JPH03227168A - Jitter correction method - Google Patents

Abstract

PURPOSE:To obtain a reproduced picture without distortion by applying one correction only at reading and recording of a series of picture while only obtaining jitter at reading and correcting it at recording in the lump. CONSTITUTION:A picture reader 10 detects a timing when a light beam 17 crosses detectors 31, 32 and a jitter detection circuit 33 obtains a read jitter signal SJI representing the main scanning speed for each main scanning, outputs the signal synchronously with a picture signal SD to provide only a jitter measuring function. A photosensitive sheet 51 is fed in a direction of Y2 in a picture recorder 50. A beam 53 of a laser light source 52 transmits through an acousto-optic modulator 54 and subject to intensity modulation based on the picture signal SD and reflected and deflected in a polygon mirror 19 driven at a high speed by a motor 55. Then the light is made incident to the sheet 51 via a lens 57 and a mirror 58, subjected to repetitive main scanning in the direction X2 and the picture signal SD is reproduced or recorded. The read jitter signal SJI is inputted to a correction clock circuit 61, in which a correction clock CA is obtained and optical modulator 62 is driven based on the picture signal SD in the timing CA. Since the mirror 56 is driven at a high speed, jitter is less and neglected in the recorder 50 and a reproduced picture is obtained with high quality.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention provides an image signal that is obtained by two-dimensionally scanning a recording sheet on which an image is recorded with a light beam deflected by an optical deflector. It relates to an image reading and recording method in which an image is reproduced and recorded on a photosensitive sheet by scanning the photosensitive sheet two-dimensionally with a second light beam modulated based on The present invention relates to a jitter correction method for correcting.

(Prior art) A recording sheet on which an image is recorded is scanned with a light beam to obtain an image signal, this image signal is subjected to image processing, and the light beam is modulated based on the image signal subjected to image processing. 2. Description of the Related Art Systems that scan a photosensitive sheet using a photosensitive sheet and reproduce and record images on the photosensitive sheet are used in various fields.

For example, recording an X-ray image using a low gamma X-ray film designed to be compatible with subsequent image processing;
The X-ray image is read from the film on which it is recorded, converted into an electrical signal, and after image processing is performed on this electrical signal (image signal), the contrast is reproduced as a visible image on a photosensitive sheet. A system that can obtain reproduced images with good image quality performance such as sharpness and graininess has been developed (see Japanese Patent Publication No. 81-5193).

In addition, the applicant has proposed radiation (X-rays, α-rays).

When irradiated with β rays, γ rays, electron beams, ultraviolet rays, etc., a part of this radiation energy is accumulated, and then when irradiated with excitation light such as visible light, stimulable fluorescence exhibits stimulated luminescence depending on the accumulated energy. A radiation image of a subject such as a human body is photographed and recorded on a sheet of stimulable phosphor using a stimulable phosphor, and this stimulable phosphor sheet is scanned with excitation light such as a laser beam. The resulting stimulated luminescent light is read photoelectrically to obtain an image signal, and based on this image signal, a radiation image of the subject can be recorded on recording materials such as photographic materials, CRTs, etc. A radiation image recording and reproducing system that outputs a visual image has already been proposed (Japanese Patent Application Laid-Open No. 1983-1989)
No.-12429, No. 5B-11395.

No. 55-163472, No. 5B-104645, No. 55-116340, etc.).

This system has the practical advantage of being able to record images over a much wider range of radiation exposure compared to conventional radiographic systems using silver halide photography. In other words, 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 the amount of radiation exposure over an extremely 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.

In the above-mentioned systems that use X-ray film, stimulable phosphor sheets, etc., and various systems that handle general images, etc., in order to read images and obtain image signals, an X-ray film on which the image is recorded is used. A light beam scans a stimulable phosphor sheet or other recording sheet,
The light representing the image obtained by this scanning (e.g.
(light transmitted through or reflected from an X-ray film, stimulated luminescence emitted from a stimulable phosphor sheet, etc.)
An image reading device is used that receives the light with a photodetector to obtain an image signal. Further, in order to obtain a visible image based on an image signal, an image recording apparatus is used that scans a photosensitive sheet such as a photosensitive film for image recording with a light beam whose intensity is modulated based on the image signal.

