JPH0130342B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a signal processing method, and more particularly, to a signal processing method for digitizing a photoelectrically converted video signal in a facsimile reader or the like.

[Prior Art] First, the above video signal is obtained as follows.

That is, an image of an original illuminated by a light source such as a fluorescent lamp is formed through a lens onto a line sensor such as a CCD (charge coupled device) sensor, and the image is converted into an electrical signal to obtain a video signal.

In such a case, due to the above-mentioned variations in the light source, reduction in peripheral light intensity of the lens, variations in line sensor sensitivity, etc., even if the original is completely white, the obtained video signal will not be uniform, and the resulting video signal will be distorted. This distortion signal is called shading.

In order to correct this distortion signal, the A/D converted shedding distortion signal is stored in memory, and then,
There is a device that enables accurate digitization by reading out this, D/A converting it, and using the reproduced shedding distortion.

FIG. 1 is a block diagram showing an example of a conventional device as described above.

In the figure, 1 is a peak hold circuit, 2 is an A/
In the D/D/A conversion circuit, 3 is a memory, 4 is a comparator, and R is a resistor.

FIG. 2 is a waveform diagram for explaining what is shown in FIG. 1.

To explain these, first, the above-mentioned shading distortion waveform is input to the peak hold circuit 1, its peak value is detected, and this value is held.

Next, the shading distortion waveform is directly input to the A/D/D/A conversion circuit 2, and the deviation from the peak value output of the peak hold circuit 1 held above, that is, the shading based on the brightest part of the original is calculated. The distortion signal is A/D converted and the digital information is written into the memory 3 as memory data.

Next, when a video signal containing information superimposed on the above-mentioned shading distortion is input, synchronized with this,
The shading distortion data stored in the memory 3 is read out and D/A converted by the A/D/D/A conversion circuit 2 to reproduce a shading distortion waveform.

This reproduced shading distortion waveform is voltage-divided by a resistor R to form a slice level.

This slice level and the video signal are compared by a comparator 4, and a digital signal is output.

FIG. 3 is a block diagram of a conventional example of the peak hold circuit 1 in the above-mentioned conventional signal processing device for digitization.

In the figure, 4A is a comparator, 5 is an address counter, 6 is a demultiplexer, 7 is an operational amplifier,
AND is an and gate, r ₀ , r ₁ , …r _o …r _n , V ₁
...V _o ...V _n is the potential of each step of the resistor string RS, V _L and V _H are the input voltages of the resistor string RS, CLK is a clock, and ST is a start signal.

Note that the operational amplifier 7 is used as a voltage follower.

In the above, when the address counter 5 is cleared by the start signal ST, the output of the demultiplexer 6 selects the lowest step in the resistor string RS, and the input and output of the operational amplifier 7 are brought to approximately the potential of _VL . Become.

If the video signal is input to comparator 4A and is larger than the output of operational amplifier 7, comparator 4
The output of A becomes “1” level, and the AND gate
AND supplies clock CLK to address counter 5.

The address counter 5 increments, and the demultiplexer 6 selects the upper step.
The input/output of the oper limp 7 is increased one step at a time.

Then, the AND gate AND supplies the clock CLK to the address counter 5 until the video signal and the output of the operational amplifier 7 become approximately equal.

When this video signal and the output of the operational amplifier 7 become approximately equal, the address counter 5 and the demultiplexer 6 stop operating, and the peak value of the video signal is obtained at the output of the operational amplifier 7.

Here, the A/D/D/A conversion circuit 2 is configured to count down the address counter 5 when the video signal is smaller than the output of the operational amplifier 7. Therefore, both the peak hold circuit 1 and the A/D/D/A conversion circuit 2 have the same problem of conversion error caused by the resistor string RS as described below. Now, the peak value of a video signal changes greatly due to variations in the light source, differences in original density, and the like.

On the other hand, the accuracy of the conventional peak hold circuit as shown in FIG. 3 is determined by the potential difference ΔV=V _o -V _o-1 between each step of the resistor string RS.

Furthermore, in the conventional peak hold circuit, each element resistance r ₀ to r _n between the steps of the resistor string R-S
The values of are almost equal, and the potential difference ΔV between each step
are also approximately equal over all steps.

In such a case, as the peak value V _P of the video signal decreases, its accuracy decreases and the conversion error ε increases. Here, the conversion error ε is given by the following equation.

ε=ΔV/V _P ...(1) [Problems to be solved by the invention] Conventional methods, including those with the above-mentioned conventional configuration, convert a shedding distortion waveform or video signal into a digital signal, or vice versa. The potential difference at each step of the voltage that is generated to convert the digital signal to the above-mentioned reproduced signal and whose magnitude changes in steps according to the magnitude of the video signal or digital signal is changed in an arithmetic series. Therefore, the conversion error of the A/D converter, D/A converter, etc. increases in a small area of the video signal, resulting in a disadvantage that signal processing accuracy decreases.

