CANVAS SIZE PROBLEM!!

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2019-09-25 10:02:55

Hi, Guys.

When I make a new project and set the canvas size to the spec of the client (magazine/poster/print)then go back into the "canvas size" dropdown menu its always a slightly different size by a few mm or pixels. This is a really annoying thing as I'm trying to set guides for exact sizes.

Whats the trick to get the canvas to stay the same size as I set it?

J
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2019-09-25 17:37:56

Hi Jarrod.
Are you talking about rounding errors? Working in metric units causes a bit of a disjoint between size (metric) and resolution (imperial). If I have an 8"x10" image at 300ppi the image is 2400 x 3000px. Easy. If my image is 210mm x 297mm at 300ppi, the image size is 2480.315 x 3,507.874px. Since pixels only come in whole units, this rounds to 2480x3508px which has a real world size of 209.97mm x 297.01mm. Ugh.
There's no easy solution. There's three compromise solutions that (and one daft non-solution) that come to mind:
1. Work in pixels. Work out how big your image has to be for the size it has to be then ignore real-world measurements from there-on in.
2. Work in imperial. Points, picas, inches etc.
3. Live with rounding errors. There's not pretty but at 300ppi, the maximum error is half a pixel so 25.4/600 = 0.04mm
4. Work in a metric ppi. Since there are *exactly* 25.4mm to an inch (the inch got redefined in the 1930s), setting a ppi of 254 will get rid of metric rounding errors. This should be used with caution as I have never heard of anyone doing this for print. Ever.
Of course, you coud be talking about a bug that I've not seen, in which case, ignore the above.
- Stef.
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2019-09-27 13:28:59

Fantastic answer.