Resizing bmp.

Greetings,

I am trying to resize a bitmap in memory using
StretchDIBits and GetDIBits and, in turn, output
the file to a BIP format.

Without resizing the following code works fine
when outputting a BIP.

Code:

  
 
   out_byte = (BYTE *) calloc(NCOLS*JP2_CHANNELS,1);
   if (out_byte == NULL) return false;
   out_data = (BYTE *) calloc(NCOLS*NROWS*JP2_CHANNELS,1);
   if (out_data == NULL)
   {
	   free(out_byte);
	   return false;
   }

   // Open output bip and hdr files.
   success = true;
   success = success && (! ((out_bip = fopen(bip_path,"wb")) == NULL));
   success = success && (! ((out_hdr = fopen(hdr_path,"w")) == NULL));

  // Get source image
  // Contains Data and BITMAPINFO header.
   GetImage(Path,this->m_timage);

   BYTE *pData = (BYTE *)this->m_timage.Data;

		// Have to flip bmp and change windows BGR to RGB.
		for(int y = NROWS - 1; y >= 0; y--)
		{
			pData2 += (y * NCOLS * JP2_CHANNELS);

			for(int x = 0; x < NCOLS*JP2_CHANNELS; x+=JP2_CHANNELS)
			{
				out_byte[x]   = pData2[2];  //R
				out_byte[x+1] = pData2[1];  //G
				out_byte[x+2] = pData2[0];  //B
				pData2 += 3;
			}
			// Write out entire line.
			fwrite(out_byte,1,NCOLS*JP2_CHANNELS,out_bip);
			// Reset pData to bottom of image.
			//pData = (BYTE *)this->m_timage.Data;
			pData2 = out_data;
		}


   free (out_byte);
   free (out_data);

The above code is not compilable but should
give a rough idea of what I am doing.

When I attempt to add resizing in the picture
I get an empty black image:

Code:

   out_byte = (BYTE *) calloc(NCOLS*JP2_CHANNELS,1);
   if (out_byte == NULL) return false;
   out_data = (BYTE *) calloc(NCOLS*NROWS*JP2_CHANNELS,1);
   if (out_data == NULL)
   {
	   free(out_byte);
	   return false;
   }

   // Open output bip and hdr files.
   success = true;
   success = success && (! ((out_bip = fopen(bip_path,"wb")) == NULL));
   success = success && (! ((out_hdr = fopen(hdr_path,"w")) == NULL));

  // Get source image
  // Contains Data and BITMAPINFO header.
   GetImage(Path,this->m_timage);

 HDC MemDC = CreateCompatibleDC(NULL);
   //HBITMAP BmpHnd = CreateBitmap(NCOLS,NROWS,1,24,NULL);
   HBITMAP BmpHnd = CreateCompatibleBitmap(MemDC, NCOLS, NROWS); 
   HBITMAP OldBmp = (HBITMAP) SelectObject(MemDC,BmpHnd);
   StretchDIBits(MemDC,0,0,NCOLS,NROWS,0,0,this->Cols,this->Rows,this->m_timage.Data,&(this->m_timage.Info),DIB_RGB_COLORS,SRCCOPY);
   int numScanned = GetDIBits(MemDC,BmpHnd,0,NROWS-1,out_data,&Info,DIB_RGB_COLORS);
   char t[256];
   sprintf(t, "num scanned: %d\n", numScanned);
   OutputDebugString(t);
   //int err = GetLastError();
   //char t[256];
   //sprintf(t, "error message: %d\n", err);
   //OutputDebugString(t);

	SelectObject(MemDC,OldBmp);
	DeleteObject(BmpHnd);

   BYTE *pData = out_data;


		// Have to flip bmp and change windows BGR to RGB.
		for(int y = NROWS - 1; y >= 0; y--)
		{
			pData2 += (y * NCOLS * JP2_CHANNELS);

			for(int x = 0; x < NCOLS*JP2_CHANNELS; x+=JP2_CHANNELS)
			{
				out_byte[x]   = pData2[2];  //R
				out_byte[x+1] = pData2[1];  //G
				out_byte[x+2] = pData2[0];  //B
				pData2 += 3;
			}
			// Write out entire line.
			fwrite(out_byte,1,NCOLS*JP2_CHANNELS,out_bip);
			// Reset pData to bottom of image.
			//pData = (BYTE *)this->m_timage.Data;
			pData2 = out_data;
		}

   free (out_byte);
   free (out_data);

Is my use of StretchDIBits and GetDIbits correct?

Am I missing something else?

Any help would be greatly appreciated.

Cheers.

Try checking return values for errors and call GetLastError() if an error occurs. The error code may help out.

gg

I have tried GetLastError in various portions of
my code, but I always get ERR_SUCCESS.

Any other ideas?

What does the stretchdibits return?




You could try.............

GetObject() and fill a BITMAP struct.

something like

BITMAP BMP;
GetObject(hBitmap,sizeof(BITMAP),&BMP);

then check the colour depth. If it is not 24 bit then I don't think your loop to convert the bits will work.

I would try using

StretchBlt()

And copying the image directly from one HDC to another.

