LR-IMP-PROFILES: red / green / blue curves only with the master curve; neutral test values

Lightroom Classic reads `ToneCurvePV2012Red/Green/Blue` only together with
`ToneCurvePV2012`: a packet with a channel curve and no master curve leaves the
photo unchanged there (rendered on a chart: the channel curve alone has no
effect, with an identity master curve it applies). Imports now do the same.

The preset-packet test helper uses made-up as-shot values.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

crates/engine/src/crs.rs

@@ -244,11 +244,14 @@ pub fn to_partial(props: &Props, raw: Option<bool>) -> Value {
             put(o, "curve.master", c);
         }
     }
-    for (crs, ch) in
-        [("ToneCurvePV2012", "master"), ("ToneCurvePV2012Red", "red"), ("ToneCurvePV2012Green", "green"), ("ToneCurvePV2012Blue", "blue")]
-    {
-        if let Some(c) = curve(props, &format!("crs:{crs}")) {
-            put(o, &format!("curve.{ch}"), c);
+    // Lightroom Classic reads the red / green / blue curves only together with the master 2012
+    // curve: a channel curve without `ToneCurvePV2012` leaves the photo unchanged
+    if let Some(c) = curve(props, "crs:ToneCurvePV2012") {
+        put(o, "curve.master", c);
+        for (crs, ch) in [("ToneCurvePV2012Red", "red"), ("ToneCurvePV2012Green", "green"), ("ToneCurvePV2012Blue", "blue")] {
+            if let Some(c) = curve(props, &format!("crs:{crs}")) {
+                put(o, &format!("curve.{ch}"), c);
+            }
         }
     }
 
@@ -572,7 +575,7 @@ mod tests {
           <rdf:Description rdf:about="" xmlns:crs="http://ns.adobe.com/camera-raw-settings/1.0/"
              crs:PresetType="Normal" crs:Cluster="" crs:UUID="0123ABCD" crs:SupportsAmount2="True" crs:SupportsAmount="True"
              crs:RequiresRGBTables="False" crs:Contrast2012="+25" crs:LensProfileEnable="0" crs:OverrideLookVignette="False"
-             crs:CropConstrainToWarp="0" crs:AsShotTemperature="7450" crs:AsShotTint="23" {extra_attrs}>
+             crs:CropConstrainToWarp="0" crs:AsShotTemperature="5500" crs:AsShotTint="10" {extra_attrs}>
             <crs:SortName><rdf:Alt><rdf:li xml:lang="x-default"/></rdf:Alt></crs:SortName>
             <crs:Description><rdf:Alt><rdf:li xml:lang="x-default"/></rdf:Alt></crs:Description>
             {extra_elems}
@@ -580,6 +583,24 @@ mod tests {
         )
     }
 
+    #[test]
+    fn channel_curves_need_the_master_curve() {
+        // Lightroom ignores a red / green / blue curve without `ToneCurvePV2012`
+        let packet = |master: &str| {
+            format!(
+                r#"<x:xmpmeta xmlns:x="adobe:ns:meta/"><rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
+          <rdf:Description rdf:about="" xmlns:crs="http://ns.adobe.com/camera-raw-settings/1.0/" crs:ToneCurveName2012="Custom">{master}
+           <crs:ToneCurvePV2012Green><rdf:Seq><rdf:li>0, 0</rdf:li><rdf:li>64, 40</rdf:li><rdf:li>255, 255</rdf:li></rdf:Seq></crs:ToneCurvePV2012Green>
+          </rdf:Description></rdf:RDF></x:xmpmeta>"#
+            )
+        };
+        let alone = to_partial(&props(&packet("")), Some(true));
+        assert!(alone.pointer("/curve/green").is_none(), "{alone}");
+        let master = "<crs:ToneCurvePV2012><rdf:Seq><rdf:li>0, 0</rdf:li><rdf:li>255, 255</rdf:li></rdf:Seq></crs:ToneCurvePV2012>";
+        let with = to_partial(&props(&packet(master)), Some(true));
+        assert!(with.pointer("/curve/green").is_some() && with.pointer("/curve/master").is_some(), "{with}");
+    }
+
     fn unmapped(x: &str) -> Vec<String> {
         to_partial_report(&props(x), None, None, 1.5).1
     }

docs/whats-new.md

@@ -49,6 +49,7 @@
   white, empty Point Color slots…) as settings that couldn't be carried over.
 - A preset whose lens-profile switch is off no longer turns off the lens corrections built into a DNG (iPhone ProRAW
   and other files with embedded distortion / vignetting corrections), matching what the preset does elsewhere.
+- A red / green / blue curve in an XMP preset without the master curve is ignored, as Lightroom ignores it.
 - Imported `.cube` LUT profiles appear in the Profile menu and the profile browser, grouped by their folder, and stay
   favourites across restarts (issue #328).
 

docs/xmp-interop.md

@@ -117,7 +117,7 @@ names are read (e.g. `Exposure2012`, not the older `Exposure`).
 | `ParametricShadows`, `ParametricDarks`, `ParametricLights`, `ParametricHighlights` | `curve.shadows/darks/lights/highlights` | |
 | `ParametricShadowSplit`, `ParametricMidtoneSplit`, `ParametricHighlightSplit` | `curve.split_shadows/split_mid/split_highlights` | |
 | `CurveRefineSaturation` | `curve.refine_saturation` | 0..100 (100 = curve saturation unchanged) |
-| `ToneCurvePV2012`, `ToneCurvePV2012Red/Green/Blue` | `curve.master/red/green/blue` | `"x, y"` points in 0..255 → 0..1; a straight 0→255 line = no curve |
+| `ToneCurvePV2012`, `ToneCurvePV2012Red/Green/Blue` | `curve.master/red/green/blue` | `"x, y"` points in 0..255 → 0..1; a straight 0→255 line = no curve; the red / green / blue curves are read only with `ToneCurvePV2012` (Lightroom Classic ignores them without it) |
 | `SplitToningShadowHue/Saturation`, `SplitToningHighlightHue/Saturation` | `grading.shadows/highlights.hue/sat` | |
 | `ColorGradeShadowLum`, `ColorGradeHighlightLum` | `grading.shadows/highlights.lum` | |
 | `ColorGradeMidtoneHue/Sat/Lum`, `ColorGradeGlobalHue/Sat/Lum` | `grading.midtones/global.*` | |