Signal to Noise
February 16, 2012 1 Comment
Today we looked at what image noise is, what creates it, and how to keep it at bay.
I started off by doing a test to see how my camera (Olympus PEN E-P1) copes with noise at various ISO settings.
Here are the results:
As you can see, the PEN really suffers from noise at high ISO’s the usable range is probably only up to about ISO1600. Anything beyond that is very noisy, suffering from luminance noise mostly, but also a bit of colour noise. Having used Olympus cameras in the past, in my opinion they always tend to create a more film-grainy kind of noise than cameras made by companies like Nikon or Canon this is probably due to the noise reduction software being less sophisticated and allowing more heavy granular noise to end up on the image. This can sometimes work in a black and white image if you want that vintage look.
I also wanted to look at how you can minimise noise when you have no choice but to use high ISO settings. I know that noise is a lot more apparent in the shadow areas of an image and that’s because there isn’t enough light to “drown out” the noise which is exacerbated by the use of high ISO settings.
I set about my test by capturing three images at ISO6400, which is the highest ISO setting the PEN can do (and VERY noisy). One exposed correctly according to the meter, one under exposed, and one over exposed.
If you look at the correct exposure you can see that there is a lot of noise at the ISO6400 setting and the image isn’t really usable without any serious noise reduction in post processing. Even then the image wouldn’t be right and would suffer from loss of detail.
This is the under exposed image once it’d been processed to look right from the raw file. As you can see, doing this has caused the image to be utterly horrendous and has rendered it completely useless unless you intend to produce some kind of artistic (horrible) “Lo-Fi” look.
This third and final image is the over exposed version. I used the raw file to bring the exposure down to look correct and low and behold, there is very little noise! This would be a perfectly usable image, the only negative thing I can say about it is that it needs a little extra work to properly correct it, as you can see the sky has quite a red tint to it for some reason.
In conclusion, when shooting in conditions which require high ISO settings, you’re much better off over exposing all of your images by a stop or two in camera using the shutter speed and aperture settings and then correcting them in Photoshop using the raw files later. Doing this means the camera picks up more light and “drowns out” much of the noise, and when you alter the exposure in Photoshop later you will more than likely end up with an image which looks as good as a correct exposure in-camera, without all of the noise.