Code:

HDC MemDC = CreateCompatibleDC(NULL);
HBITMAP BmpHnd = CreateCompatibleBitmap(MemDC, NCOLS, NROWS);

From documentation fro CreateCompatibleBitmap

Note: When a memory device context is created, it initially has a 1-by-1 monochrome bitmap selected into it. If this memory device context is used in CreateCompatibleBitmap, the bitmap that is created is a monochrome bitmap. To create a color bitmap, use the hDC that was used to create the memory device context, as shown in the following code:

HDC memDC = CreateCompatibleDC ( hDC );
HBITMAP memBM = CreateCompatibleBitmap ( hDC );
SelectObject ( memDC, memBM );

I'm not sure what you pass as the first argument to CreateCompatibleBitmap when the original hdc is null(see below) but passing the memory dc will not work.

EDIT - Try this:

Code:

HDC hdc = GetDC(NULL);
HDC MemDC = CreateCompatibleDC(hdc);
HBITMAP BmpHnd = CreateCompatibleBitmap(hdc, NCOLS, NROWS);

...

ReleaseDC(hdc);

MSDN
CreateCompatibleDC(NULL);

"If pDC is NULL, the function creates a memory device context that is compatible with the system display."

But try the GetDC() as sometimes I find that works better, particularly in MFC.

Thanks.
Not passing the memDC works much better.

However, my output is still not perfect. I get
a resized image that resembles the original,
but sometimes it comes out grayscale and a
little distorted.

I checked the return value of StretchDIBits
and for a 640x480 source image it always
returns 480. The return value of GetDIBits
is always the height of the resized image.

Would this indicate that I am messing up the
memory somewhere?

[QUOTE
EDIT - Try this:

Code:

HDC hdc = GetDC(NULL);
HDC MemDC = CreateCompatibleDC(hdc);
HBITMAP BmpHnd = CreateCompatibleBitmap(hdc, NCOLS, NROWS);

...

ReleaseDC(hdc);

[/QUOTE]

Could you define some times? With different images or the same image comes out differently?

If the latter, my guess would be that the Info structure that you pass to GetDIBits is not correctly initialised and therefore you are asking for the bits in a random format.

Originally posted by anonytmouse
Could you define some times? With different images or the same image comes out differently?

If the latter, my guess would be that the Info structure that you pass to GetDIBits is not correctly initialised and therefore you are asking for the bits in a random format.

Actually sometimes is really all the time. For my testing I am
always using the same source image.

Here is how I initialize the header:

Code:

	   BITMAPINFO Info;

	   Info.bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
	   Info.bmiHeader.biWidth = NCOLS;
	   Info.bmiHeader.biHeight = NROWS;
	   Info.bmiHeader.biPlanes = 1;
	   Info.bmiHeader.biBitCount = 24;
	   Info.bmiHeader.biCompression = BI_RGB;
	   Info.bmiHeader.biSizeImage = NROWS*NCOLS*3;
	   Info.bmiHeader.biXPelsPerMeter  = 0;
	   Info.bmiHeader.biYPelsPerMeter  = 0;
	   Info.bmiHeader.biClrUsed   = 0;
	   Info.bmiHeader.biClrImportant   = 0;

	   HDC hdc = GetDC(NULL);
	   HDC MemDC = CreateCompatibleDC(hdc);
	   HBITMAP BmpHnd = CreateCompatibleBitmap(hdc, NCOLS, NROWS);
	   HBITMAP OldBmp = (HBITMAP) SelectObject(MemDC,BmpHnd);
	   int sdibts = StretchDIBits(MemDC,0,0,NCOLS,NROWS,0,0,this->Cols,this->Rows,this->m_timage.Data,&(this->m_timage.Info),DIB_RGB_COLORS,SRCCOPY);
	   int numScanned = GetDIBits(MemDC,BmpHnd,0,NROWS-1,out_data,&Info,DIB_RGB_COLORS);
	   SelectObject(MemDC,OldBmp);
	   DeleteObject(BmpHnd);
	   DeleteDC(MemDC);
	   DeleteDC(hdc);

I'm not sure but some ideas:
What is the size of the resized image? You may be running into bit padding problems. Each line in a bitmap must end on a DWORD boundary. So choose a width that this will be the case.

eg. 100,200,300,400 etc.

Also try BitBlt-ing the memDC to the screen DC(I think this works) to see what it contains after the Stretch call.

Finally, you need to call ReleaseDC on an hdc obtained with GetDC, not DeleteDC.

Uh, right in front of my face:

The bitmap identified by the hbmp parameter must not be selected into a device context when the application calls this function.

So swap the below lines.

Code:

int numScanned = GetDIBits(MemDC,BmpHnd,0,NROWS-1,out_data,&Info,DIB_RGB_COLORS);
SelectObject(MemDC,OldBmp);

Thanks.

Working much better now.
(The alignment was definitely an issue also.)

Thanks again everyone.

Cheers.

>>I get a resized image that resembles the original,but sometimes it comes outgrayscale and a little distorted.<<

Expect poor results from an image resize unless you use an int multiple ie 0.5 (1/2) better than 0.45.

>>Info.bmiHeader.biBitCount = 24;

You create a bitmap compatible to the screen. Is the screen in 24bit or 16 or 32 bit?



>>Info.bmiHeader.biSizeImage = NROWS*NCOLS*3


For Windows NT, the width must be DWORD aligned unless the bitmap is RLE compressed.
For Windows 95/98/Me, the width must be WORD aligned unless the bitmap is RLE compressed.
try

cClrBits = (WORD)(bmp.bmPlanes * bmp.bmBitsPixel);

//will need to ensure cClrBits is 1,4,8,16,24 or 32

Info.bmiHeader.biSizeImage = ((Info.bmiHeader.biWidth * cClrBits +31) & ~31) /8 * Info.bmiHeader.biHeight;