Jesse Rosen
Forum Replies Created
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Make sure timecode on the deck is set to regen mode.
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Jesse Rosen
Director of Technical Development
Abel Cine Tech, Inc. -
Just to nitpick…
1080i/60 DVCPROHD is 1280×1080, but 1080i/50 is 1440×1080. Interestingly in FCP5 DVCPROHD/50 codec is implemented, so you can do 1080P/24 with the 50Hz codec instead of the 60Hz one and get less subsampling, for those of you offlining in this format.
I’m tired… does this post make any sense?
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Jesse Rosen
Director of Technical Development
Abel Cine Tech, Inc. -
[walter biscardi] “FCP does not run timecode out from a Timeline. “
Generally no, but for some strange reason it does in the DVCPROHD codec. Go figure.
Would be nice if it always did — would save a lot of time editing to tape.
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Jesse Rosen
Director of Technical Development
Abel Cine Tech, Inc. -
[Peter DeCrescenzo] “So, for example, one might use a lighting technique to cast a detailed, but undesirable area of the frame into deep shadow to “free up” the cam’s DCT compression to yield better quality in other, more important parts of the image.”
Perhaps this would help somewhat, but I still wouldn’t recommend basing your framing on what you think the codec will handle best — the effect is likely to be quite subtle. A quick test: record a bit of footage on the DVX100 in 4:3 mode, then without changing the framing switch to letterbox mode and record. Theoretically you’ll have more bits applied to the actual image data (well, the part that is the same between these two modes) in the letterbox one, but I’d bet you’d be hard pressed to actually see a difference — probably not enough of one to justify giving up the ability to vertically reframe in post.
As for the questions about compressing at different frame rates: again I’m not privy to what actually going on in these cameras, but I would bet that on any of the cameras that record multiple copies of frames (Varicam, DVX, SDX900) that the frames are indeed getting recompressed over and over. From an engineering standpoint, once you have a hardware-based codec that can compress your frames in under 1/60 of a second, it’s much easier to just pass the footage through it on the way to tape than to start dynamically altering the codec based on the frame rate. Also, I don’t think that more time in this case would actually help. Unlike codecs that employ temporal compression (MPEG et. al.), there’s not a lot of analysis that happens in a DV codec — the codec is designed to be applied in real time — the amount of work done by the codec actually doesn’t change based on scene content (though the results will, of course).
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Jesse Rosen
Director of Technical Development
Abel Cine Tech, Inc. -
In a DCT-based codec, all brightness information (this happens once for each channel — Y,Cb & Cr) is converted to frequency information through a DCT (Dicreet Cosine Transform). Note that this stage is theoretically lossless, meaning that if the calculations were done with infinite precision, this would be a completely reversible process. The next stage is where the actual loss comes from: the coefficients yielded from the previous step are quantized based on some formula that varies from codec to codec (this is largely what defines the bit rate and quality of a DCT-based codec). Then the quantized coefficients are run-length encoded and entropy encoded (usually a Huffman table) — this last step is also lossless, it is very much like ZIP compression.
As this greatly simplified overview shows, the image loss that occurs is all from quantization in the frequency domain. What this means is that what is lost is spacial detail. Note that this does not necessarily mean that high-frequency detail will be lost — it depends on the design of the codec. But to answer your specific questions to the best of my ability:
[Peter DeCrescenzo] “Which compresses more easily/cleanly: A B&W checkerboard pattern, or a even field of gray?)”
An even field of grey has almost no frequency information, so will compress very cleanly. (Note also that in the DV-based codecs [e.g. DVCAM, DVCPRO/50/HD, HDCAM] “left-over” bandwidth from a low-complexity portion of a frame will get allocated to more complex portions of the frame.)
[Peter DeCrescenzo] “Reducing a camera’s sharpening or detail settings make edges softer/grayer; does this improve in-camera compression results?
Some cameras have DCC features to help control/reduce undesirable contrast. Likewise, shallow depth of field can also be used to soften contrasty foregrounds & backgrounds. Skin detail controls can help reduce unwanted detail in specific colors. Do these techniques usually result in better in-camera compression results?”
In general anything that reduces image complexity will improve compression. As to whether reducing a camera’s sharpening helps, I doubt it since detail enhancement doesn’t actually add information. Also, I don’t think that gamma controls (including knee, DCC, master gamma, black stretch, etc.) will have much effect either except insofar as they may preserve detail that would otherwise have been lost. (Note that many of these codecs are proprietary, however, so I can’t say with certainty that something else is not going on in there that might tilt things more towards one part of the image or another.)
[Peter DeCrescenzo] “Does progressive shooting compress in-camera better than interlaced?”
Yes, which is why many interlaced formats are more sub-sampled than their progressive counterparts (DVCPROHD in 1080i/60 by 33% versus 25% in 720P/60). Since a whole frame is compressed as a unit, interlacing serves to increase the frame complexity which decreases the efficiency of the codec.
[Peter DeCrescenzo] “What about color? Does DCT compression “prefer” certain colors? (Can it compress certain colors more easily than others?) Are a camera’s color matrix control useful in this regard?”
No.
[Peter DeCrescenzo] “What other features in modern camcorders help get the most out of DCT?”
Nothing I can think of that wouldn’t also effect the image quality. e.g. Smear the front of your lens with Vaseline and you’ll have far fewer compression artifacts, but you may not like the resulting picture too much!
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Jesse Rosen
Director of Technical Development
Abel Cine Tech, Inc. -
I’ve been thinking about this a lot recently. I think that what really makes sense is some form of tape backup. For instance you can get an LTO-3 drive that will store 400GB per tape for about $5,000. The tapes are about $120, which will store over 20 hours of DVCPROHD at 24 fps. For comparison, a 1200a with the firewire board is about $25,000, and the tapes are about $30/32 minutes. The nice thing about this kind of archival is that you have the option of restoring your project to exactly the point you left off — the time lines, the graphics, etc. and you never have to recapture video (which may have come from various formats that you may not even have the VTRs for.) With decent backup software you can restore individual clips as well (assuming you’ve created intelligible meta-data).
That’s where my head’s at, anyway — and not just for P2 I might add.
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Jesse Rosen
Director of Technical Development
Abel Cine Tech, Inc. -
Indeed, it’s a Sony SRW-1 HDCAM-SR VTR.
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Jesse Rosen
Director of Technical Development
Abel Cine Tech, Inc. -
Yeah, unfortunately it’s normal. Kind of makes it a useless setting. 🙁
Actually, that deserves another 🙁
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Jesse Rosen
Director of Technical Development
Abel Cine Tech, Inc. -
No problem — good luck with your tests.
I live in Brooklyn, NY.
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Jesse Rosen
Director of Technical Development
Abel Cine Tech, Inc. -
I believe that that should work fine. Of course, there’s no way to test how FCP works with the HVX200 footage yet being as to the 200’s current state of nonexistence…
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Jesse Rosen
Director of Technical Development
Abel Cine Tech, Inc.