JPH0681228B2 - Image reader - Google Patents

Description

The present invention relates to an image reading apparatus that scans an object to be scanned and reads an image, and more specifically, for example, a stimulable phosphor in which a radiation image is accumulated and recorded. When the sheet is scanned with excitation light such as laser light to generate stimulated emission light, and when this stimulated emission light is read by the photodetector, the beam diameter of the laser light in the sub-scanning direction is set to the sampling pitch in the sub-scanning direction. By increasing the size within a range not exceeding twice, a part of the pixel regions adjacent to each other in the sub-scanning direction is captured, and folding noise in the sub-scanning direction generated in the reproduced image is significantly reduced, thereby obtaining a fine image. The present invention relates to an image reading device that enables the above.

BACKGROUND OF THE INVENTION Conventionally, an object to be scanned is one-dimensionally scanned (main scanning) by a light beam deflected by an optical deflecting means such as a galvanometer mirror, a rotary polygon mirror, or a hologram scanner, and at the same time, the object to be scanned is scanned. A light beam scanning reader is widely used for two-dimensionally scanning the object to be scanned and moving image information recorded on the object by relatively moving (sub-scanning) in a direction substantially orthogonal to the main-scan transport direction. Is used for.

In this case, the reading of the image in the main scanning direction is performed by sampling for each synchronization signal, so to be precise, it is performed by discrete reading processing rather than continuous reading processing. Therefore, when the highest frequency _max among the frequency components included in the read image information is a frequency equal to or more than half the synchronization signal frequency (sampling frequency) _S , aliasing noise is included in the read image information. When the image is reproduced based on this image information, streak-like unevenness occurs in the reproduced image.

Therefore, as a measure against this, conventionally, a band-limiting filter configured by an electric circuit is inserted in the main scanning direction of the light beam to attenuate a frequency component of ½ or more of the sampling frequency _S and to The generation of aliasing noise is avoided.

However, such a band limiting measure for inserting the filter according to the conventional technique is a direction orthogonal to the main scanning direction,
That is, since it cannot be applied to the sub-scanning direction of the scanned object,
There remains a problem that folding noise is mixed in a reproduced image in the sub-scanning direction.

[Object of the Invention] The present invention has been made in order to overcome the above-described problems. The object to be scanned on which an image is recorded is mainly scanned by a light beam deflected in a one-dimensional direction, and the object to be scanned is When the object to be scanned is two-dimensionally scanned by relatively moving in the sub-scanning direction substantially orthogonal to the main scanning direction and the light having the image information is detected and read by the light detecting means, the image reading light is read. By increasing the beam diameter of the beam in the sub-scanning direction within a range that does not exceed twice the sampling pitch in the sub-scanning direction, a part of the image information of the adjacent pixel region in the sub-scanning direction is taken in and a sub-scanning direction generated in the reproduced image is generated. It is an object of the present invention to provide an image reading device that can reduce aliasing noise remarkably and thereby obtain a fine image.

[Means for Achieving the Object] In order to achieve the above object, the present invention irradiates a scanned object carrying image information with a light beam deflected in a one-dimensional direction to perform main scanning, and at the same time, the scanned object. In a direction substantially orthogonal to the main scanning direction to scan the object to be scanned two-dimensionally, and to read image information by a sampling process using the light detection means. The beam diameter in the scanning direction is d <beam diameter ≦ 2d, where d is the sampling pitch in the sub-scanning direction.
It is characterized by comprising a beam diameter adjusting optical system for adjusting in the range of.

[Embodiment] Next, an image reading apparatus according to the present invention will be described in detail below with reference to the accompanying drawings, including a preferred embodiment of an apparatus for carrying out the same.

FIG. 1 is a schematic configuration diagram of an image scanning reading / reproducing system 10 incorporating the device of the present invention. The image scanning / reading / reproducing system 10 includes a laser scanning unit 12 for scanning a laser beam L on a scanned object on which image information is recorded, for example, a stimulable phosphor sheet S conveyed in the sub-scanning direction (arrow x direction). When,
An image reading unit 14 for photoelectrically converting light (stimulated emission light) having image information obtained by the laser beam L, and a synchronization signal generation unit for forming a synchronization signal from the laser beam L.
16 and a signal processing unit 18 for digitizing the signal from the image reading unit 14 based on the synchronizing signal from the synchronizing signal generating unit 16, and then performing correction processing and storing the signal in an image memory. . The stimulable phosphor means radiation (X-ray, α
Rays, β rays, γ rays, electron rays, ultraviolet rays, etc.) accumulates a part of this radiation energy, and then stimulated emission light corresponding to the accumulated energy by irradiating excitation light such as visible light. And a stimulable phosphor sheet means a sheet having a layer made of the stimulable phosphor.