An object of the present invention is to improve signal processing accuracy by making conversion errors of A/D converters, D/A converters, etc. uniform regardless of the size of a video signal.

[Means for Solving the Problems] In order to achieve the above object, the present invention converts the shedding distortion waveform into a digital signal and stores it when digitizing a video signal including shedding distortion. In a signal processing method that converts the stored digital signal into an analog shading distortion reproduction signal and digitizes the video signal using this reproduction signal, the video signal or the digital signal is converted into a step shape according to its magnitude. The signal is converted into a changing voltage, and the potential difference at each step is changed almost geometrically in proportion to the magnitude of the video signal or digital signal, so that the conversion error of the reproduced signal is almost uniform. be.

[Function] In the present invention, A/D conversion,
This has the effect that conversion errors such as D/A conversion become uniform regardless of the size of the video signal, and signal processing accuracy is improved.

[Example] An example according to the present invention will first be described with reference to FIG. 3 above.

Now, in the conventional example shown in FIG. 3, the inter-step resistances r ₀ , r ₁ . . . r _o . . .
When the value of r _n is changed, the potential difference ΔV _o between each step is defined as follows.

ΔV _o =V _o −V _o-1 (where n=0 to m) ...(2) From the equation (1) above, the conversion error _{ε a} at this time is as follows.

ε _a = ΔV _o /V _P ……(3) Also, in Fig. 3, the maximum allowable value of the peak value V _P is V _H , so when V _P = V _H , ΣΔV _o = V _H ……(4 ) ∴Σε _a =ΣΔV _o /V _H =1 ...The following relationship holds true. It is mathematically clear that under this condition, in order to minimize the maximum possible value of each ε _a , ε _a should be kept at a constant value.

That is, as shown in FIG. 3, when the number m of divided resistor strings R-S is constant, the peak value V _P
If ΔV _o is determined so that the conversion error ε _a for the minimum value of and the conversion error _{ε a} for other peak values V _P are approximately constant, then the conversion error ε _a for peak value detection for the video signal input is , always remains almost constant.

Therefore, the resistance string R-S that meets this condition is
Derive and see the value of each element.

If the peak value V _P of the video signal is approximately equal to the potential of V _o , then the following equation is obtained from equations (2) and (3) above.

ε _a ≒ (V _o −V _o-1 )/V _o ...(6) Therefore, from this equation (6), the following equation is obtained.

V _o ≒ {1/(1-ε _a )} ⁿ V ₀ ...(7) Here, V ₀ =V _L , which is a constant voltage.

Also, according to Ohm's law, it is as follows.

iγ _o =V _o −V _o-1 (8) where i is the current flowing through the resistor string R-S, and is expressed by the following equation.

i=(V _H −V _L )／ _o 〓 ⁿ⁼⁰ r _o ...(9) Here, if _o 〓 ⁿ⁼⁰ r _o = Rs, (6), (7), (8), (9)
From the equation, we get the following:

r _o ≒Rs・V _L /(V _H −V _L )・ε _a・{1/(
1−ε _a )} ⁿ …(10) Here, since ε _a is constant, from equation (10), the resistance r _o
It can be seen that it is sufficient to increase the value almost geometrically.

For this reason, in the present invention, the value of the above-mentioned resistor r _o is increased almost geometrically to process the signal, and the error in detecting the peak value is made almost constant and uniform. It is something.

According to the above, even if the peak value of the video signal is changed, the error in the peak value detected by the peak hold circuit 1 remains almost constant, and the error in the peak value detected by the peak hold circuit 1 remains almost constant. The error in the reproduced signal is also constant, and the influence on the image is also constant.

That is, even if the peak value of the video signal changes because the light source becomes darker or the original density becomes higher, the obtained image will not change.

As mentioned above, this method can be applied to A/D.
Even when used in the D/A conversion circuit 2, exactly the same effect can be obtained.

That is, the configuration of the A/D/D/A conversion circuit 2 is almost the same as the peak hold circuit block diagram shown in FIG. 3, except that the address counter 5 is an up-down counter as shown in FIG. Become.

FIG. 4 is a block diagram of an A/D/D/A conversion circuit 2 for explaining another embodiment of the present invention, and the same reference numerals as in FIGS. 1 and 3 refer to equivalent configurations. 41 is a video signal input terminal, 43 is a switch, 44 and 45 are AND gates 4B is a comparator.

