JPS61139158A - Image reading method - Google Patents

Abstract

PURPOSE:To use a high-speed optical deflector to eliminate jitter or the like and lessen influences of a shot noise by obtaining new one-scanning components of data on a basis of data obtained by plural scannings in the main scanning direction. CONSTITUTION:A polygon mirror 6 as the optical deflector is constituted with a mirror having 8 reflecting surface, and this mirror is rotated in a high speed, and a recording material 9 is moved in the running direction by a pitch width each time when the mirror is rotated once. Consequently, main scanning is performed 8 times for one scanning line A in the main scanning direction of the recording material 9, and subscanning is performed thereafter. 8 read data are average to obtain data per one scanning line (new one-scanning components of data). By the averaging processing, the S/N ratio is improved by 8<1/2> times in comparison with the case where one read data is used as it is, and jitter does not become a problem because main scanning may be performed in a high speed.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an image reading method for reading an image by scanning, and particularly relates to a method for reading an image by scanning a light beam.

(Prior Art) There is an image reading device shown in FIG. 3 that reads an image recorded on a recording medium using a light beam, for example, a laser beam. This device changes the direction of the laser from a laser oscillator 1 using mirrors 2 and 3, makes it incident on a beam expander 4, and changes the direction of the laser whose diameter has been expanded by the beam expander 4 again using a mirror 5. The laser beam is incident on the reflective surface of a polygon mirror 6 as an optical deflector, and the laser reflected from the reflective surface is incident on an X-ray transparent film 9 as a recording medium through an fθ lens 7 and a mirror 8 whose focal lengths differ depending on the angle of incidence. Then, the light transmitted through the film 9 is made incident on a photodetector 11 such as a photomultiplier by a photoconductor lO formed by bundling optical fibers, etc., and the output photoelectrically converted by this photodetector 11 is processed as appropriate. By doing this, an image is obtained.

In this device, as the polygon mirror 6 rotates, the laser reflected from its reflective surface scans the film 9 for each reflective surface in the main scanning direction (direction of arrow a). Further, the film 9 is scanned once (1 (ltJ
(once per reflecting surface).

By the way, the reading device described above uses a photodetector 11 to detect the intensity of light transmitted through the film 9 to obtain a signal of the image recorded on the film 9, but the reading accuracy in reading the image using such a method is , that is, S/ of the obtained image signal
The N ratio is affected by shot noise of the photodetection system. The magnitude of this shot noise is proportional to the square root of the frequency bandwidth of the photodetection system. Therefore, in order to alleviate the effects of this shot noise, it is necessary to narrow the bandwidth of the photodetection system, but in order to make it possible to narrow the bandwidth in this way, it is necessary to reduce the scanning speed in the main scanning direction. It is necessary to reduce the rotation speed to a required level, and for this purpose, it is conceivable to reduce the rotation speed of the polygon mirror 6. Further, when a galvanometer is used instead of a polygon mirror, it is possible to reduce the displacement speed.

However, when polygon mirrors are operated at low speeds, jitter becomes a problem, making them unsuitable for scanning systems that require strict uniformity of speed. Therefore, in order to read images of X-ray transparent films, etc., which require high positional accuracy, some kind of position correction means is required.

When using an optical encoder as this position correction means, the mirror 8 in FIG. 3 is replaced with a half mirror, and the encoder 12 detects the light beam transmitted through the half mirror 8. There is a method in which photoelectric conversion is performed by a photodetector 14 via a conductor 13 to obtain a sampling clock, and position correction due to jitter is performed using this clock.

However, since this optical encoder costs ¥1111i, it cannot avoid high cost, and there is also the problem that the sampling clock cannot be changed freely.

(Objective of the Invention) The present invention has been made in view of the above points, and its purpose is to eliminate the need for a shifter etc. by using a high-speed optical deflector, and also to reduce the influence of shot noise and improve the S/N ratio. An object of the present invention is to provide an image reading method that improves the image quality.

(Configuration of the Invention) For this purpose, the present invention is configured to obtain data for one new scan based on each data obtained by scanning in the main scanning direction a plurality of times.

(Example) Examples of the present invention will be described below. In this embodiment, the polygon mirror 6 as an optical deflector shown in FIG. A one-pitch movement in the sub-scanning direction is performed. f! lJ
First, the synchronization relationship between main scanning and sub-scanning is determined so that one sub-scanning is performed for every eight main scannings. Therefore, the recording body 9
For one scanning line A in the main scanning direction, eight main scans are performed, followed by a sub-scan, and then eight main scans are performed for the second scan line. Image reading is performed. Then, data read eight times is averaged to obtain (1) data for each scanning line (data for one new scan). Note that it is not absolutely necessary to use the encoder 12, photoconductor 13, and photodetector 14 shown in FIG.

Therefore, according to this method, by averaging the read data 8 times, the S/N ratio is improved by 8 cubed compared to the case where l (1?il read data is used as is). In addition, since the main scanning can be performed at high speed, the problem of jitter does not occur.

