question about scaling images when sending to printer

I order prints of my pictures from an online place that has a number of scaling options. I upload JPGs. They have a number of paper sizes, 17×22, 18×27 etc. I do not understand the “no scaling” option. A jpg does not have a physical size, does it? I mean, if I created a photoshop document at 24″x24″ and save it as a jpg, that jpg is not 24″x24″ is it?

And the “use smaller image” confuses me too. In order for that to make sense, I would need to know the pixel dimensions of the print job, right?

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Answer

No, an image has no physical size, you are correct (and ahead of many askers here). However, the file can contain a metadata info tag that contains a instruction what the designed print pitch of pixels should be. This tag is slightly confusingly called resolution, not to be confused with amount of pixels which is also called resolution (in the os, games and cameras. This setting defines size and is measured in PPI/DPI.

Pixel dimensions of image is irrelevant for scaling though. All the printer needs to know is asingle conversion factor, width/height or if nonuniform size is needed width and height. Rest can be calculated.

Attribution
Source : Link , Question Author : jqning , Answer Author : joojaa

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