23-01-2017, 09:40 AM
(This post was last modified: 23-01-2017, 09:44 AM by ppppenguin.)
A couple of topics come up from time to time which I haven't really covered here. I've discussed both with Darryl (the guy who makes the Aurora converters) and I think my views more or less agree with his.
HDMI and HDTV to 405
For now most Freeview boxes, DVD players and other sources of video have composite PAL/NTSC outputs. But a few now have HDMI only. It's not as simple as bolting an HDMI front end on to an Aurora, there are licensing and HDCP copy protection issues. Best bet for now is to get some cheap HDMI to composite converters such as these: https://www.amazon.co.uk/Composite-S-Vid...B00LX02LR6 No idea how they handle copy protection. I ought to get some myself.
Analogue HD outputs are effectively non-existent on new equipment so this isn't a problem.
405 to 625 - reverse conversion
There is still a small amount of archival 405 video tape, pluse those VHS tapes some of us made on 405 in the days before readily available 625 to 405 converters. I was asked about this for a commercial project a couple of years ago. In principle I could have built some dedicated hardware, in practice I suggested optical conversion.
The common decoder chips used as the front end for Aurora etc cannot cope with 405. A purpose built front end isn't a huge problem but it's not worth doing a product for sale as there's very little demand. The remainder of the job is easy using programmable logic.
Many years ago the BBC had a custom modifed Mc Michael ACE standards converter with 405 front end. This no longer exists.
That leaves optical conversion. I successfully converted some 405 tapes many years ago with a Prowest PM14/1 monitor and an EMI 2004 monochrome plumbicon camera. This worked much better than I expected. I defocussed the camera very slightly to avoid moire effects. These are caused by the interaction between the 405 and 625 line structures. There are better ways of dealing with this problem.
1: Astigmatic spot to fill in the line structure. Not the easiest thing to achieve.
2: Spot wobble. This should work but I've not tried it.
3: Reduce the height of the monitor to close up the gaps between the lines. I've tried this in a rough and ready way, it works.
In the days of tube cameras you also reduced the height of the camera scan to get the aspect ratio right. Nowadays you would capture with a HD camera and digitally post-process to get the aspect ratio. This ought to work very well, given a decent 405 line monitor.
In any optical conversion you need to line up the grey scale. When I did it years ago I used sawtooth and PLUGE (on 625 as the PM14/1 is dual standard) to do this. I adjusted the camera and monitor using a pair of waveform monitors to get the grey scale as accurate as possible.
This is speculation but a fast data acquisition system might be used to capture the entire the 405 line waveform without regard to its nature. Hence no PLL based clock etc. Then sort out the whole thing in software. It ought to work but it's well outside of my own experience.
HDMI and HDTV to 405
For now most Freeview boxes, DVD players and other sources of video have composite PAL/NTSC outputs. But a few now have HDMI only. It's not as simple as bolting an HDMI front end on to an Aurora, there are licensing and HDCP copy protection issues. Best bet for now is to get some cheap HDMI to composite converters such as these: https://www.amazon.co.uk/Composite-S-Vid...B00LX02LR6 No idea how they handle copy protection. I ought to get some myself.
Analogue HD outputs are effectively non-existent on new equipment so this isn't a problem.
405 to 625 - reverse conversion
There is still a small amount of archival 405 video tape, pluse those VHS tapes some of us made on 405 in the days before readily available 625 to 405 converters. I was asked about this for a commercial project a couple of years ago. In principle I could have built some dedicated hardware, in practice I suggested optical conversion.
The common decoder chips used as the front end for Aurora etc cannot cope with 405. A purpose built front end isn't a huge problem but it's not worth doing a product for sale as there's very little demand. The remainder of the job is easy using programmable logic.
Many years ago the BBC had a custom modifed Mc Michael ACE standards converter with 405 front end. This no longer exists.
That leaves optical conversion. I successfully converted some 405 tapes many years ago with a Prowest PM14/1 monitor and an EMI 2004 monochrome plumbicon camera. This worked much better than I expected. I defocussed the camera very slightly to avoid moire effects. These are caused by the interaction between the 405 and 625 line structures. There are better ways of dealing with this problem.
1: Astigmatic spot to fill in the line structure. Not the easiest thing to achieve.
2: Spot wobble. This should work but I've not tried it.
3: Reduce the height of the monitor to close up the gaps between the lines. I've tried this in a rough and ready way, it works.
In the days of tube cameras you also reduced the height of the camera scan to get the aspect ratio right. Nowadays you would capture with a HD camera and digitally post-process to get the aspect ratio. This ought to work very well, given a decent 405 line monitor.
In any optical conversion you need to line up the grey scale. When I did it years ago I used sawtooth and PLUGE (on 625 as the PM14/1 is dual standard) to do this. I adjusted the camera and monitor using a pair of waveform monitors to get the grey scale as accurate as possible.
This is speculation but a fast data acquisition system might be used to capture the entire the 405 line waveform without regard to its nature. Hence no PLL based clock etc. Then sort out the whole thing in software. It ought to work but it's well outside of my own experience.
www.borinsky.co.uk Jeffrey Borinsky www.becg.tv