Therefore, a laser oscillation tube 20 for outputting the laser beam L, a beam diameter adjusting optical system 21 for adjusting the diameter of the laser beam L, a galvanometer mirror 22 for deflecting the laser beam L in the arrow B direction, and the laser scanning unit 12 are provided. Is a scanning lens which makes the speed at which the stimulable phosphor sheet S is scanned by the laser beam L deflected by the vanometer mirror 22 constant.
Including 24 and. A part of the laser beam L passing through the scanning lens 24 is reflected by a half mirror 26 as a light splitting means, and scans the stimulable phosphor sheet S in the main scanning direction (direction of arrow C). The half mirror 26 is arranged such that its reflection surface is 45 ° with respect to the surface of the stimulable phosphor sheet S.

The image reading unit 14 is a light guide 28 that collects the stimulated emission light emitted from the stimulable phosphor sheet S by the laser beam L.
And a photomultiplier that photoelectrically converts the stimulated emission light
Including 30 and. In this case, the incident surface of the laser beam L in the light guide 28 is arranged close to the stimulable phosphor sheet S along the main scanning direction (direction of arrow C). In addition,
An analog signal as an output image signal from the photomultiplier 30 is introduced into a signal input terminal of the signal processing unit 18.

On the other hand, the synchronizing signal generator 16 has a grid 34 in which a transmitting portion 32a for transmitting the laser beam L passing through the half mirror 26 and a reflecting portion 32b for reflecting the laser beam L are alternately arranged along the scanning direction of the laser beam L. A cylindrical light guide 36 arranged along the rear of the grid 34, and optical sensors 38a and 38b provided at both ends of the light guide 36 for detecting the laser beam L transmitted through the grid 34, And a frequency synthesizer 40 that multiplies the frequency of the synchronization reference signals output from the optical sensors 38a and 38b. Here, the output signal of the sync signal generator 16, that is, the output signal of the frequency synthesizer 40 is introduced to the sync signal input terminal of the signal processor 18.

Next, in the signal processing unit 18, the output analog signal from the photomultiplier 30 introduced into the signal input terminal is introduced into the A / D converter 44 through the band limiting filter 42, and the A / D converter 44 is A / D conversion processing is performed on the analog signal whose band is limited for each synchronization signal. The digital signal after A / D conversion is subjected to correction processing such as gradation correction processing and contour enhancement processing in the correction circuit 46 and is introduced into the image memory 48. Then, if necessary, a reproduced image is output as a visible image to the display device 50 such as a CRT via a D / A converter (not shown) based on the image signal recorded in the image memory 48.

The apparatus for carrying out the image reading apparatus according to the present embodiment is basically constructed as described above, and its operation and effect will be described below.

In FIG. 1, the stimulable phosphor sheet S on which the image information of the subject has been accumulated by irradiating X-rays or the like is conveyed in the sub-scanning direction (arrow x direction) by a conveying mechanism (not shown). On the other hand, the surface of the stimulable phosphor sheet S is irradiated with the laser beam L emitted from the laser oscillation tube 20 in the main scanning direction (the direction of arrow C), and the object recorded on the stimulable phosphor sheet S is recorded. Image information is taken out as stimulated emission light. In this case, the diameter of the laser beam L in the sub-scanning direction is the scanning line interval d (hereinafter referred to as sampling pitch).
The beam diameter adjusting optical system 21 is adjusted so as to have a larger diameter and within twice, for example, 1.3d to 1.5d. The photostimulated luminescent light is passed through a light guide 28 arranged along the main scanning direction of the stimulable phosphor sheet S to a photomultiplier.
It is incident on 30 and converted into an electric signal and introduced into the band limiting filter 42 in the signal processing section 18.

Here, the image signal introduced into the band limiting filter 42 will be described with reference to FIGS. 2 and 3. Now, as shown in FIG. 2, the scanning line numbers of the stimulable phosphor sheet S in the sub-scanning direction x are 1, 2, 3, ..., K, k + 1 ,. When the energy distribution on the stimulable phosphor sheet S in the sub-scanning direction x is f (x), X _{k−1 of the} stimulable phosphor sheet S is
To X _k (see FIG. 3) area (hereinafter, area [X _k-1 , x _k ]
The energy D _k stored in () is expressed as shown in the following first equation.

However, F (x) = ∫f _{(x) dx} . Therefore, next, the energy D _k is stimulated to emit light by scanning with the laser beam L and is read using the photomultiplier 30.
In this case, the diameter of the reading laser beam L, as indicated by reference numeral D _L in FIG. 3, region [x _k-1, x _k] that region so selected that greater than the width of the [x _k- Letting α be the ratio of protrusions from [ ₁ , x _k ], the energy S _k read by the k-th scan can be approximated as shown in the second equation below.

S _k = (1−α) D _k + αD _{k + 1} (2) FIG. 3 shows how the laser beam L spreads and the energy state on the stimulable phosphor sheet S after being read. Now, with the laser beam L having the beam width D _L , the area [x
It shows that all the energies of _k−1 , x _k ] and a part of the region [x _k , x _{k + 1} ] (part related to α) have been read. Therefore, in order to know the physical meaning of this action on the read image signal, the first equation is substituted into the second equation, and the energy distribution f (x) is further calculated as f (x) = sin ωx (ω is the angular frequency ), The distance x _k from the origin in the sub-scanning direction x is x _k = k · d
(However, d is the sampling pitch in the sub-scanning direction and represents the interval between the main scanning lines), the read energy S _k shown in the second equation is converted as shown in the following third and fourth equations. It

In the fourth equation, the phase angle θ is defined as shown in the fifth equation.

