A discrete pattern, formed by dots discretely arranged in two dimensions,
is provided wherein the dots included in a rectangular area having a
longitudinal length of Lx and a transverse length of Ly satisfy expression
(1),
D.ltoreq.0.13N.sup.-1 15 (1)
(in expression (1), N denotes the number of dots included in a
predetermined area, and D is obtained by expression (2), wherein A(x,y)
defines the number of dots, of a total of N dots, included in a
rectangular area for which a line segment extended from reference
coordinates (0,0) to an arbitrary coordinate point (x,y) is a diagonal
line), [Ex. 2]
##EQU1##
and wherein S.sub.1 that is obtained by expression (3) [Ex. 3]
##EQU2##
is equal to or smaller than 0.7. (In expression (3), g.sub.1 is obtained by
dividing the average radial distribution function g(r) of each dot in the
area by an integration value of g(r) over a range of from r.sub.1 to
r.sub.2, and g.sub.av is the average value of g.sub.1 within the range of
from r.sub.1 to r.sub.2. When the dots are arranged in a square lattice to
satisfy a given filling rate, r.sub.1 and r.sub.2 are chosen as one and
four times the value of the lattice constant Dr respectively. The dot
filling rate is a value obtained by multiplying the square of the maximum
diameter of a dot by the number of dots, and dividing the product by the
size of the area.
