Gaussian blur/heavy blurring and banding issues

[Krijn Trimbos]

Dear all,

The last weeks I have been experimenting with more agressive ways to blur the BG of pictures where the BG is distracting (due to noise or contrast issues involving white and black spots in the BG) and doesn't add to the overall environmental feel of the photo. I tried using Gaussian blur/Lens blur/several runs of noise reduction and more than once this has resulted in mild to severe banding issues in the BG.

1. Does anybody know why this is a problem in some photo's while in others it is not?

2. Does anybody know how to solve this apart from not bluring the BG of course?

It is really frustrating because some photo's IMHO are ideal to be saved in this way.

I hope you can help!

Cheers,

Krijn

[arash_hazeghi]

Can you post an example?

[John Chardine]

I remember a thread about this a while ago but can't find the link. Essentially the gist is that if you apply heavy-handed blurring to reduce noise in an area of an image with little detail that you get banding. Apparently a certain amount of random noise is important to give you smooth total gradations, but I can't remember the physics behind it.

You can try it yourself- make an image with some noise in the sky for example, then run over the sky repeatedly with the blur brush in Ps set to 100%. You will begin to see banding.

[Fabs Forns]

And if you work in 8 bit, it may be worse.

[Roger Clark]

I remember a thread about this a while ago but can't find the link. Essentially the gist is that if you apply heavy-handed blurring to reduce noise in an area of an image with little detail that you get banding. Apparently a certain amount of random noise is important to give you smooth total gradations, but I can't remember the physics behind it.

You can try it yourself- make an image with some noise in the sky for example, then run over the sky repeatedly with the blur brush in Ps set to 100%. You will begin to see banding.

Hmmm... I can see how this could happen if your strokes were back and forth, but if you use more random motions it should not produce banding. Like try circular strokes. Or select a region then feather/refine edge and the run a blur filter and I have never seen it produce banding. Can someone post a before and after example?

Roger

[Fabs Forns]

John, is this the thread?

http://birdphotographers.net/forums/showthread.php?t=11776