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41 Cards in this Set
- Front
- Back
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What is the Nyquist Theorm? |
Relates to how many times the electrical signal is sampled to form the digital image |
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What are the 3 steps in Digitizing an image? |
• Scanning • Sampling • Quantization |
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What happens when Scanning occurs ? |
The image is divided into an array of pixels |
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When Sampling occurs what is happening? |
The photomultiplier tube measures the levels of brightness in each pixel |
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What occurs in Quantization? |
The Brightness levels are now given integers called a gray level |
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What is the gray scale composed of? |
The total number of gray levels in an image |
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When bit depth is increased what happens to the shades of gray visualized? |
The shades of gray visualized Increase as well |
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How many shades of gray can be seen in an image with a bit depth of 10? |
2^10=1024 shades of gray |
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What are the 5 Digital Imaging Processing Operations? |
• Image Enhancement • Image Restoration •Image Analysis • Image Compression • Image Synthesis |
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What are some Characteristics of the Digital Image? |
• Matrix • Pixels • Voxels • Bit depth • FOV |
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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 |
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When a Matrix size increases what happens to the pixels and Spatial Resolution? |
•Pixels size decrease ( for the same FOV) • Better Spatial Resolution |
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What happens when your FOV decreases( w/o a change in Matrix)? |
•Pixels size decrease •Details Improve |
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When an Image is Enhanced what happens to the image? |
Contours and Shapes can be enhanced to improve the overall quality of the image |
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What are some of the processes Included within Image Enhancement? |
• Contrast Enhancement • Edge Enhancement • Spatial and Frequency Filtering •Image Combining • Noise Reduction |
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What is image Restoration? |
Improves quality of images that have distortions or degradations , such as blurring |
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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 |
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What happens in Image Compression? |
Reduction in the size of the image in order to decrease transmission time and reduce storage space |
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What are 2 types of image compression? |
•Lossy •Lossless |
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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 |
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What are some examples of Point processing Operations? |
• Gray scale processing • Windowing • Image Subtraction •Temporal Averaging |
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What are some examples of Local Processing Operations? |
•Spatial Filtering • Edge Enhancement •Smoothing |
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What is an example of Global Operations? |
The Fourier transform |
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What are the 2 types of Image Domains?-Based on how they are acquired |
• Spatial location domain • Spatial frequency domain |
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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 |
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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 |
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Where are high spatial frequencies found in and image what do they effect? |
•At the edges of an image and it effects image details |
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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 |
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What occurs in the Fourier transform? |
An image in the spatial location domain can be transformed into an image in the spatial frequency domain |
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What is dose creep? |
When patient dose is increased over time |
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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 |
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When an image is Enhanced for sharpness , which frequencies are suppressed? ( high or low)? |
Low frequencies are supressed |
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When an image is Smoothed to view homogeneous structures, which frequencies are suppressed? ( high or low) |
High frequencies are suppressed |
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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 |
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If a histogram is changed what happens to brightness and contrast? |
They also change |
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A steep slope in the LUT results in what type of contrast? |
High Contrast |
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What happens to contrast in a small slope ( less than 45 degrees) of a LUT? |
Smaller scale of contrast |
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What is Aliasing? |
When two images are formed and superimpose one another but they do not align |
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What is a result of Aliasing? |
Moiré Effect |
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What does a Look up Table (LUT) do? |
Changes the low contrast numerical image to a high contrast image by assigning new values |
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Relationships between original and new values in a Look up Table LUT can be either.... |
Linear or Curved |
