Is 247 PPI okay for print?

[Eric5CCA]

I'm not sure if this is the best forum to ask this question, but I'm working on a project for print on indesign. I have one photo that I need to fill an A4 page, but the PPI is at 247. Everywhere I read says 300 PPI is optimal for print. Can I get away with 247 or will that result in blurriness/pixelation? 

[Jeffrey_Smith · Accepted solution]

300 ppi is a general rule of thumb. 247 ppi effective resolution, IMO is enough for good quality.

Note, effective is the resolution of image after scaling. A 247 ppi image scaled 200% will have an effective resolution of 123 ppi

[Eric5CCA]

Ok got it. This is a 300 PPI image with an effective PPI of 247.

[Brad @ Roaring Mouse]

Definitely fine. The 300 dpi rule of thumb is rooted in old school drum scanning where a 2 to 1 ratio to the printed line screen was "the norm", but frankly anything above the line screen values of your printed product is fine. In the "old days" the average commercial printer printed colour at 150lpi, with the better ones 175lpi and up. These days, the average is about 200lpi, which most naked eyes can't see anyway, so even having a 1 to 1 ratio wil be unnoticeable to most. The one area that does help with a higher dpi is that any artifacts from a bad JPEG compression will be less noticeable, as the macro-blocking happens in larger chunks than the dpi. At this point, it's more about the quality of the scan than the resolution of the scan.

[Creamer Training]

To add to roaringmousegraphics info, back in the old days, there were two "rules of thumb": easy and efficient (my terms). 

Easy was your PPI would equal 2X your line screen (LPI). Efficient was 1.5 the LPI (it was closer to 1.4, but 1.5 is easier to figure out). So, at 150 LPI, one could use 300 ppi or 225 ppi. If you use the lower number, you can't scale beyond 100%.

Rather than explaining all this, most printers just give an acceptable range. For example, 225-300 ppi. As mentioned, this would be the effective resolution in InDesign. 

BTW, you don't want too much PPI resolution either. This can usually be removed when created the PDF. 

[Derek Cross]

And to add to the excellent earlier answers, if you're producing a large poster that's to be viewed from a distance you can bring the resolution down to much lower amounts, such as 50PPI.