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LBitmap::GetFunctionalLookupTable

#include "ltwrappr.h"

virtual L_INT LBitmap::GetFunctionalLookupTable (pLookupTable, uLookupLen, nStart, nEnd, nFactor, uFlags)

L_INT * pLookupTable;	/* lookup table */
L_UINT uLookupLen;	/* lookup table length */
L_INT nStart;	/* first item */
L_INT nEnd;	/* last item */
L_INT nFactor;	/* factor */
L_UINT uFlags;	/* flag */

Updates a range of entries in the lookup table, based on the specified mathematical function.

Parameter	Description
pLookupTable	Pointer to the lookup table to be filled by this function. The length of the lookup table is specified in the uLookupLen parameter.
uLookupLen	Length of the lookup table pointed to by the pLookupTable parameter. It can be any value larger than 0.

nStart	Index of the first entry in the lookup table to update. The indices of the table correspond to the intensity values. If the value of this parameter is negative, the corresponding index of pLookupTable is equal to the value of this parameter + uLookupLen. The range of its possible value is between (-uLookupLen/2) and (uLookupLen/2 1).
nEnd	Index of the last entry in the lookup table to update. The indices of the table correspond to the intensity values. If the value of this parameter is negative, the corresponding index of pLookupTable is equal to the value of this parameter + uLookupLen. The range of its possible value is between (-uLookupLen/2) and (uLookupLen/2 1).
nFactor	Value that indicates the factor to be applied in the function operation specified in the uFlags parameter. This parameter is used only if uFlags is FLT_EXP, FLT_SIGMOID or FLT_LN. If FLT_EXP or FLT_SIGMOID is set in uFlags the value of this parameter can be any integer (+/-). If FLT_LN flag is set, its value should be >= 0. However, if nFactor = 0 the lookup table will be filled linearly from nStart to nEnd, regardless of the value set in uFlags.
uFlags	Flag that indicates the function used to update the lookup table and whether the pLookupTable should contain signed or unsigned data.
	Flags indicate the function used to update the lookup table:
	Value	Meaning
	FLT_EXP	[0] Apply the exponential function.
	FLT_LN	[1] Apply the natural logarithm function.
	FLT_LINEAR	[2] Apply the linear function.
	FLT_SIGMOID	[3] Apply the sigmoid function
	Flag indicates whether the pLookupTable should contain signed or unsigned data:
	FLT_SIGNED	[0x0010] pLookupTable should contain signed data.

Returns

SUCCESS	The function was successful.
< 1	An error occurred. Refer to Return Codes.

Comments

This function will update the lookup table array using the predefined function specified in the uFlag parameter. In most cases, this function is used with the LBitmap::RemapIntensity function.

If the value of (nEnd - nStart) exceeds the uLookupLen, the function returns ERROR_INV_PARAMETER error code.

The nFactor parameter is used for log , exp and sigmoid functions only. If nFactor = 0 the function performs a linear interpolation between the two points uStart and uEnd and stores the results in the lookup table, regardless of the value set in uFlag.

If uFlag is FLT_EXP the value of nFactor modifies the lookup table values (see figure below) according to the following equations:

nYStart = The Lookup table value at nStart.

nYEnd = The Lookup table value at nEnd.

nFirstValue = exp(0).

nLastValue = exp(nFactor)

x = the intensity value of the selected point

If uFlag is FLT_LN the value of nFactor modifies the lookup table values (see figure below) according to the following equations:

where:

nYStart = The Lookup table value at nStart.

nYEnd = The Lookup table value at nEnd.

nFirstValue = 0.

nLastValue = ln(1 + nFactor)

x = the intensity value of the selected point

If uFlags is FLT_SIGMOID the value of nFactor modifies the lookup table values (see figure below) according to the following equations:

Y = uStart + (nYEnd nYStart) * (1./ (1 + exp(2*nFactor/10. * (x-Center))/(nEnd- nStart)) - nFirstValue)/ (nLastValue nFirstValue)

where:

nFirstValue = 1./(1+exp(2.*nFactor/10.*(nStart - Center)/ (uEnd- uStart))).

nLastValue = 1./(1+exp(2.*nFactor/10.*(nEnd - Center)/ (uEnd- uStart))).

Center = (nEnd + nStart)/2.

x = the intensity value of the selected point

 

If uFlags is FLT_LINEAR, nFactor is ignored. The function performs a linear interpolation between the two points (nStart, nYStart) and (nEnd, nYEnd)  and stores the results in the lookup table. Where

nYStart = The Lookup table value at nStart.

nYEnd = The Lookup table value at nEnd.

 

As an example, suppose a user wants to select a point, change the intensity value of that point (x), and then perform two linear interpolations:

• from 0 to the intensity value x

• from intensity value x to the end of the range

To accomplish this, the user would proceed by doing the following:

• Select the point and get its intensity value (x)

• Change the intensity value of the selected point to some new value (newIntensity).

• Store the new intensity value in the Lookup table by assignment:

pLookupTable[0] = 0;

pLookupTable[x] = newIntensity;

 

• Call LBitmap::GetFunctionalLookupTable with nStart set to 0, nEnd set to x, and uFlags set to FLT_LINEAR.

• Store the new intensity value in the Lookup table by assignment:

pLookupTable[x] = newIntensity;//This can be ignored, because the lookup table should have the same value from the previous steps.

pLookupTable[nEnd] = uLookupLen;

• Call LBitmap::GetFunctionalLookupTable with nStart set to x, nEnd set to uLookupLen, and uFlags set to FLT_LINEAR. (For the example, assume the image is 8-bits per pixel.)

Required DLLs and Libraries

LTFIL LTIMGEFX 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.

See Also

Functions:	LBitmap::AdjustTint, LBitmap::GammaCorrectExt, LBitmap::GetUserLookupTable, LBitmap::RemapIntensity, LBitmap::ApplyVOILUT
Topics:	Changing Brightness and Contrast
	Raster Image Functions: Modifying Intensity Values
	Raster Image Functions: Changing Brightness and Contrast

Example

L_INT LBitmap__GetFunctionalLookupTableExample(LBitmap & Bitmap, L_TCHAR * pszFile)
{
   L_INT nRet;
   L_INT LookupTable[256];
   nRet =Bitmap.Load(pszFile, 24, ORDER_BGR);
   if(nRet !=SUCCESS)
      return nRet;
   nRet =Bitmap.GetFunctionalLookupTable((L_INT *)LookupTable, 256, 0, 255, 5, FLT_EXP);
   if(nRet !=SUCCESS)
      return nRet;
   nRet =Bitmap.RemapIntensity(LookupTable, 256, CHANNEL_MASTER);
   if(nRet !=SUCCESS)
      return nRet;
   return SUCCESS;
}