JPH0479504B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an image reading device that scans a light beam to read a light-transmitting image.

(Prior Art) As a device for reading film images by irradiating light, there is a device using a video camera. As shown in FIG.
A diffuser plate 3 for preventing uneven illumination is set on the open surface of a box 2 containing a built-in camera, a film 4 from which images are to be read is placed on the upper surface of the diffuser plate 3, and a video camera 5 having a lens 5a is placed above the film 4. set,
The space between the box 2 and the video camera 5 is shielded from external light by a light shielding curtain 6.

This reading device uses the video camera 5, so it can read at high speed, and has the advantage of being highly reliable because it has no mechanical moving parts. /N and lens flare, etc., which degrades the reading image quality.
There is a problem in that the read image is considerably degraded compared to the original image on the film.

On the other hand, there are also devices that use photoelectric conversion element arrays. As shown in FIG. 6, an imaging lens 8 and a CCD 9 are provided on the opposite side of the film 4 illuminated by a long fluorescent light 7, and the film 4 is moved in the direction of arrow a. The film image is read by the CCD 9 while moving. In addition,
A contact sensor array may be used instead of a CCD.

With this device, CCDs and close-contact arrays are currently becoming more widespread, so the device can be provided at a low cost, but the dynamic range is low and the S/N ratio decreases due to the effects of switching noise, making it difficult to detect images. There is a problem in that image quality inevitably deteriorates in high-density areas where the signal level is low.

FIG. 7 shows an example of another optical scanning method, in which laser beam b is deflected by an optical deflector 10 such as a polygon mirror, inputted to an fθ lens 11, converged there, and moved in the direction of arrow c. A light spot of an appropriate diameter is irradiated onto the film 4, and the light spot scans in the direction of the arrow d along the scanning line e, and the light transmitted through the film 4 is directed to the diffuser plate 12.
The light is diffused by a photomultiplier 13, detected by a photomultiplier 13, and the film image is read.

This reading device scans the image with a converged laser beam, so the resolution and dynamic range are good and it is possible to obtain a high-quality image, but since the diffused light is scattered in a 360 degree direction, the photo multiplier 13 The diffused light incident on the sensor is weak, and its detection is therefore susceptible to stray light. Therefore, it is necessary to take measures to block light, which is expensive. Furthermore, since the diffused light becomes weaker in the vicinity of scanning, countermeasures for this are also required.

(Object of the Invention) The present invention has been made in view of the above points, and its purpose is to efficiently detect a transmitted image while employing an optical scanning method, and to be able to manufacture it at a low cost. An object of the present invention is to provide an image reading device that achieves this.

(Structure of the Invention) For this purpose, the present invention scans a light-transmissive image with a light beam, diffuses the transmitted light that has passed through the image with a diffuser plate, and converts the diffused light into time-series electricity using a photoelectric converter. In an image reading device that reads the image by converting it into a signal, the diffusion plate has a property of directionally diffusing light in the scanning direction, and the light receiving portion of the photoelectric converter is directed in the diffusion direction. It is arranged and configured along the following lines.

(Example) Examples of the present invention will be described below. 1st
The figure shows one example thereof. In this embodiment, the optical scanning method as explained in FIG. 7 above is adopted. Therefore, the same reference numerals are given to the same parts as in FIG. 7. In this embodiment, a semiconductor laser is used as the light source of the laser beam b.

Reference numeral 14 denotes a long light-reflecting diffuser plate (reflecting diffuser plate) arranged along the scanning line e on the back side of the film 4, that is, on the light transmitting side, and its length is equal to the length of the light beam on the film 4. It is longer than the length in the scanning direction, and minute irregularities are formed on the reflective surface so that grooves are formed in a direction perpendicular to the scanning direction. That is, these unevenness are lined up along the scanning direction. Specifically, this reflection/diffusion plate 14 is formed by applying hairline processing to one side (reflection surface side) of an aluminum plate to form an uneven diffusion surface.

Reference numeral 15 denotes a photodetector array as a photoelectric converter that receives light reflected by the reflection and diffusion plate 14, and a plurality of photodetectors 15a ₁ to 15an are arranged in a row in a direction parallel to the reflection and diffusion plate 14. They are arranged side by side. Specifically, a PIN photodiode, which is most suitable for combination with the semiconductor laser as the light source described above in terms of spectral sensitivity, was used for each photodetector, and the area of the light receiving part was 3 x 3 ^mm2 . .

In this embodiment, the light transmitted through the film 4 moving in the direction of arrow c has its light intensity modulated depending on the image density of the film 4, and is irradiated onto the reflective diffuser plate 14. Then, the light is anisotropically diffused by the unevenness of the reflective diffuser plate 14, and the diffused light enters the photodetector array 15 to read the film image.

FIG. 2 shows a cross section of the reflective diffuser plate 14 at the scanning line position, and for ease of explanation, shows an example in which transmitted light is incident perpendicularly to the reflective surface. The light beam is slightly scattered by the surface of the film 4, but when it is irradiated onto the reflective diffuser plate 14, it is diffused by its unevenness. When light enters the diffuser plate perpendicularly, the light is diffused in the direction in which the unevenness is arranged, that is, parallel to the plane of the paper of this drawing, and is hardly diffused in the direction that intersects therewith. Therefore, the photodetector array 1 is placed on the surface formed by the diffused light in the direction of diffusion.
5 increases the efficiency of diffused light detection.

