JP2002077740A - Device and method for automatic phase adjustment for image processor and image pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently and appropriately perform pulse phase adjustment based on objective data analysis at the time of performing automatic phase adjustment on an image processor. SOLUTION: An image pickup device 1 having an automatic phase adjusting function is provided with a sampling circuit 5 for acquiring sampled data with respect to image signals, a signal generator circuit 9 which generates a timing control signal to the processing circuit 5, and a timing adjusting means 8 which performs phase adjustment on the timing control signal by controlling the generator circuit 9. When the output signal of the image pickup device 1 is inputted through the sampling circuit 5, an analyzing means 7 calculates the signal-to- noise ratio of the output signal through image analysis and the phase of the output signal is adjusted so that the timing control signal is transmitted to the sampling circuit 5 from the signal generator circuit 9 at the timing at which the signal-to-noise becomes maximum in accordance with the results of the image analysis.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to automatic phase adjustment in an image signal processing apparatus, and more particularly to a technique for optimizing phase adjustment based on image analysis and improving workability.

[0002]

2. Description of the Related Art In an image signal processing apparatus, timing control relating to various kinds of signal processing is required.
Taking an example of a circuit configuration for processing an image output photographed by a solid-state imaging device and outputting it as a composite video signal, a signal processing circuit including a sample-and-hold circuit for the output signal is provided at a subsequent stage of the solid-state imaging device. . Then, the sample data sampled by the sample and hold circuit is further subjected to a quantization process through an analog-to-digital conversion circuit.

Incidentally, the timing control relating to the sample and hold is defined by the phase of a control pulse (so-called sampling pulse) sent to the sample and hold circuit. It is necessary to adjust the phase of the pulse at the time of manufacturing, and this work is performed. If this is not assured, there is a possibility that inconveniences such as image quality deterioration may occur.

Therefore, the iris is closed so that external light does not hit the solid-state image pickup device, and the image pickup output at that time is projected on a display means such as a monitor, and the image is considered optimal by the operator while watching the image. The phase is adjusted by searching for the value to be adjusted.

[0005]

However, the conventional phase adjustment relying on the visual sense of the operator as described above has the following problems.

(1) Every time the phase of a pulse is adjusted, the result must be confirmed by the image quality of the display means, and a repetitive operation of adjusting the pulse phase again is necessary.
It is troublesome and inefficient.

(2) Regarding the image quality adjustment, the operation becomes extremely difficult when responding very sensitively to a subtle phase change of the pulse. Therefore, it is judged that the image quality of the image visually recognized from the display means is good. It is difficult to determine which state is best in the phase adjustment range. Therefore, this adjustment is time-consuming to learn and requires skill.

Accordingly, it is an object of the present invention to perform pulse phase adjustment efficiently and appropriately based on objective data analysis in automatic phase adjustment of an image processing apparatus.

[0009]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a method for receiving an output signal from a sampling circuit for acquiring sampling data for an image signal. Analysis means for calculating a signal-to-noise ratio of the output signal by image analysis, and receiving a result of the analysis from the analysis means, the timing from the signal generation circuit to the sampling processing circuit at a timing at which the signal-to-noise ratio of the output signal becomes maximum. The timing adjusting means adjusts the phase of the control signal so that the signal is transmitted.

Therefore, according to the present invention, the image quality evaluation is made objective based on the signal-to-noise ratio calculated by the image analysis, and the timing control signal when the best image quality is obtained is searched for, thereby performing the automatic phase adjustment. It can be carried out.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The automatic phase adjuster in the image processing apparatus of the present invention is quantified by a signal-to-noise ratio based on the result of image analysis, instead of the phase adjustment performed so far by visual recognition of image quality. It is capable of quickly acquiring the optimum value of the phase adjustment so as to obtain the best image quality by performing image quality evaluation, and includes the following components.

A sampling processing circuit for obtaining sampling data (sampled data) from the image signal; a signal generating circuit (or a signal generating circuit) for generating a timing control signal for the sampling processing circuit; Timing adjustment means for adjusting the phase of a timing control signal by controlling a signal generation circuit. When an output signal that has passed through a sampling processing circuit is input, a signal-to-noise ratio (S / N ratio) related to the signal is imaged. Analysis means calculated by analysis.

FIG. 1 shows a basic configuration of an image signal processing apparatus according to the present invention, and shows a main part of signal processing for image pickup output by image pickup means.

An image pickup means 3 is provided in a camera signal processing section 2 constituting the image pickup apparatus 1 (a video camera, a still camera, or a camera having both functions), and an optical system (lens not shown) is provided. (Including system and iris)
The incident light from the subject is received via the.

