2. Digital Image Processing Concepts Flashcards
the processing of images using a computer
Digital Image Processing
Steps of Digital Image Processing
- Converted into digital data
2. A digital image
utilize digital image processing as their central feature of their operations
CR / Flat-panel DR / Digital Mammography / Fluoroscopy
incorporate digital image processing as an essential tool to manipulate and enhance digital images
CT / MRI / Ultrasonography / Nuclear Medicine
image processing expert, retired NASA engineer
Castleman, Kenneth R. (1994)
uses set theory to classify images based on their form and the method used to produce them
Castleman, Kenneth R.
According to him, “Images as a subset of all objects, and that image set contains subset within it, such as visible and invisible images, optical and mathematical images”
Castleman, Kenneth R.
photographs, drawings, paintings
Visible Images
temperature, pressure, elevation maps
Invisible Images
holograms
Optical Images
continuous and discrete functions
Mathematical Images
important in the world of digital imaging
Mathematical Images
is a continuous function that can be converted into a discrete function, both of which will generate two categories of images, namely, analog and digital images
classical sine wave
is continuous wave form that changes smoothly over time
analog signal
is discrete and can only have a limited number of defined values, often as simple as 1 and 0
digital signal
to generate an image that is more pleasing to the observer
Image Enhancement
Image Enhancement includes:
- Contrast enhancement
- Edge enhancement
- Spatial and Frequency filtering
- Image combining
- Noise reduction
to improve the quality of images that have distortion or degradations
Image Restoration
blurred images can be filtered to make them sharper
Image Restoration
measurements and statistics, as well as segmentation, feature extraction, and classification of objects
Image Analysis
are used in 3D medical imaging
Segmentation operations
the goal of ______ is to simplify and/or change the representation of an image into something that is more meaningful and easier to analyze
segmentation
to reduce the size of the image in order to decrease transmission time and reduce storage space
Image Compression
Types of Image Compression
- Lossy or irreversible
2. Lossless or reversible
there is some loss of image details when the image is decompressed
Lossy or irreversible
there is no loss of any information in the image (detail is not compromised) when the image is decompressed
Lossless or reversible
More recent form of compression
wavelet compression (special waveforms) / Haar compression
Wavelet (special waveforms) compression
Main advantage:
There is no loss in either spatial and frequency information
offers an approach that allows one to reduce the size of the data while at the same time improving its quality through the removal of high-frequency noise components
Wavelet compression
these processing operations “create images from other or non-image data”
Image Synthesis
these operations are used when a desired image is either physically impossible or impractical to acquire, or does not exist in a physical form at all
Image Synthesis
Examples of Image Synthesis
- Image reconstruction techniques
- 3D visualization techniques which are based on computer graphics technology
numerical image
Matrix
a digital image is made up of a 2D array of numbers
Matrix
consists of columns (M) and rows (N) that define small square regions
Matrix
small square regions
Picture elements or Pixels
dimension of the image can be described by M, N and the size of the image is given by the relationship:
M x N x k bits (row x column)
Matrix size =
Field of view (FOV)
M=N
the image is square
Increasing FOV will result to:
- Increase Image processing time
- Increase Storage space
- Increase Transmission time
Picture element
Pixels
each pixel contains a number (discrete value) that represents a ______ level, which reflects the tissue characteristic being imaged
brightness
MRI Image matrix (in pixels)
256 x 256
CT Scan Image matrix (in pixels)
512 x 512
Ultrasound Image matrix (in pixels)
512 x 512
Color Doppler Image matrix (in pixels)
768 x 576
Digital radiography Image matrix (in pixels)
Up to 3000 x 3000
Digital mammography Image matrix (in pixels)
Up to 3328 x 4096
Computed radiography Image matrix (in pixels)
3520 x 4280
MRI Dynamic range (bits per pixel)
16
CT Scan Dynamic range (bits per pixel)
16
Ultrasound Dynamic range (bits per pixel)
8
Color Doppler Dynamic range (bits per pixel)
8
Digital radiography Dynamic range (bits per pixel)
Up to 16
Digital mammography Dynamic range (bits per pixel)
14
Computed radiography Dynamic range (bits per pixel)
12
MRI File size (per image)
131 KB
CT Scan File size (per image)
524 KB
Ultrasound File size (per image)
262 KB
Color Doppler File size (per image)
442 KB
Digital radiography File size (per image)
Up to 18 MB
Digital mammography File size (per image)
27 MB
Computed radiography File size (per image)
30 MB
related to atomic number and mass density of the tissues
Radiography / CT
represents characteristics of tissues such a proton density and relaxation times
MRI
DIFFERENTIAL ABSORPTION FACTORS
- High atomic number
- Mass Density
how tightly the atoms of tissues are packed
Mass Density
Atomic number for air and soft tissue are about the same the OD changes are due to
