| Author |
Photoshop smart blur
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| quickcur@yahoo.com 2007-01-10, 6:20 pm |
| Could anyone tell me how the photoshop "smart blur" filter was
implemented? What is the math behind it?
Thanks,
qq
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| photoshop isn't opensource so none knows how things work inside it, anyway
smartblur works like this:
to blur a pixel in regular blur you simply take the pixels surrounding it,
you sum their values then you divide by the number of pixels summed up.
To obtain the smart blur you use a threshold and sum only the pixels whose
difference with the value of the pixel you're blurring are < (or <=) the
given threshold, then you divide by the number of pixels summed.
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| Johan W. Elzenga 2007-01-10, 6:20 pm |
| 4N <xxxx@yyyy.zzz> wrote:
> photoshop isn't opensource so none knows how things work inside it, anyway
> smartblur works like this:
>
> to blur a pixel in regular blur you simply take the pixels surrounding it,
> you sum their values then you divide by the number of pixels summed up.
I don't think it's that simple. Take an empty white document, zoom in
1600% (maximum zoom) en place one black pixel in there with the pen
tool. Now use Gaussian Blur at 1 pixel. Your 'formula' suggests you
would get an even colored 3 x 3 pixel grey square, but in reality you
don't. You do get a 3 x 3 pixel quare, but with a dark grey centre
pixel, four side pixels that are lighter grey and four corner pixels
that are even lighter. That suggests a more complicated formula IMHO.
--
Johan W. Elzenga johan<<at>>johanfoto.nl
Editor / Photographer http://www.johanfoto.com
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| Kenneth Sloan 2007-01-10, 6:20 pm |
| Johan W. Elzenga wrote:
> 4N <xxxx@yyyy.zzz> wrote:
>
>
> I don't think it's that simple. Take an empty white document, zoom in
> 1600% (maximum zoom) en place one black pixel in there with the pen
> tool. Now use Gaussian Blur at 1 pixel. Your 'formula' suggests you
> would get an even colored 3 x 3 pixel grey square, but in reality you
> don't. You do get a 3 x 3 pixel quare, but with a dark grey centre
> pixel, four side pixels that are lighter grey and four corner pixels
> that are even lighter. That suggests a more complicated formula IMHO.
>
>
And the name "Gaussian Blur" suggests what the formula is.
--
Kenneth Sloan KennethRSloan@XXXXXXXXXX
Computer and Information Sciences +1-205-932-2213
University of Alabama at Birmingham FAX +1-205-934-5473
Birmingham, AL 35294-1170 http://www.cis.uab.edu/sloan/
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| quickcur@yahoo.com 2007-01-10, 6:20 pm |
| Thanks for the information. How about the "Edge Only" in that filter?
What does it do?
Thanks again.
qq
4N wrote:
> photoshop isn't opensource so none knows how things work inside it, anyway
> smartblur works like this:
>
> to blur a pixel in regular blur you simply take the pixels surrounding it,
> you sum their values then you divide by the number of pixels summed up.
> To obtain the smart blur you use a threshold and sum only the pixels whose
> difference with the value of the pixel you're blurring are < (or <=) the
> given threshold, then you divide by the number of pixels summed.
| |
| Mike Russell 2007-01-10, 6:20 pm |
| "Kenneth Sloan" <KennethRSloan@XXXXXXXXXX> wrote in message
news:endvv2$1fn$1@SonOfMaze.dpo.uab.edu...
....
> And the name "Gaussian Blur" suggests what the formula is.
LOL.
--
Mike Russell
www.curvemeister.com/forum/
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| Oliver Costich 2007-01-10, 6:20 pm |
| On Tue, 02 Jan 2007 10:06:57 -0600, Kenneth Sloan
<KennethRSloan@XXXXXXXXXX> wrote:
>Johan W. Elzenga wrote:
>
>And the name "Gaussian Blur" suggests what the formula is.
Indeed it does. http://en.wikipedia.org/wiki/Gaussian_blur
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|
| > I don't think it's that simple. Take an empty white document, zoom in
> 1600% (maximum zoom) en place one black pixel in there with the pen
> tool. Now use Gaussian Blur at 1 pixel. Your 'formula' suggests you
> would get an even colored 3 x 3 pixel grey square, but in reality you
> don't. You do get a 3 x 3 pixel quare, but with a dark grey centre
> pixel, four side pixels that are lighter grey and four corner pixels
> that are even lighter. That suggests a more complicated formula IMHO.
Gaussian blur multiply the surrounding pixels with weight that are smaller
and smaller as you go away from the center (current pixel). Those weight are
taken using a bell shape with the max in the center that's why the results
are different with regular blur.
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| > Thanks for the information. How about the "Edge Only" in that filter?
> What does it do?
if you want to show only the edges you can simply subtract to the current
pixel the value of the blurred pixel, or you can use operators like sobel
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