[RESOLVED] Why does my bitmap become all black when saved to file?
I am trying to create a bitmap. This works well as I can obtain the correct result on the screen. But when I am trying to save the bitmap to a file, it become just a black rectangle.
I have tried a lot of things, multiple functions to save bitmap taken from different places, and always obtain the same result.
Here is a simplified version of the code, which produces the same result. It can simply be called in the simplest project that uses MFC. If I put a break point just before calling the write function, I can see my picture on the screen, as expected. But the bitmap is black in the file.
Code:
void CreateDrawing()
{
CWnd wnd;
CRect rect (0, 0, 100, 100);
wnd.CreateEx(NULL, NULL, NULL,WS_POPUP | WS_CHILD | WS_CLIPSIBLINGS, rect, NULL, NULL, NULL);
CClientDC paintdc(&wnd);
paintdc.SetBkMode(TRANSPARENT);
CRect rectWnd = rect;
CPoint ptToolTipLeft = rectWnd.TopLeft();
SetWindowPos(wnd.m_hWnd, HWND_TOPMOST,ptToolTipLeft.x+1, ptToolTipLeft.y+1, rectWnd.Width(), rectWnd.Height(),SWP_SHOWWINDOW|SWP_NOOWNERZORDER|SWP_NOACTIVATE);
CBrush m_brush(RGB(255,255,255));
CPen m_pen(PS_SOLID, 0, COLORREF(RGB(0, 0, 0)));
CBrush* pOldBrush = paintdc.SelectObject(&m_brush);
CPen* pOldPen = paintdc.SelectObject(&m_pen);
paintdc.Rectangle(0,0,rect.Width(),rect.Height());
paintdc.MoveTo(0, 0);
paintdc.LineTo(100, 100);
HBITMAP hbmp = CreateCompatibleBitmap(paintdc.m_hDC, rect.Width(),rect.Height());
CBitmap bmp;
bmp.Attach(hbmp);
WriteToFile(paintdc, hbmp);
paintdc.SelectObject(pOldBrush);
paintdc.SelectObject(pOldPen);
}
bool WriteToFile(CDC& hMemDC, HBITMAP hBitmap)
{
CString strFileName = "c:\\test\\test.bmp";
int wBitCount = 32;
BITMAP Bitmap;
CPalette pal;
pal.Attach(::GetStockObject(DEFAULT_PALETTE));
hMemDC.SelectPalette(&pal, TRUE);
GetObject(hBitmap, sizeof(BITMAP), (LPSTR)&Bitmap);
BITMAPINFOHEADER bi;
bi.biSize = sizeof(BITMAPINFOHEADER);
bi.biWidth = Bitmap.bmWidth;
bi.biHeight = Bitmap.bmHeight;
bi.biPlanes = 1;
bi.biBitCount = wBitCount;
bi.biCompression = BI_RGB;
bi.biSizeImage = 0;
bi.biXPelsPerMeter = 0;
bi.biYPelsPerMeter = 0;
bi.biClrUsed = 0;
bi.biClrImportant = 0;
DWORD dwBmBitsSize = ((Bitmap.bmWidth * wBitCount + 31) / 32) * 4 * Bitmap.bmHeight;
HANDLE hDib = GlobalAlloc(GHND, dwBmBitsSize+sizeof(BITMAPINFOHEADER));
LPBITMAPINFOHEADER lpbi = (LPBITMAPINFOHEADER)GlobalLock(hDib);
*lpbi = bi;
GetDIBits(hMemDC.m_hDC, hBitmap, 0, (UINT)Bitmap.bmHeight,
(LPSTR)lpbi + sizeof(BITMAPINFOHEADER), (BITMAPINFO *)lpbi, DIB_RGB_COLORS);
DWORD dwDIBSize = sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER) + dwBmBitsSize;
BITMAPFILEHEADER bmfHdr;
bmfHdr.bfType = 'B'+('M' << 8);
bmfHdr.bfSize = dwDIBSize;
bmfHdr.bfReserved1 = 0;
bmfHdr.bfReserved2 = 0;
bmfHdr.bfOffBits = (DWORD)sizeof(BITMAPFILEHEADER) + (DWORD)sizeof(BITMAPINFOHEADER);
DWORD dwWritten;
HANDLE fh = CreateFile(strFileName,GENERIC_WRITE,0,NULL,CREATE_ALWAYS,
FILE_ATTRIBUTE_NORMAL|FILE_FLAG_SEQUENTIAL_SCAN,NULL);
ASSERT(fh != INVALID_HANDLE_VALUE);
WriteFile(fh, (LPSTR)&bmfHdr, sizeof(BITMAPFILEHEADER), &dwWritten, NULL);
WriteFile(fh, (LPSTR)lpbi, dwDIBSize, &dwWritten, NULL);
GlobalUnlock(hDib);
GlobalFree(hDib);
CloseHandle(fh);
return true;
}
I am probably missing something simple, but could not figure what.
Re: Why does my bitmap become all black when saved to file?
Instead of:Have:
Code:
bi.biSizeImage = bi.biWidth * 4 * bi.biHeight * sizeof(unsigned char);
Re: Why does my bitmap become all black when saved to file?
Tried it, but my bitmap is still black... :(
Re: Why does my bitmap become all black when saved to file?
After so many attempts, I have finally solved my problem. I had tried already using memory DC without success, creating the bitmap object at the beginning or the end... The only thing I failed to do was attaching the bitmap to the device context:
Code:
CDC memDC;
memDC.CreateCompatibleDC(&paintdc);
CBitmap bmp;
bmp.CreateCompatibleBitmap(&memDC, rect.Width(),rect.Height());
memDC.SelectObject(&bmp);
Now, the bitmap I create is in black and white (even if I use a coloured pen) so I just have to figure out how to put colour in the bitmap...
