JPH0514733A - Picture reader - Google Patents

Abstract

PURPOSE:To obtain a picture reader which executes contrast adjustment with good economical efficiency, and in addition, does not cause the deterioration of the quality of a picture. CONSTITUTION:Width between the upper limit and the lower limit of contrast is changed by the change of the voltage of one side of either a first voltage generation circuit 9 or a second voltage generation circuit 10. Since the voltage determined in this way is supplied to an A/D converter 11 as reference voltage, the contrast of the signal outputted from the A/D converter 11 varies even if the amplitude of an analog signal is constant.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image input device for photoelectrically reading an image of an original in a computer, a word processor or the like to input the image.

[0002]

2. Description of the Related Art Conventionally, an image reading apparatus for reading a printed image and converting it into an electric signal has been proposed. This type of apparatus is designed to obtain an optimum image according to a document.
A function is provided for the user to freely adjust the contrast. As shown in FIG. 4, the R, G, and B color signals output from the image sensor 1 are amplified by amplifier circuits 2, 3, and 4, and a selector circuit 5 supplied with a switching signal from a device (not shown) outputs the signals. The color signals are switched in order.

The analog signal output from the selecting circuit 5 is amplified by the amplifying circuit 6 whose gain is determined by the variable resistor 7, and is converted from MSB to L by the A / D converter 11.
The digital signal is decomposed into SB bits and output. The digital signal at this time corresponds to the values of the reference voltage H and the reference voltage L generated by the reference voltage generating circuit 8, the amplifier 9, and the amplifier 10.

Here, the contrast of the digital signal is determined by the variable resistor 7, and if the gain of the amplifier 6 is increased, the contrast becomes stronger. FIG. 5 is a waveform of each part in the circuit of FIG. 1. This example shows a case where a red original is read, and only the R signal component of FIG. 5A is generated,
The G signal component of FIG. 5B and the B signal component of FIG. 5C are not generated. FIG. 5D shows an output signal of the selection circuit 5, in which the R, G, and B signals are sequentially selected, but only the R signal is output. 5E and 5F show signals after gain adjustment. FIG. 5 (e) shows a state where the amplification factor is lowered to reduce the contrast, and FIG. 5 (f) shows a case where the amplification factor is raised to increase the contrast.

[0005]

However, in such a conventional image reading apparatus, since the amplifier 6 handles an image signal having a large amplitude, a large slew rate is required, which deteriorates the economical efficiency. If the above condition is not satisfied, the waveform becomes blunt as shown in FIG. 5 (f) and the color cannot be faithfully reproduced. Further, the variable resistor for contrast adjustment needs to be placed on the outer circumference of the case as shown in FIG. 6 so that the user can touch it. Therefore, as indicated by the thick line, an unreasonable signal routing is unavoidable and it is caused by noise. This causes deterioration of image quality. Conversely, if priority is given to image quality, the usability and external design of the user are restricted by the position of the variable resistor.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide an image reading apparatus which adjusts contrast economically and does not cause image quality deterioration.

[0007]

In order to solve such a problem, an image reading apparatus of the present invention is an image reading apparatus which reads an image signal as an analog signal and converts the analog signal into a digital signal. A first voltage generating circuit that generates a first voltage that determines an upper limit, a second voltage generating circuit that generates a second voltage that determines a lower limit of contrast, and a first analog signal supplied
And A corresponding to the second voltage and converted into a digital signal
A / D converter is provided, and at least one of the voltages generated by the first voltage generating circuit or the second voltage generating circuit is variable.

[0008]

The upper limit and the lower limit of the contrast are changed by changing the voltage of either the first voltage generating circuit or the second voltage generating circuit. Therefore, even if the amplitude of the analog signal is constant, the contrast is constant. Changes.

