Google Ads accepts an animated GIF image ad only when three things are true: the file is 150 KB or smaller, the animation stops within 30 seconds, and it plays slower than 5 frames per second. A GIF exported straight from a design tool usually breaks all three at once, because it loops forever, runs at 20 or 25 frames per second and carries a full palette in every frame.
The optimizer fixes each rule without touching the pixel dimensions, so a 300×250 ad stays exactly 300×250. Frames shorter than 200 ms are merged into the frame they belong to, and their time is added to it, so the loop lasts exactly as long as before. The number of plays is set so the total stays within 30 seconds, and a single loop longer than 30 seconds is cut so it ends on your final frame, where the call to action usually sits.
To reach 150 KB it rebuilds the colour table with a median cut quantizer, stores only the rectangle that changed from one frame to the next, and writes a fresh LZW stream. It tries 256, 128, 64 and then 32 colours, with and without dithering, and only then merges more frames. The first setting that fits is the one you get, and the report shows which one it was. If nothing fits, it says so and gives you the smallest version.
Everything runs inside your browser in a background worker. The GIF never leaves your machine. When you are done, load the file into the HTML5 Banner Validator for a final check, and read the guide to animated GIF restrictions and loop caps for the rules on other networks.
