JPS60179717A - Reading device - Google Patents

Abstract

PURPOSE:To read an original with sufficient resolution and, at the same time, reduce noises, such as Moire, etc., by inserting either one of a birefringent plate and transparent body between the original and a solid-state image pickup element. CONSTITUTION:An original 1 is lighted by a lamp 2 and respectively reflected by mirrors 3-5 and the image of the original 1 is formed on a solid-state image pickup element 7 (CCD7) by a lens 6. A switching means is provided between the lens 6 and CCD7 and a birefringent plate 8 and plate glass 9 are switched to each other in accordance with the kind of the original 1. The mirrors 3-5 are moved in the direction of the arrow 10 for making auxiliary scanning on the original 1 and the main scanning is performed by the CCD7. Rays from a blind spot picture 11 are divided into normal rays LO and abnormal rays LE when they are made incident on the birefringent plate 8 and an image 12A from the normal rays LO and another image 12B from the abnormal rays LE are formed on the CCD7 with the discrepancy DELTAx between both the images 12A and 12B. Since the superimposed images of the images 12A and 12B are read by the CCD7 in this way, high frequency components are cut off and, therefore, occurrence of Moire is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a document reading device using a solid-state imaging device, and more particularly to improving reading resolution and eliminating noise.

The reading device according to the present invention is widely applied to image reading devices such as digital copying machines and facsimile machines that use solid-state image pickup devices such as COD.

[Prior art]

In general, there are two types of originals: originals without gradation, such as characters, and originals with gradation, such as photographs and halftone originals. When reading these originals, conventional reading devices use a CCD with a configuration that has high resolution when reading characters, etc., and the output forms a dither matrix, which makes it difficult to read halftone originals etc. This had the disadvantage of causing moiré. Moiré is caused by interference between the spatial dot frequency of the original and the spatial scanning line frequency when the dip matrix is one pixel.

If a spatial i4-pass filter is inserted between the original and the solid-state image sensor in order to remove moiré, this inconvenience occurs in that the resolving power decreases when reading the original such as characters.

As described above, in conventional reading apparatuses, the types of originals must be limited for each apparatus, and when different types of originals are used, problems arise such as moiré or reduced resolution.

[Purpose of the invention]

The present invention has been made in view of the above-mentioned conventional problems.
The purpose is to provide a reading device that can read with sufficient resolution and reduce noise such as moiré, depending on the type of document.

[Structure of the invention]

In order to achieve the above object, a reading device according to the present invention is characterized in that either a spatial low-noise filter or a transparent body is selectively inserted between a document and a solid-state image sensor.

The spatial low-pass filter removes moire by cutting high spatial frequency components when forming an image on a document onto a solid-state imaging device. Specifically, a birefringent plate made of quartz or the like can be considered.

The transparent body is switched when reading a document such as characters requiring high resolution, and a flat glass or the like having an optical path length equivalent to a spatial low-gauss filter is used.

In short, when reading originals with gradation such as photographs or halftone originals, insert a spatial low/yas filter, and when reading originals without gradation such as text, insert a transparent material such as flat glass. do. In this way, reading is performed according to the type of document.

[Embodiments of the invention]

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram of an embodiment of a reading device according to the present invention.

In the figure, the original l placed on the original platen glass is
It is illuminated by lamp '2, and the reflected light is reflected by mirror 3,
4.5, and are imaged by a lens 6 onto a solid-state imaging device 7 (hereinafter referred to as CCD 7).

A switching means (not shown) is provided between the lens 6 and the CCD 7, and the birefringence plate 8 and flat glass 9 are switched depending on the type of document.

The mirror 3.4.5 moves in the direction of the arrow lO force to perform sub-scanning of the document, and main scanning is performed by the CCD 7.

Note that the moving distance ratio of mirror 3 and mirrors 4 and 5 during sub-scanning is 2:1.

FIG. 2 is an explanatory diagram of the optical path when reading an original with gradation in this embodiment. For example, when the halftone original 1 is set, the birefringent plate 8 is inserted between the lens 6 and the CCD 7.

In FIG. 2, the light rays from the halftone dot image 11 enter the birefringent plate 8 and become ordinary rays. and abnormal rays. It is divided into two, and the ordinary light line. Therefore, image 12A is an extraordinary ray. Therefore, the image 12B is formed on the COD 7 with a shift of ΔX. Therefore, the overlapping image of images 12A and 12B is CC
Since the image is read by D7, high frequency components are cut and the occurrence of moiré is reduced.

FIG. 3 is an explanatory diagram of the optical path when reading a document without gradation such as characters.

When reading text manuscripts in binary or ternary values, birefringent plate 8
If it is left inserted, the resolution will deteriorate, so it must be removed. However, when the birefringent plate 8 is removed, the lens 6 and C
The optical path length between OD 70 changes and the image formed on the CCD 7 surface becomes blurred. To prevent this, a flat glass 9 having an optical path length optically equivalent to that of the birefringent plate 8 is inserted.

In FIG. 3, the light beam from the character image 13 passes through the flat glass 9, so that the optical path length is adjusted and an image 14 with high resolution is formed on the CCD 7 surface.

〔Effect of the invention〕

°Reading according to the invention, as explained in detail above.

The device can switch between a spatial low-pass filter (birefringence plate, etc.) and a transparent material (flat glass, etc.) depending on the type of document, so it provides high resolution for text documents, etc., and for photographs, halftone dot documents, etc. In this case, the document can be read with moiré reduced.

Moreover, there is no need to change the arrangement of parts of the conventional device, and the above-mentioned great effects can be obtained with a simple configuration.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of an embodiment of a reading device according to the present invention, FIG. 2 is an illustration of the optical path of this embodiment in the case of a halftone original, and FIG. 3 is an illustration of the optical path of this embodiment in the case of a character original. It is a diagram. 1... Manuscript, 7... Solid-state imaging device (CCD), 8...
... Spatial low gas filter (birefringent plate), 9...
Transparent body (flat glass). Figure 1 Figure 2 Figure 3

Claims (2)

[Claims] (1) A reading device that reads an original image using an imaging means, characterized in that either a spatial low-pass filter or a transparent body is selectively inserted between the original image and the imaging means. Device. (2) The reading device according to claim 1, wherein the transparent body has an optical path length optically equivalent to that of the spatial low-pass filter.