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++

public class DiscreteFourierTransformCommand : RasterCommand

Public Class DiscreteFourierTransformCommand  
   Inherits RasterCommand

@interface LTDiscreteFourierTransformCommand : LTRasterCommand

public ref class DiscreteFourierTransformCommand : public RasterCommand

Remarks

This command is available in the Imaging Pro 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.

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:\Users\Public\Documents\LEADTOOLS Images"; 
}

Imports Leadtools 
Imports Leadtools.Codecs 
Imports Leadtools.ImageProcessing.Core 
 
Public Sub DiscreteFourierTransformCommandExample() 
   Dim codecs As New RasterCodecs() 
   codecs.ThrowExceptionsOnInvalidImages = True 
 
   Dim leadImage As RasterImage = codecs.Load(Path.Combine(LEAD_VARS.ImagesDir, "Master.jpg")) 
 
   ' Prepare the command 
   Dim FTArray As FourierTransformInformation = New FourierTransformInformation(leadImage) 
   Dim rcRange As LeadRect = New LeadRect(0, 0, leadImage.Width - 1, leadImage.Height - 1) 
   Dim command As DiscreteFourierTransformCommand = New DiscreteFourierTransformCommand 
 
   command.FourierTransformInformation = FTArray 
   command.Range = rcRange 
   command.Flags = DiscreteFourierTransformCommandFlags.DiscreteFourierTransform Or 
      DiscreteFourierTransformCommandFlags.Gray Or 
      DiscreteFourierTransformCommandFlags.Range Or 
      DiscreteFourierTransformCommandFlags.InsideX Or 
      DiscreteFourierTransformCommandFlags.InsideY 
   'Apply DFT. 
   command.Run(leadImage) 
 
   Dim disCommand As FourierTransformDisplayCommand = New FourierTransformDisplayCommand 
   disCommand.Flags = FourierTransformDisplayCommandFlags.Log Or FourierTransformDisplayCommandFlags.Magnitude 
   disCommand.FourierTransformInformation = command.FourierTransformInformation 
   'plot frequency magnitude 
   disCommand.Run(leadImage) 
 
End Sub 
 
Public NotInheritable Class LEAD_VARS 
   Public Const ImagesDir As String = "C:\Users\Public\Documents\LEADTOOLS Images" 
End Class