In the image reading device, image recording device, etc., a light deflector such as a galvanometer mirror or a rotating polygon mirror is used to scan a light beam onto a recording sheet or a photosensitive sheet.

However, when the above-mentioned optical deflector is used, the speed at which the deflected light beam scans the recording sheet or photosensitive sheet fluctuates, resulting in so-called jitter, which causes the image signal carried by the image reading device to read the image. In some cases, images reproduced and recorded on a photosensitive sheet in an image recording apparatus or an image recording apparatus are distorted.

In order to correct this jitter and eliminate image distortion, photodetectors that detect the light beam are placed at the starting and ending points on the scanning line.
The time required for main scanning between these photodetectors is measured, and the period of the clock is slightly changed so that the same number of clocks enters each time. Methods used for the timing of pickup and the timing of modulation of the light beam of the image recording device are adopted (for example, Japanese Utility Model Publication No. 82-8017,
(See Japanese Patent Application Laid-Open No. 60-48659).

(Problem to be Solved by the Invention) However, with the above method, a time lag occurs between detecting jitter and correcting it. The problem is that it cannot be applied unless the change in is periodic.

Furthermore, when a reproduced image is obtained using an image recording device based on an image signal obtained by an image reading device, when the jitter occurring in the image reading device and the jitter occurring in the image recording device itself becomes a problem, Conventionally, it has been necessary to provide both an image reading device and an image recording device with a jitter correction function.

In view of the above circumstances, the present invention provides a series of image reading and reproducing methods in which an image is read to obtain an image signal and a reproduced image is obtained based on the image signal. In addition, even if jitter in both the image reading device and the image recording device is a problem, distortion can be eliminated by performing jitter correction only once. It is an object of the present invention to provide a jitter correction method that can obtain a reproduced image with no noise.

(Means for Solving the Problems) The jitter correction method of the present invention includes two-dimensionally scanning a recording sheet on which an image is recorded with a light beam deflected by an optical deflector, and the image obtained by the scanning. A second light beam modulated based on the image signal is scanned two-dimensionally on the photosensitive sheet to reproduce and record the image on the photosensitive sheet. In the image reading and recording method,
At the time of reading to obtain the image signal, a read jitter signal representing jitter caused by the optical deflector is determined together with the image signal, and at the time of recording to reproduce and record the image, the jitter at the time of read is determined based on the read jitter signal. The present invention is characterized in that the second light beam is modulated at corrected timing.

(Function) The jitter correction method of the present invention does not correct jitter at the time of reading, but only obtains a read jitter signal representing the jitter that occurred during the reading, and when recording, based on the read jitter signal, the jitter correction method performs the jitter correction. Jitter can be corrected even if the jitter fluctuates during reading, and even if it is necessary to correct jitter during recording, jitter correction can be performed only once. This will suffice.

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

FIG. 1 is a schematic configuration diagram of an example of an image reading device. Here, an example of an image reading device that obtains an image signal by reading a radiation image stored and recorded on the above-mentioned stimulable phosphor sheet will be described.

A radiation imaging device (not shown) irradiates a subject with radiation, and the radiation that has passed through the subject is irradiated onto a stimulable phosphor sheet, whereby a radiation image of the subject is stored and recorded on the stimulable phosphor sheet. The stimulable phosphor sheet on which the image has been stored is stored in the image reading device 10.
is set in the specified position.

