JPH0414949A - Picture reader - Google Patents

Abstract

PURPOSE:To attain read of image with fidelity even in the case of intermittent read or even when the reflectance of an original is suddenly changed by providing an auxiliary light source capable of irradiating a light receiving picture element face of a CCD image sensor. CONSTITUTION:A picture 3 on an original is formed on a light receiving picture element of a CCD image sensor 5 by an optical lens 4 and optical information of the picture 3 is converted into an electric signal. Then an auxiliary light source 6 is arranged at a position such as a position between the optical lens 4 and the CCD image sensor 5 where any hindrance is not caused to image forming and a light receiving picture element of the CCD image sensor 5 can be irradiated. Thus, the light reflected in an original is read with fidelity even in the case of intermittent read or even when the reflectance of the original is suddenly changed.

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 an image reading device.

[Prior Art] As a means for inputting image information into information processing equipment,
An image reading device is used. This generally involves converting the optical information of the document from which image information is to be obtained into electrical information using a photoelectric conversion means, that is, an image sensor.
This enables processing of image information in information processing equipment.

In an image reading device, optical information of a document is generally imaged onto an image sensor using a light source such as a fluorescent tube, a halogen lamp, or an LED, and a lens. There are several types of image sensors depending on their method and form, but in practice, an image sensor called a CCD image sensor is widely used.

[Problems to be Solved by the Invention] A CCD image sensor generates an output voltage proportional to the amount of light incident on its light-receiving pixel surface. However, if the amount of incident light is very low and a certain amount of time has passed, the generation of the output voltage will be delayed, and an output voltage proportional to the amount of incident light will not be obtained, resulting in an output voltage that is much lower than the value that should be generated. Ta. For example, when an image reading device is used in connection with a computer, if the signal transfer speed of the interface or the processing speed of the computer is slow, the image reading device may operate intermittently. In other words, out of the entire required reading range, only the range that can be processed by the interface or computer is read and then interrupted.
Read the next part after processing is completed. During the interruption, the document illumination light source is normally turned off, so almost no light is incident on the CCD image sensor, and when reading resumes, a voltage lower than the original output voltage is output. Therefore, a boundary occurs in the read image pressure. FIG. 3(a) shows a --like gray original. FIG. 3(b) is a signal output diagram from the CCD image sensor when reading the gray original shown in FIG. 3(a).

In this way, the output voltage drops several times after reading resumes. Therefore, boundaries occur in the read output image. If there is a highly immersive part of the original with very low reflectance, the image signal of the original following that part of low reflectance, that is, the output voltage from the CCD image sensor, will have a low value as a result. In some cases, areas of the original adjacent to low-reflection areas appear darker than they actually are. When reading a black and white striped pattern, the image signal level of the white line decreases, resulting in a decrease in resolution. FIG. 4(a) shows a document whose reflectance changes rapidly and its reading direction. FIG. 4(b) is a signal output diagram from the CCD image sensor when reading as shown in FIG. 4(a).

In this case, the output voltage is low even though the white portion is actually being read because the document with low reflectance has been read for more than a certain period of time. Therefore, the black and white boundary line becomes blurred in the read output image.

The present invention solves the above-mentioned problems, and provides an image reading device that faithfully reads the reflectance of a document even when reading is performed intermittently or when the reflectance of the document changes rapidly. It is an object.

[Means for Solving the Problems] In order to solve the above-mentioned problems, the present invention provides an image reading device with an auxiliary light source that can illuminate the light-receiving pixel surface of the CCD image sensor.

[Operation] By turning on the auxiliary light source of the image reading device prior to image reading, an output voltage of a certain amount or more is generated from the CCD image sensor, thereby compensating for a signal rise delay of the CCD image sensor.

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

FIG. 1 is a conceptual diagram of the arrangement of necessary components of an image reading device according to an embodiment of the present invention. Original 1 is the original illumination light source 2
irradiated by. In this embodiment, a fluorescent lamp is used as the document illumination light source 2.

The image 3 on the document is formed into a real image by the optical lens 4 on the light-receiving pixels of the CCD image sensor 5, and the optical information of the image 3 is converted into an electrical signal. In this embodiment, the auxiliary light source 6 is placed between the optical lens 4 and the CCD image sensor 5. The auxiliary light source 6 is placed at a position that does not interfere with image formation and can illuminate the light-receiving pixel surface of the CCD image sensor 5.

