Bitmap Export Dialog Box - Bitmap Options
JPEG Quality
This setting is specific to JPEG output. A low setting will result in a small file with a loss in quality whereas a high value will give only slight file size reduction, but high quality. Note that a setting of 100% will still compress the file.
As an example, a setting of 75% gives good compression without causing a noticeable loss in quality for most uses.
Progressive
Selecting this option creates a 'progressive JPEG'. This is similar to an interlaced GIF and means that when the JPEG is displayed by a web browser that understands progressive JPEG files, it slowly comes into focus as it is downloaded. If the browser doesn't support progressive JPEG files, the JPEG is displayed only when the whole file has been downloaded, just as if the JPEG wasn't progressive.