[HQ]OpenCV访问图像像素, 数组元素等方法收集

访问图像像素的一些方法。

* Indirect access: (General, but inefficient, access to any type image)

o For a single-channel byte image:

IplImage* img=cvCreateImage(cvSize(640,480),IPL_DEPTH_8U,1);

CvScalar s;

s=cvGet2D(img,i,j); // get the (i,j) pixel value

printf("intensity=%f/n",s.val[0]);

s.val[0]=111;

cvSet2D(img,i,j,s); // set the (i,j) pixel value

o For a multi-channel float (or byte) image:

IplImage* img=cvCreateImage(cvSize(640,480),IPL_DEPTH_32F,3);

CvScalar s;

s=cvGet2D(img,i,j); // get the (i,j) pixel value

printf("B=%f, G=%f, R=%f/n",s.val[0],s.val[1],s.val[2]);

s.val[0]=111;

s.val[1]=111;

s.val[2]=111;

cvSet2D(img,i,j,s); // set the (i,j) pixel value

* Direct access: (Efficient access, but error prone)

o For a single-channel byte image:

IplImage* img=cvCreateImage(cvSize(640,480),IPL_DEPTH_8U,1);

((uchar *)(img->imageData + i*img->widthStep))[j]=111;

o For a multi-channel byte image:

IplImage* img=cvCreateImage(cvSize(640,480),IPL_DEPTH_8U,3);

((uchar *)(img->imageData + i*img->widthStep))[j*img->nChannels + 0]=111; // B

((uchar *)(img->imageData + i*img->widthStep))[j*img->nChannels + 1]=112; // G

((uchar *)(img->imageData + i*img->widthStep))[j*img->nChannels + 2]=113; // R

o For a multi-channel float image:

IplImage* img=cvCreateImage(cvSize(640,480),IPL_DEPTH_32F,3);

((float *)(img->imageData + i*img->widthStep))[j*img->nChannels + 0]=111; // B

((float *)(img->imageData + i*img->widthStep))[j*img->nChannels + 1]=112; // G

((float *)(img->imageData + i*img->widthStep))[j*img->nChannels + 2]=113; // R

* Direct access using a pointer: (Simplified and efficient access under limiting assumptions)

o For a single-channel byte image:

IplImage* img = cvCreateImage(cvSize(640,480),IPL_DEPTH_8U,1);

int height = img->height;

int width = img->width;

int step = img->widthStep/sizeof(uchar);

uchar* data = (uchar *)img->imageData;

data[i*step+j] = 111;

o For a multi-channel byte image:

IplImage* img = cvCreateImage(cvSize(640,480),IPL_DEPTH_8U,3);

int height = img->height;

int width = img->width;

int step = img->widthStep/sizeof(uchar);

int channels = img->nChannels;

uchar* data = (uchar *)img->imageData;

data[i*step+j*channels+k] = 111;

o For a multi-channel float image (assuming a 4-byte alignment):

IplImage* img = cvCreateImage(cvSize(640,480),IPL_DEPTH_32F,3);

int height = img->height;

int width = img->width;

int step = img->widthStep/sizeof(float);

int channels = img->nChannels;

float * data = (float *)img->imageData;

data[i*step+j*channels+k] = 111;

* Direct access using a c++ wrapper: (Simple and efficient access)

o Define a c++ wrapper for single-channel byte images, multi-channel byte images, and multi-channel float images:

template<class T> class Image

{

private:

IplImage* imgp;

public:

Image(IplImage* img=0) {imgp=img;}

~Image(){imgp=0;}

void operator=(IplImage* img) {imgp=img;}

inline T* operator[](const int rowIndx) {

return ((T *)(imgp->imageData + rowIndx*imgp->widthStep));}

};

typedef struct{

unsigned char b,g,r;

} RgbPixel;

typedef struct{

float b,g,r;

} RgbPixelFloat;

typedef Image<RgbPixel> RgbImage;

typedef Image<RgbPixelFloat> RgbImageFloat;

typedef Image<unsigned char> BwImage;

typedef Image<float> BwImageFloat;

o For a single-channel byte image:

IplImage* img=cvCreateImage(cvSize(640,480),IPL_DEPTH_8U,1);

BwImage imgA(img);

imgA[i][j] = 111;

o For a multi-channel byte image:

IplImage* img=cvCreateImage(cvSize(640,480),IPL_DEPTH_8U,3);

RgbImage imgA(img);

imgA[i][j].b = 111;

imgA[i][j].g = 111;

imgA[i][j].r = 111;

o For a multi-channel float image:

IplImage* img=cvCreateImage(cvSize(640,480),IPL_DEPTH_32F,3);

RgbImageFloat imgA(img);

imgA[i][j].b = 111;

imgA[i][j].g = 111;

imgA[i][j].r = 111;