The stimulable phosphor sheet 11 set at a predetermined position is transported (
sub-scanning). On the other hand, a light beam 17 emitted from a laser light source 16 is reflected and deflected by a rotating polygon mirror 19 that is driven by a motor 18 and rotates at high speed (for example, 200 rpm) in the direction of arrow z1. The light enters the sheet 11 while changing its direction, and is repeatedly scanned in the main direction in the direction of arrow X1, which is substantially perpendicular to the direction of sub-scanning (direction of arrow Y1). From the point of the sea htt that is irradiated with one light beam, stimulated luminescence light 22 is emitted in an amount corresponding to the accumulated and recorded X-ray image information, and this stimulated luminescence light 22 is guided by the light guide 23. is guided and photoelectrically detected by a photomultiplier (photomultiplier tube) 24. The light guide 23 is made by molding a light guiding material such as an acrylic plate, and has a linear entrance end surface 2.
3a is arranged so as to extend along the main scanning line on the stimulable phosphor sheet ll, and the emission end surface 23b is formed in an annular shape.
The light-receiving surface of the photomultiplier 24 is coupled to. The stimulated luminescent light 22 entering the light guide 23 from the input end surface 23a travels through the interior of the light guide 23 through repeated total reflection, exits from the exit end surface 23b, is received by the photomultiplier 24, and is converted into a radiographic image. Expressing stimulated luminescence light 2
2 is converted into an electrical signal by a photomultiplier 24.

The analog signal S^ output from the photomultiplier 24 is logarithmically amplified by the log amplifier 25 and then
The signal is input to the D converter 26 and sampled at equal time intervals to obtain a digital image signal SD. This image signal SD is sent to an image processing device (not shown), where appropriate image processing is performed on this image signal So, and then sent to an image reproduction device, which will be described later, to reproduce and display a visible image based on the image signal So. .

Here, the sampling interval when the image signal is sampled in the A/D converter 26 will be explained. The sampling intervals are preferably equal intervals in the main scanning direction on the stimulable phosphor sheet ll. However, mainly due to uneven rotation of the motor 18, the rotating polygon mirror 1
The speed of the main scanning of the light beam 17 differs for each main scanning by each mirror surface of 9. Therefore, here, the timing of A/D conversion is determined using a clock consisting of a pulse train of a constant period, so the sampling interval is determined by the accumulation They are not spaced at regular intervals on the fluorescent phosphor sheet 11, but are spaced at different intervals for each reflecting surface of the rotating polygon mirror. Therefore, the digital image signal So after A/D conversion contains image distortion due to jitter. However, this image reading device IO does not have a function to correct this distortion, but only has a function to measure jitter as described below.

That is, this image reading device 10 is equipped with photodetectors 31 and 32 at the start and end of main scanning, respectively, and the light beam 1
7 crosses each photodetector 31.32 is detected by each photodetector 31.32, and the jitter detection circuit 33
is input. The jitter detection circuit 33 determines a reading jitter signal SJI representing the main scanning speed for each main scanning based on the timing of this detection, and outputs it from the image reading device 10 in synchronization with the image signal SD.

FIG. 2 is a schematic configuration diagram of an example of an image recording device.

A photosensitive sheet 51 on which an image is recorded by a light beam 53 is set at a predetermined position in the image recording device 50, and is conveyed (sub-scanned) in the direction of arrow Y2 by a conveying means (not shown). On the other hand, a light beam 53 emitted from a laser light source 52 is intensity-modulated based on an image signal So by passing through an AOM (acousto-optic modulator) 54, and is then powered by a motor 55.
It rotates at high speed (8000 rpm) in the direction of arrow z2.
(2) It is reflected and deflected by the rotating polygon mirror 19, and after passing through the focusing lens 57, the optical path is changed by the mirror 58, and it enters the sheet 51 repeatedly in the direction of the arrow X2, which is approximately perpendicular to the sub-scanning direction (the direction of the arrow Y2). Main scanning is performed, whereby an image based on the image signal SD is reproduced and recorded on the sheet 51.

