OpenCV中实现图像翻转的函数flip，公式为：
目前fbc_cv库中也实现了flip函数，支持多通道，uchar和float两种数据类型，经测试，与OpenCV3.1结果完全一致。
实现代码flip.hpp：
// fbc_cv is free software and uses the same licence as OpenCV
// Email: fengbingchun@163.com
#ifndef FBC_CV_FLIP_HPP_
#define FBC_CV_FLIP_HPP_
/* reference: include/opencv2/core.hpp
modules/core/src/copy.cpp
*/
#include <typeinfo>
#include "core/mat.hpp"
namespace fbc {
template<typename _Tp, int chs> static int flipHoriz(const Mat_<_Tp, chs>& src, Mat_<_Tp, chs>& dst);
template<typename _Tp, int chs> static int flipVert(const Mat_<_Tp, chs>& src, Mat_<_Tp, chs>& dst);
// Flips a 2D array around vertical, horizontal, or both axes
// flipCode: 0 means flipping around the x - axis and positive value means flipping around y - axis.
// Negative value means flipping around both axes
// support type: uchar/float, multi-channels
template <typename _Tp, int chs>
int flip(const Mat_<_Tp, chs>& src, Mat_<_Tp, chs>& dst, int flipCode)
{
FBC_Assert(typeid(uchar).name() == typeid(_Tp).name() || typeid(float).name() == typeid(_Tp).name()); // uchar || float
if (dst.empty()) {
dst = Mat_<_Tp, chs>(src.rows, src.cols);
} else {
FBC_Assert(src.rows == dst.rows && src.cols == dst.cols);
}
Size size = src.size();
if (flipCode < 0) {
if (size.width == 1)
flipCode = 0;
if (size.height == 1)
flipCode = 1;
}
if ((size.width == 1 && flipCode > 0) ||
(size.height == 1 && flipCode == 0) ||
(size.height == 1 && size.width == 1 && flipCode < 0)) {
src.copyTo(dst);
return 0;
}
if (flipCode <= 0)
flipVert(src, dst);
else
flipHoriz(src, dst);
if (flipCode < 0)
flipHoriz(dst, dst);
return 0;
}
template<typename _Tp, int chs>
static int flipHoriz(const Mat_<_Tp, chs>& src, Mat_<_Tp, chs>& dst)
{
Size size = src.size();
size_t esz = sizeof(_Tp) * chs;
int i, j, limit = (int)(((size.width + 1) / 2) *esz );
AutoBuffer<int> _tab(size.width * esz);
int* tab = _tab;
size_t sstep = src.step;
size_t dstep = dst.step;
const uchar* src_ = src.ptr();
uchar* dst_ = dst.ptr();
for (i = 0; i < size.width; i++) {
for (size_t k = 0; k < esz; k++) {
tab[i*esz + k] = (int)((size.width - i - 1) * esz + k);
}
}
for (; size.height--; src_ += sstep, dst_ += dstep) {
for (i = 0; i < limit; i++) {
j = tab[i];
uchar t0 = src_[i], t1 = src_[j];
dst_[i] = t1; dst_[j] = t0;
}
}
return 0;
}
template<typename _Tp, int chs>
static int flipVert(const Mat_<_Tp, chs>& src, Mat_<_Tp, chs>& dst)
{
const uchar* src0 = src.ptr();
uchar* dst0 = dst.ptr();
Size size = src.size();
size_t sstep = src.step;
size_t dstep = dst.step;
size_t esz = sizeof(_Tp) * chs;
const uchar* src1 = src0 + (size.height - 1)*sstep;
uchar* dst1 = dst0 + (size.height - 1)*dstep;
size.width *= (int)esz;
for (int y = 0; y < (size.height + 1) / 2; y++, src0 += sstep, src1 -= sstep, dst0 += dstep, dst1 -= dstep) {
int i = 0;
if (((size_t)src0 | (size_t)dst0 | (size_t)src1 | (size_t)dst1) % sizeof(int) == 0) {
for (; i <= size.width - 16; i += 16) {
int t0 = ((int*)(src0 + i))[0];
