Primitives

Both the source and destination images can have a ROI. In such cases the sizes of ROIs are assumed to be
the same while offsets may differ. Image processing is performed on data of the source ROI, and the results
are written to the destination ROI. In function call sequences, ROI is specified by:
• roiSize parameter of the IppiSize type
• pSrc and pDst pointers to the starts of source and destination ROI buffers
• srcStep and dstStep parameters that are equal to distances in bytes between the starting points of
consecutive lines in source and destination images, respectively.
Thus, the srcStep and dstStep parameters set steps in bytes through image buffers to start processing a new
line in the ROI of an image.
The following code example illustrates the use of the dstStep parameter in function calls:
Example
IppStatus roi( void ) {
Ipp8u x[8*3] = {0};
IppiSize roiSize = {3,2};
IppiPoint roiPoint = {2,1};
/// place the pointer to the ROI start position
return ippiSet_8u_C1R( 7, x+8*roiPoint.y+roiPoint.x, 8, roiSize );
}
The resulting image x contains the following data:
00 00 00 00 00 00 00 00
00 00 07 07 07 00 00 00
00 00 07 07 07 00 00 00
If ROI is present:
• source and destination images can have different sizes;
• lines may have padding at the end for aligning the line sizes;
• application must correctly define the pSrc, pDst, and roiSize parameters.
The pSrc and pDst parameters are the shifted pointers to the image data. For example, in case of ROI
operations on 3-bytes-per-pixel image data (8u_C3R), pSrc points to the start of the source ROI buffer and
can be interpreted as follows:
pSrc = pSrcImg + 3*(srcImgSize.width * srcRoiOffset.y + srcRoiOffset.x),
where
Intel ® Integrated Performance Primitives Concepts 2
pSrcImg
srcImgSize
srcRoiOffset
points to the start of the source image buffer
is the image size in pixels (of the IppiSize type)
determines an offset of ROI relative to the start of the image as shown in
Figure Image, ROI, and Offsets.
Another example for operations on four-channel image of 32-bit floating point data type 32f_AC4:
pSrc = (Ipp32f*)((Ipp8u*)pSrcImg + srcImgStep * srcRoiOffset.y
+ 4*SizeOf(Ipp32f)*srcRoiOffset.x.
In this example the multiplier 4 is used because the AC4 pixel consists of 4 values - R, G, B, A. Pointer type
conversion is required as in Intel IPP all image steps are always in bytes, and it is not recommended to use
step/SizeOf(Ipp32f) as in a general case step value may be not a multiple of 4.
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