I have a series of questions posed in regard to Secam mode operation recently observed.
We are seeing sub-carrier breakthrough into Luma – something that we did not notice previously on the Eval board, as it is visually different and difficult to see on that platform. It is particularly noticeable, as a scrolling pattern, when converting the decoded SECAM back to PAL
a) Is SECAM sub-carrier breakthrough into Luma a known issue?
b) Is there a workaround?
c) If not, is it possible to change any parameters that influence the Luma filtering in SECAM mode, so that we might be able to reduce this effect? If so, please could you point us at the relevant registers.
d) Rather than running the decoder in auto-detect mode, if we configure for a SECAM input, can we optimise the settings?
a) SECAM is FM modulated and is more difficult to separate, leading to "colour bleeding" in some luma images. This is a know effect of SECAM standard.
For Y/C separation in SECAM, there is no operation analogous to PAL/ NTSC 2D combing in SECAM standard. The decoder can only notch the Y data and use bandpass filtering on the C data.
This leads to the effects you describe above.
c)The only available adjustments are to adjust the Shaping filters, however , these have been optimised in lab characterisation.
d)Forcing the standard over autodetect, will help performance when weak signal or poor quality signals are applied to the part.