PAL line twitter problem with CRT/

[Greg Hawkes]

I decided to check how a DVD filmed using EX1 and edited using Vegas 8b looked on my wide screen CRT TV.

Well I got a shock as parts of the picture were badly affected by what I believe is known as 'line twitter'.

I posted this news on the Sony Vegas forum and it was explained to me that the problem was excessive vertical resolution . Too much for the CRT (PAL) to handle. Pictures are fine watched on an LCD TV.

I have tried all PAL formats on the EX1 and all are affected SP and HQ

Suggested fix was to apply min. gaussion blur in the vertical direction.
This works but make the picture appear soft focus.

Has anybody in PAL countries checked their DVDs on an CRT TV?
Any idea how to fix this. Could be quite a problem.

Will call Sony Professional UK tomorrow and ask for their thoughts.

Any others appreaciated.

[Dennis Schmitz]

Do you shoot with Detail=on?
Don't do that. It causes many artifacts.
Sharpen after resize works much better without any artifacts and better overall quality (even better than many commercial DVDs!).

And don't forget to use a good resizer (like spline36 if available or lanczos4)


regards Dennis

[Paul Kellett]

Greg,don't panic,it's just your render template,i've got a CRT tv,and an EX1 and vegas pro 8 (b),my footage looks smooth,i can put progressive and interlaced in the same timeline and render it as interlaced and it's smooth,no jitter. I know what you're talking about.

What template are you using ?
Use DVD architect,widescreen video stream,make sure you tick "include audio" in he audio tab.On the video tab make sure the fields are upper field first,i've tried lower and progressive and it looks crap.

Paul.

[Bob Grant]

Hi Greg,
that would probably have been me that gave you that advice.
I've spent a lot of time wrangling this problem, starting with very high res stills for 50i DVDs. Whether or not you see the problem is very content dependant. I had one still that'd cause the whole frame to blink on a CRT.

I need to do some more testing to give you a final answer however in the interim consider this:

Down here in PAL land we have 576p, which is HD. Frame size 720x576. We also have 480i, frame size also 720x576 , that's vanilla SD PAL. Unfortunately due to how interlaced video works you cannot deliver as much resolution as the pixel count would imply. Depending on content you may well have to accept slightly less than the maximum resolution.

You also need to be careful about how you apply the GB FX, applying it after the downscale will give you more softening than doing it before. Need to check this when I have some time. Also try the median FX instead of the GB.

[Greg Hawkes]

Thanks Guys

Paul

Changing the render template in Vegas to upper field first gave a big improvement but there are is still a noticeble amount of flicker in parts of the picture. Including the audio or encoding seperateley using dolby preset makes no difference.

Maybe as Bob says it depends on content.

Will see what Sony say tomorrow.

[Steve Mullen]

Originally Posted by Greg Hawkes

I decided to check how a DVD filmed using EX1 and edited using Vegas 8b looked on my wide screen CRT TV. Well I got a shock as parts of the picture were badly affected by what I believe is known as 'line twitter'.

You don't say if you shot I or P. I assume 1080i. I also assume the CRT is only SD.

With P: yes -- the V res may be way too much for a CRT. With Panasonic's 24p DV camcorder there was a switchable low-pass filter that should be engaged when the video was intended to be shown on TV. For going to film, the filter was turned-off.

With I: unfortunately, line-twitter is inherent with all I HD and SD formats. (Yes, you can reduce it by turning down EX1 Sharpness, but doing so significantly eliminates fine detail. A bit crazy since the point of HD is recording very fine detail. (With Sony camcorders, NORMAL gives the best detail without over-enhancement.)

Downconverting is always very hard. The SD codec acts as a digital sampling system being fed a signal with a many times higher frequency. With no low-pass filter before the SD codec, Nyquist tell us there will be aliasing. Aliasing can be seen on diagonals, but on horizontal edges it can look like line twitter. The solution is correct filtering of the HD before it is downscaled.

PS: "I have tried all PAL formats on the EX1 and all are affected SP and HQ."

Strictly speaking, there are neither NTSC or PAL formats for HD. There are "Region 60" and "Region 50" formats.

[Dennis Schmitz]

Originally Posted by Steve Mullen

...
With I: unfortunately, line-twitter is inherent with all I HD and SD formats. (Yes, you can reduce it by turning down EX1 Sharpness, but doing so significantly eliminates fine detail. A bit crazy since the point of HD is recording very fine detail. (With Sony camcorders, NORMAL gives the best detail without over-enhancement.)

The EX1 already shows all detail when detail=off.
The detail function only introduces oversharpening when switching on which causes many artifacts when scaling down (e.g. Live twitter, blockiness etc.).

Sharpening with good filters after resizing leads to a much better SD picture.

And I'd always recommened shooting progressive.
It's so much easier to scale and work with :)


regards Dennis

[Greg Hawkes]

Success!!

Finally produced a PAL DVD that looks good when play on a CRT TV.

Render template in Vegas PAL widescreen. Sound encoded seperately using Dolby pro. Rendered fields none or fields upper first does not make any difference.

HQ/720/50P

looks ok on the web too.

www.professionalvideo.tv/webvideo

Thanks for all your help

[Paul Kellett]

Glad to here you've sorted it Greg.
I just looked at your site,looks good.
If you ever find yourself in need of a 2nd camera and operator over this way then give me a shout.
Paul.

[Greg Hawkes]

Hi Paul

Thanks for your kind comments and your help.

May take you up on the 2nd camera operator when the chance presents itself.

All the best Greg