Is there any way to fix this problem?

Look at the site I'm working on http://www.ferriswheelpictures.com

Notice the image degradation of the ferris wheel as it grows in. Then when it's finished loading it's horrible. As a fix, for now, I added a copy of a static image to the frame right after the final motion. You can tell by the quality change.

Is there a way to fix the degradation or is it a cost of doing the animation? I tried different file formats as well but it has to be png or gif because I need to keep the transparency.