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I was sent a photo that was scanned at 300 DPI and it’s roughly 2000 x 2500 pixels. I’ve decided that I want to print it as a large print which will measure 20 inches x 30 inches and that works out more or less 100 DPI.

Thus, the image needs to be upscaled and I want to avoid it coming out as blurry. I went into the shop earlier today where I am going to get it printed and I asked “Is it possible you can upscale my photo?” And then I explained the situation and the man said “Yes, no problem”.

How is he going to do it? I know that if you have a small photo that was printed at 300 DPI it’s possible to rescan it at 1200 DPI, but I only have the photo saved on my computer and phone (I was sent it via email). Will it take long for the man to upscale the photo? What does it involve?

If I didn’t get the photo upscaled, would it print out blurry since it’s not really enough pixels for a print that size?

Thanks.

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    \$\begingroup\$ Realistically these days: they'll put it into their automated system which does stuff and they don't think about it. \$\endgroup\$
    – Philip Kendall ♦
    Jan 6, 2022 at 14:42
  • \$\begingroup\$ What do you mean? Will he use a computer or will the printer do the work? \$\endgroup\$
    – JasonSmith927372
    Jan 6, 2022 at 15:30
  • \$\begingroup\$ Why don't you re-sample it yourself? It's easy to do in any app like Photoshop or The GIMP. As for whether or not it would "print out blurry," You may be able to "sharpen" it using an unsharp mask filter after you re-sample it, but I like to think of that as creating the illusion of sharpness because the filter won't add back any details from the scene that were too small to be recorded at the original resolution. \$\endgroup\$
    – Solomon Slow
    Jan 6, 2022 at 16:12
  • \$\begingroup\$ Hi Solomon. But, what is the formula to work out how much I need to upscale/resample it to precisely? Is it something like if I want it to be printed at 200 DPI then say a 24 x 36 inches print I would do 200 x 24 and 200 x 36 to work out what I need to upscale it to using Photoshop? So my image should be now 4,800 x 7,200 pixels. Is that right? \$\endgroup\$
    – JasonSmith927372
    Jan 6, 2022 at 16:29
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    \$\begingroup\$ Yes, those numbers look correct, Only, I would ask the printer about margins. If (and, I am completely making up a number here), they need a 1/4" margin all around, then you would want to scale it to 23 1/2" x 35 1/2" at 200 DPI so that the printer doesn't do a "shrink-to-fit" that re-samples the image a second time. \$\endgroup\$
    – Solomon Slow
    Jan 6, 2022 at 22:25

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It is not 100dpi (ink dots per inch)... the printer will run at whatever resolution it is capable of (300+ typically).

It is ~ 100ppi (pixels per inch); which is a little low for a print viewed from short distance. But it is adequate for a 20x30 print viewed from 3+ ft away (standard viewing distance).

If I didn’t get the photo upscaled, would it print out blurry since it’s not really enough pixels for a print that size?

No, it will print pixelated (to where you can see the square shape of the pixels). *Simply resampling/resizing an image does not make it sharper, nor does it add details that are not already there... it simply breaks the big squares (pixels) into smaller squares; so the printer cannot print them, or you cannot see them.

*There are programs that can/will add false detail and sharpness to a resampled/enlarged image... that result may be better or worse.

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  • \$\begingroup\$ Hi, thanks for clarifying a few things for me. I know that people use DPI and PPI interchangeably, but there is a difference which you have made clear. So, do printing shops generally speaking have the software such as photoshop on the computers in the shops to sort out the upscaling? What does upscaling actually do? Does it manipulate the change of the 2000 x 2500 pixels to say 3500 x 4000 pixels or something? I know that data can’t be added to a photo, so what does Photoshop or whatever software actually do? \$\endgroup\$
    – JasonSmith927372
    Jan 6, 2022 at 15:31
  • \$\begingroup\$ If I want to learn how to upscale photos myself, how do I know what to upscale a photo to exactly? Say I want the 2000 x 2500 pixels photo to be printed as a 24 inches by 36 inches print, how do I know what to upscale it to precisely? \$\endgroup\$
    – JasonSmith927372
    Jan 6, 2022 at 15:44
  • \$\begingroup\$ IDK what software each print shop has... usually, they will print at whatever size you ask w/o resampling the image (i.e. at a lower PPI). If you resample an image to 200% size (e.g. for 200ppi print) it basically just breaks each pixel into four pixels (it's a bit more complex than that depending on the algorithm used). \$\endgroup\$
    – Steven Kersting
    Jan 6, 2022 at 16:34
  • \$\begingroup\$ Should I upscale the photo or should I just ask for it to be printed at 100 DPI? If it’s upscaled and the right size, is the typical printing DPI 300? \$\endgroup\$
    – JasonSmith927372
    Jan 6, 2022 at 17:28
  • \$\begingroup\$ Depends on the viewing conditions/distance; but I think it would be safer to resample/upscale it to 200%. To get an idea, try viewing the image at 100% magnification... your monitor is probably right around 100ppi, so that will give you a good idea of how it will look printed at 100ppi (and the size that would be). It should actually look a little nicer if printed with an inkjet printer in terms of noise (i.e. a bit softer/smoother). \$\endgroup\$
    – Steven Kersting
    Jan 6, 2022 at 18:11

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