how to convert CBitmap to cv::Mat?

Question

How to convert CBitmap to cv::Mat? Maybe there are some libs or something else... like...

CBitmap bitmap;
bitmap.CreateBitmap(128, 128, 1, 24, someData);
cv::Mat outBitmap(128,128,someData,1,24);

but that code is incorrect.

thanks!

Answer 1

There is another way around, you can convert your CBitmap to HBitmap, then convert HBitmap to GdiPlus::Bitmap, then convert it to cv::Mat. Here's what you can do, but beware, this solution only works for RGB24 pixel format :

Step 1: CBitmap to HBITMAP

HBITMAP hBmp = (HBITMAP)yourCBitmap.GetSafeHandle();

Step 2: HBITMAP to Gdiplus::Bitmap (copied from this question)

#include <GdiPlus.h>
#include <memory>

Gdiplus::Status HBitmapToBitmap( HBITMAP source, Gdiplus::PixelFormat pixel_format, Gdiplus::Bitmap** result_out )
{
  BITMAP source_info = { 0 };
  if( !::GetObject( source, sizeof( source_info ), &source_info ) )
    return Gdiplus::GenericError;

  Gdiplus::Status s;

  std::auto_ptr< Gdiplus::Bitmap > target( new Gdiplus::Bitmap( source_info.bmWidth, source_info.bmHeight, pixel_format ) );
  if( !target.get() )
    return Gdiplus::OutOfMemory;
  if( ( s = target->GetLastStatus() ) != Gdiplus::Ok )
    return s;

  Gdiplus::BitmapData target_info;
  Gdiplus::Rect rect( 0, 0, source_info.bmWidth, source_info.bmHeight );

  s = target->LockBits( &rect, Gdiplus::ImageLockModeWrite, pixel_format, &target_info );
  if( s != Gdiplus::Ok )
    return s;

  if( target_info.Stride != source_info.bmWidthBytes )
    return Gdiplus::InvalidParameter; // pixel_format is wrong!

  CopyMemory( target_info.Scan0, source_info.bmBits, source_info.bmWidthBytes * source_info.bmHeight );

  s = target->UnlockBits( &target_info );
  if( s != Gdiplus::Ok )
    return s;

  *result_out = target.release();

  return Gdiplus::Ok;
}

Call this function and pass your HBITMAP to it.

Step 3: Gdiplus::Bitmap to cv::Mat

cv::Mat GdiPlusBitmapToCvMat(Gdiplus::Bitmap* bmp)
{
    auto format = bmp->GetPixelFormat();
    if (format != PixelFormat24bppRGB)
        return cv::Mat();

    int width = bmp->GetWidth();
    int height = bmp->GetHeight();
    Gdiplus::Rect rcLock(0, 0, width, height);
    Gdiplus::BitmapData bmpData;

    if (!bmp->LockBits(&rcLock, Gdiplus::ImageLockModeRead, format, &bmpData) == Gdiplus::Ok)
        return cv::Mat();

    cv::Mat mat = cv::Mat(height, width, CV_8UC3, static_cast<unsigned char*>(bmpData.Scan0), bmpData.Stride).clone();

    bmp->UnlockBits(&bmpData);
    return mat;
}

Pass the Gdiplus::Bitmap that you created in last step to this function and you will get your cv:Mat. As I said before this function just works with RGB24 pixel format.