Vertices of the Region Attribute
| Tag | (0028,9503) |
|---|---|
| Type | Conditionally Required (1C) |
| Keyword | VerticesOfTheRegion |
| Value Multiplicity | 2-2n |
| Value Representation | Signed Short (SS) |
Multiple Values where the first set of two values are:
row of the origin vertexcolumn of the origin vertex
Two or more pairs of values follow and are the row and column coordinates of the other vertices of the polygon region. Each polygon region is implicitly closed from the last vertex to the origin vertex and all edges shall be non-intersecting except at the vertices. See Section C.11.19.1.2.
The upper left pixel of the image has the coordinate 1\1.
Required if the pixel shift does not apply to the entire set of pixels of the frames.
Section C.11.19.1.2
C.11.19.1.2 Vertices of the Region
Each Item of the Region Pixel Shift Sequence (0028,9502) specifies both a region of the contrast frame and a mask pixel shift to be applied during the subtraction of that region.
When the Region Pixel Shift Sequence (0028,9502) contains more than one Item, each region of the contrast frame is subtracted by applying the corresponding pixel shift specified in that Item.
When an Item of the Sequence does not contain the Attribute Vertices of the Region (0028,9503), the applicable region for that Item is the whole contrast frame.
The union of all the regions defined in the Region Pixel Shift Sequence (0028,9502) does not cover necessarily the whole contrast frame, in which case the pixels outside the union of all the regions shall be subtracted with no pixel shift.
If a set of pixels of the contrast frame is contained in more than one region, the applicable pixel shift is the one of the last Item with the region that contains this set of pixels, as shown in Figure C.11.19-1.
Figure C.11.19-1. Applicable pixel shift in case of multiple pixel shift regions
Note
For example, the contrast frames 4 to 10 of a SOP Instance "A" are subtracted to the mask frame 1, the subtraction of the frames 4 to 7 being performed with three different values of mask pixel shift on overlapping rectangular regions: The (row,column) coordinates of the top-left and bottom-right vertices of the regions are 1: (1,1) to (30,60), 2: (10,40) to (50,120) and 3: (20,20) to (70,80). The mask pixel shift to be applied to the pixel (25,50) corresponds to the region 3 because this pixel is contained in the intersection of the three regions (see Figure C.11.19-2 and Figure C.11.19-3).
Figure C.11.19-2. Example of Contents of Mask Subtraction Sequence
Figure C.11.19-3. Example of three different pixel shift regions