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Old November 20th, 2007, 12:03 PM   #1
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Compression Question

Is there a specific amount of bits always allocated for a specific purpose, or does the compressor vary where it allots its bits?

For example,if I were to film in Black and White, would more bits be allocated toward motion? Likewise with Audio, if I were not to record Audio on camera would more bit be allocated towards color and motion?

These are just numbers, and minuscule numbers at that, they don't represent actual picture quality seen with one's own eyes. I was just wondering.
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Old November 23rd, 2007, 11:47 AM   #2
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Any Thoughts at all, Anyone?
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Old November 23rd, 2007, 02:01 PM   #3
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1- You can do a test. This is the best way to get answers since theory is often wrong.

2- If you were to shoot a black and white film, it can be advantageous to shoot in color since it gives you more options with color corrections.
e.g. in black and white photography, photographers will use color filters (in front of the lens) to darken skies and otherwise manipulate the image.

3-
Quote:
if I were to film in Black and White, would more bits be allocated toward motion?
When you say motion... that could mean a number of things.

In the MPEG-2 compression scheme, there is motion vector information. I don't think the amount of bitrate dedication to motion vectors will change if you were to film in black and white. (This is just my guess.)

However if you did film in black and white, there likely would be more bitrate available for other sorts of information (and that may or may not make "motion" look better).

Quote:
Likewise with Audio, if I were not to record Audio on camera would more bit be allocated towards color and motion?
Most formats store and handle audio separately from video. e.g. it might be a different track on the tape.

DV is always uncompressed audio.

4- Honestly just do a test!
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Old November 23rd, 2007, 03:04 PM   #4
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Hey Glenn,

Thanks for the reply.

If I were to shoot some test shots, I'm not sure what I would be looking for in those tests.

Yes, Audio is always stored separately so that obviously has no bearing on bit allocation in the picture.

"However if you did film in black and white, there likely would be more bitrate available for other sorts of information (and that may or may not make "motion" look better)." - That is what I'm wondering

If there are alway a certain amount of bits allocated toward chroma, or if there was no chroma to compress, would more bits then be allocated to luma (or motion for that matter)?
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Old November 23rd, 2007, 07:20 PM   #5
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It depends...

... also on the software used for compression. Not all software is intelligent enough to make the distinction. Clearly, color data takes away additional bits, so the theoretical answer is yes, you should have a sharper b/w image with more motion fluidity, but as Glenn put it very well, you have to do your own tests to find your own aswers tailored to your specific video.
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Old November 23rd, 2007, 10:48 PM   #6
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Quote:
If I were to shoot some test shots, I'm not sure what I would be looking for in those tests.
Uh... compression artifacts? :) Mosquito noise, blockiness, banding, noise, slightly horizontal edges breaking apart where the block edges are, etc.
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