Problem with Gaussian Blur

[allanrube]

I have thought about writing about this problem I have with blur in PS but always seem to forget about it. No more. :)

When I create a new layer with a bird as my subject, I can do many things to the bg without affecting the bird - noise reduction, levels, curves… However, if I apply Gaussian blur to the bg it bleeds onto the bird.

In this example, I quickly selected the bird minus the legs, made a layer , and then used Gaussian blur on the bg. I exaggerated it to show the problem I am writing about.

How can I blur a bg without the filter affecting the foreground layer?

[Joel Eade]

Could be a couple of things... 1.what settings on the gaussian blur are you using? It might be too aggressive, try something more subtle.

2. You may have do to a better job with the selection, maybe look into how to use refine edge if you have CS5. This will help smooth and "feather" the selection to avoid the cookie cutter
effect.

[allanrube]

Thanks for the comment.
1. Why should a strong bur creep onto another layer? None of the other adjustments I make do this. I could darken a bg layer as dark as I could get it but the upper (bird) level is not affected.
2. Yes, I need to learn about feathering but still, even if i wanted a cookie cutter effect, I could not do it with blur.

[Roy Priest]

Put the bird and the BG on separate layers. Make sure the bg layer is below the bird layer.

[allanrube]

That is what I did Roy. When I apply blur to bg layer it "bleeds" to the top layer. Nothing like this happens when I apply other adjustments to the bg, just blur.

[Roy Priest]

Alan, if that's the case I recommend Joel's suggestion. Try to make a better selection by using a combo of quick selection tool and magic wand tool. HOw does your selection look when you zoom in on it?

[Thanaboon Jearkjirm]

I think in your case the background layer didn't bleed into the top layer.It may look like it but here is what I think happened, when you blurred the background layer you also blur the bird in the background layer as well. So when you put the selected bird layer on top of the blur background layer, the blurred bird (which now has bigger area to due to blur effect) in the background layer looks like it spill over the top layer.You can test this out by clone out the bird in the background layer first, then blur and then put the selected bird layer on top of it.

[WIlliam Maroldo]

Thanaboom is correct, and the blurrd subject will "bleed" into the background. You could simply clone out the subject on the bottom layer, by using other areas of the background as a clone source; no subject, no bleed. However, I find the best technique is using very agressive NR on the background, which essentially removes detail and does not cause the gaussian bleeding problem at all. regards~Bill

[Thanaboon Jearkjirm]

The NR technique sound very interesting, definitely going to give that a try.

[pat lillich]

oh yeah - the NR technique sounds really interesting. will grab a picture and see what happens. Allan, thank you for posting this question!

[Michael Gerald-Yamasaki]

Allan,

Greetings. I took a close look (pixel level) at your image. There is a sharp line between focused and blurred areas. I think as Thanaboon suggested the bg has blurred outward from the mask edge.

Bill has great suggestions. The NR more or less removes micro contrast so won't bleed, while gaussian more or less averages within the radius so large radius will lead to bleading.

Cheers,

-Michael-

[allanrube]

Thanks for the help. I tried clone and blur. I tried extreme nr. While there are different looks they both work as I had hoped. No bleeding.

[Doug Brown]

Have a look at this thread for my workflow on Gaussian blurs. It may help.

[Kerry Perkins]

Allan, it requires three layers to do this properly. It is not enough to have the background layer and the bird on a layer above it. You need to have a third layer that is bg only, and you apply your blur, NR, or any other effect to that layer, not the bg. Here is a step-by-step:

1. Use whatever method you prefer to select your subject and anything else you want to protect from the blurring or NR. Use refine edge or not, try it different ways...
2. Use CMD-J (CTRL-J on PC) to copy the selection to a new layer. (I will use the Mac keys for the rest of the steps.)
3. Select the background layer in the layers palette.
4. CMD-click on the thumbnail of the layer that has only the bird - this will load the selection and give you the marching ants again.
5. Select inverse by using SHIFT-CMD-I. You will now have the bg only selected.
6. Make a new layer from the selection by using CMD-J.

You will now have three layers and effects that you apply to the "bg only" layer will not bleed into the bird as long as the "bird only" layer is on top. You need to keep the original background layer visible, as this will fill in the edges that may have been trimmed in the selection and copying processes.

Thanks Doug for posting your workflow! That is the way to do it.

[allanrube]

Thanks Kerry. I used your method last nght and it worked like a charm.