1Image Stacks15-463: Rendering and Image ProcessingAlexei EfrosAnnouncementsWe are now done with the first part of the course, broadly defined as:SINGLE IMAGE STUFFNow, we are ready to move on, but first…MID-TERM• Week from today: Thursday, Oct 21, in class• Will take about an hour• Closed books, closed notes, one double-sided “cheat-sheet” allowed• Covers everything up to this point• Review on Tuesday (bring questions!)2The story so far…So far, we dealt with but a little part of our Flenoptic Function:• A pencil of rays through one point• At one instance in time• A 2D snapshot, an instantaneous image of the worldWe have been frozen in space-time, with no way to get out……now we are reading to break out of 3DFigure by Leonard McMillanBreaking out of 2D…now we are ready to break out of 2DAnd enter the real world!3All rays are not equalSuporn’spanoramaRecovering structureQ: What must we do to uncover the structure of the world? A: Move!• in space• and/or in time• Not 2D anymore!4“Smoke” (1996), the “photo album scene”Moving in TimeMoving only in time, while not moving in space, has many advantages• No need to find correspondences• Can look at how each ray changes over time• In science, always good to change just one variable at a timeThis approach has always interested artists (e.g. Monet)Modern surveillance video camera is a great source of information• There are now many such WebCams now, some running for several years!5Image StackAs can look at video data as a spatio-temporal volume• If camera is stationary, each line through time corresponds to a single ray in space• We can look at how each ray behaves • What are interesting things to ask?t0255timeAverage ImageCompute the average value of each pixelWhat will it
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