Keep the sigmoid as the default curve; Camera Raw's tone is a choice

The Camera Raw default rested on comparing against Lightroom previews
of photographs that carry the user's Lightroom edits — HSL saturation
Blue +58, Aqua +50 and more, Highlights -40, Blacks -20, in every
DNG's XMP — so it measured the house look, not Camera Raw's base
rendering. Under the ACR3 curve _MG_9080 renders brighter than its
Lightroom preview (mean 0.39 against 0.31).

So the curve choice's first variant, the default, is the sigmoid again
and every raw renders as in 0.20.0 apart from baseline exposure. D21
and camera-profiles.md §12 now say the default is open, to be decided
by measuring against Lightroom exports of unedited photographs. Tests
that are about Camera Raw's tone choose it explicitly.

core/dr-gpu/src/adjust.rs

@@ -3420,10 +3420,8 @@ mod tests {
             read_centre(&ctx, t)
         };
 
-        // The default rendering of a raw is Camera Raw's tone (D21): a grey
-        // goes through the ACR3 curve unchanged in hue.
         let scene = 3537.0 / 16383.0;
-        let viewed = dr_types::tone::evaluate(&dr_types::tone::ACR3_DEFAULT, scene);
+        let viewed = dr_pipeline::view::Sigmoid::default_curve().channel(scene);
         let expected = (dr_types::Transfer::Srgb.encode(viewed) * 255.0).round() as i32;
         let delta = (i32::from(from_sensor[0]) - expected).abs();
         assert!(

core/dr-gpu/tests/camera_profile.rs

@@ -206,7 +206,12 @@ fn camera_raw_tone_agrees_with_its_cpu_reference() {
         .expect("demosaicer")
         .run(&frame(None))
         .expect("upload");
-    let ops: Vec<Box<dyn Operation>> = vec![Box::new(dr_pipeline::ops::ViewTransform::new())];
+    let mut view = dr_pipeline::ops::ViewTransform::new();
+    view.set_param(
+        dr_pipeline::ops::view_transform::CURVE,
+        dr_pipeline::ops::view_transform::CAMERA_RAW,
+    );
+    let ops: Vec<Box<dyn Operation>> = vec![Box::new(view)];
     let shader = dr_pipeline::compose(&ops);
     let mut adjust = AdjustPass::new(&ctx);
     adjust.render(&source, &shader, SIZE, SIZE).expect("render");

core/dr-gpu/tests/view_transform.rs

@@ -46,8 +46,8 @@ fn flat_raw(level: u16) -> RawImage {
     }
 }
 
-/// The default chain with D19's sigmoid chosen: Camera Raw's tone is the
-/// default since D21, and these tests are about the sigmoid.
+/// The default chain with D19's sigmoid chosen explicitly, so these tests
+/// stay about the sigmoid whichever curve is the default (D21).
 fn sigmoid_chain() -> EditGraph {
     let mut g = EditGraph::default_chain();
     g.set_param(
@@ -59,15 +59,21 @@ fn sigmoid_chain() -> EditGraph {
 }
 
 #[test]
-fn camera_raw_tone_is_the_default_and_agrees_with_the_acr3_curve() {
+fn camera_raw_tone_agrees_with_the_acr3_curve() {
     // TRACES: FR-DEV-3j
-    // D21: a raw with no profile renders a grey through Camera Raw's default
-    // curve, which the profile buffer's placeholder carries.
+    // D21: a raw with no profile, Camera Raw's curve chosen, renders a grey
+    // through the ACR3 default curve, which the profile buffer's placeholder
+    // carries.
     let Some(ctx) = ctx() else {
         eprintln!("skipping: no GPU adapter");
         return;
     };
-    let graph = EditGraph::default_chain();
+    let mut graph = EditGraph::default_chain();
+    graph.set_param(
+        dr_pipeline::ops::view_transform::ID,
+        dr_pipeline::ops::view_transform::CURVE,
+        dr_pipeline::ops::view_transform::CAMERA_RAW,
+    );
     for level in [500u16, 4_000, 8_520, 20_000, 40_000] {
         let scene = f32::from(level) / f32::from(u16::MAX);
         let display = dr_types::tone::evaluate(&dr_types::tone::ACR3_DEFAULT, scene);

core/dr-pipeline/src/ops/view_transform.rs

@@ -34,13 +34,15 @@ pub const ID: OpId = OpId("view_transform");
 pub const CONTRAST: ParamId = ParamId("contrast");
 pub const WHITE: ParamId = ParamId("white");
 /// TRACES: FR-DEV-3j
-/// Which curve renders: Camera Raw's (index 0, the default — D21) or D19's
-/// sigmoid.
+/// Which curve renders: D19's sigmoid (index 0, the default) or Camera
+/// Raw's (D21). Which of the two should be the default is open — the
+/// Lightroom-matching work decides it — so the default is what 0.20.0
+/// rendered.
 pub const CURVE: ParamId = ParamId("curve");
 
 /// [`CURVE`]'s values, in the order of its variants.
-pub const CAMERA_RAW: f32 = 0.0;
-pub const SIGMOID: f32 = 1.0;
+pub const SIGMOID: f32 = 0.0;
+pub const CAMERA_RAW: f32 = 1.0;
 
 static HELPERS: LazyLock<[Helper; 3]> = LazyLock::new(|| {
     [
@@ -88,8 +90,8 @@ static DESCRIPTOR: LazyLock<Arc<OpDescriptor>> = LazyLock::new(|| {
                 "curve",
                 "param.view_transform.curve",
                 vec![
-                    LocalizedKey("param.view_transform.curve.camera_raw"),
                     LocalizedKey("param.view_transform.curve.sigmoid"),
+                    LocalizedKey("param.view_transform.curve.camera_raw"),
                 ],
             ),
         ],
@@ -108,7 +110,7 @@ impl Default for ViewTransform {
         Self {
             contrast: DEFAULT_CONTRAST,
             white: DEFAULT_WHITE,
-            curve: CAMERA_RAW,
+            curve: SIGMOID,
         }
     }
 }
@@ -148,7 +150,7 @@ impl Operation for ViewTransform {
     }
 
     fn is_active(&self) -> bool {
-        self.contrast != DEFAULT_CONTRAST || self.white != DEFAULT_WHITE || self.curve != CAMERA_RAW
+        self.contrast != DEFAULT_CONTRAST || self.white != DEFAULT_WHITE || self.curve != SIGMOID
     }
 
     fn stage(&self) -> Stage {
@@ -159,9 +161,9 @@ impl Operation for ViewTransform {
         "\
 // Skipped for an already-rendered source: a JPEG is a display rendering
 // already, and rendering it again would compress it twice.
-// Camera Raw's tone by default (D21), D19's sigmoid by choice.
+// D19's sigmoid by default, Camera Raw's tone by choice (D21).
 if (!non_linear) {
-    if (mode < 0.5) {
+    if (mode > 0.5) {
         c = camera_raw_tone(c, cr_scale, cr_power, cr_grey);
     } else {
         c = view_sigmoid(c, slope, inv_k, peak);