On Tue, Nov 30, 2010 at 20:01, Abe Bachrach <[email protected]> wrote: > Sebastian, that sounds like something to try, but wouldn't that > significantly reduce the field of view?
Yes the field of view will be much smaller, you would have to select a wider angle lens to compensate. > Also, do you know if the WOI settings avoid the "horizontal blanking" issue > which is what would cause the binning/skipping solution to not provide that > great of an improvement? I don't see anything about how the windowing works > in the datasheet. Not sure, but in general the maximum possible fps is higher with reduced WOI compared to using binning to achieve the same resolution For example: 1280x720 (2x2 binning) JP4 RAW max. 46.2 fps 1280x720 (WOI setting) JP4 RAW max 60 fps Regards Sebastian > > thanks, > -=Abe > > On Mon, Nov 29, 2010 at 5:38 AM, Sebastian Pichelhofer > <[email protected]> wrote: >> >> On Mon, Nov 29, 2010 at 04:07, Abe Bachrach <[email protected]> wrote: >> > thanks for the quick response. >> > In talking with one of the other people in lab, we realized that most of >> > the >> > experience that we had working with cameras with rolling shutters was >> > with >> > cheap webcams. We hoped that the readout on the elphel sensor *might* be >> > fast enough that the rolling shutter effect would be insignificant. >> > Unfortunately it doesn't sound like that is the case. >> > - if the time gap is ~1/15 sec that means that if the camera is moving >> > at >> > 5m/s (~11mph) then camera would move 33cm during the readout period. 4X >> > binning would make it a bit better, however the sensor would move ~8cm, >> > which is still quite significant. >> >> You mentioned you need only a small fraction of the 5 megapixels >> resolution the sensor offers. If you reduce the WOI (Window of >> Interest) you can increase the framerate and therefore the readout >> time (more than with binning): >> >> For example at 640x480 you can reach a max. of 126fps which would >> reduce ERS artefacts to just a little more than 10% of the 33cm you >> mentioned at 1/15s. >> >> Regards Sebastian >> >> >> > For more info on the rolling shutter distortion that I'm referring to, >> > see: >> > http://en.wikipedia.org/wiki/Rolling_shutter >> > There are algorithms out there, that try to compensate for the rolling >> > shutter distortions: >> > http://mpac.ee.ntu.edu.tw/Exhibition/rolling-shutter.php >> > http://www.cvl.isy.liu.se/research/rs-dataset/0382.pdf >> > http://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=05459408 >> > However it is much better to avoid them altogether by using a sensor >> > with a >> > global shutter. This is the approach taken by most people in the >> > robotics >> > and machine vision communities. >> > As I said on the phone, I believe the Elphel platform would be VERY >> > attractive for many people in the machine vision/robotics community, >> > however >> > a global shutter is a must for any of the applications that involve fast >> > motion which many of them do. >> > thanks! >> > -=Abe >> > >> > On Sun, Nov 28, 2010 at 9:45 PM, Andrey Filippov <[email protected]> >> > wrote: >> >> >> >> On Sun, Nov 28, 2010 at 7:30 PM, Abe Bachrach <[email protected]> wrote: >> >>> >> >>> One other question for Andrey/someone else is: >> >>> - How much time elapses between when the first and last row are >> >>> read-out? >> >>> from looking at the datasheet, it says that the maximum datarate is >> >>> 96Mp/s, which would mean that for full resolution, the time gap would >> >>> be at >> >>> least 0.052488 seconds. >> >> >> >> Abe, >> >> >> >> It is somewhat longer than that because of the large "margins", the >> >> average data rate of the sensor running at 96MHz is ~75MPix/sec. There >> >> are >> >> formulae in the datasheet that allow to calculate line readout time >> >> for >> >> different ROI and decimation >> >>> >> >>> - is the sensor being run at the full 96MHz clock rate? Is that time >> >>> gap >> >>> number correct? >> >> >> >> 96MHz - yes, correct, but the "gap" is wrong - at full resolution >> >> readout >> >> time (and so the delay between the first and last line exposure) is >> >> ~1/15 >> >> sec >> >>> >> >>> also, >> >>> - How does the subsampling mode effect this. If we put the sensor in >> >>> binning/skipping mode, and downsample by 4x, ideally, this would mean >> >>> that >> >>> there it takes 0.0032 seconds to read out a frame. >> >> >> >> Yes, that is correct. Just keep in mind that there is a large "dead" >> >> time >> >> (horizontal blanking) added to each scan line, but small on top and >> >> bottom >> >> (vertical blanking) >> >> >> >> Andrey >> >> >> > >> > > > _______________________________________________ Support-list mailing list [email protected] http://support.elphel.com/mailman/listinfo/support-list_support.elphel.com
