Hi

I have a background, which comprises yellow and black regions only, effectively creating a monochrome image. On top of this I want to superimpose a circular outline. I want the outline colour to be the inverse of the background - i.e. as the line crosses yellow background it should be black and vice versa.

I've fiddled around with negative versions of the background and circles, but can't seem to find the right combination of effects!

Thanks for any help anyone can give.

Nick

Mhmm... is the background a vector object?

If yes, then here's what i think might be a way to do it:
1. Select the circular outline and convert it to a shape (Path -> Stroke to Path or Ctrl + Alt + C)
2. Duplicate the circular outline (Edit -> Duplicate or Ctrl + D)
3. Try to select all the regions of one colour (either yellow or black), you can select multiple shapes by shift + clicking with the tool... I'm not exactly sure how easy this will be depending on your background and how it was created
4. While having all the regions of one colour selected, duplicate them (ctrl + D) and then either Combine (Path -> Combine or Ctrl + K) or Union (Path -> Union or Ctrl + +). I recommend Combining, but both should work.
5. Select the circular outline (either the original or the duplicate) and the coloured region (the one we just duplicated and combined/united)
Note: At this point, the coloured region that you duplicated should be above the circle covering it up, with the circle only showing in parts where the colour changes (i.e. if you selected and duplicated the yellow region, then the circle will only be showing over the region where the background is black)
6. With both objects select, you can either do a clip (object -> clip -> set) or an intersection (Path -> Intersection)
7. Now, you will have two circles. One is fragmented and only shows in one region, while the other is complete but is hidden behind the fragmented circle so that it only shows where the other circle doesn't. Dunno if I'm making much sense. Just select the circles and give 'em a colour. Here's a little example of what this does: http://www.petaimg.com/uploads/1224335704.svg

If the background is a bitmap, then you need to:
1. Select background image, and duplicate it
2. Select the duplicate and go to Effects -> Raster -> Negate
3. Select the circular outline, and turn it into a path (Path -> Stroke to Path)
4. Select both the outline and the nagtive background (make sure outline is above the background) and go to Object -> Clip -> Set

After you slice the circle outline into correct regions color them each with the same color that is beneath them and use Effects > Color > Negative.

I think someone made a filter or a plugin that turns color into its negative automatically, maybe someone else can remember where this can be found.

Hi

Thanks to both of you for your posts. I will try them out soonest! The background started out life as a bitmap, but I've converted it to vector, mainly so that I could use the smoothing functions.

Thanks again

Nick

PS Just tried it and it works! The results are fantastic!

prkos wrote:I think someone made a filter or a plugin that turns color into its negative automatically, maybe someone else can remember where this can be found.

I made a filter that will do that. It's pretty simple. You can download an example file here: http://openclipart.org/media/files/kelan/8769

awesome! thank you kelan