, which is a scanned object, in the Xjj direction with a primary beam), and conveys the recording sheet 4 in the Y direction. It is composed of a sheet conveying means 6 that performs sub-scanning. The scanning optical system 5 and the sheet conveying means 6 constitute the scanning means of the present invention. Here, in the AOM 3, the ultrasonic waves are propagating in the direction of arrow Z shown in the figure. The light beam 2' emitted from the AOM 3 is emitted from the AOM 3 so that the cross-sectional shape of the front beam 2' spreads in the X direction due to the conversion of the ultrasonic energy of the AOM into thermal energy. According to the inventors' experiments, this X direction is A O
Although it varies depending on the structure of M3, the method of attaching AOM3 to mounting plate 3', etc., first select a specific AOM3 and attach it to mounting plate 3'.
Once the method of attachment to ′ is determined, the direction is almost determined.
When the driving power CA of AO~1 (ultrasonic energy propagating in OM, etc.) is changed, the force changes only to a wide extent. The light beam 2' emitted from the AOM 3 passes through the scanning optical system 5 and projects onto the recording sheet 4 (11).

At this time, the beam diameter of the light beam 2' is expanded due to the heat generation of the AOM 3, etc. The axial direction is the main scanning direction (X
The relative arrangement of the AOM 3 and the scanning optical system 5 is determined so that the AOM 3 and the scanning optical system 5 are in the same direction.

FIG. 2 is a perspective view of an embodiment of an image reading and recording apparatus using the light beam scanning device shown in FIG. This image reading and recording device has the functions of an image reading device using the above-mentioned stimulable phosphor sheet and an image recording device that reproduces and records images on a photosensitive film. Components corresponding to those shown in FIG. 1 are labeled with the same symbol.

First, a case where this image reading/recording device is used as an image reading device will be described.

A leading beam 2 of a bundle of parallel rays emitted from a laser light source 1
The beam enters the beam expander 7, is adjusted to a predetermined beam diameter, and then enters the AOM 3.

The zero-order light beam 2' emitted from the AOM 3 passes through a half mirror 8 for monitoring the amount of light, and then enters a rotating polygon mirror 5a rotating in the direction of arrow A, where it is reflected and deflected.

In this embodiment, a scanning optical system 5 is composed of a rotating polygon mirror 5a and a scanning lens 5b. After the reflected and deflected light beam 2' passes through a scanning lens 5b such as an fθ lens, it is conveyed (sub-scanned) in the direction of arrow Y by a sheet conveying means 6 (sub-scanning means) on which a radiation image is accumulated and recorded. )
The stimulable phosphor sheet 9 is repeatedly main-scanned in the main-scanning direction j (direction of arrow X shown in the figure) which is substantially perpendicular to the sub-scanning direction. In other words, two-dimensional scanning is performed by the light beam 2' over the entire surface of the stimulable phosphor sheet 9 by the main scanning and sub-scanning. In addition, in this example, 1150
The rotational speed of the rotary polygon vL5a is determined so that the sheet 9 is main scanned by 400 mi every sec.

The stimulable phosphor sheet 9 scanned by the above scanning emits stimulated light according to the image information accumulated and recorded at each scanning point, and this emitted light is emitted from the main scanning line in the vicinity of the stimulable phosphor sheet 9. The light enters a transparent light guide 10 having an entrance end face 10a formed in the V row from the entrance end face lOa. The light guide IO has an incident end face 10a formed in a planar shape, gradually becomes cylindrical toward the rear end, and is provided on the exit end face with a substantially cylindrical shape at the rear end 10b. It is coupled to a photomultiplier 11. The stimulated luminescence light entering from the input end face 10a is guided to the rear end portion 10b, and is transmitted to the photomultiplier 11 via an optical filter (not shown) that selectively transmits the stimulated luminescence light. In addition, at a position facing the entrance end surface 10a of the light guide 10 across the main and L scan lines,
A reflecting mirror 12 is provided which extends in the main scanning direction and reflects the incident stimulated luminescence light toward the incident end surface 10a. The stimulated luminescent light is converted into an electric signal (analog image signal) Sr in a photomultiplier 11.

Here, as mentioned above, it is determined whether the direction in which the light beam 2' spreads due to heat generation in A OM B or the arrangement of A OM 3 and scanning optical system 5 is determined so that it coincides with the main scanning direction (direction of arrow X). ing.

The light beam 2' reflected by the l\-fmirror 8 is monitored for its light intensity by the photodetector 13, and is passed through the AOM driver 28, which is a driving means for driving the AOM 3, to ensure that the light intensity is constant. A OM 3 is driven so that.

