Leave the profile's look table off by default

Every raw rendered through a camera profile — the library's DNGs with an
embedded profile, and CR2s given one — now renders differently: more
colourful in near-neutral tones. The profile's look table is no longer
applied unless its slider is raised; PROFILE_LOOK names the strength the
profile states.

Against the photographer's earlier exports with no look applied, the default
rendering scores the same with the look table at 100, 50 or 0 (held-out MSE
140, 140, 143), and is 9 % more colourful at 0: the table lowers the
saturation of near-neutral tones, which is exactly where the default
rendering was short of those exports. The user chose more colour.

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

@@ -47,9 +47,18 @@ pub const LOOK: ParamId = ParamId("look");
 
 /// The look's strength at which the LookTable is applied as the profile
 /// states it, in percent.
-pub const DEFAULT_LOOK: f32 = 100.0;
+pub const PROFILE_LOOK: f32 = 100.0;
+/// The look's default strength: off.
+///
+/// Measured, not chosen. Against the photographer's earlier exports with no
+/// look applied, the default rendering scores the same with the table at 100,
+/// 50 or 0 (held-out MSE 140, 140, 143), and is 9 % more colourful without
+/// it: the table desaturates near-neutral tones, which is exactly where the
+/// default rendering was short of those exports. The table stays one slider
+/// away for anyone who wants the profile's look.
+pub const DEFAULT_LOOK: f32 = 0.0;
 /// Twice the profile's look.
-pub const MAX_LOOK: f32 = 200.0;
+pub const MAX_LOOK: f32 = 2.0 * PROFILE_LOOK;
 
 /// Entries of the buffer's header, before the entries themselves: one
 /// `vec4` describing each table — `(hue divisions, saturation divisions,