McIDAS Learning Guide
Version 2006

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Loop Control System - Basic Concepts

You can define a random or sequential loop of image frames, and set the display time (dwell rate) for each frame in the loop.

Loop Bounds and Sequences

Image frames in the image window are like slides in a slide projector carousel, in that any frame can be brought easily into view or looked at in any order, but you cannot look at more than one at the same time in the same image window:

A loop has beginning and ending frames called loop bounds. When you start McIDAS, the loop bounds are set as frames one through the total number of frames. If you log on to McIDAS and initialize the workstation, the loop bounds are one through one-half the total number of image frames. You will use the commands LB and LS to set loop sequences which can be sequential or random.

When you define loop bounds, you also create opposite loop bounds. Each frame has an opposite frame that is half the total number of frames away. For example, on a session with ten frames, frames 1 and 6 are opposite, frames 2 and 7 are opposite, etc. The single letter command O toggles between a frame and its opposite, which is useful for comparing images.

Dwell Rate

The dwell rate is the amount of time each frame is displayed during automatic looping. The default dwell rate is nine units for the first frame and six units for the remaining frames. In McIDAS-X, one unit is appoximately 1/15th of a second; the fastest dwell rate is 1/15 of a second (1 unit), though some workstations will not be able to sustain that rate.

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