Working in PAL

[Bill Stephan]

Adrenaline and Symphony are native D1 format editors, so they digitize 720×486 in NTSC and 720×576 in PAL. There are no square pixels in either standard because of the way the pixels are mapped to the monitor’s scan lines. In NTSC pixels are higher than they are wide, and in PAL they are wider than they are high.

In NTSC, D1 format video is lower field first, and I think it is upper field first in PAL (but I’m not 100% sure).

Bill Stephan
Senior Editor/DVD Author
USA Studios
New York City

[Simon Roughan]

Hmmm…But when I export a movie it has the choice 4×3 square pixels. If you cant digitise with square pixels, why the option to export with square pixels? What would that bring?
But thanks for the reply. Anyone from England or Australia or somewhere working in PAL with something to add? Export BetaSP material with upper or lower fields?
Still confused,
Simon 😉

[Bill Stephan]

Simon,

You design in Photoshop or whatever, then you resize to non-square pixels. After importing the image into your Avid, the image will look correct on the video monitor.

Why does Avid allow you to export with square pixels? To solve the opposite problem. For example, let’s say that you have made a freeze frame in Avid from a video image, and now you want to take that image into Photoshop to add a circular logo. You export with square pixels (768×576) so the image looks correct on your computer. You add the circle logo. Then you resize to D1 non-square (in Photoshop or let Avid do it on import). When you look at the logo in video, the circle is still a circle. If you make a circle in a 720×576 Photoshop document and import that directly into Avid, your circle will be displayed as a slight oval because of non-square pixels.

These issues are explained in great detail in books such as “Photoshop for Non-Linear Editors”.

Bill Stephan
Senior Editor/DVD Author
USA Studios
New York City

[Mike Smith]

PAL video is 720×576, always upper field first except for DV footage, which is lower field first, strangely.

Pixels in PAL for digital video are captured using “D1 standard” which is 720×576 pixel grid to represent a “full scan” 768×576 image.

A 4×3 frame uses pixels with a 1.0666 pixel aspect ratio (which multiplies out – 720 x 1.066 – to fill your 768×576 image grid, more or less).

Widescreen uses 720×576 at 1.422 pixel aspect ratio.

Of course your component signal doesn’t have a pixel grid in the samw way: it’s an analogue signal converted by Beta SP machine to fill (more or less) the 768×576 frame.

The black bars down the side are normal: there is an explanation somewhere of how the D1 standard samples the video signal which explains them, but I can’t recall where to find it just bow,

Captured video will normally have correct pixel and frame settings – you do need to watch your graphics if you want them to look similar on video to how they look on the computer. Recent versions of Photoshop have menu options to turn this (pixel aspect ration correction) off and on.

Hope this helps.

[Simon Roughan]

Thanks for the answers guys. I have read the chapters on D1 in the “Creating Motion Graphics” book (again) and its starting to make sense.
Just one more point to clear up please. When I export BetaSP material out of avid “same as source”, why does After Effects interpret as lower field first?
Thanks again
Simon

[Mike Smith]

Are you capturing into a DV codec ….?

[Simon Roughan]

No, I digitise from the deck in 2:1 or 1:1 (I make commercials, so disk space isnt an issue), and import rendered movies and graphics always at 1:1.

[Paul Ingvarsson]

Hello Simon,

Avid capture 720×576 (assuming you are not digitising at an ‘s’ or ‘m’ resolution.

The black borders on either side of your frame are called ‘analogue blanking’, it’s a now defunct feature of older analogue systems – those black line actually occupy part of your 720 pixel horizontal picture resolution. Digibeta when digitised does not have these black lines (although I think you can set a Digibeta to blank these areas for you on playback).

Someone else very elegantly explained why we have the option of exporting to square pixels, which is now becoming more questionable as newer versions of the Photoshop family have built in support for drawing and displaying non square pixel formats.

I’m not sure if Avid fails to flag the field dominace in it’s QT exports or After Effects ignores them. But within the After Effects program directory (i think) you should find a document called ‘interpretation rules.txt’ within there is a long header that explains how to modify the document to suit your needs – basically you tell it to always import PAL footage upper field first.

If you are doing commercial work, you might very well be dealing exclusively with frame based material – if that is the case it doesn’t matter what your interpretation settings are you will always see corret results. As long as you render upper field first to get back to the avid (assuming you are rending in fields) you will also still see good results.

Hope this helps,

Paul

Freelance DS/Symphony
London

[Simon Roughan]

Thanks man, that explains it so I understand. Ive been working in video production for more than 10 years, and have only recently bothered to look into these things. Deeper you go, the more confusing it is.
But now I have it figured.
Thanks again,
Simon