Presets are set based on what I find typical for a lot of uses. Pretty standard, range is 8-inches to 10-feet. The larger print value (1 sq ft) is meant to be used to calculate the resolution need per square foot of a very large print, see the Big Prints section at the end. Print sizes are assumed to be in inches unless otherwise noted.
However, even at the minimum distance of 8 inches, the error is well below 0.001% of the actual value which is more than sufficient for these calculations. Note, this is of course a skinny triangle approximation. That gives us the diameter of a disk shaped “pixel” for the print that can’t be better resolved without moving closer or having better vision. The “spot size” on the print is then calculated using s = x × tan(0.000290888209 × f s), where s is the spot size, x is the distance to the target and f s is conversion factor from 20/20 to one of the other visual acuity ratings. The fundamental assumption is that the disc of confusion for a person with 20/20 vision is equal to 1 arc-minute (1/60 th of a degree) in diameter. This is little more than a transform from angular acuity of human vision, to spatial resolving power at the print converted to mega pixels. The required resolution is derived simply from considering the visual acuity of the human eye at a given distance and given acuity standard.
0 kommentar(er)