Re: Why does my bitmap become all black when saved to file?
I'm not sure what you're doing with the palette. You've got a 32 bit DIB so you don't need a palette. That might be causing some weirdness with your colors.
Re: Why does my bitmap become all black when saved to file?
This palette thing is a "left over" from the number of attempts I have made to get all this to work. But removing it does not solve the "colour" problem. I still be a black and with bitmap.
Well, in the posted code that makes sense because I am writing in Black on a white background, but I have changed the colour of the pen:
Code:
CPen m_pen(PS_SOLID, 0, COLORREF(RGB(255, 0, 0)));
It draws the colour fine on the screen if I display it, but the bitmap in the file does not have anycolour.
Re: Why does my bitmap become all black when saved to file?
Could you post an amended code snippit. You've apparently done some changes since your first post.
Re: Why does my bitmap become all black when saved to file?
I have put in bold what I believe are all the changes from the beginning. They do produce a usable bitmap file, but in bloack and white only.
Code:
void CreateDrawing()
{
CWnd wnd;
CRect rect (0, 0, 100, 100);
wnd.CreateEx(NULL, NULL, NULL,WS_POPUP | WS_CHILD | WS_CLIPSIBLINGS, rect, NULL, NULL, NULL);
CClientDC paintdc(&wnd);
CDC memDC;
memDC.CreateCompatibleDC(&paintdc);
CBitmap bmp;
bmp.CreateCompatibleBitmap(&memDC, rect.Width(),rect.Height());
memDC.SelectObject(&bmp);
CBrush m_brush(RGB(255,255,255));
CPen m_pen(PS_SOLID, 1, COLORREF(RGB(0, 255, 0)));
CBrush* pOldBrush = memDC.SelectObject(&m_brush);
CPen* pOldPen = memDC.SelectObject(&m_pen);
memDC.SetBkMode(TRANSPARENT);
memDC.Rectangle(0,0,rect.Width(),rect.Height());
memDC.MoveTo(0, 0);
memDC.LineTo(100, 100);
WriteToFile(memDC, (HBITMAP)bmp.m_hObject);
memDC.SelectObject(pOldBrush);
memDC.SelectObject(pOldPen);
}
bool WriteToFile(CDC& hMemDC, HBITMAP hBitmap)
{
CString strFileName = "c:\\test\\test.bmp";
int wBitCount = 32;
BITMAP Bitmap;
GetObject(hBitmap, sizeof(BITMAP), (LPSTR)&Bitmap);
BITMAPINFOHEADER bi;
bi.biSize = sizeof(BITMAPINFOHEADER);
bi.biWidth = Bitmap.bmWidth;
bi.biHeight = Bitmap.bmHeight;
bi.biPlanes = 1;
bi.biBitCount = wBitCount;
bi.biCompression = BI_RGB;
bi.biSizeImage = bi.biWidth * 4 * bi.biHeight * sizeof(unsigned char);
bi.biXPelsPerMeter = 0;
bi.biYPelsPerMeter = 0;
bi.biClrUsed = 0;
bi.biClrImportant = 0;
DWORD dwBmBitsSize = ((Bitmap.bmWidth * wBitCount + 31) / 32) * 4 * Bitmap.bmHeight;
HANDLE hDib = GlobalAlloc(GHND, dwBmBitsSize+sizeof(BITMAPINFOHEADER));
LPBITMAPINFOHEADER lpbi = (LPBITMAPINFOHEADER)GlobalLock(hDib);
*lpbi = bi;
GetDIBits(hMemDC.m_hDC, hBitmap, 0, (UINT)Bitmap.bmHeight,
(LPSTR)lpbi + sizeof(BITMAPINFOHEADER), (BITMAPINFO *)lpbi, DIB_RGB_COLORS);
DWORD dwDIBSize = sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER) + dwBmBitsSize;
BITMAPFILEHEADER bmfHdr;
bmfHdr.bfType = 'B'+('M' << 8);
bmfHdr.bfSize = dwDIBSize;
bmfHdr.bfReserved1 = 0;
bmfHdr.bfReserved2 = 0;
bmfHdr.bfOffBits = (DWORD)sizeof(BITMAPFILEHEADER) + (DWORD)sizeof(BITMAPINFOHEADER);
DWORD dwWritten;
HANDLE fh = CreateFile(strFileName,GENERIC_WRITE,0,NULL,CREATE_ALWAYS,
FILE_ATTRIBUTE_NORMAL|FILE_FLAG_SEQUENTIAL_SCAN,NULL);
ASSERT(fh != INVALID_HANDLE_VALUE);
WriteFile(fh, (LPSTR)&bmfHdr, sizeof(BITMAPFILEHEADER), &dwWritten, NULL);
WriteFile(fh, (LPSTR)lpbi, dwDIBSize, &dwWritten, NULL);
GlobalUnlock(hDib);
GlobalFree(hDib);
CloseHandle(fh);
return true;
}
Re: Why does my bitmap become all black when saved to file?
Change this line:
Code:
bmp.CreateCompatibleBitmap(&memDC, rect.Width(),rect.Height());
to this:
Code:
bmp.CreateCompatibleBitmap(&paintdc, rect.Width(),rect.Height());
Re: Why does my bitmap become all black when saved to file?
A tiny mistake:
Code:
bmp.CreateCompatibleBitmap(&memDC, rect.Width(),rect.Height());
There must be paintdc instead.
Newly created DC (like your memDC) contains B&W bitmap. Been creating compatible bitmap you create same B&W bitmap.
[Edit]Oops, hoxsiew appeared more swift. :)
Re: Why does my bitmap become all black when saved to file?
Sorry for the late answer as the week end got me going.
Thanks for the answers, that are correct and working.
