C.11.19.1 XA/XRF Presentation State Mask Attributes

C.11.19.1.1 Mask Sub-pixel Shift

A pair of floating point numbers specifying the fractional vertical [adjacent row spacing] and horizontal [adjacent column spacing] pixel shift applied to the mask before subtracting it from the specified region of the contrast frame. The row offset results in a shift of the pixels along the column axis. The column offset results in a shift of the pixels along the row axis. A positive row offset is a shift toward the pixels of the lower row of the pixel plane. A positive column offset is a shift toward the pixels of the left hand side column of the pixel plane.

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.

[pic]

Figure C.11.19-1Applicable pixel shift in case of multiple pixel shift region s

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 Figures C.11.19-2 and C.11.19-3).

Mask Subtraction Sequence (0028,6100)
Item 1
>Referenced Image Sequence (0008,1140)
Item 1
>>Referenced SOP Class UID (0008,1150) = 1.2.840.10008.5.1.4.1.1.12.1.1
>>Referenced SOP Instance UID (0008,1155) = UID "A"
>Mask Operation (0028,6101) = AVG_SUB
>Applicable Frame range (0028,6102) = 4\10
>Mask Frame Numbers (0028,6110) = 1
>Pixel Shift Sequence (0028,9510)
Item 1
>>Pixel Shift Frame range (0029,9506) = 4\7
>>Region Pixel Shift Sequence (0029,9506)
Frame Display Shutter Sequence (0018,9472) 1 Sequence of shutter specifications to be applied to groups of frames. One or more Items shall be included in this sequence.
>Referenced Image Sequence (0008,1140) 1C Sequence of Items where each Item provides reference to a selected set of Image SOP Class/SOP Instance pairs that are defined in the Presentation State Relationship Module. One or more Items shall be included in this sequence. Required if shutters in this Item do not apply to all the images and frames listed in the Presentation State Relationship Module.
>>Include ‘Image SOP Instance Reference Macro’ Table 10-3
>Include ‘Display Shutter Macro’ Table C.7-17A.