On Tue, 2 Feb 2010 16:54:09 -0800 (PST)
Rich Evans <reva...@yahoo.com> wrote:

> I'm grateful for the replies I have received, but I was thinking that
> if there isn't a well-known tool or method already, that maybe
> someone could point me to a site that describes how custom filters
> can be made from scratch. I'm not afraid to learn what I need to to
> make the filter, ...I've just never done it before. *grin* I just
> need someone to point me to a decent tutorial (I can do c programming
> if that's what it is, but my working assumption is that, all things
> being equal,  it should be easier to make a filter for GIMP than it
> would be to write a c program from scratch).Would anyone consider
> this... easy?
> 
> continue thanks,
> -Rich
> 
> 
> 
> ----- Original Message ----
> From: Cédric Gémy <radar.ma...@free.fr>
> To: Gimp-user@lists.XCF.Berkeley.EDU
> Sent: Tue, February 2, 2010 5:58:51 PM
> Subject: Re: [Gimp-user] how to invert greyscale values only...
> 
> not completely satisfied with sven's method, working on some pictures
> but not any, depending on the shades.
> I used to do it in CMYK a long time ago with photoshop by just pushing
> the image to CMYK and inverting the K curve.
> I guess something might be done with decompose color filter or so. But
> the quicker/best average i've found is just adding a mask based on the
> layer (L from Lab or N form CMYK could be used too), and play with the
> curve to adapt to the shades+refine with brush on mask. It takes few
> seconds if the picture is not too complex. Then put a white layer
> below and it's quite done. 
> But i'm not completely satisfied with it.




If you look at http://www.gimp.org/tutorials/Color2BW/ I am pretty sure
all those techniques can be scripted with with either scheme or python.


Owen

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