JPS60239178A - Black level stabilizing circuit - Google Patents

Abstract

PURPOSE:To reproduce a picture without fluctuation independently of variance in the black level due to the difference from a signal supply source for a VTR by detecting the most black level in a luminance signal in a video signal and using a level providing a prescribed time constant to the most black level as a pedestal level. CONSTITUTION:A luminance signal 8 is inputted to a noise elimination circuit 20 comprising a comparator 11, a gate signal generating circuit 12 and a multiplexer 13. The inputted luminance signal 8 is inputted to the comparator 11 and the value is compared with a comparison signal 9 having a value of zero level 0. If a noise 14 having a value below the pedestal level is mixed in the luminance signal 1, the value below zero level 0 is provided to the noise 14 in the luminance signal 8 outputted by a blanking processing circuit 10. Thus, the noise mixed portion is detected by comparing the luminance signal 8 with the comparison signal 9 at the comparator 11.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a black level stabilizing circuit that is applied to a television receiver that performs baseband video signal processing and reproduces a stable black level.

[Technical background of the invention and its problems]

The black level in the video signal transmitted from the broadcasting station (c).

In order to avoid fluctuations in the receiving screen due to differences in the values between broadcasting stations, it is determined by the broadcasting standards that the value is 7.5% ± 2.5% of the difference between the white level and the pedestal level. ing. However, the actual black level varies between broadcast stations.

Furthermore, the black level will vary due to differences in signal supply sources such as VTRs. For this reason, 1. For example, even though a certain broadcast channel reproduces an appropriate black color,
When switching to another channel, black may not be properly reproduced and black may appear too high or too low on one screen.

Therefore, the television receiver requires a black level stabilizing circuit to stably reproduce the black level. As a conventional black level stabilizing circuit, one is known that detects the lowest black level of the video information portion of the supplied video signal and resets this as a new pedestal level. When resetting, a certain reference level is set, for example, a value corresponding to about 15V, which is the difference between the white level and the conventional total level, and the blackest level is located between the pedestal level and the reference level. If so, the blackest level is set as the new pedestal level, and if the blackest level is lower than the pedestal level, the pedestal level is not reset and is set to the previous pedestal level.

Therefore, in the above-mentioned conventional black level stabilization circuit, there is a risk of noise in the supplied video signal.

In addition, if this noise has a value less than the maximum black level value, it is mistakenly detected as the maximum black level and the pedestal level is set, so even after passing through the black level stabilization circuit, the received image is still correct. There was a problem that it was not possible.

[Purpose of the invention]

The present invention has been made in view of the above problems.

To provide a black level stabilizing circuit capable of always reproducing a stable black level even if a video signal containing noise having a value below the maximum black level is supplied.

[Summary of the invention]

The present invention provides a block that fixes the signal level of a first luminance signal constituting a video signal during a sweep line period to a first level that is higher than the blackest level of the first luminance signal and outputs it as a second luminance signal. a ranking processing circuit; a noise removal circuit that removes noise having a value i below the black level included in the second brightness signal and outputs it as a third brightness signal; and a pedestal level of the first 411 sound reputation. value) Chiku 3
a black level detection circuit that outputs a minimum level value corresponding to the value up to the blackest level of the luminance signal; a time constant circuit that gives a constant time constant to the minimum level value and outputs it as a black level signal; The black level signal is applied to the first luminance signal only during the retrace period of the first luminance signal. and a pedestal level correction circuit that resets the pedestal level of the first luminance signal by adding it to the luminance signal and outputs a fourth luminance signal with a stable black level. .

[Embodiments of the Invention] The black level stabilizing circuit of the present invention will be explained in detail below using one drawing. FIG. 1 is a block diagram of a black level stabilizing circuit (100) according to an embodiment of the present invention, and the black level stabilizing circuit (100) will be explained with reference to the signal waveform diagram shown in FIG. .

The luminance signal (1) shown in FIG. 2(a) is first input to the blanking processing circuit (11) comprised of the subtracter (2) and multiplexer (5) shown in FIG. The input luminance signal (1) is subtracted from the pedestal signal <3) having the value of the pedestal level (Pl) in the subtracter (2), resulting in a luminance signal (4) (Fig. 2-)). Garu. The luminance signal (4) is sent together with the reference signal (7) having a value corresponding to the reference level (Rr) to the multiplexer (5) which selects and outputs either one of the two.
). The multiplexer (5) outputs the luminance signal (4
) is controlled by a blanking pulse (6) that coincides with the blanking period (1).
Only the level of the luminance signal (4) is set to the reference level (R
r) and output as a luminance signal (8) (FIG. 2(C)).

In the above, it is assumed that the reference level (RQ (i) is set to a value of 15% of the difference between the white level (W) and the pedestal level (Pi).

