ROI Processing in Geometric Transforms
All the transform functions described in this chapter operate in rectangular regions of interest (ROIs) that are
defined in both the source and destination images. The procedures for handling ROIs in geometric transform
functions differ from those used in other functions (see Regions of Interest in Intel IPP in chapter 2). The main
difference is that operations take place in the intersection of the transformed source ROI and the destination
ROI. More specifically, all geometric transform functions (except those which perform inverse warping operations)
handle ROIs with the following sequence of operations:
transform the rectangular ROI of the source image to quadrangle in the destination image;
find the intersection of this quadrangle and the rectangular ROI of the destination image;
update the destination image in the intersection area.
The coordinates in the source and destination images must have the same origin.
To fully describe a rectangular ROI, both its origin (coordinates of top left corner) and size must be referenced.
For geometrical transform functions, the source image ROI is specified by srcRoi parameter of IppiRect type,
meaning that all four values describing the rectangular ROI are given explicitly.
On the other hand, the destination image ROI for different functions can be specified either by dstRoi parameter
of IppiRect type, or dstRoiSize parameter of IppiSize type. In the latter case, only the destination ROI
size is passed, while its origin is referenced by pDst pointer.