Uneven noise reduction

[strongmanmike]

Recently I made some comments regarding how layer masking and selective noise reduction can impart a somewhat obvious processed look to an image, well todays APOD is a classic example of this IMO. While this is a wonderful galaxy and indeed overall a great image showing lots of interesting bits, the uneven application of the noise reduction and sharpening is obvious to me..?

http://antwrp.gsfc.nasa.gov/apod/image/0808/NGC6946_2008wendel.jpg

See how the centre is obviously sharper than the perifery, and the outer arms and sky have been overly smoothed in comparison? It looks like we are looking through a slightly steamed up window that has been cleared only in the middle.

Again I am not bagging the image as a whole (it is a great image allround) just some harmless observations regarding one aspect.

Mike

[jase]

Your observation is not necessarily related to noise reduction Mike. It could simply be the transition between sharpening masks or similar. Some noise is good. If you can smooth an image so there is not perceivable loss of detail, then IMO you're hitting close to the mark. The main goal is to hit the background noise as the foreground noise is resolved with mega data. If you don't have that luxury of mega data then some subtle noise control on the foreground can work wonders. It is a fine line and ultimately the imager needs to be pleased with the level of noise reduction - no one else. As I've said before, it doesn't matter if you've got 30 hours of data, you still need noise control in your processing routine as its introduced when performing certain processing tasks.

[strongmanmike]

Yes, that's what I said..?

"... layer masking and selective noise reduction can impart a somewhat obvious processed look to an image"

Your Helix is very smooth :D...but it looks good :thumbsup:

Mike

[jase]

The thing with layer masks is to blur them. This provides a improved transition between the sharpening or noise reduced regions depending on what the goal of the mask is. What may people forget is that a mask is simply another image. You can highlight the mask (Alt + left mouse button) to activate it. Then you can perform processing functions on the mask itself - this provides remarkable flexibility. Technically you could sharpen a sharpen layer mask if you wanted too. What is important is to understand the effect its having on the data. You can also drop the opacity of a mask so the effect is more subtle. Endless possibilities.