In a regular spreadsheet, each Cell can hold a numeric entry, or multiple entries if 'layers' are supported. In the Image SpreadSheet, each Cell can hold an Image, or a series of Images. In fact, Cells are designed to hold many Image Datasets, and support animation over them. Thus in IISS, images can be organized not only in rows and columns of Cells, but in different levels within Cells. This allows for considerable flexibility when trying to organize data spatially, temporally and spectrally.

An Image displayed in a Cell can be interactively positioned and scaled (roamed and zoomed), and these effects are propagated to all Images in a Cell. Also, Cells can be grouped, so that roam, zoom and animation effects will be distributed from one Cell to all the other Cells in a group. This synchronized interactive visualization capability is a powerful tool, allowing the user to intercompare vast amounts of data quickly and easily.

In a traditional spreadsheet, each Cell has a corresponding formula, and mathematical computation can be done over the contents of the sheet. In the Image SpreadSheet, each Cell level (called a Frame) has a corresponding formula, supporting image-based operations such as algebraic and bitwise expressions, RGB combinations, and remapping between geographic projections. Copying a formula from one Frame to another preserves the relative location of data referenced within the formula. This means that an operation can easily be applied to tens or hundreds of Frames in a Cell, with the results stored as Frames in another Cell.

Images can be geo-located scientific data from HDF-EOS format files; data types range from 8 bits per pixels to 64 bits per pixel (double precision), with colormap display capabilities. Pure imagery is also supported, as from SGI or PNG format files.

The Image SpreadSheet is a threaded, UNIX-based program written in C and C++. It runs on SGI Octane, O2 and Onyx class machines. It is currently available within NASA.

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