Spatial Information (SI) is a standardized measure, defined in ITU-T P.910 section 7.8, of how much fine detail a frame holds. Each frame's luminance - its brightness channel - is run through a Sobel filter, an edge detector, and the spread (standard deviation) of the result is the SI; more edges and texture push it higher. With Temporal Information (TI) it places any clip on a map of content difficulty: plot every source with TI on one axis and SI on the other, and you see your set's coverage at a glance. SI matters because sources differ in how hard they are to compress - a static interview compresses to nothing while grass, confetti, or water stress an encoder. A good source set spreads across the SI/TI plane, deliberately including the hard corner where encoders struggle; a convenience-sampled set clumps in the easy low corner and reports a quality production will never see. SI thus turns the vague instruction to use varied content into something measurable.
