On Fri, Apr 07, 2006 at 10:03:44AM +0200, Stefan M. Fendt wrote: > Hi Nicolas, > > Nicolas schrieb: > > > I don't apply any filter. I spent 2 evenings trying to find good > > > >settings to denoise the video without any success. Each time the result > >was blur. There was far less details on the pictures... > > > > > hmm,... > > you could (do you use the CVS version of the denoiser?) use -M 0,0,0 -m > 0,0,0 -t 8,16,16... > > Blurring only should be visable when using too high thresholds for the > spatial filters (-M and -m). When appropriatly set you shouldn't be able > to see any blurring even with these. The above example, however, turns > the spatial filters off, completely. The temporal filter, however, can > *not* reduce sharpness (it might, if using thresholds above 24 (which is > a really huge setting!) cause visable ghosts.) So, if you want to > denoise without loosing sharpness by all means use only -t... > > BTW: if it is any analoge video tape, you should use horizontal > lowpass-filtering, at least *once* in your chain. Here comes why (you > may not like to hear... Warning, long...): > > You say it's a recording of a HI8 tape. These have a bandlimit of 3Mhz > (luminance) applied before recording the video signal on tape. Sampling > theory says you'll be needing 6.000.000 samples/sec to get a fully > reconstructable digital recording of such a signal. Samples is pixels > for digital images. Asuming you're recording a PAL signal to such a > tape you have 25 frames (= 2 fields) per second. This makes > 6.000.000/25=240.000 pixels per frame. PAL has 625 scanlines per frame, > so you get 240.000/625=384 pixels/scanline. This is further reduced by > the horizontal blank-interval. For PAL it has a time-period of 4,7µs. > The complete scanline has a time-period of approximatly (I ignore vsync > here...) 64µs. So approximatly 7,3% of the complete scanline is lost for > image transmission. This makes 384*(1-0,073)=356 pixels of resolution. > Considering the active lines of a PAL-video (and I don't know a > digital-video-system which stores more than that) to be 576, you will > end up with an image of 356x576 active/usable pixels by maximum. For a > standard (that is luma correctly bandlimited to 5Mhz) PAL-signal you > will end up with an image of 593x576 pixels. Everything you record above > these limits is *noise*... That noise however may mask how bad the HI8 > recording really is... > > Furthermore the maximum vertical resolution of an interlaced image is > reduced by the Kell-factor to approximatly 2/3*nr_of_lines. This is > reflected in the method any good interlaced TV/video-camera will sample > the image off the CCD. Every halfway sane manufacturer will use > "double-scanline-readout" to > > 1. reduce noise (+3dB SNR) > 2. reduce inter-field-flicker > 3. reduce inter-field jumpyness of scanlines > 4. honour the Kell-factor as otherwise fine detail may not recorded > at all (if it has the correct, critical velocity) > > That is, given this is the CCD: > > 1. line > 2. line > 3. line > 4. line > 5. line > . > . > . > > For the first field (bottom field first) scanlines (2+3)/2 and (5+4)/2 > and so on are read out, for the second field it's (1+2)/2, (3+4)/2, ... > and so on... > Everyone clearly can see this will reduce resolution before recording > anything. To get that lovely crisp images we all like from (cheap) > video-cameras, boosting of mid to high frequencies is applied, which > makes the image even more worse...
Stefan, I thank you for all the information, but... how could I use an "horizontal lowpass-filter"? I read all the things you wrote, and even if that's probably right, I don't know how to test it. > >minutes long Hi8 cassette > > > >I fear that could reduce the video quality. > > > It's HI8... What quality? ;-) (Sorry, could not resist...) =) Nicolas. ------------------------------------------------------- This SF.Net email is sponsored by xPML, a groundbreaking scripting language that extends applications into web and mobile media. Attend the live webcast and join the prime developer group breaking into this new coding territory! http://sel.as-us.falkag.net/sel?cmd=lnk&kid0944&bid$1720&dat1642 _______________________________________________ Mjpeg-users mailing list Mjpeg-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/mjpeg-users
