Shear

Syntax

Parameters

pSrc	Pointer to the source image origin. An array of separate pointers to each plane for 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 for 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).
xShear, yShear	Coefficients of the shearing transform.
xShift, yShift	Additional shift values along the horizontal and vertical axes.
interpolation	Specifies the interpolation mode. Possible values are:
	IPPI_INTER_NN - nearest neighbor interpolation
	IPPI_INTER_LINEAR - linear interpolation
	IPPI_INTER_CUBIC - cubic interpolation
	IPPI_INTER_CUBIC2P_CATMULLROM - Catmull-Rom spline
	the following flag is used additionally to the above modes:
	IPPI_SMOOTH_EDGE - edge smoothing

Description

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

This function performs shearing transform - it maps the source image pixel coordinates (x,y) according to the following formulas:

x' = x + xShear * y + xShift

y' = yShear *x + y + yShift ,

where x' and y' denote the pixel coordinates in the sheared image. The shearing transform is a special case of an affine transform, performed by the ippiWarpAffine function.

The transformed part of the image is resampled using the interpolation mode specified by the interpolation parameter, and written to the destination image ROI.

Figure “Shearing a Sample Image” gives an example of applying the shearing transform function ippiShear to a sample image.

Example “Using the function ippiShear” shows how to use the function ippiShear_8u_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 xShear*yShear = 1.
ippStsRectErr	Indicates an error condition if width or height of the intersection of the srcRoi and source image is less than or equal to 1.
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.

Using the function ippiShear

IppiSize srcSize = { 4, 4 };

IppiSize dstSize = { 7, 4 };

IppiRect srcRect = { 0, 0, 4, 4};

IppiRect dstRect = { 0, 0, 7, 4};

Ipp8u    src[4*4] = { 4, 4, 4, 4,

          3, 3, 3, 3,

          2, 2, 2, 2,

          1, 1, 1, 1 };

Ipp8u  dst[7*4];

double xShear = -1.0;

double yShear = 0.0;

double xShift = 3.0;

double yShift = 0.0;

ippiSet_8u_C1R (0, dst, 7, dstSize);

ippiShear_8u_C1R (src,srcSize, 4, srcRect, dst, 7, dstRect,  xShear, 
                    yShear,  xShift,  yShift,  IPPI_INTER_NN );

result:

4 4 4 4

3 3 3 3   src

2 2 2 2

1 1 1 1

0 0 0 4 4 4 4

0 0 3 3 3 3 0

0 2 2 2 2 0 0   dst

1 1 1 1 0 0 0