Here, in the image reading device shown in FIG.
The read jitter signal SJ+ obtained during reading is input to the correction clock circuit 61. In this correction clock circuit 61, the rotating polygon mirror 56 is operated so that a distortion-free image is reproduced and recorded on the sheet 51 based on the read jitter signal SJI.
A corrected clock C^ with a slightly changed clock frequency is obtained for each reflecting surface. This correction clock C^ is AOM
The signal is input to the drive circuit 65. The AOM drive circuit 65 drives the AOM 54 based on the image signal So at the timing of each clock pulse of the correction clock C^. Note that since the rotating polygon mirror 56 of this image recording device rotates at a high speed of 8000 rpm, the degree of jitter is small, and therefore, jitter occurring in the image recording device is ignored here.

Next, an example will be described in which jitter correction is performed in consideration of jitter in the image recording apparatus. In the above example, the amount of jitter was determined for each scan of the image reading device, but since the jitter is largely due to uneven rotation of the motor that rotates the rotating polygon mirror, one rotation of the rotating polygon mirror was considered as one period. It is often repetitive.

Therefore, an example of correcting the amount of jitter for each reflecting surface of a rotating polygon mirror will be described below.

In the image reading apparatus shown in FIG. 1, first, the rotary polygon mirror 19 is rotated by the motor 18 in the absence of the sheet 11, and the light beam 17 repeatedly performs main scanning.

At this time, the timing at which the light beam 17 crosses the photodetector 31.32 is detected by the photodetector 31.32 and input to the jitter detection circuit 33. This jitter detection circuit 33
Then, each main scanning speed for each reflecting surface of the rotating polygon mirror 19 is determined and stored in the jitter detection circuit 33.

FIG. 3 is a diagram showing an example of each main scanning speed determined as described above.

The white circles in the figure represent the main scanning speeds determined as described above and stored in the jitter detection circuit 33, and the numbers written on each white circle are the numbers of each reflective surface of the rotating polygon mirror 19. be. However, for example, there is no need for information regarding which reflecting surface the number 1 physically corresponds to, and the number 1, 2, . It is sufficient to know that the reflecting surfaces reflect and deflect the light beam 17 in this order.

As mentioned above, the cause of jitter (variation in main scanning speed) is often due to the influence of rotational unevenness. In this case, as shown in this figure, jitter is caused by one rotation of the rotating polygon mirror 19 as one period. Changes in an approximately sinusoidal waveform.

After the above preparations have been made, the stimulable phosphor sheet 11 is scanned by the light beam 17 as described above, and an analog image signal SA is obtained. After passing through the log amplifier 25, it is sampled by the A/D converter 2B. be done.

At this time, before the stimulable phosphor sheet 11 is conveyed onto the main scanning line, the timing at which the light beam 17 crosses each of the photodetectors 81 and 32 is detected and input to the jitter detection circuit 33 in the same manner as described above. The data is compared with the main scanning speed data (jitter data) for each reflecting surface stored in the jitter detection circuit 33, and it is determined by which number of reflecting surfaces the light beam (7) is currently being reflected and deflected. A surface synchronization signal indicating whether the

An example of how to obtain this surface synchronous signal will be explained using FIG.

It is assumed that the broken line shown in the figure is a pattern (referred to as a "second pattern") of the main scanning speed of the light beam 17 currently reflected and deflected from each reflecting surface.

At this time, the main scanning speed pattern (solid line in the figure; referred to as the "first pattern") stored in the jitter correction circuit 33 is compared with the second pattern, and then the first pattern is Shift one scale bone (-reflection surface) in the direction of the arrow shown and compare in the same way, and then shift another scale bone and compare. By comparing the patterns while shifting by seven in this way, the shift amount with the highest correlation between the first pattern and the second pattern can be determined. In Figure 3, when the first pattern is shifted by two scales (two reflective surfaces) to the right in the figure,
The first pattern and the second pattern almost match and are determined as the shift amount with the highest correlation.

By determining the shift amount with the highest correlation in this way, the numbers 1, 2, etc. of the reflecting surfaces that are actually reflecting and deflecting the light beam 17 are determined based on this shift amount. . . , 6 is found, and a surface synchronization signal is obtained.

