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Rulers best in pixels?

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Old 08-09-2009, 04:34 AM
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Chain Chain is offline
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Location: Oslo, Norway
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Re: Rulers best in pixels?

Actually, I did just reply it
(1 inch = 2.54 cm, so if I use inches in an example you can easily turn that into cm)

So to repeat:

On a screen, everything is measured in pixels, not in cm (or inches). A digital image is made up of pixels - think of it as the "physical" size of the image.

When we print the image, we copy it into the "real world" where there are no pixels and it makes most sense to use cm (or inches) to measure the size.
How large the image will print is calculated using the image's PPI-setting (how many pixels per inch). Look in previous post where i told you to check out the image size and try it and you will see how it works.

We could instead of pixels/inch (PPI) use pixels/cm (PPCM), but nobody in the graphics business that I've seen does that. The reason is that the equipment seems to have been built around Inches and PPI creates easier to remember numbers.
You can change what measurement you want to view it as in the image size dialogue in Photoshop (remember to uncheck "resample image" when changing resolution).

300 px wide image, will print 1 inch wide at 300 pixels/inch (top quality).
or if you prefer cm:
300 px wide image, will print 2.54 cm wide at 118,11 pixels/cm (top quality).


When you say "pixel aspect ratio" you mean to say "resolution" (PPI or DPI). Pixel aspect ratio is as I said something you use when the pixels are not perfectly square (do not bother your head with this unless you will be creating content for standard definition TV).
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