photos in iMovie become horrible, how do I fix it?

[Ja Di ksw]

I just made an iMovie, and all the photos in it lose a LOT of quality. Any place that has a good amount of one color (the sky, dark clothes, even large areas of skin) show either lots of noise or banded patterns. Is there any way to make these photos look like they do in Aperture or iPhoto, or does iMovie always make the photos bad?

 

[Dave Braine]

They should look the same, they do with me, iMovie11.

 

[Ja Di ksw]

With my iMovie 11, they look nowhere near the same, especially things like sunsets. The sky is very, very grainy and the color transitions are not smooth at all, they have huge lines in them.