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Say in the textures README that the mission mosaics' brightness is not albedo, as Iapetus shows

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Iapetus's leading hemisphere has an albedo of 0.03-0.05 and its trailing one 0.5-0.6, about a
tenth. On iapetus.jpg, between 30 S and 30 N, the leading side (30-150 W) averages 83.4 of 255 and
the trailing (30-150 E) 108.2, a ratio of 0.77, measured here again; the USGS source gives the same
(83.3 and 108.1), so it is the mosaics' frame-by-frame contrast stretch, not the processing. The
README's Iapetus row checked only where Cassini Regio lies, and nothing said the brightness is not
albedo; it now does, with those figures. The map is not rescaled: no photometric model was applied
to any body, and one hemisphere's worth of scaling would be invented for this one.

Documentation only; no behaviour changes.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
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Senrokai
2026-09-29 19:58:52 +02:00
co-authored by Claude Opus 5.5
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@@ -45,6 +45,14 @@ Each was then checked by eye against the IAU Gazetteer: the named feature lies w
coordinates put it on the processed map. "Black" is the share of pixels darker than 8 of 255 after coordinates put it on the processed map. "Black" is the share of pixels darker than 8 of 255 after
processing; the disc photographs dropped in PR #33 were 20-43% black sky. processing; the disc photographs dropped in PR #33 were 20-43% black sky.
Their brightness is the mosaics' own, contrast-stretched frame by frame to show terrain: it places
features, not albedo. Iapetus shows it most. Its leading hemisphere, Cassini Regio, has an albedo of
0.03-0.05 and its trailing one 0.5-0.6 (NASA), about a tenth; on `iapetus.jpg`, between 30 S and
30 N, the leading side (30-150 W) averages 83.4 of 255 and the trailing (30-150 E) 108.2, a ratio of
0.77, as in the USGS source (83.3 and 108.1) and the DLR PDS map. So the drawn Iapetus is a shade
darker on one side, where the real one is coal against snow. No map here was rescaled to published
photometry.
| Map | Source | Mission, credit | Checked against | Unmapped (grey) | Black | Size | | Map | Source | Mission, credit | Checked against | Unmapped (grey) | Black | Size |
| --- | --- | --- | --- | --- | --- | --- | | --- | --- | --- | --- | --- | --- | --- |
| `phobos.jpg` | [USGS](https://asc-pds-services.s3.us-west-2.amazonaws.com/mosaic/Phobos_Viking_Mosaic_40ppd_DLRcontrol.tif) Phobos Viking Mosaic 40ppd (DLR controlled) | Viking Orbiter, with Mars Express images; P. Stooke after Simonelli et al. 1993, PDS Stooke Small Bodies Maps | Stickney (1 N, 49 W) | 0.03% | 0.008% | 1024x512, 119 KB | | `phobos.jpg` | [USGS](https://asc-pds-services.s3.us-west-2.amazonaws.com/mosaic/Phobos_Viking_Mosaic_40ppd_DLRcontrol.tif) Phobos Viking Mosaic 40ppd (DLR controlled) | Viking Orbiter, with Mars Express images; P. Stooke after Simonelli et al. 1993, PDS Stooke Small Bodies Maps | Stickney (1 N, 49 W) | 0.03% | 0.008% | 1024x512, 119 KB |