noise and average-stacking
noise and average-stacking
Submitted by Art_Wannabe on April 15, 2009 - 9:30am
I feel like I've had some success in reducing noise by average-stacking. I'm pretty happy, and want to share this and see if anyone else finds it useful or has any comments.
The idea of average-stacking is to take several identical shots and then average them into one. Noise being random, the tiny random color spots should be reduced in proportion to the number of pictures you are stacking. Just stacking 2 shots should cut your noise in half!
What this means to me: I've been trying to take shots where the tones go gradually from light to dark, so I inevitably had noisy darkish areas. Even at my lowest ISO, noise was showing up where there was less light. I had resigned myself to having noise in the darker areas. The only ways to reduce the noise seemed to be to
•add blur to the dark areas during editing,
•take brighter pictures that you then darken during editing, or to
•get a more expensive camera (ouch).
Selective blurring and taking brighter shots are useful techniques but they don't always work. I'm happy to have found another approach that won't cost me any money.
Other kinds of stacking, exposure "HDR" stacking and focus stacking, seem to increase noise. I'm happy to find something that can make these techniques work better.
Software: PS elements and photomatix (free version) can average-stack. Maybe other software too.
When it could help: tripod shots when the subject doesn't move.
Boringness alert! The following content may be interesting only to the author. Continue at your own risk!
Example: For the "oyster Mushroom (4)" shot, I took pictures at 7 different focal lengths (each had a different part in focus). For each of these 7 focal lengths, I took 3 different exposures (to have some choice of exposure later and to allow exposure-stacking if I wanted to). For each of these 21 focus and exposure combinations, I took two identical sets of pictures, totaling 42 pictures.
I decided that the medium exposures were adequate, so I discarded the brighter and darker shots. Now I was working with 2 identical shots at each of 7 focal lengths.
I average-stacked each identical pair using photomatix, creating 7 averaged shots (one at each focal length). The average-stacking process didn't take long (unlike focus stacking). I noticed that the process seemed to reduce the contrast. I'm not sure what to make of that. Anyway, the results were pleasing.
I then focus-stacked the 7 averaged shots using combineZM, which I've described elsewhere in this forum. I finally edited the shot in PS Elements.
By the way, I took the pictures with my Rebel xsi, a 100mm 2.8 macro lens, set at f/11.
Here's the result, so you can judge for yourself.