FIG. 1 shows a read data averaging circuit. In this embodiment, the analog signal photoelectrically converted by the photodetector 11 in FIG. Averaging processing is performed using digital signals. The eight memories 21+ to 21g are 8-bit memories 221 to 221 with a capacity of pixels for scanning lines, for storing data read by each of the reflecting surfaces (eight surfaces) of the polygon mirror 6.
22. is a 9-bit adder, 231 and 232 are 10-bit adders, and 24 is an 11-bit adder. Also,
25 is an address controller that controls the addresses of each memory 21+ to 218.

Now, the address controller 25 obtains a clock signal from an encoder (not shown) that detects the rotation of the polygon mirror 6, and stores the read data obtained by main scanning by each surface of the polygon mirror 6 in each of the memories 21+ to 218. Specify the address when doing so. That is, the memory 211 stores the data read from the first surface of the polygon mirror 6, the memory 212 stores the data read from the adjacent second surface, and the same goes to the memory 208.

Then, the data in the two memories 21+ and 212 are added to the memories 213 and 21. adder 2
22, the data in the memories 215 and 216 is added to the adder 223.
and the data in the memories 217 and 21g are added to the adder 224.
Add them sequentially. At this time, the bit becomes 9 due to the carry.
Becomes a bit. Furthermore, the data of adders 221 and 222 are added by an adder 231, and the data of adders 223 and 224 are added by an adder 232. At this time, one bit is further increased due to the carry, resulting in 10 bits. Furthermore, adders 231 and 232
By adding the data in the adder 24, 11-bit data is obtained.

Therefore, the upper 8 bits of the data obtained from the adder 24 can be considered to be the average of the data in each of the memories 211 to 218, so the upper 8 bits are taken out and the data obtained from the current main scan is calculated. It is transferred to the next processing circuit as read data of the scanning line of the book (data for one new scan). After that, averaging processing is performed in the same way for the first scanning line.

As described above, it is possible to obtain the average data of the read data of the same scanning line obtained by scanning eight times, so as described above, the S/N ratio is improved to the fourth power of 8, and the reading accuracy is improved.

This has the same effect as reducing the reading speed to ⅛. Also, no special optical encoder is required. Furthermore, the sampling clock can also be obtained freely from an encoder that detects the rotation of the polygon mirror.

The reading pitch (scanning pitch) is defined as the value obtained by dividing the length of the recording medium by the number of pixels read (pixel pitch), which is further divided by the average number of times (multiple times to obtain one new scanning line). be done. Further, at this time, the scanning spot (beam spot) does not need to be the same as the scanning pitch value. However, if the spot is small, it will also pick up unnecessary high frequency components of the original image itself, that is, noise.
This is determined by the required reading characteristics, since it may cause roughness in the reproduced image, and conversely, if it is too large, it may cause blurring of the image.

Further, in the above-described embodiment, the recording body is moved in the sub-scanning direction after one scan of the recording body is scanned multiple times, that is, substantially the same line is read and scanned multiple times, but the present invention is not limited to this.
The recording medium may be moved continuously.

In addition, each reading scanning line on the recording medium for obtaining data for one new scanning line is substantially all set (Fig. 2 (al.
(see Figure 2 (see C1)), partially set (see Figure 2 fbl), or non-overlapping (see Figure 2 (C1)); It is fine as long as the lines are not far apart.In addition, in FIG. 3, an example is shown in which data for three scans j and l are changed by 1/3 to create data for one new scan.

Note that as the optical deflector, a galvanometer can also be used in addition to the polygon mirror. Further, as the recording medium, in addition to a radiation-transparent film using X-rays or the like, a stimulable phosphor film on which images are stored and recorded may also be used. When used in storage phosphor recording, the laser light acts as excitation light. Further, in the above, new data is obtained by averaging the data of a plurality of scans, but the calculation method is not limited to this, and the calculation method may be changed as appropriate. Further, even if a line COD is used as the reading means, the reading accuracy can be improved.

(Effects of the Invention) As described above, according to the present invention, since data for one new scan is obtained from data obtained by scanning multiple times,
The influence of shot noise is also alleviated, improving the S/N ratio and reading accuracy. Also, when reading with a light beam, the optical deflector can be operated at high speed, eliminating jitter. can do.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of an averaging processing circuit according to an embodiment of the present invention;
Figure 2 (al~(C1 is a diagram explaining the reading scanning line, Figure 3
The figure is a diagram showing a general configuration of an image reading device. 1...Beam oscillator, 2.3...Mirror, 4...
Beam expander, 5... Mirror, 6... Polygon mirror, 7... fθ lens, 8... Mirror, 9...
... X-ray transparent film, 10... Photoconductor, 11...
- Photodetector, 12... Encoder, 13... Photoconductor, 14... Photodetector, 20... A/D converter, 2
11-213...memory, 221-22-. 23+
, 232.24...Adder, 25...Address controller. Joy 1 diagram (b) JIJ layer 1'8

Claims (2)

[Claims] (1) In an image reading method in which a light beam is scanned in a main scanning direction, a recording medium is moved in a sub-scanning direction substantially orthogonal to the main scanning direction, and an image recorded on the recording medium is read, the image recorded on the recording medium is read. An image reading method in which data for one new scan is obtained based on each data obtained by scanning in the main scanning direction twice. (2) The image reading method according to claim 1, wherein the data for one new scan is obtained by averaging the respective data.