JPH0348715B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a signal processing circuit applied to separate a luminance signal and a chroma signal (Y/C separation) from a composite color television signal of the NTSC system or the PAL system. Taking the NTSC system as an example, the signals F ₁ , F ₂ , and F ₃ of specific lines of each of three consecutive frames in the case of a still image are as shown in FIG. That is, while the luminance signal Y is the same, the color signal has a phase inversion between two consecutive frames. Taking advantage of these properties,
The configuration shown in FIG. 2 or 3 makes it possible to perform Y/C separation. In FIG. 2, 1 is an input terminal to which a composite color television signal that is locked to the phase of the color subcarrier and digitized at a sampling frequency three or four times that frequency (3f _sc or 4f _sc ) is supplied. As a result, the chroma signal component is extracted by bandpass filter 2, and 1
It is supplied to the series connection of frame memories 3 and 4. Signals F ₂ and F ₁ are obtained from the respective outputs of the one-frame memories 3 and 4, and a signal F ₃ is obtained from the output of the bandpass filter 2. , 7 and switch circuits 8, 9, and 10, respectively, to a synthesizer 11, and the output of this synthesis path 11 is taken out as a chroma signal to an output terminal 12, and the synthesizer 1
3. This synthesizer 13 is given a delay equal to the delay of the bandpass filter 2 by a delay circuit 14, and is further provided with a one-frame memory 15.
A composite color television signal is supplied through the synthesizer 13, and a luminance signal Y is taken out to an output terminal 16 of the synthesizer 13. Since such Y/C separation utilizes frame correlation, the presence or absence of correlation is checked by the motion detection and control circuit 17, and the switch circuits 8, 9, and 10 are controlled based on the determination. If there is no movement between frames, then C = 1/2 [F ₂ - 1/2 (F ₁ + F ₃ )], Y = 1/2 [F ₂ + 1/2 (F ₁ + F ₃ )]. Y/C separation can be performed. 1 frame memory 3 indicated by a broken line in FIG.
and 15 may be omitted and only one one-frame memory may be used. In this case, the operation is controlled by the following algorithm. When (F ₁ = F ₂ ), C=1/2 (F ₁ - F ₂ ) Y=1/2 (F ₁ + F ₂ ) When F ₁ ≠ F ₂ does not hold, C=0 Y=F ₂ The configuration shown in FIG. 3 supplies a composite color television signal to one frame memories 3 and 4, and outputs the output of one frame memory 3 to a delay circuit 14.
which supplies the output of the synthesizer 11 to the synthesizer 13 via the bandpass filter 2 and also supplies the signals F ₁ and F ₃ to the motion detection and control circuit 17. It is. If there is a correlation between frames, Y/C separation can be performed in the same manner as described above. This invention makes effective use of the frame memory by providing a noise reduction function for static surfaces in a Y/C separation circuit using a frame memory as described above, and also detects motion and converts it into a moving image. To deal with this, the functions of a comb filter (referred to as a three-dimensional comb filter) that uses the noise reduction function and frame correlation are stopped, and a comb filter that uses line correlation (referred to as a quadratic comb filter) is used. Therefore, Y/C separation is performed. Hereinafter, one embodiment of the present invention will be described with reference to FIG. 4. A three-dimensional comb filter for Y/C separation has a configuration using one 1-frame memory of the basic configuration shown in FIG. 3. It is said that In each block diagram, the flow of video signals is shown by solid lines, and the flow of control signals is shown by broken lines. The three-dimensional comb filter supplies the input signal F ₂ of the one frame memory 4 to the synthesizer 11 via the multiplier 6 to which a 1/2 coefficient is supplied, and also supplies the output of the one frame memory 4 to the delay circuit. 18 and 19
The signal F ₁ through which the
1 is supplied to a combiner 21 via a bandpass filter 2 and a multiplier 20 to which the coefficients of _KM are supplied. In addition, the output of the one frame memory 4 is passed through a band pass filter 22 to a two-dimensional comb filter 2.
3, and its output is supplied to the delay circuit 24 and (1
−K _M ) is supplied to the combiner 21 via a multiplier 25 to which the coefficients of the coefficients are supplied. If (K _M = 0), then
A two-dimensional comb filter 2 is applied to the output of the synthesizer 21.
The chroma signal C separated by 3 is extracted,
When (K _M =1), a chroma signal C separated by a three-dimensional comb filter is extracted. This coefficient K _M is generated in a motion detection and control circuit 17 and is supplied via a delay circuit 26 . Assuming that the delay time caused by the bandpass filter 22 is T ₁ , the delay time caused by the two-dimensional comb filter 23 is T ₂ , and the delay time caused by the bandpass filter 2 is T ₃ , the delay time of the delay circuit 18 is T ₁ , The delay time of the delay circuit 19 is T ₂ , the delay circuits 14, 24, 2
6 delay times are selected as T ₃ respectively. Also,
To remove noise, the signal to be fed back must be delayed by one frame (T _F ) in order to average it with the signal one frame before.
