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I import VECTORS in illustrator that i want to lasercut but they are measured in pixels. I want to output that to DXF. However i am wondering if pixels are converted to mm using a standard formula in Illustrator.

From what i am guessing however Illustrator is set to default DPI at 72 so the formula is standard (pixels*25.4)/dpi. Is this correct? Also is this the standard that Illustrator uses?

If i take this and reverse it i can see that illustrator multiplies the pixels by 2.8347. If i always scale the pixels using 283.47% will i always get the same result in mm? Is there anyway this can go wrong or is it hardwired and non-changeable in Illustrator?

Thank you

Mario

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possibly related: graphicdesign.stackexchange.com/questions/13162/… – DA01 Dec 5 '12 at 20:23
thank you but this is not related. – Mario Joan Dec 5 '12 at 20:29
I don't have AI in front of me, but lots of software does let you change the software's pixel-to-real-measurement formula. If that's an option, then I suppose you can't rely on pixels having a consistent correlation to a real world physical measurement. – DA01 Dec 5 '12 at 20:34
The question DA01 links to describes essentially the same problem - receiving art measured in pixels and needing to convert to real-world measurements. – e100 Dec 6 '12 at 12:20
Why are you getting artwork for print that is measured in pixels in the first place? This is your real problem. – e100 Dec 6 '12 at 12:28

1 Answer

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Illustrator doesn't measure anything in pixels primarily because Illustrator, being vector-based, is math-based and a pixel has no size.

Illustrator has no "default [PPI]" because it's a vector-based, resolution-independent, application. The only time PPI is used within Illustrator is when placing raster images - in which case the image PPI is used, or creating raster effects - in which case the settings under Effect > Document Raster Effects Settings are used.

Illustrator essentially uses 1 point to equal 1 pixel for measurements. While this is not really accurate and pixels can easily vary in size, this is done to preserve at least some logic in the application. Again, because you can't measure a pixel. You'd be better served with a point to millimeter conversion. This is also where you've "guessed" at Illustrator using 72ppi. It's not, it's using points and there are 72 points to an inch. Or 2.834645669 points to a millimeter. That formula which was posted, while accurate for points is completely *inaccurate* if referring to pixels.

You can't think of pixels as having a size. They do not. So to answer your question.... no. Because there's no way of determining the size of a pixel without also knowing the width and height of the entire image, as well as the total number of pixels contained in the image.

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However illustrator does measure it right? What you are saying is that illustrator actually gives a size to a pixel created within it. 1 pixel = 1/72 of an inch so its actually hardwired within illustrator. If i create a VECTOR that is 72 pixels in illustrator this will give me a size of 1 inch. As you say then what i understand is that this will ALWAYS be the case in Illustrator since it is hardwired in it. – Mario Joan Dec 5 '12 at 20:52
Yes but if i create something in illustrator in pixels then it is 1point=1pixel=1/72 of an inch. I am not talking about importing raster images i talked about importing an SVG which is a vector in pixels. – Mario Joan Dec 5 '12 at 20:55
No, I did not post that Illustrator gives a size to a pixel. It does not. What I posted was Illustrator uses POINTS for measurements. If you measure anything in pixels you are not being accurate and are destined to think of pixels as a unit when it's not. Just because Illustrator uses 1pt = 1px that doesn't mean it's accurate. That pixel could actually measure 4pt x4pt. But again, without width, height, and total pixels there's no way of knowing. – Scott Dec 5 '12 at 20:56
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If all you want is a different measurement unit within Illustrator, right-click/control-click a ruller and choose MM. All measurements will then be read in MM. Let the app do the math. You don't need to convert anything, just change what Illustrator shows you. – Scott Dec 5 '12 at 21:55
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I think part of the problem is that svg files do in fact allow one to specify pixels. This clouds the issue. In many examples, one sets the viewport size to pixel dimensions (usually for the web-based applications), and then uses dimensionless values for the objects and primitives. Set the pasteboard or document to the dimensions and units which you desire the printed product to be, Place... the SVG file, and then scale it to fit the pasteboard. – horatio Dec 5 '12 at 22:47
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