Working with EXIF data

简介

我们继续关注Windows Mobile 5.0关于图像的API特性。前面我们展示了如何使用API加载并显示图像，在这片文章里，我将展示如何读取图像中的Exif数据。

Exif是数码相机中存储照片元数据的地方。它可以存储包括相机制造商、相机型号、相机的参数设置，设置可以存储拍照时刻所在的地理位置，如果你的数码相机支持GPS的话。下面我们就来看看我们如何读取这些数据。

实现

这个测试应用只是展示读取Exif信息

IStream* pStream = CreateStreamByFileName(strFileName);

IStream* CTestExifDlg::CreateStreamByFileName(const CString& strFileName)

{

HANDLE hFile = CreateFile(strFileName, GENERIC_READ, 0, NULL, OPEN_EXISTING, 0, NULL);

if (hFile == INVALID_HANDLE_VALUE) {

return 0;

}

DWORD dwFileSize = GetFileSize(hFile, NULL);

if (dwFileSize == (DWORD)-1)

{

CloseHandle(hFile);

return 0;

}

HGLOBAL hGlobal = GlobalAlloc(GMEM_MOVEABLE, dwFileSize);

if (hGlobal == NULL) {

CloseHandle(hFile);

return 0;

}

LPVOID pvData = GlobalLock(hGlobal);

if (pvData == NULL) {

GlobalUnlock(hGlobal);

CloseHandle(hFile);

return 0;

}

DWORD dwBytesRead = 0;

BOOL bRead = ReadFile(hFile, pvData, dwFileSize, &dwBytesRead, NULL);

GlobalUnlock(hGlobal);

CloseHandle(hFile);

if (!bRead)

{

return 0;

}

IStream* pStream = 0;

if (FAILED(CreateStreamOnHGlobal(hGlobal, TRUE, &pStream))) {

return 0;

}

return pStream;

}

现在我们有一个IStream，可以创建Image Decoder来读取Exif数据了。

IImagingFactory *pImgFactory = 0;

if (SUCCEEDED(CoCreateInstance (CLSID_ImagingFactory, NULL, CLSCTX_INPROC_SERVER, IID_IImagingFactory, (void **)&pImgFactory))) {

IImageDecoder* pDecoder = 0;

if (SUCCEEDED(pImgFactory->CreateImageDecoder(pStream, DecoderInitFlagNone, &pDecoder))) {

UINT nCount = 0;

if (SUCCEEDED(pDecoder->GetPropertyCount(&nCount)) && nCount) {

PROPID* pIds = new PROPID[nCount];

if (SUCCEEDED(pDecoder->GetPropertyIdList(nCount, pIds))) {

for (UINT i = 0; i < nCount; i++) {

UINT nPropSize = 0;

if (SUCCEEDED(pDecoder->GetPropertyItemSize(pIds[i], &nPropSize))) {

BYTE* pBuff = new BYTE[nPropSize];

PropertyItem* pItem = (PropertyItem*)pBuff;

if (SUCCEEDED(pDecoder->GetPropertyItem(pIds[i], nPropSize, pItem))) {

AddPropertyItemToList(i, pList, pItem);

}

delete[] pBuff;

}

}

}

delete[] pIds;

}

pDecoder->Release();

}

pImgFactory->Release();

}