Options for the heatmap

How should the "heatmap" be realized?

The simplest approach would be to use a grayscale bitmap and interpreting the different values as "precision" between "as precise as possible" and "not so precise" (i.e. "float ranges"). However, these boundaries are to be defined...

Ideally, we can find a solution that makes it possible for the user to specify a floating-point-number for this.