op dftSpectrum

The FireSight dftSpectrum pipeline stage wraps several OpenCV calls that help you visualize a Fourier transform.

• delta A value to add to all elements of the spectrum. Normally used in conjunction with log to ensure that all values are positive. Default is 1
• shift Default is true, which shifts the Fourier spectrum from the top left corner to the center of the Mat.
• mirror Default is true, which mirrors the shifted spectrum across the y-axis for the negative frequency portion of the spectrum.
• log Default is true, which replaces each Mat value with its logarithm to decrease the dynamic range of the spectrum for easier visualization.
• show magnitude (Default) Replaces working image with the CV_32F1 magnitude of the complex spectrum
• show phase Replaces working image with the CV_32F1 phase of the complex spectrum
• show real Replaces working image with the CV_32F1 real part of the complex spectrum
• show imaginary Replaces working image with the CV_32F1 imaginary part of the complex spectrum

Stage Model

{}

Examples

White rectangle DFT pipeline

firesight -p json/dft-rect.json -o target/dft-rect.jpg

Here's the output, which shows how the spectrum is massaged into a JPG that a human can understand:

CV_32FC2(400x400) show:[0-9,0-9] Complex spectrum, real part
  7.5  -7.3   6.8  -6.0   5.0  -3.8   2.6  -1.4   0.3   0.5
 -6.8   6.6  -6.2   5.4  -4.5   3.4  -2.3   1.2  -0.3  -0.5
  4.9  -4.8   4.4  -3.9   3.2  -2.5   1.7  -0.9   0.2   0.4
 -2.4   2.3  -2.2   1.9  -1.6   1.2  -0.8   0.4  -0.1  -0.2
  0.2  -0.1   0.1  -0.1   0.1  -0.1   0.1  -0.0   0.0   0.0
  1.3  -1.2   1.1  -1.0   0.8  -0.6   0.4  -0.2   0.1   0.1
 -1.6   1.6  -1.5   1.3  -1.1   0.8  -0.5   0.3  -0.1  -0.1
  1.1  -1.1   1.0  -0.9   0.7  -0.5   0.4  -0.2   0.0   0.1
 -0.2   0.1  -0.1   0.1  -0.1   0.1  -0.1   0.0  -0.0  -0.0
 -0.6   0.6  -0.6   0.5  -0.4   0.3  -0.2   0.1  -0.0  -0.0
CV_32FC2(400x400) show:[0-9,0-9] Complex spectrum, imaginary part
  0.0  -0.1   0.1  -0.1   0.2  -0.1   0.1  -0.1   0.0   0.0
 -0.1   0.1  -0.1   0.2  -0.2   0.2  -0.1   0.1  -0.0  -0.0
  0.1  -0.1   0.1  -0.2   0.2  -0.1   0.1  -0.1   0.0   0.0
 -0.1   0.1  -0.1   0.1  -0.1   0.1  -0.1   0.0  -0.0  -0.0
  0.0  -0.0   0.0  -0.0   0.0  -0.0   0.0  -0.0   0.0   0.0
  0.0  -0.1   0.1  -0.1   0.1  -0.1   0.0  -0.0   0.0   0.0
 -0.1   0.1  -0.1   0.1  -0.1   0.1  -0.1   0.0  -0.0  -0.0
  0.1  -0.1   0.1  -0.1   0.1  -0.1   0.0  -0.0   0.0   0.0
 -0.0   0.0  -0.0   0.0  -0.0   0.0  -0.0   0.0  -0.0  -0.0
 -0.0   0.0  -0.1   0.0  -0.0   0.0  -0.0   0.0  -0.0  -0.0
CV_32FC1(400x400) show:[0-9,0-9] Spectrum magnitude
  2.1   2.1   2.1   1.9   1.8   1.6   1.3   0.9   0.3   0.4
  2.1   2.0   2.0   1.9   1.7   1.5   1.2   0.8   0.2   0.4
  1.8   1.7   1.7   1.6   1.4   1.2   1.0   0.6   0.2   0.3
  1.2   1.2   1.2   1.1   1.0   0.8   0.6   0.4   0.1   0.2
  0.1   0.1   0.1   0.1   0.1   0.1   0.1   0.0   0.0   0.0
  0.8   0.8   0.8   0.7   0.6   0.5   0.4   0.2   0.1   0.1
  1.0   0.9   0.9   0.8   0.7   0.6   0.4   0.3   0.1   0.1
  0.7   0.7   0.7   0.6   0.5   0.4   0.3   0.2   0.0   0.1
  0.1   0.1   0.1   0.1   0.1   0.1   0.1   0.0   0.0   0.0
  0.5   0.5   0.5   0.4   0.4   0.3   0.2   0.1   0.0   0.0
CV_32FC1(400x400) show:[195-204,195-204] Centered spectrum
 0.00  0.00  0.00  0.00  0.00  0.82  0.80  0.76  0.70  0.61
 0.00  0.00  0.00  0.00  0.00  0.14  0.14  0.13  0.12  0.10
 0.00  0.00  0.00  0.00  0.00  1.22  1.21  1.16  1.07  0.95
 0.00  0.00  0.00  0.00  0.00  1.77  1.75  1.69  1.59  1.44
 0.00  0.00  0.00  0.00  0.00  2.05  2.03  1.97  1.86  1.70
 0.00  0.00  0.00  0.00  0.00  2.14  2.12  2.06  1.95  1.79
 0.00  0.00  0.00  0.00  0.00  2.05  2.03  1.97  1.86  1.70
 0.00  0.00  0.00  0.00  0.00  1.77  1.75  1.69  1.59  1.44
 0.00  0.00  0.00  0.00  0.00  1.22  1.21  1.16  1.07  0.95
 0.00  0.00  0.00  0.00  0.00  0.14  0.14  0.13  0.12  0.10
CV_32FC1(400x400) show:[195-204,195-204] Mirrored spectrum
 0.61  0.70  0.76  0.80  0.82  0.82  0.80  0.76  0.70  0.61
 0.10  0.12  0.13  0.14  0.14  0.14  0.14  0.13  0.12  0.10
 0.95  1.07  1.16  1.21  1.22  1.22  1.21  1.16  1.07  0.95
 1.44  1.59  1.69  1.75  1.77  1.77  1.75  1.69  1.59  1.44
 1.70  1.86  1.97  2.03  2.05  2.05  2.03  1.97  1.86  1.70
 1.79  1.95  2.06  2.12  2.14  2.14  2.12  2.06  1.95  1.79
 1.70  1.86  1.97  2.03  2.05  2.05  2.03  1.97  1.86  1.70
 1.44  1.59  1.69  1.75  1.77  1.77  1.75  1.69  1.59  1.44
 0.95  1.07  1.16  1.21  1.22  1.22  1.21  1.16  1.07  0.95
 0.10  0.12  0.13  0.14  0.14  0.14  0.14  0.13  0.12  0.10
CV_8UC1(400x400) show:[195-204,195-204] Normalized spectrum
  255   255   255   255   255   255   255   255   255   255
   92   110   124   133   136   136   133   124   110    92
  255   255   255   255   255   255   255   255   255   255
  255   255   255   255   255   255   255   255   255   255
  255   255   255   255   255   255   255   255   255   255
  255   255   255   255   255   255   255   255   255   255
  255   255   255   255   255   255   255   255   255   255
  255   255   255   255   255   255   255   255   255   255
  255   255   255   255   255   255   255   255   255   255
   92   110   124   133   136   136   133   124   110    92

See Also

op dft