Returns the transparency
mode used by this png image.
type TPNGTransparencyMode = (ptmNone, ptmBit, ptmTranslucid);
property TransparencyMode: TPNGTransparencyMode;
Description
There are currently three transparency modes for png: none when all the
image is opaque, bit when one color will be fully transparent and
translucid when all colors may have transparent values. This property is
mainly to mantain compability with Windows Delphi TBitmap since it
supports only None and Bit (Translucid data is lost when assigning to a
TBitmap).