Digital Photo Printing

What is our visual resolution?

Human visual resolution limits:
  • Distortion in the corena accounts for a tiny fraction of the fisual limit
  • The density of retinal cells, rods and cones, are the primary limitation. Their distribution is non-uniform where the rod cells cover most of the retina but the cone cells (which are more responsible for color perception when light intensity is higher) are concentrated in the Fovae.
  • This accounts for why the eye sees details only where it is focused and everything else is fuzzy. Human vision sense of clarity of an entire view results from the brain remembering visual details as the eyes continually scan a scene to acquire a complete picture.
  • Accurate measurement of visual resolution is difficult but one estimate suggests that the eye can resolve detail equivalent to about 500 PPI at a distance of 20 inches.
  • Therefore, it should be theoretically possible to distinguish individual printer dots in a 13x19-in 400 DPI print at 23 inches viewing distance.
Human visual color differentiation limits:
  • In 1931, MacAdams described ellipses of "just noticable color change" as a means of describing human visual color differentiation limits. These were elliptical shaped areas within the standard CIE color gamut graph.
  • The largest ellipses, indicating the color values which are the least descriminating to human perception, are in the Greens, then the Reds and then followed by the Blues. This is logical because the eye is more sensitive and has the broadest response to Green light.
The CT-PrinterTest image can help estimate printer color resolution.