L_DFTBitmap

Summary

Computes the Discrete Fourier transform of an image or the Inverse Discrete Fourier transform, as specified in the uFlags parameter.

Syntax

L_LTIMGCOR_API L_INT L_DFTBitmap (pBitmap, pFTArray, prcRange, uFlags)

Parameters

pBITMAPHANDLE pBitmap

Pointer to the bitmap handle that references the bitmap object of the transformation.

pFTARRAY pFTArray

Pointer to an FTARRAY structure. The acxData member of the FTARRAY structure is a two-dimensional array that holds the frequency components of the image. Its size must be the same as the image. This array is filled by the function when DFT_DFT flag has been chosen, and it must be sent to the function to construct the image from it when DFT_IDFT flag has been chosen.

RECT *prcRange

Specifies the frequency range to be computed when DFT_DFT flag is chosen. It specifies the frequency range that will be used in the image construction when DFT_IDFT is chosen. The left value refers to the minimum X harmonic, the right refers to the maximum X harmonic, the top refers to the minimum Y harmonic and the bottom refers to the maximum Y harmonic. The maximum X harmonic equals (Width 1) and the maximum Y harmonic equals (Height 1). The minimum X harmonic equals 0 and the minimum Y harmonic equals 0.

L_UINT uFlags

Flags that indicate the transformation type, operation channel, frequency data type used to reconstruct the image, the clipping type, the used or computed frequencies range, the operation on the specified X harmonics range , and the operation on the specified Y harmonics range. You can use a bitwise OR ( | ) to specify one flag from each group.

The following flags represent the transformation type:

The following flags represent the operation channel type:

The following flags represent the frequency data type used for constructing the image. This flag is used only if DFT_IDFT is set and will be ignored if DFT_DFT is set:

The following flags represent the clipping type. This flag is used only if DFT_IDFT is set and ignored if DFT_DFT is set:

The following flags represent which harmonics are used:

The following flags represent the operations on the X Harmonics range:

The following flags represent the operations on the Y Harmonics range:

Returns

Comments

This function converts the image from the time domain to the frequency domain and vice versa using the Discrete Fourier Transform algorithm. Use the L_FFTBitmap to use a Fast Fourier Transform algorithm on a bitmap. Please note however, that this function does not impose the size restrictions (the width and height having to be powers of 2) that the Fast Fourier Transform function, L_FFTBitmap, imposes upon bitmaps.

Before using this function, you need to use the L_AllocFTArray function to allocate a FTARRAY structure large enough to hold Fourier Transform coefficients for pBitmap. When you are finished, you should free the allocated array by calling the L_FreeFTArray function.

This function does not work on regions. If a bitmap has a region the function ignores it and processes the entire bitmap.

To update a status bar or detect a user interrupt during execution of this function, refer to L_SetStatusCallback.

This function does not support 12 and 16-bit grayscale and 48 and 64-bit color images. If the image is 12 and 16-bit grayscale and 48 and 64-bit color, the function will not return an error.

This function does not support 32-bit grayscale images. It returns the error code ERROR_GRAY32_UNSUPPORTED if a 32-bit grayscale image is passed to this function.

This function does not support signed data images. It returns the error code ERROR_SIGNED_DATA_NOT_SUPPORTED if a signed data image is passed to this function.

Calculating Master Channel Values

In order to speed up widely used image processing filters in LEADTOOLS, the grayscale value (master channel) of a colored image is calculated using the following formulas:

#define CalcGrayValue(r, g, b) ((L_UCHAR)(((L_UCHAR) (((2 * (L_UINT) (r)) + (5 * (L_UINT) (g)) + (L_UINT) (b) + 4) / 8)))) 
#define CalcGrayValue16(r, g, b) ((L_UINT16) (((2 * (L_UINT32) (r)) + (5 * (L_UINT32) (g)) + (L_UINT32) (b) + 4) / 8)) 
#define CalcGrayValue32(r, g, b) ((L_UINT32) (((2 * (L_UINT32) (r)) + (5 * (L_UINT32) (g)) + (L_UINT32) (b) + 4) / 8)) 

View additional platform support for this DFT function.

Required DLLs and Libraries

• LTIMGCOR
• 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.

See Also

Functions

• L_FFTBitmap
• L_FrqFilterBitmap
• L_FTDisplayBitmap
• L_FrqFilterMaskBitmap
• L_AverageFilterBitmap
• L_MedianFilterBitmap
• L_AddBitmapNoise
• L_IntensityDetectBitmap
• L_SpatialFilterBitmap
• L_BinaryFilterBitmap
• L_MaxFilterBitmap
• L_MinFilterBitmap
• L_AddShadowBitmap
• L_ChangeHueSatIntBitmap
• L_ColorThresholdBitmap
• L_AllocFTArray
• L_DirectionEdgeStatisticalBitmap
• L_FFTBitmap
• L_FreeFTArray
• L_FrqFilterBitmap
• L_FrqFilterMaskBitmap
• L_GetBitmapStatisticsInfo
• L_GetFeretsDiameter
• L_GetObjectInfo
• L_GetRgnContourPoints
• L_GetRgnPerimeterLength
• L_MathFunctionBitmap
• L_RevEffectBitmap
• L_SegmentBitmap
• L_SubtractBackgroundBitmap
• L_UserFilterBitmap
• L_FragmentBitmap
• L_HighPassFilterBitmap
• L_UnsharpMaskBitmap

Topics

• Raster Image Functions: Fourier Transform
• Removing Noise

Example

This example loads a bitmap and applies DFT function.

L_INT DFTBitmapexample(L_VOID) 
{ 
   L_INT nRet; 
   RECT    rcRange; 
   BITMAPHANDLE LeadBitmap;   /* Bitmap handle to hold the loaded image. */ 
   pFTARRAY  pFTArray; 
 
   /* Load the bitmap, keeping the bits per pixel of the file */ 
   nRet = L_LoadBitmap(MAKE_IMAGE_PATH(TEXT("IMAGE1.CMP")), &LeadBitmap, sizeof(BITMAPHANDLE), 0, ORDER_BGR, NULL, NULL); 
   if (nRet != SUCCESS) 
      return nRet; 
 
   /*Allocate FT buffer*/ 
   nRet = L_AllocFTArray(&LeadBitmap, &pFTArray, sizeof(FTARRAY), 0); 
   if (nRet != SUCCESS) 
      return nRet; 
 
   rcRange.left = 0; 
   rcRange.right = LeadBitmap.Width / 4; 
   rcRange.top = 0; 
   rcRange.bottom = LeadBitmap.Height / 2; 
 
   /* Apply DFT*/ 
   nRet = L_DFTBitmap(&LeadBitmap, pFTArray, &rcRange, DFT_DFT | DFT_GRAY | DFT_RANGE | DFT_INSIDE_X | DFT_OUTSIDE_Y); 
   if (nRet != SUCCESS) 
      return nRet; 
 
   /* Free FT buffer */ 
   nRet = L_FreeFTArray(pFTArray, 0); 
   if (nRet != SUCCESS) 
      return nRet; 
 
   nRet = L_SaveBitmap(MAKE_IMAGE_PATH(TEXT("Result.BMP")), &LeadBitmap, FILE_BMP, 24, 0, NULL); 
   if (nRet != SUCCESS) 
      return nRet; 
 
   //free bitmap 
   if (LeadBitmap.Flags.Allocated) 
      L_FreeBitmap(&LeadBitmap); 
 
   return SUCCESS; 
}