Application of Filters in Image Reconstruction
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After all this talk about filters do you really understand their application?

Here are the extremes in filtering - Application of Orders

• Regard the Nyquist value in this lecture all images are set to cycles/pixel
• Considering the graph that has the cut off setting at 1.0, how does this effect your imaging results? Overall, why is transverse slice so grainy?
• When you change the order to 1 the transverse slice becomes very blurry. Why does this occur?
• How do orders work. What might be a happy medium in their application? In addition, the cut off is set at 0.55. What role does that have in effecting image quality?
• Hypothetically, what should the cut off be set at?

Changing the Order - Cut Off remains the same

• Evaluate both graph's nyquist frequency at 0.25 range. What happens to 0.25 as the order increases?
• How does this affect the image quality?
• At the Nyquist frequency of 0.45, look at what happens between 17 to 25. The imaging resutls indicates a slight increase in graininess. Why does this happen?

Consider the difference between a Low Pass and High Pass filter

• What is the role of a Low Pass filter?
• The only adjustment with low pass is in its cut off. What would happen to the image if the cut off was changed to 1.0? More grainy or blurry?
• Give an example of a High Pass filter and discuss how it affects image quality/nyquist frequency

Application of a Hanning Filter

• This filter has a different type of setting known as the alpha setting. Its lowest setting is 0.5, which apparently has no specific results on the filtering process
• However, with when the alpha number increased to a 50% mark the image becomes significantly more grainy. Why do you think this happens?

Variations in filters, cut offs, and orders

• Looking at the above images give comment to what part of the Nyquist frequency is being filtered out
• How does changing the cut off effect imaging quality?
• Of the different examples given, which setting do you prefer? Why?

Yet another example using a Hanning with a cut off of 0.5 and an alpha of 0.55

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