Thread: Raw RGB image in memory - how to create a bitmap and palette I can use?

I suspect this is a trivial problem to solve but it's driving me nuts.


I have functioning code that uses LoadBitmapFromBMPFile() which I lifted from Microsoft's web site to load a bitmap and display it so:

Code:

HBITMAP hOldBitmap, hBitmap;
HPALETTE hOldPalette, hPalette;
HDC hDC, hMemDC;
BITMAP bm;

[...]

LoadBitmapFromBMPFile( L"somefile.bmp", &hBitmap, &hPalette );

GetObject( hBitmap, sizeof(BITMAP), &bm );
hMemDC = CreateCompatibleDC( hDC );
hOldBitmap = (HBITMAP)SelectObject( hMemDC, hBitmap );
hOldPalette = SelectPalette( hDC, hPalette, FALSE );
RealizePalette( hDC );

BitBlt( hDC, x, y, bm.bmWidth, bm.bmHeight, hMemDC, 0, 0, SRCCOPY );

No problem.


At a later point, I have a raw image in memory. RGB format, 8 bits per pixel. I want to BitBlt() this onto the display, same as above.

I have functioning code that takes that image in memory, writes it to a file in BMP format, and then calls LoadBitmapFromBMPFile() as above ... but this is silly. I ought to be able to skip the file writing and reading.

LoadBitmapFromBMPFile() starts off so:

Code:

BOOL LoadBitmapFromBMPFile( LPTSTR szFileName, HBITMAP *phBitmap,
   HPALETTE *phPalette )
   {

   BITMAP  bm;

   *phBitmap = NULL;
   *phPalette = NULL;

   // Use LoadImage() to get the image loaded into a DIBSection
   *phBitmap = (HBITMAP)LoadImage( NULL, szFileName, IMAGE_BITMAP, 0, 0,
               LR_CREATEDIBSECTION | LR_DEFAULTSIZE | LR_LOADFROMFILE );

Surely there's some analogue to LoadImage() that, instead of taking a filename as a parameter, can accept a pointer to the already-in-memory RGB image data?

If there is, I haven't found it.



Google has suggested I use CreateDIBSection(). This represents my non-successful attempt:

Code:

unsigned char *display_image_data;  // image data in 8 bpp RGB format

[...]

BITMAPINFO pbmi;

pbmi.bmiheader.biSize = sizeof(BITMAPINFO);
pbmi.bmiheader.biWidth = DISPLAY_X;  // img width in pixels
pbmi.bmiheader.biHeight = DISPLAY_Y;  // img height in pixels
pbmi.bmiheader.biPlanes = 1;
pbmi.bmiheader.biBitCount = 24;  // also tried 8 here
pbmi.bmiheader.biCompression = BI_RGB;
pbmi.bmiheader.biSizeImage = 0;  // docs say 0 if BI_RGB is used
pbmi.bmiheader.biXPelPerMeter = 0;  // no idea what to do with this
pbmi.bmiheader.biYPelPerMeter = 0;  // or this
pbmi.bmiheader.biClrUsed = 0;
pbmi.bmiheader.biClrImportant = 0;
// pbmi.bmiColors    shouldn't need for RGB

hBitmap = CreateDIBSection( hDC, &pbmi, DIB_RGB_COLORS, (void **)display_image_data, NULL, 0 );

GetObject( hBitmap, sizeof(BITMAP), &bm );
hMemDC = CreateCompatibleDC( hDC );
hOldBitmap = (HBITMAP)SelectObject( hMemDC, hBitmap );
hOldPalette = SelectPalette( hDC, hPalette, FALSE );
RealizePalette( hDC );

BitBlt( hDC, x, y, bm.bmWidth, bm.bmHeight, hMemDC, 0, 0, SRCCOPY );

And what I get is a big black rectangle painted to the screen.

I would appreciate some tips here ... thank you.

pbmi.bmiheader.biSize = sizeof(BITMAPINFO);

shouldn't this be
pbmi.bmiheader.biSize = sizeof(BITMAPINFOHEADER);
displaying bitmap

Do set the struct to zero (ZeroMemory(&pbmi, sizeof BITMAPINFO) so any members you do not fill will not hold rubbish?

Have you tried SetDiBits() ?
Dynamic Bitmap Display

Does CreateDIBSection() return an error?

From memory, is over 10 years since I did BMP capture for a RAT app...

Only 24 bit images require the RGB reversed, based on the original OS/R implementation.