Document physical target visualization color scales

README.md

@@ -222,6 +222,14 @@ psi_gray = psi / pi + 0.5
 R_gray = R / pi
 ```
 
+Visualization note: after applying this optional physical-range mapping, use the
+nominal physical ranges for color scales when comparing samples or models:
+`D/Delta` in `[0, 1]`, `eta/R` in `[0, pi]`, and `theta/psi` in
+`[-pi/2, pi/2]`. Per-sample min/max color scales are useful for inspection, but
+they can make cross-sample or cross-modality comparisons visually misleading.
+The helper script `scripts/test2.py` demonstrates both normalized targets and
+physical targets with fixed physical colorbar ranges.
+
 ## Reference Label Generation
 
 The target modalities are generated using Lu-Chipman decomposition from measured