2.2.3
Luminance Processing
The digitized composite video signal passes through either a luminance comb filter or a chroma trap filter, either of
which removes chrominance information from the composite signal to generate a luminance signal. The luminance
signal is then fed into the input of a peaking circuit. Figure 2−12 illustrates the basic functions of the luminance data
path. In the case of S-video, the luminance signal bypasses the comb filter or chroma trap filter and is fed directly
to the circuit. High frequency components of the luminance signal are enhanced by a peaking filter (sharpness).
Figure 2−13, Figure 2−14, and Figure 2−15 show the characteristics of the peaking filter at four different gain settings
programmable via the host port.
Gain
IN
Peak
Detector
Bandpass
Filter
x
Peaking
Filter
Delay
+
OUT
Figure 2−12. Luminance Edge-Enhancer Peaking Block Diagram
7
6
5
Amplitude − dB
4
3
2
1
0
Gain = 0
−1
0
1
2
3
4
5
6
7
f − Frequency − MHz
−1
0
1
2
3
4
5
6
7
f − Frequency − MHz
Gain = 0.5
Amplitude − dB
Gain = 1
Peak at
f = 2.40 MHz
Gain = 2
5
4
3
Gain = 0.5
2
1
0
Gain = 0
Gain = 1
7
6
Peak at
f = 2.64 MHz
Gain = 2
Figure 2−13. Peaking Filter Response, NTSC
Square Pixel Sampling
Figure 2−14. Peaking Filter Response,
NTSC/PAL ITU-R BT.601 Sampling
2−7
TI [ TEXAS INSTRUMENTS ]