On the other hand, the synchronized beam 15 emitted from the laser light source 14 enters the rotating polygon mirror 5a, is reflected and deflected, and is reflected by the mirror 16.
The beam is reflected by the beam, enters the synchronous beam detector 17, and scans the grid 17a of the synchronous beam detector 17. The grid 17a has a large number of slits 17b lined up in the direction of the scanning path, and the synchronized beam 15 passes backward only when it irradiates the slits 17b.
When irradiating the intermediate position between 7b and slit +7b,
The optical path is blocked by the slit plate 17a. slit +7
The monitor destination that has passed through b enters the light guide 17c, propagates inside the light guide 17c, and enters the photomultiplier 17.
d and is converted into an electrical signal S3. Electrical signal S3
corresponds to the fact that the synchronous beam 15 is intermittently interrupted when scanning over the grid 17a, and becomes a pulse signal (here, a 100 KHz pulse signal) that changes repeatedly. This pulse signal is sent to the A/D converter 23 and used as a sampling timing signal when sampling an analog image signal.

The analog image signal S1 output from the photomultiplier 11 is amplified by the amplifier 21 and then input to the analog filter 22. The analog filter 22 has frequency characteristics such that when the beam diameter of the light beam 2' expands in the main scanning direction, blurring due to this expansion is corrected. This analog filter 22 is designed so that its frequency characteristics can be changed according to the average power for driving the AOM 3 by inputting the output of the AOM driver 28 . Alternatively, a plurality of analog filters may be prepared and used by switching according to the average power.

The image signal Sl', which is output from the analog filter 22 and whose blur has been improved, is sampled and digitized by the A/D converter 23 in synchronization with the sampling timing signal S3. The digital image signal S2 obtained in this way is stored in the storage means 24, and then sent to the image processing means 25 as necessary to undergo necessary image processing. Here, since the analog image signal Sl' outputted from the analog filter 22 is a signal that has already been blurred or sued for, it is necessary to perform image processing on the digital image signal S2 in the image processing means 25 to eliminate the blurring. The speed of image processing can be improved accordingly.

Here, the analog filter 22 will be explained in further detail.

FIG. 3 shows the beam diameter of the light beam 2' and the image signal obtained by scanning the stimulable phosphor sheet 9 with the beam 2' beyond the beam diameter without frequency processing. When the visible image is reproduced and output based on
It is a graph showing the relationship between sharpness [%] and sharpness [%]. As the beam diameter increases, the sharpness decreases almost linearly.

FIG. 4A is a circuit diagram showing an embodiment of an analog filter to correct the blur caused by the deterioration of sharpness, etc., and FIG.
The figure shows the step response characteristics of the circuit shown in Fig. 4A, with the horizontal axis representing the distance (dragon) on the seat 9 (see Fig. 2), and Fig. 4C shows the step response characteristics of the circuit shown in Fig. 4A. FIG. 3 is a diagram showing t and l elements with improved t and l values, with the spatial frequency on the sheet 9 taken as the horizontal axis.

In this embodiment, as described above, the sheet 9 is
Since the main scan is performed at 400 mII in sec and the resulting analog image signal 81' is sampled at 100 KHz, 0.2
It corresponds to sampling at m11 intervals (5 cycles/mi).

The analog filter 22 is configured as follows, as shown in FIG. 4A.

An input terminal 51 to which the analog image signal S1 output from the amplifier 21 is input, and an input terminal 52 of the operational amplifier 52.
a and the same resistance value R- connected in series with each other.
Two resistors 53 and 54 with a resistance of 6.1 kΩ are connected. In addition, a capacitor 5 having a capacitance of QCt -100 pF is connected between the input terminal 52a and the ground line 55.
6 are connected. Further, a capacitor 58 having a capacitance of C2-680pF is connected between a connection point 57 between the resistor 53 and the resistor 54 and one input terminal 52b of the operational amplifier ri52.
b and the output terminal 52c (ie, the output terminal 59 of the analog filter 22) are directly connected.

When this analog filter 22 is manually supplied with an analog image signal S1 having a characteristic H corresponding to the rising characteristic shown in graph E of FIG. 4B, the output of the analog filter 22 has the rising characteristic shown in graph F of FIG. 4B. 'IJ
An analog image signal 81' having corresponding characteristics becomes white.

In other words, when the rise time of the input signal S1 (time from 10% rise to 9096 rise) is expressed in distance (mm) on the sheet 9, TF is -0,0955.
(m+*), and that of the output signal 81' is Tp -
0,0775 (m+s), which is a sufficient improvement. When this characteristic is shown in the spatial frequency domain, as shown in FIG. 4C, the graph E' showing the spatial frequency characteristic corresponding to the human input signal Sl is converted into the graph F' showing the spatial frequency characteristic corresponding to the output signal 81'. Ru. In other words, the human signal Sl (
Graph E) has a characteristic of falling gently from a low spatial frequency region to a high spatial frequency region, but in the output signal 81' (graph F'), the visible image changes around 5 cycles/square. The characteristics of the low spatial frequency region, which has a large influence on characteristics such as contrast and sharpness, are improved so as to be almost flat, and the signals in the unnecessary high spatial frequency region are suppressed, and as a result, the input signal S1 carries The blur in the radiographic image is corrected. This analog filter 2
The characteristics of C2 can be changed by changing the capacitance of capacitor CI+C2 and/or the resistance value of resistor R.

