Noise reduction; where does it fit in the workflow?

[peterst6906]

Lani,

There are a few different workflows around, however the general consensus among the recognised workflow experts (Jeff Schewe, Andrew Rodney, Bert Monroy, Eddie Tapp, etc.) is that noise reduction should be done before any sharpening.

Whether or not you complete your tonal adjustments first or second, is a bit more individual, however one commonly used workflow if you have to use dedicated noise reduction software is:

1. RAW conversion (with no noise reduction or sharpening if you are going to use 3rd party software)
2. global tone adjustments (white point, black point, curves, color cast removal)
3. noise reduction
4. capture sharpening (if you use a multi-pass sharpening workflow)
5. local tone adjustments, cloning, compositing, etc.
6. output sharpening
7. printing

Noise reduction and sharpening are very closely related subjects in that sharpening aims to increase contrast along edges, whereas noise reduction aims to reduce contrast in non-edge areas. Noise reduction effectively involves blurring parts of the image and if it has to be applied too strong, fine detail can be blurred away.

If you apply sharpening before noise reduction, you run the risk of sharpening the noise and making the image look much noisier. Then when you apply noise reduction, you have to apply stronger settings to overcome the increased appearance of the noise. This then reverses the effect of the sharpening and also leads to more detail loss.

By conducting noise reduction first, you can reduce the contrast in the large surface areas of the image and make the noise almost invisible to subsequent sharpening. This also allows you to apply less noise reduction and maintain more detail in the image (especially images with a lot of fine detail) and still gives you a good base for subsequent sharpening.

In general though, it's better to apply noise reduction at the RAW conversion stage if you shoot in RAW and then avoid using 3rd party software if possible. This is because all the settings you make in the RAW converter are applied in an ordered sequence designed to produce the best result. Some adjustments are made on the linear RAW data and some on the gamma corrected image data, but in either case, the noise reduction will be applied at the best point in the workflow and you can avoid using 3rd party applications.

In my own workflow with my D200, I use the RAW converter (Lightroom and/or ACR) noise reduction algorithms for anything below ISO800. At ISO 800 and above, I generally then switch over to using 3rd party software.

Hope that helps.

Regards,

Peter