I\'ve posted this once before (sorry for the repeat, but it may be useful to some)
in researching this for myself (most of the frames in my house are 3\' x 5\', see below), I came across the following bits of info.
But before I share the formulas, I\'d also agree that A *LOT* depends on your subject matter and how detailed it is to begin with. A shot of waves on a beach at sunset is unlikely to require as much resolution to portray as a close up of the scales of an creature, for example.
So, while I offer numerical ideas, please do not mistake my comments as gospel, but rather one piece to a complex puzzle.
In order to determine the required file resolution to print,
Step 1 is to establish the viewing distance. If you\'re printing something to hang on the wall, you\'re probably going to look at it from a greater distance than a 5x7.
Formula 1: Viewing Distance = 1.5 x diagonal of print. However, I tend to set a max viewing distance of 24 inches for anything indoors.
Formula 2: required print ppi = 3438 ÷ Viewing Distance
3438 is derived from the following formulas:
1 ÷ ppi = 2 x Viewing Distance x tan(.000290888 ÷ 2)
1 ÷ ppi = Viewing Distance x tan(.000290888)
ppi = 3438 ÷ Viewing Distance
.000290888 is the visual acuity angle, a measure of how much resolution the human visual system can perceive.
Example: if you are printing a large print for the wall, I\'d use 24\" for the viewing distance, so the required print resolution is:
3438 ÷ 24 = 143.25 ppi
Because my printer\'s resolution is 1440 ppi, I use 144 ppi to calc my target file size. So a 36MP file from a Sony a7r (4912 x 7360) could be used to print as large as 34\" x 51\"
I then use Genuine Fractals (now called Perfect Resize, part of onOne software) to uprez to 720 ppi (5x) and then let the printer uprez to 1440 (2x).
If it is a print that I really care about, I\'ll print small portions of the full rez file with various sharpening levels applied as well.
Oct 28, 2014 at 01:30 PM
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