* DIP L4 - Image Enhancement 1

Question 1

What is the difference between point and local operations? (Specific)

Answer 1

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.

Question 2

What is the filter that reduces noise in an image called? How would you remember this?

Answer 2

MEDIAN FILTER - Median because it takes the neighbouring values and makes everything AVERAGED out; averages out the noise

Question 3

What is clipping?

Answer 3

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

Question 4

What is rounding error?

Answer 4

Operation on the image results in pixel values that may not be a whole value - have to round it up or down. Is subjective

Question 5

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)

Answer 5

T

Question 6

How many look up tables do we have associated with an image?

Answer 6

Two - one for storage, one for viewing

Question 7

What is the difference between grey scale monitors and colour monitors? Also explain using grey and colour images w/their approriate displays

Answer 7

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

Question 8

Describe pseudo-colour display

Answer 8

There is only 1 value but using 3 LUT’s (colour display). The guns are not equal value, therefore colour is shown!

Question 9

LUT - How to change brightness of an image?

Answer 9

Addition/subtraction

Question 10

LUT - How to change contrast of an image?

Answer 10

Multiplication/divison

Question 11

Histogram - How to increase brightness?

Answer 11

Shift right - closer to 255 (8bit)

Question 12

Histogram - How to decrease brightness?

Answer 12

Shift left- closer to 0

Question 13

If you increase the slope/gradient of the LUT, would contrast increase or decrease?

Answer 13

Increase - the values are further away from each other, so more black/white on the image; contrast higher

Question 14

If you increase the slope/gradient of the LUT, would brightness increase or decrease?

Answer 14

Increase - more white because values further away from each other

Question 15

Describe each Boolean operation:

Answer 15

AND, OR, NOT, XOR

Question 16

What does XOR in Boolean stand for?

Answer 16

eXclusive OR - Exactly like OR except when both is on, then it is 0

Question 17

What is local operations primarily used for?

Answer 17

To change SPATIAL RESOLUTION - sharp, smooth, reduce noise

Question 18

Where is the new pixel value stored for Local operations?

Answer 18

In the middle of all the pixel values operated on for that particular operation

Question 19

T or F: High pass filters allow high freq to pass and stops low freq

Answer 19

FALSE - High pass filters also allow low freqs to pass (just less of them)

Question 20

T or F: Low pass filters pass over low frequency areas and work on high frequency areas

Answer 20

True ! They work on high freq areas to blur them

Question 21

What is the main function of low and high pass filters?

Answer 21

Low pass blurs images, high pass enhances the edges

Question 22

Size of low freq filter matrix increases - would this increase or decrease blurring?

Answer 22

INCREASE

Question 23

Low pass follow Gaussian…

Answer 23

True

Question 24

What is a median filter?

Answer 24

They REDISTRIBUTE noise - does NOT reduce it!!! Non-linear filter

Question 25

Are median filters linear or non-linear?

Answer 25

Non-linear: they produce different values using different operations for each pixel value

Question 26

Are median filters low or high pass?

Answer 26

They are low pass filters, even though they multiply pixel values by non-linear way

Question 27

Does a median filter smooth the image?

Answer 27

NO - it just averages the values

Question 28

What do high pass filters predominantly do?

Answer 28

They detect edges/sharpen them

Question 29

What is the difference between high pass filter of 0 and 1

Answer 29

0 gets rid of the LOW FREQ; background info!!!

Question 30

Median filter is a linear filter for sharpening, a type of local operator

Answer 30

NO, it is a non-linear filter, removes noise, and is a point operator

Question 31

Where are S-shaped LUT found? (What imaging modality)?

Answer 31

DR/CR radiography

Question 32

Which operation requires filters/masks?

Answer 32

LOCAL. Point is LUT!!!