鸣蝉建站平台,做网站需要专业,公司网站建设基本流程图,东营网站关键词优化转自#xff1a;http://blog.csdn.net/skeeee/article/details/13297457 OpenCV图像像素操作及效率分析 在计算机视觉应用中#xff0c;对于图像内容的读取分析是第一步#xff0c;所以学习高效的处理图像是很有用的。一个图像有可能包含数以万计的像素#xff0c;从根本上… 转自http://blog.csdn.net/skeeee/article/details/13297457 OpenCV图像像素操作及效率分析 在计算机视觉应用中对于图像内容的读取分析是第一步所以学习高效的处理图像是很有用的。一个图像有可能包含数以万计的像素从根本上说图像就是一系列像素值所以OpenCV使用数据结构cv::Mat来表示图像。矩阵中每一个元素都代表一个像素对于灰度图像像素用8位无符号数0表示黑色255表示白色。对于彩色像素而言每个像素需要三位这样的8位无符号数来表示即三个通道R,G,B矩阵则依次存储一个像素的三个通道的值然后再存储下一个像素点。 cv::Mat中成员变量cols代表图像的宽度图像的列数成员变量rows代表图像的高度图像的行数step代表以字节为单位的图像的有效宽度elemSize返回像素的大小像素的大小 颜色大小字节*通道数比如三通道short型矩阵CV_16SC3的大小为2*3 6像素的channels方法返回图像的通道数total函数返回图像的像素数。 闲话少说直接介绍几种读取方式 RGB图像的颜色数目是256*256*256本文对图像进行量化缩减颜色数目到256的1/8即32*32*32为目标分别利用一下几种方法实现比较几种方法的安全和效率。 1.ptr遍历图像 cv::Mat中提供ptr函数访问任意一行像素的首地址特别方便图像的一行一行的横向访问如果需要一列一列的纵向访问图像就稍微麻烦一点。但是ptr访问效率比较高程序也比较安全有越界判断。 [cpp] view plain copy int nl image.rows; //行数 int nc image.cols * image.channels(); // 每行的元素个数每行的像素数*颜色通道数RGB 3 for (int j0; jnl; j) { uchar* data image.ptruchar(j); for (int i0; inc; i) { // process each pixel --------------------- data[i] data[i]/div*div div/2; // end of pixel processing ---------------- } // end of line } 也可以使用[cpp] view plain copy for (int j0; jnl; j) { uchar* data image.ptruchar(j); for (int i0; inc; i) { // process each pixel --------------------- *data *data/div*div div/2; // end of pixel processing ---------------- } // end of line } 2.使用迭代器遍历图像 cv::Mat 同样有标准模板库STL可以使用迭代器访问数据。 用迭代器来遍历图像像素可简化过程降低出错的机会比较安全不过效率较低如果想避免修改输入图像实例cv::Mat可采用const_iterator。iterator有两种调用方法cv::MatIterator_cv::Vec3b it;cv::Mat_cv::Vec3b::iterator it;中间cv::Vec3b是因为图像是彩色图像3通道cv::Vec3b可以代表一个像素。 [cpp] view plain copy // get iterators cv::Mat_cv::Vec3b::iterator it image.begincv::Vec3b(); cv::Mat_cv::Vec3b::iterator itend image.endcv::Vec3b(); for ( ; it! itend; it) { // process each pixel --------------------- (*it)[0] (*it)[0]/div*div div/2; (*it)[1] (*it)[1]/div*div div/2; (*it)[2] (*it)[2]/div*div div/2; // end of pixel processing ---------------- } 3.at方法遍历 cv::Mat也是向量可以使at方法取值使用调用方法image.atcv::Vec3b(j,i)at方法方便直接给ij赋值就可以随意访问图像中任何一个像素其中j表示第j行i表示该行第i个像素。但是at方法效率是这3中访问方法中最慢的一个所以如果遍历图像或者访问像素比较多时建议不要使用这个方法毕竟程序的效率还是比程序的可读性要重要的。下面是完整的调用方法其运行时间在下面会介绍。 [cpp] view plain copy int nl image.rows; // number of lines int nc image.cols; // number of columns for (int j0; jnl; j) { for (int i0; inc; i) { // process each pixel --------------------- image.atcv::Vec3b(j,i)[0] image.atcv::Vec3b(j,i)[0]/div*div div/2; image.atcv::Vec3b(j,i)[1] image.atcv::Vec3b(j,i)[1]/div*div div/2; image.atcv::Vec3b(j,i)[2] image.atcv::Vec3b(j,i)[2]/div*div div/2; // end of pixel processing ---------------- } // end of line } [cpp] view plain copy 4.rowicol(i) cv::Mat提供image.row(i)和image.col(j)对图像整行和整列进行处理处理比较方便因为很少遇到所以就没有进行效率比较 程序代码如下三通道 [cpp] view plain copy result.row(0).setTo(cv::Scalar(0,0,0));//将第一行数据设为零 result.row(result.rows-1).setTo(cv::Scalar(0,0,0));//将最后一行数据设置为零 result.col(0).setTo(cv::Scalar(0,0,0));//将第一列数据设为零 result.col(result.cols-1).setTo(cv::Scalar(0,0,0));//将最后一列数据设为零 5.