JPH01194581A - Video signal processor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a video signal processing device that reduces noise in a video signal and adds predetermined special effects.

[Conventional technology]

Silver halide cameras are known for special effects and special photography, such as keeping an object still by using a high-speed shutter and leaving an afterimage on the object by using a low-speed shutter.

On the other hand, in video cameras, a high-speed shutter function that shortens the charge accumulation time of an image sensor has already been realized, but a low-speed shank function has not yet been realized. However, it is known that a predetermined afterimage effect can be imparted by changing the coefficients of a cyclic noise reduction circuit that utilizes field correlation.

FIG. 2 shows a block diagram of a conventional field cyclic noise reduction circuit. The input video signal is converted into a digital signal by an A/D converter 10, and a subtracter 12 calculates the difference between the input video signal and the video signal supplied from the field memory 14 one field period before. The difference signal output from the subtracter 12 is applied to a coefficient multiplier 16, where it is multiplied by a coefficient A. The adder 18 adds the signal from the field memory 14 one field period ago to the output of the coefficient multiplier 16, and the output of the adder 18 is applied to the D/A converter 20 and the field memory 14. be done. The field memory 14 functions as a delay element for one field period as described above, and the D/A converter 20 converts the digital video signal back into an analog signal. becomes a noise reduction output.

In the circuit shown in FIG. 2, by appropriately setting the coefficient A of the coefficient multiplier 16, it is possible to reduce noise components having no field correlation and to give an afterimage to a moving object.

[Problem to be solved by the invention]

However, this type of conventional circuit has the following problems.

Specifically, the coefficient multiplier 16 in FIG.
The shift operation performs the operation of dividing the input by 2" (n ≥ 1), but division by bit shift discards the decimal parts, so for example, to increase the afterimage effect, input 25 with n = 5. When the signal is divided, a problem arises in that the screen does not change in the negative direction if the level changes between fields by less than 32 levels.Therefore, there are also restrictions on adjusting the coefficient A.

Further, in a normal motion adaptive noise reduction circuit, when the input of the coefficient multiplier 16 is smaller than a predetermined value, the coefficient A is set to almost "0", but even in such a case, the screen does not change at all with a small level change. The problem is that it does not change.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a video signal processing device that can solve these problems, respond to even small level changes, and provide appropriate afterimage effects and noise reduction effects.

[Means to solve the problem]

A video signal processing device according to the present invention includes: a subtraction unit that calculates a difference signal between an input video signal and a video signal obtained a predetermined period before the input video signal; and a calculation unit that performs a predetermined calculation on the difference signal. , an addition means for adding the calculation result to the input video signal or a video signal before the predetermined period and outputting the result, a delay means for delaying the output of the addition means for the predetermined period, and a dither generation means for generating a dither pattern. The dither pattern from the dither generating means is added to the signal from the calculating means to the delay means.

[Effect]

By adding the dither pattern from the dither generating means to the signal resulting from multiplying the difference signal by a predetermined coefficient, the calculation result can be reliably changed even if the difference signal is a small value.

Therefore, even if there is only a small screen change during the predetermined period, the screen will certainly change.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a configuration block diagram of an embodiment of the present invention.

The same components as in FIG. 2 are given the same reference numerals. 30
is a coefficient multiplier that replaces the coefficient multiplier 16, and can change the coefficient A according to a control signal from the control circuit 32. 36 is 1. According to instructions from the control circuit 32, 0≦α
This is a dither generator that generates one dither pattern. Adder 38 adds the dither pattern from dither generator 36 to the output of coefficient multiplier 30 and applies the addition result to adder 18 . The components after the adder 18 are the same as those described in the conventional example.

Next, an example of ideal input/output characteristics and special effects of the coefficient multiplier 30 will be explained with reference to FIG.

When the illuminance at the time of photographing is sufficiently high, there is no problem with S/N, and therefore the coefficient A of the coefficient multiplier 30 is set to 1, and the dither generator 36 does not generate a dither pattern. At this time, the difference between the input video signal and the video signal one field before (the output of the subtracter 12) is directly added to the video signal one field before, that is, it simply passes through.

