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L_GetBitmapRowCol

Summary

Accepts a column offset to retrieve data from a bitmap and place it in a buffer. The buffer to which pBuffer points will be filled with uncompressed data.

Syntax

#include "l_bitmap.h"

L_LTKRN_API L_SSIZE_T L_GetBitmapRowCol(pBitmap, pBuffer, nRow, nCol, uBytes)

Parameters

pBITMAPHANDLE pBitmap

Pointer to the bitmap handle referencing the bitmap to get the image data from.

L_UCHAR* pBuffer

Pointer to the buffer to hold the image data that this function gets. You must allocate the buffer before calling this function, and the buffer must be large enough to hold the image data.

L_INT nRow

The number of the row to retrieve. The first row is 0, and the last row is 1 less than the bitmap height.

L_INT nCol

The column offset within the row to retrieve. The first column offset is 0, and the last column offset is 1 less than the bitmap width.

L_SIZE_T uBytes

The number of bytes to retrieve. Consider the bits per pixel, and avoid specifying a number that goes past the end of the row.

Value	Meaning
1-bit bitmap	Each byte represents 8 pixels.
4-bit bitmap	Each byte represents 2 pixels.
8-bit bitmap	Each byte represents 1 pixel.
16-bit bitmap	Every 2 bytes represents one pixel.
24-bit bitmap	Every three bytes represents one pixel.
32-bit bitmap	Every four bytes represents one pixel.
48-bit bitmap	Every six bytes represents one pixel.
64-bit bitmap	Every eight bytes represents one pixel.

You can use the bitmap handle's BitsPerPixel field with integer math to calculate the number of bytes needed for a particular number of pixels. For example:

NumberOfBytes = (Bitmap.BitsPerPixel * NumberOfPixels) / 8; 
if ((Bitmap.BitsPerPixel * NumberOfPixels) % 8) 
   ++NumberOfBytes; /* Round up if necessary for a 1- or 4-bit image */

Returns

Value	Meaning
>=1	The number of bytes copied.
< 1	An error occurred. Refer to Return Codes.

Comments

By using this low-level function to get any part of a row, you can write a procedure that accesses a single pixel or a rectangular area within the bitmap.

This function accepts an offset parameter nCol in pixels and a length uBytes in bytes. Therefore, you must consider the bits per pixel of the bitmap when specifying these parameters. The following table describes the rules:

Bits Per Pixel	Column Offset (in Pixels)	Bytes to Get
1	Must be a multiple of 8 (such as 0, 8, or 16).	Can be any number up to the end of the row. Consider that there are 8 pixels per byte.
4	Must be an even number (such as 0, 2, or 4).	Can be any number up to the end of the row. Consider that there are 2 pixels per byte.
8	Can be any column within the bitmap.	Can be any number up to the end of the row. Consider that there is 1 pixel per byte.
16	Can be any column within the bitmap.	Must be a multiple of 2 (such as 2, 4, or 6), because there are 2 bytes per pixel.
24	Can be any column within the bitmap.	Must be a multiple of 3 (such as 3, 6, or 9), because there are 3 bytes per pixel.
32	Can be any column within the bitmap.	Must be a multiple of 4 (such as 4, 8, or 12), because there are 4 bytes per pixel.

The bitmap memory must be locked when you use this function. Normally, you can call L_AccessBitmap to lock the memory before starting an operation that uses this function, then call L_ReleaseBitmap when the operation is finished.

Color order is determined by the Order field in the bitmap handle. This value can be ORDER_RGB, ORDER_BGR, ORDER_GRAY or ORDER_ROMM. ORDER_GRAY is only valid for 12, 16 and 32-bit grayscale images. Support for 12, 16 and 32-bit grayscale images is only available in the Document and Medical Imaging toolkits.

Required DLLs and Libraries

LTKRN
For a listing of the exact DLLs and Libraries needed, based on the toolkit version, refer to Files To Be Included With Your Application.