高效率图像遍历循环 对于迭代的for循环外面一层的循环次数越少速度越快同样是cols*rows*channels()次循环使用nc colsnl rows*channels()与使用nc cols*rows*channelsnl 1以及nc colsnl rowsfor函数最里层运行三次颜色的处理。这三种方法最快的是第二种第三种其次最慢的是第一种.[cpp] view plain copy int nl image.rows; // number of lines int nc image.cols * image.channels(); // total number of elements per line if (image.isContinuous()) { // then no padded pixels nc nc*nl; nl 1; // it is now a 1D array } int n static_castint(log(static_castdouble(div))/log(2.0)); // mask used to round the pixel value uchar mask 0xFFn; // e.g. for div16, mask 0xF0 for (int j0; jnl; j) { uchar* data image.ptruchar(j); for (int i0; inc; i) { // process each pixel --------------------- *data *datamask div/2; // end of pixel processing ---------------- } // end of line } 6.位运算代替乘法和除法 [cpp] view plain copy int nl image.rows; // number of lines int nc image.cols * image.channels(); // total number of elements per line int n static_castint(log(static_castdouble(div))/log(2.0)); // mask used to round the pixel value uchar mask 0xFFn; // e.g. for div16, mask 0xF0 for (int j0; jnl; j) { uchar* data image.ptruchar(j); for (int i0; inc; i) { // process each pixel --------------------- *data *datamask div/2; // end of pixel processing ---------------- } // end of line } 运行时间比较以测试图片为例Debug模式下的时间 ptr函数的两种方法的时间using .ptr and []
3.50202msusing .ptr and *
3.26124ms迭代器方法using Mat_ iterator
143.06msat方法的运行时间using at
252.779ms高效率迭代方法:using .ptr and * and bitwise (continuous)
2.68335ms位运算方法using .ptr and * and bitwise 2.59823ms 还有一些比较的函数方法现在只给出运行时间using .ptr and * and modulo 3.78029msusing .ptr and * and bitwise 2.59823msusing direct pointer arithmetic 2.57317msusing .ptr and * and bitwise with image.cols * image.channels() 22.864msusing Mat_ iterator and bitwise 139.92msusing MatIterator_ 185.996msusing .ptr and * and bitwise (continuouschannels) 2.11271msusing input/output images 2.97717msusing overloaded operators 2.7237ms 源图像 量化处理结果 image1 量化处理后的结果 image2 附OpenCV数据类型列表 class cv::_InputArray This is the proxy class for passing read-only input arrays into OpenCV functions. More... class cv::_InputOutputArray class cv::_OutputArray This type is very similar to InputArray except that it is used for input/output and output function parameters. More... class cv::Algorithm This is a base class for all more or less complex algorithms in OpenCV. More... class cv::Complex _Tp A complex number class. More... class cv::DataDepth _Tp A helper class for cv::DataType. More... class cv::DataType _Tp Template trait class for OpenCV primitive data types. More... class cv::DMatch Class for matching keypoint descriptors. More... class cv::Formatted class cv::Formatter class cv::KeyPoint Data structure for salient point detectors. More... class cv::Mat n-dimensional dense array class More... class cv::Mat_ _Tp Template matrix class derived from Mat. More... class cv::MatAllocator Custom array allocator. More... class cv::MatCommaInitializer_ _Tp Comma-separated Matrix Initializer. More... class cv::MatConstIterator class cv::MatConstIterator_ _Tp Matrix read-only iterator. More... class cv::MatExpr