Develop longer, from the measurements rather than from a contrast slider

Pushing was not a thing to simulate. It was measured data being thrown
away: Double-X and 2302 each ship five characteristic curves, one per
development time, and this shipped the 6.5-minute column and discarded
four. All five now ship and interpolate.

The axis is real. Double-X runs 4 to 12 minutes, and across it the average
gradient goes 0.472 to 1.034 while Dmax goes 1.19 to 2.56.

The control is in stops, because that is what a photographer means, and one
stop is a factor of about 1.41 in time. That mapping is checked rather than
assumed: against Double-X's own axis it lands within 2% of the 9-minute
column for +1, and near 12 minutes for +2, which are the times the datasheet
gives for exactly that. There is a test.

**Pushing must not recover shadow detail, and this does not.** Across the
whole measured range the speed point moves about a third of a stop while the
gradient doubles; three stops under mid-grey, density goes from 0.008 to
0.035, which is still nothing. Developing longer multiplies what was already
recorded and cannot record what never hit the film. A push built as added
exposure or global contrast brightens those shadows instead and looks
convincing until someone who shoots film sees it, so that property has a
test of its own.

Interpolated in *log* time, because development is multiplicative: 4 to 5
minutes is the same amount of push as 9 to 12, and interpolating linearly
would bunch the control at one end. Clamped at both ends, because past the
published range there is no data and extrapolating a contrast curve invents
an emulsion nobody tested. A stock measured at one process ignores the
control entirely rather than inventing a curve for it -- Portra 800's pushes
are separate *measured* profiles, which is the honest way to offer those.

Costs nothing per pixel and changes no shader. The curves are a per-stock
table, so the interpolation happens on the CPU at bake time, where choosing a
stock and moving its sliders already rebakes. The Vulkan shader is untouched.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

tools/film-profiles/convert.py

@@ -74,13 +74,11 @@ STOCKS = [
 # moving everything to `dev`, so the colour stocks stay on the released branch.
 DEV_BRANCH = {"kodak_trix", "kodak_doublex", "kodak_2302"}
 
-# Which development time to ship, for a stock whose curves are measured at
-# several. Index into the profile's own `development_time` array.
+# Which development time is "normal" for a stock measured at several.
 #
 # The middle of the published range, which is the manufacturer's standard
-# process: 6.5 minutes for Double-X, 5 for 2302. The others are push and pull,
-# and are the obvious next control -- the data for them ships in the upstream
-# file and is dropped here only because nothing can yet ask for it.
+# process: 6.5 minutes for Double-X, 5 for 2302. The rest of the range is push
+# and pull, and all of it now ships -- see `development_times` in the profile.
 DEVELOPMENT_INDEX = 2
 
 # ---------------------------------------------------------------------------
@@ -218,9 +216,17 @@ def convert(stock):
 
     # A monochrome stock may be measured at several development times. Take one
     # column before anything else, so everything below sees the usual shape.
+    development_times = data.get("development_time")
+    development_set = None
     if monochrome:
         curves = data["density_curves"]
         if curves and isinstance(curves[0], list) and len(curves[0]) > 1:
+            # Keep the whole axis: one 256-sample curve per development time.
+            # Pushing is measured data on these stocks, not an effect, and
+            # throwing away four of five columns threw the measurement away.
+            development_set = [
+                [[r[t]] * 3 for r in curves] for t in range(len(curves[0]))
+            ]
             data["density_curves"] = pick_development(curves, DEVELOPMENT_INDEX)
         base = data.get("base_density")
         if base and isinstance(base[0], list):
@@ -286,6 +292,25 @@ def convert(stock):
     ]
     for triple in columns(data["density_curves"]):
         out.append(f"  - {row(triple, 5)}")
+
+    if development_set and development_times:
+        normal = development_times[min(DEVELOPMENT_INDEX, len(development_times) - 1)]
+        out += [
+            "",
+            "# The development axis, in minutes. Pushing is measured on this",
+            "# stock rather than modelled: developing longer raises the contrast",
+            "# and the maximum density, and *barely moves the speed point* --",
+            "# which is why pushing buys contrast and not shadow detail.",
+            "#",
+            "# `development_normal` is the manufacturer's standard process and is",
+            "# the curve `density_curves` above carries.",
+            f"development_normal: {num(normal)}",
+            f"development_times: {row(development_times)}",
+            "development_curves:",
+        ]
+        for t, curves_at_t in zip(development_times, development_set):
+            out.append(f"  # {t:g} minutes")
+            out.append("  - " + "[" + ", ".join(row(c, 5) for c in curves_at_t) + "]")
     return "\n".join(out) + "\n"