Analog Devices ADV7850 Hardware Manual page 93

improves visual picture quality. This feature can also be used to reduce the bandwidth of the luma video as required prior to scaling.
For input signals in CVBS format, the luma shaping filters play an important role in removing the chroma component from a composite
signal. YC separation must aim for the best possible crosstalk reduction while still retaining as much bandwidth as possible, especially on
the luma component.
The ADV7850 contains 33 different Y shaping filters available for selection using a 6-bit selection value. Four selection registers are
provided so that different Y shaping filter can be selected for the VBI region, high quality inputs, low quality inputs, and SECAM inputs.
The quality of the input signal is based on the HSync PLL speed, and some or all of the following metrics:
•
Input is noisy (based on synchronization tip noise measurement and noisy threshold)
• Head switch detected (indicating the input is from a VCR)
•
Input has incorrect number of lines per frame
• Block length is non standard
•
Field length is non standard
• Frame length is non standard
•
Input is very noisy (based on synchronization tip nose measurement and very noisy threshold)
Each of these metrics has an enable/disable bit to specify if it is included in the quality determination of the input signal. The amount of
filtering on the standard/non standard decision for these metrics is user programmable from no filtering up to two seconds. There is also
a single bit control to disable all of these metrics, and base the quality decision solely on the HSync PLL speed.
A filter selection guide is used to choose the appropriate filter depending on the input signal format, type, quality, and user settings. In
automatic mode, the system preserves the maximum possible bandwidth for good CVBS sources since they can be combed successfully, as
well as for luma components of YUV and YC sources since they need not be combed. For poor quality signals, the system selects from a
set of proprietary shaping filter responses that complement the comb filter operation in order to reduce visual artifacts.
selectable filters types.
A flow diagram showing the selection process is shown in
Rev. A May 2012
Figure 19. Filter response plots are included from
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ADV7850
Table 10 lists the
Figure 20 to Figure 25.