从零开始 OpenCV (三) —— 矩阵/图像的基本操作

基本操作

“加” 操作: `cvAdd()`, `cvAddS()`, `cvAddWeighted()`

cvAdd 将 mask 指定的元素相加;
cvAddS 将 mask 指定的元素与标量 value 相加;
cvAddWeighted 将 mask 指定区域的元素按权重相加, 并加上 gamma;

函数定义

// dst(mask) = src1(mask) + src2(mask)
// mask specifies elements of destination array to be changed.
void cvAdd(const CvArr* src1, const CvArr* src2, CvArr* dst, const CvArr* mask = NULL);

// dst(mask) = src(mask) + value
void cvAddS(const CvArr* src, const CvScalar value, CvArr* dst, const CvArr* mask = NULL);

// dst = src1 * alpha + src2 * beta + gamma
void cvAddWeighted(const CvArr* src1, double alpha, const CvArr* src2, double beta, double gamma, CvArr* dst);

举个例子: 选择两张图片的感兴趣区域, 按照一定的比例相叠加。

#include "opencv/highgui.h"
#include "opencv/cv.h"

int main()
{
    // load image from file
    IplImage* src1 = cvLoadImage("C:\\Users\\yanglion\\Pictures\\Img\\Ali.jpg");
    IplImage* src2 = cvLoadImage("C:\\Users\\yanglion\\Pictures\\Img\\SpongeBob.JPG");
    IplImage* dst  = cvLoadImage("C:\\Users\\yanglion\\Pictures\\Img\\Ali.jpg");

    // set image's ROI
    cvSetImageROI(src1, cvRect(217, 116, 100, 80));
    cvSetImageROI(src2, cvRect(106, 58, 100, 80));
    cvSetImageROI(dst, cvRect(217, 116, 100, 80));

    // dst = src1 * alpha + src2 * beta + gamma
    double alpha = 0.4;
    double beta  = 1 - alpha;
    double gamma = 0.0;
    cvAddWeighted(src1, alpha, src2, beta, gamma, dst);

    // Resets the image ROI to include the entire image and releases the ROI structure.
    cvResetImageROI(src1);
    cvResetImageROI(src2);
    cvResetImageROI(dst);

    // create window
    cvNamedWindow("Ali");
    cvNamedWindow("SpongeBob");
    cvNamedWindow("AliWithSpongeBobFace");
    // display image within window (highgui windows remember their content)
    cvShowImage("Ali", src1);
    cvShowImage("SpongeBob", src2);
    cvShowImage("AliWithSpongeBobFace", dst);
    // wait for key event infinitely (delay<=0) or for "delay" milliseconds
    cvWaitKey();

    return 0;
}

运行效果:

“减” 操作: `cvSub()`, `cvSubS()`, `cvSubRS()`

类似于操作，
cvSub 将 src1 和 src2 中对应的元素进行减法运算;
cvSubS 将 src 中的每个元素依次减去标量 value 的值;
cvSubRS 则是将标量 value 的值减去 src 中的每个元素的值;

// dst(mask) = src1(mask) - src2(mask)
void cvSub(const CvArr* src1, const CvArr* src2, CvArr* dst, const CvArr* mask = NULL);

// dst(mask) = src(mask) - value;
void cvSubS(const CvArr* src, CvScalar value, CvArr* dst, const CvArr* mask = NULL);

// dst(mask) = value - src(mask)
void cvSubRS(const CvArr* src, CvScalar value, CvArr* dst, const CvArr* mask = NULL);

其他基本操作

差值的绝对值: `cvAbs()`, `cvAbsDiff()`, `cvAbsDiffS()`

两个矩阵的元素依次求差: `cvDiv()`

两个矩阵的元素依次求积: `cvMul()`

按位与操作: `cvAnd()`, `cvAndS()`

按位非: `cvNot()`

按位或: `cvOr()`, `cvOrS()`

按位异或: `cvXor()`, `cvXorS()`

统计操作

求和, 平均值, 标准差, 协方差: `cvSum()`, `cvAvg()`, `cvAvgSdv()`, `cvCalcCovarMatrix()`

// Finds sum of array elements
CvScalar cvSum(const CvArr* arr);   

// Calculates mean value of array elements
CvScalar cvAvg(const CvArr* arr, const CvArr*mask = NULL);

// Calculates mean and standard deviation of pixel values
void cvAvgSdv(const CvArr* arr, CvScalar* mean, CvScalar* std_dev, const CvArr* mask = NULL);

// Calculates covariation matrix for a set of vectors
void cvCalcCovarMatrix(const CvArr** vects, int count, CvArr* cov_mat, CvArr* avg, int flags);

统计非0的个数: `cvCountNonZero()`

// Calculates number of non-zero pixels
int cvCountNonZero(const CvArr* arr);

获取最大值和最小值: `cvMinMaxLoc()`

// Finds global minimum, maximum and their positions
void cvMinMaxLoc(const CvArr* arr, double* min_val, double* max_val, 
                 CvPoint* min_loc = NULL, CvPoint* max_loc = NULL, const CvArr* mask = NULL);

矩阵操作

计算矩阵的特征值和特征向量: `cvEigenVV()`

// Finds eigen values and vectors of a symmetric matrix
void cvEigenVV(CvArr* mat, CvArr* evects, CvArr* evals, double eps = 0, int lowindex = -1, int highindex = -1);

计算矩阵的逆矩阵, 转置和迹： `cvInvert()`, `cvTranspose()`, `cvTrace()`

// Inverts matrix
double cvInvert(const CvArr* src, CvArr* dst, int method = 0);  

// Tranposes matrix. Square matrices can be transposed in-place
void cvTranspose(const CvArr* src, CvArr* dst);

// Calculates trace of the matrix (sum of elements on the main diagonal)
CvScalar cvTrace (const CvArr *mat);

计算矩阵的行列式: `cvDet()`

// Calculates determinant of input matrix
double cvDet(const CvArr* mat);

求线性方程组的解: `cvSolve()`

// Solves linear system (src1)*(dst) = (src2) (returns 0 if src1 is a singular and CV_LU method is used)
int cvSolve(const CvArr* src1, const CvArr* src2, CvArr* dst, int method = 0);

图像操作

将多通道图像切割成多个单通道数组: `cvSplit()`

// Splits a multi-channel array into the set of single-channel arrays or extracts particular [color] plane void cvSplit(const CvArr* src, CvArr* dst0, CvArr* dst1, CvArr* dst2, CvArr* dst3);

将多个单通道图像合并为一个多通道图像: `cvMerge()`

// Merges a set of single-channel arrays into the single multi-channel array
// or inserts one particular [color] plane to the array
void cvMerge (const CvArr *src0, const CvArr *src1, const CvArr *src2, const CvArr *src3, CvArr *dst);