Quick Start

Install

Download the latest release from GitHub Releases.
Drag StepWedgeDensitone into your Applications folder.
Double-click it. The build is signed and notarized by Apple, so there is no Gatekeeper warning to click past and no right-click Open trick to remember.

StepWedgeDensitone requires macOS 13 (Ventura) or later and a Mac with a Metal-capable GPU.

What you need

A step wedge printed through your process — 21, 31 or 51 steps are the common choices — and dried.
A scan of that print — RAW with a straight curve, no auto-exposure, no auto-levels, no sharpening, and the same settings every time. See Scanning a Print for Measurement.
Optionally, the .acv curve that was active in Photoshop when the negative for that wedge was made.

1. Open the app

A fresh launch shows an empty canvas. Everything else — toolbar, inspector, step table, graphs — is already in place and waiting for an image.

The empty canvas: a photo icon over the lines “No image loaded” and “Use Open Wedge — or drag an image or .wdge here”

2. Load your scan

Drag the scan onto the canvas, or click Open Wedge in the toolbar. PNG, JPEG, TIFF, GIF, BMP, HEIC/HEIF and Apple-supported RAW (DNG, NEF, CR2/CR3, ARW, ORF, RAF, RW2) all open directly. If the scan is sideways, the two rotate buttons beside Open Wedge turn the working image in 90° steps — the file on disk is never modified.

3. Set the layout, then detect

Detection lives in the inspector’s Measurement section, at the top of the right-hand column. Set Cols, Rows and Steps to the wedge you are holding — that is the order they read — then click Detect Corners.

The Measurement section: Cols, Rows and Steps, then Detect Corners and Detect Corners and Steps

It finds the wedge in the scan and keeps the layout you just entered. The canvas gets a dashed outline with four colour-coded corner handles, and every patch gets a measurement circle labelled with its step percentage.

If you do not know the layout, Detect Corners and Steps below it predicts that too — step count, grid, and cell order — and overwrites the three pickers with what it read.

The whole window after detection: 51 points on a scanned platinotype wedge, with the inspector, step table, response-curve graph and statistics panel filled in

4. Check the placement

Click the ⧉ viewfinder button in the toolbar’s zoom chip to fill the canvas with the detected wedge, then look at where the circles landed.

The wedge filling the canvas: three rows of patches with per-cell measurement circles and step-percentage labels, inside the dashed quad

A circle sitting on a dust speck or a coating flaw can be dragged onto clean paper.
If the outline is off, drag the corner handles.
If detection missed entirely, Shift+⌘+drag a rectangle over the wedge to lay out every cell by hand.

5. Load the curve you printed through

In the inspector’s Curve section, click Load .acv and choose the curve that was active when the negative was made. The response graph updates immediately. Skip this if the negative was printed with no curve applied.

6. Export the corrected curve

Toolbar → Export → Save Adjusted Curve… writes a replacement .acv. Load it into Photoshop’s Curves dialog in place of the old one — it already includes the curve you just loaded, so it is not something to stack on top.

Your work is autosaved continuously and restored on the next launch; use Save Session (⌘S) when you want a named .wdge file you can come back to.

Where to go next

Interface Reference — every control in the window, named and explained
Measuring a Wedge — detection, manual placement, grids, cell order, smoothing
Curves, Reports & Exports
Typical Workflow — the whole calibration loop, end to end