JPS62165498A - Method for measuring characteristic of video tape recorder - Google Patents

Abstract

PURPOSE:To accurately measure the frequency characteristics of a small amplitude signal and to correctly evaluate the reproducibility of a detailed image or an SN ratio by executing recording/reproducing by a signal superposed by a random noise and measuring noise spectrum. CONSTITUTION:The noise spectrum of a signal obtained by superposing a white noise based on a noise generating circuit 2 to a 50% while noise generated from a video signal generating circuit 1 is measured to obtain a curved line (a). The noise spectrum is supplied to a recorder 100 through a change-over switch 4 and recorded in a magnetic tape T. A noise component of reproduced outputs from noise reduction circuits 110, 120 is removed by an averaging circuit, only the noise component is outputted from an adder 16 and a curve (b) is obtained from a level displayed by a spectrum analyzer 18. Thus, the reproducibility or the SN ratio can be correctly evaluated by calculating the differences between the curves (a) and C and between (b) and (c).

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a method of measuring the characteristics of a video tape recorder, for example, for evaluating image quality, and particularly to a method of measuring characteristics of a small amplitude video signal.

B1 Summary of the Invention The present invention is, for example, a method for measuring the characteristics of a video tape recorder for image quality evaluation, in which a video signal of a predetermined level with random noise superimposed is supplied to the video tape recorder, recorded and played back, and the noise spectrum is measured. By measuring the frequency characteristics of a small amplitude video signal, it is possible to accurately measure the frequency characteristics of a video signal of small amplitude, and it is possible to accurately evaluate the reproducibility of image details and S/N of a video tape recorder.

C0 Prior Art In general, the reproducibility of image details is an important factor in determining the quality of the image quality of a video tape recorder. It is known that in order to evaluate the reproducibility of image details, for example, it is sufficient to record and reproduce a small amplitude video signal and measure the frequency characteristics.

B0 Problems to be Solved by the Invention However, even if a video sweep signal or the like is used, it is difficult to accurately measure the frequency characteristics of a small amplitude video signal, and it is difficult to accurately evaluate the reproducibility of image details. I couldn't do it.

SUMMARY OF THE INVENTION The present invention has been proposed in view of the above-mentioned conventional problems. The purpose of this invention is to provide a method for measuring recorder characteristics.

Means for Solving the E0 Problem In order to achieve the above-mentioned object, the method for measuring the characteristics of a video tape recorder according to the present invention involves superimposing random noise on a video signal of a predetermined level and supplying it to the video tape recorder. The present invention is characterized in that the characteristics of the video tape recorder are measured by removing the video signal component from the playback output from the video tape recorder and observing the noise component with a spectrum analyzer.

20 Effects According to the present invention, a video signal of a predetermined level on which random noise is superimposed is supplied to a video tape recorder, only noise components are output from the playback output by the video tape recorder, and the noise spectrum is measured. .

0. Example Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing an example of a measuring device for realizing the present invention. First, this measuring device will be explained. A video signal generation circuit 1 that generates a video signal of a predetermined level and a noise generation circuit 2 that generates random noise are each connected to an adder 3. In this embodiment, the video signal generation circuit 1 outputs a 50% white signal, and the noise generation circuit 2 outputs white noise. The adder 3 is directly connected to the selected terminal 4a of the changeover switch 4, and is also connected to the selected terminal 4b of the changeover switch 4 via a comb filter 10 consisting of a 1B delay circuit 11 and an adder 12. Delay circuit 21, HPF (bypass filter) 22, and adder 23
The selected terminals 4C of the selector switch 4 are connected to the selected terminals 4C of the selector switch 4 through a comb filter 20 consisting of the following. Above HPF
22 has a cutoff frequency of several hundred KHz.

The selection terminal 4d of the changeover switch is connected to the input terminal 101 of the video tape recorder 100. Regarding this video tape recorder 100, only the main configuration is shown. That is, the input terminal 101 uses frequency modulation (
FM), and the modulation circuit 102 is connected to a magnetic head 103. Further, the magnetic head 104 is connected to the demodulation circuit 1 via the magnetic tape T.
05, and the demodulation circuit 105 is connected to a noise reduction circuit 110 that reduces noise in the vertical direction and a noise reduction circuit 1 that reduces noise in the horizontal direction.
20 (noise canceller) to the output terminal 106. One noise reduction circuit 110
is a feedback comb filter consisting of an adder 111, 112.1H delay circuit 113, a limiter 114, and a coefficient multiplier 115, in which the output from the coefficient multiplier 115 is fed back to the adder 111. have. Further, the other noise reduction circuit 120 is H, PF121,
It consists of a limiter 122 and an adder 123.

The output terminal 106 of the video tape recorder 100 is connected to an aggregating circuit 5 for removing noise components and an adder 6, and the adder 6 is connected to a noise meter 7 having a gate for eliminating the synchronizing signal portion. It is connected to the spectrum analyzer 8 via the spectrum analyzer 8.

Next, the measurement method will be explained step by step.

■ First, a white noise superimposed 50q6 white signal obtained by superimposing white noise from the noise generation circuit 2 on the 50-chip signal from the video signal generation circuit 1 (see Figure 2)
Noise spectrum (spectrum of source noise)
Measure.

(2) Next, the selected terminal 4a of the changeover switch 4 is selected, and the 50% white signal and the 50% white noise superimposed signal are supplied to the video tape recorder 1°O and recorded on the magnetic tape T.

