Carry Lightroom's tone sliders across at measured strengths

Contrast2012 and the four recovery sliders were imported one to one. They do
not mean the same thing here: fitted on the library's Lightroom 6 exports and
their raws — each photograph's sliders carried across as slider × factor, one
factor per slider, on about 90 exports with no look applied, on the Camera Raw
default rendering — ours needed contrast at about a tenth (Lightroom's −100
imported as ours flattens a frame to grey), highlights ×1.4, shadows ×1.9 and
blacks ×1.25. Whites fitted below 1 every time without agreeing where; 0.5 is
a hedge, and says so. Vibrance stays one to one: the op itself is now
calibrated to Lightroom's.

core/dr-preset-xmp/src/lib.rs

@@ -83,35 +83,43 @@ const MAPPINGS: &[Mapping] = &[
         param: "exposure",
         convert: Convert::Direct,
     },
+    // The five tone sliders do not mean the same thing in the two applications,
+    // whatever their shared ±100 suggests. The factors were fitted against the
+    // library's own Lightroom 6 exports and their raws (darkroom-lrfit, 2026-10):
+    // each photograph's sliders carried across as `slider × factor`, one factor
+    // per slider, on ~90 exports with no look applied. Contrast is ours at a
+    // tenth — at −100 ours flattens a frame to grey — and our shadows need
+    // nearly twice Lightroom's number. Whites barely appears in those exports;
+    // every fit put it under 1 but none agreed where, so 0.5 is a hedge.
     Mapping {
         crs: "Contrast2012",
         op: "contrast",
         param: "contrast",
-        convert: Convert::Direct,
+        convert: Convert::Scale(0.1),
     },
     Mapping {
         crs: "Highlights2012",
         op: "highlights_shadows",
         param: "highlights",
-        convert: Convert::Direct,
+        convert: Convert::Scale(1.4),
     },
     Mapping {
         crs: "Shadows2012",
         op: "highlights_shadows",
         param: "shadows",
-        convert: Convert::Direct,
+        convert: Convert::Scale(1.9),
     },
     Mapping {
         crs: "Whites2012",
         op: "blacks_whites",
         param: "whites",
-        convert: Convert::Direct,
+        convert: Convert::Scale(0.5),
     },
     Mapping {
         crs: "Blacks2012",
         op: "blacks_whites",
         param: "blacks",
-        convert: Convert::Direct,
+        convert: Convert::Scale(1.25),
     },
     Mapping {
         crs: "Clarity2012",
@@ -566,8 +574,8 @@ mod tests {
         assert_eq!(get("colour_mixer", "violet_sat"), Some(23.0));
         assert_eq!(get("colour_mixer", "red_hue"), Some(-5.0));
         assert_eq!(get("colour_mixer", "green_lum"), Some(7.0));
-        assert_eq!(get("highlights_shadows", "highlights"), Some(-40.0));
-        assert_eq!(get("blacks_whites", "blacks"), Some(-20.0));
+        assert_eq!(get("highlights_shadows", "highlights"), Some(-40.0 * 1.4));
+        assert_eq!(get("blacks_whites", "blacks"), Some(-20.0 * 1.25));
     }
 
     #[test]
@@ -588,7 +596,7 @@ mod tests {
         let get = |op: &str, param: &str| p.get(&(op.to_string(), param.to_string())).copied();
         assert_eq!(get("colour_mixer", "blue_sat"), Some(58.0));
         assert_eq!(get("colour_mixer", "cyan_sat"), Some(50.0));
-        assert_eq!(get("highlights_shadows", "highlights"), Some(-40.0));
+        assert_eq!(get("highlights_shadows", "highlights"), Some(-40.0 * 1.4));
     }
 
     #[test]
@@ -642,14 +650,20 @@ mod tests {
     fn the_settings_that_share_a_convention_come_across_unchanged() {
         let import = read_xmp(ATTRIBUTE_FORM).unwrap();
         assert_eq!(value(&import, "exposure", "exposure"), Some(0.75));
-        assert_eq!(value(&import, "contrast", "contrast"), Some(25.0));
+        assert_eq!(value(&import, "contrast", "contrast"), Some(25.0 * 0.1));
         assert_eq!(
             value(&import, "highlights_shadows", "highlights"),
-            Some(-40.0)
+            Some(-40.0 * 1.4)
+        );
+        assert_eq!(
+            value(&import, "highlights_shadows", "shadows"),
+            Some(30.0 * 1.9)
+        );
+        assert_eq!(value(&import, "blacks_whites", "whites"), Some(10.0 * 0.5));
+        assert_eq!(
+            value(&import, "blacks_whites", "blacks"),
+            Some(-15.0 * 1.25)
         );
-        assert_eq!(value(&import, "highlights_shadows", "shadows"), Some(30.0));
-        assert_eq!(value(&import, "blacks_whites", "whites"), Some(10.0));
-        assert_eq!(value(&import, "blacks_whites", "blacks"), Some(-15.0));
         assert_eq!(value(&import, "clarity", "amount"), Some(12.0));
         assert_eq!(value(&import, "texture", "amount"), Some(8.0));
         assert_eq!(value(&import, "vibrance", "vibrance"), Some(20.0));
@@ -690,7 +704,7 @@ mod tests {
         // does not say which shape it used.
         let import = read_xmp(ELEMENT_FORM).unwrap();
         assert_eq!(value(&import, "exposure", "exposure"), Some(0.75));
-        assert_eq!(value(&import, "contrast", "contrast"), Some(25.0));
+        assert_eq!(value(&import, "contrast", "contrast"), Some(25.0 * 0.1));
     }
 
     #[test]