USM with radiuses smaller than 1 pixel

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lutz
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USM with radiuses smaller than 1 pixel

Post by lutz » Tue 25 Apr 2006 08:48

I have the impression that unsharpmasking does not work as it is supposed to for radiuses smaller than 1 pixel.
Sometimes PL32 seems to interpret a "0.5" even as a "5" . Am I doing something wrong? Do I have to use a period or a comma?

Martin Huber
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Re: USM with radiuses smaller than 1 pixel

Post by Martin Huber » Tue 25 Apr 2006 18:12

lutz wrote:I have the impression that unsharpmasking does not work as it is supposed to for radiuses smaller than 1 pixel.
Sometimes PL32 seems to interpret a "0.5" even as a "5" .
I couldn't reproduce this error. Further informations would be helpful.
lutz wrote:Am I doing something wrong? Do I have to use a period or a comma?
You can use both: a period or a comma. But in the current version the smallest possible filter radius is 1.0.
We will try to reduce the minimum filter radius to 0.6 in one of the next versions. Values smaller than 0.6 would have no effect, because with those values the filter would cover only a single pixel.

Martin

lutz
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Re: USM with radiuses smaller than 1 pixel

Post by lutz » Wed 26 Apr 2006 05:35

Hello Martin,

thanks for the reply. Maybe I got it wrong. I have tried it again at extreme settings and the result for 0.5 and 1 pixel radius seem indeed to be the same.
It would be great if you could get smaller radiuses than 1 going as announced.
Even radiuses smaller than 0.5 can produce very usable results. Please see the attached USM example with a radius of 0.4 . On the left the original, on the right the sharpened version.
Image

Martin Huber
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Re: USM with radiuses smaller than 1 pixel

Post by Martin Huber » Wed 26 Apr 2006 09:22

lutz wrote:Hello Martin,

thanks for the reply. Maybe I got it wrong. I have tried it again at extreme settings and the result for 0.5 and 1 pixel radius seem indeed to be the same.
It would be great if you could get smaller radiuses than 1 going as announced.
Even radiuses smaller than 0.5 can produce very usable results. Please see the attached USM example with a radius of 0.4 . On the left the original, on the right the sharpened version.
In PL32 radii smaller than or equal to 0.5 pixel can't produce any effect, because the resulting filter matrix will cover only one pixel and interpolating a single pixel always results in the given pixel.
If a software allows radii smaller than 0.5 pixel, it probably uses a different definition of radius. Perhaps the 0.5 pixel, that do not have a effect, are excluded from the radius. This way a radius of 0.5 pixel in that software would correspond to 1.0 pixel in PL32.

Martin

lutz
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Thanks!

Post by lutz » Wed 26 Apr 2006 10:51

Thanks!

all this math !!


:?

Peter Heckert
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Post by Peter Heckert » Thu 11 May 2006 22:28

Try this:

Custom filter (Userdefined filter) with this matrix:

0 -1 0
-1 5 -1
0 -1 0

You can weeken the effect, when you reduce Amount.

Peter

lutz
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custom filter settings

Post by lutz » Sat 13 May 2006 04:26

Hello Peter,

I am really not sure if I do see a sharpening effect using your settings or not? I have applied them to 3 by 3 matrix.
Do I have to set a divisor?


Yes, I guess. I just tried it (set divisor to 1). Now I do see the effect.
That seems very useful.

thanks a lot!




Peter Heckert wrote:Try this:

Custom filter (Userdefined filter) with this matrix:

0 -1 0
-1 5 -1
0 -1 0

You can weeken the effect, when you reduce Amount.

Peter

Peter Heckert
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Post by Peter Heckert » Tue 16 May 2006 17:56

Hello Lutz,

yes, I have also checked the "clip" box to avoid color artifacts.

This mask:

-1 -2 -1
-2 13 -2
-1 -2 -1

makes stronger sharpening, possibly too strong.
It can be used for problem images, but then a mask needs to be used, so that edges
only are sharpened but not the noise.

greetings,

Peter