SOI Image Processing 3
To perform the filtering operation, the value of each pixel of the filter must be
multiplied by the value of each pixel of the transform of the original image, and
then the inverse Fourier transform performed on the product. Note that the
filter must have complex values, so that the Gaussian surface must be duplicated
in both the real and the imaginary parts of the filter.
Here is the image after:
- It has been Fourier transformed.
- Its transform has been multiplied by the filter.
- The result of the filter has been inverse Fourier transformed.
- The reconstructed image has been contrast (scale) expanded.
To make a movie of all images, it was desired to eliminate the variation in all
pixel values which were not part of the solar disk. To do this, a simple
circular mask was created around the image:
Filtered and Masked Image
This mask was then applied to the filtered image. All pixels which fall inside
the mask retain their values, while all those which fall outside of the mask are
set to the average value of a 25x25 pixel area in the upper left corner of the
Filtration in this way effectively removes the low-frequency noise, while
preserving the data content of the image.
For more information
For more info about the SOHO spacecraft, see
For more info about the SOI project, see
To see the software used in this analysis, see
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Last updated: 11/22/95