Photoshop smart blur

Could anyone tell me how the photoshop "smart blur" filter was implemented? What is the math behind it?

Thanks,

qq

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.

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.

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

Johan W. Elzenga wrote:

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.

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
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/

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.

"Kenneth Sloan" wrote in message
....

And the name "Gaussian Blur" suggests what the formula is.

LOL.
--
Mike Russell
www.curvemeister.com/forum/

On Tue, 02 Jan 2007 10:06:57 -0600, Kenneth Sloan
wrote:

Johan W. Elzenga wrote:

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.

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.

Indeed it does. http://en.wikipedia.org/wiki/Gaussian_blur

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.

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

Have a look at http://www.jhlabs.com/ip/filters/index.html and http://www.jhlabs.com/ip/blurring.html for the best explantion I have found

Davo

wrote in message

Could anyone tell me how the photoshop "smart blur" filter was implemented? What is the math behind it?

Thanks,

qq