When an A/D conversion method called successive approximation is used in the configuration shown in the figure, the video signal input from 41 and the output 42 of the operational amplifier 7 are compared by the comparator 4B, and the signal is reproduced as the output of the operational amplifier 7. If the shedding distortion waveform is larger than the input signal to the terminal 41, the address counter 5 is incremented, and if it is smaller, it is decremented, and the output of the operational amplifier 7 is automatically brought closer to the shedding distortion waveform.

Next, this will be explained in detail. First, the shaded distortion waveform is input to the terminal 41, digitized, and stored in the memory 3. At this time, the output of the address counter 5 is the A/D of the shaded distortion waveform.
This is the D-converted output. The signal for controlling the up-down is stored in the memory 3 as a digital signal of "1" and "0" as the output of the comparator 4B, and the switch 43 is closed and the signal is output to the terminal 31. Next, the operation when D/A converting this stored data will be explained. Open switch 43,
The clock is clocked by the AND gates 44 and 45 according to the digital signal read from the memory 3.
Open and close CLK, drive address counter 5,
Play digital values. As a result, a reproduced shading distortion signal approximately having a shading distortion waveform is obtained at the output 42 of the operational amplifier 7 through the demultiplexer 6 and the resistor string RS.

As mentioned above, the above A/D・
The present invention applies in exactly the same way to one example of the D/A conversion circuit 2, and the values of the inter-step resistances r ₀ ...r _n in the resistor string RS are increased almost sequentially in a geometric progression. Therefore, A/D・
Errors in the original shading distortion waveform of the D/A converted reproduced shading distortion signal can be made uniform.

Further, the present invention can have the same effect even when applied to a digitizing apparatus of the same category of circuit type, which does not include the peak hold circuit 1 and directly performs A/D conversion.

In each of the above embodiments, the potential difference of each step was changed using the resistor string R-S, and the potential difference was gradually increased. However, this is not limited to the resistor string R-S, and the capacitance or resistor It does not prevent the potential difference from changing by using impedance such as a combination of a capacitor and a capacitor, and in short, if it is related to a method that can change the step potential difference of A/D or D/A conversion. It's good.

[Effects of the Invention] The conventional method is generated for converting a video signal or a shedding distortion waveform into a digital signal, or conversely, converting a digital signal into the above-mentioned reproduction signal, and the magnitude thereof is equal to that of the above-mentioned video signal or digital signal. Since the potential difference at each step of the voltage that changes in steps according to the size is changed in an arithmetical series, errors in A/D converters, D/A converters, etc. become large in small areas of the video signal. However, there was a drawback that the signal processing accuracy decreased. In contrast, in the present invention, the potential difference between the steps of voltage change is changed almost in a geometric series in proportion to the magnitude of the video signal. This has the effect of improving signal processing accuracy because errors such as these become uniform regardless of the size of the video signal.

Also, when A/D conversion and D/A conversion are performed in the same circuit, the conversion error during A/D conversion and the conversion error during D/A conversion are almost canceled out, so two conversions are performed. It has the advantage that conversion errors are extremely small despite the fact that

[Brief explanation of drawings]

FIG. 1 is an illustrative block diagram of a conventional device used to explain the conventional system, FIG. 2 is a waveform explanatory diagram of the device according to FIG. 1, and FIG. FIG. 4 is an exemplary block diagram of an A/D/D/A conversion circuit for explaining another embodiment of the present invention. 1...Heat hold circuit, 2...A/D・
D/A conversion circuit, 3...Memory, 4, 4A, 4B
... Comparator, 5 ... Address counter, 6
... Demultiplexer, 7... Operational amplifier,
AND...And gate, _r0 to _ro ...Resistance between each step of the resistor string RS, _V0 to _Vn ...Potential of each step of the resistor string R-S, _VL to
V _H ...Input voltage of resistor string R-S, R...
...Resistance, ST...Start signal, CLK...Clock.

Claims (1)

[Scope of Claims] 1. When digitizing a video signal containing shedding distortion, converting the shedding distortion waveform into a digital signal and storing it, converting the stored digital signal into an analog shedding distortion reproduction signal, In a signal processing method that digitizes a video signal using this reproduced signal, the video signal or digital signal is converted into a voltage that changes in steps according to its magnitude, and the potential difference at each step is A signal processing method characterized in that the conversion error of the reproduced signal is made almost uniform by changing the signal in a substantially geometrical series in proportion to the magnitude of the signal. 2. When converting the shedding distortion waveform into a digital signal and storing it, a peak value of the video signal including the shedding distortion is held, and an amount of shedding distortion based on the peak value is converted into a digital signal. The signal processing method according to item 1. 3. The electric potential difference of each step is changed by setting the resistance value between each step of the resistor string to change almost geometrically. Signal processing method.