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pandy · 11th February 2015, 21:13

Thank You Guys, few additional info's from my side,

Decoding HAM (6 or 8 or any other) is not a problem - HW is fully predictable, side to this ffmpeg support decoding.
Encoding is an issue - as Stainless pointed - there is at least few areas - edge detection as rapid change of color may need 2 pixels (fringe), color model (perhaps it is good to perform conversion in linear space not gamma?, perhaps different than RGB color space should be used and later mapped in RGB?, 16 color for CLUT not produce any distortions so their selection is crucial i assume).
So i think about Avisynth more like preprocessor than real encoder.

Two words on Atari ST (mentioned by Stainless).
Atari ST use different approach - Photochrome/Spectrum change color multiple time per 1 video line - this usually gives 48 different colors in 1 video line.
There is code with nice explanation:
http://www.leonik.net/dml/sec_pcs.py
And example how it works in case of video:
http://www.youtube.com/watch?v=w5EbCT0W_Ds
http://www.youtube.com/watch?v=urgixT_MPCU
Impressive!!!

Amiga may use similar tricks (but it may use specialized coprocessor "Copper" to perform such task instead CPU or it can use both - there is few video modes based on this principle such as SlicedHAM, Dynamic Hires, PCHG etc).

But for me interesting is plain HAM mode (so no dynamic color change) - for dynamic color change Amiga may use software from Atari ST (after porting).

HAM6 example (no color cycling)
http://www.youtube.com/watch?v=_7IYxjNaCd8
http://www.youtube.com/watch?v=TiPZdAdLtdg

There is some software for Amiga to convert RGB555 > HAM6 but i have impression that quality is suboptimal (conversion is very simple) that's why i have idea to use Avisynth as kind of preprocessing solution.

Btw im really impressed with overall high quality (better than VHS) offered by those mid 80's computers - not widely known fact is that probably one of first multimedia standards was created on Amiga (IFF - and it is still used today as RIFF/AIFF etc), CDXL was probably first video file format http://en.wikipedia.org/wiki/CDXL

Thanks once again.

11th February 2015, 21:13	#8 \| Link
pandy Registered User Join Date: Mar 2006 Posts: 1,049	Thank You Guys, few additional info's from my side, Decoding HAM (6 or 8 or any other) is not a problem - HW is fully predictable, side to this ffmpeg support decoding. Encoding is an issue - as Stainless pointed - there is at least few areas - edge detection as rapid change of color may need 2 pixels (fringe), color model (perhaps it is good to perform conversion in linear space not gamma?, perhaps different than RGB color space should be used and later mapped in RGB?, 16 color for CLUT not produce any distortions so their selection is crucial i assume). So i think about Avisynth more like preprocessor than real encoder. Two words on Atari ST (mentioned by Stainless). Atari ST use different approach - Photochrome/Spectrum change color multiple time per 1 video line - this usually gives 48 different colors in 1 video line. There is code with nice explanation: http://www.leonik.net/dml/sec_pcs.py And example how it works in case of video: http://www.youtube.com/watch?v=w5EbCT0W_Ds http://www.youtube.com/watch?v=urgixT_MPCU Impressive!!! Amiga may use similar tricks (but it may use specialized coprocessor "Copper" to perform such task instead CPU or it can use both - there is few video modes based on this principle such as SlicedHAM, Dynamic Hires, PCHG etc). But for me interesting is plain HAM mode (so no dynamic color change) - for dynamic color change Amiga may use software from Atari ST (after porting). HAM6 example (no color cycling) http://www.youtube.com/watch?v=_7IYxjNaCd8 http://www.youtube.com/watch?v=TiPZdAdLtdg There is some software for Amiga to convert RGB555 > HAM6 but i have impression that quality is suboptimal (conversion is very simple) that's why i have idea to use Avisynth as kind of preprocessing solution. Btw im really impressed with overall high quality (better than VHS) offered by those mid 80's computers - not widely known fact is that probably one of first multimedia standards was created on Amiga (IFF - and it is still used today as RIFF/AIFF etc), CDXL was probably first video file format http://en.wikipedia.org/wiki/CDXL Thanks once again.