This is simply the RMS of the three images. Although the CCD camera converts
the optical image into a digital image, we reference position in both images as
x and y, implicitly assuming real numbers in the former and integers in the latter.
To compute an M N-pixel optical section image, Eq. 17.5 is applied on a pixel-
by-pixel basis for all positions, (x, y), with 0 # x < M and 0 # y < N.
At this stage care must be taken to avoid loss of information. The sectioned
image should be computed with high numerical precision (e.g., double-precision
floating point). Then one can apply further image processing if necessary. If so,
high precision should be used there as well. The values resulting from the
floating point calculations must be scaled to the integer ...