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If I wanted to print an image found online and get a typical 27" x 40" sized poster what resolution image do I need? 4000 x 6000 or double that? I am confused over DPI and PPI.

  • That question doesn't have this brilliant online calculator linked, however! I found the answer I got very relevant. – chx Jun 8 '16 at 7:29
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It depends on how close you expect the viewer to stand, as vision is based on angular frequency. If your image has a certain size and you need to print it at some size then there is not much you can do about the resolution.

150 PPI is usually quite acceptable for items you view at a distance. Most human sized outdoor commercials are at that kind of resolution. Especially if your text items are vectors.

You could use online calculators to verify your values, if you have no idea what your doing.

  • That calculator is immensely helpful! Since I want to see these things from my desk on the opposite wall apparently much lower resolution is enough. Looks like I could even print a screenshot from a 1920x1080 movie (I've gotten 972 x 1440 as minimal resolution). That's so cool, thanks much! – chx Jun 8 '16 at 6:28
  • @chx why do you think they are acceptable on a monitor? But yes these are just guidelines you also need to account for printer realities and the fact that somebody might be temporarily closer. – joojaa Jun 8 '16 at 10:36
  • Not on a monitor. I want to print , frame and hang on the wall. – chx Jun 8 '16 at 12:07
  • @chx no i meant why do you think 90-100 ppi is fine on a monitor we just sit further away from the medium than say a art magazine. The need for a print to rasterize means a print needs 20% -60% more points to build a well weighted raster but thats just about it. – joojaa Jun 8 '16 at 12:10
  • Ah I get it. A typical PC monitor is 96 dpi and it's OK. Gotcha. – chx Jun 8 '16 at 12:56
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Sounds like you're confusing dimensions with resolution. Go for the dimensions as close to 27x40 as possible (using the online calculator that joojaa mentioned to convert inches --> pixels). When choosing resolution for printing, 300 is best for high-res graphics or fine details, but if it's okay to lose some detail you can go with 150.

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