Opencv step by step - 基本数据类型
CvArr,CvMat,IplImage这三者是继承的关系。
打开opencv 3.0的源码：
cvArr
/* CvArr* is used to pass arbitrary
* array-like data structures
* into functions where the particular
* array type is recognized at runtime:
*/
typedef void CvArr;
oh god，它是可变类型的数据
cvMat
再看一下cvMat。
typedef struct CvMat
{
int type;
int step;
/* for internal use only */
int* refcount;
int hdr_refcount;
union
{
uchar* ptr;
short* s;
int* i;
float* fl;
double* db;
} data;
#ifdef __cplusplus
union
{
int rows;
int height;
};
union
{
int cols;
int width;
};
#else
int rows;
int cols;
#endif
#ifdef __cplusplus
CvMat() {}
CvMat(const CvMat& m) { memcpy(this, &m, sizeof(CvMat));}
CvMat(const cv::Mat& m);
#endif
}
CvMat;
这里先不管C++了，纯c的做法是：
typedef struct CvMat
{
int type;
int step;
/* for internal use only */
int* refcount;
int hdr_refcount;
union
{
uchar* ptr;
short* s;
int* i;
float* fl;
double* db;
} data;
int rows;
int cols;
}
CvMat;这里，cvMat有几个属性，到底是干什么的呢？
可以看看它的初始化函数：
CV_INLINE CvMat cvMat( int rows, int cols, int type, void* data CV_DEFAULT(NULL))
{
CvMat m;
assert( (unsigned)CV_MAT_DEPTH(type) <= CV_64F );
type = CV_MAT_TYPE(type);
m.type = CV_MAT_MAGIC_VAL | CV_MAT_CONT_FLAG | type;
m.cols = cols;
m.rows = rows;
m.step = m.cols*CV_ELEM_SIZE(type);
m.data.ptr = (uchar*)data;
m.refcount = NULL;
m.hdr_refcount = 0;
return m;
}
看了之后恍然大悟：
type是矩阵中每一个数据点的类型。
cols是矩阵的列数。
rows当然是行数。
step是每一行的数据大小(应该是byte数吧）。
data是一个union的类型，里面是不同类型的指针，这样做的目的应该是可以接收 不同的数据类型吧。
比如你传了一个float*的指针进去，他就是float*了，反正这个联合体的大小就是sizeof(pointer) = 4了
internal use的先不管了。
在其他版本中把rows和height写在union里面的做法应该是做变量的兼容性吧。
IplImage
下面来重点看一下这个结构体:
typedef struct
#ifdef __cplusplus
CV_EXPORTS
#endif
_IplImage
{
int nSize; /* sizeof(IplImage) */
int ID; /* version (=0)*/
int nChannels; /* Most of OpenCV functions support 1,2,3 or 4 channels */
int alphaChannel; /* Ignored by OpenCV */
int depth; /* Pixel depth in bits: IPL_DEPTH_8U, IPL_DEPTH_8S, IPL_DEPTH_16S,
IPL_DEPTH_32S, IPL_DEPTH_32F and IPL_DEPTH_64F are supported. */
char colorModel[4]; /* Ignored by OpenCV */
char channelSeq[4]; /* ditto */
int dataOrder; /* 0 - interleaved color channels, 1 - separate color channels.
cvCreateImage can only create interleaved images */
int origin; /* 0 - top-left origin,
1 - bottom-left origin (Windows bitmaps style). */
int align; /* Alignment of image rows (4 or 8).
OpenCV ignores it and uses widthStep instead. */
int width; /* Image width in pixels. */
int height; /* Image height in pixels. */
struct _IplROI *roi; /* Image ROI. If NULL, the whole image is selected. */
struct _IplImage *maskROI; /* Must be NULL. */
void *imageId; /* " " */
struct _IplTileInfo *tileInfo; /* " " */
int imageSize; /* Image data size in bytes
(==image->height*image->widthStep
in case of interleaved data)*/
char *imageData; /* Pointer to aligned image data. */
int widthStep; /* Size of aligned image row in bytes. */
int BorderMode[4]; /* Ignored by OpenCV. */
int BorderConst[4]; /* Ditto. */
char *imageDataOrigin; /* Pointer to very origin of image data
(not necessarily aligned) -
needed for correct deallocation */
#ifdef __cplusplus
_IplImage() {}
_IplImage(const cv::Mat& m);
#endif
}
IplImage;
可以看出来，这个结构体和cvMat很像。
下面通过实际操作来understand一下这个结构体：
#include <cv.h>
#include <highgui.h>
#define u8 unsigned char
void image_operation(IplImage *image)
{
printf("nchannels:%d\n",image->nChannels);
printf("depth:%d\n",image->depth);
/* ./modules/core/include/opencv2/core/types_c.h:
* #define IPL_DATA_ORDER_PIXEL 0
*/
printf("dataOrder:%d\n",image->dataOrder);
printf("width:%d\n",image->width);
printf("height:%d\n",image->height);
printf("origin:%d\n",image->origin);
printf("widthStep:%d\n",image->widthStep);
for (int y = 0; y<image->height ; y++) {
u8* row = (u8*)(image->imageData + y*image->widthStep);
for(int x = 0; x<image->width; x++) {
row[3*x + 1] = 0;
row[3*x + 2] = 0;
}
}
}
int main(int argc,char **argv)
{
printf("this is image transforming plus\n");
IplImage *image;
image = cvLoadImage(argv[1]);
if(argc != 2)
{
std::cout << "No image data\n";
return -1;
}
cvNamedWindow("image input");
cvNamedWindow("image output");
cvShowImage("image input", image);
image_operation(image);
cvShowImage("image output", image);
cvReleaseImage(&image);
cvWaitKey(0);
cvDestroyWindow("image input");
cvDestroyWindow("image output");
return 0;
}
这里读取一个图像，并且将两个通道变成0，结果如下：
tan@ubuntu:~/cv$ ./TransformImage image/1.jpg this is image transforming plus nchannels:3 depth:8 dataOrder:0 width:400 height:300 origin:0 widthStep:1200
从结果来看，这里把蓝色通道提取了，再次验证一下就可以发现opencv的存储是 BGR 顺序存储的。
重要的一个变量是image->widthStep，因为opencv会把图像数据4字节对齐，每过一行需要加上这个值而不是自己进行处理。
