WarpAffineBack

Syntax

Parameters

pSrc	Pointer to the source image origin. An array of separate pointers to each plane in case of data in planar format.
srcSize	Size in pixels of the source image.
srcStep	Distance in bytes between starts of consecutive lines in the source image buffer.
srcRoi	Region of interest in the source image (of the IppiRect type).
pDst	Pointer to the destination image origin. An array of separate pointers to each plane in case of data in planar format.
dstStep	Distance in bytes between starts of consecutive lines in the destination image buffer.
dstRoi	Region of interest in the destination image (of the IppiRect type).
coeffs	The affine transform coefficients.
interpolation	Specifies the interpolation mode. Use one of the following values: IPPI_INTER_NN nearest neighbor interpolation IPPI_INTER_LINEAR linear interpolation IPPI_INTER_CUBIC cubic interpolation

Description

The function ippiWarpAffineBack is declared in the ippi.h file. It operates with ROI (see ROI Processing in Geometric Transforms).

This function performs the inverse transform to that defined by ippiWarpAffine function. Pixel coordinates x' and y' in the transformed image are obtained from the following equations:

c₀₀* x' + c₀₁* y' + c₀₂ = x

c₁₀* x' + c₁₁* y' + c₁₂ = y

where x and y denote the pixel coordinates in the source image, and coefficients c_ij are given in the array coeffs. Thus, you do not need to invert transform coefficients in your application program before calling ippiWarpAffineBack.

Note that inverse transform functions handle source and destination ROI in a different way than other geometric transform functions. Their implementation include the following logic:

• backward transform is applied to coordinates of each pixel in the destination ROI, which gives as a result coordinates of some pixel in the source image
• if the obtained source pixel is inside source ROI, the corresponding pixel in destination ROI is modified accordingly; otherwise no change is made.

The above algorithm can be represented in pseudocode as follows:

for (j = dstRoi.y; j < dstRoi.y + dstRoi.height; j ++) {

for (i = dstRoi.x; i < dstRoi.x + dstRoi.width; i ++) {

sx = TransformX(i, j); sy = TransformY(i, j);

if (sx >= srcRoi.x && sx < srcRoi.x + srcRoi.width && sy >= srcRoi.y && sy < srcRoi.y + srcRoi.height) {

dst[i, j] = Interpolate(sx, sy);} } }

Example “Using the function ippiShear” shows how to use the function ippiWarpAffineBack_32f_C1R.

Return Values

ippStsNoErr	Indicates no error. Any other value indicates an error or a warning.
ippStsNullPtrErr	Indicates an error condition if one of the specified pointers is NULL.
ippStsSizeErr	Indicates an error condition if any image dimension has zero or negative value.
ippStsStepErr	Indicates an error condition if srcStep or dstStep has a zero or negative value.
ippStsInterpolationErr	Indicates an error condition if interpolation has an illegal value.
ippStsCoeffErr	Indicates an error condition if c00*c11 - c01*c10 = 0.
ippStsWrongIntersectROIErr	Indicates an error condition if srcRoi has no intersection with the source image.
ippStsWrongIntersectQuad	Indicates a warning that no operation is performed if the transformed source ROI has no intersection with the destination ROI.