Twenty-five terms that come up in the practice of alternative processes and in Calibration Flow. Each with its definition, its English equivalent and a link to the pages where the concept is used.

The order is alphabetical.

#ACV (.acv)

Adobe Curves. Adobe's proprietary format for storing a tonal response curve, read natively by Photoshop (Curves panel → Load) and indirectly by Lightroom (via a Photoshop preset). A binary format in version 1, with up to 16 curve points stored as 16-bit big-endian integers. Calibration Flow exports

.acv

files that resample the internal 256-value LUT down to the number of points the format allows. The final file fits in under one kilobyte.

#Aquaprint

Vision Picturale's proprietary name for gum bichromate (dichromated gum). A pictorial process with powder pigments incorporated into the pre-sensitized gum arabic VP N°04, activated by the VP N°03 sensitizer. Three commercial variants: Monochrome (carbon black in 1-2 layers), Sanguine (burnt sienna), Four-colour CMYK (4 successive layers). Generic English equivalent: gum printing. See https://en.wikipedia.org/wiki/Gum_printing.

See also: CMYK four-colour.

#Bichromate

A chemical salt historically used to sensitize gum arabic or gelatin to UV (potassium dichromate, ammonium dichromate). Vision Picturale uses a non-toxic alternative sensitizer, VP N°03 Universal Sensitizer, which replaces the bichromate in all of its hardening processes (Aquaprint, Charbon, Bromoil, Gumoil, Résinotype).

#Alignment (registration)

The operation of positioning the scanned test chart inside Calibration Flow's reference frame so the app knows where to measure each patch. It can be done by finger (drag, pinch) or with the Smart Analyzer's automatic detection, which proposes better centering and more tolerance to slight rotations.

See also: Pro Mode, Smart Analyzer.

#Charbon (carbon transfer)

A pigment process invented by Joseph Wilson Swan in 1864. Vision Picturale uses the VP N°05 pigmented gelatins sensitized by VP N°03, with no bichromate. Two variants: Musée Black (monochrome, 1 transfer) and Couleur Profonde (CMY three-colour in 3 successive transfers). dMax > 2.1. Signature look: a slight matte bas-relief in raking light. See https://en.wikipedia.org/wiki/Carbon_print.

See also: CMYK four-colour, Registration marks.

#CMY

Cyan, Magenta, Yellow. Three-channel colour with no separate black, used by Vision Picturale's Charbon Couleur Profonde process (3 successive cyan/magenta/yellow transfers). Distinct from CMYK (4 channels) used in Aquaprint four-colour.

#CMYK

Cyan, Magenta, Yellow, Key. Four-channel colour used by Vision Picturale's Aquaprint Four-colour (4 successive layers). In French: CMJN (N for Noir, the black). Distinct from CMY (3 channels with no black, used in Charbon Couleur Profonde).

See also: CMYK four-colour, Color Venn.

#Color Venn

A visual CMYK preview in the form of a Venn diagram in Calibration Flow. A tool that highlights the contributions of each channel (Cyan, Magenta, Yellow, Black) for each zone of a source image. Indispensable for preparing a Colour Aquaprint. The 3c CMYK Color Venn is available in Free Mode — it's the entry pass into four-colour. The 6c/7c Full Gamut (experimental) is reserved for Pro Mode (€9.90/month subscription) or the Luminograph code.

See also: Venn CMYK, Pro Mode.

#Positive interpositive

The chart polarity used only for calibrating résinotype. The inverse of the standard negative: the image appears in the same orientation as the original photo. Physical rationale: in résinotype, the pigments settle on the black zones of the negative (the unexposed zones), unlike the other hardening processes where the pigments stay in the exposed zones. All the other VP processes use a standard negative chart.

See also: Positive vs negative chart.

#Curve (corrective)

A mathematical function that transforms an input tonal value into a corrected tonal value, so as to compensate for the non-linear response of a chemical process or a printing chain. Represented graphically by a curve in a plane where the x-axis is the target density and the y-axis is the density to print to reach it. Calibration Flow exports its curves to

.acv

#Density (optical)

The historical measurement of the opacity of a patch or zone, originally defined as the negative logarithm of transmittance (density 1.0 = 10% of light transmitted; 2.0 = 1%). In the alternative literature, "density" is shorthand for talking about the darkness of a zone. Calibration Flow does not use optical density in the hardware-densitometer sense: it measures the perceptual luminance L* CIELAB of the pixel, the scale that matches human perception of grey.

