Hi everyone. Long time user; first-time questioneer.

I was wondering if anyone knew of a way to create "Ishihara" style images -- essentially, filling a region with lots of small, non-overlapping objects. The canonical example is the Ishihara color-blindness test, which I assume most everyone has seen before. The pics at http://en.wikipedia.org/wiki/Color_perception_test are good examples.

It seems like something that you ought to be able to generate -- I've tried starting with a circle and then using Create Tiled Clones -- that works well enough to generate a mass of sample circle paths, with randomization changing the size and color (or just lightness). But it's evenly spacing them around that I can't figure out how to do. The "real" tests are generally circular, but regardless of the shape of the region, Align & Distribute don't really do it.... Neither does "Unclump" in the Tiled Clones panel....

Any thoughts?

Thanks,
DD

There is an online ishihara generator here. You can download the result as an svg file. I don't think you can set a "hidden" number though with this one. And the circles are all touching (you may want to add a white border in inkscape to cheat).

Another generator here - with numbers, but only generates a bitmap image (not svg).

Other than that, I guess you could try out generating clones with random sizes and random positions, very packed together, and then use Align & Distribute > Remove overlaps (with a small distance). It wouldn't be in a circle, and it wouldn't have number, so you would have to correct it by hand...

Yeah, I found the online generator already actually. Problem is that it doesn't actually work -- it lets the circles overlap, and the controls for changing the "brush" size don't actually do that. At least in any browser I've got. They stay on random mode, which creates circle way too big to use (like where 10 or so would fill up the whole field), so then you have to go back in with the "kill" button and kill about 75% of them. The hold-down-control-to-change-size feature just jumps immediately to "full size" as stays there permanently, which is essentially useless.

I guess I don't understand why A&D-> Remove overlaps doesn't do what I want -- remove the overlaps between the paths. It just removes the overlaps between the *bounding* boxes, which leaves tons of gap around every circle. Is there no way to fix that? Like set the bounding box to be the circle? Or some other way to "pack" a region?

I've just tested the online generator in firefox, and the size of the brush works for me.
- You need to make at least one circle first (then remove it with Shift-click)
- Then you need to hold down the Control key, and move the cursor either to the left (for smaller brush) or to the right (for larger brush).
Changing the brush size seems also to disable the "random size" (clicking R didn't work).

You may want to start with bigger circles, and end with smaller circles, as starting with smaller circles makes them all go to the edge of the perimeter.

Maybe the overlap occured because there where too many circles?



See image (screenshot) and attached file (svg) for what I made with the generator.

(I don't know about changing the behavior of Remove overlap.)