opencv/modules/features2d/src/fast.cpp

/* This is FAST corner detector, contributed to OpenCV by the author, Edward Rosten.
   Below is the original copyright and the references */

/*
Copyright (c) 2006, 2008 Edward Rosten
All rights reserved.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions
are met:

	*Redistributions of source code must retain the above copyright
	 notice, this list of conditions and the following disclaimer.

	*Redistributions in binary form must reproduce the above copyright
	 notice, this list of conditions and the following disclaimer in the
	 documentation and/or other materials provided with the distribution.

	*Neither the name of the University of Cambridge nor the names of
	 its contributors may be used to endorse or promote products derived
	 from this software without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR
CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/

/*
The references are:
 * Machine learning for high-speed corner detection,
   E. Rosten and T. Drummond, ECCV 2006
 * Faster and better: A machine learning approach to corner detection
   E. Rosten, R. Porter and T. Drummond, PAMI, 2009
*/

#include "precomp.hpp"

namespace cv
{

static void makeOffsets(int pixel[], int row_stride)
{
    pixel[0] = 0 + row_stride * 3;
    pixel[1] = 1 + row_stride * 3;
    pixel[2] = 2 + row_stride * 2;
    pixel[3] = 3 + row_stride * 1;
    pixel[4] = 3 + row_stride * 0;
    pixel[5] = 3 + row_stride * -1;
    pixel[6] = 2 + row_stride * -2;
    pixel[7] = 1 + row_stride * -3;
    pixel[8] = 0 + row_stride * -3;
    pixel[9] = -1 + row_stride * -3;
    pixel[10] = -2 + row_stride * -2;
    pixel[11] = -3 + row_stride * -1;
    pixel[12] = -3 + row_stride * 0;
    pixel[13] = -3 + row_stride * 1;
    pixel[14] = -2 + row_stride * 2;
    pixel[15] = -1 + row_stride * 3;
}

static int cornerScore(const uchar* ptr, const int pixel[], int threshold)
{
    const int K = 8, N = 16 + K + 1;
    int k, v = ptr[0];
    short d[N];
    for( k = 0; k < N; k++ )
        d[k] = (short)(v - ptr[pixel[k]]);

#if CV_SSE2
    __m128i q0 = _mm_set1_epi16(-1000), q1 = _mm_set1_epi16(1000);
    for( k = 0; k < 16; k += 8 )
    {
        __m128i v0 = _mm_loadu_si128((__m128i*)(d+k+1));
        __m128i v1 = _mm_loadu_si128((__m128i*)(d+k+2));
        __m128i a = _mm_min_epi16(v0, v1);
        __m128i b = _mm_max_epi16(v0, v1);
        v0 = _mm_loadu_si128((__m128i*)(d+k+3));
        a = _mm_min_epi16(a, v0);
        b = _mm_max_epi16(b, v0);
        v0 = _mm_loadu_si128((__m128i*)(d+k+4));
        a = _mm_min_epi16(a, v0);
        b = _mm_max_epi16(b, v0);
        v0 = _mm_loadu_si128((__m128i*)(d+k+5));
        a = _mm_min_epi16(a, v0);
        b = _mm_max_epi16(b, v0);
        v0 = _mm_loadu_si128((__m128i*)(d+k+6));
        a = _mm_min_epi16(a, v0);
        b = _mm_max_epi16(b, v0);
        v0 = _mm_loadu_si128((__m128i*)(d+k+7));
        a = _mm_min_epi16(a, v0);
        b = _mm_max_epi16(b, v0);
        v0 = _mm_loadu_si128((__m128i*)(d+k+8));
        a = _mm_min_epi16(a, v0);
        b = _mm_max_epi16(b, v0);
        v0 = _mm_loadu_si128((__m128i*)(d+k));
        q0 = _mm_max_epi16(q0, _mm_min_epi16(a, v0));
        q1 = _mm_min_epi16(q1, _mm_max_epi16(b, v0));
        v0 = _mm_loadu_si128((__m128i*)(d+k+9));
        q0 = _mm_max_epi16(q0, _mm_min_epi16(a, v0));
        q1 = _mm_min_epi16(q1, _mm_max_epi16(b, v0));
    }
    q0 = _mm_max_epi16(q0, _mm_sub_epi16(_mm_setzero_si128(), q1));
    q0 = _mm_max_epi16(q0, _mm_unpackhi_epi64(q0, q0));
    q0 = _mm_max_epi16(q0, _mm_srli_si128(q0, 4));
    q0 = _mm_max_epi16(q0, _mm_srli_si128(q0, 2));
    threshold = (short)_mm_cvtsi128_si32(q0) - 1;
#else
    int a0 = threshold;
    for( k = 0; k < 16; k += 2 )
    {
        int a = std::min((int)d[k+1], (int)d[k+2]);
        a = std::min(a, (int)d[k+3]);
        if( a <= a0 )
            continue;
        a = std::min(a, (int)d[k+4]);
        a = std::min(a, (int)d[k+5]);
        a = std::min(a, (int)d[k+6]);
        a = std::min(a, (int)d[k+7]);
        a = std::min(a, (int)d[k+8]);
        a0 = std::max(a0, std::min(a, (int)d[k]));
        a0 = std::max(a0, std::min(a, (int)d[k+9]));
    }