Here, the amplitude portion of the read energy S _k excluding sin (ωkd + θ) in the fourth equation is the beam width of the laser beam L.
For each ratio α that D _L exceeds the sampling pitch d, the characteristic diagram in FIG. 4 (horizontal axis: angular frequency, vertical axis: amplitude) is obtained. As is clear from FIG. 4, the amplitude is a function that decreases with respect to the angular frequency ω.
That is, reading an image with the laser beam L having a diameter larger than the sampling pitch d in the sub-scanning direction is, after all, substantially equivalent to inserting a low-pass filter necessary for preventing aliasing noise in the sub-scanning direction. It can be said that the role is played.

In this case, as the beam width D _L increases, the angular frequency π / d ~ 2
The beam width of the aliasing noise part in the range of π / d is D _L = d
It gradually decreases as it increases from around. Further, when the beam width D _L is increased to 2d or more, the effective attenuation of the folding noise does not occur, but the angular frequency part of 0 to π / d is attenuated, and the information in that range is also largely lost. As a result, the sharpness (resolution) of the reproduced image is deteriorated. Therefore, the optimum range of the beam width D _L adjusted by the beam diameter adjusting optical system 21 needs to be set to d <D _L ≦ 2d.

On the other hand, the laser beam L that has passed through the half mirror 26 is incident on the grid 34 that constitutes the synchronization signal generator 16. Then, the laser beam L is scanned in the direction of arrow B by the swing motion of the galvanometer mirror 22, and moves from one end side of the grid 34 to the other end side.

Then, the laser beam L transmitted through the transmission part 32a of the grid 34 is diffused in various different directions by a diffusion surface (not shown) integrally fixed to the grid 34 and is incident on the light guide 36. Then, the laser beam L totally reflected in the light guide 36 reaches the optical sensors 38a and 38b and is photoelectrically converted to form a synchronization reference signal. Then, the synchronization reference signal is multiplied by the frequency synthesizer 40 and introduced as a synchronization signal into the clock input terminal of the A / D converter 44.

On the other hand, in the A / D converter 44, the analog signal from the photomultiplier 30 which has passed through the band limiting filter 42 and whose aliasing noise has been substantially reduced is processed by the frequency synthesizer.
Each sampling clock signal from 40 is quantized, binarized, and introduced into the correction circuit 64. The digital signal introduced into the correction circuit 46 is stored in the image memory 48 after being subjected to corrections such as gradation correction and contour enhancement, and is displayed on the display device 50 such as a CRT if necessary.

As described above, according to the present invention, when the object to be scanned on which an image is recorded is two-dimensionally scanned by the light beam and the light having the image information is detected and read by the light detecting means. The diameter of the light beam in the sub-scanning direction is set to a value within 2 times the sampling pitch in the sub-scanning direction. For this reason, it is possible to extremely easily reduce the aliasing noise in the sub-scanning direction that occurs in a reproduced image, which has been extremely difficult to reduce in the related art, and thereby an effect of obtaining a fine reproduced image can be obtained.

Although the present invention has been described with reference to the preferred embodiment, the present invention is not limited to this embodiment,
For example, the reading energy S _k is set as S _k = (1−α) D _k + αD _{k−1 so} as to capture the energy of one previous region, and the beam diameter in the main scanning direction and the sub scanning direction Various improvements are made within the scope not departing from the gist of the present invention, such as using a beam having a different beam diameter, and configuring only the beam diameter in the sub-scanning direction to be larger than and smaller than twice the sampling pitch in the sub-scanning direction. Of course, it is possible to change the design.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a schematic configuration of an image scanning reading / reproducing system incorporating an image reading device according to the present invention, FIG. 2 is an explanatory diagram of scanning on a stimulable phosphor sheet, and FIG. 3 is an energy distribution of a laser beam. FIG. 4 is a schematic explanatory diagram of energy in the sub-scanning direction carried on the stimulable phosphor sheet after reading, and FIG. 4 is an explanatory diagram of frequency response in the image scanning reading / reproducing system shown in FIG. 10 ... Image scanning reading / reproducing system 12 ... Laser scanning section, 14 ... Image reading section 16 ... Synchronous signal generating section, 18 ... Signal processing section 21 ... Beam diameter adjusting optical system S ... Storable phosphor sheet

Claims (1)

[Claims] 1. An object to be scanned carrying image information is irradiated with a light beam deflected in a one-dimensional direction for main scanning, and the object to be scanned is relatively moved in a direction substantially orthogonal to the main scanning direction. In an image reading device which scans a scanning body two-dimensionally and reads image information by a sampling process using a photodetector, a beam diameter of the light beam in the sub-scanning direction is defined as a sampling pitch in the sub-scanning direction. Where d <beam diameter ≤ 2d
An image reading device comprising a beam diameter adjusting optical system for adjusting the beam diameter within the range.