darktable preset inspired by KodakTri-X 400

What the style changes

The style converts the photo to black and white the way Tri-X sees color, then adds its contrast and grain. What it is based on is detailed on the Kodak Tri-X 400 film page. All figures below come from renders made with darktable-cli 5.6.0 at 1000 px, measured in CIELab.

• Gray from the film’s spectral sensitivity. A color calibration instance named “N&B” mixes the channels with weights computed from Kodak’s published sensitivity curve for Tri-X. The curve is integrated against the CIE 1931 color matching functions: this is how darktable builds its own film presets, such as “monochrome | ILFORD HP5+”. Checked on HP5 Plus, the method reproduces darktable’s preset weights within 0.004.
  • Compared with a plain luminance conversion, and before any curve or grain, the sky gets lighter (L 55.2 → 58.4), while skin (79.3 → 75.5) and a pink T-shirt (47.8 → 46.6) get darker. That matches the datasheet and the reviews.
• Contrast with a long toe and no shoulder. The tone curve lowers the shadows gradually, steepens the midtones and lets the highlights keep separating up to white. Contrast rises from 14.3 to 18.0 on one test photo and from 30.7 to 33.5 on another. The darkest 5 % of the frame drop from L 2.6 to 0.8.
• Visible grain. Grain is sized from the RMS granularity of 17. Its strength (32) is higher than in the T-Max 400 (21) and HP5 Plus (26) styles.
• A truly neutral gray. Chroma falls from 8.6 to 0.0: no color cast is left.

What it leaves alone

• Your base development. The style contains no exposure, no sigmoid or filmic and no LUT. Those settings stay as you made them.

• But it switches off your main color calibration. The style contains two color calibration instances:

  • a disabled one with no instance name, which replaces your main color calibration and switches it off. It is set to “as shot in camera” with CAT16, like darktable’s default, so you can switch it back on;
  • the “N&B” instance, which is added and does the black-and-white conversion.

  Why: when an active color calibration runs after the black-and-white conversion, its chromatic adaptation tints the gray. We measured a blue cast of b* −4 to −8 in our renders before adding the disabled instance. darktable’s built-in black-and-white presets also bypass chromatic adaptation, and film does not white-balance either.

• It also replaces your tone curve and grain. When you apply a style from the lighttable or the darkroom, each of its modules replaces the instance of the same module with the same name, if the photo has one, and is added otherwise. The style’s tone curve and grain carry no instance name, so they replace any settings you had already made in those two modules. Your earlier settings remain in the history.

• Your pipeline order. The style file carries no module order list, so it does not impose one on your image.

Exporting with a style, or rendering with darktable-cli, works differently: every module of the style is added as a separate instance, and the disabled color calibration still switches off the existing one. Our measurements were made that way, on darktable’s default rendering. The details are in Install and apply darktable styles.

Limits

• An interpretation, not a calibration. No film was scanned or measured to tune the style.
• The spectral curve. Kodak measured it on the older Tri-X Pan 5063 emulsion. The style’s weights were computed from a reading of the graph by eye (±0.05 log). A later, finer trace of the same graph, shown on the film page, agrees within 0.011 log from 350 to 620 nm; the differences are in the fall-off beyond 640 nm.
• The developer. Real Tri-X changes with the developer (D-76, HC-110, Rodinal…). The style aims at a classic D-76 rendering.
• The grain. darktable’s grain is procedural noise: it imitates the texture of film grain, not the shape of real silver grains.

Tips

• Apply it early. If you plan to fine-tune the tone curve or grain yourself, apply the style first: it would replace those settings if you made them before.
• See the spectral conversion alone by switching off the tone curve and grain modules the style set.
• Back to color: switch the main color calibration back on and switch off the “N&B” instance.
• Installation: see Install and apply darktable styles.