JPS6232764A - Image reader - Google Patents

Abstract

PURPOSE:To read an original image at the optimum sensitive level by changing electrically the emitting light quantity of a light source so that the reading level of a line image sensor is set within a prescribed setting level range. CONSTITUTION:The original image is read by performing slit exposure with a fluorescent lamp 15 on a carrying original and image-forming reflected light from the original on a CCD16. Before the reading of the original is started, for the first, the reading of a white image that is a reference is performed by the CCD16, and the read data is stored at a shading correction RAM21. Also, the peak value of the white level is inputted to a skin level detector 22, and an output corresponding to the white level is inputted to a light adjusting control circuit 25. Thereby, a fluorescent lamp driver 26 is controlled, the emitting light quantity of the fluorescent lamp 15 being controlled. The control is performed so that the output level of the CCD16 is set within the prescribed level range set in advance.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to an image reading device such as a part of a facsimile scanner, an Intelligent 1-copying machine, and an image reading terminal.

2. Description of the Related Art Conventionally, there is a scanner device as shown in FIG. 2 that uses a line image sensor.

In this case, a document placed on a document table 1 is fed by a conveyance roller 2, separated into individual sheets by a separation roller 3 and a separation plate 4, and sent to a reading section. On the reading section side, the document is conveyed between a contact glass 7 and a pressure plate 8 at a predetermined speed by a driving roller 5 and a driven roller 6. At this time, the document is exposed to slit light using the fluorescent lamp 9, and the reflected light from the document is imaged by the lens block 12 through the lens h1Oa of the bracket 10 and the mirror 11 on a line image sensor 13 such as a COD. be.

In such a scanner device, as is well known, the level of light received by the line image sensor 13 decreases at both ends and is not uniform due to the illuminance distribution characteristics of the fluorescent lamp 9 and the imaging characteristics of the lens block 12. A shading correction plate 14 is interposed in the optical path to optically equalize the level of received light. There are also devices that are equipped with an automatic correction circuit to electrically equalize the received light level, or that employ both the above-mentioned shading correction method to achieve uniformity.

By the way, a CCD is most commonly used as a line image sensor. The photoelectric conversion characteristics of this CCD generally have characteristics as shown in FIG. According to this characteristic, the output level will be saturated even if it is irradiated with light that exceeds the output saturation exposure, so when designing the light source unit, care must be taken to ensure that the saturation level is not reached even with the expected maximum exposure. There is. Also, if the amount of light is low,
The output level approaches VDR, and the S of the video output processing section
/N may deteriorate and the quality of the read image may deteriorate. In particular, in modern scanner devices that require a multi-tone reading function, better images can be obtained by setting the peak value in a linear region close to the saturation level, where the S/H is as good as possible. Therefore, such a light source unit design has been desired. However, in the case of light sources used in the conventional method, especially fluorescent lamps, which are generally used because they cannot obtain a large amount of light.

The amount of light changes greatly due to the ambient temperature and self-heating after lighting. As a result, even if the light source unit is optimally designed to provide the maximum amount of light, it may be used at a considerably low output level in some cases, often resulting in a reduction in image quality.

The amount of light emitted by a fluorescent lamp fluctuates in this way mainly because the number of excited thermoelectrons changes depending on the temperature, and the amount of light changes by a maximum of three times in a general operating temperature range. In order to suppress such light intensity fluctuations to some extent, some fluorescent lamps have a preheater installed around them.

Fine control of the amount of light cannot be performed, and the cost increases by the amount of the heater. In addition, some devices flow more current than necessary during normal use in order to compensate for the expected minimum light amount, but this wastes current consumption and is disadvantageous in terms of the life of the light source. Such light intensity fluctuations are not limited to fluorescent lamps, but also LE
This may also occur when using other light sources such as a D light source.

Purpose The present invention was made in view of the above points, and an object thereof is to obtain an image reading device that can read an original image at the optimum sensitivity level of a line image sensor and improve the quality of the read image. do.

