Impress becomes slow when background picture was added

I find this problem in LibreOffice 3.4.4 (Ubuntu 11.10), and LibreOffice 3.5.4 (OpenSUSE 12.2).

When I use Impress to edit file with many images, it still run fast. But if I add a simple background picture, Impress becomes extremely slow. Even when the file contains few pictures, and has a small size, Impress failed to run at normal performance.

I have tried to change the memory options, but it doesn’t work.

I finally find the reason. Because the background picture I use is PNG format and contains transparent area. After convert it to JPG format, Impress works as fast as normal.
Maybe the background picture we use should be JPG. PNG format with Alpha channel doesn’t fit for background picture.

Thank all of you!

Try to disable hardware acceleration or anti-aliasing for graphics output: menu Tools > Options > LibreOffice > View

That said, you should upgrade to the current release : LibreOffice 3.6.3