mass density difference
INTERACTIONS OF X-RAYS WITH MATTER
- No interaction
- Complete absorption
- Partial absorption with scatter
x-ray passes completely through tissue and into the image receptor
No interaction (ex. air)
x-ray energy is completed absorbed by the tissue. No imaging information results
Complete absorption (ex. bone)
involves a partial transfer of energy to tissue, with the resulting scattered x-ray having less energy and trajectory
scattering
degrades image quality and causes patient and staff dose
Partial absorption with scatter
For digital imaging modalities, the ____ the matrix size, the ____ the pixel size, the better the spatial resolution
larger,
smaller
Pixels in a digital image represent the information contained in a volume of tissue in the patient
VOXEL (3D)
Tissue voxel information is converted into numerical values and expressed in the pixels, and these numbers are
assigned brightness levels
8-bit = ____ tonal levels
256 tonal levels
5-bit = ____ tonal levels
32 tonal levels
3-bit = ____ tonal levels
8 tonal levels
implies that every pixel in the digital image matrix M x N is represented by k binary digits
K bits
The number of bits per pixel is the
bit depth
K bits =
2^k
The bit depth has an effect on the number of shades of gray, hence the _____ of the image
density resolution
3 STEPS IN DIGITIZING AN IMAGE
- Scanning
- Sampling
- Quantization
the image is first divided into an array of pixels
Scanning
involves measuring the brightness level of each of the pixels using special devices such as PMT (Photomultiplier Tube)
Sampling
the signal from the PMT is an analog signal (voltage waveform) that must be a converted into a digital image for processing by a computer
Sampling
it determines the spatial resolution of the digitized images
Sampling
it determines the number of grey levels in the digitized images
Quantization
brightness levels obtained from sampling are assigned an integer (zero or negative or positive number) called a
gray level
the image is now made up of a range of gray levels
Quantization
total number of grays levels
Gray scale
Common Image Processing Operations:
Image Reformatting, Windowing, Region of Interest (ROI), Magnification, Surface and Volume Rendering, Profile, Histogram, Collage, Image Synthesis
Computed Tomography
Common Image Processing Operations:
Windowing, Region of Interest (ROI), Magnification, Surface and Volume Rendering, Profile, Histogram, Collage, Image Synthesis
Magnetic Resonance Imaging
Common Image Processing Operations:
Analytic Processing, Subtraction of images out of a sequence, Gray-scale Processing, Temporal Frame Averaging, Edge Enhancement, Pixel Shifting
Digital Subtracting Angiography/ Digital Fluoroscopy
Common Image Processing Operations:
Partitioned Pattern Recognition, Exposure Field Recognition, Histogram Analysis, Normalization of Raw Image Data, Gray-Scale Processing (Windowing), Spatial Filtering, Dynamic Range Control, Energy Subtraction, etc.
Computed Radiography/ Digital Radiography
simple and the most frequently used operation in digital diagnostic imaging
Point Processing Operations
the value of the one (point) input image pixel is mapped onto the corresponding output image pixel
Point Processing Operations
a graph of numbers of pixels in the entire image or part of the image having the same gray levels (density values) plotted as a function of the gray levels
Histogram
graphical display of the pixel intensity distribution for a digital image / graphical representation of the image
Histogram
plots the number of pixels found at each pixel value
Histogram
Changing the histogram of the image can alter its
brightness and contrast
If the histogram is modified or change, the _____ will change as well
brightness and contrast
Wide histogram implies _____ contrast
more
Narrow histogram will show _____ contrast
less
If the values of the histogram are concentrated in the lower end of the range of values, the image appears _____; conversely, the image appears _____ at the end of the range
dark,
bright
determines the numbers assigned to the input pixel values that change them into output pixel values resulting in a change in contrast and brightness of the image
Look-up table
change the contrast and brightness of an image
Windowing
a digital image is made up of numbers, the range of numbers is the _____, controls the contrast or gray scale
Window Width (WW)
the center of the range is define as the _____, controls the brightness of the image
Window Level (WL)
_____ Window Width provides higher image contrast (short-scale)
Narrow
_____ Window Width will show an image with less contrast
Wide
one of the first step in becoming aware of and versatile with digital image processing is to understand the general nature of images
Image Formation and Representation
SUBSETS OF IMAGES
CLASSIFICATION
- Visible Images
- Invisible Images
- Optical Images
- Mathematical Images
5 CLASSES OF DIGITAL IMAGE PROCESSING OPERATIONS
- Image Enhancement
- Image Restoration
- Image Analysis
- Image Compression
- Image Synthesis
combination of lossy and lossless compression
Wavelet compression
How is matrix named
N x M
rows x columns
horizontal x vertical
High atomic number = _____ atoms
larger
a series of mathematical equations that are used for post processing in radiography
Look-up table
It is used to correct values using a mapping function
Look-up table