JPH03278674A - Automatic adjustment method for white level compression characteristic and decoding characteristic for image pickup device - Google Patents

Abstract

PURPOSE:To adjust a white level compression start point accurately automatically by inputting a digital reference pulse resulting from A/D conversion to a digital computing element, comparing with a prescribed reference digital value and feeding back the signal to a white level compression and reference pulse insert circuit. CONSTITUTION:A white level compression and reference pulse insert circuit 3 inserts a reference pulse 12 to an input signal based on a command given from a reference pulse insert command line 8 and decides a peak value of the reference pulse 12 and a white level compression start point to a same level according to a digital data or a DC level given through a white level compression start point control line 9. Then a digital value of a reference pulse after A/D conversion is fetched in a digital computing element 7 such as a microcomputer and compared with a prescribed reference digital value, and the result is fed back to a white level compression start point control section of the white level compression and reference pulse insert circuit 3 to make the digital value of the white level compression start point with a prescribed reference digital value. Thus, the white level compression start point of the white level compression stage is accurately adjusted automatically.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention automatically adjusts the white compression start point of an imaging device, and in particular, white compression processing is performed on an output signal of an imaging device and then converted into a digital signal. This is effective in an imaging device that performs subsequent processing using digital processing.

[Conventional technology]

In imaging devices, the aperture of the lens is manually or automatically adjusted so that the average brightness of the entire screen is approximately constant. However, when a subject with particularly high brightness enters a part of the screen, the output signal amplitude of the image sensor exceeds the rated value in that part. The output signal amplitude of the imaging device is prevented from significantly exceeding the rated value. In such white compression characteristics, it is important that the white compression starting point matches a predetermined value near the rated value, and a method for automatically adjusting this is shown in Japanese Patent Publication No. 1-53546. There is.

[Problem that the invention sought to solve]

However, the above-mentioned conventional technology requires a plurality of sampling pulses having a complicated time relationship, and the adjustment procedure is also complicated.

In addition, in so-called digital signal processing type imaging devices that process video signals in the state of digital signals, the processing frequency of approximately 172 to 174 is Although A/D conversion (analog-to-digital conversion) may be performed after relatively light white compression, the prior art does not take this into account.

Furthermore, in the above-mentioned digital signal processing type imaging device, it is possible to restore the linear shape by performing expansion processing complementary to the above-mentioned white compression characteristic at the digital processing stage, but this point also differs from the above-mentioned conventional method. Technology is not considered.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for accurately and easily automatically adjusting the white compression start point of a white compression stage installed before an A/D conversion stage in a digital signal processing type imaging device.

Another object of the present invention is to provide a method for obtaining linearly restored digital signal values by performing expansion processing complementary to the white compression characteristic at the stage of digital processing, and a method for obtaining a digital signal value restored in a linear manner, and an expansion starting point in the expansion processing. An object of the present invention is to provide an automatic adjustment method for matching the white compression start point with the white compression start point.

[Means to solve the problem]

In order to achieve the above object, the present invention provides a digital signal processing type imaging device with a white compression function and a function of inserting a reference pulse whose peak value coincides with the white compression start point at a stage before the A/D conversion stage. A white compression and reference pulse insertion circuit having the following characteristics is arranged, and the digital value of the reference pulse portion of the digital signal after A/D conversion is inputted into a digital arithmetic unit such as a microcomputer, and the digital value is compared with a predetermined reference digital value, The result of the comparison calculation is fed back to the white compression start point control section of the white compression and reference pulse insertion circuit, and the
The digital value of the white compression start point in the digital signal after /D conversion is made to match the predetermined reference digital value.

Further, in order to restore the white-compressed signal to a linear characteristic in the digital signal processing stage, the present invention includes a digital correction circuit having a white expansion characteristic complementary to the white compression characteristic in the digital signal processing stage. By using a back system in combination, the white compression start point is made to coincide with the white expansion start point.

