Method · No preset
Calibration Flow measures a result, not a method. It reads the lightness of a printed target — which means a process it has never heard of calibrates exactly like one it ships with. Bromoil, gumoil and resinotype are in that case.
The method
Print the target
The 25-patch target from the app, or the 21-step chart you can download right here. No preset is needed to print it.
Print it with your process
Your usual exposure time, your chemistry, your paper. Change nothing: we measure what you actually do, not an ideal protocol.
Scan or photograph the result
Flat, even lighting, no automatic correction. A flatbed scanner is enough; a phone works if the light is steady.
Let the app read the L* values
Calibration Flow reads the lightness of each patch and derives your process’s real response. This is where the missing preset stops mattering: there is no model to pick, there is a measurement to take.
Export the .acv curve
You apply the curve to your images before printing, in Photoshop, Affinity, GIMP or Lightroom. The process never needed to be “known” by the app.
Need the target first? download the free 21-step chart, or read how to choose and measure a target.
The three cases
Here we only cover what affects the calibration. The chemistry, the papers and the kits are described by Vision Picturale, whose pages are linked below — we do not duplicate them.
Target polarity · negative
A bleached silver matrix, then the gelatin is inked with a brush or a roller.
Final density comes from the inking, not from the exposure: two prints off the same negative can differ by one pass of the roller. So calibrate your inking gesture before your curve — print the target three times in a row and keep the median, not the best attempt.
The bromoil process and its kit, at Vision Picturale →Target polarity · negative
Exposed gum bichromate, then oil pigments laid into the relief of the gum.
Two stages in series, so two sources of error. Calibrate the gum layer ALONE first, with the target, and only add the oil once that first curve is stable. Otherwise you are correcting an exposure with an inking adjustment, and the curve never converges.
The gumoil process and its kit, at Vision Picturale →Target polarity · positive
UV-hardened gelatin revealed with pigment — a proprietary Vision Picturale process.
It is the one polarity exception in the whole list: resinotype prints from a POSITIVE target, not a negative one. Send it the usual target and your curve comes out inverted while still looking perfectly coherent — that is the trap. Expect a Dmax around 1.7.
The resinotype process and its kit, at Vision Picturale →The one trap
An inverted polarity produces a curve that looks perfectly normal. Nothing warns you — neither the app nor the print. Resinotype is the only process on this page that prints from a positive target: check it before you expose, not after. Positive vs negative target.
Going further
