"Jon Harris" <goldentully@hotmail.com> wrote in message news:2unfejF2d22i0U1@uni-berlin.de...> That's what my digital camera (and many others) do automatically. On the > Canon > G5, for any exposure longer than 1 second, it takes the picture normally, > and > then takes another identical exposure with the shutter closed and then > does some > filtering to remove the noise. I presume it could be as simple as just > subtracting the second from the first, but it might be something more > complex. >HI Harris, That' s interesting... I have not known that before... How about Nikon D100?
need advice on image filter?
Started by ●October 31, 2004
Reply by ●November 1, 20042004-11-01
Reply by ●November 1, 20042004-11-01
"lucy" <losemind@yahoo.com> wrote in message news:cm68sp$ooc$1@news.Stanford.EDU...> > "Jon Harris" <goldentully@hotmail.com> wrote in message > news:2unfejF2d22i0U1@uni-berlin.de... > > That's what my digital camera (and many others) do automatically. Onthe> > Canon > > G5, for any exposure longer than 1 second, it takes the picturenormally,> > and > > then takes another identical exposure with the shutter closed and then > > does some > > filtering to remove the noise. I presume it could be as simple as just > > subtracting the second from the first, but it might be something more > > complex. > > > > HI Harris, > > That' s interesting... I have not known that before... > > How about Nikon D100? >With the Nikon, you can select this feature via a menu item. Clay
Reply by ●November 2, 20042004-11-02
lucy wrote:>"Jerry Avins" <jya@ieee.org> wrote in message >news:2ulnp6F2d39jaU1@uni-berlin.de... > > >>lucy wrote: >> >> >>>Hi all, >>> >>>We used camera to do some imaging and got some raw image data, which are >>>very noisy at the low signal end(where there should be some low signal) >>>or >>>the dark end(where there should be no signal theoratically)... >>> >>>And there are some some spikes on both dark and bright regions. The >>>bright >>>parts of the image are also noisy... >>> >>>Please advise which type of filter can be best for denoising of such >>>images, >>>hopefully the useful image parts will not be affected or minorly >>>affected... >>> >>>Thanks a lot! >>> >>>-L >>> >>> >>Before you go on, take a few pictures of a featureless object, with the >>camera held stationary between exposures. Any noise correlation >>represents defects in the sensor array and van be subtracted out of the >>images you want to process. Dark noise and highlight noise might be >>different, but taking advantage of that might be hard. >> >>Jerry >>-- >>Engineering is the art of making what you want from things you can get. >>����������������������������������������������������������������������� >> >> > >Hi Jerry, > >That's a very good point. We have not thought about that... yeah, we should >take a picture of completely dark NULL object and then do a subtraction: > >picture with meaningful object images - picture with NULL object = >noise-reduced image... > >Then what do we do after that? Use what filter to reduce noise? > >Thanks a lot! > >L > > > >Lucy, Astronomers pioneered the use of these techniques and there is a lot of software around to take care of erors in the CCD black level, erors in pixel sensitivity, and pixels that are stuck high or stuck low. You could try a search using: "ccd astronomy" or "astronomical image processing" or similar and you should get a lot of material, or you could try the astronomy newsgroups. Regards, John
Reply by ●November 2, 20042004-11-02
On Sun, 31 Oct 2004 22:44:10 -0800, "lucy" <losemind@yahoo.com> wrote: (snipped)>> >> Before you go on, take a few pictures of a featureless object, with the >> camera held stationary between exposures. Any noise correlation >> represents defects in the sensor array and van be subtracted out of the >> images you want to process. Dark noise and highlight noise might be >> different, but taking advantage of that might be hard. >> >> Jerry >> -- >> Engineering is the art of making what you want from things you can get. >> ����������������������������������������������������������������������� > >Hi Jerry, > >That's a very good point. We have not thought about that... yeah, we should >take a picture of completely dark NULL object and then do a subtraction: > >picture with meaningful object images - picture with NULL object = >noise-reduced image... > >Then what do we do after that? Use what filter to reduce noise? >Perhaps a "median filter" would be helful. Searching the Internet for "median filter" will give you much information. Good Luck, [-Rick-]
Reply by ●November 2, 20042004-11-02
