Curves in ImageMagick

Hello,

How to simulate Curves tool from GUI programs?

I suppose there is some smart meddling with fx option but I
would be
grateful for any hints.

Specifically I am interested in effects like described
here:

http://www.outbackphoto.com/workflow/wf_81/essay.html

TIA

m.
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ikolaj
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Mikolaj Machowski on  wrote...
| Hello,
| 
| How to simulate Curves tool from GUI programs?
| 
| I suppose there is some smart meddling with fx option but
I would be
| grateful for any hints.
| 
Yes and with the help of an external script (which uses
gnuplot
underneath),
    http://www.imagemagick.org/Usage/scripts/im_fx_curves
or a perl version (using Math::Polynomial library module)
    http://www.imagemagick.org/Usage/scripts/im_fx_curves.pl

it is very easy to convert a set of curve 'points' into a
mathematical
expression for the -fx function to use.

See  IM Examples, Color Modifications,
  Histogram 'Curves' Adjustments
    http:/
/www.imagemagick.org/Usage/color/#curves

A practical example is at
  IM Examples, Advanced, "Aqua" Effects
    http://www.imagemagick.org/Usage/advanced/#aqua_effects

For a speed up technue using a Color Lookup Table
   htt
p://www.imagemagick.org/Usage/color/#fx_to_lut


| Specifically I am interested in effects like described
here:
| 
| http://www.outbackphoto.com/workflow/wf_81/essay.html
| 

That is not a 'curve' but a linear change.  Though not a
typical one as
you are doing a contrast change rather than a color limit
change.

However given the two points the curves technique will still
give you
the linear equation for the adjustment.

At this time there is no IM contrast option with specific
arguments to
control the contrast adjustment.  There are some automatic
ones simular
to normalize, but no non-normalizing linear contrasting
functions.

The closest would be a curved contrast adjustment known as
-sigmodial-contrast.


  Anthony Thyssen ( System Programmer )    <A.Thyssengriffith.edu.au>
 -----------------------------------------------------------
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peoples needs.
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there is symmetry!
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Without End''
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Anthony Thyssen scripsit:
> Mikolaj Machowski on  wrote...
>| Hello,
>| 
>| How to simulate Curves tool from GUI programs?
>| 
>| I suppose there is some smart meddling with fx option
but I would be
>| grateful for any hints.
>| 
> Yes and with the help of an external script (which uses
gnuplot
> underneath),
>     http://www.imagemagick.org/Usage/scripts/im_fx_curves

Thanks but something doesn't work. I tried to use it as
explained to get
line going through 10,0 and 90,100 points but in with -d
option I get
line going through 0,50 and 50,100 with output:
1,000*u+0,000

>| Specifically I am interested in effects like described
here:
>| 
>| http://www.outbackphoto.com/workflow/wf_81/essay.html
>| 
>
> That is not a 'curve' but a linear change.  Though not
a typical one as
> you are doing a contrast change rather than a color
limit change.
>
> However given the two points the curves technique will
still give you
> the linear equation for the adjustment.
>
> At this time there is no IM contrast option with
specific arguments to
> control the contrast adjustment.  There are some
automatic ones simular
> to normalize, but no non-normalizing linear contrasting
functions.
>
> The closest would be a curved contrast adjustment known
as
> -sigmodial-contrast.

Somewhere is typo: in my docs distributed with IM 6.3.0-3 in
docs is
option called "sigmoidal-contrast". Also this
whole trick is to *avoid*
contrast change. As explained in tutorial operating on HSB
changes
contrast, but in L*a*b* it doesn't happen.

m.

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