Further, in order to restore the white-compressed signal to linear characteristics in the digital signal processing stage, other means of the present invention include:
A digital correction circuit having a white expansion characteristic complementary to the white compression characteristic is provided in the digital signal processing stage, the digital value of the reference pulse portion is input to a digital computing unit such as a microcomputer, and the digital correction is performed according to a command from the digital computing unit. The white expansion start point of the circuit is controlled so that the white expansion start point coincides with the white compression start point.

[Effect]

The white compression and reference pulse insertion circuit uses the output signal of the image sensor or a signal after preprocessing such as noise removal and automatic gain control as an input signal, and starts white compression selected near the rated amplitude value. The part of the signal waveform on the white side that exceeds the point is compressed to a fraction and output. In addition, according to instructions from a digital calculator such as a microcomputer, a reference pulse is added to the input signal during the vertical blanking period when the imaging device is in normal operation or during the characteristic period when the imaging device is in the reference state.

Insert and output. Then, the bias potentials are related to each other so that the peak value of the reference pulse coincides with the white compression start point of the white compression or has a certain difference, and the comparison calculation result output from the microcomputer is used. controlled.

Therefore, the feedback system automatically controls the digital value of the reference pulse portion to match the reference digital value, so that the white compression start point is automatically adjusted to the reference value in the digital signal.

Regarding the restoration of white compression, the digital correction circuit has white expansion characteristics that are complementary to the white compression characteristics, and acts to cancel the compression characteristics of the signal that has undergone white compression, so that it Outputs the restored digital signal. Since the white expansion start point is made to match the reference digital value, when the digital value of the reference pulse portion matches the reference digital value by the feedback system, as a result, the white compression start point in the digital signal becomes the same as the reference digital value. Matches the white stretch start point.

In still another method, the white expansion start point of the digital correction circuit is determined based on the digital value of the reference pulse portion, so that the white compression start point and the white expansion start point coincide as a result.

〔Example〕

A first embodiment of the present invention will be described below with reference to FIGS. 1 to 3.

In FIG. 1, 1 is an image sensor, 2 is a pre-processing stage such as noise removal by CD5 (correlated double sampling) and AGC (automatic gain control), 3 is a white compression and reference pulse insertion circuit,
4 is an ADC (analog/digital converter), 5 is a digital signal processing stage, 6 is an ADC (digital/analog converter), 7 is a microcomputer, 8 is a reference pulse insertion command line,
9 is a white compression start point control line, and 10 is a video signal output line.

The white compression and reference pulse insertion circuit inserts a reference pulse into the input signal based on a command given by the reference pulse insertion command line 8. Further, the peak value of the reference pulse and the white compression start point are determined to be the same value according to digital data or DC potential given through the white compression start point control line 9. FIG. 2 shows an example of an output signal waveform of the white compression and reference pulse insertion circuit. This is the case when a ramp waveform is used as an input signal, which is convenient for understanding the white compression characteristics. In the waveform portion where the input signal exceeds the white compression start point A (the potential at which white compression starts), the slope is compressed to 1/3, and the signal is output as shown in C. Further, a reference pulse 12 having a peak value B is inserted into a part of the vertical blanking period. The white compression start point A and the peak value B of the reference pulse are set to be equal.

This waveform is converted into a digital signal by the ADC 4, various processes necessary for the camera are performed in the digital signal processing stage 5, and the output signal is converted back into an analog signal by the DAC 6 and output to the video signal output line 10. The digital value is taken into the microcomputer at the timing of the reference pulse part from the middle of the digital signal processing stage, and the microcomputer performs a comparison calculation with the reference digital value, and the calculation result is used for white compression and reference pulse insertion through the white compression start point control line 9. Feedback to the circuit. If the digital value taken into the microcomputer is higher than the reference value, the white compression start point is controlled to be lowered, and vice versa, it is controlled to be raised.By repeating this, the digital value of the reference pulse area is The digital signal is converged to match the reference digital value, and as a result, the digital value at the start point of white compression in the digital signal is automatically adjusted to match the predetermined reference digital value, achieving the object of the present invention. be done.