See also: Tonal analysis.

#Dithering (bitmap)

A halftoning technique that simulates intermediate grey levels by alternating black and white pixels according to a pattern. Calibration Flow uses the Floyd-Steinberg algorithm. Recommended specifically for charbon and Aquaprint (gum print), where pigment chemistry renders a dither pattern better than a flat grey. For cyanotype, bromoil, gumoil, résinotype and printer calibration: prefer plain flat-tint charts.

See also: A4 300 dpi chart with dithering, Dither.

#Pro Mode

Calibration Flow's paid access tier at €9.90/month (web + iOS, unified account via picturale.app). Unlocks: full-gamut CMYK Color Venn, advanced export options and extended quotas (5 GB cloud, unlimited curves, unlimited presets). The Luminograph code grants 1 year of Pro Mode with the purchase of a Luminograph from Vision Picturale, then switches to Free Mode. There is no separate "advanced functions" tier apart from Pro Mode.

See also: Pro Mode, Luminograph code.

#Gamma

The exponent that describes the non-linearity of a tonal response. A linear response has a gamma of 1.0; sRGB screens have a gamma around 2.2; alternative processes have their own effective gamma that varies with paper, chemistry and UV source. Calibration Flow does not ask you to set the gamma — it absorbs it into the corrective curve.

See also: Understanding the curve.

#HEIC

High Efficiency Image Container. The native iPhone image format since iOS 11 (2017). More compact than a JPEG for equivalent quality. Calibration Flow reads HEIC directly, with no prior conversion on the user's side.

See also: HEIC and RAW.

#Hub (auth)

Picturale Hub auth is the single sign-on of the ecosystem (Vision Picturale, Maison Picturale, NOEME, Calibration Flow). One account opens all four apps. Bouncing between apps happens by transferring a temporary token, transparent to the user — you log in once on any of the ecosystem apps and you're recognized everywhere else.

See also: Picturale Hub auth.

#UV exposure

The phase of exposing the sensitized paper to UV light through the negative. Duration varies with process, chemistry, UV source and negative density. For the Vision Picturale processes with the Luminograph: cyanotype 5-15 min, Aquaprint 2-5 min per layer, charbon 3-6 min, bromoil ~2 min, gumoil 2-5 min, résinotype 3-6 min. With a compatible UV controller (Luminograph), Calibration Flow drives the exposure directly over Bluetooth: the timer fires and cuts the UV LED, with safety guardrails. And calibration makes it reproducible — once the curve is generated, the negative's densities are calibrated.

#Luminograph

Vision Picturale's proprietary UV source (365 nm UV LED, uniform surface, controllable duration). Two models: A4 (€449) and A3+ (€699) — both give the same software bonus. Compatible with all alternative processes that use UV exposure. The purchase of a Luminograph from Vision Picturale includes an activation code that grants 1 year of Calibration Flow Pro Mode (equivalent to €118.80 of value).

See also: Luminograph code.

#Test chart

A grid of grey patches ordered from pure white to the densest black, printed then exposed like a normal negative to measure the tonal response of a process on a given paper. Calibration Flow provides six ready-to-print charts. Creating a custom test chart (non-A4 formats, custom patch count) is not yet available in the app — when that function is integrated, it will be documented on Creating a custom test chart.

See also: Test Chart module, Chart types.

#Patch

A constant grey-level square cell in a test chart. A Calibration Flow test chart contains 25 patches in a 5×5 grid, ordered from white (0%) to black (100%) in steps of about 4% intensity. The app measures a mean L* luminance per patch and uses it as an input point to build the corrective curve.

See also: Tonal analysis.

#White point (Dmin)

The minimum density a process can reach on a given paper. In practice, it's the paper white after washing. The corrective curve never brings a zone to a density lower than the white point — that's physically impossible.

#Black point (Dmax)

The maximum reachable density. Limited by the process, the paper, the chemistry and the exposure time. Figures confirmed by Vision Picturale: charbon > 2.1, résinotype ~1.7. For the other VP processes (cyanotype, Aquaprint, bromoil, gumoil): the process's standard tonal range, with no canonical published figure.

