JPH0122791B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an optical reading device, and particularly to an optical reading device, in which light from a document irradiated by a light source is imaged onto an image sensor by an imaging system, and from the image sensor. The present invention relates to an optical reading device for correcting the white level of each image signal, which detects the brightness of a light source and controls the output of a drive circuit for the light source in stages based on this detection signal.

[Technology background]

Generally, in optical reading devices such as copying machines and fax machines, a document is illuminated with a light source, and the reflected light is imaged on a parallel light-receiving element such as a CCD and converted into an electrical signal. Then, this electrical signal is converted into a binary or multivalued image and is copied as an image or sent out as a digital signal. In this case, in order to always obtain a high-quality image signal, it is necessary to reduce the white level of the image signal due to differences in the reflectance of the base due to differences in originals, variations in sensitivity between parallel light-receiving elements such as CCDs, and changes in the brightness of the light source over time. Fluctuations need to be controlled.

For this reason, conventionally, the image output signal from a photoelectric conversion element such as a CCD is used to obtain, for example, a white level using a so-called white level hold circuit, and the image output signal is binarized based on this white level. However, when the brightness of the light source decreases significantly, the image signal output from the light receiving element such as a CCD becomes smaller and it is no longer possible to obtain a high-quality image signal using only this white level hold circuit. It disappears. For this reason, the output signal from the detector that detects the brightness of the light source provides continuous feedback to the power source of the light source for illuminating the document, and the output signal from the brightness detector of the light source is held constant. was. This is because the output signal from the light source brightness detector is held constant, so if paper dust from a copying machine or the like adheres to the brightness detector or moves, the brightness of the light source changes. This fluctuation in brightness causes fluctuations in the image signal from the CCD, causing problems such as deterioration of the image signal or overdrive of the light source, such as a fluorescent lamp.

[Objective and Structure of the Invention] An object of the present invention is to correct minute changes in the white level signal due to differences in original documents using a white level follower circuit in an optical reading device having a white level hold circuit. Significant changes in brightness due to deterioration over time are corrected in stages by the light source drive circuit, ensuring stable and high-quality image signals are always read.
The purpose is to extend the life of the light source.

In order to achieve the above object, the present invention includes a photoelectric conversion unit that converts an image of a document illuminated by a light source into an electrical signal, and a white level of each pixel of the image of the document output from the photoelectric conversion unit. In an optical reading device having a white level follower circuit that respectively corrects the white level based on the data signal,
It is characterized by comprising a brightness sensor that detects the brightness of the light source, and a brightness control section that controls the drive circuit of the light source in stages based on the brightness signal from the brightness sensor.

[Embodiments of the invention]

The details of the present invention will be explained below with reference to Examples.

FIG. 1 shows the configuration of one embodiment of the present invention, and in the figure,
1 is the original, 2 is the fluorescent light, 3 is the mirror, 4 is the lens, 5
is a CCD photoelectric converter, 6 and 11 are amplifiers,
7 is a DC regeneration circuit, 8 is a white level follower circuit,
9 and 12 are A/D converters, 10 is a brightness detector, 13 is a system controller, 14 is a drive circuit, and 15 is a fluorescent lamp deterioration indicator.

First, the white level follower circuit 8
A case in which minute white level fluctuations due to differences in color, etc. are corrected will be described in detail.

In FIG. 1, reflected light from an original 1 that is irradiated by a fluorescent lamp 2 that is a light source is reflected by a mirror 3 and enters a lens 4, and the lens 4 captures an image of the original.
The image is formed on a photoelectric converter 5 such as a CCD. An image corresponding to one scanning line of the original is inputted to an amplifier 6 as a serial signal by the photoelectric converter 5, amplified, passed through a DC reproducing circuit, and inputted to a white level follower circuit 8. On the other hand, the original 1 is mechanically moved in the direction indicated by the arrow and plane scanning is performed.

The white level follower circuit 8 is a known circuit that maintains a constant white level signal corresponding to each pixel of the serial image signal, and
It operates as an AGC (automatic gain adjustment circuit). With this white level follower circuit 8,
It compensates for minute changes such as differences in reflectance due to different originals, differences in sensitivity between elements such as CCDs, and fluctuations in brightness of the light source. The output signal from the white level follower circuit 8 is input to the A/D converter 9, converted into a digital signal, and output as a digital image output signal.

Next, a case will be described in detail in which a large change in brightness due to deterioration of the light source is corrected by the light source drive circuit 14, for example, an inverter.

In FIG. 1, light from a fluorescent lamp 2 as a light source is detected by a brightness detector 10 and converted into an electrical signal. The converted electrical signal is amplified by an amplifier 11, converted into a digital quantity by an A/D converter 12, and inputted to a system controller 13. The system controller 13 is the brightness detector 1
When the output signal from 0 is below a predetermined value, that is, when the brightness of the light source has deteriorated due to changes over time and has fallen below the predetermined value, the output of the drive circuit 14 is 1
Raise the stage. This increases the brightness of the light source by one level. Further, when the drive circuit 14 is at its maximum drive limit, it can no longer be raised, so the fluorescent lamp deterioration indicator 15 is turned on to issue an alarm.

FIG. 2A shows a diagram for explaining the variable range of white level correction by the white level follower circuit 8 mentioned above, and FIG. 2B shows a diagram for explaining the output state of the drive circuit 14.

In FIG. 2A, the horizontal axis represents the white level of an output signal from a light receiving element such as a CCD, and the vertical axis represents the white level correction range G of the white level follower circuit 8. This white level correction amount is a continuous amount,
Corrects minute white level fluctuations such as differences in reflectance due to different documents and slight fluctuations in light source brightness.

In FIG. 2B, the vertical axis is the output of the drive circuit 14 of the light source such as the fluorescent lamp 2, and the output of the drive circuit 14 of the light source such as the fluorescent lamp 2.
When the detection signal from 0 becomes less than a predetermined value,
The output of the drive circuit 14 increases by one step, that is, by S shown in the figure. This allows coarse adjustment of white level fluctuations.

〔Effect of the invention〕

As described above, according to the present invention, even if there are differences in reflectance due to differences in original documents, fluctuations in brightness during replacement and inspection of light sources, etc., stable and high-quality image signals can always be obtained without being affected by these factors. It can be obtained at low cost and the life of the light source can be extended. In particular, if the brightness of the light source is not modulated even if paper dust adheres or moves to the brightness detector, and if the brightness of the light source decreases significantly, the image signal is not being read. Sometimes it increases the brightness of the light source, so it does not affect image reading in any way.

[Brief explanation of drawings]

FIG. 1 shows the configuration of an embodiment of the present invention, and FIGS. 2A and 2B are diagrams for explaining white level correction. In the figure, 1 is an original, 2 is a fluorescent lamp, 3 is a mirror, 4 is a lens, 5 is a photoelectric converter, 6 and 11 are amplifiers, 7 is a DC regeneration circuit, 8 is a white level follower circuit, 9,
12 is an A/D converter, 10 is a brightness detector, 13 is a system controller, 14 is a drive circuit, 1
5 represents a fluorescent lamp deterioration indicator.

Claims (1)

[Claims] 1. A photoelectric conversion unit that converts the image of the document illuminated by the light source into an electrical signal, and corrects the white level based on the white level data signal for each pixel of the image of the document output from the photoelectric conversion unit. An optical reading device having a white level follower circuit includes a brightness sensor that detects the brightness of the light source, and a brightness control unit that controls a drive circuit of the light source in stages based on a brightness signal from the brightness sensor. Features an optical reading device.