Having discussed sampling and the Nyquist frequency we are in a position to see what properties a display must have in order to be able to reproduce signals that span the complete range of human visual capabilities say from 0-80Hz temporally and 0 to 40cpd spatially. To satisfy the Nyquist criterion in time we should have a sample frequency of at least 2*80=160Hz; on a CRT monitor this translates to a frame-rate of the same value, while to satisfy the Nyquist criterion in space we need a sampling frequency (f_s) of at least 2*40=80cpd. A standard colour monitor will have a mask pitch (d_mask) of about 0.28mm so this implies a viewing distance (d_view) of

d_view= f_s/ 2*d_mask/ tan(0.5) = 1.3m.

Remember that with modern colour displays increasing the frame rate will cause a corresponding decrease in the number of lines on the screen, and therefore the vertical sampling frequency, without a commensurate change in the horizontal sampling frequency.
If the resolution on the display is rather low and therefore a large viewing distance is needed for recreating high spatial frequencies it is probably easier to use a mirror than find a bigger lab. The software can easily be adjusted to correct the image reversal that this will introduce.

^ Back to top