darktable preset inspired by KodakT-Max 400

What the style changes

The style converts the photo to black and white the way T-Max 400 sees color, then adds its tonality and its fine grain. What it is based on is detailed on the Kodak T-Max 400 film page. The style applies equally to Ektapan 400, which the press describes as the same film under a new name. 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 T-Max 400. The curve is integrated against the CIE 1931 color matching functions, the way darktable builds its own film presets. Compared with Tri-X (0.3149 / 0.2994 / 0.3857), T-Max weighs green more and blue less.
  • Compared with a plain luminance conversion, and before any curve or grain, the sky gets lighter (L 55.2 → 57.9) and a blue box much lighter (48.4 → 52.9), while skin (79.3 → 76.3) and a pink T-shirt (47.8 → 47.1) get darker. The direction is the same as with Tri-X, but milder: the Tri-X weights give 58.4 for the sky and 75.5 for skin. That matches Kodak’s note that T-Max is slightly less blue-sensitive than its other films.
• A short toe and a long, straight midtone. The tone curve lowers the shadows less than the Tri-X style does and keeps a constant midtone slope (about 1.15, against 1.3 for Tri-X) up to 0.85, so the highlights keep separating. Contrast rises from 14.3 to 16.6 on one test photo and from 30.7 to 32.7 on another, less than with Tri-X (18.0 and 33.5).
• Open shadows, but deep blacks where they belong. A patch of ground in shadow goes from L 7.6 to 4.4, against 2.6 with Tri-X, and the share of nearly black pixels (5/255 or less) on the same photo rises from 1.7 % to 6.5 %, against 16 % with Tri-X. The darkest 5 % of the frame drop from L 2.6 to 1.4.
• Bright, unclipped highlights. Only 13 of the 667,000 pixels of one test photo reach 250/255 or more (Tri-X style: 11), with the brightest 5 % at the level of Tri-X.
• Fine grain. Grain is sized from the RMS granularity of 10. Measured as high-frequency noise on 2560 px renders, it reaches 0.62 times that of the Tri-X style, close to the ratio of the two RMS values (10 / 17 = 0.59).
• 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.
• Sharpness. Kodak’s modulation transfer curve exceeds 100 % (an edge effect of development), but at 1000 or 2560 px a digital sensor is already sharper than any 35 mm film. The style adds no sharpening: the difference from Tri-X lies in the grain.

Limits

• An interpretation, not a calibration. No film was scanned or measured to tune the style.
• The spectral curve. The weights were computed from a reading of the dotted D = 1.0 curve by eye (±0.05 log), assuming a fall to zero at 650 nm after the curve ends at about 640 nm. A later, finer trace of the same graph, shown on the film page, agrees within 0.01 log from 380 to 580 nm; the largest gap is 0.04 log at 600 nm. With the datasheet’s other curve (D = 0.3), the sky would come out 0.6 L* darker and skin 0.9 L* lighter: a small difference.
• Reds. A 2010 test by 125px found T-Max less sensitive to red than Tri-X. Computed from the datasheet, the style gives the opposite, by a small margin (pink T-shirt 0.5 L* lighter than with Tri-X). The style follows the datasheet.
• Skies. A 35mmc reader saw lighter skies than with HP5 Plus. Kodak describes T-Max as slightly less blue-sensitive than its other films, and the weights computed from the datasheets give it less blue than HP5 Plus and Tri-X, hence a slightly darker sky. The style follows the datasheet.
• Contrast. Reviews disagree: more contrasty than other 400s for some, less punchy than Tri-X for others. The style sits in between: more contrast than the base rendering, less than Tri-X, with more open shadows.
• The developer. The tone curve translates the shape of Kodak’s D-76 curve by hand; it is not fitted to densities. Real T-Max changes with the developer and the time.
• The grain. darktable’s grain is procedural noise: it imitates the texture of film grain, not the flat shape of T-Grain crystals.

Tips

• See the spectral conversion alone by switching off the style’s tone curve and grain instances.
• For a punchier T-Max, as some reviewers see it, steepen the midtones of the tone curve slightly.
• Back to color: switch the main color calibration back on and switch off the “N&B” instance.
• Installation: see Install and apply darktable styles.