Values in between represent varying degrees of partial transparency. Unfortunately, the Java implementation of transparency is fairly simplistic. As a result, it is not very useful to have more than one semi-transparent layer or to try to use shades of transparency to represent other information. Furthermore, the transparency value is only used for filled areas, not for lines or points. Transparent areas are much slower to render than solid filled areas, so it should be used sparingly.
Transparency is the inverse of the typical graphics alpha-blending.
The bounds parameter specifies the location of the upper-left corner of the image. The scale parameter specifies the size of the image pixels in the base units of viewer's coordinate system. The image parameter specifies the URL to be used in loading the image. The imageURL must not be enclosed in quotes and cannot include whitespace. This should be a decimal value between zero and one.