* DIP L4 - Image Enhancement 1 Flashcards
What is the difference between point and local operations? (Specific)
Point operations act on a single pixel at a time. Local operations act on a whole group at a time. Further, point operations do not depend on neighbours whereas local operations does. Point operations is usually for contrast/brightness/colour enhancement whereas local operations is for spatial resolution; smooth/sharp/reduce noise.
What is the filter that reduces noise in an image called? How would you remember this?
MEDIAN FILTER - Median because it takes the neighbouring values and makes everything AVERAGED out; averages out the noise
What is clipping?
Clipping is like when you do an operation on an image and the pixel values change and become above or below the limit for that particular bit depth image. You have to ‘clip’ the value to the extremities
What is rounding error?
Operation on the image results in pixel values that may not be a whole value - have to round it up or down. Is subjective
Point operations: T or F: the new image O(x,y) will be the same size, rows and columns, and have the same bit depth, as the original image I(x,y)
T
How many look up tables do we have associated with an image?
Two - one for storage, one for viewing
What is the difference between grey scale monitors and colour monitors? Also explain using grey and colour images w/their approriate displays
Grey has 1 LUT, colour has 3 LUT –> Grey scale only has ONE value for all RBG ‘gun’, whereas colour has 3 diff values for each of RBG ‘gun’. Grey has 1 value to go to 1 LUT. Colour images have 3 values going to their corresponding LUTs
Describe pseudo-colour display
There is only 1 value but using 3 LUT’s (colour display). The guns are not equal value, therefore colour is shown!
LUT - How to change brightness of an image?
Addition/subtraction
LUT - How to change contrast of an image?
Multiplication/divison
Histogram - How to increase brightness?
Shift right - closer to 255 (8bit)
Histogram - How to decrease brightness?
Shift left- closer to 0
If you increase the slope/gradient of the LUT, would contrast increase or decrease?
Increase - the values are further away from each other, so more black/white on the image; contrast higher
If you increase the slope/gradient of the LUT, would brightness increase or decrease?
Increase - more white because values further away from each other
Describe each Boolean operation:
AND, OR, NOT, XOR
What does XOR in Boolean stand for?
eXclusive OR - Exactly like OR except when both is on, then it is 0
What is local operations primarily used for?
To change SPATIAL RESOLUTION - sharp, smooth, reduce noise
Where is the new pixel value stored for Local operations?
In the middle of all the pixel values operated on for that particular operation
T or F: High pass filters allow high freq to pass and stops low freq
FALSE - High pass filters also allow low freqs to pass (just less of them)
T or F: Low pass filters pass over low frequency areas and work on high frequency areas
True ! They work on high freq areas to blur them
What is the main function of low and high pass filters?
Low pass blurs images, high pass enhances the edges
Size of low freq filter matrix increases - would this increase or decrease blurring?
INCREASE
Low pass follow Gaussian…
True
What is a median filter?
They REDISTRIBUTE noise - does NOT reduce it!!! Non-linear filter
Are median filters linear or non-linear?
Non-linear: they produce different values using different operations for each pixel value
Are median filters low or high pass?
They are low pass filters, even though they multiply pixel values by non-linear way
Does a median filter smooth the image?
NO - it just averages the values
What do high pass filters predominantly do?
They detect edges/sharpen them
What is the difference between high pass filter of 0 and 1
0 gets rid of the LOW FREQ; background info!!!
Median filter is a linear filter for sharpening, a type of local operator
NO, it is a non-linear filter, removes noise, and is a point operator
Where are S-shaped LUT found? (What imaging modality)?
DR/CR radiography
Which operation requires filters/masks?
LOCAL. Point is LUT!!!
