Basic data structure of OpenCV

Refer to "OpenCV Chinese Reference Manual"

1. Image data structure

(1) IPL :
    IplImage
    |-- int nChannels; // number of color channels (1,2,3,4)
    |-- int depth; // Bit depth of pixels:
    |                             // IPL_DEPTH_8U, IPL_DEPTH_8S,
    |                             // IPL_DEPTH_16U,IPL_DEPTH_16S,
    |                             // IPL_DEPTH_32S,IPL_DEPTH_32F,
    |                             // IPL_DEPTH_64F
    |-- int width; // image width (in pixels)
    |-- int height; // image height
    |-- char* imageData; // image data pointer
    | // Note that color images store data in BGR order
    |-- int dataOrder; // 0 - Interleave the values ​​of different channels of the pixel to form a single pixel plane
    | // 1 - Arrange all pixels with the channel value to form several channel planes, and then arrange the planes
    | // cvCreateImage can only create images with interleaved pixels
    |-- int origin; // 0 - the pixel origin is the upper left corner,
    | // 1 - Pixel origin is bottom left corner (Windows bitmaps style)
    |-- int widthStep; // number of bytes between points in the same column of adjacent rows
    |-- int imageSize; // image size (in bytes) = height*widthStep
    |-- struct _IplROI *roi; // The region of interest (ROI) of the image. When the ROI is not empty, the image
    | // Processing is limited to the ROI area.
    |-- char *imageDataOrigin; // The data origin pointer when the image data is not aligned
    | // (need to reallocate image memory correctly)
    |                             // （needed for correct image deallocation）
    |-- int align; // Row alignment of image data: 4 or 8 byte alignment
    | // There is no such item in OpenCV, use widthSt

2. Matrices and Vectors

(1) Matrix:
    CvMat // 2D matrix
    |-- int type; // element type (uchar,short,int,float,double) and flag
    |-- int step; // The number of bytes of the entire line length
    |-- int rows, cols; // number of rows and columns
    |-- int height, width; // matrix height, width, corresponding to rows, cols
    |-- union data;
        |-- uchar* ptr;           // data pointer for an unsigned char matrix
        |-- short* s;             // data pointer for a short matrix
        |-- int* i;               // data pointer for an integer matrix
        |-- float* fl;            // data pointer for a float matrix
        |-- double* db;           // data pointer for a double matrix
    CvMatND // N-dimensional matrix
    |-- int type; // element type (uchar,short,int,float,double) and flag
    |-- int dims; // matrix dimensions
    |-- union data;
    |   |-- uchar* ptr;           // data pointer for an unsigned char matrix
    |   |-- short* s;             // data pointer for a short matrix
    |   |-- int* i;               // data pointer for an integer matrix
    |   |-- float* fl;            // data pointer for a float matrix
    |   |-- double* db;           // data pointer for a double matrix
    |
    |-- struct dim[]; // each dimension information
        |-- size; // number of elements
        |-- step; // element spacing (bytes)
    CvSparseMat // N-dimensional sparse matrix

(2) General matrix:
    CvArr* // only used as parameter of function definition,
            // Indicates that the function can accept different types of matrices as parameters,
            // For example: IplImage*, CvMat* or even CvSeq*.
            // The type of matrix is ​​determined by the first 4 bytes of information in the matrix header
        

(3) Scalar:
    CvScalar
        |-- double val[4]; //4D vector
    Initialization function:
        // Example:
        CvScalar s = cvScalar(double val0, double val1=0, double val2=0, double val3=0);
        CvScalar s = cvScalar(20.0);
        s.val[0]=20.0;
        

3. Other structure types

(1 o'clock:
    CvPoint p = cvPoint(int x, int y);
    CvPoint2D32f p = cvPoint2D32f(float x, float y);
    CvPoint3D32f p = cvPoint3D32f(float x, float y, float z); //E.g.:
    p.x=5.0;
    p.y=5.0;

(2) Rectangular frame size (in pixels):
    CvSize r = cvSize(int width, int height);
    CvSize2D32f r = cvSize2D32f(float width, float height);

(3) Offset and size of the rectangular box:
    CvRect r = cvRect(int x, int y, int width, int height);