SWF Settings
The JPEG quality number affects the quality of all images in the SWF except 8-bit GIFs and PNGs. The quality of a background image is entered in Movie > Background Image.
A low number means low quality and small SWF and a high number means high quality and a large SWF. All images are converted to bitmap format internally on import so the quality factor of imported JPGs is ignored. All images except 8-bit GIFs and PNGs are JPEG compressed on export to the SWF with the quality factor indicated here.