darktable preset inspired by IlfordHP5 Plus

What the style changes

The style converts the photo to black and white the way HP5 Plus sees color, then adds its medium contrast and its grain. What it is based on is detailed on the Ilford HP5 Plus film page. All figures below come from renders made with darktable-cli 5.6.0 at 1000 px, measured in CIELab, and compared with the Tri-X style.

• Gray from the film’s spectral sensitivity. A color calibration instance named “N&B” uses the weights of darktable’s own “monochrome | ILFORD HP5+” preset, built from Harman’s spectrogram. Our independent reading of the same graph gives weights within 0.008 of the preset. Harman measured the spectrogram under tungsten light; once that is compensated for, blue weighs more than on Tri-X (Z weight 0.49 against 0.39).
  • Compared with a plain luminance conversion, and before any curve or grain, the sky gets lighter (L 55.2 → 59.3), while skin (79.3 → 73.6) and a pink T-shirt (47.8 → 45.2) get darker. The effect is stronger than with Tri-X (58.4, 75.5 and 46.6).
• Medium contrast. The tone curve has a gentler midtone slope than the Tri-X style, and its toe stays close to the identity. Contrast rises only slightly on one test photo (Lsd 14.3 → 15.8, Tri-X 18.0) and not at all on another (30.7 → 30.6, Tri-X 33.5).
• Open shadows. 3.6 % of one test photo is nearly black (5/255 or less), against 1.7 % for the base rendering and 16 % with Tri-X. A wall in shade stays readable at L 3.3 (base 5.1, Tri-X 1.6).
• Held highlights. Burnt-out pixels (250/255 or more) stay at 0.3 % of a bright test photo, as in the base rendering, against 9.9 % with Tri-X.
• Present but soft grain. With no published RMS, the grain is set a little coarser than the Tri-X style (2000) but weaker (26 against 32), and concentrated in the midtones. Measured as high-frequency noise in the sky of a 2560 px render, it falls between Fomapan 100 (4.7) and Tri-X (6.6), at 5.5.
• 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 a disabled color calibration with no name. Applied from darktable’s interface, it replaces your main instance and switches it off, while the “N&B” instance is added. Without this, the chromatic adaptation of your main instance would tint the gray image: in our renders, we measured a blue cast of b* −4 to −8. The disabled instance is set to “as shot in camera” with CAT16, like darktable’s default, so you can switch it back on. darktable’s built-in black-and-white presets also bypass chromatic adaptation, and film does not white-balance either.
• And it replaces your tone curve and grain. Applied from the lighttable or the darkroom, each unnamed module of the style replaces your instance of the same module, if you have one. Your earlier settings stay in the history stack. Only exporting with a style, or darktable-cli (which we used for the measurements), adds the style’s modules as separate instances; there too, the disabled color calibration switches off your main one. The installation guide explains both cases.
• Your pipeline order. The style file carries no module order list, so it does not impose one on your image.

Limits

• An interpretation, not a calibration. No film was scanned or measured to tune the style.
• The spectral curve. Harman’s graph has no unit: its 0.5 to 1.0 scale is read as a log sensitivity, as darktable does. A later, finer trace of the same graph, shown on the film page, differs mostly on the steep red cutoff (0.56 against 0.64 at 640 nm).
• The developer. HP5 Plus changes a lot with the developer and the time. The style aims at normal development at EI 400, not at a push, which gives more contrast and grain.
• The grain is the least certain setting. There is no datasheet figure, and reviews disagree on whether HP5 Plus is grainier than Tri-X. If you see it as grainier, raise the strength toward 32.
• Shadows. The style follows the majority of sources, which find detailed shadows; Casual Photophile describes the opposite.
• Procedural grain. darktable’s grain imitates the texture of film grain, not the real shape of silver grains.

Tips

• For a pushed HP5 Plus (EI 1600 or 3200), steepen the tone curve and raise the grain strength: pushing adds contrast and grain.
• See the spectral conversion alone by switching off the style’s tone curve and grain instances.
• Back to color: switch the main color calibration back on and switch off the “N&B” instance.
• Installation: see Install and apply darktable styles.