The two engines

Open a photo in Develop (d) and the Dev tab starts with a row of three buttons: None, Spektra and Rapid. That row is the engine. Everything below it, the sliders and menus, is whatever the chosen engine declares.

Two engines because film and digital are two different crafts. A film emulsion answers to a chain of physical things: the stock, the paper, the enlarger’s filters. A digital file answers to a list of adjustments. Forcing both into one panel gives a tool that lies to both, so Reveal does not.

None

A photo with no saved engine is shown as the camera made it: the embedded JPEG, or a plain preview of the RAW. Nothing is developed. Choosing an engine, or touching a control, is what starts a development.

Settings can pick which engine a photo starts with. The default is None.

Film: Spektra

Spektra does not apply a “film look”. It simulates the chain: your exposure lands on a film stock, the negative is developed, and it is printed through an enlarger onto paper. The model is spektrafilm-rs; Reveal runs it on the GPU.

Because it is a model, it does what it does rather than what you ask. You learn it, as you would learn a stock.

Emulsions

• Film is the negative or slide you shot. Reveal ships 25 stocks: Kodak Gold 200, Ektar 100, Portra 160, 400 and 800 (and 800 pushed one and two stops), Ultramax 400, Fujifilm C200, Pro 400H and X-Tra 400, Double-X; the slides and reversal stocks Provia 100F, Velvia 100, Ektachrome 100, Kodachrome 64 and Tri-X; and the cinema stocks Vision3 50D, 200T, 250D and 500T, Verita 200D, and the print films 2302, 2383 and 2393.
• Paper is what the negative is printed on: Kodak Portra, Supra, Ultra and Endura Premier, Ektacolor Edge, and Fujifilm Crystal Archive Type II.
• Format (mm) is the size of the frame the film was exposed in, from 4 to 120. 35 mm is the usual starting point; the range runs up to large format.

A slide or reversal stock has no negative to print, so it skips the paper and is scanned directly.

Before the film

• Local contrast (off by default, 0 to 100 %) arranges the picture’s texture for the film, before the film sees it. The broad tones are pressed together a little around the photo’s middle, so the film’s curve has more room to separate the textures, and the textures of three scales come back with a gain that follows how clean the signal is at that brightness: full in the midtones, less in the deep shadows where detail is mostly noise. The darkest tones stay where they were, colour is the photo’s own, and the middle of the picture keeps its exposure.

It is not a recovery of anything the camera did not record. With Auto exposure on, Spektra re-exposes after it, so a very contrasty photo comes out a little lighter in its shadows and midtones, which Exposure can bring back. Start around 50 %.

Exposure and printing

• Auto exposure and Exposure set how much light reaches the film. Print is the enlarger’s exposure, the second decision of the darkroom.
• Y Filter and M Filter are the enlarger’s yellow and magenta filtration, from −10 to 10. They are how a printer corrected colour.
• Pre-flash gives the paper a small fogging exposure before the main one. It lifts the shadows and compresses contrast, an old trick for printing a hard negative. It is off until you raise its exposure; its own Y and M filters only matter once it is on.

Development

• Duration (min) is how long the film is developed. At 0 the stock’s own standard is used; any other value snaps to the nearest time the stock has data for.
• Contrast shifts the density curve.
• DIR couplers model the interaction between the dye layers during development, real film chemistry, on by default. Intensity, Diffusion, Tail and Tail Weight tune it while it is on.

Rendering

Halation (the glow around bright edges, with its size), Diffusion, Grain, Sharpen, Glare (with its amount, roughness and blur).

Spektra has no Highlights, Shadows, Whites or Blacks sliders. They would be digital adjustments laid over a physical model, and they conflict with it. If you want them, use Rapid.

Digital: Rapid

Rapid is the engine for a file that is not pretending to be film. It is parametric: each control does one thing, and you can read the result off the control.

