On Wed, 2004-05-26 at 00:40, Steven M. Schultz wrote: > > From what I have read the human eye is able to determine > > black/gray/white much better than colors. You can fool the eye with only > > Right - which is why we see the blocks/splotches in dark scenes. The > slight variations in Y' become more visible as the overall brightness > become lower. That's the reason I think averaging/smoothing more > heavily at the lower Y' values will be effective.
Doesn't the ' in Y' indicate that the digital data has been gamma-corrected to compensate for the nonlinear CRT response? In that case the digital codes are approximately visually uniform. Out of curiosity, does the noise of the uncompressed recording look worse in black frames than regular ones, or is it only after mpeg compression that things look bad? If the latter, than perhaps you want to try to filter with the encoder in mind, possibly testing and conditionally filtering the video in 8x8 (or is it 16x16?) blocks. I don't really know enough about mpeg2 encoding internals to speculate much on that. > I got the idea of 'subtraction' from an advertisement for a digital > camera (forget which one). Basically to subtract/cancel the CCD noise > the camera took a picture with the "lens cap on" (i.e. black) and then > computed the differences between that black picture and a theoretical > black frame from the real picture it takes a split second later. 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 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 quickly over time it wouldn't lead to noisy backgrounds, just nonuniformly black backgrounds. 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