Matrix expression representation. More... class cv::MatIterator_ _Tp Matrix read-write iterator. More... class cv::MatOp struct cv::MatSize struct cv::MatStep class cv::Matx _Tp, m, n Template class for small matrices whose type and size are known at compilation time. More... class cv::MatxCommaInitializer _Tp, m, n Comma-separated Matrix Initializer. More... class cv::NAryMatIterator n-ary multi-dimensional array iterator. More... struct cv::Param struct cv::ParamType _Tp struct cv::ParamType Algorithm struct cv::ParamType bool struct cv::ParamType double struct cv::ParamType float struct cv::ParamType Mat struct cv::ParamType std::vector Mat struct cv::ParamType String struct cv::ParamType uchar struct cv::ParamType uint64 struct cv::ParamType unsigned class cv::Point3_ _Tp Template class for 3D points specified by its coordinates x, y and z. More... class cv::Point_ _Tp Template class for 2D points specified by its coordinates x and y. More... struct cv::Ptr T Template class for smart pointers with shared ownership. More... class cv::Range Template class specifying a continuous subsequence (slice) of a sequence. More... class cv::Rect_ _Tp Template class for 2D rectangles. More... class cv::RotatedRect The class represents rotated (i.e. not up-right) rectangles on a plane. More... class cv::Scalar_ _Tp Template class for a 4-element vector derived from Vec. More... class cv::Size_ _Tp Template class for specifying the size of an image or rectangle. More... class cv::SparseMat The class SparseMat represents multi-dimensional sparse numerical arrays. More... class cv::SparseMat_ _Tp Template sparse n-dimensional array class derived from SparseMat. More... class cv::SparseMatConstIterator Read-Only Sparse Matrix Iterator. More... class cv::SparseMatConstIterator_ _Tp Template Read-Only Sparse Matrix Iterator Class. More... class cv::SparseMatIterator Read-write Sparse Matrix Iterator. More... class cv::SparseMatIterator_ _Tp Template Read-Write Sparse Matrix Iterator Class. More... class cv::String class cv::TermCriteria The class defining termination criteria for iterative algorithms. More... class cv::TypeDepth _depth class cv::TypeDepth CV_16S class cv::TypeDepth CV_16U class cv::TypeDepth CV_32F class cv::TypeDepth CV_32S class cv::TypeDepth CV_64F class cv::TypeDepth CV_8S class cv::TypeDepth CV_8U class cv::UMat struct cv::UMatData struct cv::UMatDataAutoLock class cv::Vec _Tp, cn Template class for short numerical vectors, a partial case of Matx. More... class cv::VecCommaInitializer _Tp, m Comma-separated Vec Initializer. More... Typedefs typedef Complex double cv::Complexd typedef Complex float cv::Complexf typedef const _InputArray cv::InputArray typedef InputArray cv::InputArrayOfArrays typedef const _InputOutputArray cv::InputOutputArray typedef InputOutputArray cv::InputOutputArrayOfArrays typedef Mat_ uchar cv::Mat1b typedef Mat_ double cv::Mat1d typedef Mat_ float cv::Mat1f typedef Mat_ int cv::Mat1i typedef Mat_ short cv::Mat1s typedef Mat_ ushort cv::Mat1w typedef Mat_ Vec2b cv::Mat2b typedef Mat_ Vec2d cv::Mat2d typedef Mat_ Vec2f cv::Mat2f typedef Mat_ Vec2i cv::Mat2i typedef Mat_ Vec2s cv::Mat2s typedef Mat_ Vec2w cv::Mat2w typedef Mat_ Vec3b cv::Mat3b typedef Mat_ Vec3d cv::Mat3d typedef Mat_ Vec3f cv::Mat3f typedef Mat_ Vec3i cv::Mat3i typedef Mat_ Vec3s cv::Mat3s typedef Mat_ Vec3w cv::Mat3w typedef Mat_ Vec4b cv::Mat4b typedef Mat_ Vec4d cv::Mat4d typedef Mat_ Vec4f cv::Mat4f typedef Mat_ Vec4i cv::Mat4i typedef Mat_ Vec4s cv::Mat4s typedef Mat_ Vec4w cv::Mat4w typedef Matx double, 1, 2 cv::Matx12d typedef Matx float, 1, 2 cv::Matx12f typedef Matx double, 1, 3 cv::Matx13d typedef Matx float, 1, 3 cv::Matx13f typedef Matx double, 1, 4 cv::Matx14d typedef Matx float, 1, 4 cv::Matx14f typedef Matx double, 1, 6 cv::Matx16d typedef Matx float, 1, 6 cv::Matx16f typedef Matx double, 2, 1 cv::Matx21d typedef Matx float, 2, 1 cv::Matx21f typedef Matx double, 2, 2 cv::Matx22d typedef Matx float, 2, 2 cv::Matx22f typedef Matx double, 2, 3 cv::Matx23d typedef Matx float, 2, 3 cv::Matx23f typedef Matx double, 3, 1 cv::Matx31d typedef Matx float, 3, 1 cv::Matx31f typedef Matx double, 3, 2 cv::Matx32d typedef Matx float, 3, 2 cv::Matx32f typedef Matx double, 3, 3 cv::Matx33d typedef Matx float, 3, 3 cv::Matx33f typedef Matx double, 3, 4 cv::Matx34d typedef Matx float, 3, 4 cv::Matx34f typedef Matx double, 4, 1 cv::Matx41d typedef Matx float, 4, 1 cv::Matx41f typedef Matx double, 4, 3 cv::Matx43d typedef Matx float, 4, 3 cv::Matx43f typedef Matx double, 4, 4 cv::Matx44d typedef Matx float, 4, 4 cv::Matx44f typedef Matx double, 6, 1 cv::Matx61d typedef Matx float, 6, 1 cv::Matx61f typedef Matx double, 6, 6 cv::Matx66d typedef Matx float, 6, 6 cv::Matx66f typedef const _OutputArray cv::OutputArray typedef OutputArray cv::OutputArrayOfArrays typedef Point2i cv::Point typedef Point_ double cv::Point2d typedef Point_ float cv::Point2f typedef Point_ int cv::Point2i typedef Point3_ double cv::Point3d typedef Point3_ float cv::Point3f typedef Point3_ int cv::Point3i typedef Rect2i cv::Rect typedef Rect_ double cv::Rect2d typedef Rect_ float cv::Rect2f typedef Rect_ int cv::Rect2i typedef Scalar_ double cv::Scalar typedef Size2i cv::Size typedef Size_ double cv::Size2d typedef Size_ float cv::Size2f typedef Size_ int cv::Size2i Enumerations enum { cv::ACCESS_READ 124, cv::ACCESS_WRITE 125, cv::ACCESS_RW 324, cv::ACCESS_MASK ACCESS_RW, cv::ACCESS_FAST 126 } enum cv::UMatUsageFlags { cv::USAGE_DEFAULT 0, cv::USAGE_ALLOCATE_HOST_MEMORY 1 0, cv::USAGE_ALLOCATE_DEVICE_MEMORY 1 1, cv::USAGE_ALLOCATE_SHARED_MEMORY 1 2, cv::__UMAT_USAGE_FLAGS_32BIT 0x7fffffff } Usage flags for allocator. More... Functions templatetypename _Tp , int m static double cv::determinant (const Matx _Tp, m, m a) templatetypename T Ptr T cv::makePtr () templatetypename T , typename A1 Ptr T cv::makePtr (const A1 a1) templatetypename T , typename A1 , typename A2 Ptr T cv::makePtr (const A1 a1, const A2 a2) templatetypename T , typename A1 , typename A2 , typename A3 Ptr T cv::makePtr (const A1 a1, const A2 a2, const A3 a3) templatetypename T , typename A1 , typename A2 , typename A3 , typename A4 Ptr T cv::makePtr (const A1 a1, const A2 a2, const A3 a3, const A4 a4) templatetypename T , typename A1 , typename A2 , typename A3 , typename A4 , typename A5 Ptr T cv::makePtr (const A1 a1, const A2 a2, const A3 a3, const A4 a4, const A5 a5) templatetypename T , typename A1 , typename A2 , typename A3 , typename A4 , typename A5 , typename A6 Ptr T cv::makePtr (const A1 a1, const A2 a2, const A3 a3, const A4 a4, const A5 a5, const A6 a6) templatetypename T , typename A1 , typename A2 , typename A3 , typename A4 , typename A5 , typename A6 , typename A7 Ptr T cv::makePtr (const A1 a1, const A2 a2, const A3 a3, const A4 a4, const A5 a5, const A6 a6, const A7 a7) templatetypename T , typename A1 , typename A2 , typename A3 , typename A4 , typename A5 , typename A6 , typename A7 , typename A8 Ptr T cv::makePtr (const A1 a1, const A2 a2, const A3 a3, const A4 a4, const A5 a5, const A6 a6, const A7 a7, const A8 a8) templatetypename T , typename A1 , typename A2 , typename A3 , typename A4 , typename A5 , typename A6 , typename A7 , typename A8 , typename A9 Ptr T cv::makePtr (const A1 a1, const A2 a2, const A3 a3, const A4 a4, const A5 a5, const A6 a6, const A7 a7, const A8 a8, const A9 a9) templatetypename T , typename A1 , typename A2 , typename A3 , typename A4 , typename A5 , typename A6 , typename A7 , typename A8 , typename A9 , typename A10 Ptr T cv::makePtr (const A1 a1, const A2 a2, const A3 a3, const A4 a4, const A5 a5, const A6 a6, const A7 a7, const A8 a8, const A9 a9, const A10 a10) InputOutputArray cv::noArray () templatetypename _Tp , int m, int n static double cv::norm (const Matx _Tp, m, n M) templatetypename _Tp , int m, int n static double cv::norm (const Matx _Tp, m, n M, int normType) templatetypename _Tp , int cn static Vec _Tp, cn cv::normalize (const Vec _Tp, cn v) templatetypename T bool cv::operator ! (const Ptr T ptr1, const Ptr T ptr2) static String cv::operator (String out, Ptr Formatted fmtd) static String cv::operator (String out, const Mat mtx) templatetypename T bool cv::operator (const Ptr T ptr1, const Ptr T ptr2) templatetypename T void cv::swap (Ptr T ptr1, Ptr T ptr2) templatetypename _Tp , int m, int n static double cv::trace (const Matx _Tp, m, n a) Shorter aliases for the most popular specializations of VecT,n typedef Vec uchar, 2 cv::Vec2b typedef Vec uchar, 3 cv::Vec3b typedef Vec uchar, 4 cv::Vec4b typedef Vec short, 2 cv::Vec2s typedef Vec short, 3 cv::Vec3s typedef Vec short, 4 cv::Vec4s typedef Vec ushort, 2 cv::Vec2w typedef Vec ushort, 3 cv::Vec3w typedef Vec ushort, 4 cv::Vec4w typedef Vec int, 2 cv::Vec2i typedef Vec int, 3 cv::Vec3i typedef Vec int, 4 cv::Vec4i typedef Vec int, 6 cv::Vec6i typedef Vec int, 8 cv::Vec8i typedef Vec float, 2 cv::Vec2f typedef Vec float, 3 cv::Vec3f typedef Vec float, 4 cv::Vec4f typedef Vec float, 6 cv::Vec6f typedef Vec double, 2 cv::Vec2d typedef Vec double, 3 cv::Vec3d typedef Vec double, 4 cv::Vec4d typedef Vec double, 6 cv::Vec6d http://docs.opencv.org/trunk/dc/d84/group__core__basic.html
