Rich Evans wrote:
> 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
> 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
Meanwhile (and bearing in mind you haven't let us see the image in
question), would this work?:
Duplicate layer, invert bottom layer and cut all blacks and whites out
of (transparent) top layer (of course, if there's a range of greys it
gets more complicated).
> 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
> 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,
> ----- 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
> 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,
>> ----- 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.
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