JPH1169242A - Image signal processor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a device capable of always inputting an image signal of proper amplitude to an A/D converter by enabling controlling the reference voltage value of the A/D converter to control the reference voltage value of the A/D converter, when a prescribed amplitude can not be obtained for an image signal inputted to the A/D converter. SOLUTION: A line sensor 1 converts an optical signal into an image signal which is an electrical signal and a sample-and-hold circuit 2 which follows the signal sample-and-holds the image signal by each pixel. The output of the circuit 2 is sent to a VCA circuit 3 to be amplified so as to be a signal of a prescribed amplitude. The circuit 3 is given a VCA setting signal sent from a CPU 10 via a D/A converter 6 and amplifies it to make the prescribed amplitude. The output of the circuit 3 enters a clamp circuit 4, and the output of the circuit 4 enters the A/D converter 5 to be converted into digital image data. UPU 10 monitors the output of the converter 5 at all times and changes a VCA set value, when the output is small.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an image signal processing device.

[0002]

2. Description of the Related Art Generally, image analog signal processing in an image information reading apparatus is performed by sampling and holding an image signal and an amplifier with automatic amplification control for automatically keeping the amplitude of the image signal constant. (Hereinafter referred to as VCA), a clamp circuit for limiting the output of the VCA to a constant value, and an A / D converter (A / D converter) for converting an analog image signal into digital image data.

FIG. 4 is a block diagram showing a configuration example of a conventional circuit. In FIG. 1, reference numeral 1 denotes a line sensor configured by arranging photoelectric conversion elements such as CCDs in a straight line.

Reference numeral 2 denotes a sample and hold circuit which samples and holds the output of the line sensor 1. As shown in FIG. 5, for example, the sample-and-hold circuit 2 includes a buffer amplifier 10 for receiving an output (image signal) of the line sensor 1, a switch SW for switching the output of the buffer amplifier 10, and a switch for switching the output of the buffer amplifier 10. It is composed of a capacitor C that is held via SW.

[0005] Reference numeral 3 denotes an amplifier (VCA) with an automatic amplification control which receives the VCA set value as a control signal and automatically keeps the output amplitude of the sample hold circuit 2 constant.
This is a clamp circuit for limiting the lower limit of the output of CA3.
A VCA set value for adjusting the gain is input to VCA3. Further, an offset for limiting the lower limit value is input to the clamp circuit 4. 5
Is an A / D converter (A / D converter) which receives the output of the clamp circuit 4 and converts it into digital data. Then, a digital output is obtained from the A / D converter 5.

[0006] In such a circuit, VCA3 has an A / D
In order to increase the conversion efficiency, it is necessary to amplify the image analog signal over the entire conversion range (full scale) of the A / D converter 5. For this reason, the amplification range must be sufficiently wide because the light source varies in light amount and changes with time, the reflection efficiency varies in the optical system (mirror) and the efficiency decreases due to dirt, and the sensitivity variation and sensitivity in the line sensor 1 increase. There are changes.

Therefore, the present inventors consider the variation in the light amount of the light source and the change with time, the variation in the reflection efficiency of the optical system (mirror) and the decrease in efficiency due to dirt, the variation in the sensitivity of the line sensor 1 and the change in the sensitivity, and the like. The VCA 3 is designed by investigating the light amount of the light source, the reflection efficiency of the optical system, and the sensitivity of the line sensor 1 to determine the required central value of the amplification degree and its range.

[0008]

However, in general, it is not easy to secure a wide range of amplification degree of an amplifier due to the limitation of input / output characteristics due to the power supply voltage and the required frequency characteristics. For this, the light intensity of the light source,
If the reflection efficiency of the optical system and the variation of the sensitivity of the line sensor are biased to the maximum or the minimum, respectively, the range of the amplification degree may be exceeded and the A / D converter may have an appropriate amplitude. Shading correction (adjustment of image signal density) where signals cannot be input and the proper density of the image cannot be obtained
There has been a problem that the image quality is deteriorated such as a defect and a deterioration of the S / N ratio.

FIG. 6 is a diagram showing a variation example of the VCA set value. The horizontal axis is the data section (VCA set value), and the vertical axis is the frequency. As shown in the figure, the set value of VCA
There is a wide range of variation up to 70 levels up to 130, and furthermore, considering the sensitivity variation (± 20%) due to the difference between CCD manufacturing lots, the distribution of the figure shifts to the left as a whole, so the VCA control range (0 to 2 in 8 bits
55). Also, depending on the set of machines, a lamp with a large rating and a large amount of light may be used. In this case, the distribution also shifts to the left and deviates from the control range.

