Interpolation is basically a means of making something larger and filling in the resultant 'spaces', in the case of a photo with similar surrounding pixels. That's why the file size gets bigger - more data. The image won't really be any better printed at the original size because the human eye, and printers work at an optimum resolution. It's more of an issue when you blow up an image to a larger physical size. If I have an image 3000x2000 pixels and it prints fine at A4, if I print it at A3 it has to cover twice the physical area with the same number of pixels. The pixels therefore start to look degraded. By interpolating I make the physical size larger and it fills in the gaps with relevant pixels, so I could end up with say 6000x4000 - and it would print OK.


Have a look at this,

http://www.ephotozine.com/article/In...-images-bigger

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