Let's suppose I'm on a tripod, photographing a perfectly still scene (also dark) and I take these photos:
- 5 photos at ISO 3200 and 1s exposure
- 1 photo at ISO 100 and 5s exposure
There is a common thing between the items, and it's the total time used.
The EV of the first item is much higher, right? Now suppose I average the 5 photos at ISO 3200 to reduce noise, producing a single image.
After that, I take the ISO 100 photo and I adjust levels (which would increase noise) to reach the same EV of the blended photo, in a way if I look these 2 photos from far away they'd look the same.
Would the noise level be equal, comparing the blended photo and the levels adjusted photo?
I hope you understand my point.
In response to drewbenn's commentary
Also, I don't think that blending the 5 photos will reduce noise the way you think it will
Blending photos reduce noise a lot, in fact here is an example:
I took 20 photos of a tree with: ISO 1600, F4.1 and 2s exp. The upper image is showing how much noise any of those images have. The lower is showing the result of averaging the 20 photos in one.
Sory for the bad focus.
As you can see, the noise gets almost completely deleted
For the ones who are asking, I used a very simply command of imagemagick to average the images:
convert [input1.JPG input2.JPG ...] -average output.JPG
If I have some time later, I'll try to conduct one of those experiments you're talking about. I guess there is no a static pattern and it'll vary on each camera.
I've also done a experiment a little more different:
This is the Scene:
And I've taken these set of photos (the aperture is always the same), I used manual mode.
- 01 @ ISO 100, 0.6s
- 02 @ ISO 200, 0.3s (averaged later)
- 04 @ ISO 400, 1/6s (averaged later)
- 08 @ ISO 800, 1/13s (averaged later)
- 16 @ ISO 1600, 1/25s (averaged later)
Each set has the exactly same EV, these are the results, in the same order:
It seems that a higher ISO, there is less noise but less details as well.