Depending on your system, you can specify the bit depth for images rendered by the graphics card. The bit depth affects the quality of the resulting clip. The images can be rendered with 8-bit or 16-bit FP precision.
As a rule, if you are working with mixed resolutions and some clips are higher than 8-bit, you should select 16-bit FP graphics display. Even if you work only with 8-bit images, you can get better rendered results with 16-bit FP graphics rendering when transparencies, blending, and gradients are part of your effect. 16-bit FP graphics rendering produces better results but takes longer.