Basic Digital Imaging Concepts Flashcards
What are voxels?
3D pixels
each of an array of elements of volume that constitute a notional three-dimensional space
What is the metric of resolution commonly used across all imaging modalities?
line pairs/ mm (lp/mm)
What is does 1 lp/mm mean in radiology?
that the image is able to distinguish parallel lines of lead with 1 line per mm
(0.5mm of lead separated by 0.5mm of filler)
What is shannon’s sampling theory:
that to sample at a frequency f, you need to sample a regularly spaced intervals of 2f
What does image depth data mean in radiology?
The information stored per pixel/ voxel
(e.g. 8 bits of each of RGB possible).
Metric for image compression?
Compression Ratio (C lower-case R)
Does a low or high compression ratio indicate a lot of compression?
high
e.g. 5:1
What is ‘Run Length Encoding’
Arun of characters is replaced with the number of the same characters and a single character.
E.g.
C B G H H H S S O O O O M M K
->
C B G *3H S S *4O M M K
What is Huffman compression
Make the most commonly occurring colours in an image be represented by the smaller portion of data
(e.g. most common color represented by 1 bit of data)
What is Differential Pulse Code Modulation (DPCM) or Delta Compression
Each pixel is described relative to the pixel next to it, unless it would be easier to just say its value
What is Lossless Block Coding
Where blocks of pixels that commonly occur together are stored in a ‘codebook’
What are some ‘LOSSY’ image compression techinques?
Truncation (cropping, reduce size)
Decrease image depth (24 bit to 8 bit)
Transform coding (get a cos function to represent it etc)
How does motion image compression techniques work
a key-frame is transcoded every few seconds, and then changes from that frame are programmed in
What is DICOM in radiology?
Digital Imaging and Communications in Medicine
- the industry standard for transferal of radiological images and other medical information between different systems