The signal representing the main scanning speed (jitter) for each reflective surface of the rotating polygon mirror and the surface synchronization signal (herein collectively referred to as the reading jitter signal S Jl') obtained in this way are digitalized. It is output in synchronization with the image signal So.

FIG. 4 is a schematic diagram of another example of the image recording apparatus. Components that are the same as those of the image recording apparatus shown in FIG. 3 are given the same numbers as those shown in FIG. 3, and their explanations will be omitted.

Photodetectors 62 and 63 are provided at the start and end of the main scan, and a pulse signal representing the timing at which the light beam 53 passes through these photodetectors 62 and 63 is input to a jitter detection circuit 64. In the jitter detection circuit 64, a recording jitter signal (including the surface synchronization signal) SJ2 representing the amount of jitter is obtained in the same manner as in the image reading apparatus described above, and is inputted to the correction clock circuit 81'. This correction clock circuit 6
1' is a reading jitter signal S obtained by the image reading device;
1' is also input, and in this correction clock circuit 61', 2
By combining the two jitter signals SJI r SJ2, a corrected clock C^' whose clock frequency is slightly changed for each reflecting surface of the rotating polygon mirror 5B is obtained so that a distortion-free image is reproduced and recorded on the C) 51. . This correction tarot C
^' is input to the AOM drive circuit 65. The AOM drive circuit 65 drives the AOM 54 based on the image signal So at the timing of each clock pulse of the correction clock C^.

In this way, in the image recording device 50', this image recording device 5
In addition to correcting the jitter caused by the zero itself, the jitter caused by the image reading device 10 (see FIG. 1) is also corrected, and an undistorted image is reproduced and recorded on the photosensitive sheet 51.

In the above embodiment, a photodetector was provided at both the start and end of the main scan to determine the jitter. The jitter may be determined based on the timing at which the light beam passes through the photodetector.

Further, in each of the above embodiments, a case has been described in which a rotating polygon mirror is used as an optical deflector, but it goes without saying that the present invention is similarly applicable to a case where a galvanometer mirror or the like is used as an optical deflector.

(Effects of the Invention) As explained in detail above, the jitter correction method of the present invention only determines jitter during reading and performs jitter correction all at once during recording, so that jitter is not regular during reading. This jitter can be corrected even if it fluctuates, and a reproduced image without distortion can be obtained by performing jitter correction only once in a series of image reading and recording. A system using this method requires only one jitter correction means, making it possible to simplify the system and reduce costs.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram of an example of an image reading device, FIG. 2 is a schematic configuration diagram of an example of an image recording device, and FIG. 3 shows each main scanning speed for each reflective surface of a rotating polygon mirror. FIG. 4 is a schematic configuration diagram of another example of the image recording apparatus. 10... Image reading device 1B... Laser light source 1
9... Rotating polygon mirror 22... Stimulated luminescence light 26
...A/D converter 31.32...Photodetector 3
3... Jitter detection circuit 34... Memory circuit 50,
50'... Image recording device 51... Photosensitive sheet 52... Laser light source 5
4...AOM (acousto-optic light modulator) 5B...Rotating polygon mirror 81, 61'...Correction clock generation circuit 62...A
OM drive circuit 83.84...Photodetector B5...
Jitter detection circuit 0 Figure 8-t Figure 2

Claims (1)

[Claims] (1) Two-dimensionally scanning a recording sheet on which an image has been recorded with a light beam deflected by an optical deflector and photoelectrically reading the light representing the image obtained by the scanning to obtain an image signal; In an image reading and recording method in which a second light beam modulated based on the image signal scans a photosensitive sheet two-dimensionally to reproduce and record the image on the photosensitive sheet, during reading to obtain the image signal. , obtain a read jitter signal representing jitter caused by the optical deflector together with the image signal, and when recording to reproduce and record the image, calculate the jitter at the time of correction of the jitter during reading based on the read jitter signal. A jitter correction method characterized by modulating two light beams.