High iso noise removal

[calypsob]

MY T3i gets insanely bad noise when I shoot at iso 12,800. Is there a ratio of dark frames I would need in order to remove iso 12,800 noise from my images? Or is this just to much noise?

[ohata0]

it's not so much the dark frames (although it helps a little), but the light frames you need to take. With ISO 12,800...probably a lot of light frames.

Deep Sky Stacker has an example here using 32 lights and 20 of everything else. The added darks, bias and flats didn't seem to affect the noise, but did bring out the details (it looked pretty washed out without it). They also explain the purpose of each (darks, bias, and flats) in the FAQ off the main site.

I'd say try 50 light frames and see how much better it looks. Maybe you can compare your images (at 100%) with the noise of the single light frame in the link. If your images at 12,800 look about the same, then maybe you can get away with 32 (if that's acceptable for you)

[hollis_f]

Your sensor will produce two types of noise - random and systematic. Systematic noise is when the same pixel will give a false signal (almost) every time. Random noise is when any pixel on the sensor can give a false signal. DSS uses dark frames to identify the systematic noise - and subtract that from the signals in all of your light frames.

But it needs to be able to distinguish between random and systematic noise. It does this by combining multiple dark frames. Systematic noise will be present in the same pixels, so combining them will boost the signal at those locations. With random noise only some of the dark frames will have a false signal, so combining them will result in those signals being 'diluted' with nice dark signals.

This results in a difference between the intensity of the systematic and random noise levels. Statistically, that difference should increase by the square root of the number of dark frames. So, shooting 9 dark frames will make the systematic noise 3 times 'brighter' than the random noise. Shooting 49 darks will make them 7 times brighter. The returns start diminishing fairly quickly.

All you need is enough darks for the software to easily identify the systematic noise. Any more is not going to give any better results.

Like ohata0 says - increasing the number of light frames will make more of a difference (although that to is subject to the square-root law of dimishing returns).

[calypsob]

!!! Guys you are awesome this is going to help tremendously! Thanks, the mathmatical factor is exactly what I was hoping for! One more question. I have been shooting raw but i notice that most stack programs don't like RAW files so should I just go back to shooting jpeg? Also for dark frames is it ok if I switch to the smallest size jpeg file option available on my camera or do I need to maintain the same file size as my original shots?

[DC Fan]

Originally Posted by calypsob

MY T3i gets insanely bad noise when I shoot at iso 12,800. Is there a ratio of dark frames I would need in order to remove iso 12,800 noise from my images? Or is this just to much noise?

You need noise reduction software to handle this task.

These images were shot at ISO 12,800 and then cleaned with Imagenomic Noiseware.







Along with Noiseware, there are several other programs that accomplish the same task. Some of them offer free trial versions.

[calypsob]

Yes I have attempted to manually remove the noise but stacking is my first priority as it seems to defeat the noise without softening the image. I have been trying to figure out how to properly stack for a while now and I think this thread may be the last bit of info I need hopefully to get good results. What camera did you use to take those basketball shots?

[hollis_f]

Originally Posted by calypsob

What camera did you use to take those basketball shots?

it really is fairly irrelevant. Shrinking an 18 megapixel image down to less than one megapixel is another good way of removing noise from any image.

[DC Fan]

Originally Posted by calypsob

Yes I have attempted to manually remove the noise but stacking is my first priority as it seems to defeat the noise without softening the image. I have been trying to figure out how to properly stack for a while now and I think this thread may be the last bit of info I need hopefully to get good results. What camera did you use to take those basketball shots?

The images came from a Canon 60D. The noise reduction program was the standalone version of Noiseware, which is easy to use and effective for a low price.

With so much unhappiness over image noise, it's good to have software solutions that ease the use of high ISO's with no extreme effort.

[John Sheehy]

Originally Posted by calypsob

MY T3i gets insanely bad noise when I shoot at iso 12,800. Is there a ratio of dark frames I would need in order to remove iso 12,800 noise from my images? Or is this just to much noise?

Unless you are doing long exposures, very little of the noise is going to be the same in every frame, so there really is nothing you can subtract.

Using something like Topaz Denoise 5 and nudging the "remove blur" control up a bit to get back edges without sharpening noise can help a bit.

Careful how you process the images - using a "Nearest Neighbor" type of pixel count reduction actually increases noise, as does unnecessary sharpening (get it as sharp as possible in-camera).

[smitroc]

Convert your RAWS to Tiffs I think is the answer to your other question... looking at the date on this thread you may have already found it... Hope it helps

[calypsob]

everything is good now, got an eq mount so no need to shoot 12,800 anymore