Photo Editing: Blur instead of noise filter.
Posted by cascadehush on September 20, 2006
One of the odd things about my Canon PowerShot S3 IS is that whilst the noise level is lower than the previous model, it seems to be a type of noise that is not so easily filtered out. The S2 IS exibited a lot of colour noise at high ISOs, but this type of noise is actually easier to filter.
The main problem with the type of noise is that it interferes with the sharpening process. You can end up with artifacts where the sharpening algorithm tries to sharpen something which isn’t a feature of the shot but blob of noise.
To get around this I have been selectively applying sharpening only to the subject of the shot (where there is one central feature of interest). In order to do this I use the polygonal selection tool to mark out the main subject, and then only apply sharpening to that.
But here’s the trick.
Before sharpening, invert your selection and blur the rest of the shot using a gausian blur. This creates an illusion of depth of focus, which you can adjust, but more importantly, it also smoothes over any noise in the background of the image.
You can re-invert your selection and still apply selective sharpening, or else you can deselect and apply sharpening over the whole image, knowing that only the subject will have small detail which can be sharpened.
The bottom line: don’t filter out the noise, blur it out instead.
I use on Photoshop Elements 3 OSX, but the principles here should equally apply to other decent photo editing applications.
Any time you apply edits like this, you should be feathering your selections appropriately. This post is only meant to convey an idea to those who already have the relevant skills. It’s not meant to be a comprehensive tutorial.