Unsharp Mask in Digikam

[TransFXB]

Hello,

I am continuing my review of Digikam for my next article on [fr] http://www.questionsphoto.com
Deeper I go, more I realize that Digikam is the most advanced picture manager in Linux world, by far.

Beside my early comment on thumbnail display process (a bit long to built...), I have a question regading Unsharp Mark function:

Lower limit of radius range setting is 1 pixel, which is a bit unusual.
1 pixel radius is convenient for pictures within 7 to 10Mpix and more but is to high for lower resolution pictures, resulting in some oversharpening even is "gain" is set to a low value.
One should be able to go down to 0.1 pixel radius instead of 1 as the lower limit.

Is it possible, please, to start at 0.1 instead of 1?

Thanks in advance.

Dnia Thursday 03 of April 2008, TransFXB napisał:

> Hello,
>
> I am continuing my review of Digikam for my next article on [fr]
> http://www.questionsphoto.com
> Deeper I go, more I realize that Digikam is the most advanced picture
> manager in Linux world, by far.
>
> Beside my early comment on thumbnail display process (a bit long to
> built...), I have a question regading Unsharp Mark function:
>
> Lower limit of radius range setting is 1 pixel, which is a bit unusual.
> 1 pixel radius is convenient for pictures within 7 to 10Mpix and more
> but is to high for lower resolution pictures, resulting in some
> oversharpening even is "gain" is set to a low value.
> One should be able to go down to 0.1 pixel radius instead of 1 as the
> lower limit.

Joke with subpixel radius in USM is that is only a tricky way to
calculate standard deviation of the Gaussian as far as I understand GIMP
code. So there are two ways to fulfill this comment: add subpixel radius
(like GIMP) or add explicit control of standard deviation (like
ImageMagick, which has both ways BTW).

m.

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[Gilles Caulier-4]

2008/4/3, Mikolaj Machowski <[hidden email]>:

> Dnia Thursday 03 of April 2008, TransFXB napisał:
>
> > Hello,
>  >
>  > I am continuing my review of Digikam for my next article on [fr]
>  > http://www.questionsphoto.com
>  > Deeper I go, more I realize that Digikam is the most advanced picture
>  > manager in Linux world, by far.
>  >
>  > Beside my early comment on thumbnail display process (a bit long to
>  > built...), I have a question regading Unsharp Mark function:
>  >
>  > Lower limit of radius range setting is 1 pixel, which is a bit unusual.
>  > 1 pixel radius is convenient for pictures within 7 to 10Mpix and more
>  > but is to high for lower resolution pictures, resulting in some
>  > oversharpening even is "gain" is set to a low value.
>  > One should be able to go down to 0.1 pixel radius instead of 1 as the
>  > lower limit.
>
>
> Joke with subpixel radius in USM is that is only a tricky way to
>  calculate standard deviation of the Gaussian as far as I understand GIMP
>  code. So there are two ways to fulfill this comment: add subpixel radius
>  (like GIMP) or add explicit control of standard deviation (like
>  ImageMagick, which has both ways BTW).
>

Mik,

unsharpmask code is no inpired from ImageMagick, not Gimp. I have
changed that for 0.9.0 to support 16 bits color depth. Gimp code is
too complex to support 16 bits color depth. ImageMagick is more clean
to understand, but parameter is not the same.

Gilles
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[TransFXB]

Thanks Mik and Gilles for your answers.

You know, for a end-user like me, not a developer but a photographer, I think I understand the technical background but still wondering how I can have a 0.1 radius for USM in Digikam.
Is there something that I am missing?