FastN

Intel® Integrated Performance Primitives Developer Guide and Reference

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ID 790148

Date 11/07/2023

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FastN

Detects corners in an image using the FastN algorithm.

Syntax

IppStatus ippiFastN_8u_C1R(const Ipp8u* pSrc, int srcStep, Ipp8u* pDstCorner, int dstCornerStep, Ipp8u* pDstScore, int dstScoreStep, int* pNumCorner, IppiPoint srcRoiOffset, IppiSize dstRoiSize, IppiFastNSpec* pSpec, Ipp8u* pBuffer);

Include Files

ippcv.h

Domain Dependencies

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

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

Parameters

pSrc: Pointer to the source image.
srcStep: Distance, in bytes, between the starting points of consecutive lines in the source image.
pDstCorner: Pointer to the destination image with corners.
dstCornerStep: Distance, in bytes, between the starting points of consecutive lines in the destination image with corners.
pDstScore: Pointer to the destination image with scores.
dstScoreStep: Distance, in bytes, between the starting points of consecutive lines in the destination image with scores.
pNumCorner: Pointer to the calculated number of corners.
srcRoiOffset: Offset in the source image.
dstRoiSize: Size of the destination ROI, in pixels.
pSpec: Pointer to the specification structure.
pBuffer: Pointer to the work buffer.

Description

The ippiFastN function implements the FastN corner detection algorithm. This function detects corners in the source image, calculates orientation and score of corners.

The figures below show pixels location for different radius values.

Radius = 1

Radius = 2

Radius = 3

Radius = 5

Radius = 7

Radius = 9

The function defines a pixel as a corner if the value of N consecutive pixels located on the circle with the center at the current pixel is greater (less) than the value of the current - central pixel. Differences between the values of pixels on the circle and the central pixel value must be greater than the threshold value. In this case, the corresponding pixel of the pDstCorner image is set to the following values in binary format:

If greater - 01xxxxxx
If less - 10xxxxxx

If the IPP_FASTN_ORIENTATION mode is not set, xxxxxx = 000000, otherwise, xxxxxx = the number of sector (bin) to which the corner directs. The orientationBin parameter defines the number of sectors that is computed from the bottom clockwise. If the source pixel is not a corner, the corresponding pixel of pDstCorner is set to zero.

If the IPP_FASTN_SCORE_MODE0 mode is set, the corresponding pixel of pDstCorner is set to the corner score. Score is a maximum among minimal differences with threshold calculated for every N consecutive pixels. If the source pixel is not a corner, the corresponding pixel of pDstScore is set to zero.

If the IPP_FASTN_NMS mode is set, the corners that have a corner with the greater score among neighboring pixels are cancelled.

Return Values

ippStsNoErr

Indicates no error. Any other value indicates an error.

ippStsNullPtrErr

Indicates an error when:

pSrc, pDstCorner, pNumCorner, pSpec, or pBuffer is NULL
pDstScore is NULL if option is not equal to IPP_FASTN_SCORE_MODE0

ippStsSizeErr

Indicates an error when dstRoiSize is less than, or equal to zero.

ippDataTypeErr

Indicates an error when dataType has an illegal value.

ippNumChannelsErr

Indicates an error when numChannels has an illegal value.

ippOutOfRangeErr

Indicates an error when orientationBins or N has an illegal value.

ippBadArgsErr

Indicates an error when option or circleRadius has an illegal value.

ippThresholdErr

Indicates an error when threshold is negative.

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 corner finding FastN algorithm using Intel(R) Integrated Primitives (Intel(R) IPP) functions:
//     ippiFastNGetSize
//     ippiFastNInit
//     ippiFastNGetBufferSize
//     ippiFastN_8u_C1R
//     ippiFastN2DToVec_8u


