Custom Filter

E
Posted By
emencz
Jul 13, 2003
Views
481
Replies
7
Status
Closed
How do you use it?

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CW
Colin Walls
Jul 13, 2003
I believe its quite an obscure feature. You need to get a book like PS Bible to get any details.
P
Phosphor
Jul 13, 2003
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whozit
Jul 13, 2003
Actually, Colin, if you check out the Help files in PS regarding Filter/Other/Custom you will discover that Phos’ link explains the convolution properties discussed in the help files to a much better degree, and DOES fit what emencz is looking for, WITHOUT the extra expenditure for an additional book.
E
emencz
Jul 13, 2003
Thanks for the link, Phodphor. Sorry about the 3 times this past week thing.

And yes, I did mean filter>other>custom. Does anybody use it? I’ve seen some tuts regarding this feature, but all they do is tell me what values to enter.
P
Phosphor
Jul 14, 2003
No worries, E-Mendch! ;o)

I don’t know how to use it either, and quite frankly, I don’t care. I’m just happy that there are number-crunchers out there that are able to put a pretty face on image manipulating algorithms so I can look like a whiz, doing what I do.

Look around for Gernot Hoffman’s name. He’s pretty good at that stuff, and I’m sure he’d be happy to spell it all out for you.
CW
Colin Walls
Jul 14, 2003
I stand corrected.
GH
Gernot Hoffmann
Jul 14, 2003
Thanks for the compliment.
A filter works as follows:
The numbers in the box are weighting factors.
The center pixel is replaced by the weighted sum of all
pixels in the box (empty=zero weight)

E.g. a blurring filter, sort of primitive Gaussian:
1 2 1
2 7 2
1 2 1

The problem in PhS is the scaling – doesn´t work automatically: Scale by the sum of all factors: 7+4*2+4*1 =19
Offset 0

The most "stupid" blur filter is the box filter: 1 1 1
1 1 1
1 1 1
Scale=9

This is a highpass, the sum of all factors is 0. A bad highpass. -1 -1 -1
-1 +8 -1
-1 -1 -1

Scale=1 (not understandable), offset=128.

Sharpening filters are a little more complex.

A rather simple illustrated explanation is here.
<http://www.fho-emden.de/~hoffmann/gauss25092001.pdf>

Best regards –Gernot

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