There is much confusion about bitmap handles (HBITMAP) and device independent bitmaps (DIB). The terms are often interchanged and functions that you would expect to return a DIB, such as CreateDIBitmap, do in fact return a value of type HBITMAP.
HBITMAP’s are handles to memory objects containing a BITMAP structure followed by palette information and bitmap data and should be processed by ScanBarCodeFromBitmap:
DIB’s are handles to memory objects that have the same format as a BMP file minus the file header (BITMAPFILEHEADER) and should be processed by ScanBarCodeFromDIB. The following MFC C++ code can be used to load a small BMP file into a DIB:
#include <limits.h>
HGLOBAL LoadDIB( LPCSTR sBMPFile)
{
CFile file;
if( !file.Open( sBMPFile, CFile::modeRead) )
return NULL;
BITMAPFILEHEADER bmfHeader;
ULONGLONG nFileLen;
nFileLen = file.GetLength();
if (nFileLen > UINT_MAX)
{
AfxMessageBox(“File is too big to load with a single read”);
return NULL ;
}
// Read file header and ignore
if (file.Read((LPSTR)&bmfHeader, sizeof(bmfHeader)) != sizeof(bmfHeader))
return NULL;
// File type should be ‘BM’
if (bmfHeader.bfType != ((WORD) (‘M’ << 8) | ‘B’)) return NULL;
HGLOBAL hDIB = ::GlobalAlloc(GMEM_FIXED, (SIZE_T) nFileLen);
if (hDIB == 0)
return NULL;
// Read the remainder of the bitmap file.
if (file.Read((LPSTR)hDIB, (UINT) nFileLen – sizeof(BITMAPFILEHEADER)) !=
(UINT) nFileLen – sizeof(BITMAPFILEHEADER) )
{
::GlobalFree(hDIB);
return NULL;
}
return hDIB;
}
The following wikipedia article contains a more detailed explanation: http://en.wikipedia.org/wiki/BMP_file_format
