darktable preset inspired by IlfordDelta 400 Professional

What the style changes

The style converts the photo to black and white the way Delta 400 sees color, then adds its contrast and a fine grain. What it is based on is detailed on the Ilford Delta 400 film page. It aims at the film exposed at 400 and developed normally (Ḡ 0.62). 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” uses the weights of darktable’s own preset, “monochrome | ILFORD DELTA 400 - 3200”. Our reading of the Delta 400 spectrogram gives 0.2552 / 0.2364 / 0.5084, against 0.2438 / 0.2361 / 0.5201 for the preset: a maximum difference of 0.012. The two Ilford films share one curve.
  • Compared with a plain luminance conversion, and before any curve or grain, the sky gets lighter (L 55.2 → 59.6), while skin (79.3 → 73.0) and a pink T-shirt (47.8 → 44.8) get darker. These are the measurements of the Delta 3200 style, which uses the same weights.
• Contrast a little above HP5 Plus. Contrast rises from 14.3 to 17.3 on one test photo and from 30.7 to 32.1 on another. The HP5 Plus style gives 15.8 and 30.6, the Tri-X style 18.0 and 33.5. That fits the review saying Delta 400 has “slightly more contrast at box speed than HP5”.
• Deep blacks that keep detail. The darkest 5 % of the frame drop from L 2.6 to 1.1, and 9.8 % of the pixels end up near black on the second photo (HP5 Plus style 3.6 %, Tri-X style 16.0 %). The soft shoulder leaves the highlights alone: no pixel is clipped on the portrait (Tri-X style 9.9 %).
• Fine grain. Grain is finer than in the HP5 Plus (2200 / 26) and Tri-X (2000 / 32) styles. Measured on the 2560 px examples, its noise level is 4.0, against 5.6 and 6.7. It stays visible.
• 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 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.
• No push. At EI 1600 or 3200, Delta 400 gains contrast and grain, according to Casual Photophile and Ilford’s datasheet. The style does not render that. For a fast-film look, see the Delta 3200 style, built for an exposure at EI 3200.
• Underexposure is not rendered. Analog.cafe describes shadows that fade quickly below correct exposure. The style keeps the RAW file’s shadow detail in the blacks.
• The spectral curve. It was read by eye from the datasheet graph, and its axis is treated as a log sensitivity, as darktable does. Our weights and the preset’s differ by at most 0.012.
• The tone curve. It is tuned by comparison with neighboring styles and reviews, not fitted numerically to the datasheet’s density curve, which depends on the developer.
• The grain. It was tuned without a datasheet figure and aims at 35 mm: in 120, real grain is less obtrusive. darktable’s grain is procedural noise: it imitates the texture, not the shape of tabular crystals. Its visibility depends on the export size.

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.
• Expose correctly. The style assumes a correct exposure, the case where reviews agree the film holds shadow detail.
• 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.