Region Pixel Shift Sequence Attribute
| Tag | (0028,9502) |
|---|---|
| Type | Required (1) |
| Keyword | RegionPixelShiftSequence |
| Value Multiplicity | 1 |
| Value Representation | Sequence (SQ) |
Sequence containing the pixel shifts for this frame(s).
Only one sub region of this frame(s) shall be specified when the pixel shift is applicable for the full size or a single region of the frame(s).
More than one sub region of this frame(s) may be specified when pixel shift is different in different regions.
The order of Items in this Sequence is significant, see Section C.11.19.1.2.
One or more Items shall be included in this Sequence.
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