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L7+Notes - (a(b(c(d Digital Subtraction Angiography(a...

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Barrett - CS450 Winter 2011 Lecture 7 Image Arithmetic Objectives : To understand the use of frame-level operations (addition, subtraction, AND, OR, etc.), frame averaging, etc. in image processing. As an excellent supplemental resource on Image Arithmetic see: http://homepages.inf.ed.ac.uk/rbf/HIPR2/arthops.htm 1. Image Addition Adding a constant: H ( x , y ) = I ( x , y ) + C Adding two images: H ( x , y ) = I ( x , y ) + J ( x , y ) Blending two images: H ( x , y ) = α I ( x , y ) + (1- ) J ( x , y ) Applications Brightening an image, Image Compositing, (Additive) Dissolves DEMO : Register two images and blend with the opacity function in Photoshop 2. Image Subtraction Subtracting two images: H ( x , y ) = I ( x , y ) - J ( x , y ) Applications Motion Detection, Frame Differencing for Object Detection, Digital Subtraction Angiography DEMO : Show before and after with Digital Subtraction Angiography
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Unformatted text preview: (a) (b) (c) (d) Digital Subtraction Angiography. (a) Original “mask” – no contrast (b) with contrast – not vessels (c) Subtraction of (a) and (b) followed by subpixel registration. Note motion artifacts from patient movement. (d) Subtraction with subpixel warping of foreground mask to compensate for motion. 3. Motion Applications Surveilance, Image Compression Barrett - CS450 Winter 2011 4. Frame Averaging Noise Suppression: Suppose n frames, gaussian noise. Why should frame-averaging work? (Gaussian noise: zero mean => noise should cancel. Calculate the SNR.) 5. Logical Operators Applications Masking, Antialising, Blue Screening. (What is an alpha channel? Alpha Blending?)...
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L7+Notes - (a(b(c(d Digital Subtraction Angiography(a...

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