C / C++ / MFC

void PaintBkgImage(__in HWND hWnd, 
		__in HDC PaintDC, 
		__in BITMAP bmp, 
		__in HDC prevDC,
		__in int StretchFromLeft,
		__in int StretchFromRight,
		__in int StretchFromTop,
	        __in int StretchFromBottom)
{
	SetStretchBltMode(PaintDC, HALFTONE);
	StretchBlt(PaintDC, 
			   StretchFromLeft, 
			   StretchFromTop, 
			   _client_rect.right, 
			   _client_rect.bottom - StretchFromBottom,
			   prevDC, 
			   StretchFromRight, 
			   0, 
			   bmp.bmWidth, 
			   bmp.bmHeight, 
			   SRCCOPY);
}

DWORD destRedColor   = 0;
DWORD destBlueColor  = 0;
DWORD destGreenColor = 0;
DWORD destAlphaColor = 0;
DWORD SrcRedColor     = 0;
DWORD SrcBlueColor    = 0;
DWORD SrcGreenColor   = 0;
DWORD SrcAlphaColor   = 0;
int src_const_alpha   = 0;

// After all the inits we can do the job : Replace Color
for ( int i = ( ( bm.bmWidth * bm.bmHeight ) - 1 ); i >= 0; --i )
 {
	COLORREF clrRef =  ptPixels[i]; //Bitmap pixel color taken with CreateDIBSection's void* lpBits;
	clrRef = COLORREF2RGB( clrRef );
        
        //taking alpha,red,green and blue values.
	DWORD redDest   = GetRValue( clrRef );
	DWORD greenDest = GetGValue( clrRef);
        DWORD blueDest  = GetBValue( clrRef);
	BYTE *ptrAlphaDest = reinterpret_cast<BYTE*>( &clrRef );
	DWORD alphaDest;
	alphaDest = ptrAlphaDest[0];

        //taking alpha,red,green and blue values.
	DWORD redSrc   = GetRValue( _cNewColor ); //Shadow Color ( of user's choice )
	DWORD greensrc = GetGValue( _cNewColor );
        DWORD blueSrc  = GetBValue( _cNewColor );
	BYTE *ptrAlphaSrc = reinterpret_cast<BYTE*>( &_cNewColor );
	DWORD alphaSrc;
	alphaSrc = ptrAlphaSrc[0];

	src_const_alpha  = int( m_intensity * 2.55 );
	SrcRedColor   = redSrc   * src_const_alpha / 255.0;
        SrcGreenColor = greensrc * src_const_alpha / 255.0;
	SrcBlueColor  = blueSrc  * src_const_alpha / 255.0;
	SrcAlphaColor = alphaSrc * src_const_alpha / 255.0;

        destRedColor   = SrcRedColor    + ( 1 - SrcAlphaColor ) * redDest;
	destGreenColor = SrcGreenColor  + ( 1 - SrcAlphaColor ) * greenDest;
	destBlueColor  = SrcBlueColor   + ( 1 - SrcAlphaColor ) * blueDest;
	destAlphaColor = SrcAlphaColor  + ( 1 - SrcAlphaColor ) * alphaDest;

	ptPixels[i]
	= (destAlphaColor << 24 ) |                       
	  (destRedColor   << 16 ) |  
	  (destGreenColor << 8  ) | 
	  (destBlueColor);
}