Long exposure noise reduction

[gregcoad]

<p>I have searched the forums and read a number of posts on this topic, but I'm not convinced that a definitive answer to this question has been found. The question is:</p>

<p>"Can post-processing effectively deal with long exposure noise, or is it imperative to use the in-camera (dark frame) noise reduction?"</p>

<p>I understand how the in-camera function works and what it does and why it is needed, but my question is whether the same thing can be accomplished during the post-processing of the raw file or if PP noise reduction can even achieve a somewhat close result to what the in-camera function can. It would sure make shooting a little less painful if I could turn that function off and deal with the noise in PP. I've missed quite a few awesome lighting strikes while the dark frame was being recorded.</p>

[garydem]

<p>you should be using a dark frame and let the dslr do its subtracting in the camera. it is the best solution for what it does. there is no way in the world that you can duplicate the EXACT NOISE AND HEAT INTERFERANCE/NOISE THAT YOUR CAMERA MAKES. that is whole point of dark frame-you let the camera make a frame but without any signal, anything that is recorded is what the camera's electronics and heat buldup is putting into the regular image but without the data. you know that the dark frame should be done IMMEDIATELY after the regular shot and for the same length of time.<br>

how can you duplicate the noise and heat noise from the camera in a computer exactly rpt EXACTLY, and in the exact spots or areas that the buildup occurs? you cannot. this is why doing digital starttrails is such a problem. you not only have to let the dslr stay open for the time required to make the startrail but right afterward you make the dark frame for the same length of time. unless you have an exterior power source it makes a real problem for the dslr's battery. it just will not run long enough. if you shoot a 1hr trail then you have a1hr dark frame, that is 2hrs worth of shutter open. and for all that you still only get 1/24 of a circle. that is not miuch. yrs ago with slide film i used to make 4 and 6hr startrails, that is 1/6 and 1/4 of a circle, much more impessive. and a lot less problems. just set up the camera and go do something else for the time, and no dark frame. if i had to make a startrail now i would go with film and scan in the slide/negative. i would not even attempt to do digital with all the headaches. if you wish to do a startrail digitally, see google for startrails.exe and registax. 2 different programs for 2 different purposes but they work, and for free. and take a look at the registax website some of the pics are amazing. the startrails web site also has the info on how to shoot the trail.</p>

 

[jonathan_lui]

<p>Actually you can turn it off, then shoot a dark-frame manually.<br>

Let's say for example that you want to shoot 10 shots at 1sec each: 2 seconds total for each shot is not so bad, so leave the Long Exp. NR on and let the camera take care of the work.<br>

If you need longer exposures though, let's say 10 shots at 1 minute each, and you're trying to do this quickly, you just shoot 1 dark frame before your series.<br>

Cover the lens, and shoot at the exact same exposure you'll be using. Then, shoot all the shots that you need, at the same exposure. Then when you get back to your computer, you subtract the hot-pixels manually, using this dark-frame with the rest of the shots. How you do this depends on the software you use.</p>

 

[bob_k5]

<p>Re: Jonathan Lui wrote: "How you do this (off camera NR) depends on the software you use." Can you tell me<br>

how in PhotoshopCS$, or where i can find literature on it?<br>

Thanks. Bob K.</p>