opencv：L1距离，L2距离，颜色失真（color distortion），汉明距离（hamming distance），LUT

#pragma once

#include <opencv2/core/types_c.h>

//! computes the L1 distance between two integer values
template<typename T> static inline typename std::enable_if<std::is_integral<T>::value,size_t>::type L1dist(T a, T b) {
return (size_t)abs((int)a-b);
}

//! computes the L1 distance between two float values
template<typename T> static inline typename std::enable_if<std::is_floating_point<T>::value,float>::type L1dist(T a, T b) {
return fabs((float)a-(float)b);
}

//! computes the L1 distance between two generic arrays
template<size_t nChannels, typename T> static inline auto L1dist(const T* a, const T* b) -> decltype(L1dist(*a,*b)) {
decltype(L1dist(*a,*b)) oResult = 0;
for(size_t c=0; c<nChannels; ++c)
oResult += L1dist(a[c],b[c]);
return oResult;
}

//! computes the L1 distance between two generic arrays
template<size_t nChannels, typename T> static inline auto L1dist(const T* a, const T* b, size_t nElements, const uchar* m=NULL) -> decltype(L1dist<nChannels>(a,b)) {
decltype(L1dist<nChannels>(a,b)) oResult = 0;
size_t nTotElements = nElements*nChannels;
if(m) {
for(size_t n=0,i=0; n<nTotElements; n+=nChannels,++i)
if(m[i])
oResult += L1dist<nChannels>(a+n,b+n);
}
else {
for(size_t n=0; n<nTotElements; n+=nChannels)
oResult += L1dist<nChannels>(a+n,b+n);
}
return oResult;
}

//! computes the L1 distance between two generic arrays
template<typename T> static inline auto L1dist(const T* a, const T* b, size_t nElements, size_t nChannels, const uchar* m=NULL) -> decltype(L1dist<3>(a,b,nElements,m)) {
CV_Assert(nChannels>0 && nChannels<=4);
switch(nChannels) {
case 1: return L1dist<1>(a,b,nElements,m);
case 2: return L1dist<2>(a,b,nElements,m);
case 3: return L1dist<3>(a,b,nElements,m);
case 4: return L1dist<4>(a,b,nElements,m);
default: return 0;
}
}

//! computes the L1 distance between two opencv vectors
template<size_t nChannels, typename T> static inline auto L1dist_(const cv::Vec<T,nChannels>& a, const cv::Vec<T,nChannels>& b) -> decltype(L1dist<nChannels,T>((T*)(0),(T*)(0))) {
T a_array[nChannels], b_array[nChannels];
for(size_t c=0; c<nChannels; ++c) {
a_array[c] = a[(int)c];
b_array[c] = b[(int)c];
}
return L1dist<nChannels>(a_array,b_array);
}

///////////////////////////////////////////////////////////////////////////////////////////////////

//! computes the squared L2 distance between two generic variables
template<typename T> static inline auto L2sqrdist(T a, T b) -> decltype(L1dist(a,b)) {
auto oResult = L1dist(a,b);
return oResult*oResult;
}

//! computes the squared L2 distance between two generic arrays
template<size_t nChannels, typename T> static inline auto L2sqrdist(const T* a, const T* b) -> decltype(L2sqrdist(*a,*b)) {
decltype(L2sqrdist(*a,*b)) oResult = 0;
for(size_t c=0; c<nChannels; ++c)
oResult += L2sqrdist(a[c],b[c]);
return oResult;
}

//! computes the squared L2 distance between two generic arrays
template<size_t nChannels, typename T> static inline auto L2sqrdist(const T* a, const T* b, size_t nElements, const uchar* m=NULL) -> decltype(L2sqrdist<nChannels>(a,b)) {
decltype(L2sqrdist<nChannels>(a,b)) oResult = 0;
size_t nTotElements = nElements*nChannels;
if(m) {
for(size_t n=0,i=0; n<nTotElements; n+=nChannels,++i)
if(m[i])
oResult += L2sqrdist<nChannels>(a+n,b+n);
}
else {
for(size_t n=0; n<nTotElements; n+=nChannels)
oResult += L2sqrdist<nChannels>(a+n,b+n);
}
return oResult;
}

//! computes the squared L2 distance between two generic arrays
template<typename T> static inline auto L2sqrdist(const T* a, const T* b, size_t nElements, size_t nChannels, const uchar* m=NULL) -> decltype(L2sqrdist<3>(a,b,nElements,m)) {
CV_Assert(nChannels>0 && nChannels<=4);
switch(nChannels) {
case 1: return L2sqrdist<1>(a,b,nElements,m);
case 2: return L2sqrdist<2>(a,b,nElements,m);
case 3: return L2sqrdist<3>(a,b,nElements,m);
case 4: return L2sqrdist<4>(a,b,nElements,m);
default: return 0;
}
}

