Re: ImageMagick's convert's equivalent to (gimp-brightness-contrast)

On Wednesday 06 Jan 2010 04:34:03 Fred Weinhaus wrote:
> Here is a short set of IM commands to do the equivalent to my script
> without all the argument prompting and trapping and documentation.
> This is the guts of the script except here I use -function polynomial
> rather than computing a lookup table as in my script.
> 

Thanks, I've taken a look and it looks fine.

> You can do the computations for the slope and intcp arguments that
> lead up to the convert $infile -function polynomial "$slope,$intcp"
> $outfile any way you can within your Window Batch script. I used some
> unix variables created by using IM -fx calculations. But in my
> original script I used unix bc to do the calcs. Presumably you have
> some way to do those computations to set up slope and intcp arguments.

Yes.

> 
> You can get help from other Window users, such as Bonzo or el_supremo
> on the Discourse forum at
> http://www.imagemagick.org/discourse-server/viewforum.php?f=1 if you
> need help. They are two Windows users that I know about.
> Unfortunately I don't use or know much about Windows scripting as I
> use a Mac.

Well, I'm using Mandriva Linux Cooker, but I have to prepare this script for 
Windows. But I can take it from here. Maybe I'll use something like Lua or GNU 
Awk for that.

> 
> 
> infile="zelda3.png"
> bri=20
> con=20
> inname=`convert $infile -format "%t" info:`
> outfile1=${inname}_b${bri}_c${con}_A.png
> diffc=`convert xc: -format "%[fx:100-$con]" info:`
> con=`convert xc: -format "%[fx:$diffc<=0.1?99.0:$con]" info:`
> arg=`convert xc: -format "%[fx:pi*((($con*$con)/20000) +
> (3*$con/200))/4]" info:`
> slope=`convert xc: -format "%[fx:1+atan($arg)]" info:`
> slope=`convert xc: -format "%[fx:$slope<0?0:$slope]" info:`
> echo "diffc=$diffc; con=$con; arg=$arg; slope=$slope;"
> pivot=`convert xc: -format "%[fx:(100-$bri)/200]" info:`
> intcpbri=`convert xc: -format "%[fx:$bri/100]" info:`
> intcpcon=`convert xc: -format "%[fx:$pivot*(1-$slope)]" info:`
> intcp=`convert xc: -format "%[fx:$intcpbri+$intcpcon]" info:`
> echo "pivot=$pivot; intcpbri=$intcpbri; intcpcon=$intcpcon; intcp=$intcp;"
> convert $infile -function polynomial "$slope,$intcp" $outfile1
> 
> 
> See the notes in my script for a discussion of the formulae that I
> used for these calculations and the graphs on my web page at
> http://www.fmwconcepts.com/imagemagick/bcimage/index.php

OK.

Regards,

	Shlomi Fish

> 
> 
> Regards,
> 
> Fred
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> Magick-users mailing list
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> http://studio.imagemagick.org/mailman/listinfo/magick-users
> 

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