[0009]

1 is a circuit diagram showing an embodiment of an image reading apparatus to which the present invention is applied, and the same portions as those in FIG. 4 are designated by the same symbols. Reference numeral 12 is a reference voltage generating circuit, which is a variable resistor 1
3 changes the level of the reference voltage H

In the device constructed as described above, the operation up to the selection circuit 5 is the same as that in FIG. In the selection circuit 5, the R, G, and G analog signals are sequentially selected to be A /
It is supplied to the D converter 11. A / D converter 11
Then, as in the case of FIG. 4, the analog signal between the reference voltages H and L is converted into a digital signal having, for example, 256 gradations (when the digital signal from MSB to LSB is 8 bits).

Since the amplitude of the analog signal is constant, the contrast at this time is dominated by the level difference between the reference voltages H and L. Therefore, in this embodiment, the contrast is changed by changing the level of the reference voltage H to change the level difference between the reference voltages H and L.

FIG. 2 is a waveform of each part in the apparatus of FIG. 1, showing a case where a red original is read as in FIG.
Only the R signal component is generated in FIG.
The G signal component of (b) and the B signal component of FIG. 2 (c) are not generated. FIG. 2D shows an output signal of the selection circuit 5, which has a constant level.

On the other hand, as shown in FIG. 2 (e), since the reference voltage H changes over the range indicated by the dotted line, the level difference between the reference voltages H and L changes from the symbols a to b. As described above, the contrast changes depending on the relative relationship between the amplitude of the analog signal and the level difference between the reference voltages H and L. Therefore, by adjusting the variable resistor 13, the contrast is changed from the state corresponding to the level difference a of the reference voltage to
It is possible to change to a state corresponding to the level difference b.

FIG. 3 shows the signal flow of this embodiment. Since the reference voltage is direct current, it can be freely routed.
There is no restriction on the place where the variable resistor 13 for adjusting the reference voltage is placed, and there is no concern that performance degradation will occur no matter where it is placed. Even if noise is superimposed, it can be removed by the capacitor 14, so that a long distance can be extended. For this reason, the mounting position of the variable resistor 13 only needs to be considered in terms of usability or design.

Further, since it is not necessary to amplify the analog signal for adjusting the contrast, not only the economy is improved, but also it is not necessary to consider the rounding of the waveform due to the slew rate of the amplifier, and the characteristic becomes faithful.

Although the above embodiment is an example in which the reference voltage H is changed, the same result can be obtained by changing the reference voltage L.

[0017]

As described above, according to the image reading apparatus of the present invention, since the reference voltage supplied to the A / D converter is changed to adjust the contrast, it is not necessary to amplify the analog signal. The economy is improved, the fidelity is improved, and because the adjustment point is DC, it is easy to take measures against noise, and as a result, there is no restriction on the installation location of the variable resistor for adjustment, which improves usability. This also has the effect of increasing the degree of freedom in design.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a configuration of an embodiment of the present invention.

FIG. 2 is a waveform diagram of each part in the circuit of FIG.

3 is a diagram showing a signal flow of the device of FIG.

FIG. 4 is a circuit diagram showing a configuration of an example of a conventional device.

5 is a waveform chart of each part in the circuit of FIG.

6 is a diagram showing a signal flow of the apparatus of FIG.

[Explanation of symbols]

 1 Image Sensor 2, 3, 4, 9, 10 Amplifier Circuit 5 Selection Circuit 11 A / D Converter 12 Reference Voltage Generation Circuit 13 Variable Resistor 14 Capacitor

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Masaru Sugimoto, No. 10 Hanazono Dodo-cho, Ukyo-ku, Kyoto City, Kyoto Prefecture Omron Co., Ltd. Within Muron Co., Ltd.

Claims (1)

Claim: What is claimed is: 1. An image reading apparatus for reading an image signal as an analog signal and converting the analog signal into a digital signal, the first voltage generating a first voltage for determining an upper limit of contrast.
Voltage generating circuit, a second voltage generating circuit that generates a second voltage that determines the lower limit of contrast, and an A / A that converts the supplied analog signal into a digital signal corresponding to the first and second voltages. An image reading apparatus comprising a D converter, wherein at least one of the voltages generated by the first voltage generating circuit and the second voltage generating circuit is variable.