Operation Photo Rescue's Online Community

OPR Workshop Information Exchange => Photoshop Discussion => Topic started by: Hannie on September 26, 2011, 05:41:59 AM

Title: To blur or not to blur....
Post by: Hannie on September 26, 2011, 05:41:59 AM
Hi Everyone,

I have been trying to find out more what the difference is between Lens blur and Gaussian blur. 
Read some stuff but still, in practice I don't see a difference between the 2. 
Does anyone know, or even better have a suggestion/example when to use one or the other?

I assume that if you want to add depth of field to a photo you can use Lens blur but I have used Gaussian blur as well with the same effect. 
Apparently there is a difference in the 2 filters as to how they work? 

Hannie


Title: Re: To blur or not to blur....
Post by: Tori803 on September 26, 2011, 09:40:36 AM
There's a Wikipedia article about it at http://en.wikipedia.org/wiki/Gaussian_blur (http://en.wikipedia.org/wiki/Gaussian_blur) which looks like it gets into the technical details pretty well. I just read up to where the equations start.

Tori
Title: Re: To blur or not to blur....
Post by: Jonas.Wendorf on September 26, 2011, 10:06:00 AM
Hi Hannie,

if you're not as interested in the technical differences as in the practical ones, the differences can be explained very easily.

1) Unlike Gaussian blur Lens blur can preserve edges. So if you're using a mask to create your blur from, Lens blur won't blur edges and give transition areas.
2) Unlike Gaussian blur Lens blur can be used with a so-called depth-mask, which is used to determine the radius of blur depending on the distance from the focal point. If you try this with Gaussian blur, you'll get the same radius of blur reduced in opacity over different areas (which looks quite bad).
3) Because of 2) Lens blur can by default not be used in combination with smart objects. Only if you enable all plugins for smart filters ("File"-"Scripting"-"Browse"-"PS_DIRECTORY\Scripting\Sample Scripts\JavaScript\EnableAllPluginsForSmartFilters.jsx") you can apply it as a smart filter. But be sure not to delete your depth mask!

I guess that's the most important parts.
Plus Lens blur has different forms of blur and allows you to add noise in the same step.
Title: Re: To blur or not to blur....
Post by: Mhayes on September 26, 2011, 11:33:13 AM
Hi Jonas,

I knew that there was a choice of different forms of blue on the Lens Blur, but you gave me a lot better understanding of what's under the hood with it.

Thanks!

Margie
Title: Re: To blur or not to blur....
Post by: schen on September 26, 2011, 08:38:13 PM
If you like a short version of a photographer's perspective,
Gaussian blur is to put a frosty glass over the picture.
Lens blur is an approximation of bokeh.
Title: Re: To blur or not to blur....
Post by: Hannie on September 27, 2011, 06:22:03 AM
Thanks everyone!

It is very clear to me now what the difference is, the comments were very helpful.
I even did a few experiments to see if I could tell the difference. 

One of the things I tried was depth of field, tree in focus but not the background.
From left to right: original, Gaussian blur, lens blur. (never mind the sloppy selection!)
Notice in the middle how the selected tree "bleeds" into the Gaussian blur.

Hannie

(http://i210.photobucket.com/albums/bb18/marijtje2/OPR/tree.jpg)
Title: Re: To blur or not to blur....
Post by: schen on September 27, 2011, 09:57:42 AM
Here are the samples of blurs.  The left two are lens blur and the right ones are Gaussian.

I set the lens to pentagon to simulate five blades of the iris.

(http://i195.photobucket.com/albums/z298/schen_album/blurs.jpg)
Title: Re: To blur or not to blur....
Post by: Theresa H on November 15, 2011, 11:03:47 PM
good definition article of the different blurs available in PShttp://help.adobe.com/en_US/Photoshop/11.0/WSfd1234e1c4b69f30ea53e41001031ab64-796ea.html (http://help.adobe.com/en_US/Photoshop/11.0/WSfd1234e1c4b69f30ea53e41001031ab64-796ea.html)