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Old February 18th, 2004, 12:12 PM   #1
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Image sequence output question...

I think I remember seeing some theories on this but a search hasn't brought up what I was looking for...

Anyway, for whatever reason the best thing for getting a post house where I am to take my footage in is to give them an image sequence. They usually take in tga sequences but can also take jpg sequences. I'd be outputting these images from Adobe After Effects. Now I've checked both tgas and jpegs (at maximum quality) and there is a massive difference in filesize. My short as a tga sequence will be over 20 gigs which means a lot of burning onto dvds and a far longer time for them taking it in (they're doing me a favour). A jpeg sequence should be just over 4 gigs and so would fit on 1 dvd which would be a lot handier for both me and them. The short is running at almost 14 minutes.

The issue, of course, is loss of quality. Looking at both tgas and jpegs there is an ever so slight difference. The tgas seem to be completely lossless. The jpegs look fine (to me) but aren't exactly the same. You have place one image on top of the other and zoom right into the pixels to see it but there is a difference. It doesn't seem to be noticeable when moving but maybe my eyes aren't as tuned to picking things like that up.

I suppose I'm just wondering if people reckon I'd get away with a jpeg sequence? Probably the best thing would be to post up a couple of samples so you can see what I mean, but I'm in the middle of a mammoth render at the moment so it might not be today. Has anyone been down this road before and come to any conclusions? The footage was DV (Canon XL1) and, to be brutally honest, isn't perfect as it is so it's whether it won't really make a difference if the footage isn't perfect anyway or whether that would be one degredation too many.

Any opinions (or alternatives) would be really appreciated.
TIA,
Jay.
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Old February 18th, 2004, 01:02 PM   #2
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In "natural" images, JPEGs can be really really close to the original. With CG elements (titles, thin lines, etc.), JPEGs will have noticeable mosquito noise on sharp color transitions.

Try to find the hardest to compress section of your video (lots of fine detail, sharp transitions) and look at it from a normal viewing distance. If you can't see a difference, then there probably won't be.
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Old February 18th, 2004, 07:19 PM   #3
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You will be schocked at how much information is actually lost
when you substract an uncompressed image from a compressed
one in a photo program.

Anyway, I would definitely go with an uncompressed or lossless
compressed format. Did you know that targa (TGA) can actually
be compressed (lossless! so no quality loss). Not a whole lot of
applications support it though.

Which NLE are you using? Depending on that it might support
compressed TGA or TIFF's for example. 20 GB is only 5 DVD's. That
isn't so bad?

I think maintaining the highest quality possible is very important
because you are sending it to post house. I'm assuming they are
going to do corrections on your footage, blue/green screen work
or CGI work. All of this requires the cleanest source possible. The
cleaner the better.

Ofcourse it already came from DV, so your source will never be
very clean. But I would not add extra compression dirt if I could
prevent it (money etc.).

Just my two cents.
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Old February 19th, 2004, 07:51 AM   #4
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Rob's right, go with Targa.

JPEG will definitely result in quality loss. Targa is 4:4:4, while JPEG is (I believe) based on a 4:2:0 chroma subsampling - 1/4 of the colour data as Targa. So colour will be fuzzy, in addition to the funny edge effects you get in JPEG.

Regards,

Julian
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Old February 19th, 2004, 08:19 AM   #5
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I agree with all comments so far. To add more technical jargon into the mix, the reason your TGA sequence is larger is because it also natively supports an alpha channel, which will also help if they plan to do any compositing or effects with your work. JPGs do not natively contain an alpha channel, which, along with more compression, helps keep the filesize smaller.

Go with TGAs. When all is said and done, you won't even remember considering JPGs.
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Old February 19th, 2004, 10:48 AM   #6
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Thanks

Thanks you everyone,
The input is appreciated. Big difference or small difference, I'll take your advice and go the tga road. Thanks.

One more related question - does anyone know a way of renumbering an image sequence in a batch without rerendering or reoutputting them? I have my full and (at the time) finished render already as a tga sequence but there is actually one bit right in the middle that I cut and then realised I want to put it back in. Now rather than give the post house several files and ask them to insert it in the middle or rerender the files (I'm having space issues at the moment) I'm wondering if I can renumber the middle batch to slot right in and then renumber everything after that so that the entire render is sequential. Of course it could be done by simply renaming each file but it's tens of thousands of images.

I can just clear off some space and rerender but I thought I'd ask anyway.

I've actually done almost all of the colour and compositing work myself in After Effects so it will be a simple once-over-final-black-crushing-type-grading in the post house and, as it will be a favour, I'm just trying to make everything as easy as possible for them.

Thanks,
Jay.
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Old February 20th, 2004, 06:08 AM   #7
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What you need is a batch file rename utility. There are loads of
those and quick search came up with these 4:

http://www.softpile.com/search.phtml...pp=10&in=title

They all seem to be shareware so might have limitations. I also
found one freeware (completely free) that also might do the trick:

http://www.1-4a.com/rename/

I do suggest you backup your directory first before starting the
rename, just in case something goes wrong.
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