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

>I've taken a look and unfortunately there's no way I can use it. I need the
>program to run under Win32 with as few dependencies as possible, and I cannot
>translate a 100's lines long Bash program and one that makes many calls to
>"convert" to something more Windows friendly. I'd rather use gimp-console
>instead if that's all I can.
>
>>  In IM, you can control the brightness using the -modulate function
>>  (as well as saturation and hue) and IM also has a -contrast function.
>>  (My script however, does not use either, but goes at it a more direct
>>  way by building a lookup table to adjust brightness and contrast)
>>
>>  see http://www.imagemagick.org/script/command-line-options.php
>>
>
>I find the relevant documentation confusing.
>
>I'd like a more specific answer please.



If you can, you can use my scripts under cygwin on Windows or under 
PHP exec. Otherwise, I am sorry I cannot help (other than to suggest 
you recommend to the IM folk to convert my script to am IM function).

-modulate B,S,H or -modulate L,S,H

allows you to adjust the Brightness/Lightness, Saturation and Hue 
(HSB or HSL colorspaces). 100 means no change. Increase or decrease 
it for brighter or darker.

see http://www.imagemagick.org/Usage/color/#color_mods


-contrast increase contrast some amount (unknown) and +contrast 
decrease the contrast (again unknown). That is all there is about it.

But you can use -level and +level to adjust contrast, via a linear 
transformation. See http://www.imagemagick.org/Usage/color/#level and 
http://www.imagemagick.org/Usage/color/#level_plus


or you can use -function polynomial "a,b" to create a linear 
transformation with a as slope and b as intercept. slope is like 
contrast and intercept is like brightness. see 
http://www.imagemagick.org/Usage/transform/#function_polynomial

you can also use -evaluate add  and also -evaluate multiply to do 
similar, but -function polynomial is better as it does it in one step 
and so avoids clipping between operations. see 
http://www.imagemagick.org/Usage/transform/#evaluate

My bcimage script is similar to creating the linear transformation 
and then converting it to a lookup table so it can be used 
efficiently by -clut.

But it is possible to do the calculations I have to set up the a and 
b coefficients and then just use -function polynomial.


Fred