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Chapter 9:
Window and Level
Not to be confused with contrast and brightness, window and level provide a tool to select a range of tonal information from within the total image and present it on the display using the display’s full tonal range as calibrated. Brightness and contrast appear to influence the same attributes of an image, and that makes them appear functionally equal. That is roughly where any similarity ends and the need to understand what is different begins. The two sides of this process can be separated at the DAC conversion on the video graphic card. PreDAC is completely digital and where the native image is manipulated, and post-DAC is the analog video signal to the display. The former permits the selection of a range (window and level) of tonal information to be presented while the latter is for setting the display’s dynamic response from black to peak white, i.e., operational settings (brightness and contrast) that are to be maintained to a specification.
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