FIG. 3 shows each photodetector 15 of the photodetector array 15.
It shows a timing chart of the outputs of a ₁ to 15an and the sum of the outputs. In this case, for ease of understanding, the film 4 was made to have a uniform density.
The light reflected and diffused by the reflection diffuser plate 14 most intensely reaches the nearest photodetector. This is because the distribution of diffusion is not uniform; it is strongest in the direction of reflection (determined by the angle of incidence) and becomes weaker as the angle from there increases. Therefore, as the laser beam is scanned, each photodetector 15a ₁ to 15
The peak of the output of an is 15a ₁ → 15a ₂ → 15a ₃ →
...and it moves on.

However, as an image signal, all photodetectors 15a ₁ -
For example, obtain a signal of the sum of the outputs of 15an using an adder,
The sum signal may be output in time series. If the film has a uniform density as described above, the image signals obtained over time will have the same level. Of course, if there is an image on the film 4, the output of the adder over time will be a modulated signal carrying the image.

FIG. 4 shows a specific circuit of the detection part. Here, the output currents of photodetectors 15a ₁ to 15an using PIN photodiodes are converted into voltage signals by I/V conversion by operational amplifiers 16 ₁ to 16n.
The voltages V ₁ to Vn from there are added by an adder 17,
A voltage carrying the above-mentioned sum signal is obtained at the output terminal 18.

Note that if the spacing between each photodetector in the photodetector array 15 is too wide, a difference will occur in the detection level between an image near the photodetector and an image far away. For example, in the case of uniform density, Since the sum signal will not be flat and will have ripples, it is necessary to set it appropriately. In this embodiment, the interval is approximately 1/2 of the distance between the photodetector array 15 and the reflective diffuser plate 14. However, by increasing the spacing between photodetectors, the number of photodetectors can be reduced. However, in order to maintain the above conditions, the distance between the reflective diffuser plate 14 and the photodetector array 15 becomes large, which significantly reduces the efficiency, so it is necessary to set an appropriate distance. However, this does not apply if electrical correction such as shading correction is possible.

Further, in this embodiment, the area of the light receiving portion of the PIN photodiode as a photodetector is 3×3 mm ² , but the efficiency will be further improved if the area is increased. However, since the junction capacitance becomes large for large area ones,
It cannot be used in reading devices that require high speed.
However, in the present invention, in order to achieve high efficiency, it is sufficient to be large in one dimension. It can be much more efficient and cheaper than doing so.

The irregularities on the reflective surface of the reflective diffuser plate 14 need to be smaller and random than the spot diameter of the light transmitted through the film 4 in order to make the diffused light more uniform. The transmitted light has a larger spot diameter as it moves away from the scanning surface of the film 4, so the reflection diffuser plate 14 and the film 4 are
Set the distance between.

Further, in this embodiment, the reflective diffuser plate 14 is used to diffuse the transmitted light, but a transmissive type diffuser plate may be used. As this transmission type diffuser plate, transparent glass or resin with minute scratches in one direction, transparent fibers arranged in one direction and bundled, etc. can be used. When using this transmission type diffuser plate, a photodetector array is placed on the back side of the diffuser plate.

In addition, in this example, a photoelectric converter that directly receives light from the diffuser plate is arranged, but a mirror or a polarizing plate is provided next to the diffuser plate to change the surface formed by the diffused light. Of course, a photoelectric converter may be provided on the other surface.

(Effects of the Invention) As described above, since the present invention employs an optical scanning method in which a transparent image is scanned with a light beam, it is possible not only to read images with good resolution and gradation, but also to improve diffusion. The plate has the property of diffusing with directionality in the scanning direction, and the light-receiving part of the photoelectric converter is arranged along the direction of diffusion, so the diffused light can be detected efficiently and the image can be read. efficiency is greatly improved, and therefore there is no need to take special measures against stray light, and the device can be manufactured at low cost.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of an image reading device according to an embodiment of the present invention, FIG. 2 is a cross-sectional view of a reflective diffuser plate, FIG. 3 is a timing chart for explaining diffused light detection by light beam scanning, and FIG. 4 is the circuit diagram of the detection section, Figure 5~
FIG. 7 is an explanatory diagram of a conventional image reading device. 4... Film, 10... Optical deflector, 11...
fθ lens, 14... reflective diffuser half, 15... photodetector array.

Claims (1)

[Claims] 1. Scanning a light-transmissive image with a light beam, diffusing the transmitted light that has passed through the image with a diffuser plate, and converting the diffused light into a time-series electrical signal with a photoelectric converter. In the image reading device for reading the image, the diffusion plate has a characteristic of directionally diffusing light in the scanning direction, and the light receiving portion of the photoelectric converter is arranged along the diffusion direction. An image reading device characterized by: