Any difference between visual items.
In typography and the graphic design thereof, contrast can include point size (10-point vs. 24-point), character weight (plain vs. bold), character width (condensed vs. expanded), character form (uppercase vs. lowercase), character placement (next to each other vs. at oblique angles to each other), character structure (serif vs. sans serif), character posture (normal vs. oblique), and various combinations of these properties. The use of contrasting type in design is useful and effective, but as a general rule the contrast needs to be strong to be effective. Varying fonts can be effective (not within a single text paragraph, of course), but there should be a large degree of difference between the fonts. Contrasting Helvetica with Times Roman is effective; contrasting Bookman with Palatino looks like an error.
In printing (or other forms of reproduction), contrast refers to the degree of perceptible difference between a duplicate and the original from which it was made.
'Contrast is also used to refer to a specific mathematical relationship between the tonal qualities of the original and a reproduction. A gray scale can be used to compare and contrast each density of the original—from the shadows through the middle tones to the highlights—with the corresponding densities of the reproduction. These densities can be graphed with the densities of the original on the x axis and those of the reproduction on the y axis, to generate a gamma curve. The slope of the resulting line is an indication of the fidelity of the reproduction. A gamma—or slope—of 1.0 describes a line at a 45o angle from both the horizontal and the vertical, corresponding to a perfect reproduction (or, in other words, each density on the original is matched identically with those on the reproduction). Portions of the curve with less than a 45o angle indicate low contrast. Commonly, color reproductions have low contrast in the shadows, but normal contrast in middletones and highlights.
The gamma can be calculated mathematically according to the following formula:
where represents gamma, DRo represents the density range of the original, and DRr represents the density range of the reproduction.