    int b0 = -a0;
    for( k = 0; k < 16; k += 2 )
    {
        int b = std::max((int)d[k+1], (int)d[k+2]);
        b = std::max(b, (int)d[k+3]);
        b = std::max(b, (int)d[k+4]);
        b = std::max(b, (int)d[k+5]);
        if( b >= b0 )
            continue;
        b = std::max(b, (int)d[k+6]);
        b = std::max(b, (int)d[k+7]);
        b = std::max(b, (int)d[k+8]);

        b0 = std::min(b0, std::max(b, (int)d[k]));
        b0 = std::min(b0, std::max(b, (int)d[k+9]));
    }

    threshold = -b0-1;
#endif

#if 0
    // check that with the computed "threshold" the pixel is still a corner
    // and that with the increased-by-1 "threshold" the pixel is not a corner anymore
    for( int delta = 0; delta <= 1; delta++ )
    {
        int v0 = std::min(ptr[0] + threshold + delta, 255);
        int v1 = std::max(ptr[0] - threshold - delta, 0);
        int c0 = 0, c1 = 0;

        for( int k = 0; k < N; k++ )
        {
            int x = ptr[pixel[k]];
            if(x > v0)
            {
                if( ++c0 > K )
                    break;
                c1 = 0;
            }
            else if( x < v1 )
            {
                if( ++c1 > K )
                    break;
                c0 = 0;
            }
            else
            {
                c0 = c1 = 0;
            }
        }
        CV_Assert( (delta == 0 && std::max(c0, c1) > K) ||
                   (delta == 1 && std::max(c0, c1) <= K) );
    }
#endif
    return threshold;
}


void FAST(InputArray _img, std::vector<KeyPoint>& keypoints, int threshold, bool nonmax_suppression)
{
    Mat img = _img.getMat();
    const int K = 8, N = 16 + K + 1;
    int i, j, k, pixel[N];
    makeOffsets(pixel, (int)img.step);
    for(k = 16; k < N; k++)
        pixel[k] = pixel[k - 16];

    keypoints.clear();

    threshold = std::min(std::max(threshold, 0), 255);

#if CV_SSE2
    __m128i delta = _mm_set1_epi8(-128), t = _mm_set1_epi8((char)threshold), K16 = _mm_set1_epi8((char)K);
#endif
    uchar threshold_tab[512];
    for( i = -255; i <= 255; i++ )
        threshold_tab[i+255] = (uchar)(i < -threshold ? 1 : i > threshold ? 2 : 0);

