Photoshop Blur function

SP
Posted By
Son_Preminger
Nov 20, 2006
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1572
Replies
17
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Closed
Hi,

Does anyone know how the Blur and Gaussian blur filters are implemented (I mean what is the mathematical calculation for each pixel). In particular what exactly is the radius in the Gaussian blur and how is it used in the calculation.
Or do you know where can I find this information?

Many thanks,
Son
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blur function

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SP
Son_Preminger
Nov 20, 2006
Hi,

Does anyone know how the Blur and Gaussian blur filters are implemented (I mean what is the mathematical calculation for each pixel). In particular what exactly is the radius in the Gaussian blur and how is it used in the calculation.
Or do you know where can I find this information?

Many thanks,
Son
CC
Chris_Cox
Nov 20, 2006
The "radius" in Gaussian blur is equal to the sigma of the gaussian kernel.

But the mathematical details are not documented, for obvious reasons.
SP
Son_Preminger
Nov 21, 2006
Dear Chris,

MAny thanks for your reply.
I need to know the exact calculation since I’m using the images in a scientific work… do you know who can I contact to find out the exact calculation? (I tried to reproduce the Baussian blur using the radius as the sigma and reached different results..)

Thanks again
Son
CC
Chris_Cox
Nov 21, 2006
Any basic book on image processing will give you the information you need.
I
ImageSkill
Nov 21, 2006
""" писал(а):
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Dear Chris,

MAny thanks for your reply.
I need to know the exact calculation since I’m using the images in a scientific work… do you know who can I contact to find out the exact calculation? (I tried to reproduce the Baussian blur using the radius as the sigma and reached different results..)

Thanks again
Son

Usually Radius is a Sigma*3
But I do not belive that Adobe implemented "true" Gaussian blur. If convolution kernel is critical for your applications (for example inverse problem solution etc)
I do not recommend use it.

Dmitry

———————————————————— ———– Software for digital image processing
http://www.imageskill.com
MD
Michael_D_Sullivan
Nov 21, 2006
<http://en.wikipedia.org/wiki/Gaussian_blur>
D
deebs
Nov 21, 2006
Hmmm! What is interesting on the Wiki page is that the link to cee.hw.ac.uk (Heriot Watt University) seems to be bounced to Edinburgh Uni. OT but interesting.
SP
Son_Preminger
Nov 23, 2006
Thanks Chris and Michael for your relpies. I was not asking how to calculate the Gaussian blur in general (this I know, and tried to implement myself and got results different from what I get with Photoshop). I was asking how to get information on how it is implemented in Photoshop. Anyone has an idea who I can contat to ask?

Thanks again,
Son
P
PECourtejoie
Nov 23, 2006
Look at your startup screen, then at the name of the posters in this thread…
CC
Chris_Cox
Nov 23, 2006
Well, you can submit your resume to Adobe, and try to join the Photoshop team….
MR
Mark_Reynolds
Nov 24, 2006
Ouch
S
Sepen
Nov 26, 2006
Son,

In case you aren’t getting the point Chris is trying to make here, you are asking for the recipe for Coca Cola. Nobody at Adobe is about to give up trade secret information which is what you are asking for – even if your purposes are purely benign and academic in nature.

You are out of luck.
D
deebs
Nov 26, 2006
Unless he has an acceptable (to Adobe) CV/resume, an aspiration for Adobe to appear on the wageslip and with suitably qualified trust and integrity?

Isn’t there a website somewhere that tried to compare the algorithms used in commercial image processing packages?

I seem to recall seeing it once or twice with suitable example images alongside.
GH
Gernot_Hoffmann
Nov 26, 2006
Son,

‘I tried to reproduce the Gaussian blur using the radius as the sigma and reached different results..’

The reason is, that the filter box can have any width
by pixels, 3,5,7,..
There is no unique assignment of the Gaussian bell to
the pixels.
Just a general rule: larger sigma – larger box.
The filter weight factors are anyway only samples of
the Gaussian bell.
We have always approximations. Nothing bad, but always
slightly different.

<http://www.fho-emden.de/~hoffmann/gauss25092001.pdf>

Best regards –Gernot Hoffmann
CC
Chris_Cox
Nov 27, 2006
Gernot – there is a unique assigment, because we do fractional sigma values and integer distances, and the radius in the UI is exactly equal to sigma for the gausssian distribution used to create the filter.
P
Phosphor
Nov 27, 2006
<SteveV>"I’m almost certain that means stuff"</SteveV>

😉 XD
CC
Chris_Cox
Nov 27, 2006
(and that was the simplified version)

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