WarpPerspectiveNearest

Intel® Integrated Performance Primitives Developer Guide and Reference

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ID 790148

Date 11/07/2023

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WarpPerspectiveNearest

Performs warp perspective transformation of an image using the nearest neighbor interpolation method.

Syntax

IppStatus ippiWarpPerspectiveNearest_<mod>(const Ipp<datatype>* pSrc, int srcStep, Ipp<datatype> pDst, int dstStep, IppiPoint dstRoiOffset, IppiSize dstRoiSize, const IppiWarpSpec* pSpec, Ipp8u* pBuffer);

Supported values for mod:

8u_C1R	16u_C1R	16s_C1R	32f_C1R
8u_C3R	16u_C3R	16s_C3R	32f_C3R
8u_C4R	16u_C4R	16s_C4R	32f_C4R

Include Files

ippi.h

Domain Dependencies

Headers: ippcore.h, ippvm.h, ipps.h

Libraries: ippcore.lib, ippvm.lib, ipps.lib

Parameters

pSrc	Pointer to the source image.
srcStep	Distance, in bytes, between the starting points of consecutive lines in the source image buffer.
pDst	Pointer to the destination image ROI.
dstStep	Distance, in bytes, between the starting points of consecutive lines in the destination image buffer.
dstRoiOffset	Offset of the destination image ROI with respect to the destination image origin.
dstRoiSize	Size of the destination image ROI, in pixels.
pSpec	Pointer to the specification structure for the warp operation.
pBuffer	Pointer to the work buffer.

Description

This function transforms the source image pixel coordinates (x, y) according to the following formulas:

x' = (c₀₀*x + c₀₁*y + c₀₂)/ (c₂₀*x + c₂₁*y + c₂₂)

y' = (c₁₀*x + c₁₁*y + c₁₂)/(c₂₀*x + c₂₁*y + c₂₂)

where

x' and y' are the pixel coordinates in the transformed image
c_ij are the affine transform coefficients passed to the coeffs array during initialization

The ippiWarpPerspectiveNearest function operates with ROI (see Regions of Interest in Intel IPP). The transformed part of the source image is resampled with the nearest neighbor interpolation method and stored in the destination image ROI. You need to define the destination image ROI origin by the following parameters: the offset of the destination ROI with respect to the destination image origin and the destination image ROI size. The parameter pDst must point to the processed destination image ROI.

If you initialize the warp specification structure using the WarpPerspectiveNearestInit function, you can specify the source image ROI in the following ways:

Set the srcRoi value to ippRectInfinite, which means that the ROI is not specified. In this case, pSrc must point to the processed source image. Pixels that are outside the source image boundaries are computed according to the specified border type.
Set the srcRoi value to the part of the processed source image. In this case, pSrc must point to the processed source image ROI. The operations take place only inside the specified region of interest srcRoi. It means that the destination image pixels mapped to the outer pixels of the specified source image region are not changed.

If you initialize the warp specification structure using the WarpQuadNearestInit function, set the pSrc value to the processed source image. The operations take place only inside the source quadrangle srcQuad that is specified in the WarpQuadNearestInit function.

To specify the algorithm for borders processing, set the borderType and pBorderValue parameters when initializing the IppiWarpSpec structure. The data type of borderValue is automatically converted from Ipp64f to the data type of the processed images. The function supports the following algorithms for borders processing:

If the border type is equal to ippBorderRepl, the source image outer pixels are replicated from the edge pixels.
If the border type is equal to ippBorderConst, the outer pixels are set to the constant value specified in pBorderValue.
If the border type is equal to ippBorderTransp or ippBorderInMem, destination image pixels mapped to the outer source image pixels are not changed.

Before using the ippiWarpPerspectiveNearest function, you need to initialize the IppiWarpSpec structure using the WarpPerspectiveNearestInit function and compute the size of the external buffer pBuffer using the WarpGetBufferSize function.

To compute the perspective transform parameters, use the GetPerspectiveQuad, GetPerspectiveBound, and GetPerspectiveTransform functions.

Return Values

ippStsNoErr	Indicates no error.
ippStsNullPtrErr	Indicates an error when one of the specified pointers is NULL.
ippStsNoOperation	Indicates a warning when width or height of the destination image is equal to zero.
ippStsContextMatchErr	Indicates an error when context data is invalid.
ippStsNotSupportedModeErr	Indicates an error when the requested mode is not supported.
ippStsSizeErr	Indicates an error when width or height of the source or destination image ROI is negative.
ippStsStepErr	Indicates an error when the step value is not a multiple of data type.
ippStsOutOfRangeErr	Indicates an error when the destination image offset point is outside the destination image origin.
ippStsSizeWrn	Indicates a warning when the destination image ROI size is more than the destination image origin size.
ippStsWrongIntersectQuad	Indicates a warning that no operation is performed if the transformed source image extended with borders has no intersection with the destination image.

