Overlays Overview

An "Overlay Plane" describes graphics or bit-mapped text that is associated with an image or has its own existence within a series. It may also describe a ROI in an Image. Each "Overlay Plane" is one bit deep (1BPP). Sixteen separate planes may be associated with an image or exist as "Standalone Overlays" in a series. Overlay pixel data is stored either in "Overlay Data" (60xx,3000) or embedded in the "Image Pixel Data" (7FE0,0010).

LEADTOOLS provides functionality to manipulate overlays in DICOM. The OverlayCount property specifies the number of overlays in the DICOM Data Set. The attributes of an overlay can be obtained using the following methods/properties:

$image\sqrblit.gif$ GetOverlayAttributes method: This method updates the properties of the OverlayAttributes property with the values of the attributes of the specified overlay. Most of the properties specified by the OverlayAttributes property are based on the Attributes of the Overlay Plane Module in the DICOM Standard.

$image\sqrblit.gif$ IsOverlayInDataSet method: This method specifies whether the overlay data of the specified overlay exists inside this Data Set.

$image\sqrblit.gif$ OverlayActivationLayer property: This property specifies the "Overlay Activation Layer" (60xx,1001) of the specified overlay.

$image\sqrblit.gif$ OverlayAttributes property: This property specifies the attributes of an overlay.

$image\sqrblit.gif$ OverlayGroupNumber property: This property specifies the group number of the specified overlay.

Use the GetOverlayBitmap method to retrieve the "Overlay Data" (60xx,3000) for a single-frame overlay or the GetOverlayBitmapList method for a multi-frame one. The GetOverlayBitmap method updates the OverlayBitmap property (ILEADDicomDS Interface) with the bitmap of an overlay, while the GetOverlayBitmapList method updates the OverlayBitmapList property (ILEADDicomDS Interface) with the frames of an overlay.

LEADTOOLS also allows you to insert a new or update an existing overlay. Use the SetOverlayAttributes method to set the attributes of a certain overlay and then use the SetOverlayBitmap method or the SetOverlayBitmapList method to set its data.

Call the DeleteOverlay method to delete all the elements related to an overlay.