Controlling optimization (ImageReady)
By default, Photoshop and ImageReady automatically regenerate the optimized image when you click the Optimized, 2-Up, or 4-Up tab at the top of the document (if you have modified the image since the last optimization), when you change optimization settings with the optimized image displayed, or when you edit the original image.
In ImageReady, you can turn off auto-regeneration so that the last version of the optimized image remains in the image window until you manually reoptimize the image or reactivate auto-regeneration. This feature is useful if you want to edit the image without pausing for reoptimization with each modification. You can also cancel optimization while it's in progress, and preserve the previous image.
When auto-regeneration is turned off, the Regenerate button 
appears in the lower-right corner of each optimized image view. A regeneration alert symbol also appears in the Color Table palette if the optimized image is in GIF or PNG-8 format, indicating that the color table is out of date.
To turn Auto Regenerate on or off:
In the Optimize palette, choose Auto Regenerate from the palette menu. A check mark indicates that the option is turned on.
To manually optimize an image:
- Click the Regenerate button in the lower right corner of the optimized image (if it appears).
- Choose Regenerate from the Optimize palette menu.
Choose a method for optimizing:
Note: Manually optimizing an image does not turn auto-regeneration on.
To cancel optimization:
Click the Stop button next to the progress bar at the bottom of the image window.