Opacity Masks

Opacity masks use the luminosity of the uppermost object to produce a transparent pattern on lower objects. When the masking object is filled with a solid color, the mask is uniform. If the luminosity is high (bright colors), the mask appears to have little or no effect. If the masking object is filled with a dark color, the artwork below appears more transparent. When the masking object is filled with a pattern or a gradient, the results can vary substantially. Figure 17.9 compares opacity masks created with various solid color, gradient, and pattern fills.

Figure 17.9. On the left are the original objects. To the right, the background image has been divided into five pieces and different opacity masks have been applied to each. From the top: white, neutral gray, black, pattern, and gradient.