FCP export for image work question

[Andrew Rendell]

What they want is the quicktimes in the original format, without having any further processing done to them at all, e.g., changing the codec, as that’s the best way for them to maintain quality. (24 bit is right, as that’s 8 bits, i.e., 256 defined levels, per colour channel.)

[Timothy Anderson]

Hi Andrew –

Thanks so much for the response and the help. The original daily quicktimes were in DVCPRO HD (1080p30) which is why I selected that setting in sequence settings under ‘compressor’ type. However the color profile for each clip is HD (1-1-1) whereas as the uncompressed are 24 bit RGB as previously mentioned.

So my question is, since a simple export under ‘current settings’ would be in DVCPRO HD (and thus I wouldn’t be changing the codec) can I just deliver that instead of an uncompressed version? Or, is the 24 bit RGB going to add something that wouldn’t otherwise be there?

The reason I ask is a. for quality and b. the difference is a 70 GB QT versus a 450 GB QT …

Thanks again!

Tim

[Andrew Rendell]

The uncompressed 24 bit setting is theoretically better than the DVCPro HD, so if you were to convert something that was Uncompressed 24 bit to DVCPRO HD you would theoretically be reducing the quality, but it’s not going to add anything that’s not already there, so although it would do no harm to go up to uncompressed, there’d be nothing gained, except perhaps if the post house couldn’t handle DVCPRO HD.

[Timothy Anderson]

Hey Andrew –

Thanks again – I just want to make sure I give them what they need without a doubt –

Quick curiosity – so if going uncompressed wouldn’t necessarily add anything to the image/frames for the post house to do their color correction/grading, etc. – what accounts for such a vast difference in file size if the codecs are the same?

Does the 24 bit RGB just add redundant information to the file? Is this additional data relevant to the post image process?

Thanks! Tim

[Gary Askham]

Think of it like this…

if you shoot something on your mobile phone you can convert that footage to uncompressed HD. But it will still look like it was shot on a mobile phone. But it will now take up about 10GB for ever minute of footage.

If you shot DVCPro HD, then edit DVCPro HD, and export DVCPro HD.

(the only reason you might want to go for a higher quality codec is if you have a lot of graphics or titles which have been added in post – these would then benefit from that extra quality. There are also a few plugins that can cheat better quality colour space but they add render times and sometimes don’t add anything)

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FCP and Avid Technical Support
Air Post Production
Shoreditch – London

[Andrew Rendell]

Well, the codecs aren’t the same and there’s a bunch of differences. DVCPRO HD uses 4:2:2 colour sampling, where the red, green and blue parts of an image are processed into Y (luminance, which is brightness) and U and V, which are called the colour difference signals (also known as R-Y and B-Y or Pr and Pb) and those colour difference signals are recorded with half the resolution of the luminance. The upshot of that is that a TV picture has lower colour resolution than brightness resolution, and gets away with it as the human eye is much better at seeing detail in brightness than in colours (a full explanation is a bit more lengthy, but that’s the gist of it). 24 bit RGB doesn’t reduce the resolution in any way, so it’s going to be something like twice the data of a 4:2:2 encoding even before you take into account any other data compression techniques (which is what accounts for the rest of the size difference).

[Timothy Anderson]

Thanks Andrew …

Your end of things is very interesting to me and I don’t really know much about it.

So, to sum things up – in my case does the post house’s ability to color grade/correct improve or increase if they receive an uncompressed QT from me or in this case does it matter given the footage was originally DVCPRO HD? Is it always better to have 24 bit RGB even if it won’t ‘add’ anything per se over what’s already there in the DVCPRO HD…?

Thanks for your time. Tim

[Andrew Rendell]

It’s very likely that the post house will actually do their work (grading, graphics, etc) in a 24 bit RGB colour space, so the question that arises is where and when that conversion takes place. When I was a staff editor (I’m now freelance) we preferred to take the most raw unprocessed source and be in control of the conversion ourselves, but that might be different in your particular case. Could be worth a call to a technician the post house in question.