Just down loaded Inkscape so I am starting from scratch.
I have a photograph, a JPEG, that I want to convert to halftone and extract the dot information - diameters and centre coordinates - so I would need to save as a EPS or DXF file.
Is this possible and if so how? A nudge in the right direction will suffice - I'll ask questions if I get stuck.
regards
patchw

Welcome to InkscapeForum!

I don't think Inkscape can do halftones. Although I could be wrong about that. Inkscape can save as DXF or EPS. As for extracting the dot info, the dots would have to be vector, first of all. I'm not very familiar with halftones, so I'm not sure if perhaps it's inherently a vector element, or not. If they're vector, and you can open the image in Inkscape, you could probably write some kind of script to get that info. Possibly the Find dialog could be used, but if not, it would need a script. If the halftone dots are not vector....well, it would be tricky at best.... Theoretically you can convert raster images to vector using Inkscape's Trace Bitmap, or other trace engines. But the kind of scale needed to get an accurate trace (and "accurate trace" is a little bit of a misnomer, since trace engines can only approximate)....anyway, the kind of scale needed to trace an image with halftone color, so that the individual dots are evident....could seriously challenge the memory of typical personal computers. Your diameter measurements will surely be.....tiny.....unless this image is something like a billboard.

Hopefully someone who's more familiar with halftones will be able to give you more helpful info

maybe try to follow this

create halftone

by tracing (bitmap to halfton to vector)
http://www.youtube.com/watch?v=QHaPLOyQbeo

by cloning (more vector oriented)
http://www.youtube.com/watch?v=aFCZhchGA4A

Hi.
For dot halftone see manual
http://theamateurdesigner.blogspot.com/2011/08/how-to-make-halftones-with-gimp-and.html

For line halftone see
http://maxim-s-barabash.github.com/ZebraTrace/