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41 Cards in this Set

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What is the Nyquist Theorm?

Relates to how many times the electrical signal is sampled to form the digital image

What are the 3 steps in Digitizing an image?

• Scanning


• Sampling


• Quantization

What happens when Scanning occurs ?

The image is divided into an array of pixels

When Sampling occurs what is happening?

The photomultiplier tube measures the levels of brightness in each pixel

What occurs in Quantization?

The Brightness levels are now given integers called a gray level

What is the gray scale composed of?

The total number of gray levels in an image

When bit depth is increased what happens to the shades of gray visualized?

The shades of gray visualized Increase as well

How many shades of gray can be seen in an image with a bit depth of 10?

2^10=1024 shades of gray

What are the 5 Digital Imaging Processing Operations?

• Image Enhancement


• Image Restoration


•Image Analysis


• Image Compression


• Image Synthesis

What are some Characteristics of the Digital Image?

• Matrix


• Pixels


• Voxels


• Bit depth


• FOV

What is the effect of Matrix size on picture quality?

As the Matrix size increases for the same FOV, picture quality improves ; Images become sharper

When a Matrix size increases what happens to the pixels and Spatial Resolution?

•Pixels size decrease ( for the same FOV)


• Better Spatial Resolution

What happens when your FOV decreases( w/o a change in Matrix)?

•Pixels size decrease


•Details Improve

When an Image is Enhanced what happens to the image?

Contours and Shapes can be enhanced to improve the overall quality of the image

What are some of the processes Included within Image Enhancement?

• Contrast Enhancement


• Edge Enhancement


• Spatial and Frequency Filtering


•Image Combining


• Noise Reduction

What is image Restoration?

Improves quality of images that have distortions or degradations , such as blurring

What does Image Analysis do to an image?

Allows measurements and stats to be performed, as well as image segmentation, feature extraction and classification of objects

What happens in Image Compression?

Reduction in the size of the image in order to decrease transmission time and reduce storage space

What are 2 types of image compression?

•Lossy


•Lossless

What is image Synthesis and when is it used?

•Creates images from other images or non-image data



•It is used when a desired image is either physically impossible or impractical to acquire or does not exist in a physical form at all

What are some examples of Point processing Operations?

• Gray scale processing


• Windowing


• Image Subtraction


•Temporal Averaging

What are some examples of Local Processing Operations?

•Spatial Filtering


• Edge Enhancement


•Smoothing

What is an example of Global Operations?

The Fourier transform

What are the 2 types of Image Domains?-Based on how they are acquired

• Spatial location domain


• Spatial frequency domain

What is the primary goal of the Fourier transform/ Inverse Fourier transform?

To facilitate image processing that can enhance or suppress certain features in an image

What is the primary goal of the Fourier transform/ Inverse Fourier transform?

To facilitate image processing that can enhance or suppress certain features in an image

Where are high spatial frequencies found in and image what do they effect?

•At the edges of an image and it effects image details

Where are low spatial frequencies found in an image and what do they effect?

In the center of an image and they effect image contrast

What occurs in the Fourier transform?

An image in the spatial location domain can be transformed into an image in the spatial frequency domain

What is dose creep?

When patient dose is increased over time

What does the Inverse Fourier transform do to an image?

It takes an image in the spatial frequency domain and transforms it into the spatial location domain

When an image is Enhanced for sharpness , which frequencies are suppressed? ( high or low)?

Low frequencies are supressed

When an image is Smoothed to view homogeneous structures, which frequencies are suppressed? ( high or low)

High frequencies are suppressed

What is a histogram?

Graph of the number of pixels in an image: the same gray levels are plotted as a function of the gray levels

If a histogram is changed what happens to brightness and contrast?

They also change

A steep slope in the LUT results in what type of contrast?

High Contrast

What happens to contrast in a small slope ( less than 45 degrees) of a LUT?

Smaller scale of contrast

What is Aliasing?

When two images are formed and superimpose one another but they do not align

What is a result of Aliasing?

Moiré Effect

What does a Look up Table (LUT) do?

Changes the low contrast numerical image to a high contrast image by assigning new values

Relationships between original and new values in a Look up Table LUT can be either....

Linear or Curved