Showing papers on "Alpha compositing published in 1993"

Method and apparatus for presenting information in a display system using transparent windows

Abstract: A central processing unit (CPU) is provided and is coupled to a display for displaying graphic and other data in multiple overlapping windows. The CPU is further coupled to one or more input devices which permits a user to selectively position a cursor and input and manipulate data within each of the windows on the display. The windows include defined areas having window features such as text, icons and buttons corresponding to functions to be executed by the CPU. Multiple applications may be executed concurrently by the CPU such that each application is associated with one or more windows. Each display element (“pixel”) comprising the display is represented by multiple bits in a computer frame buffer memory coupled to the CPU. An alpha value (α) is associated with the intensity of each pixel of the display, such that multiple images may be blended in accordance with a predefined formula utilizing the alpha values. By setting the alpha values appropriately, transparency may be accomplished such that data associated with underlying windows may be rendered visible to the user. Effectively, the present invention merges multiple images through alpha “blending” such that several images appear transparently on top of one another. The present invention, through the selective use of alpha blending, permits underlying windows to display data visible to the user through windows which are overlaid above an underlying window.

Method and apparatus for displaying an alpha channel virtual image

Abstract: The present invention is directed to a method and apparatus for displaying a virtual image and for providing control over the "alpha channel" or transparency of the virtual image. The present invention uses a beam splitter to provide a virtual image to a viewer. Behind the beam splitter is a liquid crystal region for controlling the transparency of the virtual image. Behind the liquid crystal region is a background image. Control of the liquid crystal region is coordinated with control of the virtual image so as to make transparency and opacity of the liquid crystal region follow the portions of the virtual image that are intended to be transparent and opaque, respectively.