The delay time T _F ′ caused by the frame memory 4 is
It is made equal to T _F - (T ₁ + T ₂ ). Also, to explain the two-dimensional comb filter 23, when there is a uniform color in the same field, the NTSC signals T, M,
B is shown as in FIG. Y/C separation can be performed by performing processing depending on the presence or absence of correlation between the three lines of signals. FIG. 6 shows the basic configuration of the two-dimensional comb filter 23, in which input signals are supplied to IH delay circuits 37 and 38, and three signals T, M, B
are taken out and sent to the synthesizer 4 via multipliers 39, 40, 41 and switch circuits 42, 43, 44, respectively.
5, and the chroma signal C is separated from the output of this combiner 45. In this case, the signals T, M, and B are supplied to the correlation determination circuit 46, and the switch circuits 42, 43, and 44 are controlled based on the determination. The correlation determination circuit 46 determines the presence or absence of correlation based on the absolute value of the sum of signals between two lines. That is, |M
If +T|>ε holds, it is determined that there is no correlation between the signals M and T, and if this does not hold, it is determined that there is a correlation between the signals M and T. Signal M
The correlation between and B is similarly determined. Then, when it is determined that there is a correlation among all of the signals T, M, and B, the chroma signal C is separated by C=1/2 [M-1/2 (T+B)]. Furthermore, when it is determined that there is a correlation only between signals T and M, C=1/2(MT). Furthermore, when it is determined that there is a correlation only between signals M and B, C=1/2(MB). Furthermore, when there is no correlation between signals T, M, and B, one of the color subcarriers of signal M
A comparison is made with a sample at a position separated by a period, and if the value is approximately the same, it is determined that (C=M), otherwise, (C=0) is determined. Further, in one embodiment of the present invention, the synthesizer 27 forms a frame difference signal ΔF with the signal of one frame before, and supplies this frame difference signal ΔF to the motion detection control circuit 17 and the nonlinear circuit 28. However, by supplying the output of this non-linear circuit 28 to a combiner 29, it is subtracted from the input signal to perform a noise reduction operation. The signal of one frame before is sent to a synthesizer 30 to which the output of the delay circuit 19 and the output of the two-dimensional comb filter 23 are supplied, a chroma inverter 31 that inverts the output of the two-dimensional comb filter 23, and this synthesizer. 30 and a combiner 32 to which the output of the chroma inverter 31 is supplied. Motion detection is performed based on whether the frame difference signal ΔF exceeds a certain threshold level within a certain plane area. As an example, there is a system in which the frame difference signal ΔF is subjected to Hadamard transformation, and the non-linear circuit 28 provides input/output characteristics K as shown in FIG. 7 for each sequence. In FIG. 7, ΔF _R indicates the threshold level. When the frame difference signal ΔF exceeds the threshold level ±ΔF _R , it is assumed that there is no correlation between frames, and (K _N =
0). The operation of the embodiment of the present invention described above can be summarized as follows. When there is frame correlation (F ₁ = F ₂ ) Y = 1/2 [F ₁ + F ₂ ] C = 1/2 [F ₁ - F ₂ ] K _N = K, K _M = 1 When there is no frame correlation ( F ₁ ≠ F ₂ ) Y/C separation by two-dimensional comb filter 23. K _N =0 K _M =0 Note that the threshold level, which is the reference when shifting to the operation of the two-dimensional comb filter 23, and the threshold level, which is the reference when canceling the noise reduction operation, are completely different. Instead of making them equal, it is also possible to shift to Y/C separation using the two-dimensional comb filter 23, where there is some noise reduction effect. In addition, as a noise reduction circuit, as shown in FIG. Alternatively, a structure in which the output of the one frame memory 4 is supplied to the synthesizer 48 may be used. FIG. 9 shows another embodiment of the invention. In this method, the motion detection and control circuit 17 uses three frames of signals F ₁ , F ₂ , and F ₃ to detect motion. When signals F ₁ and F ₃ that are two frames apart are used, This solves the problem of not being able to detect fast movements. First, from one frame T _F , the delay time T ₁ of the bandpass filter 22 and the two-dimensional comb filter 2
The signal delayed by T _F ′, which is the sum of the delay times T ₂ (T ₁ + T ₂ ) of 3, is taken out from the 1-frame memory 3 and sent to the delay circuit 18 and the bandpass filter 2.
2, and the synthesizer 3 similarly to the configuration shown in FIG.
0, 32 and the signal by the chroma inverter 31.
F ₂ and feeds it together with signals F ₃ and F ₁ to the motion detection and control circuit 17 . Also, the signal
F ₁ , F ₂ , and F ₃ are supplied to the synthesizer 11 via the multipliers 5 , 6 , and 7 and the gate circuit 36 , and the gate circuit 36 is controlled by the motion detection and control circuit 17 . By controlling the Y/C separation operation as shown in the table below, the Y/C separation operation is performed.

