L_FFTBitmap

#include "l_bitmap.h"

L_LTIMGCOR_API L_INT L_FFTBitmap(pBitmap, pFTArray, uFlags)

Computes the Fast Fourier transform of an image or the Inverse Fast Fourier transform as specified in the uFlags.

Returns

Comments

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.

This function converts the image from the time domain to the frequency domain and vice versa using a Fast Fourier Transform algorithm. Fast Fourier Transform algorithms are a simplification of a Discrete Fourier Transform and require that the image dimensions must be power of two (i.e. 2, 4, 8, 16, 32etc). The number of computations needed are reduced from 2N2 to 2N LgN. Use the L_DFTBitmap to use a Discrete Fourier Transform algorithm on a bitmap. If you try to use this function with a bitmap with dimensions that are not a power of two, the function will return an ERROR_INV_PARAMETER error.

Before using this function, call the L_AllocFTArray function to allocate a FTARRAY structure large enough to hold the Fourier Transform coefficients for pBitmap. When the array is no longer needed, 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.

Required DLLs and Libraries

Platforms

Windows 2000 / XP/Vista.

See Also

Example

This example loads a bitmap and applies a FFT transformation.

 L_INT FFTBitmapExample(L_VOID)
{
   L_INT nRet;
   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(TEXT("C:\\Program Files\\LEAD Technologies\\LEADTOOLS 15\\Images\\IMAGE1.CMP"), &LeadBitmap, sizeof(BITMAPHANDLE), 0, ORDER_BGR, NULL, NULL);
   if(nRet !=SUCCESS)
      return nRet;

   /* Resize the bitmap to make sure the bitmap dimensions are power of two*/
   nRet = L_SizeBitmap(&LeadBitmap, 256, 512, SIZE_BICUBIC);
   if(nRet !=SUCCESS)
      return nRet;

   /* Allocate FFT buffer*/
   nRet = L_AllocFTArray(&LeadBitmap, &pFTArray, sizeof(FTARRAY));
   if(nRet !=SUCCESS)
      return nRet;

   /* Apply FFT*/
   nRet = L_FFTBitmap(&LeadBitmap, pFTArray, FFT_FFT | FFT_GRAY);
   if(nRet !=SUCCESS)
      return nRet;

   /* Free FFT buffer */
   nRet = L_FreeFTArray(pFTArray);
   if(nRet !=SUCCESS)
      return nRet;
   nRet = L_SaveBitmap(TEXT("C:\\Program Files\\LEAD Technologies\\LEADTOOLS 15\\Images\\Result.BMP"), &LeadBitmap, FILE_BMP, 24, 0, NULL);
   if(nRet !=SUCCESS)
      return nRet;
   //free bitmap 
   if(LeadBitmap.Flags.Allocated)  
      L_FreeBitmap(&LeadBitmap);  
   return SUCCESS;
}