//! computes the squared L2 distance between two opencv vectors
template<size_t nChannels, typename T> static inline auto L2sqrdist_(const cv::Vec<T,nChannels>& a, const cv::Vec<T,nChannels>& b) -> decltype(L2sqrdist<nChannels,T>((T*)(0),(T*)(0))) {
T a_array[nChannels], b_array[nChannels];
for(size_t c=0; c<nChannels; ++c) {
a_array[c] = a[(int)c];
b_array[c] = b[(int)c];
}
return L2sqrdist<nChannels>(a_array,b_array);
}

//! computes the L2 distance between two generic arrays
template<size_t nChannels, typename T> static inline float L2dist(const T* a, const T* b) {
decltype(L2sqrdist(*a,*b)) oResult = 0;
for(size_t c=0; c<nChannels; ++c)
oResult += L2sqrdist(a[c],b[c]);
return sqrt((float)oResult);
}

//! computes the L2 distance between two generic arrays
template<size_t nChannels, typename T> static inline float L2dist(const T* a, const T* b, size_t nElements, const uchar* m=NULL) {
decltype(L2sqrdist<nChannels>(a,b)) oResult = 0;
size_t nTotElements = nElements*nChannels;
if(m) {
for(size_t n=0,i=0; n<nTotElements; n+=nChannels,++i)
if(m[i])
oResult += L2sqrdist<nChannels>(a+n,b+n);
}
else {
for(size_t n=0; n<nTotElements; n+=nChannels)
oResult += L2sqrdist<nChannels>(a+n,b+n);
}
return sqrt((float)oResult);
}

//! computes the squared L2 distance between two generic arrays
template<typename T> static inline float L2dist(const T* a, const T* b, size_t nElements, size_t nChannels, const uchar* m=NULL) {
CV_Assert(nChannels>0 && nChannels<=4);
switch(nChannels) {
case 1: return L2dist<1>(a,b,nElements,m);
case 2: return L2dist<2>(a,b,nElements,m);
case 3: return L2dist<3>(a,b,nElements,m);
case 4: return L2dist<4>(a,b,nElements,m);
default: return 0;
}
}

//! computes the L2 distance between two opencv vectors
template<size_t nChannels, typename T> static inline float L2dist_(const cv::Vec<T,nChannels>& a, const cv::Vec<T,nChannels>& b) {
T a_array[nChannels], b_array[nChannels];
for(size_t c=0; c<nChannels; ++c) {
a_array[c] = a[(int)c];
b_array[c] = b[(int)c];
}
return L2dist<nChannels>(a_array,b_array);
}

///////////////////////////////////////////////////////////////////////////////////////////////////

//! computes the color distortion between two integer arrays
template<size_t nChannels, typename T> static inline typename std::enable_if<std::is_integral<T>::value,size_t>::type cdist(const T* curr, const T* bg) {
static_assert(nChannels>1,"cdist: requires more than one channel");
size_t curr_sqr = 0;
bool bSkip = true;
for(size_t c=0; c<nChannels; ++c) {
curr_sqr += curr[c]*curr[c];
bSkip = bSkip&(bg[c]<=0);
}
if(bSkip)
return (size_t)sqrt((float)curr_sqr);
size_t bg_sqr = 0;
size_t mix = 0;
for(size_t c=0; c<nChannels; ++c) {
bg_sqr += bg[c]*bg[c];
mix += curr[c]*bg[c];
}
return (size_t)sqrt(curr_sqr-((float)(mix*mix)/bg_sqr));
}

//! computes the color distortion between two float arrays
template<size_t nChannels, typename T> static inline typename std::enable_if<std::is_floating_point<T>::value,float>::type cdist(const T* curr, const T* bg) {
static_assert(nChannels>1,"cdist: requires more than one channel");
float curr_sqr = 0;
bool bSkip = true;
for(size_t c=0; c<nChannels; ++c) {
curr_sqr += (float)curr[c]*curr[c];
bSkip = bSkip&(bg[c]<=0);
}
if(bSkip)
return sqrt(curr_sqr);
float bg_sqr = 0;
float mix = 0;
for(size_t c=0; c<nChannels; ++c) {
bg_sqr += (float)bg[c]*bg[c];
mix += (float)curr[c]*bg[c];
}
return sqrt(curr_sqr-((mix*mix)/bg_sqr));
}

