User Programmable Standards Converter

[`FRANK.C]

Just been doing a little more work on this and I have noticed that with a 525 line source the the output looks a little woolly when compared with a 625 line source.
With a 525 line source some artefacts can be seen before and after any vertical lines. Horizontal lines are not affected. 
The source that I am using is a test card from another Hedghog PSC. Viewed on a monitor the 525 and 625 line test cards look equally good and sharp.
I know that this test card can be a bit harsh but it is not causing any problems at 625 lines.
As it is only vertical lines that is effected what ever is causing this must be in or around the decoder.
The converter should only effect horizontal lines.

It does not photo easily but I have tried. Photo below.

Frank

[Murphyv310]

Looks like under and overshoot on the photo.
Or ringing.

[`FRANK.C]

Hi Trevor.
That's a good description of what it looks like.
I must have a look at what filters the TVP5150 uses. From memory I think some are switchable.

Frank.

[`FRANK.C]

Well that was a fruitless time spent with that. I eventual tried a different 525 line signal source and it is fine.
It must be down to the harshness of the card.

Frank

[ppppenguin]

I don't think the testcards that you generate in a Hedghog have strict bandwidth limiting. I know it's ultimately limited by sampling frequency but it may still upset the filtering in the decoder chip.

[`FRANK.C]

Hi Jeffrey
As you have said the test card is only limited by the video clock frequency. There are some transitions from mid grey to/from peak white and even some peak white to/from black which just takes one cycle. This is far from ideal.
I had thought that it would effect 625 and 405 similarly but there you go.

Frank

[ppppenguin]

Reminds me of the time I was doing some work on standards converters years ago. I was getting odd results with crosshatch. Turned out that the generator had it's interlace backwards. So the white line on the 2nd field was above the 1st. This completely fouled up the interpolation.

Worst part was that I had designed the crosshatch generator.