Saving a DIB to a file

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2 total messages Started by finkcr1 Fri, 19 Jan 1996 14:35

#12

Author: finkcr1
Date: Fri, 19 Jan 1996 14:35

34 lines
2201 bytes

I'm using VC++ 1.5 and have successfully saved the image I drew in an MDI 
child window to a file as a DIB.  I used as a model the code in the MS example 
program DIBVIEW.  The problem is that the bitmap I've saved to the file shows 
up as a monochrome bitmap; the colors displayed in the window do not show up. 
Here is the code I used to copy the bitmap to a memory DC:

	memDC.CreateCompatibleDC(GetDC())
                     .
		     .	
    	bm.CreateCompatibleBitmap(&memDC,rect.Width(),rect.Height());
    		     .
		     .		
       oldbm = memDC.SelectObject(&bm);
       memDC.BitBlt(0, 0, rect.Width(),rect.Height(), GetDC(), 0, 0, SRCCOPY); 


When I do a GetObject on the bitmap, it says it has 1 bit per pixel.  I'm 
confused. I don't completely understand the intricacies of palettes, etc.. The 
palette associated with the memory DC seems to be OK (20 entries). I call a 
routine, WinDibFromBitmap (copied from DIBVIEW), it calls GetDibBits and 
passes back a handle to the DIB.  It also sets up the BITMAPINFO header and 
allows space for the color table.  It sets the BiBitCount entry in the 
BITMAPINFOHEADER to a value calculated from the product of the BmPlanes and 
BmBitsPixel entries in the BITMAP structure.  BiBitCount is then used to 
determine the number of entries in the color table. The palette is passed to 
the routine as an HPALETTE structure. This is selected into a DC and then 
RealizePalette is called. This DC (Creates with a GetDC(NULL)) is used as a 
parameter to GetDibBits.   

If there are any DIB experts out there, please respond to me at 
finkcr1@jhuapl.edu or to one of these newsgroups.  Thanks.

Clay Fink

Re: Saving a DIB to a file

#13

Author: Chris Marriott
Date: Fri, 19 Jan 1996 19:12

44 lines
2328 bytes

In article <NEWTNews.822065811.24940.finkcr1@ptu-crf-pc.jhuapl.edu>
           finkcr1@ptu-crf-pc.jhuapl.edu  writes:

>
>I'm using VC++ 1.5 and have successfully saved the image I drew in an MDI 
>child window to a file as a DIB.  I used as a model the code in the MS example 
>program DIBVIEW.  The problem is that the bitmap I've saved to the file shows 
>up as a monochrome bitmap; the colors displayed in the window do not show up. 
>Here is the code I used to copy the bitmap to a memory DC:
>
>        memDC.CreateCompatibleDC(GetDC())
>                     .
>                     .  
>        bm.CreateCompatibleBitmap(&memDC,rect.Width(),rect.Height());
>                     .
>                     .          
>       oldbm = memDC.SelectObject(&bm);
>       memDC.BitBlt(0, 0, rect.Width(),rect.Height(), GetDC(), 0, 0, SRCCOPY); 
>
>
>When I do a GetObject on the bitmap, it says it has 1 bit per pixel.  I'm 
>confused. I don't completely understand the intricacies of palettes, etc.. The 

The problem here is your "CreateCompatibleBitmap" call. You need to create
a bitmap that's compatible with the SCREEN dc, not the MEMORY one.

Change your code to say:

    CDC *pDC = GetDC();
    memDC.CreateCompatibleDC(pDC);
    bm.CreateCompatibleBitmap( pDC, ..... );

and it will work fine.

Chris


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