//! computes the color distortion between two generic arrays
template<size_t nChannels, typename T> static inline auto cdist(const T* a, const T* b, size_t nElements, const uchar* m=NULL) -> decltype(cdist<nChannels>(a,b)) {
decltype(cdist<nChannels>(a,b)) oResult = 0;
size_t nTotElements = nElements*nChannels;
if(m) {
for(size_t n=0,i=0; n<nTotElements; n+=nChannels,++i)
if(m[i])
oResult += cdist<nChannels>(a+n,b+n);
}
else {
for(size_t n=0; n<nTotElements; n+=nChannels)
oResult += cdist<nChannels>(a+n,b+n);
}
return oResult;
}

//! computes the color distortion between two generic arrays
template<typename T> static inline auto cdist(const T* a, const T* b, size_t nElements, size_t nChannels, const uchar* m=NULL) -> decltype(cdist<3>(a,b,nElements,m)) {
CV_Assert(nChannels>1 && nChannels<=4);
switch(nChannels) {
case 2: return cdist<2>(a,b,nElements,m);
case 3: return cdist<3>(a,b,nElements,m);
case 4: return cdist<4>(a,b,nElements,m);
default: return 0;
}
}

//! computes the color distortion between two opencv vectors
template<size_t nChannels, typename T> static inline auto cdist_(const cv::Vec<T,nChannels>& a, const cv::Vec<T,nChannels>& b) -> decltype(cdist<nChannels,T>((T*)(0),(T*)(0))) {
T a_array[nChannels], b_array[nChannels];
for(size_t c=0; c<nChannels; ++c) {
a_array[c] = a[(int)c];
b_array[c] = b[(int)c];
}
return cdist<nChannels>(a_array,b_array);
}

//! computes a color distortion-distance mix using two generic distances
template<typename T> static inline T cmixdist(T oL1Distance, T oCDistortion) {
return (oL1Distance/2+oCDistortion*4);
}

//! computes a color distoirtion-distance mix using two generic arrays
template<size_t nChannels, typename T> static inline typename std::enable_if<std::is_integral<T>::value,size_t>::type cmixdist(const T* curr, const T* bg) {
return cmixdist(L1dist<nChannels>(curr,bg),cdist<nChannels>(curr,bg));
}

template<size_t nChannels, typename T> static inline typename std::enable_if<std::is_floating_point<T>::value,float>::type cmixdist(const T* curr, const T* bg) {
return cmixdist(L1dist<nChannels>(curr,bg),cdist<nChannels>(curr,bg));
}

///////////////////////////////////////////////////////////////////////////////////////////////////

//! popcount LUT for 8-bit vectors
static const uchar popcount_LUT8[256] = {
0, 1, 1, 2, 1, 2, 2, 3, 1, 2, 2, 3, 2, 3, 3, 4,
1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,
1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,
2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,
2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,
1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,
2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,
2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,
3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,
4, 5, 5, 6, 5, 6, 6, 7, 5, 6, 6, 7, 6, 7, 7, 8,
};

//! computes the population count of an N-byte vector using an 8-bit popcount LUT
template<typename T> static inline size_t popcount(T x) {
size_t nBytes = sizeof(T);
size_t nResult = 0;
for(size_t l=0; l<nBytes; ++l)
nResult += popcount_LUT8[(uchar)(x>>l*8)];
return nResult;
}

//! computes the hamming distance between two N-byte vectors using an 8-bit popcount LUT
template<typename T> static inline size_t hdist(T a, T b) {
return popcount(a^b);
}

//! computes the gradient magnitude distance between two N-byte vectors using an 8-bit popcount LUT
template<typename T> static inline size_t gdist(T a, T b) {
return L1dist(popcount(a),popcount(b));
}

//! computes the population count of a (nChannels*N)-byte vector using an 8-bit popcount LUT
template<size_t nChannels, typename T> static inline size_t popcount(const T* x) {
size_t nBytes = sizeof(T);
size_t nResult = 0;
for(size_t c=0; c<nChannels; ++c)
for(size_t l=0; l<nBytes; ++l)
nResult += popcount_LUT8[(uchar)(*(x+c)>>l*8)];
return nResult;
}

//! computes the hamming distance between two (nChannels*N)-byte vectors using an 8-bit popcount LUT
template<size_t nChannels, typename T> static inline size_t hdist(const T* a, const T* b) {
T xor_array[nChannels];
for(size_t c=0; c<nChannels; ++c)
xor_array[c] = a[c]^b[c];
return popcount<nChannels>(xor_array);
}

//! computes the gradient magnitude distance between two (nChannels*N)-byte vectors using an 8-bit popcount LUT
template<size_t nChannels, typename T> static inline size_t gdist(const T* a, const T* b) {
return L1dist(popcount<nChannels>(a),popcount<nChannels>(b));
}