在cvCreateImageHeader之后,JPG图像从30KB变为300KB

这是我计划的一部分:

// let's get jpg image from socket
int iRcvdBytes=recvfrom(iSockFd, buff, bufferSize, 0, 
(struct sockaddr*)&cliAddr, (socklen_t*)&cliAddrLen);

// buff now contains 30KB jpg image

// let's load the jpg image to IplImage
IplImage* fIplImageHeader;
fIplImageHeader = cvCreateImageHeader(cvSize(640, 480), 8, 1);
fIplImageHeader->imageData = (char *)buff;

// now let's check the size difference
cout << "Received " << iRcvdBytes << " bytes from the client" << endl;
cout << fIplImageHeader->imageSize << endl;

结果是:

Received 31860 bytes from the client
307200

为什么呢?cvCreateImageHeader()是在内部将jpg图像转换为RGB还是类似的内容?我希望它保持JPG格式,并用cvShowImage()显示它。

求求你,欢迎任何帮助。