Keeping Constant Alpha when Exporting Image Sequences or Movies

Just had a support call from my favorite subtitle company, whether I know a solution for a problem they had for month.

They export all subtitles created in FCP as TIFF with alpha (They really use FCP only for subtitling their AVID stuff to go to film - they have 4 FCP systems and never do an edit on those, except subtitle edits).
The rendered image sequence looks fine, but everytime no title is there they get a black picture with no alpha which has to be replaced in their final application.
So the easy solution is to put a text generator without anything above all subtitles with the length of the sequence - this will "force alpha"
This works for all "black holes" in the timeline and any kind of timeline export which needs alpha channel.

Thought this might be interesting for some of you as well.

Andreas

Some workflow tools for FCP [www.spherico.com]
TitleExchange -- juggle titles within FCS, FCPX and many other apps.
[www.spherico.com]

Interesting...would I be wrong in thinking this issue is related to that tidbit about *not* rendering an Animation Sequence if you wanted to retain the alpha channel?


www.derekmok.com

The rendering thing can be quirky. Are they cutting in an Animation timeline set to render with an embedded alpha channel?



www.strypesinpost.com

Quote
Derek
Interesting...would I be wrong ?

Derek, you know - you're never wrong

Quote
strypes
Are they cutting in an Animation timeline set to render with an embedded alpha channel?

If they would do they already would have thrown their Final Cut Pro systems out of the window. And I think working with Animation Codec in FCP is really not a good choice. Anyway the exported files look perfect expect the "blacks". And if you out for the movies sometimes you may have seen one or more movies where the subtitling is done with TitleExchange and Final Cut Pro. There will be hopefully a lot more of them next year in the UK.
They import the whole movie from Avid as rendered file (HD). Then they use the subtitle files they got from the subtitling companies for the different languages to bring them into Final Cut Pro using TitleExchange Pro. This way they do have real time feedback on their cinema projection system. They do timing corrections or sometimes text corrections. When done they delete/disable the background movie split the sequence into rolls and export as TIFF sequence (one sequence per language). These sequences will be imported into another application which will beside some other things create the final "ready to laser" images.

Andreas

EDIT: just tested Animation Codec wouldn't make anything better other then you need to render in FCP.

I made couple tests following your description: and I can confirm your results. Where there is no clip with transparency (text clips, but any other clip with transparency will do) the Export creates black TIFF without alpha channel (None/Ignore, when imported back to FCP), while the alpha channel (premultiplied Black) is generated for the TIFF images when the exported clips have transparency.

I'm afraid however there is no way out except what you already found out: "to put a text generator without anything above all subtitles with the length of the sequence - this will "force alpha". In fact I found no way to apply any value to the Alpha property of the sequence: so, no clip in a timeline section (black holes) = black opaque.

BTW: it seems that rendering or not rendering before export does not alter transparency during the TIFF image sequence export (as it does with Animation): once more, transparency in clips is exported, black holes are opaque.

Piero

Thanks Piero for taking the time to confirm what I said.
And you're right - it doesn't matter whether you're rendering the timeline or not. If you export it will be rendered anyway.

Andreas

Just did a few short tests (export a tiff image sequence via QT conversion, 'flattened' to a quicktime movie in QT Pro, imported back into FCP). Exported Tiff sequence settings- Millions of Colors+, compression: none. Works out as I expected.

There are 3 ways to export from FCP with an embedded alpha channel (depending on settings)- export QT movie, QT conversion and batch export.

I can confirm that if you have text generators unrendered in an SD sequence (should work the same for HD sequences), it exports the alpha, BUT where there is a gap in the timeline, it is replaced by video black (just as you mentioned). This is because for broadcast videos, gaps should be black, not transparent, as broadcast video (YUV) does not embed alpha channels.

Rendered, and you lose the alpha channel (this is an FCP QT conversion quirk, I'm suspecting QT conversion works off rendered files when available).

ALSO, if you set your sequence to Animation, and enable the alpha channel in "advanced settings" (set to Millions of Colors+) You DO get alpha channel throughout whether you render or not.

To clarify. I won't advise editing the whole thing in the Animation codec in FCP (short pieces perhaps, but not full on features or long form), as you'll need to render, and some machines/interfaces may not be able to handle playing it back in RT. However, if you toggle the sequence to Animation (as I did) just before you do the export, it works.

Good tip on having an empty text generator to generate an alpha channel. I can think of a few other uses for that (although a completely transparent tiff still above the video should also work).



www.strypesinpost.com

Hi strypes,
"a completely transparent tiff still above the video should also work": I tried that... but it does not work! (I didn't expect it either...).

It seems that for transparency to be exported (at least with Export/Using Quicktime Conversion - Image Sequence - TIFF) the alpha channel of the exported clip must not be fully transparent... I made 2 tests, both applying my new filter Make Transparent to the Video Generators/Render/Color, set alone in the timeline with checkboard background:

- when the selected color in Color is grey or any color different from white, Make Transparent makes it partially transparent (it uses luma channel for transparency): you see checkboard background in the canvas, and if you export this section of timeline you get a partially transparent TIFF, with Alpha = Black (when imported back into the browser)

- when the selected color in Color is white, Make Transparent makes it totally transparent: again you see checkboard background in the canvas, but if you export this section of timeline you get black opaque TIFF with Alpha = None/Ignore...

The same seem to happen also when exporting using Export/Using Quicktime Conversion - Still Image - TIFF.
I'm really curious to know if this depends on some particular configuration, or it is a general behaviour of FCE/FCP.

Piero

>"a completely transparent tiff still above the video should also work"

Just did it. works for me. I'm on a DV PAL timeline this time. QT conversion without rendering. Instead of black video in the middle, it's an alpha channel with the tiff file.



Animation sequence...


Gaps are now transparent instead of video black. Won't recommend cutting, but you can export a SCQT movie (which will be Animation), or QT conversion (tiff/tga sequences) and it will preserve the alpha channel, rendered or not. Although i would recommend rendering before exporting.



www.strypesinpost.com

I'll try that too (my test though was with Image sequence as Andreas, not Animation)
Piero

The 2 workarounds, are:

1. Work in an SD/HD timeline, but drag either a transparent tif file or empty text generator to "force" alpha. And make sure nothing is rendered before running QT conversion.

Or

2. Work in an SD/HD timeline, and when you're going to export, switch sequence codec to Animation with an embedded alpha channel and export.

See if that works, Piero, Andreas. I'm on FCP 6.0.3 (i think...).



www.strypesinpost.com

OK I did compare the tests:

- as I already wrote above, using Export/Using Quicktime Conversion, Format: Still Image or Image Sequence, TIFF does not export transparency, if the clip is fully transparent (alpha channel filled with 0; otherwise, if transparency is partial, it is exported in TIFF - as in the text clips used by Andreas).

- following strypes suggestion I did export the same fully transparent clip (alpha channel filled with 0), and in fact I found that Animation does export full transparency (namely I used Export/Using Quicktime Conversion, Format: Quicktime, Options/Settings/Compression TYpe: Animation and Depth: Millions of Colors+...)

So... we were both right!

Tests were made with FCE 4.0.1, Leopard 10.5.5 and iMac G5. But my guess FCP behaves the same...

Piero

Hi,

Just tried Gerards way and it does work as well.

For me just the easy workaround I suggested was a the empty text generator as nearly all are coded to produce an alpha like below
"group "Text";
AlphaType(kblack);
fullFrame;"
So they only have to change the sequence's size.

Regards
Andreas