Discrete Fourier Transform Program Coding

1. input image : created image with proper size

2. program code must be your own

3. Display

□ image -> DFT -> log scale transform -> Display

512×512 image

1024×1024 image

왼쪽: 원본 이미지

중간 :  normal display of FFT transform

오른쪽 : log display of FFT transform

Code

public Bitmap ToBitmap(bool logTransform)

{

// create new image

Bitmap dstImage = YU.Imaging.Image.CreateGrayscaleImage(width, height);

// lock destination bitmap data

BitmapData dstData = dstImage.LockBits(

new Rectangle(0, 0, width, height),

ImageLockMode.ReadWrite, PixelFormat.Format8bppIndexed);

int offset = dstData.Stride - width;

double scale = (fourierTransformed) ? Math.Sqrt(width * height) : 1;

double minMagnitude = double.MaxValue;

double maxMagnitude = double.MinValue;

double minLog = double.MaxValue;

double maxLog = double.MinValue;

for (int y = 0; y < height; y++)

{

for (int x = 0; x < width; x++)

{

minMagnitude = Math.Min(minMagnitude, data[y,x].Magnitude);

maxMagnitude = Math.Max(maxMagnitude, data[y,x].Magnitude);

minLog = Math.Min(minLog, Math.Log(data[y, x].Magnitude));

maxLog = Math.Max(maxLog, Math.Log(data[y, x].Magnitude));

}

}

// do the job

unsafe

{

byte* dst = (byte*)dstData.Scan0.ToPointer();

for (int y = 0; y < height; y++)

{

for (int x = 0; x < width; x++, dst++)

{

if (logTransform)

*dst = (byte)System.Math.Max(0, System.Math.Min(255, (Math.Log(data[y, x].Magnitude) - minLog) * 255 / (maxLog - minLog)));

else

*dst = (byte)System.Math.Max(0, System.Math.Min(255, data[y, x].Magnitude * scale * 255));

}

dst += offset;

}

}

// unlock destination images

dstImage.UnlockBits(dstData);

return dstImage;

}

관련문서 : http://lab.must.or.kr/Fourier-Transform-Properties.ashx