Mask tab for objects
Offset: The pixel offset of the top left corner of the bounding rectangle of the mask relative to the top left corner of the image. If you import a mask , set the offset (usually to 0,0) before loading the mask image.
Load: Use this option to import a mask from external applications, such as Photoshop. When you load mask information, you replace the mask for the current object without changing the masks for adjacent objects. Use this option when you import masks that are already synched to each other and do not overlap, or if you plan to move mask information back and forth between Image Authoring and another image editing application. After you import a mask with this option set, resync your image on the Mask page.
Show: Creates a view of the mask for this object in a separate window. You can save this view at its actual size using the Save As command. This is a read-only view, so you can't edit it.
Export: Saves the mask image at the same size as the full image, filling in the area around the mask with black. You can export in .PNG format only.