*DIP L5 - Image Enhancement 2 Flashcards
What is the difference between point, local and global operation?
An image is changed, but it depends on how much of the image is changed at a time - i.e. one pixel, group of pixel or whole image
What is the difference between spatial domain and frequency domain?
Spatial: XYZ… Frequency: specific place?
What is “segmentation”?
Like.. cropping. This is considered a global operation
Can point and local operators act in frequency domain?
NO! They are only spatial domain!!! Global is in BOTH spatial and frequency
Histogram averaging optimises contrast
True
How do you do simple mag and simple min
Mag: all same values, just multiple of them
Min: take average and divide, then round
What is the difference between zooming and magnification?
Zooming does not change any property of the image. Magnification changes pixel value, size and matrix size
In Simple magnification, the increases must be multiples of an integer
T
In simple magnification, are the pixel sizes increasing or decreasing?
Neither - they remain the same. There are just more of them created
What are other methods of mag? Why do we use these?
We use these because sometimes we want to magnify images that arent integer values etc… We can use nearest neighbour, bilinear interpolation and bicubic interpolation
What is coordinate matrix? What is the purpose of this?
Pixel values represented at corners. For simplicity for when we do stuff like rotate with a non-orthagonal value… You literally draw lines in the middle of the boxes of the original… (lol)
Bicubic method uses a polynomial fir across 8 neighbours
True
What is the difference between bilinear and bicubic?
Bilinear uses 4 neighbours, bicubic uses 16!
For coordinate matrixes, the pixel values are located where?
At the intersection/corners of the lines!
Nearest neighbour: extreme values and subtle values are lost
False. They are still clearly represented bcos the pixel numbers are not changing
What is the disadvantage of using nearest neighbour? What is adv?
Adv is that it is fast. disadv is aliasing
Bilinear assumes a linear relationship between pixel values
true- think of it biLINEAR
In Bilinear method, extreme data is lost/devalued
True - because you are taking an average. i.e. Research.. you got HD but you only gonna get P on exam - Averages down to alike a credit… HD is devalued
What is the adv/disadv of bilinear method of mag?
Adv: more smooth, less alisaing. Disadv: extreme values are devalued
What are your two options for non-orthagonal image rotation?
- Crop the edges off (keep same size matrix)
2. MAke the matrix larger (with blank spaces)
How do you do non-orthagonal image rotation?
USE THE FORMULA!!! Those rlly weird looking ones
Image addition: NM use?
For noise reduction - average all the images
Image addition: DSA use?
Remove anatomy to only show contrast
RT
overlaying isodose lines
