lightcraft/docs/process-versions.md

Process versions

Changes: revision history

Every photo's develop settings record the rendering process they are interpreted by (DevelopSettings::process, a ProcessVersion in crates/develop/src/settings.rs). Lightroom calls this the process version. It lets the look of LightCraft improve (a new default tone curve, issue #146; stronger Light sliders, issue #196) without changing a single photo someone has already edited.

Process	What it changes
V1	LightCraft's rendering from before process versions existed. Frozen.
V2	Highlights and Shadows keep fine detail (issue #632): their base layer (local::tone_base) is the edge-aware filter of a separable median of log luminance (radius 0.15 % of the long edge, at most 24 px, local::BASE_DETAIL) instead of log luminance itself, so twigs, lines and texture take their surroundings' shift and keep their contrast; region edges stay sharp. CPU (local::prepare) and GPU prepare branch on local::tone_base_detail (0 = no median under V1); the base plane is cached per process (local::BaseKey). Renders without Highlights or Shadows (global or local) are the same as V1's. Tone map unchanged.
V3	Pixel-scale sharpening (issue #757): Radius uses the original photo’s pixels, Detail controls halo damping, and downsized sources retain a response-matched sharpening band. V1 and V2 keep texture-band sharpening exactly. The sharpen plane is keyed by radius and process and invalidated after noise-reduction changes. The Highlights/Shadows base and tone map are unchanged from V2.
V4	V3 plus calibrated global Contrast (per channel) and Blacks (per-channel/luminance mix) on raws with a camera tone curve. Whites behaves exactly as V2, both signs; its calibration is a planned follow-up. Other sources and local adjustments retain V2 operators. See calibrated Light operators.
V5	V4 plus: a raw's tone curve rolls off into white in stops instead of reaching it within about a stop of the sensor's white, so raising Exposure keeps the highlights the sensor recorded (issue #1632). Camera curve (the look fitted to the embedded JPEG, or a DNG's ProfileToneCurve; CameraTone): past its last knot CameraTone::apply_rolloff closes the gap to white by gap / (1 + c·(2^t − 1)) at t stops past the knot, with c matching the curve's slope there and the gap halving every stop in the end (tone::ROLLOFF_STOPS); ToneMap::camera_rolloff_hdr builds the table from it. Under V1 to V4 the curve past its last knot (fitted only to camera JPEG tones below 0.85, so 1 to 3 stops below the sensor's white on most photos) closes on white exponentially in linear light: the sensor's white renders at 8-bit 246 to 254 at Exposure 0 and 254 to 255 from Exposure +1. On the 11 CC0 corpus files with a fitted look (8 Sony, 2 Nikon, 1 Fujifilm) it now renders at 239 to 250 at Exposure 0 and 247 to 253 at +1. A DNG curve that reaches white at the sensor's white renders as before. Generic curve (raws without a camera curve, ToneMap::rolloff_hdr): from half a stop below its white point (tone::GENERIC_KNEE_STOPS) the same shoulder takes over, with the extended Reinhard curve's value and slope at the join, where V1 to V4 clip at the white point (scene 1.18 at default settings, ¼ stop above the sensor's white). The sensor's white renders at about 235, 248 and 252 at Exposure 0, +1 and +2 (V1 to V4: 239, 255, 255; the CC0 Canon R8 file and 6 CC0 DNGs without a camera curve). Content past the old clip point, such as a clipped sky, now renders up to 15 codes below white at Exposure 0 and reaches 255 about 5 stops past the sensor's white. Below the last knot or the join, JPEGs and other display-referred sources, and the camera fit itself are unchanged; CPU and GPU share the tone LUT.
V6	V5 plus: colour noise reduction filters the linear colour differences R−Y and B−Y with the joint method (issue #815, docs/nr-color-joint.md): edge-aware weights from a denoised guide shared by both differences, anisotropic diffusion over scales, a brake for isolated colour specks; Y is kept exactly. V1 to V5 keep the blurred chromaticity (local::denoise). CPU (local::denoise) and GPU (render::denoise) branch on local::joint_colour_nr. Renders with Color 0 are the same as V2's.
V7 (the latest)	V6 plus: film grain from crystal layers (grain.md, crates/pipeline/src/crystal.rs), after Aurélien Pierre's model: resolution independent (a preview is the export's grain box-downscaled), fading out at black and white, calibrated to Lightroom Classic's strength and width at mid grey. V1 to V6 keep their two-octave value noise exactly (finish::ValueGrain; on the GPU F_GRAIN_MODEL 0); finish::GrainModel::new picks the model per process. Renders without grain don't depend on this.

The rule

A change that alters how existing settings render ships as a new process. V1 is frozen.

• A deliberate change of look (tone model, slider response, default curve, how a stage interprets a value) goes into a new process. Photos stay on the process they have until someone runs Update to Current Process (or Reset).
• Bug fixes that make output correct where it was broken (a crash, NaN or black output, a decoder error, CPU and GPU disagreeing) are not looks and can land in place, as before.
• Changes to how a file is decoded or which camera colour it gets change the source, not how settings are interpreted; the process doesn't reach that stage today.

