raster image quality

[nchome]

Hi all, can anybody let me know how to improve the quality of images inserted into autocad.
I have been sent an image in PDF which i have scanned to create a TIFF. I have then inserted this into raster design which is where the quality is lost.
Is this an inherent problem which can't be avoided or should i be scanning to JPEG for instance.

Many thanks for any replies

[Railrose]

When you scan the image, is it scanned as a color, or bitonal image? Also, what resolution are using for scans?

If possible, I scan everything as a bitonal image at a resolution of 400 dpi.