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My girlfriend is making an art project where she is having an image printed and cut out on a metal plate.

The firm responsible for doing this is demanding a .dwg file (and something called polyline; some sort of setting maybe?).

Neither of us have heard about this file format, and I find the information about it quite confusing. Most pages seem to link to some schetchy "FooToBarConverter" software, that I frankly don't trust.

Could someone please enlighten us on what we need to do, or point to some safe and preferably free software that could do this?

(An explanation of the dwg format and the polyline thing would also be much appreciated)

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up vote 4 down vote accepted

A .dwg file is a CAD (Computer Aided Design) file format used by AutoCAD.

It's a vector (line based) file format - which is where the "polyline" comes from - as opposed to a pixel file format. A polyline is simply a list of points (either 2D or 3D) which when displayed are joined by straight lines. See this Wikipedia article

I would assume that the tool the firm uses takes this format to set up the commands needed to move the cutter over the metal sheet to cut the design.

What is your girlfriend using to design the image?

She needs to use a program that uses vector (line based) format rather than a pixel (bitmap) format to store it's data. While you can get programs that take bitmaps and attempt to convert them to vectors (in the same way that optical character recognition software works) they aren't 100% accurate as the bitmap could be of anything. OCR works because the program "knows" that the image represents text so it can go looking for characters.

There are ways you can convert photos to vectors - you need to look at edge detection algorithms. These edges can then be converted to polylines. I don't know of any software that does this so would be probably finding the same links as you have.

One last question - is this a personal project or something from university/college? If it's the latter then the school should be able to help.

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It's an old photo. jpeg edited in Gimp – erikric Mar 13 '11 at 14:20
How do you cut a photo out of a piece of metal? – Majenko Mar 13 '11 at 14:33

Taking a photo and making it vector is tough, you will find the results of programs that do this automatically are usually unacceptible unless it's a very simple picture with only a few solid shapes (e.g. a wine bottle against a plain background is much easier than a human standing in front of a tree). It's best done by hand with someone with a talent for this sort of thing (you'll find such people at design firms, sign shops, etc).

If you can't find someone willing to do this, or the cost is too high... but you're good with photoshop or gimp, then you can prepare the photo in a way that makes it easier to vectorize, and then vectorize it yourself.

Your goal is to reduce the number of colors and shapes, and get rid of fine details and complex bits. It depends on the final output though, is this metal printing the sort of thing where the final result is everything is cut out of the metal? Does it permit different depths of cutting? If the machine can only cut one depth, then basically there can be no shading... just solid shapes or outlines. Everything is either cut or not cut. In that case, you would want to make the image just 2 colors, one for cut and one for not cut. Something like the photoshop command image --> adjust --> threshold will do this. You could also trace the image in illustrator if you're good with the pen tool.

If you can somehow do multiple depths or colors, you need to find out from the firm exactly how many are possible. Say it's possible to cut 4 different depths... in photoshop you might do something like this: image --> mode --> indexed color --> number of colors (4). Then in addition I'd do filters like dust & scratches or median to clear out tiny details like hair or leaves while leaving larger shapes intact (unless the firm says their machine can handle small details).

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There is an open-source project ( that can save the detected edges into the vector format SVG or PDF. But I do not know whether there is a utility to convert SVG or PDF into DWG.

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Use Illustrator ...

Import image into a new .ai document and then export as .dwg

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