Undo Active Step (Ctrl+Alt+Z (z -Option-Z)) keyboard shortcut, 344, 345, 348
Undo Edit and Apply New Edit (Ctrl+Alt+Z (z -Option-Z)) keyboard shortcut, 57
Undo (Ctrl+Z (z -Z)) keyboard shortcut, 155, 234, 258, 309, 344, 345, 347, 622, 678, 994
undoing
brushstrokes, 234
distortions, 622–623
History palette, 346–349
keyboard shortcuts, 1030
multiple, 22
painting, 234
Revert command, 344
sequence of filters, 498
state change, 347
steps, 56
text modifications, 822
traditional functions, 345
Units & Rulers panel (Ctrl+5 (z -5)) keyboard shortcut, 66
units & rulers preferences, 66–68
units of measurement
images, 86–87
keyboard shortcuts, 1026–1027
rulers, 67
type, 825
type tool, 67
UNIX
case sensitivity, 61
workstation formats, 142
Unsharp Mask dialog box, 499
Amount value, 505
applying color channels in RGB image, 502
Radius value, 503–505
specifying amount of sharpening, 500–503
Threshold option, 500, 506, 508–509
Unsharp Mask filter, 209, 497, 498–506, 508–511, 533–534, 546, 552–553, 557, 590, 592, 719, 941
unstable colors, 909–910
Up one screen (Control-K) keyboard shortcut, 50
Up one screen (Page Up) keyboard shortcut, 50
Up slightly (Control-Shift-K) keyboard shortcut, 50
Up slightly (Shift+Page Up) keyboard shortcut, 50
Uppercase to Lowercase (Ctrl+Shift+K (z -Shift-K)) keyboard shortcut, 824
U.S. Prepress Defaults option, 858
user-created brush shapes, 238–242