In order to achieve the above object, the present invention provides an image reading device that exposes a document to light using a light source and reads reflected light from the document using a line image sensor. A control means is provided for electrically changing the amount of light emitted from the light source in accordance with the white level read by the line image sensor so that the level read by the line image sensor falls within a preset level range. It is characterized by:

An embodiment of the present invention will be described below with reference to FIG.

First, a fluorescent lamp 15 is provided as a light source for exposing and illuminating the original, and a reduced type C is used as a line image sensor that reads the original image by forming an image of the reflected light from the original.
A CD16 is provided. A video amplifier 17. A variable amplifier 18, an A/D conversion circuit 19, and a digital comparator/dither processing circuit 20 are connected, and the output from the digital comparator/dither processing circuit 20 is sent to an image signal processing section. Here, the output of the A/D conversion circuit 19 is fed back to the variable amplifier 18 side via the shading correction RAM 21. Further, the output from the video amplifier 17 is input to a background level detection circuit 22, and the peak value of the background level is detected. The output of the background level detection circuit 22 is input to the A/D conversion circuit 19 as a reference level signal, and is also input to the dimming control circuit 25 either directly by switching the switch 23 or via the latch circuit 24. and is configured to control a fluorescent lamp driver 26 for the fluorescent lamp 15. This dimming control circuit 25 itself is constructed using a power control element such as an SCR.

In such a configuration, the document being transported is illuminated by fluorescent light 15.
The document image is read by performing slit exposure and focusing the reflected light from the document on the CCD 16. Here, in this embodiment, before starting such document reading, a reference white image is read by the CCD 16. The read data at this time is stored in the shading correction RAM 21 as shading correction data.

On the other hand, the peak value of the white level at this point is input to the background level detection circuit 22, and an output corresponding to the white level is input to the dimming control circuit 25. As a result, the fluorescent lamp driver 26 is controlled, and the amount of light emitted from the fluorescent lamp 15 is controlled. This control is performed so that the output level of the CCD 16 is within a certain level range set in advance. Therefore, the lighting state of the fluorescent lamp 15 is controlled so that the tube current for the fluorescent lamp 15 increases when the fluorescent lamp 15 is used at low temperatures or immediately after the power is turned on, and decreases when the fluorescent lamp 15 is used at room temperature, high temperature, or continuously. Such dimming before the shading white waveform storage operation stores the white waveform at the optimum sensitivity of the CCD 16, which is also useful for improving the accuracy of shading correction.

Incidentally, it is also possible to hold the light control value 1 to 1 before the shading correction while reading one page (one document), and to switch and control the light control state on a page-by-page basis. Further, even while reading one page, the dimming value for the fluorescent lamp 15 may be varied in accordance with variations in the background level, that is, the output of the CCD 16 may be fed back to the light source side. This results in differences in the paper quality of the manuscript.

For example, normal white originals, originals with gray background, etc. will be irradiated with the amount of light that corresponds to the respective background, making it possible to read at the optimal sensitivity of C0D16 depending on the original or the image in the original. Therefore, the image reading quality is improved. Furthermore, when considering the fluorescent lamp 15, it does not cause problems such as constantly flowing a large tube current, resulting in wasted current, or shortening its lifespan.

Although this embodiment has been described using an example in which the fluorescent lamp 15 is used as a light source, the invention is not limited to a fluorescent lamp, and can be similarly applied to a case where, for example, an LED light source, a fluorescent display tube, or the like is used as a light source.

Effects As described above, the present invention reads the reference white image before starting to read the original and controls the amount of light emitted from the light source according to this white level, so that the image is always read at the optimum sensitivity level of the line image sensor. Therefore, the read image quality can be improved, and unnecessary lamp current is not passed through the light source, eliminating wasted current and extending the life of the light source. .

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a side view showing a conventional example, and FIG. 3 is a photoelectric conversion characteristic diagram of a CCD.

Claims (1)

[Claims] In an image reading device that exposes a document to light using a light source and reads reflected light from the document using a line image sensor, before starting to read the document, the line image sensor reads a white image that serves as a reference, and the white image is read according to the white level. An image reading device comprising: a control means for electrically changing the amount of light emitted from the light source so that a reading level by a line image sensor falls within a preset level range.