• Exposure & Contrast: Exposure, Brightness, Contrast, Saturation, Vibrance.
• White Balance: Temperature and Tint.
• Tones: Highlights, Whites, Midtones, Shadows, Blacks. Blacks and Shadows are measured from this photo’s darkest tones, Highlights and Whites from its brightest, not from the edge of the sensor’s scale: a low-key photo that never reaches white still has highlights, and Highlights acts on them. Whites opens or closes the top of the photo and leaves its shadows alone. The photo’s black and white are measured once on the whole frame (the 0.1th and 99.9th percentile of its luminance), so one hot pixel decides nothing, and the zones read the same measurement as the global layer.
• Tone Curve: a curve editor for Luma and for Red, Green and Blue separately.
• Color Mixer: Hue, Saturation and Luminance for eight colour bands. Pick a band, then adjust it.
• Clarity & Haze: Clarity, Structure, Dehaze. Clarity and Structure add local contrast to the mid-tones and leave a flat area exactly as it was.
• Local Tone: exposure, contrast and saturation for the shadows, midtones and highlights separately. Mask reach sets the tone, in percent, where the Shadows mask has fallen to nothing (the Highlights mask starts at the mirror tone). At 50 the three zones split the tones without overlapping; the default. A longer reach, 75 for instance, spreads each zone over a longer gradient with a gently eased end, which keeps a strong lift (up to about +3 EV) from folding the picture back on itself and drawing contour lines in a smooth sky, at the cost of touching the far tones a little.
• Digital Effects: Vignette (with midpoint, roundness and feather) and Highlight Desaturation.
• Film Grain: Intensity and Roughness. A grain, not a stock.

How it maps tones

Rapid renders to the screen through an AgX tone map, which compresses a wide-range scene into a picture without clipping the highlights flat. Look AgX chooses how: Base Contrast, Punchy, Golden, Soft, or Filmic B&W.

LUTs and the Encoding menu

Rapid takes LUTs before the grade (Pre-Lut) and after it (Post-Lut), each a stack of layers with an opacity. Spektra has none: its film and paper already are the grade.

A .cube file is made for one encoding of the picture: a print emulation such as a 2383 wants Cineon, a LogC3 look wants LogC3, a finishing look wants the picture as it is displayed. The Encoding menu, above the Pre-Lut, names the one format the whole chain works in:

• Display (sRGB): the default. The render leaves through the AgX tone map, as a finished picture.
• LogC3 (ARRI), Cineon: the tone map is off and the signal leaves in that log format. On its own it is supposed to look flat and dark; it exists to feed the LUTs after it.
• Linear: scene-linear, no curve.

The Pre-Lut receives the photo encoded in that format, and the Post-Lut receives the render’s output in that format. Reveal converts nothing in between, and it does not undo the format after the Pre-Lut: what the stack returns is taken as it is. When a stack works in a log format, end it with the conversion LUT that brings the signal back (for example a LogC to Cineon LUT between a LogC3 look and a Cineon print LUT, in the Post-Lut). Only the colour primaries are looked after, so a Linear stack that does nothing leaves the photo untouched.

Photos edited before the menu existed keep their look: the old LogC switch reads as LogC3.

Speed

Rapid’s per-pixel work runs on the GPU. If the GPU cannot be used for any reason, it runs on the CPU instead: a photo never fails to develop because of the graphics card, it only develops slower.

Choosing an engine

• Shot on film, or want the look of a print: Spektra. Choose the stock you want to answer to, then expose and print.
• A digital file you want to grade: Rapid. It is the one with the sliders you already know.
• A cinema print look on a digital file: Rapid with Encoding on LogC3 or Cineon and a 2383 print LUT in the Post-Lut.
• Not sure: leave it on None, look at the photo as shot, and pick when you know what it needs.

Both engines write to the same per-photo recipe, and neither ever touches the original. See Develop controls for the parts of the panel that do not depend on the engine: crop, presets and LUT files.