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16:9 FHA SD clips in a 4:3 SD timeline – the mathematics?
Hi
This is not a PAL-specific problem – in NTSC-land the same problem will exist, but the numbers may be a bit different 😉I need to add 16:9 FHA PAL SD ex-DigiBeta (720×576) clips to a SD PAL 4:3 sequence, clipping off the sides to scale the image to the full height of the 4:3 frame.
So I need to overcome FCP’s (5.1.4 as it happens) default to letterbox/scale-down the clips on adding them to the timeline.
Mathematically what I need to do is keep the clip’s vertical resolution (576 lines) unchanged. The clip’s pixel aspect ratio needs to be retained (at 118:81 for PAL, google tells me) rather than changed to the 4:3 PAL sequence’s 59:54.
All this maths is in intergers – in fact in reality all this comes down to check-box switches:
Vertical line count: Unchanged
Horizontal Pixel Aspect Ratio for clip: Unchanged @ 118:81However – in the reality of FCP’s Motion tab a setting of Distortion>Aspect Ratio>-33.33%, and Scale +133.33% are needed to get the clip correctly placed in the timeline.
My gut feeling is that these two .33% mathematical sub-pixel floating-point rescaling parameters DON’T add up to applying two integer-like check-box changes to the clip.
My eyes reinforce that, by giving me a timeline clip that seems considerably less sharp vertically than when the clip’s Anamorphic property is unchecked when its added to the timeline (unscaled).
Also there’s the constant admonishment to keep Motion tab placement parameters an equal whole number, to keep field order unaltered.
Now the FCP GUI designers could be very clever, and code the Motion tab operations so Scale = +132% or +134% is seen as a floating-point rescale. And Scale = +133.33% is seen as a command to leave the frame vertical line-count unchanged.
Or not. Seems to me that a couple of check boxes would have been more elegant (neither here or there) or effective (which is crucial) solution.
Actually the same scaling-to-fit process can be achieved, by changing the Distort corner coordinates, so leaving Aspect Ratio at 0 and Scale at 100%. All numbers then remain integers….
Is this the correct way to do this?
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6 Replies
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Whoah…too much maths!! – i became an editor so i wouldn’t have to do much math!
Anyway, when i have to do this its simply a matter of using distort at 33.33% and scale at 136% ( i find this scale gives a cleaner edge of frame).
You might also want to try importing the material with the anamorphic option in your capture settings switched off.
There will be a degradation of the image – after all, you are effectively scaling up by a third. You just have to remember that those watching the final edit don’t have the 16:9 originals running concurrently to compare it to..
adam
Editor/Mixer
Character Options Ltd
Oldham, UK -
[lightning ad] ”
There will be a degradation of the image – after all, you are effectively scaling up by a third. You just have to remember that those watching the final edit don’t have the 16:9 originals running concurrently to compare it to..”Yep, there’s no way to get around 16:9 anamorphic SD footage being up-scaled to fit a 4:3 SD timeline with cropping. We generally run this footage letterboxed in SD mode.
Walter Biscardi, Jr.
https://www.biscardicreative.com
HD Editorial & Animation for Broadcast and independent productions.All Things Apple Podcast! https://cowcast.creativecow.net/all_things_apple/index.html
Read my blog! https://blogs.creativecow.net/WalterBiscardi
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[lightning ad] “…importing the material with the anamorphic option in your (clip) settings switched off.”
Hi
Dohh! Blindingly simple lateral thinking….
The Preview window will be just like watching TVs for sale in the electrical superstores – every one scaling differently 🙂
Cheers -
I’m not sure that will give you what you want though – the aspect ratio will be wrong and left/right sides won’t be cropped.
As you say, an Aspect Ratio value of -33.33 and scale of 133.33% won’t get the scanlines to line up exactly and there will be a slight softening of the image. BTW the scale of 133.33% is deceiving – in reality it doesn’t mean that the image is zoomed in by a third because the scale and distort values work together to produce the final effect. Also, the field order of a clip will always be correct, regardless of the position of the clip. What does happen is the image loses sharpness if it is moved vertically by an odd number of pixels.
So if you need to be “super picky” about image quality, then the best way to do it is set the Aspect Ratio and Scale to “0” and change all the “-360/360” values in the Distort section to “-480/480”. That guarantees you’re only doing a horizontal scale with no change to the vertical.
Martin
Digital Heaven, London UK
Unique plug-ins and tools for Apple Pro Apps
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Avid2FCP
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Hi
Thank you, I was working towards that in my last post – Zen and the Art of leaving check-boxes unticked… 😉
The clip Anamorphic check-box is ONLY for using clips in a 16:9 sequence. For 4:3 timelines leave it alone!!!!
I’ll use the Distort coordinates you’ve listed. 🙂Through a glass darkly you can know an application for years, use it daily, RTFM frequently, yet not UNDERSTAND how its underlying philopsophy.
So today’s significant 4th July insight – leave the fri**ng checkbox unchecked!
(If it does something you don’t think is working). Hallelujah! -
thanks Martin, thats useful to know. I shall have to remember that one.
adam
Editor/Mixer
Character Options Ltd
Oldham, UK
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