DiscreteFourierTransformCommand Class

Summary

Computes the Discrete Fourier transform of an image or the Inverse Discrete Fourier transform as specified by the flags.

Syntax

Objective-C

C++/CLI

Python

public class DiscreteFourierTransformCommand : RasterCommand

@interface LTDiscreteFourierTransformCommand : LTRasterCommand

public ref class DiscreteFourierTransformCommand : public RasterCommand

class DiscreteFourierTransformCommand(RasterCommand):

Remarks

This command is available in the Imaging and above toolkits.

This command converts the image from the time domain to the frequency domain and vice versa using the Discrete Fourier Transform algorithm. Use the FastFourierTransformCommand to use a Fast Fourier Transform algorithm on an image.
Before using this command, you need to construct an instance from FourierTransformInformation.
The image can be transformed back into the original image minus the noise using the InverseDiscreteFourierTransform
This command does not work on regions. If the image has a region the command ignores it and processes the entire image.
This command 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 method will not threw an exception.
This command does not support 32-bit grayscale images.
This command does not support signed images.

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))

For more information, refer to Removing Noise.

DFT Function - Before

DFT Function - After

View additional platform support for this DFT function.

Example

Run the DiscreteFourierTransformCommand on an image.

using Leadtools; 
using Leadtools.Codecs; 
using Leadtools.ImageProcessing.Core; 
 
public void DiscreteFourierTransformCommandExample() 
{ 
   // Load an image 
   RasterCodecs codecs = new RasterCodecs(); 
   codecs.ThrowExceptionsOnInvalidImages = true; 
 
   RasterImage image = codecs.Load(Path.Combine(LEAD_VARS.ImagesDir, "Master.jpg")); 
 
   // Prepare the command 
   FourierTransformInformation FTArray = new FourierTransformInformation(image); 
   LeadRect rcRange = new LeadRect(0, 0, image.Width - 1, image.Height - 1); 
   DiscreteFourierTransformCommand command = new DiscreteFourierTransformCommand(); 
 
   command.FourierTransformInformation = FTArray; 
   command.Range = rcRange; 
   command.Flags = DiscreteFourierTransformCommandFlags.DiscreteFourierTransform | 
      DiscreteFourierTransformCommandFlags.Gray | 
      DiscreteFourierTransformCommandFlags.Range | 
      DiscreteFourierTransformCommandFlags.InsideX | 
      DiscreteFourierTransformCommandFlags.InsideY; 
   //Apply DFT. 
 
   FourierTransformDisplayCommand disCommand = new FourierTransformDisplayCommand(); 
   disCommand.Flags = FourierTransformDisplayCommandFlags.Log | FourierTransformDisplayCommandFlags.Magnitude; 
   disCommand.FourierTransformInformation = command.FourierTransformInformation; 
   // plot frequency magnitude 
   disCommand.Run(image); 
 
} 
 
static class LEAD_VARS 
{ 
   public const string ImagesDir = @"C:\LEADTOOLS23\Resources\Images"; 
}