Ken --- close. but no cigar... the steps: 1) Colors -> Desaturate; 2) Colors -> Invert leaves me with a greyscale image... all color is gone :-( I'm looking for a filter that will invert only black, white and grey pixels... leaving color saturated pixels alone.
Owen --- I will investigate the python solution. thanks for the advice. All --- Maybe the best question to ask is this... where online should I go to learn about how GIMP filters are developed? I suppose once I learn how to make on filter.. I suspect I will quickly conjure up other filter ideas as well... For completeness, my original question is this: I have an RGB image that is basically a black background with many colorful objects and white text. --- I'd like to invert the image so that it is a white background with black text but a simple invert inverts the colors in all the colored objects as well. Is there a technique or tool to invert any part of the image that is only a shade of grey? i.e. invert pixeils with a saturation of ~0 (if that is how you say it). I could imagine a filter that does a simple RGB invert for any pixel whose calculated RGB saturation value is below a set threshold. Does this type of tool/script exist? continued thanks, -rich ----- Original Message ---- From: Ken Warner <kwarner...@verizon.net> To: Rich Evans <reva...@yahoo.com> Cc: Gimp-user@lists.XCF.Berkeley.EDU Sent: Tue, February 2, 2010 8:12:09 PM Subject: Re: [Gimp-user] how to invert greyscale values only... Colors -> Desaturate; Colors -> Invert No? Rich Evans 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. > > _______________________________________________ > Gimp-user mailing list > Gimp-user@lists.XCF.Berkeley.EDU > https://lists.XCF.Berkeley.EDU/mailman/listinfo/gimp-user > > > > _______________________________________________ > Gimp-user mailing list > Gimp-user@lists.XCF.Berkeley.EDU > https://lists.XCF.Berkeley.EDU/mailman/listinfo/gimp-user > _______________________________________________ Gimp-user mailing list Gimp-user@lists.XCF.Berkeley.EDU https://lists.XCF.Berkeley.EDU/mailman/listinfo/gimp-user