Visual inspection of alpha channel values is aided by displaying a partially transparent image rendered over an animated background pattern. The background pattern is user-specified or chosen automatically. The background pattern has colors, shapes, position, orientation, magnification, and distortion. The visual appearance of the background pattern is automatically altered, and the partially transparent image is redisplayed, this time rendered over the altered background pattern. The background pattern may scroll, rotate, change shape, pulse, morph shape, and/or change colors during animation. The background includes a checkerboard or another tessellation, a color gradient, a transparency heat map, a procedurally generated texture, and/or other patterns. A color identified in the partially transparent image may provoke use of a complementary color in the background. The image whose transparency is being visually inspected zooms independently of the background pattern. Animation of the background helps reveal unwanted transparency values, which the user edits as desired.