SUMMARY OF THE INVENTION The present invention has been made in view of such a problem, and has as its object to provide an image processing apparatus capable of always inputting an image signal having an appropriate amplitude to an A / D converter. .

[0011]

According to the present invention, there is provided an image signal processing apparatus for amplifying an image signal to a predetermined amplitude and converting the signal into digital image data by an A / D converter. A reference voltage control means for changing a reference voltage value of the A / D converter is provided, and when a predetermined amplitude is not obtained in an image signal input to the A / D converter, the reference voltage control means controls the A / D converter. It is characterized in that the conversion range of the D converter is controlled.

According to the configuration of the present invention, the reference voltage control means changes the reference voltage of the A / D converter, so that A
By controlling the conversion range of the / D converter, an image signal having an appropriate amplitude can always be obtained. Further, as a result, the S / N ratio is improved, and the image quality is also improved.

(2) In this case, if the signal inputted to the A / D converter does not have a predetermined amplitude even if the amplification degree of the image signal is maximized, the reference voltage control means sets the A / D It is characterized in that the conversion range of the A / D converter is narrowed by changing the reference voltage value of the converter.

According to the configuration of the present invention, when the signal input to the A / D converter does not reach the full scale even if the amplification degree is maximized, the reference voltage of the A / D converter is changed to change the A / D converter.
By narrowing the conversion range of the converter, an image signal having an optimum amplitude can always be obtained.

(3) If the signal inputted to the A / D converter does not have a predetermined amplitude even when the amplification degree of the image signal is minimized, the reference voltage control means may be provided by the A / D converter. Is changed to extend the conversion range of the A / D converter.

According to the configuration of the present invention, even when the amplification degree is minimized, when the signal input to the A / D converter is larger than the full scale value, the reference voltage of the A / D converter is changed. By expanding the conversion range of the A / D converter, it is possible to always obtain an image signal having an optimum amplitude.

[0017]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of the present invention. The same components as those in FIG. 4 are denoted by the same reference numerals. In the figure, 1 is a line sensor in which a plurality of photoelectric conversion elements such as CCDs are arranged in a straight line, 2 is a sample and hold circuit that samples and holds the output of each pixel of the line sensor 1, and 3 is an external VCA set value. In response, the amplifier with automatic amplification control (VCA) automatically makes the output amplitude of the sample and hold circuit 2 constant.

Reference numeral 4 denotes a clamp circuit for clamping the output of the VCA 3 so as not to exceed a lower limit value. Reference numeral 5 denotes an A / D converter for converting the output of the clamp circuit 4 into digital image data. The output of No. 5 is a digital output.

Reference numeral 10 denotes a CPU for controlling the entire operation. Reference numeral 6 denotes a converter for converting the output of the CPU 10 into an analog signal and
, A D / A converter that converts the output of the CPU 10 into an analog signal and supplies the analog signal as an offset voltage to the clamp circuit 4;
Is a D / A converter that converts the output of the CPU 10 into an analog signal and supplies the analog signal to the A / D converter 5 as a reference voltage Vref. The output of the A / D converter 5 is provided to the CPU 10. The operation of the circuit thus configured will be described as follows.

According to such a configuration, the reference voltage control means (CPU 10 + D / A converter 8) changes the reference voltage Vref of the A / D converter 5, thereby changing the conversion range of the A / D converter 5. By controlling, an image signal having an appropriate amplitude can always be obtained.

The optical information is converted into an electric signal by the line sensor 1. This image signal is sampled and held by the subsequent sample and hold circuit 2 for each pixel. The output of the sample and hold circuit 2 enters the VCA 3 and is amplified to a signal having a predetermined amplitude. VCA3 has CPU
A VCA setting signal from 10 is provided via a D / A converter 6, and the VCA 3 amplifies the input signal to a predetermined amplitude at an amplification (gain) determined by the setting signal.

The output of the VCA 3 enters the subsequent clamp circuit 4. The clamp circuit 4 passes the output of the VCA 3 as it is. The output of the clamp circuit 4 enters the A / D converter 5 and is converted into digital image data. Here, the conversion range of the A / D converter 5 is
It is determined by the reference voltage Vref provided via the / A converter 8. Then, the output of the A / D converter 5 becomes a digital output.

The CPU 10 constantly monitors the output of the A / D converter 5, and when the output is small, changes the VCA set value of the VCA 3 so that the amplitude of the VCA 3 becomes large. As a result, when the input signal of the A / D converter 5 is near the full scale, the reading of the image signal is continued as it is.

