AlexZ005 · Nov 4, 2026 · Nov 1, 2026
diff --git a/hdri/CREDITS.md b/hdri/CREDITS.md
@@ -20,4 +20,20 @@ All five are **CC0** (public domain) from [Poly Haven](https://polyhaven.com/hdr
 | Starlight | `dikhololo_night_1k.hdr` | [Dikhololo Night](https://polyhaven.com/a/dikhololo_night) | Greg Zaal |
 | Photo studio | `studio_small_09_1k.hdr` | [Studio Small 09](https://polyhaven.com/a/studio_small_09) | Sergej Majboroda |
 
+## UltraHDR sizes (roadmap 72, LK2)
+
+Beside each `.hdr` sit `_1k.jpg`, `_2k.jpg` and `_4k.jpg` (Meadow also has `_8k.jpg`, the showcase): the
+same Poly Haven skies at those sizes, CC0, encoded as UltraHDR (an SDR JPEG + a gain map) by the core
+repo's `scripts/hdri-uhdr.cjs` from Poly Haven's own `.hdr` of that size.
+The `.hdr` files stay: older releases fetch them, and they are the fallback.
+
+```
+node scripts/hdri-uhdr.cjs <id>_1k.hdr <id>_1k.jpg --gs 1 --gq 95 --q 92 --check   # the light: full-size gain map
+node scripts/hdri-uhdr.cjs <id>_4k.hdr <id>_4k.jpg --check                         # sky only: half-size gain map
+```
+
+The 1K file is what the app LIGHTS a scene from, so `--check` must read energy within 2% of the source
+(measured 0.992 to 1.018). The larger files only draw the sky; there the sun's disc loses energy to the
+half-size gain map (0.59 to 0.99) and still clips to white on screen.
+
 `sha256sum -c hdri/SHA256SUMS` verifies the bytes (and a jsDelivr purge: fetch each URL and compare).
diff --git a/hdri/SHA256SUMS b/hdri/SHA256SUMS
@@ -1,5 +1,21 @@
 6861489f983cdc0c22435b781a3487171bd25f25f9cc52c46ac402d48e08249e  dikhololo_night_1k.hdr
+2aed91260bad4a760f748d6a2446a9d2a0fa3d9212ec56710bcf5a3069f1e269  dikhololo_night_1k.jpg
+7dbd4fec43642defe3e2394fec68d59360240bbad26719ccf97c3558219fa227  dikhololo_night_2k.jpg
+9537afbecc7b43a9c9d9b2671ff9b728273192d6ecd4a2156fc9fdf0f0bff07c  dikhololo_night_4k.jpg
 fd94c84997b8a3c353b62c2125a9b44e19509956986a126e472684432a02d798  kloofendal_48d_partly_cloudy_puresky_1k.hdr
+a75496f7f0370e6840bd90b9fb50ff0164166a4c8b4221608e242c788fa2cbdb  kloofendal_48d_partly_cloudy_puresky_1k.jpg
+0973953a6e71aa14919c1688f93f3a6e30e6fd6b06e1805a77f799556c50e676  kloofendal_48d_partly_cloudy_puresky_2k.jpg
+0c350818949eda434035ba7d1dbc0c482c856ebcf8a0cb7869fe602f12047829  kloofendal_48d_partly_cloudy_puresky_4k.jpg
 8601506df47f06cd52a3a4f3a14663d463d6ac924c986f15737bcc2a3840480c  meadow_2_1k.hdr
+8bc3939bb90d0b1eec2d9c0dc9777c813617f2178c872e3f6b7f9e50e11a0b33  meadow_2_1k.jpg
+070ca9b6f5a3773b1884f076a14308f2a6dd0fba733a10f4ae9167438ceaf2e0  meadow_2_2k.jpg
+d669dea1711c56e5f870db593519bfd68466b4c244b3c091cd7347e538ea80df  meadow_2_4k.jpg
+f6a107602b436bc54a89a56351d2a444db02257253125cbfb7692074630c21f6  meadow_2_8k.jpg
 38199a31e945906f6778431e989256a92d9d78b0cfc0f902accad9f5244bf50f  spruit_sunrise_1k.hdr
+5aa41078f83ae78d2b1ca243d9bebdaad94ea9725a944c0e739a0a9ae260dfb1  spruit_sunrise_1k.jpg
+2ccf1ebff616403316ccd4cd2fb882ed61f906e3c0d22e69ac772f4433414daf  spruit_sunrise_2k.jpg
+6e354095dddae08516fed0864bbad214ad53577476650b05e0210f68cf0365db  spruit_sunrise_4k.jpg
 e7cfda5f4e98e623db12b8bfd0184e048488e4855d9c83e2751fb44a32e80c45  studio_small_09_1k.hdr
+8582bd82da6c777528f817e944dc0399006252e9baa22b39f80e21448d2d8ea5  studio_small_09_1k.jpg
+f4ee55c8ab1610e10ef88b8a255afafd03d226d318fd1a59cec3a611c3e3051b  studio_small_09_2k.jpg
+b6308be75e50aee9175c12be7578ecb6cf3d03e16baa0ee02e4a2ad8919bf472  studio_small_09_4k.jpg
diff --git a/hdri/dikhololo_night_1k.jpg b/hdri/dikhololo_night_1k.jpg
diff --git a/hdri/dikhololo_night_2k.jpg b/hdri/dikhololo_night_2k.jpg
diff --git a/hdri/dikhololo_night_4k.jpg b/hdri/dikhololo_night_4k.jpg
diff --git a/hdri/kloofendal_48d_partly_cloudy_puresky_1k.jpg b/hdri/kloofendal_48d_partly_cloudy_puresky_1k.jpg
diff --git a/hdri/kloofendal_48d_partly_cloudy_puresky_2k.jpg b/hdri/kloofendal_48d_partly_cloudy_puresky_2k.jpg
diff --git a/hdri/kloofendal_48d_partly_cloudy_puresky_4k.jpg b/hdri/kloofendal_48d_partly_cloudy_puresky_4k.jpg
diff --git a/hdri/meadow_2_1k.jpg b/hdri/meadow_2_1k.jpg
diff --git a/hdri/meadow_2_2k.jpg b/hdri/meadow_2_2k.jpg
diff --git a/hdri/meadow_2_4k.jpg b/hdri/meadow_2_4k.jpg
diff --git a/hdri/meadow_2_8k.jpg b/hdri/meadow_2_8k.jpg
diff --git a/hdri/spruit_sunrise_1k.jpg b/hdri/spruit_sunrise_1k.jpg
diff --git a/hdri/spruit_sunrise_2k.jpg b/hdri/spruit_sunrise_2k.jpg
diff --git a/hdri/spruit_sunrise_4k.jpg b/hdri/spruit_sunrise_4k.jpg
diff --git a/hdri/studio_small_09_1k.jpg b/hdri/studio_small_09_1k.jpg
diff --git a/hdri/studio_small_09_2k.jpg b/hdri/studio_small_09_2k.jpg
diff --git a/hdri/studio_small_09_4k.jpg b/hdri/studio_small_09_4k.jpg