Tonal correction tools often offer two schools. The first school — Photoshop, Lightroom, Darktable — lets the user draw their curve by grabbing points with the mouse. Maximum precision, steep learning curve. The second school — the cameras of the 1970s and 80s — offers two or three dials to set. Less precision, immediate handling.
Calibration Flow chose the second school. Three sliders, one reset button. For alternative process calibration, where what matters is stability over time and reproducibility, it's the right tradeoff. Three notable numbers, three numbers comparable from one calibration to another, three numbers whose mechanical memory builds in a few sessions.
#What you do
Below the preview of your image, you see three horizontal sliders and a reset button.
The black point slider determines where the dark values begin in your corrected image. At minimum (on the left), the shadows stay as they were in the source image. The more you push to the right, the more you crush the dark zones to absolute black — useful when your image has washed-out shadows that you want to densify.
The white point slider does the same thing in mirror for the highlights. At maximum, you crush toward white. Useful for giving punch to a flat image where no zone really reaches white.
The midtone gamma slider bends the transformation between the two extremes. Upward, your image lightens globally (the midtones become lighter). Downward, it darkens. It's the general brightness control, more precise than a simple exposure slider because it preserves the blacks and the whites.
At each slider movement, the Web Worker recomputes the correction in a few milliseconds. You see three things update together — the image preview, the correction curve drawn on the graph, and the corrected histogram. The feedback is immediate and synchronous.
The reset button puts the three sliders back to their neutral position — black point at minimum (nothing crushed), white point at maximum (nothing crushed), gamma at 1.0 (neutral curvature). The curve returns to a perfect diagonal, the image goes back to its original state.
You can always undo an adjustment individually by putting a single slider back to its neutral position without touching the others.
#Why it matters
For reproducibility. Three numeric values noted in a preset, and you find exactly the same correction six months later. With a curve drawn by hand at 25 points, you have no chance of reproducing the gesture identically.
For quick handling. Someone who opens Calibration Flow for the first time understands the three sliders in thirty seconds. A point-dragging interface would require a tutorial and a learning period. For occasional calibration, speed of access matters more than absolute precision.
For consistency across images. If you calibrate ten images of the same series, having three sliders lets you apply the same values to all ten without drawing anything by hand. If you had to draw ten curves, you'd have ten slightly different curves, and the consistency of the series would suffer.
#When you don't need it
For a very specific correction not covered by three sliders. If you want to push only the bluish shadows of your image without touching the rest, the three sliders can't do it — that's a per-channel or per-zone correction that requires Photoshop or another tool. Step out of Calibration Flow for that need.
For the automatic preset from the Smart Analyzer. If the strategy proposed by the Smart Analyzer suits you, you don't have to touch any slider. You confirm and you generate your negative. Manual adjustment is only necessary when you want to deviate from the preset.
For ultra-fine modification in post-processing. If you want value-by-value adjustments on a specific point of your curve, open your exported
.acv#Worth remembering
| Element | Value |
|---|---|
| Controls | 3 sliders + 1 reset button |
| Slider 1 | Black point (shadow compression) |
| Slider 2 | White point (highlight compression) |
| Slider 3 | Midtone gamma (global brightness) |
| Reset | Puts everything back to neutral, perfect diagonal |
| Update | Real time — image, curve and histogram synchronous |
| No dragging | The curve is not manipulated directly with the mouse |
#The test
Load an image, wait for the Smart Analyzer to propose its preset. Note the three proposed values. Push the black point one notch to the right — check that the image darkens in the shadows only, without touching the highlights. Now click Reset: the three sliders should return to their neutral position and the image should go back to identical to the import (before Smart Analyzer too). If Reset doesn't bring back the raw source image, either it does something else, or the Smart Analyzer applied a transformation that Reset doesn't undo.