    AutoBuffer<uchar> _buf((img.cols+16)*3*(sizeof(int) + sizeof(uchar)) + 128);
    uchar* buf[3];
    buf[0] = _buf; buf[1] = buf[0] + img.cols; buf[2] = buf[1] + img.cols;
    int* cpbuf[3];
    cpbuf[0] = (int*)alignPtr(buf[2] + img.cols, sizeof(int)) + 1;
    cpbuf[1] = cpbuf[0] + img.cols + 1;
    cpbuf[2] = cpbuf[1] + img.cols + 1;
    memset(buf[0], 0, img.cols*3);

    for(i = 3; i < img.rows-2; i++)
    {
        const uchar* ptr = img.ptr<uchar>(i) + 3;
        uchar* curr = buf[(i - 3)%3];
        int* cornerpos = cpbuf[(i - 3)%3];
        memset(curr, 0, img.cols);
        int ncorners = 0;

        if( i < img.rows - 3 )
        {
            j = 3;
    #if CV_SSE2
            for(; j < img.cols - 16 - 3; j += 16, ptr += 16)
            {
                __m128i m0, m1;
                __m128i v0 = _mm_loadu_si128((const __m128i*)ptr);
                __m128i v1 = _mm_xor_si128(_mm_subs_epu8(v0, t), delta);
                v0 = _mm_xor_si128(_mm_adds_epu8(v0, t), delta);

                __m128i x0 = _mm_sub_epi8(_mm_loadu_si128((const __m128i*)(ptr + pixel[0])), delta);
                __m128i x1 = _mm_sub_epi8(_mm_loadu_si128((const __m128i*)(ptr + pixel[4])), delta);
                __m128i x2 = _mm_sub_epi8(_mm_loadu_si128((const __m128i*)(ptr + pixel[8])), delta);
                __m128i x3 = _mm_sub_epi8(_mm_loadu_si128((const __m128i*)(ptr + pixel[12])), delta);
                m0 = _mm_and_si128(_mm_cmpgt_epi8(x0, v0), _mm_cmpgt_epi8(x1, v0));
                m1 = _mm_and_si128(_mm_cmpgt_epi8(v1, x0), _mm_cmpgt_epi8(v1, x1));
                m0 = _mm_or_si128(m0, _mm_and_si128(_mm_cmpgt_epi8(x1, v0), _mm_cmpgt_epi8(x2, v0)));
                m1 = _mm_or_si128(m1, _mm_and_si128(_mm_cmpgt_epi8(v1, x1), _mm_cmpgt_epi8(v1, x2)));
                m0 = _mm_or_si128(m0, _mm_and_si128(_mm_cmpgt_epi8(x2, v0), _mm_cmpgt_epi8(x3, v0)));
                m1 = _mm_or_si128(m1, _mm_and_si128(_mm_cmpgt_epi8(v1, x2), _mm_cmpgt_epi8(v1, x3)));
                m0 = _mm_or_si128(m0, _mm_and_si128(_mm_cmpgt_epi8(x3, v0), _mm_cmpgt_epi8(x0, v0)));
                m1 = _mm_or_si128(m1, _mm_and_si128(_mm_cmpgt_epi8(v1, x3), _mm_cmpgt_epi8(v1, x0)));
                m0 = _mm_or_si128(m0, m1);
                int mask = _mm_movemask_epi8(m0);
                if( mask == 0 )
                    continue;
                if( (mask & 255) == 0 )
                {
                    j -= 8;
                    ptr -= 8;
                    continue;
                }

                __m128i c0 = _mm_setzero_si128(), c1 = c0, max0 = c0, max1 = c0;
                for( k = 0; k < N; k++ )
                {
                    __m128i x = _mm_xor_si128(_mm_loadu_si128((const __m128i*)(ptr + pixel[k])), delta);
                    m0 = _mm_cmpgt_epi8(x, v0);
                    m1 = _mm_cmpgt_epi8(v1, x);

                    c0 = _mm_and_si128(_mm_sub_epi8(c0, m0), m0);
                    c1 = _mm_and_si128(_mm_sub_epi8(c1, m1), m1);

                    max0 = _mm_max_epu8(max0, c0);
                    max1 = _mm_max_epu8(max1, c1);
                }