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

/* 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 */

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

Ipp8u pSrc[16 * 16] = {/* Pointer to source images */
    0,     0,   0,   0,   0,   0,   0,   0,   0,   0,  70,  70,  70,  70,  70,  70,
    0,     0,   0,   0,   0,   0,   0,   0,   0,   0,  70,  70,  70,  70,  70,  70,
    0,     0,   0,   0,   0,   0,   0,   0,   0,   0,  70,  70,  70,  70,  70,  70,
    0,     0,   0,   0,   0,   0,   0,   0,   0,   0,  70,  70,  70,  70,  70,  70,
    0,     0,   0,   0,   0,   0,   0,   0,   0,   0,  70,  70,  70,  70,  70,  70,
    0,     0,   0,   0,   0,   0,   0,   0,   0,   0,  70,  70,  70,  70,  70,  70,
    0,     0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,
    255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
    255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
    255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
     10, 10,   10,  10,  10,  10, 255, 255, 255, 255, 255, 100, 100, 100, 100, 100,
     10, 10,   10,  10,  10,  10, 255, 255, 255, 255, 100, 100, 100, 100, 100, 100,
    10,  10, 10, 10, 10, 10, 255, 255, 255, 255, 100, 100, 100, 100, 100, 100,
    10,  10, 10, 10, 10, 10, 255, 255, 255, 255, 100, 100, 100, 100, 100, 100,
    10,  10, 10, 10, 10, 10, 255, 255, 255, 255, 100, 100, 100, 100, 100, 100,
    10,  10, 10, 10, 10, 10, 255, 255, 255, 255, 100, 100, 100, 100, 100, 100
};
IppiSize    srcSize = { 16 , 16 };   /* Size of source/destination ROI in pixels */
IppiSize    dstSize = { 16, 16 };
IppStatus   status = ippStsNoErr;
Ipp8u       pDstCorner[16 * 16];            /* Pointer to destination images */
IppiCornerFastN *pDstStruct = NULL;
int         srcStep = 16, dstCornerStep = 16; /* Steps, in bytes, through the source/destination images */
int         circleRadius = 3;     /* Radius for corner finding */
int         N = 9;                /*  Critical number of pixels that have different value */
int         orientationBins = 64; /* Number bins for defining direction */
int         option = IPP_FASTN_CIRCLE; /* Defines the mode of processing */
const IppDataType dataType = ipp8u;
int         nChannels = 1;
int         specSize = 0;       /* Size, in bytes, of the spec */
IppiFastNSpec *pSpec = NULL;    /* Pointer to Spec */
Ipp32f      threshold = 50.0f;  /* Level for definition of critical pixels */
int         bufSize = 0;        /* Work buffer size */
Ipp8u       *pBuffer = NULL;    /* Pointer to the work buffer */
int         maxLen = 0;         /* Length of array of structures */
IppiPoint   srcRoiOffset = { 0, 0 };   /* Offset in source image */
int         numRealCorners;   /* Number of corners */

int main(void)
{
    /* Initialization of Spec for FastN */
    check_sts( status = ippiFastNGetSize(srcSize, circleRadius, N, orientationBins, option, dataType, nChannels, &specSize) )

    pSpec = (IppiFastNSpec *)ippsMalloc_8u(specSize);

    /* Define spec size for FastN */
    check_sts( status = ippiFastNInit(srcSize, circleRadius, N, orientationBins, option, threshold, dataType, nChannels, pSpec) )

    check_sts( status = ippiFastNGetBufferSize(pSpec, dstSize, &bufSize) )

    pBuffer = ippsMalloc_8u(bufSize);

    /* Define size of working buffer for FastN */
    check_sts( status = ippiFastN_8u_C1R(pSrc, srcStep, pDstCorner, dstCornerStep, NULL, 0, &maxLen, srcRoiOffset, dstSize, pSpec, pBuffer) )

    pDstStruct = (IppiCornerFastN *)ippsMalloc_8u(sizeof(IppiCornerFastN)*maxLen);

    /* Corner finding with FastN */
    check_sts( status = ippiFastN2DToVec_8u(pDstCorner, dstCornerStep, NULL, 0, pDstStruct, dstSize, maxLen, &numRealCorners, pSpec) )

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

Parent topic: Feature Detection Functions

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Intel® Integrated Performance Primitives Developer Guide and Reference

FastN

Syntax

Include Files

Domain Dependencies

Parameters

Description

Return Values

Example

See Also