JPH0265462A - Picture reader - Google Patents

Abstract

PURPOSE:To eliminate a picture distortion with simple circuit constitution by selecting and outputting a read picture signal outputted from plural variable gain circuits amplifying or attenuating a read picture signal of an image sensor by a preset gain through a prescribed sequence and correcting the shading distortion included in an output signal. CONSTITUTION:The reader is provided with plural variable gain circuits 2 amplifying or attenuating a read picture signal of an image sensor by a preset gain, a selection circuit 3 selecting and outputting a read picture signal outputted from the circuit 2 according to a prescribed sequence and a shading correction circuit 4 correcting the shading distortion included in an output signal from the selection circuit 3. Since the distortion correction is applied by the plural variable gain circuits 2 and the selection circuit 3 in the stage of an analog signal in this way, a multiplier, an A/D converter and a fixed distortion correction signal generator or the like are omitted and the distortion collection processing is applied with simple circuit constitution with low cost.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an image reading apparatus equipped with a circuit for reading an original and correcting a read image signal.

2. Description of the Related Art In recent years, there has been a growing demand for image reading devices that can read documents with high resolution and precision.

If the shading correction circuit has only one stage, there is a possibility that large shading distortion cannot be completely corrected.

Therefore, shading correction has a two-stage configuration, in which large distortions are removed in the first stage, and fine distortions that cannot be corrected in the first stage are removed in the second stage.

As an image reading apparatus having such a two-stage shading correction configuration, a circuit configuration as shown in Japanese Patent Application Laid-open No. 152177/1983 is known.

An example of the above-mentioned conventional image reading device will be described below with reference to the drawings.

FIG. 4 shows the circuit configuration of a conventional image reading device. In FIG. 4, 1 is an image sensor, 7 is a fixed distortion correction signal generator, 8 is a multiplier, 4 is a shading correction circuit, 5 is an A/D converter, and 6 is an arithmetic circuit.

The operation of the image reading device configured as described above will be explained below.

Image sensor I receives image light reflected from the top of the document
An image signal with less distortion is obtained by multiplying the output signal by a reverse distortion signal (adjusted and fixed in advance) generated from a fixed distortion correction signal generator 7 as a first correction means in a multiplier 8. . This less distorted image signal is then
The signal is converted into a signal completely free of shading distortion in the shading correction circuit 4, which is a correction means for the signal.

Problems to be Solved by the Invention However, with the method described above, the fixed distortion correction signal generator is composed of an address generation circuit, a ROM, an A/D converter, etc., so the number of parts increases and the circuit scale becomes large. turn into. If even higher-speed processing is to be performed, a higher-speed multiplication circuit or the like will be required, resulting in an increase in cost.

Further, since the correction signal is fixed and the conditions are the same in any case, if a brightness difference or the like occurs in the light source, there is a risk that the first correction means will not be able to cope with it.

In view of the above-mentioned problems, the present invention provides an image reading device that can correct a read image signal of an image sensor at low cost and with a simple circuit configuration.

Means for Solving the Problems In order to solve the above problems, an image reading device of the present invention includes a plurality of variable gain circuits that amplify or attenuate a read image signal of an image sensor by a preset gain, and a plurality of variable gain circuits that amplify or attenuate a read image signal of an image sensor. This device includes a selection circuit that selects and outputs read image signals output from the circuit in a predetermined sequence, and a shading correction circuit that corrects shading distortion contained in the output signal from the selection circuit.

Function The present invention corrects the distortion of the read image signal using a plurality of variable gain circuits and selection circuits as the first correction means in the above-described configuration, thereby producing an image signal with less distortion at low cost and with a simple circuit configuration. It can be sent to the shading correction circuit which is the second correction means.

Embodiment Hereinafter, an image reading apparatus according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows the main parts of an image reading device in an embodiment of the present invention. In FIG. 1, 1 is an image sensor, 2 is a variable gain circuit, and 3 is an image sensor.
is a selector, 4 is a shading correction circuit, and A/D
It consists of a conversion circuit 5 and an arithmetic circuit 6.

The operation of the reading circuit of the image reading apparatus configured as described above will be explained below with reference to FIGS. 1, 2, and 3.

Image sensor 1 receives image light reflected from above the document
Assume that the output signal (FIG. 3(a)) has a distortion of ΔA that exceeds the correction range of the second correction means. Figure 3 (
As shown in b), division is performed according to the magnitude of distortion. In this embodiment, it is divided into three parts. The predetermined gain values of the variable gain circuit are as shown in FIG. 2, and there are three types in this embodiment.

In the period 9 in FIG. 3(b), the gain value a shown in FIG. 2 is selected, and in the period 10, the gain value C is selected, and 1
In period 1, by selecting the gain value and performing distortion correction, the distortion of ΔA as shown in FIG. 3(C) can be corrected to distortion of about ΔB. The signal that has undergone the first correction is converted into a signal completely free of shading distortion by the shading correction circuit 4, which is the second correction means.

As described above, according to this embodiment, since distortion correction is performed using a plurality of variable gain circuits and selection circuits at the analog signal stage, multipliers, A/D converters, fixed distortion correction signal generators, etc. can be omitted. Can be done. Therefore, distortion correction processing can be performed at low cost and with a simple circuit configuration.

In addition, since distortion correction is performed not by a fixed distortion correction signal but by multiple variable gain circuits and selectors depending on the degree of distortion for each image reading device, it can also respond to changes in conditions such as brightness differences of light sources. It is possible.

In this embodiment, three variable gain circuits are used, but there is no problem even if the number of variable gain circuits is increased further.

Effects of the Invention As detailed above, the present invention includes a plurality of variable gain circuits that amplify or attenuate a read image signal of an image sensor by a preset gain, and a read image signal output from the plurality of variable gain circuits. By providing a selection circuit that selects and outputs in a predetermined sequence and a shading correction circuit that corrects shading distortion included in the output signal from the selection circuit, sufficient distortion correction can be made even when shading distortion becomes large. Therefore, image distortion can be removed more reliably at low cost and with a simple circuit configuration.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the main parts of an image reading device according to an embodiment of the present invention, Fig. 2 is a main scanning direction sensor output waveform diagram showing the gain value of the variable gain circuit, and Fig. 3 is a shading distortion correction method. FIG. 4 is a block diagram showing the main parts of a conventional image reading device. DESCRIPTION OF SYMBOLS 1... Image sensor, 2... Variable gain circuit, 3... Selector, 4... Shading correction circuit, 5... A /D converter, 6
・・・・・・Arithmetic circuit. Agent's name: Patent attorney Shigetaka Awano

Claims (1)

[Claims] a plurality of variable gain circuits that amplify or attenuate the read image signals of the image sensor by a preset gain; and a selection circuit that selects and outputs the read image signals output from the plurality of variable gain circuits in a predetermined sequence; An image reading device comprising: a shading correction circuit that corrects shading distortion included in an output signal from a selection circuit.