Next, the luminance signal (8) is input to a noise removal circuit consisting of a comparator a1), a gate signal generation circuit a, and a multiplexer (131).The input luminance signal (8) is input to a comparator 11. The value is compared with the comparison signal (9) having a value of zero level (0).Here, noise I having a value below the pedestal level (P□) is mixed into the luminance signal (1). (Fig. 2(a)), the blanking processing circuit (in the luminance signal (8) outputted by the IQ, the noise < 14) has a value below the zero level (0). By comparing the values of the luminance signal (8) and the comparison signal (9) in the comparator (11), it is possible to detect the part where the noise Q4 is mixed. Comparison results.

When the luminance signal (8) is below the zero level (0), the noise detection signal [9 is supplied to the comparator (1υ) and the gate pulse generation circuit (I2).The gate pulse generation circuit a receives this noise detection signal. A certain period before and after the occurrence period of aQ (n
outputs a gate pulse that occurs over the clock).

Therefore, this gate pulse has a pulse width centered around the noise point 4 and has a pulse width large enough to sufficiently cover the crack, and becomes a signal indicating the part where the noise I is mixed.

Now, multiplexer +13 has the luminance signal (8) and 9
7 alignment signal (7) is supplied, and one of the two signals is selected and outputted from the multiplexer α by the gate pulse αe. That is, the multiplexer a (to) selects the reference signal (7) during the period corresponding to the part where the noise I is mixed into which the gate pulse αe is input, and selects and outputs the luminance signal (8) during the other periods. . As a result, the output signal of multiplexer Q3 becomes a luminance signal as shown in FIG. 2(d).

Next, the luminance signal (17) is input to a black level detection circuit consisting of a comparator αυ, a multiplexer (2), and a latch (2). The latch (the luminance signal (L7) output by 2D
) the minimum (worst) level signal t2 having a minimum level value of
2 and supplies a determination signal (to) indicating the comparison determination result to the multiplexer. The multiplexer is supplied with the luminance signal and the minimum level signal gradient, and the -cr multiplexer selects and outputs the smaller of the two values as the judgment signal (to).

The output of multiplexer (2) is fed to latch Qυ.

The latch multiplies the outputs of the multiplexer (11) supplied over one horizontal scanning period and outputs it as the highest temperature level signal (2).

The hottest level signal (24 is the latch (c) + (21191 subtractor) having the minimum level value of the brightness signal (17)
, a coefficient multiplier (c), and an adder (to). The inputted hottest level signal e4 is latched in the latch (c) in a vertical scanning period. The latch output (three swords is subtracted via the subtractor (5) between the black level signal (to) which is the output of the subsequent latch (c),
Then the coefficient multiplier (to) K is multiplied by a constant coefficient, the number
Furthermore, it is added to the output device of Latch 7 (C) by an adder. The addition output (to) thus obtained is latched in the latch (e) at the vertical scanning period and output as the aforementioned latch output o (black level signal). In the end, the circuit has a time constant of one time constant circuit and outputs it as a black level signal cI.

The black level signal c3 outputted by the time constant circuit (40) is input to the pedestal level correction circuit (A).The peg 4 tal level correction circuit (■) converts the winter death level of the luminance signal (1) into the black level signal (to). The adjustment delay circuit (
The luminance signal (1) (luminance signal (to)) adjusted to match the phase with the black level signal (33) is input via the black level signal c (2 is the gate circuit (to), and the gate circuit (to) passes the black level signal G only during the retrace period of the luminance signal (to), and supplies the black level signal G to the adder C3η. As a result, the pedestal level (PI) of the luminance signal (1) (luminance signal (to)) is equal to the pedestal level (to) as the output of the adder (b).
Luminance signal (to) reset to Pz) (Figure 2 (e))
will be obtained. The pedestal level (Pg) of the brightness signal (to) thus obtained matches the level obtained by adding a constant time constant to the blackest level of the brightness signal (1).

This makes it possible to obtain an appropriate reproduced image regardless of variations in black level due to differences between channels or signal supply sources such as VTRs.

[Other embodiments of the invention]

FIG. 3 shows a black level stabilizing circuit (
200) is shown. This black level stabilization circuit (20
0) differs from the previous black level stabilization circuit (100>) in that it does not perform the subtraction between the luminance signal (1) and the pedestal signal (3) that was performed in the blanking processing circuit Ql, but instead The point is that the pedestal signal (3) is subtracted immediately before the constant circuit.That is, in this embodiment, the plugging processing circuit (XOa) is constructed as a multiplexer (5).

The luminance signal (1) (Fig. 4 (a') '') input to the multiplexer (5) is fixed at the reference level (Rf) only during the retrace period, and is expressed as the luminance signal ■ shown in Fig. 4 Φ>FC. It is supplied to the next stage noise removal circuit (203).The noise removal circuit (203) is supplied to the black level stabilization circuit (1
This circuit has the same configuration as the noise removal circuit (2) of No. 00).