[Table] As can be understood from the description of the embodiments above, according to the present invention, a frame memory and a motion detection and control circuit are used to realize both Y/C separation and noise reduction functions. Since it is also used, frame memory can be used effectively. Furthermore, when there is movement, according to the present invention, the noise reduction operation and the operation of the three-dimensional comb filter are stopped, and the transition is made to the Y/C separation operation using the two-dimensional comb filter. You can minimize the annoying blur.

[Brief explanation of drawings]

FIG. 1 is a waveform diagram used to explain an NTSC signal, FIGS. 2 and 3 are block diagrams of one example and other examples of a three-dimensional comb filter, and FIG. 4 is a block diagram of an embodiment of the present invention. Figures 5 and 6 are waveform diagrams and block diagrams used to explain the two-dimensional comb filter, Figures 7 and 8 are schematic diagrams and block diagrams used to explain the noise reduction circuit, and Figure 9 is the waveform diagram and block diagram used to explain the noise reduction circuit. FIG. 3 is a block diagram of another embodiment of the invention. 1...Input terminal, 3, 4, 15...1 frame memory, 12...Chroma signal output terminal, 16
...Brightness signal output terminal, 17...Motion detection and control circuit, 23...Two-dimensional comb filter.

Claims (1)

[Claims] 1. A signal processing circuit that performs Y/C separation using frame correlation of a color television signal, which includes a frame memory and a circuit that detects motion based on the difference between input and output of the frame memory, and a circuit that detects motion based on the difference between the input and output of the frame memory, and A feedback circuit for noise removal that returns the output signal of the frame memory to the input side of the frame memory and adds this output signal to the input signal at a predetermined ratio, and the predetermined ratio is controlled by the output of the detection circuit. and a comb frame using line correlation used for Y/C separation when the detected motion is large.