JPH0343949A - Fluorescent tube - Google Patents

Abstract

PURPOSE:To carry out shading correction with a dynamic range of uniform image signals in the whole surface of an original document by forming a not coated part only int he peripheries in both ends in the longitudinal direction of a glass tube. CONSTITUTION:A fluorescent tube 1 is used as a light source 6 of a image reading apparatus, a fluorescent material 4 or a reflecting material 3 is applied to the inside of a glass tube 2 of the fluorescent tube 1, and a not coated part 5 is formed only in the peripheries in both ends in the longitudinal direction of the glass tube. In the case that the open part 5 not coated with the fluorescent material or the reflecting material faces to an original document, the illuminance of the original document becomes high as compared to the case that the open part 5 does not face to the original document. In this way, without mechanical shading correction, shading correction is carried out and the image signals of a line image sensor 9 become almost uniform.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to the field of information processing and office equipment, and more particularly to illumination means used in image reading devices and copying machines.

[Prior art 1 As a means for inputting image information into information processing equipment,
An image reading device is used. In this method, the optical information of a document from which image information is to be obtained while fishing on a boat is converted into electromagnetic information by a photoelectric conversion means, that is, an image sensor, and the image information can be processed by an information processing device.

FIG. 5 shows a conceptual diagram of the arrangement of optical system elements in an image reading apparatus using a conventional reduction optical system. The light emitted from the light source 6 is reflected on the surface of the original 7, passes through the lens 7, and reaches the line image sensor 9. The image of the original 7 is reduced and formed on the light-receiving pixels of the line image sensor 9. Image reading involves main scanning and sub-scanning, and in FIG. 5, the light-receiving pixel row of line image sensor 9 is arranged in the main scanning direction, and main scanning is performed by electrical operation of line image sensor 9. . The sub-scanning is perpendicular to the main scanning, and is performed by relatively moving the original 7 and the reading optical system.

[Problems to be Solved by the Invention] In an image reading device configured with an optical system as shown in FIG. 5, a fluorescent tube is generally used as the light source 6.

FIG. 4(a) shows an illuminance distribution 400 in the main scanning direction on the document surface by the fluorescent tube. The dotted lines are the positions of both ends of the document. In this way, when fluorescent tubes are used, the illuminance distribution on the document surface becomes almost uniform. FIG. 4(b) shows the relationship between the half angle of view of the lens and the image plane illuminance when the object surface illuminance is constant. A solid line 420 is the illuminance characteristic. Since the lens has a property called the cosine fourth law and a decrease in aperture efficiency due to vignetting in the peripheral area, the distribution as shown in this figure is obtained. Normally, the illuminance in the peripheral area is around 60% of the central area. FIG. 4(C) shows an image signal 430 of the line image sensor, which has a mountainous distribution due to the characteristics shown in FIG. 4(b). This phenomenon is called shading, and is equivalent to uneven illuminance distribution on the document surface, and some kind of correction means is required.

It is possible to perform shading correction using electrical calculations based on the image signal obtained when reading a document at a temperature similar to that of -, and this is a method often used in practice. There is a considerable difference in the dynamic range of the image signal depending on the area. Therefore, mechanical shading correction is performed. In the case of mechanical shading correction, a member that partially blocks the optical path and adjusts the amount of light is inserted in the optical path, which results in incomplete use of the effective diameter of the lens and degrades the performance of the lens. Furthermore, the number of parts and assembly man-hours also increase.

[Means for Solving the Problems] In order to solve the above-mentioned problems, the present invention uses a fluorescent tube as a light source of an image reading device, and coats the inner surface of the glass tube of the fluorescent tube with a fluorescent substance or a reflective substance. , uncoated portions were provided only near both longitudinal ends of the glass tube.

[Function] The part where no fluorescent material or reflective material is applied is called an opening. When the aperture directly faces the document surface, the illuminance on the document surface is higher than when the aperture does not face the document, making it possible to perform shading correction without using mechanical shading correction means, which improves line image quality. The image signal of the sensor becomes almost uniform.

[Example] A detailed description of the present invention will be given according to examples.