#Polarity (negative chart / positive chart)

All the Vision Picturale processes (cyanotype, Aquaprint, bromoil, charbon, gumoil) use a negative chart. Only résinotype uses a positive chart (positive interpositive), because its pigments settle on the unexposed zones of the negative. To calibrate a digital printer: negative chart as well.

#Cubic polynomial

A historical term from the literature on tonal calibration, sometimes used as shorthand for a smooth curve. Calibration Flow does not use a cubic polynomial in the strict sense. The app builds its 256-value LUT by linear interpolation between the thresholds set by the sliders, then smooths that LUT with robust LOWESS + monotone PCHIP (or a weighted average depending on the mode). The result is a smooth curve with rounded transitions, with no angular breaks — hence the possible confusion with a "cubic polynomial".

See also: The 25-point curve.

#Preset

A corrective curve saved with its metadata (process, paper, chemistry, UV source, calibration date). Lets you find and reuse a calibration without redoing it. Synced across devices via Firestore when the Pro tier is active (iOS subscription).

See also: Preset library, Cross-device sync.

#RAW

An undeveloped image format coming straight from a camera's sensor. Keeps all the sensor data (10 to 14 bits per channel, wide gamut). RAW support is not yet implemented in Calibration Flow — the universal decoder returns an explicit error if you try to import a RAW file. For chart measurement, a high-quality JPEG or HEIC is more than enough; for your final images, export to JPEG, PNG or HEIC from your usual tool before importing.

See also: HEIC and RAW, HD media.

#Registration (marks)

Small marks printed around a negative to precisely align several layers printed one after another on the same paper. Calibration Flow uses mini CMY Venn diagrams (three overlapping circles) rather than simple crosses — correct overlap produces a visible Venn, the slightest misalignment breaks it. Particularly useful for multi-layer processes: Aquaprint Four-colour and Charbon Couleur Profonde. The single-layer VP processes (cyanotype, bromoil, gumoil, résinotype) don't need them.

See also: Registration marks.

#Résinotype

A Vision Picturale process with a natural varnished finish. Chemistry: VP N°05 (pigmented gelatin) sensitized by VP N°03, supplemented with powder pigments and a proprietary VP resin. Prepared in a 40 °C water bath. Luminograph A3+ exposure: 3-6 min. Development in warm water at 30 °C, 10-15 min. Natural polymerization on final drying. dMax ~1.7. The only VP process that calls for a positive chart (positive interpositive).

#Universal Sensitizer (VP N°03)

A Vision Picturale non-toxic, bichromate-free sensitizer, used in five VP processes that harden under UV: Aquaprint, Charbon, Bromoil, Gumoil, Résinotype. Historically replaces potassium dichromate in aqueous hardening processes. Cyanotype does not use VP N°03 (it has its own chemistry: VP N°01 + VP N°02).

#Smart Analyzer

The tonal-intent classifier for the imported image. It reads the perceptual L* luminance distribution and assigns the image one of seven profiles (Normal, Low Key, High Key, Charcoal, Soft Mist, Underexposed, Uncertain), which automatically adapts the correction strategy proposed by the three sliders. The Smart Analyzer does not detect the chart's patches — centering the measurement zones is a separate function.

See also: Smart Analyzer.

#Spline (cubic)

A classic mathematical method for building a smooth curve passing through given points, in cubic segments with continuity of the derivatives at the joins. Calibration Flow does not use a cubic spline — the corrective curve is built by linear interpolation between thresholds, then smoothed with LOWESS + PCHIP. The term appears now and then in calibration literature but doesn't match this app's implementation. See Cubic polynomial for the details.

#UV (ultraviolet)

Electromagnetic radiation of a wavelength shorter than the visible (10 to 400 nm). Alternative processes that use UV exposure mostly rely on UV-A (315-400 nm) — the band of the Luminograph and tanning tubes. The sun emits UV-A in amounts that vary with the time of day and the season, which explains the difficulty of reproducibility under natural light.

See also: UV calibration.

A glossary in progress. If you're missing a term, flag it to support@picturale.app — we'll add it if you're not the only one who looked for it.