# What is the definition in contrast-invariant?

I came across this "texture analysis" technique in a paper called "Identifying structural complexity in aeromagnetic data: An image analysis approach to greenfields gold exploration" by E. Holden et al. and I couldn't really find the meaning of whatever this is anywhere.

context: "In this paper, we detect edges (i.e., magnetic discontinuities) by firstly enhancing local magnetic variations using texture analysis and then finding ridges within the texture analysis outputs using a contrast-invariant line detection technique. Finally, the texture ridges are identified and vectorised."

A contrast-invariant function is one that yields the same output before or after scaling intensities (i.e. increasing or decreasing contrast). For example, the function $$g$$ is contrast invariant if
$$g(f) = g(Cf)\;,$$
given an image $$f$$ and a positive constant $$C$$ (some contrast-invariant line detection algorithms might also yield the same results if $$C$$ is negative, but obviously not if it is zero).