The auxiliary light source 6 may be a generally easily available and low-cost item such as a small filament lamp or an LED.

FIG. 2 is an operational diagram of the document illumination light B2, the auxiliary light source 6, and the CCD image sensor 5 in one embodiment of the present invention. C
In a CD image sensor, the time between shift pulses constitutes one optical accumulation period, and optical information in one optical accumulation period is output as electrical information, that is, output voltage, in the next optical accumulation period. In this embodiment, as shown in the figure, the auxiliary light source 6 is turned on prior to normal reading. In this embodiment, the auxiliary light source 6 is turned on for two light accumulation periods, then turned off, and then the document illumination light source 2 is turned on. By performing such an operation, the output voltage of the CCD image sensor 5 rises sufficiently due to light irradiation from the auxiliary light source 6, and normal reading becomes possible. When the amount of light irradiated by the auxiliary light source 6 to the light receiving pixels of the CCD image sensor 5 is set to be 50% or more of the saturated output light amount, the effect of compensating for the output voltage is large.

FIG. 3(c) is a signal output diagram from the CCD image sensor in one embodiment of the present invention when reading the gray original shown in FIG. 3(a). Here, when reading is resumed after reading is interrupted, the auxiliary light source is turned on prior to reading, so the image signal does not change before and after reading is interrupted, and no boundaries occur in the read output image.

FIG. 4(b) is a signal output diagram from a CCD image sensor in another embodiment of the present invention when a document as shown in FIG. 4(a) is read. In this embodiment, the auxiliary light source is turned on for all image signal readouts, so even when reading an original whose reflectance changes rapidly, the output voltage of the CCD image sensor can completely follow the change in reflectance. Accurate reading is possible [Effects of the Invention] As described above, according to the present invention, by adding an auxiliary light source to a conventional image reading device and performing appropriate control, it is possible to perform accurate reading even when reading intermittently. Alternatively, it is possible to provide an image reading device that can faithfully read the reflectance of a document even when the reflectance of the document changes rapidly. Also,
As an auxiliary light source, a common and inexpensive miniature light bulb or LED is sufficient to satisfy the function, so the cost increase is minimal.

[Brief explanation of drawings]

FIG. 1 is a conceptual diagram of the arrangement of necessary components of an image reading device showing an embodiment of the present invention. FIG. 2 is an operational diagram of a light source and a CCD image sensor in one embodiment of the present invention. Figure 3 (a
) is a figure of a gray manuscript. FIG. 3(b) is a signal output diagram from the CCD image sensor in the conventional example when reading the gray original shown in FIG. 3(a). FIG. 3(c) is a signal output diagram in the present invention. FIG. 4(a) is an explanatory diagram of reading a document whose reflectance changes rapidly. FIG. 4(b) is a signal output diagram from the CCD image sensor in the conventional example when reading as shown in FIG. 4(a). FIG. 4(C) is a signal output diagram in the present invention. 1...Original 2...Original illumination light source 3...Image 4...Optical lens 5...CCD image sensor 6...Auxiliary light source or more Shift 1 and Lux 1 Figure 2 (Q)

Claims (5)

[Claims] (1) In an image reading device using a CCD image sensor, an auxiliary light source is provided separately from a light source for document illumination, and the auxiliary light source is capable of illuminating at least the light-receiving pixel surface of the CCD image sensor, and is suitable for reading out image signals. An image reading device characterized in that the auxiliary light source is turned on during at least one preceding light accumulation period. (2) The image reading device according to claim 1, wherein the amount of light irradiated by the auxiliary light source to the light receiving pixels of the CCD image sensor is 50% or more of the saturated output light amount. (3) The image reading device according to claim 1 or 2, wherein the auxiliary light is turned on only when reading is restarted after image reading is interrupted. (4) The image reading device according to claim 1 or 2, wherein the auxiliary light is turned on for reading all image signals. (5) The auxiliary light can be selected to be turned on only when reading is resumed after image reading is interrupted, or to be turned on for all image signal reading. The image reading device described.