darktable preset inspired by AgfaUltra 100

What the style changes

The style sets five darktable modules. It aims at a very saturated, fine-grained Agfa Ultra 100 with deep blacks, as the datasheet and the reviews on the Agfa Ultra 100 film page describe. All figures below come from renders made with darktable-cli 5.6.0 at 1000 px, measured in CIELab, and one version of the style was rendered: its direction matched the sources, so it was kept as it was. The Ektar 100 style is added for comparison, rendered on the same files.

• Steeper contrast, deep blacks, open highlights. The tone curve is steeper than the one of the Ektar 100 style, and it has no marked shoulder because the datasheet curve shows none. Contrast rises by 2.8 and 3.4 (Lsd 14.3 → 17.1 and 30.7 → 34.1), a little above the Ektar 100 style. The darkest 5 % of the frame drop from L 2.6 to 0.9, close to the “pure black” one review reports without blocking up to the eye. Highlights open up (L95 87.9 → 91.7).
• Very high saturation. The “film” color balance rgb and the color equalizer raise chroma: over the whole of photo 0775 it goes from 21.4 to 31.6, against 28.2 for the Ektar 100 style. Sky chroma rises by 46 %, sea by 59 % and the pink T-shirt by 58 %, where the Ektar 100 style gives +30 %, +42 % and +39 %. This follows the sources’ “the most saturated film” description.
• Pure reds, yellows that stand out. rgb primaries raises the purity of red (1.10), green (1.06) and blue (1.06). The color equalizer adds saturation to red (×1.14), yellow, green (×1.10), blue and cyan (×1.08).
• Skies and sea stay neutral in hue. Blue is turned by −0.03 rad to offset the shift that blue purity adds. Sky hue moves from 273.6° to 272.1° and sea hue from 270.1° to 270.3°; the Ektar 100 style pulls both toward cyan.
• Skin more saturated, not shifted. Skin chroma rises by 63 % (16.4 → 26.7) while its hue barely moves (44.2° → 45.9°). The style does not turn skin red like the Ektar 100 style does (40.2°), because no source says the film does. On the 2560 px render, skin still leans toward orange because of the saturation.
• A faint tint, by prudence. Highlights get a slightly warm tint and shadows an almost imperceptible blue one. No source describes an Ultra 100 cast, so both are kept light.
• Fine grain, sized from the datasheet’s RMS granularity of 3.8.

What it leaves alone

• Your base development. The style contains no exposure, no sigmoid or filmic, no white balance, no color calibration and no LUT, so those settings stay as you set them.
• Your color balance rgb. The style’s instance is named “film”, so it is added next to the color balance rgb you tuned on the photo instead of replacing it.
• Your pipeline order. The style file carries no module order list, so it does not impose one on your image.
• But not your settings in its other modules. When you apply the style from the lighttable or the darkroom, darktable 5.6 replaces an existing instance of the same module: if you had already adjusted rgb primaries, color equalizer, tone curve or grain, the style’s settings take their place. Your earlier settings stay in the history stack. Applying the style at export, or with darktable-cli as in our measurements, adds every module as a separate instance instead. See Install and apply darktable styles for the details.

Limits

• An interpretation, not a calibration. The datasheet gives the curve, the grain and the spectral sensitivity, not the colorimetry. Almost all of the color rests on reviews.
• The datasheet dates from 2003. According to 35mmc, Ultra 50 was warmer and redder than Ultra 100. The style follows Ultra 100 only.
• No source on skin or on a cast. The slight warm tint in the highlights is a cautious choice, not a measurement.
• Sources disagree on grain. One review sees no visible grain, another finds the film fairly grainy. The style follows the datasheet (RMS 3.8): fine grain.
• Reds shift toward red-magenta. The pink T-shirt goes from 359° to 4°, an effect of the red purity. The sources do not say whether the film does it.
• Strong saturation has side effects. It can turn fair skin orange and burn reds that are already saturated.
• The grain shows only at 100 % on a large export; at 1000 px it is invisible.
• Close to the Ektar 100 style in spirit. The differences are the stronger saturation, the deeper blacks and the skin hue that is left alone. They remain modest.

Tips

• On portraits, lower the color equalizer’s saturation for red and orange, or switch that instance off, if skin turns orange.
• Apply it early. If you plan to fine-tune the tone curve, rgb primaries, color equalizer or grain yourself, apply the style first: it would replace those settings if you made them before.
• Everything stays editable. Each module the style sets is an ordinary module instance: you can adjust it or switch it off afterwards, for example the grain strength.
• Installation: see Install and apply darktable styles.