Optics: cache pixel-area Moffat kernels

README.md

@@ -158,6 +158,19 @@ Point sources use a flux-normalized circular Moffat PSF by default
 1.15-pixel Gaussian core while the Moffat wings remain continuous; both values
 are display/optics calibration parameters.
 
+The default renderer builds one immutable, process-wide 64-by-64 sub-pixel
+Moffat lookup kernel.  Its weights are pixel-area integrals and are bilinearly
+interpolated between phase tables.  The renderer reports its build time and
+cached/direct-fallback image counts.  Pass `--psf-direct` to use the slower
+8-point quadrature reference evaluator for regression comparisons; an image
+whose required HDR-tail support exceeds the cache radius selects that reference
+path automatically.
+
+For PSF validation only, `make psf-hdr-test` builds
+`build/minkowski_psf_hdr_test`, a separate binary with a `--hdr-output PATH`
+option.  It writes the pre-tone-mapping RGB framebuffer as a 32-bit float PFM
+image; the ordinary binaries do not contain this option or writer.
+
 Pass `--draw-mesh` to alpha-composite image-plane triangle edges as
 one-pixel-wide 0.5 linear-gray diagnostic lines at 0.5 opacity. The line
 rasterizer uses coverage-based antialiasing.