Platforms

Win32, x64, Linux.

Example

The following example is designed to work with bitmaps that have a bottom-left
or top-left view perspective:
This example uses L_GetBitmapRowCol and L_PutBitmapRowCol to invert
the colors of a rectangle in the upper left part of the displayed image.

L_INT GetBitmapRowColExample(L_VOID) 
{ 
   L_INT nRet; 
   BITMAPHANDLE   LeadBitmap; /* Bitmap handle to hold the loaded image */ 
   L_INT          XOffset;    /* Column offset of the rectangle to process */ 
   L_INT          XSize;      /* Pixel width of the rectangle to process */ 
   L_INT          YOffset;    /* Row offset of the rectangle to process */ 
   L_INT          YSize;      /* Pixel height of the rectangle to process */ 
   L_UCHAR*       pBuf;       /* Buffer to hold the row */ 
   HGLOBAL        hBuf;       /* Handle to the buffer */ 
   L_INT          i, n;       /* Counters */ 
 
   /* Load the bitmap, at 24 bits per pixel */ 
   nRet = L_LoadBitmap (MAKE_IMAGE_PATH(TEXT("ImageProcessingDemo\\Image3.cmp")), &LeadBitmap, sizeof(BITMAPHANDLE), 24, ORDER_BGR, NULL, NULL); 
   if(nRet != SUCCESS) 
      return nRet; 
   /* This example does not work with rotated view perspectives */ 
   if ( (LeadBitmap.ViewPerspective != TOP_LEFT) || (LeadBitmap.ViewPerspective != BOTTOM_LEFT) ) 
   { 
      nRet = L_ChangeBitmapViewPerspective ( NULL, &LeadBitmap, sizeof(BITMAPHANDLE), TOP_LEFT ); 
      if(nRet != SUCCESS) 
         return nRet; 
   } 
   /* Specify a rectangle in the top left part of the displayed image */ 
   XOffset = BITMAPWIDTH(&LeadBitmap) / 8; 
   XSize = BITMAPWIDTH(&LeadBitmap) / 3; 
   YOffset = BITMAPHEIGHT(&LeadBitmap) / 8; 
   YSize = BITMAPHEIGHT(&LeadBitmap) / 3; 
   /* Adjust the YOffset if the view perspective is bottom left */ 
   if (LeadBitmap.ViewPerspective == BOTTOM_LEFT) 
   { 
      YOffset = LeadBitmap.Height - YOffset - YSize; 
   } 
   /* Allocate the buffer */ 
   hBuf = GlobalAlloc(GMEM_MOVEABLE, XSize * 3); 
   pBuf = (L_UCHAR*)GlobalLock( hBuf ); 
   /* Invert the colors of pixels in the rectangle */ 
   L_AccessBitmap(&LeadBitmap); 
   for(i=YOffset; i < (YOffset + YSize); i++) 
   { 
      nRet = (L_INT)L_GetBitmapRowCol(&LeadBitmap, pBuf, i, XOffset, XSize * 3); 
      if(nRet < 1) 
         return nRet; 
      for(n=0; n < (XSize * 3); n++) 
         pBuf[n] = pBuf[n] ^ 0xFF; 
      nRet =(L_INT) L_PutBitmapRowCol(&LeadBitmap, pBuf, i,  XOffset, XSize * 3); 
      if(nRet < 1) 
         return nRet; 
   } 
   L_ReleaseBitmap(&LeadBitmap); 
 
   nRet = L_SaveBitmap(MAKE_IMAGE_PATH(TEXT("Result.BMP")), &LeadBitmap, FILE_BMP, 24, 0, NULL); 
   if(nRet != SUCCESS) 
      return nRet; 
   L_FreeBitmap(&LeadBitmap); 
 
   /* Free memory that we no longer need */ 
   GlobalFree(hBuf); 
   return SUCCESS; 
}