MEDRADSC 2Y03 Lecture 17: Week 10 Lecture 2
25 Oct 2019
School
Department
Course
Professor
Week 10 Lecture 2
November 15th, 2018
Objectives
• Global processing
• Point processing
• Deconvolution
• Monitors
• Gray scale adjustment, windowing
• Zoom
• Pan
Convolution and Digital Images
• Either point or global processing involves mathematics
• The kernel applies the mask to either one area or the whole
image
Digital Image Display
• Prior to display,matrix exists as an array of numbers
• No visible image until final step: display
• Requires DAC device (digital to analong concerter)
• DAC receives matrix values, provides analog electrical signals to display device
• Remember the digital signal is still stored in the CPU
o Central processing unit
Image Processing Options
• Global processing: applies same mathematical function to each pixel value to create
new matrix of processed values for display
o Each pixel undergoes identical transformation process
• Point processing: applies same category of mathematical function, but using different
values for different locations
o Each pixel undergoes a transformation that is determined by its location and
neighbours
• Of window width or window level, window level changes the brightness
o Think of blinds on a window, shutting or opening it will adjusts the brightness
Post Procesing Concepts
• Use: for controlling image display
• Typical options
o Grayscale adjustment
o Image size adjustment
▪ Magnification
▪ An advantage of this would the radiologist would be able to look for any
fractures
Grayscale Adjustment
Goal
• Improve visibility of structure of interest by control of brightness and contrast
• Also called
o Contrast enhancement
o Grayscale mapping
• These happen through windowing
Two main categories
1. Look up tables (translation tables)
a. Applied to all matrix values
2. Windowing
a. Applied to a subset of matrix values
Grayscale Adjustment using Look-Up tables
Concept: assign each signal value magnitude a specific brightness level using a specified
proportionality relationship
• Table translates pixel value (a number) into a corresponding brightness for the pixel
location on the display
Image – ON EXAM
• This will display contrast evenely throught the whole image
• When it goes out from the analog signal
Image
• This will give you reverse contrast
• Bone will be black
• Higher atomic numbers will be darker
• Good to see foreign bodies (anything in soft tissue)