As mentioned above, the alignment between the AOM 3 and the scanning optical system 5 is adjusted so that the beam diameter of the front beam 2' by the AOMB (see Fig. 2) is in the main scanning direction (arrow X direction). The radiation image stored and recorded on the stimulable phosphor sheet 9 is read using a pre-beam scanning device with a predetermined arrangement, and the analog image signal obtained by this reading is input to an analog filter to improve the blurring of the radiation image. By doing so, image processing for improving blur in the image processing means 25 can be omitted, the speed of image processing is improved accordingly, and the time until a visible image is reproduced and output is shortened.

Next, the case where an image is reproduced and recorded using the image reading and recording apparatus shown in FIG. 2 will be described. Duplicate explanations of points common to the case of image reading will be omitted.

When reproducing and recording an image, the first-order light beam 2' output from the AOM 3 is used, and this first-order light beam 2' passes over the photosensitive film 29 conveyed in the direction of the arrow Y.
Images are reproduced and recorded on the photosensitive film 29 by main scanning in the direction. Although the zero-order light beam 2' and the first-order light beam 2' differ in the direction in which they are emitted from the AOMB, they are represented here as having the same optical path for the sake of simplicity. . Due to this difference, the main scanning lines are slightly different between the stimulable phosphor sheet 9 and the photosensitive film 29, but this can be corrected by adjusting the timing of driving the AOMB by one. Furthermore, although the stimulable phosphor sheet 9 and the photosensitive film 29 are drawn to refer to the same sheet, they represent the stimulable phosphor sheet 9 during reading, and the photosensitive film 29 during recording. do.

The image signal S2 read out from the first storage stage 24 is input to the D/A converter 26 and converted into an analog image signal 82'. The analog image signal 82' output from the D/A converter 26 is input to an analog filter 27. The analog filter 27 has a configuration between the analog filter 22 and the circuit H, and its characteristics are changed according to the output of the AOM driver 28 (driving power of the AOM 3). This analog filter 27 prevents the image recorded on the photosensitive film 29 from becoming blurred in the X direction due to the diameter of the primary light beam modulated by the AOM 3 extending in the X direction on the photosensitive film 29. In anticipation of this, frequency processing is performed to enhance the high frequency components of the analog image signal 82' to compensate for this. The analog image signal output from the analog filter 27 is input to the AOM driver 28, and the AOM driver 28 drives the AOM 3 so that an image based on this analog image signal is reproduced and recorded.

In the above embodiment, a system using a stimulable phosphor sheet has been described, but the light beam scanning device of the present invention is not limited to a system using a stimulable phosphor sheet. It goes without saying that the present invention can also be implemented in systems that scan line films to obtain image signals.

Furthermore, in the above embodiment, an example was explained in which the light beam scanning device is applied to an image reading/recording device that can perform both image reading and reproduction/recording, but the light beam scanning device of the present invention can only read images. The present invention can also be applied independently to an image reading device that performs image reading or an image recording device that only performs reproduction and recording of images.

Further, in the above embodiment, the analog filters 22 and 27 are used to perform frequency processing on the image signal so that the blurring of the image is There is no need to use them in combination, and by taking advantage of the fact that the direction of blur is in the main scanning direction, it is possible to perform calculations to compensate for blur in the main scanning direction when image processing is performed by the image processing means 25. Processing may also be performed.

(Effects of the Invention) In the light beam scanning device of the present invention, the relative arrangement of the AOM and the scanning means is determined so that the light beam emitted from the AOM main scans the object to be scanned in the direction in which the diameter is widest. Therefore, it is possible to compensate for blurred images on the product. Especially when using an analog filter as a means of correction,
Image blur can be corrected in real time.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an embodiment of a front beam scanning device of the present invention, and FIG. 2 is a perspective view showing an embodiment of an image reading and recording device using the light beam scanning device shown in FIG. Figure 3 is a graph showing the correspondence between beam diameter and sharpness. Figure 4A is a circuit diagram showing an example of an analog filter. Figures 4B and 4C are shown in Figure 4A. FIG. 3 is a diagram showing step response characteristics and frequency characteristics of the circuit, respectively. ]... Laser light source 2.2', 2'... Destination beam -3... AOM (η optical light modulation 'ri) 4...
Recording sheet 5...Scanning optical system 5a...Rotating polygon mirror 9...Storage phosphor sheet 11...Photomultipliers 22, 27...Analog filter 29...Photosensitive film

Claims (1)

[Scope of Claims] A light source that generates a light beam, an acousto-optic light modulator that adjusts or modulates the intensity of the light beam, and emits the light beam; In a light beam scanning device comprising a scanning means for scanning and sub-scanning in a direction substantially perpendicular to the main scanning direction, the light beam emitted from the modulator moves over the scanned object in a direction in which the diameter of the light beam is widest. A light beam scanning device, characterized in that the relative arrangement of the modulator and the scanning means is determined so as to perform main scanning.