JPH0437252A - Original read optical device - Google Patents

Abstract

PURPOSE:To improve a half tone picture, to make a waveform stable after automatic shading and to prevent occurrence of a defective picture by providing a lens shape part collecting light to a white reference face to a contact glass in a way that the illuminance of the white reference face and the illuminance of an original face are almost the same. CONSTITUTION:A light radiating from a light source 1 transmits through a contact glass 11 and lights an original 3 and a pressing plate 4, the light directed in the direction of the pressing plate 4 is collected in a direction orthogonal to a scan line with a lens shaping part and the illuminance at a part A of the original 3 and the illuminance of a part B of the pressing plate 4 are made almost the same. Thus, the effect due to difference between an optical path from the light source 1 to a lens via the pressing plate 4 and an optical path from the light source 1 to the lens via the original 3 is less and a white level of the pressing plate 4 and a white level of the original 3 are made almost the same. Thus, the half tone picture is improved, the automatic shading correction is made accurate and the picture quality is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an optical device for a document reading device that illuminates the surface of a document, scans the reflected light along a scan line, and converts the light into electricity.

(Prior Art) An outline of a conventional device of this type will be explained with reference to FIG. In FIG. 3, 1 is a light source that is long in the direction perpendicular to the plane of the paper, and 2 is a contact glass, over which the original 3 is conveyed in the direction of the arrow. 4 is a pressure plate that prevents the original 3 from lifting; 5 is a plurality of mirrors; 6 is an imaging lens; and 7 is an image reading element, usually a CCD.

When reading an original, the transported original 3 is illuminated by a light source 1, and reflected light from a portion A corresponding to a scan line is guided to a lens 6 by a mirror 5, and an image is formed on a reading element 7 by the lens 6. The reading element 7 electronically scans and sequentially performs photoelectric conversion to perform reading.

Incidentally, the white level output is set prior to reading the original, and this white level serves as a reference for setting the peak level during auto shading and halftone. for that,
A white tape is placed on a portion B of the pressure plate 4 corresponding to the scan line, and normally, by the time the document 3 is conveyed to the scan line, the reflected light from the white tape on the pressure plate 4 is
The reading element 7 converts it into an electrical signal, and the white waveform data is taken in as image information correction data.

In this case, as shown in FIG. 4, compared to the length R of the optical path from light source 1 → document 3 → lens 6, the optical path from light source 1 (1' in FIG. 4) → pressure plate 4 → lens 6 is longer. The length R' is longer, so the white waveform level of the pressure plate 4 is lower than the white waveform level of the original 3, as shown in FIG.

Furthermore, another reason why the white level of the pressure plate 4 becomes low is that the surface illuminance changes drastically depending on the distance from the light source 1. That is, as shown in FIG. 6, the illuminance on one surface changes in inverse proportion to the distance from the light source.

(Problems to be Solved by the Invention) From the above, the white waveform data produced by the pressure plate has a lower output level than the white waveform data of the original, and the peak hold level during halftone is lower than that when the actual original is read. Since it becomes lower than the peak hold level, it will affect the halftone image. Also,
The white waveform data produced by the pressure plate has a slightly different shape from the white waveform of the actual original due to the difference in the length of the optical path, so autoshading is applied differently, which may affect the white waveform after autoshading. Conceivable.

The present invention aims to solve the above-mentioned problems of the prior art, and includes an original reading optical system that improves halftone images, stabilizes the waveform after auto shading, and prevents abnormal images from occurring. The purpose is to provide equipment.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides at least a white light so that the illuminance of the white reference surface on the pressure plate and the illuminance of the document surface at different distances from the light source are approximately the same. The contact glass is provided with a lens-shaped portion that condenses the light irradiated onto the reference surface.

(Function) According to this configuration, the white waveform level of the pressure plate and the white waveform level of the document can be made to be approximately the same level, and the shapes can also be made close to each other, so that halftone images can be improved and image quality can be improved. Improvements can be made.

(Example) An embodiment will be described in detail below with reference to one drawing.

FIG. 1(a) shows the configuration of a large-scale embodiment of the present invention, in which 1 is a light source, 3 is an original, 4 is a pressure plate, and 11 is a contact glass, in which a part of the light source 1 is connected to the pressure plate 4. It has a lens-shaped portion 12 that focuses the light irradiated onto the white reference plane in a direction perpendicular to the scan line.

In such a configuration, the light emitted from the light source 1 is
The original 3 and the pressure plate 4 are illuminated by passing through the contact glass 11, but the light directed toward the pressure plate 4 is focused by the lens shape in a direction perpendicular to the scan line, so as shown in FIG. 1(b). In this case, the illuminance at part A of the original 3 and the illuminance at part B of the pressure plate 4 are approximately the same, so that the light source 1
The influence of the difference between the optical path from the light source 1 to the lens via the pressure plate 4 and the optical path from the light source 1 to the document 3 to the lens is reduced, and the white waveform level of the pressure plate 4 and the white waveform level of the document 3 are approximately at the same level. This makes it possible to improve halftone images.

FIG. 2 shows another embodiment of the present invention.
A contact glass 15 having a lens-shaped portion 16 is used to condense the light directed toward the pressure plate 4 in the same way as the light directed toward the pressure plate 4. In this case, in addition to the same effect as the embodiment shown in FIG. 1, even if the height H of the transported document 3 from the contact glass 15 changes, the illuminance on the document surface hardly changes, so that a stable white image can be obtained. There is also the effect of obtaining a waveform level.

(Effects of the Invention) As explained above, according to the present invention, ■The white waveform level of the pressure plate can be made approximately the same as the white waveform level of the original, so the peak hold level during halftone can be adjusted to the white waveform level of the original. Halftone images can be improved by bringing the waveform closer to its peak level.

(2) Since the white waveform of the pressure plate and the white waveform of the document can be made similar in shape and level, auto shading correction can be performed accurately and the quality of one image can be improved.

■Even if the height of the original from the contact glass changes, the white waveform level of the original can be kept constant, resulting in stable images.

(2) Since the light is focused, the white waveform level is higher than when the light is not focused, making it possible to compensate for the lack of light from the light source.

[Brief explanation of the drawing]

FIG. 1(a) is a block diagram of an embodiment of the present invention.
b) is a diagram showing the illuminance of the document surface and the pressure plate surface in the same embodiment, FIG. 2 is a configuration diagram of another embodiment of the present invention, and FIG. 3 is a configuration diagram of a conventional document reading optical system. Fig. 4 is a diagram showing the length of the optical path from the light source to the imaging lens via the original or pressure plate, and Fig. 5 is a diagram showing the white waveform level of the original and pressure plate with different optical path lengths. FIG. 6 is a diagram showing the illuminance of the document surface and the pressure plate surface in a conventional example. 1...Light source, 3...Original, 4...Press plate,
11.15...Contact glass, 12.16...
Lens shape part. Patent applicant Rico Co., Ltd.

Claims (1)

[Scope of Claims] In an optical system of a document reading device that performs shading correction by reading the white of a white reference plane provided on a pressure plate surface in order to set a white level output in an image reading element when reading a document, a light source includes: The contact glass is provided with a lens-shaped portion that condenses at least the light irradiated onto the white reference surface so that the illuminance of the white reference surface and the document surface, which are different in distance from the white reference surface, is approximately the same. Original reading optical device.