FIG. 3 shows a specific example of the white compression and reference pulse insertion circuit. In the figure, 31 is an input terminal, 32 is an output terminal,
81 is a reference pulse insertion command terminal, and 91 is a white compression start point control terminal. Other circuit symbols are well known. First, the effect of white compression is that the transistors Q1 to Q
4. DC current source II.

I1/2 and resistors R1 and R2. The potential of the input terminal 31 is the potential of the white compression start point control terminal 91 (
VA), Q3 is cut off and the potential at point B becomes the same as the potential at input terminal 31, so the same potential as input terminal 31 also appears at point 6. When the potential of input terminal 31 is higher than VA, Q2
is cut off, and the potential at point B is fixed at VA. Therefore, at point 6, the voltage obtained by dividing the voltage at input terminal 31 and the voltage vA at point B proportionally by resistors R1 and R2 is cursed. That is, for the part of the input signal waveform that exceeds the potential of the white compression start point control terminal, the voltage change is R2/(R1+R2
).

Next, the effect of reference pulse insertion is the effect of transistors Q5 to Q
IO, DC current source I2. I2/2. Obtained by bias power supply VD. When the potential of the reference pulse insertion command terminal 81 is lower than the bias potential VD, Q7. Q
8. The QIO is cut off, and a signal output equal to the six-point video signal waveform is obtained at the output terminal 32. Conversely, terminal 8
When the potential of Q5.1 is higher than VD, Q5. Q6
．． Q9 is cut off, and a voltage equal to the voltage 6 at the white compression start point control terminal appears at the output terminal 32. As described above, by applying a pulse to the terminal 81 that becomes high during a part of the vertical blanking period according to a command from a microcomputer, etc., a reference pulse having a peak value that matches the white compression starting point potential is generated. can be inserted.

Next, a second embodiment of the present invention will be described with reference to FIGS. 4 and 5. In FIG. 4, 5 is a digital signal processing stage, which includes 51 and 52. 51 is a digital correction circuit, and 52 is another digital processing circuit. Further, other symbols are the same as those described above.

The digital correction aperture INt51 has a white expansion characteristic as shown in FIG. 5(b), and acts to magnify the change in response to a digital value input larger than the white expansion start point.

This white expansion characteristic is preset to a complementary characteristic that cancels out the white compression characteristic (shown in FIG. 5(a)) applied at the analog signal stage, and the white expansion starting point is
This is to match the reference digital value of the microcomputer. In such a configuration, when the digital value of the reference pulse portion is automatically adjusted to match the reference digital value of the microcomputer in the same way as in the first embodiment, as a result, the white compression starting point of the digital signal is The digital value coincides with the digital value of the white expansion start point of the digital correction circuit, and a digital signal with restored linearity is obtained at the output of the digital correction circuit. Incidentally, the polygonal line-shaped white expansion characteristic as shown in FIG. 5(b) can be easily realized by well-known digital calculation, and detailed explanation will be omitted. Additionally, the characteristics of white compression processed by analog circuits may exhibit characteristics with rounded corners rather than a simple polygonal shape, but if you want to obtain white expansion characteristics that are complementary to such characteristics, , a generally known look-up table type digital correction circuit may be used.

Next, a third embodiment of the present invention will be described with reference to FIG. In the figure, each symbol is the same as above.

The difference from the second embodiment is that a fixed voltage 9 is applied to the white compression start point control line 9, and that the digital correction circuit 51 is controlled by the microcomputer. The digital value of the reference pulse part of the analog-to-digital converted digital signal is taken into the microcomputer.

With reference to this value, a correction constant for the digital correction circuit is calculated and stored in the correction circuit. Since the peak value of the reference pulse coincides with the white compression start point, by passing it through a digital correction circuit with correction characteristics created based on the digital value of the reference pulse, the white compressed signal becomes almost completely linear. Restored to characteristics. One way to calculate the correction constant of the microcomputer is to set the standard white expansion characteristic in advance according to the standard value of the white compression characteristic, and then check the digital value of the reference pulse taken into the microcomputer against the standard value. The above-mentioned white extension characteristic is shifted up and down by the amount of deviation.

