In case of black and white graphs or images gray scaling with different density of black ink, black dots and black screen mesh should be carefully designed to represent density difference better.
Psychological perception of the gray scale is not proportional to the physical difference.
Table 6.1 and Figure 6.2 show the ratio of black area with respect intensity based on psychological perception.
In case of dot map or bit map, users should design dot patterns to generate the gray scale by assigning either 0 (white) or 1 (black) to n x n dot matrix.
One should note the following special knowledges about the psychological effect.
a. homogeneous pattern with regularly spaced dot pattern will make the impression of continuous tone or density rather than texture.b. discrete data patterns with specially recognized forms, symbols and/or directional lines will make the stronger impression of texture rather than continuous tone.
c. horizontal and vertical pattern in squarely spaced dots (0-90 degree), will make more static and stable vision of the dot structure, while obliquely cross patterns of 45-135 degree will give human eye some sort of dynamic confusion in its visual field, which results in more tonal impression. In designing gray scale, horizontal and vertical patterns should be alternatively assigned with obliquely cross patterns in order to make visual difference between neighbor classes.
Figure 6.3 shows example of 4x4 dot pattern for density and textural representation.
Figure 6.4 shows the dot map with use of 4 x 4 dot patterns shown in Figure 6.3.