The image pickup means 3 includes a solid-state image pickup device such as a CCD (charge coupled device) type and a MOS (metal oxide semiconductor) type, an image pickup tube, and the like, and a single plate type (or single tube type). It is needless to say that the present invention can be applied to a multi-plate type or the like. At the time of phase adjustment described later, the iris is closed so as not to irradiate the image pickup means 3 with external light, and an output signal of substantially black level obtained at that time is output to the image signal processing section 4 ( For example, the signal is sent to a CDS (correlated double sampling) circuit or the like.

The image signal processing section 4 has a role of performing waveform shaping, sampling processing, random noise elimination, and the like relating to the output waveform of the image pickup means 3.
(Abbreviated as “S / H” in FIG. 1), an automatic gain control circuit (AGC), and the like. For example, in the CDS, the output of the imaging unit 3 branches into two, and one of the two branches is used as a sample-and-hold circuit of the first stage (the signal “S
Sample hold is performed at the timing of “HP”. )
After that, the signal is passed through the next-stage sample-and-hold circuit (sample-and-hold is performed at the timing of a signal "SHD" to be described later) to be a first extracted signal. (Sampling and holding are performed at the timing of a signal “SHD” described later.) Then, the difference between the two signal levels is calculated by inputting the first and second extracted signals to the differential amplifier circuit and performing a subtraction process.

The sample-and-hold circuit 5 outputs a pulse signal (SHP, SHP) from a timing generator described later.
HD) and receives the image signal level at a predetermined timing, and constitutes a sampling processing circuit.

The signal that has passed through the sample-and-hold circuit 5 is sent to an analog-to-digital (A / D) conversion circuit 6, where it is converted into digital data of a predetermined bit (for example, 10 bits). 7

An image analysis section 7 constituting an analysis means receives an output signal of the analog-digital conversion circuit 6, calculates an average value and a standard deviation (square root of a root mean square) of the signal level, and outputs a signal pair. Noise ratio (hereinafter referred to as “S
NR ". ) Is calculated as a log quantity (log value) according to the following equation.

SNR = 20 · log ((maximum input signal amount of analog-digital conversion circuit) / standard deviation) In the above equation, “log (X)” indicates a common logarithmic function of variable X, and The “maximum input signal amount of the analog-digital conversion circuit” corresponds to the full-scale range of the input signal, and in n bits, the quantum number (quantu) is 2 to the nth power.
m).

The analysis result obtained by the image analysis unit 7 is sent to the timing adjustment unit 8, where the S
An optimal value of timing adjustment is set so that the value of NR becomes the best (maximum). That is, the timing adjustment unit 8 constitutes a timing adjustment means, and receives an analysis result from the image analysis unit 7 and sets a timing at which the signal-to-noise ratio of the output signal of the analog-digital conversion circuit 6 becomes maximum. The phase of the signal is adjusted so that a timing control signal (sample and hold pulse signal) is transmitted from the generator (signal generation circuit) 9 to the sample and hold circuit 5. At this time, a driving pulse signal (for example, C
In the case of a CD-type solid-state imaging device, a drive pulse for controlling charge accumulation, transfer, charge detection, and the like is sent from the timing generator 9, and the phase of the signal is also adjusted. As for the form of the timing adjustment unit 8, a configuration in which the timing adjustment unit 8 is built in the timing generator 9 and a configuration in which the adjustment unit is externally attached to the timing generator 9 are exemplified.

As a method of adjusting the phase of the timing control signal, there are various methods such as, for example, using a delay amount of an inverter train, or using a delay circuit capable of variably controlling the delay amount.

For displaying the analysis result, a display means for displaying the phase adjustment mode and displaying the SNR value may be provided. Various embodiments, such as performing only display, are possible. Further, a microcomputer can be used as the image analysis unit 7, but it is needless to say that the image analysis unit 7 may be configured as a dedicated digital operation circuit.

FIG. 2 is a diagram for explaining the outline of the signal waveform and the timing adjustment range. The meaning of each symbol is as follows.

"OUT" = output signal of the imaging means 3 "SHP" = sample-hold pulse signal for the precharge portion of OUT (a component in a so-called feedthrough period and including reset noise) "SHD" = SHP and SHD are pulses used in correlated double sampling, and a range indicated by “Rang_P” is a phase adjustment range of the signal “SHP” for a data portion of OUT (a component in a signal output period). "Rang_
A range indicated by “D” indicates a phase adjustment range of the signal “SHD”.

Regarding "OUT", since the iris is closed and the external light is cut off when the phase adjustment operation is performed, the actual data portion shows a waveform almost close to the black level.

