darktable preset inspired by KodakPortra 400 VC

What the style changes

The style sets five darktable modules. It aims at the Vivid Color version of Portra 400: stronger color and slightly firmer contrast than the Portra 400 style, with warm skin, blue-green shadows and fine grain, as Kodak’s datasheet and the reviews describe on the Kodak Portra 400 VC film page. All figures below come from renders made with darktable-cli 5.6.0 at 1000 px, measured in CIELab.

• More vivid color. A color equalizer instance pushes red, green, cyan and blue by 6 to 10 % and leaves orange, the skin channel, almost untouched. color balance rgb adds global saturation and vibrance, and the highlights keep full saturation instead of turning pastel. Sky chroma goes from 27.5 to 30.0, sea chroma from 22.2 to 24.8 and the pink T-shirt from 33.7 to 42.6, where the Portra 400 style lowers the first two.
• A slightly firmer tone curve. Contrast (Lsd) rises from 14.3 to 16.1 on photo 0775 and from 30.7 to 32.5 on photo 1014. The darkest 5 % of the frame stay low (L 3.0 against 2.6 in the base rendering), where the Portra 400 style lifts them to 4.2. The curve acts on each channel without color preservation, so saturation follows contrast as it does on film. Its nodes are in perceptual lightness: 0.5 is about middle gray.
• Blues and greens. rgb primaries turns greens slightly toward yellow, keeps blue purity at 1.02 and moves blue a little toward cyan. The sky hue stays at 272.9° (273.6° in the base rendering): blue, not violet.
• Warm skin, blue-green shadows. A color balance rgb instance named “film” adds a faint warm tint to the midtones and highlights and a blue-green tint to the shadows. Skin hue moves from 44.2° to 48.4°.
• Fine grain, sized from Kodak’s Print Grain Index of 42 for a 4×6 print from 35 mm, against 37 for the current Portra 400.

For comparison, the t3mujinpack Portra 400 style rendered on the same files reaches similar sky and sea chroma (29.4 and 23.7) and a slightly higher contrast (Lsd 16.4 on photo 0775) but keeps the base skin hue (44.2°) and lightens the image more (L 58.6 against 55.4).

What it leaves alone

• Your base development. The style contains no exposure, no sigmoid or filmic, no white balance and no LUT. Those settings stay as you made them.
• Your color balance rgb. The style’s color balance rgb is a separate instance named “film”: it is added next to yours, which stays untouched.
• But not your tone curve, rgb primaries, color equalizer or 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, rgb primaries, color equalizer and grain carry no instance name, so they replace any settings you had already made in those four 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. 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. The style is built from Kodak’s datasheet and published reviews. No fresh roll of 400VC was scanned to tune it.
• The VC/NC gap is not quantified. Kodak’s datasheet gives no figure for the difference in saturation. The saturation level (+9 % to +26 % over the base rendering on our measured zones) is a choice based on the words “vivid” and “well balanced”. Camera-wiki mentions a gap of less than 5 % between the last NC and VC versions, without a source, so the style may be more vivid than the original.
• Deep blues and greens come from a user review and unmeasured descriptions. A review of an expired roll describes “subdued” color instead, which contradicts them.
• Skin. Skin chroma rises by about 43 % (16.4 to 23.4) and its hue moves 4° toward orange. This is the most debatable point: the datasheet speaks of natural skin.
• Grain follows the datasheet’s PGI of 42, not a measurement of how it renders.
• No overexposure or aging effect. The pastel look of overexposed film and the faded look of expired rolls are not reproduced.

Tips

• For a pastel look, overexpose slightly with the exposure module.
• If the color is too strong, lower the “film” color balance rgb saturation or vibrance, or the color equalizer channels.
• 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.