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If I have a photo scanned at 300dpi and the dimensions are 4x6, if I need to print to 8x10 or larger from the scan would the print quality be not as good?

Should I scan at higher resolution for larger prints?

I'm not asking about rescaling digital images or bumping the DPI value. I simply wanted to see if really need to rescan from 4x6 to something just a bit bigger like 8x10.

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My tests of printers is that they rolloff pretty strongly at 150 PPI so upsizing and then possibly slightly sharpening a 300 DPI 4x6 scan should print just fine at 8x10. Try it. You'll be surprised at how good it is.

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The question is really, what resolution degradation are you willing to accept? Simply going from 300PPI at 4x6 to 150PPI at 8x12 isn't terrible (oh, it isn't great either) but if you are staying a few feet away from the photo, I doubt you'd notice.

Notice I said "8x12." Do keep in mind that 8x10 mean you need to do some cropping of your image to fit the new ratio.

But, if you're going to hold the image quite close, you'd want to get more PPI. This is a balancing act: interpolate too far and the image falls apart...not enough and you haven't given yourself enough PPI for the print.

I'd be comfortable going 150% of the original - so 225PPI at 8x10. You'll probably need to sharpen it a tad once at that size.

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    Agree with much of this but there is a big difference when the starting point is a scanned image. Any print, excepting certain special cases like high resolution black/white, is already rolled off below the 300 PPI of the scan. And the scan doesn't have the camera imager CFA issue that blues/reds are already reduced 2x. The scan contains the full Nyquiest content of the original print which contains virtually nothing beyond that. However, it's still important to print an image at a high resolution for other reasons to long to go into here. – doug Sep 5 at 17:04
  • @doug That's very true. I thought about getting into the difference in inherent resolution of film -> print or digital -> print and how the print scan is terrible in comparison. Maybe I'll update this later with those details. You're right though - starting from a scan is an inherent disadvantage and there's usually very little to do to increase size. – Hueco Sep 5 at 17:17
  • If you're scanning 4×6" drugstore prints from the 80s, there's probably not 300dpi of actual detail in the first place. – mattdm Sep 5 at 21:51
  • @mattdm True. It's surprising how few printed images have content that exceeds a 300 PPI scanner. The only ones I've been able to create are synthetic images and only if printed on a good printer at the highest possible resolution w/o bi-directional printing. I did a Kodak PDI print at 600 DPI on a Pro1000 at the highest possible setting and scanned it at 300 as well as 600 then uprezed the 300 to 600. Toggling back and forth there is no difference in the images aside from one tiny area in a synthetic portion close to the 300 Nyquist I purposely zoomed in on. – doug Sep 5 at 23:53
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That's still 180PPI, which is "draft" quality. If you want a really good print (300PPI or more), better rescan.

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