On Wed, 2004-05-26 at 12:18, Steven M. Schultz wrote: > On Wed, 26 May 2004, Dan Scholnik wrote: > > > Doesn't the ' in Y' indicate that the digital data has been > > gamma-corrected to compensate for the nonlinear CRT response? In that > > I'd guess so - what does one get (Y or Y') when running a S-Video > cable from a VCR to a Canopus box and then via IEEE1394 into a > system?
Y', I would think. I'm not sure we ever really have Y unless we CCD'd the video ourselves: Y is what you would get by transforming RGB directly from a camera CCD (which is linear), but presumably digital cameras have already applied gamma correction before they give you the digital data. Certainly still digital cameras apply gamma correction to all but their raw formats. > > Temporally stationary CCD noise, AKA dark noise, can be subtracted out > > of long exposures (usually greater than 1 second) to improve low-light > > SNR. At shorter exposures, such as 1/30 or 1/60 of a second, > > time-varying noise usually dominates and dark frame subtraction would > > The camera (which was a still camera, not movie/camcorder) claimed > it did it for the shorter exposures - but perhaps it was just > advertizing hype. Let me qualify my answer: if you have a true dark frame image for a given shutter time with no noise other than the temporally stationary dark noise, then you can of course subtract out the dark noise. But for CCD's that I'm aware of, there isn't anything significant to subtract for short exposures, unless the CCD gain is really cranked up. My Olympus 5060wz, for example, won't apply noise reduction for less than 1s. > > only make things worse. At best you could subtract out the mean if > > "black" has a constant bias. Besides, since dark noise doesn't change > > That's what some captures appear to have - the black levels are 4 to > 6 units high from the looks of it. Perhaps I'll add an option to > specify an offset to be uniformily subtracted from the luma value. I do this routinely with yuvcorrect, as black is never "black" (and also I think my japanese-made camera doesn't remove the US NTSC setup on capture). I usually run some of the video through "yuvcorrect -M STAT" to get a histogram, and then set "black" to the mean of a black frame. I also reset the white level a lot, although mostly I only have to do that for my own videos. It would be nice to automate the process. Dan Scholnik ------------------------------------------------------- This SF.Net email is sponsored by: Oracle 10g Get certified on the hottest thing ever to hit the market... Oracle 10g. Take an Oracle 10g class now, and we'll give you the exam FREE. http://ads.osdn.com/?ad_id=3149&alloc_id=8166&op=click _______________________________________________ Mjpeg-users mailing list [EMAIL PROTECTED] https://lists.sourceforge.net/lists/listinfo/mjpeg-users
