darktable preset inspired by FomaRetropan 320 Soft

What the style changes

The style converts the photo to black and white the way Retropan 320 Soft sees color, then adds its soft contrast, lifted blacks, a light glow and grain. What it is based on is detailed on the Foma Retropan 320 Soft 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 Foma’s spectrogram, corrected for its 2850 K tungsten light and integrated against the CIE 1931 color matching functions. On the finished style, the sky gets lighter (L 55.3 → 57.5) and skin darker (78.2 → 75.5), as with other panchromatic films.
• Low contrast and lifted blacks. The tone curve follows the high base density and low slope of Foma’s 5-minute curve, read by eye. Contrast (Lsd) falls from 14.3 to 12.4 on one test photo and from 30.7 to 28.4 on another. The darkest 5 % of the frame rise from L 2.6 to 7.2 (photo 1014) and from 29.4 to 33.6 (photo 0775). The white reaches 1, and the brightest 5 % go from L 87.9 to 90.9.
• A light glow. The bloom module adds a discreet halo around highlights. It comes from a single review (EMULSIVE), so it is an interpretation. We checked it by eye on the JPEGs (glow visible without burnt whites) but did not measure it.
• Medium, soft grain. Foma publishes no RMS value, so the grain (coarseness 1900, strength 28) is tuned from reviews, between our Fomapan 200 Creative (1600) and 400 Action (2200) 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. 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, bloom 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, bloom and grain carry no instance name, so they replace any settings you had already made in those 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

• The spectrogram has no vertical scale. We assumed about one log unit between the axis and the maximum, as for the other Fomapan films. With 0.8 to 1.3 log units, the X weight moves from 0.283 to 0.316.
• Read from a raster image, not from vectors: an uncertainty of a few nanometers, larger at the red cut-off. (The published curve data on the film page was later traced from the PDF’s vectors.)
• The tone curve is read by eye. The datasheet gives no numerical values and the style’s curve simplifies it. Real contrast depends on the development time (3, 5 or 8 minutes) and the developer.
• The glow rests on one source (EMULSIVE), and the bloom module only approximates a halo that depends on the support: 35 mm has no anti-halation backing listed, 120 and sheet film do.
• The grain has no official measurement, and reviews disagree with each other and depend on the format. The setting is an average for 35 mm.
• The erratic behavior in very contrasty scenes that EMULSIVE reports is not simulated.
• An interpretation, not a calibration. No film was scanned or measured to tune the style.

Tips

• Apply it early. If you plan to fine-tune the tone curve, bloom 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, bloom 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.