As for the phase adjustment of the sample-and-hold pulse signal, the range of Range_P or Range_D is divided stepwise, and the number of combinations of both is subject to trial. For example, each of the phase adjustment ranges is “−8n
s to +7 ns "(" ns "= nanosecond) and 1 ns
When it is assumed that the adjustment is performed in increments, “16 × 1
6 = 256 "combinations are obtained. Therefore, the number of SNR values corresponding to the number of the combinations is calculated by the image analysis unit 7, and the timing at which the SNR value reaches the maximum value is searched for and sent to the timing adjustment unit 8. That is, by defining the sample-and-hold pulse signal at this timing, the best image quality that does not rely on visual perception is guaranteed.

FIG. 3 is an explanatory diagram relating to the SNR calculation processing by the image analysis unit 7.

In the calculation of the SNR, the imaging output when the iris is closed goes through a sample hold, an analog-digital (A / D) conversion, and an average value and a standard deviation relating to the signal level are calculated. Equations are used. At this time, the average value and the standard deviation can be obtained from the signal level values of all the pixels constituting the screen. However, as shown in the figure, a partial area of the entire screen G is extracted as the measurement area g, and The method of calculating the average value and the standard deviation of the signal level for the pixel is preferable in terms of simplification of processing and reduction of calculation time.

When the measurement area g is set as a single area, the measurement area g should include the center of the screen (the characteristics of the pixels are best in the center of the screen, the lens and the image pickup device). This is because it is preferable to select a region including the center position of the screen and extract the data because the characteristics of the pixel are changed, though minutely, depending on the distance between.) , About 1/4 of the entire screen. Alternatively, the measurement range g may be divided into a plurality of regions so that the measurement range may be dispersed at several locations.

The procedure when the above-described method of adjusting the phase of the timing control signal relating to the sampling processing for the image signal is applied to the processing of the image signal by the imaging means is as follows.
The following is a summary of the items in the bullets.

(1) With the iris fully closed,
(2) Calculate the average value and the standard deviation of the signal level of the signal after the sampling process for the output signal of the imaging means 3 (3) Obtained in (2) SNR based on the value of the standard deviation
(4) Calculate the value of (signal-to-noise ratio) as an image analysis result. (4) Based on the image analysis result of (3), a timing control signal (sample hold) at a timing at which the SNR value of the output signal after image processing becomes maximum. Pulse signal) is generated so that the signal is adjusted in phase. As a result, the optimal phase adjustment setting value is determined.

As described above, according to the present invention, an output of a substantially black level is obtained over the entire screen, and the fluctuation is analyzed to obtain the average value and the standard deviation of the black level, and the SNR value is calculated in accordance with the above equation. Then, this is used as judgment data.

If the image pickup apparatus is provided with the above-mentioned timing adjusting means and realizes automatic phase adjustment of the timing control signal based on the SNR data by the analyzing means, the phase adjusting work in the manufacturing process can be performed efficiently. It can be effective.

That is, the following forms can be given for the image pickup apparatus.

A mode in which, when an output signal that has passed through the sampling processing circuit is input, analysis means for calculating a signal-to-noise ratio of the signal by image analysis is built in the imaging apparatus.

A terminal section (connection terminal section) is provided so that the analyzing means can be connected to the main body of the image pickup apparatus as an external device, and at the time of phase adjustment, an analysis result of an SNR value of an image signal sent from the terminal section to the analyzing means is provided. Is sent to timing adjustment means in the imaging apparatus to adjust the timing control signal.

Accordingly, the phase adjustment mode is provided, and the manufacturer, the maintenance service provider, or the user selects the mode and performs the above-described automatic phase adjustment, thereby guaranteeing the best image quality display for the image output signal of the imaging apparatus. can do.

However, according to the configuration described above,
The following advantages are obtained.

The image quality can be evaluated based on objective data without relying on visual judgment of an individual having a strong analog element, so that quick and appropriate phase adjustment can be performed.

The phase adjustment operation can be automated based on the image analysis result, that is, the SNR value, so that the time required for the adjustment operation can be greatly reduced, and furthermore, anyone can make fine adjustments accurately. become.

The problem of the phase shift when the mounting condition of the device is changed can be solved, and the optimal phase adjustment can be always performed.

By mounting the above-described automatic phase adjustment function in the image pickup apparatus, the optimum phase adjustment and readjustment can be performed for each apparatus, so that the image quality deterioration due to the phase shift can be prevented and the image quality can be maintained at a certain level. Can be kept.

[0044]

As is apparent from the above description, according to the first and fourth aspects of the present invention, the image quality evaluation is made objective and quantitative based on the signal-to-noise ratio calculated by the image analysis. Since the phase adjustment can be automatically performed by searching for a timing control signal when the best image quality is obtained, the work time can be reduced. Since the best phase adjustment timing can be determined based on the signal-to-noise ratio instead of human vision, the inconvenience of taking time to learn the adjustment work can be eliminated, and a constant adjustment result can always be obtained. it can.

