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Daniel Stepp

Digital Master?

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Hi, I shot a feature on MiniDV awhile back, and need to make the best possible digital master for archival. What format is the best for this? Thanks,

 

Daniel

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Well, actually the best archival form would be to transfer it to 35mm b&w separations, plus a 35mm color internegative... but I don't think that is the answer you wanted to hear. There is no consensus on long-term digital storage, other than the fact that every five years or so, you should copy it digitally to whatever the current storage format that is most popular.

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Of course, the problem with copying digital repeatedly is that there is some generation loss that even digital formats suffer from after about 10 generations if the copying isn't done perfectly each time. Since a lot of digital copying is done in real time, or onto formats such as DVDs or CDs that will corrupt and become unusable should the data stream stop, whenever there is a pause during copying these devices will try and make up by interpolating the information where these errors or stops occur. Be careful what you use when you're copying digital files. Also, DVDs and CDs are not arechival storage media. They are finding that such media can corrupt and oxidize in as little as 20 years.

 

Regards.

~Karl Borowski

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Thanks for the replies.

 

I don't know what to do. 35mm is out of question for me. But I want something that will be full quality. I'm thinking about rendering the whole movie as an .avi file (isn't that lossess?) and storing it on an external hard drive. This doesn't seem stable somehow, but its the best I can figure. Tape and DVD don't seem stable at all.

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Hi,

 

I just archived a major project. I made several DV copies of it and sent them to various locations, including two remote client offices; I burned the final production to several sets of two DVD-R discs (it wouldn't fit on one, being forty minutes of DV) as DVSD codec AVIs and sent those out with the tapes.

 

Reading any of these formats is no small technological feat. I think it is likely that reading DVD data will be commonplace for at least the next twenty years or so, and probably more - it's still easy to have 78RPM records and 1/4" audio tape played back. This of course assumes the dye in the DVD-Rs is stable. If they're kept away from excessive heat and UV radiation, CDs I wrote in the mid-90s are still readable (on the other hand, a week of sunshine will bleach most DVD and CD recordable media to complete colourlessness!)

 

Long-term stability of DV tape is probably as good as any other kind of magnetic media, with high-frequency information being slowly erased by the rotation of the earth's magnetic field. Digital formats only need partial readability to reconstruct the full signal, which is good, so it's really a case of maintaining the media physically. Magnetic tape of any description should ideally be stored in stable humidity and temperature and rewould periodically - rather like film stock.

 

Availability of equipment to read DV tape is not something that concerns me. The combined market penetration of miniDV and the related DVCAM and DVCPRO formats (and many DVCPRO decks will read any of them) is massive on a scale not witnessed before, largely because of the use of the format in both amateur and professional applications. 1" C format has been obsolete since the mid-80s and dubbing suites have a replay machine as a matter of course, twenty years later. People are actually aware of the archive situation, it isn't overlooked.

 

The only advantage that film has is that its longevity is known from experience whereas VT only has accelerated aging tests, at least beyond 30 years or so. However, I am concerned about the long term dye stability of recordable optical media such as DVD-R and CD-R, especially considering it's actually designed to be easily modified by the laser in the drive.

 

Phil

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I wonder if John can tell us how Kodak's project to write digital information to 35mm film is going? The plan was I believe to use some sort of dot matrix at near-grain size. In theory anyone with a filmout system could offer this service, and at 4k probably approaching the maximum resolution even Kodak could do it at.

 

This could be a nice alternative to huge tape backups for digital masters as well as all sorts of valuable data - and it could be read back fast on a datacine. A finer mind than mine could probably work out the likely data density... Phil?

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Hi,

 

Assuming a 2K image and that you can only read two states reliably from the pixels (which you might be able to better, but I don't know) - it's only 380-odd kilobytes a frame. Film is a terribly noisy medium to try and resolve bits from, at that level. Intermediate or hi-con stock might be better, but what's it ever going to get you - a couple of megs a frame? Mneh.

 

Phil

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Come to think of it, if you could rely on the colour fidelity lasting you could use different colour 1's and 0's to represent more complex strings of information. I've no idea how many discernable hues you could reliably use, but at 16bit linear RGB that's a lot of information. Even leaving large safe gaps in the colour space you could get a LOT more data on a roll.

 

If Kodak added a few layers off the visible spectrum you could really go to town. If they went so far as to make the film unuseable for film work by using color layers designed purely for data storage, they wouldn't be obliged to charge film prices for it. Skip the perfs off and use the whole neg area, say 6 layers from IR to UV, sell specially designed fast laser printers and line scanners. You could get into the terrabytes per roll, maybe sell the rolls for less than a few 150gb tape cartridges.

 

Sorry for hijacking the thread Daniel! Back to reality - I make a few tape backups (not DVD-R or CD-R for the reasons given) and store them seperately, and duplicate them every 5 years or so.

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Hi,

 

I'm sure you could use colour stock and certainly get at least a single bit per colour layer - I'd have thought more but the colour changes over a single grain's worth of dye are large, just due to the shape of the grain itself. Let's assume you can get at least 4 bits per pixel.

 

Overlooking sprocket holes you begin to realise that assuming it'd have a control track along one edge the writer wouldn't even have to be that accurate, least not in the way that a motion picture pulldown is accurately repeatable.

 

Still, with Moore chasing down the capacity of things like CDs and Zip disk-alikes, you'd have to be able to store a hell of a lot of information on a photochemical medium before the processing, which would still be a big deal, would become viable. After all, 100Gb is less than four blue-ray optical discs, and that kit exists (even if it's kind of hard to buy at the moment.) I think this may be a technology that has been and gone before it started. Although as an archival medium...

 

Phil

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I'm sure there are a number of good digital ways to store digital data -- just don't expect to leave it parked in a vault untouched for 50 years and hope that the recovery technology exists or that the storage media has not decayed in some way. As a safety precaution, re-examine it every five years and decide whether to move or copy the data to some other format. That's the safest approach. There should be fairly lossless ways of merely cloning data from one medium to another. We're not talking about uncompressing and reprocessing the data, merely cloning it.

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Time will tell what Kodak has coming from its Research and Development labs, I won't. :rolleyes:

 

But the Kodak Cinema Digital Sound (CDS) system did lay alot of bits onto film over a decade ago. It was the first practical digital sound-on-film system:

 

http://members.aol.com/cds3570/cds.html

 

http://members.aol.com/cds3570/cds1.jpg

 

http://members.aol.com/cds3570/specs.html

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