〔Effect of the invention〕

According to the present invention, since the white compression start point is automatically controlled so that the digital value of the reference pulse having the same peak value as the white compression start point matches the reference value, the white compression start point can be set to the desired digital value. This has the effect of allowing accurate and easy automatic adjustment.

In addition to the above, since the white expansion characteristic complementary to the white compression characteristic can be digitally corrected, there is an effect that the linear characteristic can be restored at the digital signal stage.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a first embodiment of the present invention;
The figure is a waveform diagram explaining the operation of the first embodiment, FIG. 3 is a circuit diagram showing a specific example of the white compression and reference pulse insertion circuit, and FIG. 4 is a block diagram showing the second embodiment of the present invention. , FIG. 5 is a characteristic diagram illustrating the operation of the embodiment shown in FIG. 2, and FIG. 6 is a block diagram showing a third embodiment of the present invention. 1 Image sensor f-12...Pre-processing stage, 3... White compression and reference pulse insertion circuit. 4--Analog-digital converter, 5--Digital signal processing stage, 6--Digital-analog converter, 7--Microcomputer, 8--Reference pulse insertion command line, 9--White compression Starting point control line, 51...Digital correction circuit. Taku〕 evil

Claims (1)

[Claims] 1. In a digital signal processing type imaging device, a white compression function and a reference pulse whose peak value coincides with the white compression start point of the white compression or a constant difference are inserted at a stage before the analog-to-digital conversion stage. A white compression and reference pulse insertion circuit having the function of The result of the comparison operation is fed back to the white compression and reference pulse insertion circuit to control the white compression start point of the circuit, and the digital value of the white compression start point in the digital signal after the analog-to-digital conversion is set to the predetermined digital value. A method for automatically adjusting white compression characteristics to make the values match or have a constant difference. 2. The method for automatically adjusting white compression characteristics according to claim 1, wherein the white compression and reference pulse insertion circuit inserts a reference pulse during a part of a vertical blanking period. 3. The method for automatically adjusting white compression characteristics according to claim 1, wherein the white compression and reference pulse insertion circuit inserts the reference pulse during a specific period when the imaging device is in a state of preparation for imaging. 4. A digital signal processing type imaging device has a white compression function and a function of inserting a reference pulse whose peak value coincides with the white compression start point of the white compression or a constant difference in the stage before the analog-to-digital conversion stage. A white compression and reference pulse insertion circuit is arranged, and a digital correction circuit having white expansion characteristics complementary to the white compression characteristics is arranged after the analog-to-digital conversion stage, and the digital signal of the analog-to-digital conversion stage is The digital value of the reference pulse portion is taken into a digital arithmetic unit and compared with a digital value that is equal to or has a constant difference from the white expansion start point of the digital correction circuit, and the result of the comparison operation is used for the white compression and reference. Feedback is given to the pulse insertion circuit to control the white compression start point of the circuit, and the digital value of the white compression start point in the digital signal after the analog-to-digital conversion is made to match the digital value of the white expansion start point of the digital correction circuit. A method for automatically adjusting white compression characteristics and restoration characteristics in such a manner as to 5. A digital signal processing type imaging device has a white compression function and a function of inserting a reference pulse whose peak value coincides with the white compression start point of the white compression or a constant difference in the stage before the analog-to-digital conversion stage. A white compression and reference pulse insertion circuit is arranged, and a digital correction circuit having white expansion characteristics complementary to the white compression characteristics is arranged after the analog-to-digital conversion stage, and the digital signal after analog-to-digital conversion is The digital value of the reference pulse portion is taken into a digital arithmetic unit, the correction constant of the digital correction circuit is calculated by referring to the digital value, and this is stored in the digital correction circuit, and the white expansion characteristic of the digital correction circuit is calculated. A method for automatically adjusting white compression characteristics and restoration characteristics so as to match characteristics complementary to the white compression characteristics.