Example

/*******************************************************************************
* Copyright 2015 Intel Corporation.
*
*
* This software and the related documents are Intel copyrighted materials, and your use of them is governed by
* the express license under which they were provided to you ('License'). Unless the License provides otherwise,
* you may not use, modify, copy, publish, distribute, disclose or transmit this software or the related
* documents without Intel's prior written permission.
* This software and the related documents are provided as is, with no express or implied warranties, other than
* those that are expressly stated in the License.
*******************************************************************************/

// A simple example of the warp perspective transform 
// using Intel(R) Integrated Primitives (Intel(R) IPP) functions:
//     ippiWarpPerspectiveGetSize
//     ippiWarpPerspectiveCubicInit
//     ippiWarpGetBufferSize
//     ippiWarpPerspectiveCubic_8u_C3R


#include <stdio.h>
#include "ipp.h"

#define WIDTH  640 /* Source image width */
#define HEIGHT 480 /* Destination image width */

/* Next two defines are created to simplify code reading and understanding */
#define EXIT_MAIN exitLine:                                  /* Label for Exit */
#define check_sts(st) if((st) != ippStsNoErr) goto exitLine; /* Go to Exit if Intel(R) IPP function returned status different from ippStsNoErr */

static const double coeffs[3][3] = { /* Coefficients for the perspective transform */
    { 2.3439242437790240     , 0.0025160437043002296  , -499.09988916944815, },
    { 0.0058031616363677600  , 1.4997057893818542     , -181.04366815436885, },
    { 1.1527998857985334e-005, 1.9607666631981373e-006, 0.99730924424366529  }
};

/* Results of ippMalloc() are not validated because Intel(R) IPP functions perform bad arguments check and will return an appropriate status  */

int main(void)
{
    IppStatus status = ippStsNoErr;
    Ipp8u* pSrc = NULL, *pDst = NULL; /* Pointers to source/destination images */
    int srcStep = 0, dstStep = 0;     /* Steps, in bytes, through the source/destination images */
    IppiSize srcSize = { WIDTH, HEIGHT }, dstSize = { WIDTH, HEIGHT }; /* Size of source/destination ROI in pixels */
    IppiWarpSpec* pSpec = NULL; /* Pointer to the specification structure */
    Ipp8u* pInitBuf = NULL;     /* Pointer to temporary buffer for transform initialization*/
    Ipp8u* pBuffer  = NULL;     /* Pointer to the work buffer */

    pSrc = ippiMalloc_8u_C3(srcSize.width, srcSize.height, &srcStep);
    pDst = ippiMalloc_8u_C3(dstSize.width, dstSize.height, &dstStep);

    /* Start perspective transform */
    {
        int    specSize = 0;        /* Size, in bytes, of the specification structure */
        int    initSize = 0;        /* Size, in bytes, of the temporary buffer */
        int    bufSize  = 0;        /* Size, in bytes, of the work buffer */
        const Ipp32s numChannels = 3;
        IppiPoint dstOffset = { 0, 0 }; /* Offset of the destination image ROI with respect to the destination image origin */
        IppStatus status = ippStsNoErr;
        IppiBorderType   borderType = ippBorderConst;
        IppiWarpDirection direction = ippWarpForward; /* Transformation direction */
        Ipp64f pBorderValue[3];
        Ipp64f valB = 0.0, valC = 0.5;     /* Catmull-Rom filter coefficients for cubic interpolation */
        IppiRect srcRoi = ippRectInfinite; /* Region of interest is not specified */
        int smoothEdge = 0; /* Flag for edge smoothing */
        IppiInterpolationType interpolation = ippCubic;
        int i = 0;

        for (i = 0; i < numChannels; ++i) pBorderValue[i] = 255.0;

        /* Computes the size of the specification structure and the size of the external work buffer for the warp perspective transform */
        check_sts( status = ippiWarpPerspectiveGetSize(srcSize, srcRoi, dstSize, ipp8u, coeffs, interpolation, direction, borderType, &specSize, &initSize) )

        pSpec    = (IppiWarpSpec*)ippsMalloc_8u(specSize);
        pInitBuf = ippsMalloc_8u(initSize);

        /* Initializes the specification structure for image perspective warping with the cubic interpolation method */
        check_sts( status = ippiWarpPerspectiveCubicInit(srcSize, srcRoi, dstSize, ipp8u, coeffs, direction, numChannels, valB, valC, borderType, pBorderValue, smoothEdge, pSpec, pInitBuf) )

        /* Work buffer size */
        check_sts( status = ippiWarpGetBufferSize(pSpec, dstSize, &bufSize) )

        pBuffer = ippsMalloc_8u(bufSize);

        /* Performs warp perspective transformation of an image using the cubic interpolation method */
        check_sts( status = ippiWarpPerspectiveCubic_8u_C3R(pSrc, srcStep, pDst, dstStep, dstOffset, dstSize, pSpec, pBuffer) )
    }

EXIT_MAIN
    ippsFree(pInitBuf);
    ippsFree(pSpec);
    ippsFree(pBuffer);
    ippiFree(pSrc);
    ippiFree(pDst);
    printf("Exit status %d (%s)\n", (int)status, ippGetStatusString(status));
    return (int)status;
}

Parent topic: Warp Functions with Prior Initialization

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Intel® Integrated Performance Primitives Developer Guide and Reference

WarpPerspectiveNearest

Syntax

Include Files

Domain Dependencies

Parameters

Description

Return Values

Example

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