An adaptive luminance signal/chrominance signal separation filter receiving sample values obtained by sampling a composite video signal at a predetermined sampling frequency in synchronism with a horizontal scanning frequency in such a manner that the corresponding sample points are arranged in a grating on the screen, and digitally separating the luminance signal component and the chrominance signal component, and comprising:
- delay means for delaying the sample values for concurrently producing a sample value corresponding to a first sample point which is being subjected to the separation of the luminance signal and the chrominance signal, sample values corresponding to a second and a third sample points positioned on the same scanning line and at the left of and at the right of the first sample point and being identical in the phase of the color subcarrier and sample values corresponding to a fourth and a fifth sample points positioned over and under the first sample point and being identical in the phase of the color subcarrier,
- a separation horizontal direction filter for the separation of the luminance signal and the chrominance signal receiving the sample values corresponding to the first sample point and the second and the third sample points, and extracting the frequency component corresponding to the color subcarrier component from the series of the signal values in the horizontal direction on the screen,
- a separation vertical direction filter for the separation of the luminance signal and the chrominance signal receiving the sample values corresponding to the first sample point and the fourth and fifth sample points, and extracting the frequency component corresponding to the color subcarrier component from the series of the signal values in the vertical direction on the screen,
- a first judgment horizontal direction filter for receiving the sample values corresponding to the first sample point and the sample values corresponding to the second and third sample points and extracting the frequency component corresponding to the color subcarrier component from the series of the signal values along the horizontal direction on the screen,
- a first judgement vertical direction filter for receiving the sample value corresponding to the first sample point and the sample values corresponding to the forth and the fifth sample points and extracting the frequency component corresponding to the color subcarrier component from the series of the signal values along the vertical direction on the screen,
- a second judgement horizontal direction filter for receiving the sample values corresponding to the second and the third sample points and extracting the frequency component corresponding to 1/2 of the color subcarrier component from the series of the signal values along the horizontal direction on the screen,
- a second judgement vertical direction filter for receiving the sample values corresponding to the fourth and the fifth sample points and extracting the frequency component corresponding to 1/2 of the color subcarrier component from the series of the signal values along the vertical direction on the screen,
- horizontal direction high band energy detecting means for adding, in a predetermined ratio, the outputs of the first and the second judgement horizontal direction filters, thereby to extract a high frequency component along the horizontal direction on the screen,
- vertical direction high band energy detection means for adding, in a predetermined ratio, the outputs of the first and the second judgement vertical direction filters, thereby to extract a frequency component along the vertical direction on the screen,
- comparison means for comparing the results of the separation detection by the energy detecting means,
- a switch circuit for selecting the output of the separation horizontal direction filter, when the comparison means finds that the high frequency component as detected by the horizontal direction high band energy detecting means is smaller than the high frequency component as detected by the vertical direction high band energy detecting means, and for selecting the output of the separation vertical direction filter, when the comparison means finds that the high frequency component as detected by the horizontal direction high band energy detecting means is not smaller than the high frequency component as detected by the vertical direction high band energy detecting means, the selected one of the outputs constituting the chrominance signal component, and
- an operation circuit for subtracting the output of the switch circuit from the composite video signal to produce the luminance signal component.