Low-quality background in quiz slides

Hello,

I made some slides on Powerpoint in order to use them as background in Captivate.

It works fine, but when I use them as background of a quiz slide, then the quality of the background is very low. Whereas backgrounds of non-quiz questions keep looking good.

I've checked each slide quality parameters.

How could I get a high quality background for my quiz slides?

Thanks

Regards