On the other hand, when the output of the A / D converter 5 becomes the maximum and the output data shows the full scale even if the input signal changes, and it is considered that the input signal is saturated or the input signal is too large, The VCA set value of VCA3 is changed so that the amplitude of VCA3 becomes small. Now A
If the input signal of the / D converter 5 is near full scale,
Reading of the image signal is continued as it is.

Next, when a predetermined amplitude cannot be obtained in the image signal input to the A / D converter 5 even when the amplification degree is maximized, C
The PU 10 reduces the digital data supplied to the D / A converter 8 via the D / A converter 8 so that the reference voltage Vref is reduced.

FIG. 2A is an explanatory diagram of the reference voltage changing operation of the A / D converter at this time. In (a), the amplification degree is maximized (FFh: h indicates hexadecimal), but the image signal output amplitude is small and falls within the range of the target upper limit value Va of the signal level and the target lower limit value Vb of the signal level. Not. In this case, as described above, the reference voltage Vref of the A / D converter 5 is reduced as shown in the figure so that the maximum signal level falls between Va and Vb as shown in FIG. .

According to this embodiment, when the signal input to the A / D converter 5 does not reach the full scale even if the amplification degree is maximized, the reference voltage Vref of the A / D converter 5 is changed. By narrowing the conversion range of the A / D converter,
An image signal having an optimum amplitude can always be obtained. Also,
As a result, the S / N ratio is improved, and the image quality is also improved.

Next, when the image signal input to the A / D converter 5 is saturated even if the amplification degree is maximized and a predetermined amplitude cannot be obtained, the CPU 10 outputs the reference signal via the D / A converter 8. Digital data given to the D / A converter 8 is increased so that the voltage Vref increases.

FIG. 2B is an explanatory diagram of the reference voltage changing operation of the A / D converter at this time. In (b), although the amplification degree is minimized (00h), the image signal output amplitude is large and exceeds the target upper limit value Va of the signal level, and the range between the target upper limit value Va and the target lower limit value Vb of the signal level is obtained. Not in In this case, as described above, the reference voltage Vref of the A / D converter 5 is increased as shown in FIG.
The maximum value of the signal level is set between Va and Vb as shown in FIG.

According to this embodiment, even when the amplification degree is minimized, when the signal input to the A / D converter 5 exceeds the full scale, the reference voltage Vref of the A / D converter 5 is obtained.
Is changed to widen the conversion range of the A / D converter, an image signal having an optimum amplitude can always be obtained. Further, as a result, the S / N ratio is improved, and the image quality is also improved.

When the amplitude of the image signal input to the A / D converter 5 becomes proper by the operation described above, the normal image information reading operation as described above is performed. FIG. 3 is a flowchart showing the operation of the embodiment of the present invention. Here, Vini is an initial setting value of the reference voltage Vref, for example, 2.5 V, and Vmin is the reference voltage Vref.
At the set lower limit of 2.0 V, Vmax is the reference voltage V
The set upper limit of ref, for example, 3.0 V, Va is a target upper limit of the signal level, and is represented by Va = Vref × 0.95. Vb is a target lower limit of the signal level, and Vb =
It is represented by Vref × 0.9. Vstep is the reference voltage V
ref is a variable step. MAX is the maximum signal level, and Amp is the set value of VCA.

First, the CPU 10 sets the reference voltage Vref of the A / D converter 5 to an initial value Vini (S1). Next, the CPU 10 checks whether or not Vmin ≦ Vref ≦ Vmax (S2). If this condition is not satisfied, an error is made (S3).

Next, the CPU 10 sets the set value of the VCA 3 to the maximum value FFh (S4). This means that the gain of VCA3 is maximized. Then, it is checked whether the maximum signal level MAX is smaller than the target lower limit value Vb (S5). If the maximum signal level MAX is smaller than the target lower limit value, it means that the adjustment range by the VCA 3 has been exceeded, and the CPU 10 calculates Vref-Vstep to narrow the conversion range of the A / D converter 5. The reference voltage Vref is reduced, and the process returns to step S2.

In step S5, the maximum signal level M
If AX is larger than the target lower limit value Vb, the CPU 1
A value of 0 checks whether the maximum signal level MAX is smaller than the target upper limit value Va (S7). Maximum signal level MA
If X is smaller than the target upper limit value Va, it means that preferable conditions have been reached as shown in FIG. 2 (a) or (b), and the setting processing of the A / D converter 5 ends. .