Neutral display tone map (JPEG, PNG and other display-referred sources with Contrast, Whites and Blacks at 0) is the identity up to white: the SDR shoulder no longer pulls 1.0 down to 0.9875 (8-bit 255 to 254, issue #1945). It landed in place as a bug fix, since the tone map promised identity at neutral settings; edited curves keep the shoulder and their V1 look.

AI mask edges (Object and Describe selections stored as a model's grid) follow the photo's edges when they are enlarged to the output (issue #3272): the plain enlargement spilled 1–2 px onto the background, which a raised Exposure turned into a bright outline around the subject in previews and exports. Existing AI masks become 1–2 px tighter at a subject's edges, on every process; their inside, their outside and edges without contrast in the photo are unchanged. It landed in place as a bug fix: the outline is output that isn't in the photo nor in the edit, not a look anyone chose.

A mask whose first component is Intersect starts from that component, on the CPU and the GPU (issue #1889). It used to start from nothing, so alone it selected nothing, with a later Add it gave only what was added, and with the mask's Invert it gave the whole photo. Such masks now include the first component, on every process. It landed in place as a bug fix: intersecting with nothing is not a look anyone chose.

Adding a process

1. Add a variant to Process (V2), append it to Process::ALL (oldest first), give it its number in Process::version and make it Process::LATEST.
2. The compiler then points at every match on Process. The base tone map is chosen in one place, lightcraft_pipeline::finish::base_tone (both the CPU and the GPU renderer take it from there): give V2 its own arm and leave V1's alone. A process that changes another stage branches there the same way, on s.process.process(); if that stage is cached (Plan::lin_key, the planes in local.rs), add the process to its key.
3. Keep settings_saved_before_process_versions_load_as_v1 (crates/develop/src/tests_process.rs) passing: settings saved without the field must stay V1, not become the new latest. That is the field's #[serde(default = "ProcessVersion::legacy")]; the struct-level Default gives new settings the latest instead.
4. Render a few procedural scenes on both processes and compare, and update docs/parity-checklist.md.

What gets which process

	Process
A newly imported, merged or Lightroom-imported photo	the latest
Settings saved without the field (catalogs and their snapshots, versions and history, lc:settings in XMP sidecars, browser libraries: everything from before process versions), or with a damaged value	V1
Reset (develop.reset)	the latest
Reset of a section or a slider	unchanged
Update to Current Process (develop.updateProcess)	the latest, for photos on an older one; one undo step. The menu item follows the selection; a call with ids / id acts on those photos whatever is selected
Virtual copy, duplicate	the source's
Copy / paste / sync / Auto Sync / presets	unchanged (see below)
crs: edits (XMP from other raw developers, Lightroom catalogs, imported presets)	unchanged; a new photo has the latest
Restoring a version or history step	the one it had

Copy, paste, sync and presets never carry the process: it is in no settings group, so the photos they change keep their own and interpret the pasted values with it. (Lightroom offers the process version as a separate checkbox when syncing; LightCraft's groups are coarser and keep it out.) Partial settings JSON that names process itself (develop.merge, a hand-written preset) sets it.

Lightroom edits are re-interpreted by LightCraft's mapper (crates/engine/src/crs.rs), which is written against the current rendering. crs:ProcessVersion numbers Adobe's renderer, not ours, and is ignored; a photo imported with Lightroom edits is on LightCraft's latest process, and an existing LightCraft photo that receives them keeps its own.

A number above this build's latest (a library or sidecar written by a newer LightCraft) loads, is kept when saved, and renders with the newest process this build has. Update to Current Process never moves a photo to an older process; Reset does move it to this build's latest.

A damaged value (anything but a whole number from 0 to 2^32 - 1; 2.0 counts as 2) reads as V1, like a missing field, and costs nothing else: the rest of the settings load from the catalog, a snapshot, the op log or an lc:settings sidecar as usual. The damaged value isn't kept: the photo is saved as V1.

Storage

The process is saved as "process": <number> in the settings JSON, except V1, which is left out. Settings made before process versions existed are therefore saved exactly as before, and their preview-cache keys (DevelopSettings::hash64) don't change. develop.get (MCP get_develop) always states the process.

From process V3 on, persistent thumbnail, view-render and variant keys also include the resolved rendering process. A future number can keep the same settings hash across builds while resolving to different operators, so those keys must differ. V1 and V2 omit this extra field and retain their existing cached renders. No cache-version bump is needed.

Revision history

Date	Change	Summary
2026-11-07	minor	V7: film grain from crystal layers (grain.md); V1 to V6 keep their value noise
2026-11-05	minor	V5: a raw's tone curve rolls off into white in stops, so raising Exposure keeps recorded highlights (#1632)
2026-10-12	minor	Calibrated Contrast and Blacks, V2 Whites, resolved-process cache keys and number coordination