cv::imread image is not show on MFC's picture box - opencv

Question

I'm building the dialog-based MFC application.
When I click the Button then I can choose the image from the file explorer and that image is also loaded into cv::imread(). And also shows in the Picture Control.
I can load and show an image in the Picture Control with the following code.
void CMFCApplication3Dlg::OnBnClickedButton1()
{
cv::Mat src = cv::imread("D:/source/repos/Testing_Photos/Large/cavalls.png");
Display(src);
}
But not with the following code.
void CMFCApplication3Dlg::OnBnClickedButton1()
{
TCHAR szFilter[] = _T("PNG (*.png)|*.png|JPEG (*.jpg)|*.jpg|Bitmap (*.bmp)|*.bmp||");
CFileDialog dlg(TRUE, NULL, NULL, OFN_HIDEREADONLY | OFN_OVERWRITEPROMPT, szFilter, AfxGetMainWnd());
if (dlg.DoModal() == IDC_BUTTON1)
{
CString cstrImgPath = dlg.GetPathName();
CT2CA pszConvertedAnsiString(cstrImgPath);
std::string strStd(pszConvertedAnsiString);
cv::Mat src = cv::imread(strStd);
Display(src);
}
}
And the following is the "Display" function.
void CMFCApplication3Dlg::Display(cv::Mat& mat) {
CStatic * PictureB = (CStatic *)GetDlgItem(IDC_STATIC);
CWnd* cwn = (CWnd *)GetDlgItem(IDC_STATIC);
CDC* wcdc = cwn->GetDC();
HDC whdc = wcdc->GetSafeHdc();
RECT rec;
cwn->GetClientRect(&rec);
cv::Size matSize;
matSize = cv::Size(rec.right, rec.bottom);
BITMAPINFO bitmapinfo;
bitmapinfo.bmiHeader.biBitCount = 24;
bitmapinfo.bmiHeader.biWidth = mat.cols;
bitmapinfo.bmiHeader.biHeight = -mat.rows;
bitmapinfo.bmiHeader.biPlanes = 1;
bitmapinfo.bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
bitmapinfo.bmiHeader.biCompression = BI_RGB;
bitmapinfo.bmiHeader.biClrImportant = 0;
bitmapinfo.bmiHeader.biClrUsed = 0;
bitmapinfo.bmiHeader.biSizeImage = 0;
bitmapinfo.bmiHeader.biXPelsPerMeter = 0;
bitmapinfo.bmiHeader.biYPelsPerMeter = 0;
StretchDIBits(
whdc,
0, 0,
matSize.width, matSize.height,
0, 0,
mat.cols, mat.rows,
mat.data,
&bitmapinfo,
DIB_RGB_COLORS,
SRCCOPY
);
}
I am very new to MFC and I really don't have any idea where I'm wrong.
Please help me!
Thank you.

Answer 1

This is not the correct method to paint. The picture will be erased every time there is a paint request.
That's what happens with CFileDialog which forces another repaint immediately after you paint the image. You have to respond to OnPaint or OnDrawItem, or use CStatic::SetBitmap as noted in comment.
You can do this with CImage class, there is no need for OpenCV:
CImage img;
if(S_OK == img.Load(L"unicode.jpg"))
{
CStatic *control = (CStatic*)GetDlgItem(IDC_STATIC);
control->ModifyStyle(0, SS_BITMAP);
auto oldbmp = control->SetBitmap(img.Detach());
if(oldbmp)
DeleteObject(oldbmp);
}
Or you can use OpenCV to create HBITMAP handle.
Note that OpenCV does not handle Unicode filenames. CW2A converts Unicode to ANSI character encoding. This fails if one or more code points cannot be represented in the currently active code page. To work around it, we can open the file with CFile or std::ifstream, read it as binary, then open with cv::imdecode instead. Example:
//open the file from unicode path:
const wchar_t *filename = L"unicode.jpg";
std::ifstream fin(filename, std::ios::binary);
if(!fin.good())
return;
//read from memory
std::vector<char> vec(std::istreambuf_iterator<char>(fin), {});
cv::Mat src = cv::imdecode(vec, cv::IMREAD_COLOR);
if(!src.data)
return;
//create hbitmap
BITMAPINFOHEADER bi = { sizeof(bi), src.cols, -src.rows, 1, 24 };
CClientDC dc(this);
auto hbmp = CreateDIBitmap(dc, &bi, CBM_INIT, src.data, (BITMAPINFO*)&bi, 0);
//send hbitmap to control
auto control = (CStatic*)GetDlgItem(IDC_STATIC);
auto oldbmp = control->SetBitmap(hbmp);
if (oldbmp)
DeleteObject(oldbmp);