In step S7, the maximum signal level M
If AX is larger than the target upper limit value Va, the CPU 1
If it is 0, it is checked whether the VCA setting is 00h (S8). If the setting is 00h,
It is determined that the input voltage of the A / D converter 5 cannot be reduced to a predetermined amplitude level in the adjustment of the VCA 3, and the step voltage Vstep is added to the reference voltage Vref to reduce the reference voltage of the A / D converter 5 by one step. Increase and step S2
Return to In step S8, the setting of VCA is 00h.
If not, it is still in the range where the adjustment by the VCA 3 can be performed, so the VCA set value is subtracted by 1, and the process returns to the step S7.

According to this operation, when the signal input to the A / D converter does not reach the full scale even if the amplification degree is maximized, the reference voltage of the A / D converter is changed to change the A / D converter. By always narrowing the conversion range, an image signal having an optimum amplitude can always be obtained.

According to this operation, even when the amplification degree is minimized, when the signal input to the A / D converter is larger than the full scale value, the reference voltage of the A / D converter is changed. By expanding the conversion range of the A / D converter, it is possible to always obtain an image signal having an optimum amplitude.

Further, according to this operation, even if the light amount of the light source, the reflection efficiency of the optical system, the variation in the sensitivity of the line sensor, etc. are biased to the maximum or minimum, respectively, the A / D converter has an appropriate amplitude. Can be input, and the deterioration of the image quality can be prevented.

[0039]

As described in detail above, according to the present invention, (1) an image signal processing apparatus which amplifies an image signal to a predetermined amplitude and converts it into digital image data by an A / D converter; A reference voltage control means for changing a reference voltage value of the A / D converter, wherein when a predetermined amplitude is not obtained in an image signal input to the A / D converter, the reference voltage control means By controlling the conversion range of the A / D converter, the reference voltage control means changes the reference voltage of the A / D converter, controls the conversion range of the A / D converter, and always outputs an image signal having an appropriate amplitude. Obtainable.

(2) In this case, if the signal inputted to the A / D converter does not have a predetermined amplitude even when the amplification degree of the image signal is maximized, the reference voltage control means sets the A / D By changing the reference voltage value of the converter to narrow the conversion range of the A / D converter, even if the amplification degree is maximized, A
When the signal input to the A / D converter does not reach the full scale, the reference voltage of the A / D converter is changed to narrow the conversion range of the A / D converter, and always obtain an image signal having an optimum amplitude. Can be.

(3) If the signal inputted to the A / D converter does not have a predetermined amplitude even when the amplification degree of the image signal is minimized, the reference voltage control means may control the A / D converter. Is changed to extend the conversion range of the A / D converter, so that the signal input to the A / D converter is larger than the full scale value even if the amplification degree is minimized. By changing the reference voltage of the D converter and expanding the conversion range of the A / D converter, it is possible to always obtain an image signal having an optimum amplitude.

[Brief description of the drawings]

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

FIG. 2 is an explanatory diagram of a reference voltage changing operation of an A / D converter.

FIG. 3 is a flowchart showing the operation of the embodiment of the present invention.

FIG. 4 is a block diagram illustrating a configuration example of a conventional circuit.

FIG. 5 is a diagram illustrating a configuration example of a sample and hold circuit.

FIG. 6 is a diagram showing a variation example of a VCA set value.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Line sensor 2 Sample hold circuit 3 VCA circuit 4 Clamp circuit 5 A / D converter 6 D / A converter 7 D / A converter 8 D / A converter 10 CPU

Claims (3)

[Claims] 1. Amplifying an image signal to a predetermined amplitude,
An image signal processing device for converting digital image data into digital image data by a D converter, wherein reference voltage control means for changing a reference voltage value of the A / D converter is provided, and a predetermined image signal inputted to the A / D converter is provided. An image signal processing device, wherein when the amplitude cannot be obtained, the conversion range of the A / D converter is controlled by the reference voltage control means. 2. When the signal inputted to the A / D converter does not have a predetermined amplitude even when the amplification degree of the image signal is maximized, the reference voltage control means controls the reference voltage of the A / D converter. 2. The image signal processing device according to claim 1, wherein the conversion range of the A / D converter is narrowed by changing a value. 3. If the signal input to the A / D converter does not have a predetermined amplitude even when the amplification degree of the image signal is minimized, the reference voltage control means controls the reference voltage of the A / D converter. 2. The image signal processing apparatus according to claim 1, wherein a value is changed to extend a conversion range of the A / D converter.