405 to 625 conversion

[ppppenguin]

I thought about counting after slicing and it should work. But by slicing you throw away information so I followed the thought and ended up with accumulating the whole waveform. It's a sort of integrator which will reject impulse noise.

I'm also thinking about improving the sync edge detector, either by counting a few pixels after the slicer and saying they all have to be sync or possibly some kind of correlator that looks for the shape of a sync edge. The snag with correlation is that it needs multiplication and I don't have hardware multipliers in my ancient FPGA.

[`FRANK.C]

I have no proper VCR to record and play 405 lines.
But I have found one that will record short clips of  405 lines poorly and another VCR that will play them.

A short video at this link of play back of the 405 lines and conversion to 625 lines. It is actually better than I expected.
https://youtu.be/WyC1bevzMQM

The VCR's are fairly modern and far from ideal. The record one appears to have some form of black level clamp that goes haywire when it sees a 405 signal. As times goes by the recorded sync pulses gets shorter eventually disappearing altogether. With the result I can only record just over a minuet with sync pulses. There is also line tearing.

Frank

[Jac Janssen]

Impressive results Frank!

The converted picture (if indeed 625 is the left one) is more stable than the input.

Jac

[`FRANK.C]

Hi Jac
It makes a big difference to have a VCR that can play 405 tapes. Even if it plays them poorly.
Link to a short clip after I improved the filter to the sync separator.
https://youtu.be/JonVRZsErSU
Remember that the 405 video off the tape is being view on a pre video recorder TV but the 625 video is displayed on a modern monitor which would be better able to cope with the video from a VCR.

Frank

[Jac Janssen]

Hi Frank,

A big improvement in picture stability!

Jac

[Murphyv310]

Hi Frank.
That's a truly amazing result. I'm going to get one sometime before Christmas. Lots of projects in the pipeline.

[`FRANK.C]

Thanks Jac and Trevor.
One has to keep in mind that what I am using is a clean 405 signal recorded with a modern VCR and played back on another modern VCR.
What it would be like with material that was recorded off air with an older VCR is unknown.
There are some other things that I can try and see will they will improve things.

Frank

[Murphyv310]

Hi Frank.
Is there a software update for the Hedghog Dual for the above changes or are they hardware?

[`FRANK.C]

Hi Trevor
There will be no hardware changes. When complete I will update the firmware on the website.

Jac has kindly tried it out for me with some off-air recorded material and it still leaves a lot to be desired. So there is some fettling to be done yet.
But at least now that I have a VCR that will play 405 I can try some different approaches.

Frank

[Murphyv310]

Hi.
Tried my Hedghog Dual on Tuesday from 405 to 625 for the first time. Signal source was the test card from the Aurora and 625 out to my Sony monitor. Although the 625 was locked the 405 looked as if there were no syncs. Switching off and on the picture could be four segments or shifted up, down, left or right or even have a part missing.
Any ideas?