19-02-2019, 01:40 PM
The Aurora does indeed use 3 line interpolation. Darryl reckoned there was no signifcant difference between 3 and 4 lines. The BBC research said the difference was minimal. I don't think 4 line was feasible in the small FPGA that Darryl uses in the Aurora.
The OSD will have sharp horizontal edges that will cause aliasing which will defeat just about any interpolator. I once had a crosshatch generator with the interlace the wrong way round. That caused havoc with interpolators.
Using line based interpolation on interlaced pictures will always be a compromise. The lines being interpolated are not spatially adjacent. But spatially adjacent lines are a field apart in time. The Pineapple converter which had field stores had a gorgeous looking interfield interpolation option. Until something moved. Then the result was unspeakbly hideous. You got similar effects with early LCD TVs where the de-interlacing was poor. De-interlacing is very hard to do well. Ultimately the vertical and temporal information are very entangled and hard to separate.
While the 1970s BBC report that I cited said there was no benefit in going above 4 lines, I've seen other work suggesting that up to 9 lines can be beneficial. I think this was only on progressive material and probably only worked if there was no vertical aliasing. Neither of these is a practical situation for a 625 to 405 converter.
The OSD will have sharp horizontal edges that will cause aliasing which will defeat just about any interpolator. I once had a crosshatch generator with the interlace the wrong way round. That caused havoc with interpolators.
Using line based interpolation on interlaced pictures will always be a compromise. The lines being interpolated are not spatially adjacent. But spatially adjacent lines are a field apart in time. The Pineapple converter which had field stores had a gorgeous looking interfield interpolation option. Until something moved. Then the result was unspeakbly hideous. You got similar effects with early LCD TVs where the de-interlacing was poor. De-interlacing is very hard to do well. Ultimately the vertical and temporal information are very entangled and hard to separate.
While the 1970s BBC report that I cited said there was no benefit in going above 4 lines, I've seen other work suggesting that up to 9 lines can be beneficial. I think this was only on progressive material and probably only worked if there was no vertical aliasing. Neither of these is a practical situation for a 625 to 405 converter.
www.borinsky.co.uk Jeffrey Borinsky www.becg.tv
