Color mapping of difference

Question

I have two arrays A and B. I want to do color mapping of their difference A - B. So far, I am doing this:

1) calculate d = A - B
2) find min / max in d
3) linear mapping of d from (min, max) to (0, 1)
4) convert (0, 1) to color

The problem is, that sometimes, there are noise values in my data. For example, several values in B are too large (like 100 times bigger than the rest) and it leads to enormous difference and increased min or max. After mapping to (0, 1) all other values are "wiped". How can I solve this?

Answer 1

I would suggest two options:

1. use percentile instead of min/max (e.g. 95/5%, you need to experiment here), with linear mapping clamped to (0,1) range. To do so sort the d array and pick (N - 1) * percentile + 1th member as minimum/maximum, map as normal and clamp r = Min(1.0, Max(0.0, r)) the results in (0,1) range
2. Use non linear mapping, for example the logarithmic scale is often used in scientific applications d = log (d)

The option 1 attempts to filter the data from erroneous values rather than displaying them, the quality heavily relies on on percentile settings, which is (input)data-dependent. The option 2 tries to use non-linear mapping in order to display meaningful values even for erroneous data, but requires users to understand logarithmic scale.