405 to 625 conversion

[`FRANK.C]

Hi Trevor
The first thing to check is to make sure that the equalising pulses are turned off on the Aurora. Because if there are equalising pulses on the 405 it will not sync.

Frank

[Murphyv310]

Hi Frank.
That's most likely the issue.
I'll check later.

[Murphyv310]

Hi.
Indeed the equalisation pulses were on from the Aurora.
I'm gobsmacked by the results. On my Sony monitor its very difficult to actually see the difference between a 625 line test card C and one converted to 405 and back to 625, totally amazing.

[peter scott]

Full marks to Frank for that! Could you post the straight 625 and 405 converted to 625 screen shots Trevor?

Peter

[`FRANK.C]

The converter does a fairly descent job. It is a pity that it is let down by the decoder not being able to cope with VCR recordings etc.
I have a couple of things to try. They might help or could just go flop  
It will be a while before I get try them.

Frank

[ppppenguin]

I was working on making my 405 to 625 converter a bit more rugged against VCR playback.  Everything was OK apart from field sync which was fragile. I had designed a sort of field rate digital flywheel, really more of a gating and lockout system, when I got distracted and have never got back to it.

Frank, all my thoughts are in the attached VHDL file if you want to try and make any sense of them. No idea if they really work with VCR replay. File is zipped because .VHD files won't directly attach to a post.

[`FRANK.C]

Hi Jeffrey
Thanks for your files.
I will keep them safe until I start at this again. I am distracted at the moment too.

Getting good clean reliable sync from a VCR is a real problem.
Lately I did try and use a LM1881 to extract the odd/even field from the VCR signal.  But it didn't fare any better than doing it digitally. Both failed to the same extent.
I have to say though that the test I did with the LM1881 was a very brief one and I didn't try changing the values of the R's and C's in the circuit so there may be potential for some improvement.

Frank

[ppppenguin]

It's an annoyance that while a monitor doesn't need to know anything of the odd/even field sequence a standards converter does. At least I think it does. In my case I wonder if I could change it from a framestore to a fieldstore. Not sure how the output side would know which field is which, for sync insertion. In Frank's case with only line stores, the output field is, by definition, the same as the input. Perhaps something is possible? I think not.

[Murphyv310]

Full marks to Frank for that! Could you post the straight 625 and 405 converted to 625 screen shots Trevor?

Peter

Hi Peter.
I'm hoping to get some good shots on Thursday. The issue I have is to get shots with a slow shutter speed for best results, my old Fuji is the best but there is now an issue with focus, both auto and manual. It's all in hand hopefully.

[Murphyv310]

Hi.
I've done two quick photos off the screen of my 625line Sony Monitor. I had to reduce the contrast and brightness to get a picture that didn't give me bad results of to fast a shutter.
I will do this again if I can fix my old Fugi that I can adjust the shutter on and get a better overall result.
You can see the two conversions are pretty good one remember is converted from 625 to 405 then back again so there are two sets of degradation. Pretty impressive though.

The odd effect that shows up like feint vertical lines cannot be seen on the naked eye, something the camera seems to be picking up on the converted test card.... odd!