In order to fix the noise in the luminance signal level to the reference level (Rr) as in the case of the luminance signal (8), its value is set to zero level as the comparison signal supplied to the comparator <11). There is a slight difference in that a value having a pedestal level (PI) is used instead of (0). This difference is due to the blanking processing circuit (103) in the previous stage.
), the pedestal signal (
This is due to the fact that 3) is not subtracted.

Next, the luminance signal (173) (Fig. 4 (C)) to be output from the blanking processing circuit (103) is inputted to the black level detection circuit (303), and the minimum (gradual black) level in the luminance signal (173) is inputted to the black level detection circuit (303). is detected, and the blackest level signal (223)
Touch C! ]) is supplied to the subtracter (302) in the detection circuit ('303). The maximum black level detected at this time is the maximum black level detected in the previous black level detection circuit (7), which is substantially the pedestal level (P,
), but it should be noted that the value is 1 from the zero level (0). therefore.

In order to correct this difference, the blackest level signal (223) is supplied to the subtracter (302), where the pedestal signal (3) having the value of the pedestal level (Pl) is subtracted from the level detection circuit (to). The output blackest level signal (corrected to be equal to 2nd level and supplied to the 5th stage time constant circuit.Hereafter, 1 time constant circuit decoy, pedestal level correction circuit)
The basic signal processing is carried out by the black and yellow stabilization circuits (Zo
o) K Oh, too. Although the explanation will be omitted, the luminance signal c! which has been subjected to the pedestal level correction circuit is finally outputted from the adder el't) of the pedestal level correction circuit.
ij<FIG. 4(d)) is obtained in the same way as in the case of the black level stabilizing circuit ("100") shown in FIG.

〔Effect of the invention〕

As explained above, 1. According to the black level stabilizing circuit of the present invention, the lowest black level in the luminance signal constituting the video signal is detected, and the highest black level with a certain time constant is set as the pedestal level. , regardless of variations in point levels between broadcasting stations and variations in black level due to differences in signal supply sources such as VTRs, images without ups and downs can be reproduced. On this occasion.

Even if the feeder is placed on the video information part of the video signal, the i′ black level can be detected without error! ,
It is possible to always reproduce an appropriate image without causing fluctuations in the reproduced image due to the influence of the noise as in the prior art.

Fig. 1 is a block diagram of a black level stabilizing circuit according to an embodiment of the present invention; Fig. 2 is an output waveform diagram of each part of the black level stabilizing circuit shown in Fig. 1; A block diagram of the black level stabilizing circuit according to the embodiment, FIG. 4 is an output waveform diagram of each part of the black level stabilizing circuit shown in FIG. 3.

(1), (8), η, (to), @l, (173
)...Brightness signal.

(11, (103)...Blanking processing circuit.

αhiro...Noise, @, (203)...Noise removal circuit.

(2)...minimum level signal, (To), (303)...Black level detection circuit.

(To)...Black level signal, 顛...Time constant circuit.

■...Pedestal level correction circuit.

(Rr)...Reference level, -(0)...
Zero level.

(PI),' (Pt)...hetestal level.

(100), (200)...Black level stabilization circuit.

Agent: Patent Attorney Noriyuki Chika Figure 2 Figure 4

Claims (4)

[Claims] (1) Fixing the signal level during the retrace period of the first luminance signal constituting the video signal to a first level that is higher than the hottest level of the first luminance signal and outputting it as a second luminance signal) linking processing circuit. a noise removal circuit that removes noise having a value below the highest level contained in the second brightness signal and outputs it as a third brightness signal; a black level detection circuit that outputs a minimum level value corresponding to the value up to the hottest level of the signal;
a time constant circuit that gives a constant time constant to the minimum level value and outputs it as a black level signal; and □ adds the black level signal to the first luminance signal only during the retrace period of the first luminance signal. Then, reset the pedestal level of the first luminance signal to stabilize the black level.
□ A black level stabilizing circuit characterized in that it is equipped with a correction circuit and a correction circuit. (2) The noise removal circuit receives a second luminance signal and converts a signal region over a certain period before and after a specific signal portion of the second luminance signal whose signal level is below a predetermined level into a signal region whose signal level is above the first level. 2. The black level stabilizing circuit according to claim 1, wherein the black level stabilizing circuit is fixed at a certain level and is used as the third luminance signal. (3) The blanking processing circuit inputs the first luminance signal and subtracts a value corresponding to the pedestal level of the first luminance signal from this %1 luminance signal, thereby making the pedestal level match the zero level. Obtain a signal, fix the signal level during the retrace period of the first luminance signal whose pedestal level has changed to the first level, and fix the signal level of the first luminance signal to the first level.
The third luminance signal is output as a luminance signal, and the black level detection circuit detects the hottest level value of the supplied third luminance signal and outputs this as the minimum level value. Range of genus level customers listed in item 1] 1 (4) The black level detection circuit detects the lowest black level value of the supplied third luminance signal, and sets the minimum level value by subtracting the pedestal level value of the first luminance signal from this highest black level value. 2. The black level stabilizing circuit according to claim 1, wherein the black level stabilizing circuit outputs an output.