Digital Image Enhancement & Noise Suppression Guide
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54 cards
Question: What is a piece-wise linear enhancement function and when is it used in image contrast adjustment?
Answer: A piece-wise linear enhancement maps input intensities to output using linear segments with thresholds; it’s used to enhance contrast by applying diff
Question: How is a radiological window defined and what are its two main parameters?
Answer: A radiological window is a dynamic range selection for increasing visible contrast; its two parameters are width (W) — the range width with increasing
Question: How are the two thresholds T1 and T2 of a radiological window related to width W and level L?
Answer: Thresholds are defined by T1 = L - W/2 and T2 = L + W/2, marking the lower and upper bounds of the window.
Question: What is the output mapping for pixel values f(i,k) inside and outside the radiological window?
Answer: Pixels below T1 map to 0, above T2 map to max (e.g., 255), and values between T1 and T2 are linearly scaled to the full output range (piece-wise linea
Question: Give two example window settings used in CT and what they correspond to.
Answer: Bone window: W = 3000 HU, L = 1524 HU; Brain window: W = 80 HU, L = 1064 HU.
Question: Give two example window settings for MRI mentioned in the content.
Answer: Cardiac T2: W = 120 ms, L = 60 ms; Cardiac T1: W = 2000 ms, L = 1500 ms.
Question: What is the goal of using the full grayscale range and how is it commonly achieved?
Answer: The goal is to utilize the full dynamic range (all shades of gray) to improve appearance; commonly achieved via piece-wise transformation by finding t
Question: How are Threshold T1 and T2 chosen when using full grayscale range scaling?
Answer: T1 is set to the minimum intensity of all pixels and T2 to the maximum intensity of all pixels; normalization maps f(i,k) to (f - min)/(max - min) for
Question: What is a potential problem when using image minima and maxima as thresholds for full-range scaling?
Answer: Artefacts or outliers can skew the extreme values, causing inappropriate scaling and loss of useful contrast.
Question: What is gamma contrast transformation and what must be done before applying it?
Answer: Gamma transformation is a nonlinear (power-law) point-wise operator adjustable by parameter γ; image values must be normalized into the range 0–1 befo