FIG. 1 is a perspective view of a fluorescent tube according to an embodiment of the present invention. FIG. 2 is a cross-sectional view of the fluorescent tube. The fluorescent tube 1 has a sealed structure with electrodes at both ends of a glass tube 2, and the interior thereof is filled with mercury vapor, xenon gas, or neon gas. A reflective film 3 coated with a reflective material is formed on the inner surface of the glass tube 2, and a fluorescent film 4 coated with a fluorescent material is formed thereon. A portion of a certain length in the circumferential direction of the glass tube 2 is an opening 5 from which the reflective film 3 and the fluorescent film 4 are removed. The fluorescent film 4 emits fluorescence when a fluorescent substance is excited by ultraviolet light or the like. The reflective film 3 is made of a white reflective material such as titanium oxide, and has the function of reflecting light generated inside the glass tube 2 . The opening 5 functions as a window that intensively emits the light reflected by the reflective film 3 to the outside.

In this way, the fluorescent tube 1 having the reflective film 3 and the opening 5 has an illuminance about 50% to 80% higher than a general fluorescent tube having only a fluorescent film, when focusing on the illuminance directly under the opening 5. It is known that

FIG. 1 shows a case where the openings 5 are formed on the fluorescent tube 1 only in the vicinity of both ends. Since the opening 5 is formed by peeling off the reflective film 3 and the fluorescent film 4 with a piece of metal, etc., the opening shape according to the present invention can be achieved by forming the opening 5 for the required length from both ends of the glass tube 2. , is easily realizable.

FIG. 3(a) is an illuminance distribution diagram on the surface of a document when a fluorescent tube according to an embodiment of the present invention is used as illumination for an image reading device. A solid line 100 indicates the illuminance characteristic, and a dotted line lO1 indicates the positions of both ends of the document. The case is shown in which the openings 5 at both ends of the fluorescent tube 1 are arranged to directly face the document surface, resulting in a step-like distribution in which the illuminance is about 50% to 80% higher at both ends than at the center. . Since the directivity of the light flux is not very high, the illuminance does not change suddenly even at the boundary of illuminance, but changes smoothly. By combining this with a general lens having the characteristics shown in FIG. 4(b), the image signal 200 of the line image sensor when reading a white document, for example, becomes as shown in FIG. 3(b). It will be almost flat. Since the illuminance distribution on the document surface is step-like, it is not completely flat, but this is not a problem in practical use. In addition, it is desirable to adjust the length of the opening 5 according to the characteristics of the lens, but the length of the opening 5 is suitably between 1/6 and 1/3 of the length of the glass tube 2. . As a result, it is possible to realize shading correction having a dynamic range of image signals over the entire document surface while fully using the effective diameter of the lens.

[Effects of the Invention] As described above, according to the present invention, a fluorescent tube is manufactured by adding some ingenuity to the conventional manufacturing method of a fluorescent tube having an opening,
By configuring an image reading device using these fluorescent tubes, it is possible to achieve shading that has a similar dynamic range of image signals over the entire document surface while completely using the effective diameter of the lens without increasing costs. Correction can be achieved. Moreover, since the number of parts does not increase, there is an advantage that there is no need for parts costs or assembly costs.

[Brief explanation of drawings]

FIG. 1 is a perspective view of a fluorescent tube according to an embodiment of the present invention. Second
The figure is a cross-sectional view of a fluorescent tube. FIG. 3(a) is an illuminance distribution diagram on the document surface when a fluorescent tube according to an embodiment of the present invention is used. FIG. 3(b) is a white original image signal distribution diagram of a line image sensor using a fluorescent tube according to an embodiment of the present invention. Figure 4 (
a) is an illuminance distribution diagram on the document surface in a conventional image reading device. FIG. 4(b) is an image plane illuminance distribution diagram of the lens. Figure 4 (C)
1 is a white document image signal distribution diagram of a line image sensor in a conventional image reading device. FIG. 5 is a conceptual diagram of the arrangement of optical system elements in a conventional image reading device. 1... Fluorescent tube 2... Glass tube 3... Reflective film 4... Fluorescent film 5... Opening 6... Light source 7... Document 8...・Lens 9・・・Line image sensor

Claims (1)

[Claims] (1) In a fluorescent tube in which the inner surface of the glass tube is coated with a fluorescent substance or a reflective substance, and the fluorescent substance or reflective substance is not coated on the entire length of the glass tube with a constant width in the circumferential direction, the said uncoated area A fluorescent tube characterized in that the fluorescent tube is provided only near both longitudinal ends of the glass tube. (2) The fluorescent tube according to claim 1, wherein the length of the uncoated portion from the end of the glass tube is 1/6 to 1/3 of the total length of the glass tube.