Each frame of a GIF animation file has the same characteristics of a GIF, which you learned about in Chapter 10. For example, each frame must have 256 colors or fewer, and can have no more than one transparent color.
Just as with static GIFs, animated GIFs will be much smaller if you keep the number of colors to a bare minimum. I recommend choosing a small color palette and then using only those few colors to create all the frames in your GIF animation. For this reason, drawings, text, and illustrations tend to work better as GIF animations. Photographic and continuous tone imagery don't compress well at all and often cause GIF animations to be much too large in file size—meaning they take so long to download that no one ever gets to watch them all the way through.
Aside from the basic GIF optimization settings discussed in Chapter 10, there are a few additional characteristics you need to know when optimizing GIF animations, as discussed in this technique.
TRY IT To optimize a GIF animation, make sure the file is open in ImageReady. (Remember that Photoshop cannot display or process animation files.) Then, perform the following tasks to prepare for optimization:
• Set the disposal method. For each frame, indicate what happens after it's displayed by right-clicking (Windows) or CTRL-clicking (Mac) on the frame in the Animation palette and choosing one of the following options:
• Choose Do Not Dispose to cause the next frame to be placed on top of this one. (If the next frame contains transparent areas, this frame may then be visible in those areas.)
• Choose Restore To Background to disable the current frame after it's viewed, so it's not visible if the next frame contains any transparent areas.
• Choose Automatic to allow ImageReady to select the disposal method it thinks is best.
• Adjust the looping. Specify how many times the animation repeats. Click the looping option selection box—which is set to Forever by default—and choose Once, Forever, or Other (to specify an exact number of times to repeat).
• Adjust the timing. For each frame, specify how long the program should wait before displaying the next frame. Click the current delay value below each frame—which is set to 0.0 sec by default—and choose a value from the menu, or choose Other to enter your own value using decimals (for example, 1/2 second should be entered as .5).
• Specify the portion of each frame that should be redrawn as each new frame is placed on top of it. For example, the program defaults to only redrawing those portions that change from frame to frame, to save in file size. If you need to force the program to redraw the entire screen for every frame, click the triangle in the upper-right corner of the Animation palette and choose Optimize Animation. Then, uncheck Bounding Box and Redundant Pixel Removal. Otherwise, leave them checked for optimal performance.
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