                max0 = _mm_max_epu8(max0, max1);
                int m = _mm_movemask_epi8(_mm_cmpgt_epi8(max0, K16));

                for( k = 0; m > 0 && k < 16; k++, m >>= 1 )
                    if(m & 1)
                    {
                        cornerpos[ncorners++] = j+k;
                        if(nonmax_suppression)
                            curr[j+k] = (uchar)cornerScore(ptr+k, pixel, threshold);
                    }
            }
    #endif
            for( ; j < img.cols - 3; j++, ptr++ )
            {
                int v = ptr[0];
                const uchar* tab = &threshold_tab[0] - v + 255;
                int d = tab[ptr[pixel[0]]] | tab[ptr[pixel[8]]];

                if( d == 0 )
                    continue;

                d &= tab[ptr[pixel[2]]] | tab[ptr[pixel[10]]];
                d &= tab[ptr[pixel[4]]] | tab[ptr[pixel[12]]];
                d &= tab[ptr[pixel[6]]] | tab[ptr[pixel[14]]];

                if( d == 0 )
                    continue;

                d &= tab[ptr[pixel[1]]] | tab[ptr[pixel[9]]];
                d &= tab[ptr[pixel[3]]] | tab[ptr[pixel[11]]];
                d &= tab[ptr[pixel[5]]] | tab[ptr[pixel[13]]];
                d &= tab[ptr[pixel[7]]] | tab[ptr[pixel[15]]];

                if( d & 1 )
                {
                    int vt = v - threshold, count = 0;

                    for( k = 0; k < N; k++ )
                    {
                        int x = ptr[pixel[k]];
                        if(x < vt)
                        {
                            if( ++count > K )
                            {
                                cornerpos[ncorners++] = j;
                                if(nonmax_suppression)
                                    curr[j] = (uchar)cornerScore(ptr, pixel, threshold);
                                break;
                            }
                        }
                        else
                            count = 0;
                    }
                }

                if( d & 2 )
                {
                    int vt = v + threshold, count = 0;

                    for( k = 0; k < N; k++ )
                    {
                        int x = ptr[pixel[k]];
                        if(x > vt)
                        {
                            if( ++count > K )
                            {
                                cornerpos[ncorners++] = j;
                                if(nonmax_suppression)
                                    curr[j] = (uchar)cornerScore(ptr, pixel, threshold);
                                break;
                            }
                        }
                        else
                            count = 0;
                    }
                }
            }
        }

        cornerpos[-1] = ncorners;

        if( i == 3 )
            continue;

        const uchar* prev = buf[(i - 4 + 3)%3];
        const uchar* pprev = buf[(i - 5 + 3)%3];
        cornerpos = cpbuf[(i - 4 + 3)%3];
        ncorners = cornerpos[-1];

        for( k = 0; k < ncorners; k++ )
        {
            j = cornerpos[k];
            int score = prev[j];
            if( !nonmax_suppression ||
               (score > prev[j+1] && score > prev[j-1] &&
                score > pprev[j-1] && score > pprev[j] && score > pprev[j+1] &&
                score > curr[j-1] && score > curr[j] && score > curr[j+1]) )
            {
                keypoints.push_back(KeyPoint((float)j, (float)(i-1), 7.f, -1, (float)score));
            }
        }
    }
}


/*
 *   FastFeatureDetector
 */
FastFeatureDetector::FastFeatureDetector( int _threshold, bool _nonmaxSuppression )
: threshold(_threshold), nonmaxSuppression(_nonmaxSuppression)
{}

void FastFeatureDetector::detectImpl( const Mat& image, vector<KeyPoint>& keypoints, const Mat& mask ) const
{
    Mat grayImage = image;
    if( image.type() != CV_8U ) cvtColor( image, grayImage, CV_BGR2GRAY );
    FAST( grayImage, keypoints, threshold, nonmaxSuppression );
    KeyPointsFilter::runByPixelsMask( keypoints, mask );
}

}