* Instead of baking these into the overlay texture and trying to decode them
afterwards, we instead write a grayscale 16F value into the overlay texture,
and add a special decode display mode that will use the heatmap and bucketing
provided.
* This means that saving these overlay textures now saves grayscale. When saving
to an 8-bit format, we remap to 0-255 so that greater than 1.0 values are
mapped lower.