int t1 = ((int*)(src1 + i))[0];
((int*)(dst0 + i))[0] = t1;
((int*)(dst1 + i))[0] = t0;
t0 = ((int*)(src0 + i))[1];
t1 = ((int*)(src1 + i))[1];
((int*)(dst0 + i))[1] = t1;
((int*)(dst1 + i))[1] = t0;
t0 = ((int*)(src0 + i))[2];
t1 = ((int*)(src1 + i))[2];
((int*)(dst0 + i))[2] = t1;
((int*)(dst1 + i))[2] = t0;
t0 = ((int*)(src0 + i))[3];
t1 = ((int*)(src1 + i))[3];
((int*)(dst0 + i))[3] = t1;
((int*)(dst1 + i))[3] = t0;
}
for (; i <= size.width - 4; i += 4) {
int t0 = ((int*)(src0 + i))[0];
int t1 = ((int*)(src1 + i))[0];
((int*)(dst0 + i))[0] = t1;
((int*)(dst1 + i))[0] = t0;
}
}
for (; i < size.width; i++) {
uchar t0 = src0[i];
uchar t1 = src1[i];
dst0[i] = t1;
dst1[i] = t0;
}
}
return 0;
}
} // namespace fbc
#endif // FBC_CV_FLIP_HPP_
测试代码test_flip.cpp：
#include "test_flip.hpp"
#include <assert.h>
#include <iostream>
#include <string>
#include <flip.hpp>
#include <opencv2/opencv.hpp>
int test_flip_uchar()
{
cv::Mat matSrc = cv::imread("E:/GitCode/OpenCV_Test/test_images/1.jpg", 1);
if (!matSrc.data) {
std::cout << "read image fail" << std::endl;
return -1;
}
int width = matSrc.cols;
int height = matSrc.rows;
int flipCode[3] {-1, 0, 1}; // both axes, x axis, y axis
for (int i = 0; i < 3; i++) {
fbc::Mat_<uchar, 3> mat1(height, width, matSrc.data);
fbc::Mat_<uchar, 3> mat2(height, width);
fbc::flip(mat1, mat2, flipCode[i]);
cv::Mat mat1_(height, width, CV_8UC3, matSrc.data);
cv::Mat mat2_;
cv::flip(mat1_, mat2_, flipCode[i]);
assert(mat2.rows == mat2_.rows && mat2.cols == mat2_.cols && mat2.step == mat2_.step);
for (int y = 0; y < mat2.rows; y++) {
const fbc::uchar* p1 = mat2.ptr(y);
const uchar* p2 = mat2_.ptr(y);
for (int x = 0; x < mat2.step; x++) {
assert(p1[x] == p2[x]);
}
}
std::string name = std::to_string(i);
std::string file_path = "E:/GitCode/OpenCV_Test/test_images/";
std::string name_fbc = file_path + "flip_fbc_" + name + ".jpg";
std::string name_cv = file_path + "flip_cv_" + name + ".jpg";
cv::Mat matSave(height, width, CV_8UC3, mat2.data);
cv::imwrite(name_fbc, matSave);
cv::imwrite(name_cv, mat2_);
}
return 0;
}
int test_flip_float()
{
cv::Mat matSrc = cv::imread("E:/GitCode/OpenCV_Test/test_images/1.jpg", 1);
if (!matSrc.data) {
std::cout << "read image fail" << std::endl;
return -1;
}
cv::cvtColor(matSrc, matSrc, CV_BGR2GRAY);
matSrc.convertTo(matSrc, CV_32FC1);
int width = matSrc.cols;
int height = matSrc.rows;
int flipCode[3] {-1, 0, 1}; // both axes, x axis, y axis
for (int i = 0; i < 3; i++) {
fbc::Mat_<float, 1> mat1(height, width, matSrc.data);
fbc::Mat_<float, 1> mat2(height, width);
fbc::flip(mat1, mat2, flipCode[i]);
cv::Mat mat1_(height, width, CV_32FC1, matSrc.data);
cv::Mat mat2_;
cv::flip(mat1_, mat2_, flipCode[i]);
assert(mat2.rows == mat2_.rows && mat2.cols == mat2_.cols && mat2.step == mat2_.step);
for (int y = 0; y < mat2.rows; y++) {
const fbc::uchar* p1 = mat2.ptr(y);
const uchar* p2 = mat2_.ptr(y);
for (int x = 0; x < mat2.step; x++) {
assert(p1[x] == p2[x]);
}
}
}
return 0;
}