Image Post Processing and Segmentation Flashcards
What are VOXELS?
A 3D volume used in a similar manner as a pixel
What is the HOUNSFIELD SCALE?
Used to express the attenuation coefficient (density) of different tissues
Measured in Hounsfield Units (HU)
What are HISTOGRAMS USED FOR?
- Similar to EQ for sound, they can amplify/remove/dampen certain frequencies to clean up an image or amplify certain sections
What is MORPHOLOGY?
Refers to the study of the form and structure of organisms
What is meant by CONNECTIVITY?
What is 6-CONNECTIVITY and how does it compare to 26-CONNECTIVITY?
How many voxels are effected around the target voxel, used to smooth effects and remove hard lines
6-connectivity means that only the central square of each face of a cube is affected while 26-connectivity means all voxels surrounding the point of interest is affected.
What is a STRUCTURING ELEMENT?
A group of pixels of a given size, centred around a central pixel
What is the UNION OPERATION?
A logic ‘or’ - either element + their overlap
What is the INTERSECTION OPERATION?
A logic ‘and’ - only the area of overlap
What is the DIFFERENCE OPERATION?
A monodirectional subtraction
What is the COMPLEMENT OPERATION?
A logic ‘not’ - everything but the object
What is a TRANSLATION?
The relocation of a given set to another location inside an image
What are the STEPS TO DILATION (4)?
An operation that expands a set
1) The structuring element superimposes itself on a given pixel
2) It examines whether all of the pixels under the element have a value of 1
3) If no, sets all to 1
4) The structuring element repeats this for every element in the set
What is meant by a MASK?
Used to protect/isolate an area so it isn’t affected by further modifications
What are the STEPS TO EROSION?
An operation that diminishes a set
1) The structuring element superimposes itself onto a given pixel outside the dataset
2) Examines whether any of the pixels of the set are adjacent
3) if so, sets them to 0
4) The structuring element repeats this process for every element outside the set
What is THRESHOLDING and WHEN IS IT USED?
A process of isolating a defined range of values
Used to convert from grayscale to binary, creating masks and discarding unwanted information.
Using a threshold value, T to differentiate between what is part of the image and what is background
