Type Default Value Read Only Static Description
Nullable<Boolean> null No No Whether to use the alpha channel.

Some file formats, such as PNG, allow an alpha channel to be exported to provide transparency. If you want an alpha channel in your saved image this value must be set to true. The alpha channel is derived from the alpha values in the Bitmap you are exporting.

If you leave this property as null then ImageGlue will decide whether to export alpha based on the image format you are using. In practical terms that means yes for PNG and no for everything else - which is what System.Drawing does.