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Figure 13. Frequency domian image at 
0.25 inch radius. 
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Figure 14. Frequency domain FFT at 0.25 inch radius. 
RESULTS ANALYSIS 
In the spatial domain, larger kernels size resulted in less 
noise and duller edges, regardless of filter type. The 
images generated from the median filter differed from the 
images resulting from a low-pass filter in that the edges 
were not as blurred, however, the differences were 
minimal. The mode filter generated images which 
contained more noise compared to either the low-pass or 
median filtered images. 
Difference in the visual appearances of the obtained images 
can be seen, on the other hand, the histogram and statistic 
. for all filters (table 1) show little or no variation. This is 
due to the original low contrast image. 
In the frequency domain, a low-pass filter was applied to 
the power spectrum for various radii. In general, the larger 
the radius, the less it effect the noise. Larger radius is 
corresponded to smaller kernel size in the spatial domain. 
The physical appearances of the resultant images look 
different and once again the obtained histogram and 
statistic show little change (table 2). The ringing 
phenomenon can be seen only in frequency domain this can 
be easily explained by sorting to the convolution theorem 
(Gonzalez,1987). 
  
  
  
  
Figure 15. Frequency domian image at 
2.75 inchs radius. 
  
  
  
  
  
  
  
  
  
  
  
  
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Figure 16. Frequency domain at 
2.75 inch radius. 
The decision as to which filter generates the "best" image 
based on physical appearance depends upon the 
application. For an X-ray image, the "best" image resulting 
from low-pass filtering would depend upon the use of the 
X-ray. Removing too much noise could result in losing 
vital details, while removing too little noise could result in 
vital details remaining obscured. This determination can be 
made to some extent by someone familiar with image 
processing, however, the final determination as to which is 
the "best" resulting X-ray image should be made by a 
qualified radiologist.