According to the second and fifth aspects of the present invention,
By analyzing an output signal output from the imaging unit while external light is blocked, data serving as a basis for a signal-to-noise ratio can be easily obtained.

According to the third and sixth aspects of the invention,
The standard deviation of the image signal level is obtained, and the signal-to-noise ratio can be easily calculated from the logarithm of the ratio between the standard deviation and the maximum input signal amount of the analog-digital conversion circuit.

According to the seventh aspect of the present invention, the function of adjusting the phase of the timing control signal sent to the sampling processing circuit is mounted on the imaging device, so that the phase shift of the signal can be adjusted for each imaging device. Re-adjustment can be easily performed.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration example of the present invention.

FIG. 2 is a diagram for explaining various signal waveforms and a timing adjustment range.

FIG. 3 is a diagram illustrating calculation of an SNR value by image analysis.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Imaging device, 3 ... Imaging means, 5 ... Sampling processing circuit, 6
... Analog-digital conversion circuit, 7 ... Analysis means, 8 ...
Timing adjustment means, 9 ... Signal generation circuit

Claims (7)

[Claims] 1. A sampling processing circuit for acquiring sampling data for an image signal, a signal generation circuit for generating a timing control signal for the sampling processing circuit, and a control of the signal generation circuit An automatic phase adjustment device in an image processing device, comprising: a timing adjustment unit that adjusts a phase of a timing control signal. When an output signal that has passed through the sampling processing circuit is input, a signal-to-noise ratio of the signal is adjusted. Is provided by an image analysis unit. Upon receiving the analysis result from the analysis unit, a timing control signal is sent from the signal generation circuit to the sampling processing circuit at a timing when the signal-to-noise ratio of the output signal is maximized. An image characterized in that the timing adjustment means adjusts the phase of the signal so that the signal is transmitted. Automatic phase adjustment device in the physical device. 2. The automatic phase adjusting device according to claim 1, further comprising an image pickup device, wherein the image pickup device outputs the image signal in a state where the image pickup device is shielded from external light. An automatic phase adjustment device in an image processing apparatus, wherein an output signal of the image processing apparatus is sent to an analysis means through an analog-digital conversion circuit after passing through a sample-hold circuit constituting a sampling processing circuit. 3. The automatic phase adjusting apparatus according to claim 2, wherein the standard deviation of the image signal level is calculated by the analyzing means, and the signal-to-noise ratio is calculated by the maximum input signal of the analog-digital conversion circuit. An automatic phase adjuster in an image processing apparatus, wherein the automatic phase adjuster is calculated as a logarithm of a ratio value between the amount and the standard deviation. 4. An automatic phase adjustment method in an image processing apparatus for performing a phase adjustment of a timing control signal related to a sampling process on an image signal based on an image analysis result, after the sampling process is performed. After the step of calculating the signal-to-noise ratio by image analysis for the output signal, the timing control signal is generated based on the result of the image analysis so that the signal-to-noise ratio for the output signal is maximized. Automatically adjusting the phase of the signal. 5. An automatic phase adjustment method in an image processing apparatus according to claim 4, wherein an output signal of said imaging means is acquired in a state where incident light to said imaging means is blocked so that external light is not irradiated. hand,
An automatic phase adjustment method in an image processing apparatus, wherein after performing a sampling process, an analog-digital conversion is performed, and then a signal-to-noise ratio is calculated by image analysis. 6. An automatic phase adjustment method in an image processing apparatus according to claim 5, wherein a standard deviation is calculated for an image signal level,
An automatic phase adjustment method in an image processing apparatus, wherein a signal-to-noise ratio is calculated as a logarithm of a ratio value between a maximum input signal amount of an analog-digital conversion circuit and the standard deviation. 7. An imaging unit, a sampling processing circuit for obtaining sampling data for a signal obtained by the imaging unit, a signal generation circuit for generating a timing control signal for the sampling processing circuit, A timing adjusting means for adjusting the phase of a timing control signal by controlling the signal generation circuit; an image pickup apparatus comprising: a signal relating to the signal when an output signal passing through the sampling processing circuit is input; An analysis means for calculating a noise-to-noise ratio by image analysis is provided in advance, or a terminal section is provided so that the analysis means can be connected to an imaging apparatus main body as an external device. A timing control signal is sent from the signal generation circuit to the sampling processing circuit at the timing when the signal-to-noise ratio of the signal is maximized. Imaging device phase adjustment of the signal is characterized by being carried out by the timing adjustment means to be.