JPH0298285A - Image reading device - Google Patents

Abstract

PURPOSE:To prevent density deterioration due to light bypassing to a dark part in an edge part with a large brightness density difference by providing an optical absorbing member in the very vicinity of or in contact with the surface of an optical window glass so as to avoid the light incidence to a part other than the photodetection face. CONSTITUTION:A frosting and insulating black paint member 101 is applied or printed onto the surface (except the upper side of the photodetection face) of an optical window glass 2. Thus, since the light having being incident in the face of a photodetector mask 42 in a conventional device is absorbed by the paint member 101, the scattering is prevented. Since the direct incident light is surely made to the photodetection face 43, the size of the part 101a not applied with black paining is slightly larger thant the size of the photodetecting face 43. Thus, the generation of contour of the edge part is suppressed and a picture with high density resolution and sharpness is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention (Industrial Field of Application) The present invention relates to a plane scanning type image reading device using an image sensor.

(Prior art) Image sensor, for example, CCO that constitutes a line sensor
The image light incident on the light receiving surface of the photoelectric conversion element includes, in addition to the image light that is directly incident (hereinafter referred to as direct incident light), the image light that is incident on the light receiving surface of the photoelectric conversion element and inside the optical window glass to protect the photoelectric conversion element. There is light that enters after being reflected by a mask surface of a light-receiving section provided in the vicinity of the light receiving section (hereinafter referred to as flare light). This flare light enters the light-receiving surface of the photoelectric conversion element at a position different from the light-receiving surface of the photoelectric conversion element at the position where it should originally enter, and thus has an adverse effect on the image obtained.

Therefore, the applicant of the present invention developed the line sensor described below in order to prevent bad snow caused by the flare light. FIG. 4 is a perspective view schematically showing an example of the line sensor, and FIG. 5 is a sectional view taken along the line A-. In this line sensor, an optical window glass 2 is attached to the casing 1 above the light receiving surface of the photoelectric conversion element 4 in order to protect the light receiving surface of the photoelectric conversion element 4 mounted on the casing 1 from scratches caused by dust and deterioration due to outside air. It is attached with an inert gas interposed therebetween, and the photoelectric conversion element 4 is sealed. A film (for example, MgF2, 5iOz, etc.) for preventing reflection of image light is provided on the front and back surfaces of the optical window glass 2.
is coated. Such optical window glass 2
The image light whose flare light has been reduced is converted into an electric signal by the photoelectric conversion element 4, and the electric signal is outputted to the outside via the lead pin 3, so that a good image can be obtained. (See No. 1983-71798).

(Problems to be Solved by the Invention) Although it is possible to reduce flare light to some extent in the line sensor in which the optical window glass described above is coated with an antireflection film, there is a limit.

For example, as shown in FIG. 6, the light is transmitted through the optical window glass 2 and the protective layer (for example, 5i02) 41 of the photoelectric conversion element 4 and onto the surface of the light receiving mask (for example, an aluminum evaporation layer for light speed light) 42. A part of the reflected light may be reflected again by the antireflection coating 11.12 of the optical window glass 2 and enter the light receiving surface 43.

Therefore, for example, when light with the distribution shown in Figure 7 is incident, the blurring of the incident position is emphasized at the boundary between the bright and dark areas, so the level of the electrical signal output from the charging conversion element is as shown in Figure 8. become that way. That is, the light in the bright area is reflected and enters the light receiving surface of the photoelectric conversion element that detects the dark area, and the density change in the Sakai boundary area between the bright area and the dark area becomes ambiguous. In particular, in devices that need to read, reproduce, and record image density at multiple levels, when changes in density at the boundary between bright and dark images are converted into warm electric signals, the reproduced image has a sharp contrast. There is a problem in that the image becomes unclear.

This invention was made due to the circumstances mentioned above,
SUMMARY OF THE INVENTION An object of the present invention is to provide an image reading apparatus that can eliminate the phenomenon in which light enters a dark area at an edge area where there is a large difference in density between light and dark, causing a decrease in density.

Composition of the Invention: (Means for Solving the Problems) The present invention relates to a plane scanning type image reading device using an image sensor having an optical window glass for protecting a light-receiving surface. This is achieved by providing a light absorbing material in contact with or very close to the surface of the optical window glass so that light does not enter any part other than the light receiving surface.

(Function) The image reading device of the present invention has a means for preventing light other than regular image light from entering the light receiving surface, that is, a means for absorbing light near the optical window glass of the image sensor. can be significantly reduced.

(Example) FIG. 1 is a perspective view schematically showing an example of a line sensor used in the image reading device of the present invention, corresponding to FIG. 4, and FIG. It is a diagram showing parts corresponding to FIG. 6, and the same components are given the same reference numerals and explanations are omitted. This line sensor has a matte black coating material (for example, product name: Sunday Paint (Dainippon Paint ■) 101 painted or printed on the surface of the optical window glass 2 (excluding the upper part of the light receiving surface) (see the diagonal lines in Figure 1). Department).

Therefore, the light that conventionally entered the surface of the light-receiving mask 42 is absorbed by the coating material 101, so that scattering of the light can be prevented. In order to ensure that direct incident light is incident on the light receiving surface 43, it is desirable that the size of the portion 101a that is not painted black be slightly larger than the size of the light receiving surface 43.

Note that the same effect can be obtained by installing a matte black plate with a slit slightly larger than the light-receiving surface in place of the black coating material 101 in contact with or very close to the optical window glass 2. You can get it.

Figure 3 (A) shows the output signal level (absolute value) from a line sensor coated with black paint, and Figure 3 (II) shows the output signal level (absolute value) from a line sensor that is not painted black. This shows that black paint is effective in reducing flare light, as is clear from the perspective of Japan.

Claims (1)

[Claims] 1. In a plane scanning image reading device using an image sensor having an optical window glass for protecting the light receiving surface, a light absorbing material is attached to the optical window glass to prevent light from entering other than the light receiving surface. An image reading device characterized in that the image reading device is provided in contact with or very close to the surface of the image reading device.