openCV源码阅读(1)loadimage.doc

/-cvLoadImage-Using the go to definition and go to declarlization in the VS, I find the cvLoadImage function in highgui module.It returns an IplImage structure calling imread_().And I also find a similar function called cvLoadImageM(). It returns a CvMat structure.CV_IMPL IplImage*cvLoadImage( const char* filename, int iscolor ) return (IplImage*)cv:imread_(filename, iscolor, cv:LOAD_IMAGE );CV_IMPL CvMat*cvLoadImageM( const char* filename, int iscolor ) return (CvMat*)cv:imread_( filename, iscolor, cv:LOAD_CVMAT );/-Tracking for the imread:enum LOAD_CVMAT=0, LOAD_IMAGE=1, LOAD_MAT=2 ;static void*imread_( const string& filename, int flags, int hdrtype, Mat* mat=0 )It declears the variables one of them (IplImage* image, CvMat *matrix) will be returned at the end of the function. IplImage* image = 0; CvMat *matrix = 0;And the temporary variables: Mat temp, *data = &temp;Find a decoder for the picture according its name. We will talk about the decoder later.There is an abstract class BaseImageDecoder which was inherited by 7 embodied class for various picture file forms, such as *.bmp, *.jpg.These embodied class has been stored in a vector called decoders.Using the findDecoder() to choose a decoder for current object. ImageDecoder decoder = findDecoder(filename);Defend the faluire from finding a decoder: if( decoder.empty() ) return 0;setSource for decoder member m_filename, and release its buffer m_buf. decoder-setSource(filename);read files head to get the informations in the picture, such as the width, height. if( !decoder-readHeader() ) return 0;store the size information into a CvSize variable. CvSize size; size.width = decoder-width(); size.height = decoder-height();the type information: int type = decoder-type(); if( flags != -1 ) if( (flags & CV_LOAD_IMAGE_ANYDEPTH) = 0 ) type = CV_MAKETYPE(CV_8U, CV_MAT_CN(type); if( (flags & CV_LOAD_IMAGE_COLOR) != 0 | (flags & CV_LOAD_IMAGE_ANYCOLOR) != 0 & CV_MAT_CN(type) 1) ) type = CV_MAKETYPE(CV_MAT_DEPTH(type), 3); else type = CV_MAKETYPE(CV_MAT_DEPTH(type), 1); Charge whether you want an image or a mat:Hdtype is a parameter of the loadImage function. if( hdrtype = LOAD_CVMAT | hdrtype = LOAD_MAT ) if( hdrtype = LOAD_CVMAT ) matrix = cvCreateMat( size.height, size.width, type ); temp = cvarrToMat(matrix); else mat-create( size.height, size.width, type ); data = mat; else Create an image based on the size and type we have just get, and convert the temporary arry into Mat. image = cvCreateImage( size, cvIplDepth(type), CV_MAT_CN(type) ); temp = cvarrToMat(image); Read the data of the pixels:If falure then release the storage and return 0 if( !decoder-readData( *data ) cvReleaseImage( &image ); cvReleaseMat( &matrix ); if( mat ) mat-release(); return 0; Return the result: return hdrtype = LOAD_CVMAT ? (void*)matrix : hdrtype = LOAD_IMAGE ? (void*)image : (void*)mat;To the mat read, just call the image function and give a LOAD_MAT hdtype:Mat imread( const string& filename, int flags ) Mat img; imread_( filename, flags, LOAD_MAT, &img ); return img;/-findDecoder-Those coders which will be used are stored in these two vectors.static vector decoders;static vector encoders;The findDecoder find a decoder from the above decoders for the application.ImageDecoder findDecoder( const string& filename )Find the length of the longest signature. size_t i, maxlen = 0; for( i = 0; i signatureLength(); maxlen = std:max(maxlen, len); Open the file in read and binary mode and return an ImageDecoder which is an abstract class as a NULL. FILE* f= fopen( filename.c_str(), rb ); if( !f ) return ImageDecoder();get the signature which can tell us which form the picture is and which decoder we need. string signature(maxlen, ); maxlen = fread( &signature0, 1, maxlen, f ); fclose(f); signature = signature.substr(0, maxlen);check the signature with each decoder in the decoders vector to decide the decoder. for( i = 0; i checkSignature(signature) ) return decodersi-newDecoder(); If the signature does not anyone we return a NULL. return ImageDecoder();class BaseImageDecoder;class BaseImageEncoder;typedef Ptr ImageEncoder;typedef Ptr ImageDecoder;/ base class for decoders /class BaseImageDecoderpublic: BaseImageDecoder(); virtual BaseImageDecoder() ; int width() const return m_width; ; int height() const return m_height; ; int type() const return m_type; ; virtual bool setSource( const string& filename ); virtual bool setSource( const Mat& buf ); virtual bool readHeader() = 0; virtual bool readData( Mat& img ) = 0; virtual size_t signatureLength() const; virtual bool checkSignature( const string& signature ) const; virtual Ima