(2) Next, reproduce the 50-chiro signal and measure the noise spectrum. At this time, two noise reduction circuits 1
10 and 120 of course operate, but due to the influence of the magneto-electric conversion system and the like, a reproduced output in which noise is superimposed on the signal as shown in FIG. 3(A) is output from the output terminal 106. Additionally, the waveform changes slightly at the rising edge of the signal compared to the original signal. The averaging circuit 5 performs averaging processing in synchronization with the horizontal synchronizing signal, that is, processing for removing noise components, on the reproduced output on which noise has been superimposed, and reproduces a signal having only waveform characteristics as shown in FIG. 30. I get a signal. As a result, only the noise component is output from the adder 6, the absolute value of the noise level is displayed on the noise meter 7, and the noise level of each frequency component is displayed on the spectrum analyzer 8. Is displayed.

■Next, reproduce the 50% confidence signal with white noise superimposed and measure the noise spectrum. In this case as well, a reproduced output with noise superimposed on the signal is output from the output terminal 106. The noise (fiC level) at this time is greater than the amount of noise in step (2) above by the amount of white noise. Then, the noise meter 7 and the spectrum analyzer 8) respectively display the results.

When measurements are performed according to the above-described procedure, a noise spectrum as shown in FIG. 4, for example, is obtained.

In this Figure 4, curve a is the noise spectrum of the 50% white noise superimposed signal (spectrum of source noise) measured in procedure [F], and curve a is the noise spectrum of the 50% white noise superimposed signal (source noise spectrum) measured in procedure [F]. In the noise spectrum during signal reproduction, song @c is the noise spectrum during reproduction of the white noise weight i50% confidence signal measured with hand Jll■. From these noise spectra, for example, the difference between curves a and C. It is possible to evaluate the reproducibility of the detail of the 9th image by taking the curve, and the S/N of the detail of the 9th image by taking the difference of the curve C.

As described above, the characteristic measuring method of this embodiment uses a noise-superimposed 50-chip white signal, and by supplying this signal to the video tape recorder 100, recording and reproducing it, and measuring the noise spectrum, the noise spectrum can be measured. It is possible to accurately measure the frequency characteristics of an amplitude video signal. Based on this measurement result, it is possible to accurately evaluate the reproducibility of image details and S/N, which are important factors in image quality evaluation.

Further, according to the measuring device of this embodiment, the noise reduction circuits 110 and 120 in the video tape recorder 100
It is possible to quantitatively measure the respective noise reduction amounts. That is, a 50% white noise superimposed source signal is passed through a comb filter 10 having characteristics as shown in FIG. By doing so, the influence of the noise reduction circuit 110 is reduced, and the effect (noise reduction amount) of the noise reduction circuit 120 in the horizontal direction can be measured. In addition, the above-mentioned white noise superimposed 50-white signal is filtered by a comb filter 20 having characteristics as shown by b in FIG.
If so-called non-correlated noise is formed through the noise reduction circuit 110 and supplied to the video tape recorder 100, the noise caused by the vertical noise reduction circuit 110 can be compared with the measurement results using the correlated noise described above. The amount of reduction can be measured. Note that fH in FIG. 5 is the horizontal scanning frequency, and n is a natural number.

Furthermore, for example, if the playback output of the 50% white noise-superimposed signal from the video tape recorder 100 is filtered using a comb filter having the characteristics indicated by a in FIG. 5, no visually noticeable interleaving occurs. Noise components can be extracted, and applications such as measuring this can also be considered.

Furthermore, the configuration of the measuring device is not limited to the configuration shown in FIG. 1; for example, comb filters 30 and 40 as shown in FIG. 6 may be used in place of the comb filters 10 and 20. The comb filter 30 includes adders 31 and 32
．． 1H delay circuit 33 limiter 34 and coefficient multiplier 3
5, the comb filter 0 is an adder 41,
42, IH delay circuit 43, HPF44, limiter 45,
and a coefficient multiplier, both of which are comb-type filters.

Note that the video signal to be used is not limited to 50% white confidence, but may be any video signal of a predetermined level, and the noise is not limited to white noise, but may be any sufficiently random noise.

H0 Effects of the Invention As is clear from the description of the embodiments described above, according to the method for measuring characteristics of a video tape recorder of the present invention, a video signal of a predetermined level with random noise superimposed is used, and this is recorded on a video tape. By supplying it to a recorder, recording and reproducing it, and observing the noise spectrum with a spectrum analyzer, it is possible to accurately measure the frequency characteristics of a small amplitude video signal. Therefore, based on this measurement result, it is possible to correctly evaluate the reproducibility of image details and S/N, which are important factors in image quality evaluation. This evaluation also corresponds to visual evaluation. Also,
Since quantitative data can be obtained, comparisons can be made between models and between sets.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an example of a measuring device, Fig. 2 is a waveform diagram showing a 50-chip signal superimposed with white noise, and Fig. 3 is a waveform diagram illustrating the operation of the averaging circuit.
FIG. 4 is a characteristic diagram showing an example of a noise spectrum obtained as a result of measurement, FIG. 5 is a characteristic diagram showing amplitude characteristics of a comb filter, and FIG. 6 is a block diagram showing another example of a comb filter. W, 74 tones can be 50% 90% 100% Fig. 2 (A) (B
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Claims (1)

[Claims] Random noise is superimposed on a video signal of a predetermined level and supplied to a video tape recorder, the component of the video signal is removed from the playback output by the video tape recorder, and the noise component is observed with a spectrum analyzer. 1. A method for measuring characteristics of a video tape recorder, comprising: measuring characteristics of a video tape recorder.