Chapter 8 INTRODUCTION TO EFFECTS 179 often. Most of the time, however, you won't even be aware that Partial Render is at work. The best features, many times, are the ones that make you more productive without attracting atten- tion. Long after the sizzle of the product demo is over, you will be making your deadlines with projects you are proud of, and you won't really care why! Keyframes Almost all effects can be manipulated by keyframes. The only exceptions are the color corrections and a few other segment effects like flip and flop. Keyframes are the method to change an effect over time, and you always need at least two keyframes if you want the parameters to change. At the first keyframe, certain values about position, shape, or color are entered, and the set- tings change to match the values on the next keyframe. The change, if there is any, is smoothly interpolated between the key- frames. Keyframes can be added in Effects mode on-the-fly while playing and pressing the Keyframe key (the ' [apostrophe] key is