When the illuminance is sufficiently low, the control circuit 32 reduces the coefficient A to 1/2, and the dither generator 36 generates a dither pattern of 0≦α and 1. In this case, the output of the coefficient multiplier 30 becomes 1/2, and noise can be reduced to the extent that no afterimage remains.

Furthermore, by adding the dither pattern in the adder 38, the screen can be rewritten reliably even with a small level change.

If you want to give a trailing afterimage, for example, A=
The size is reduced to about 1/16, and O≦α is set by the dither generator 36.
<Generate a dither pattern of 1. In this case,
The noise reduction effect is large, and in moving parts, trailing afterimages occur as the subject moves. Furthermore, although it takes some time to add the dither pattern, the screen changes reliably.

If you want to erase the moving part, use the coefficient A=1/
64, and a dither pattern of 0≦α×1 is generated from the dither generator 36. In this case, the coefficient multiplier 30 reduces the signal of the moving part to 1/64, so
No moving parts appear on the screen, and a still image with significantly reduced noise is output. In this case, the screen changes gradually by adding the dither pattern.

Furthermore, even in a motion adaptive noise reduction circuit having an arithmetic circuit that adaptively switches the value of the coefficient A of the coefficient multiplier according to the level of the input signal, as shown in FIG. By adding a dither pattern to the output of the coefficient multiplier for the input, even small level fluctuations can be reliably tracked. In this case, it is convenient to use a ROM table as a coefficient multiplier.

In the embodiment shown in FIG. 1, the dither pattern adder 38 is provided between the coefficient multiplier 30 and the adder 18, but it may also be provided between the adder 18 and the field memory 14. A similar effect can be obtained.

FIG. 5 is a block diagram of a noise reduction circuit according to another embodiment of the present invention. The input video signal digitized by the A/D converter 10 and the video signal delayed by one field period in the field memory 54 are processed by a subtracter 5.
2 to obtain a differential signal. This difference signal is input to a coefficient multiplier 46 via a limiter 44. That is, a signal with a small level below the dark value of the limiter 44 is considered to be mostly noise, and is subtracted from the signal output from the A/D converter 10. The closer the value of the coefficient multiplied by the coefficient multiplier 46 is to 1, the higher the noise reduction effect is, but when K=1, the limiter becomes unresponsive to image movement for level changes below the darkness value.

Therefore, it is common to set K to about 15/16. However, in this case as well, if the level of the difference signal is extremely small, the calculation result will be the same as when the coefficient K is set to 1.

Therefore, in this embodiment, by adding the dither pattern generated by the dither generator 48 to the output of the coefficient multiplier 46 using the adder 50, it becomes possible to follow image movements caused by small level fluctuations. .

It goes without saying that the same effect can be obtained even if the dither pattern is added to the output of the adder 52 in the embodiment of FIG.

〔Effect of the invention〕

As can be easily understood from the above explanation, according to the present invention, by adding only a few circuit elements, various special effects can be created that can respond to even small level fluctuations, and noise components can be suppressed without leaving an afterimage. removal can be achieved.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of the configuration of the embodiment of the present invention, FIG. 2 is a block diagram of the configuration of the conventional example, FIGS. 3 and 4 are explanatory diagrams of the operation of the embodiment of the present invention, and FIG. FIG. 3 is a configuration block diagram of another embodiment.

Claims (1)

[Claims] subtraction means for calculating a difference signal between an input video signal and a video signal obtained a predetermined period before the input video signal; a calculation means for performing a predetermined operation on the difference signal; It is equipped with an adding means for adding and outputting a video signal of a predetermined period before, a delay means for delaying the output of the adding means for the predetermined period, and a dither generating means for generating a dither pattern, A video signal processing device characterized in that a dither pattern from the dither generating means is added to a signal reaching the delay means.