Quick start
- Load an image — click "Load image" and pick a JPG or PNG of the chart or drawing.
- Calibrate the axes — pick two known points on the X axis and two on the Y axis, enter their real values.
- Extract points — click along the curve (Add mode) or drag along it (Trace mode) to place points automatically.
- Export — download a CSV, or an interactive HTML report you can share with anyone.
1. Loading & editing the image
Use "Load image" to upload a JPG or PNG. If the scan is rotated, cropped wrong, or mirrored, the Edit image panel can fix it before you calibrate:
- Rotate L / R — quick 90° turns.
- Fine rotate — drag the slider (or type a precise angle) to straighten a slightly skewed scan. You'll see a live preview; click "Apply rotation" to confirm.
- Flip H / V — mirror the image horizontally or vertically.
- Crop — drag a rectangle on the image, then "Apply crop".
- Reset image — reverts to the file you originally uploaded.
Any of these clear your current calibration and points, since pixel positions change — you'll always get a confirmation first.
2. Calibrating the axes
Under "Calibrate X axis" and "Calibrate Y axis":
- Click pick next to P1, then click the corresponding tick mark on the image. Type that tick's real value into the field.
- Do the same for P2 — pick a point far from P1 for better accuracy.
- Each axis can be linear, log10, ln, or 1/x (reciprocal) — pick whichever matches how the chart's axis is actually drawn.
Once both axes have two calibrated points, you're ready to extract data.
3. Extracting points
Three modes, in the "Extract points" panel:
- AAdd — click directly on the curve to place a point. In this mode you can also drag an existing point to reposition it.
- TTrace — click and drag along the curve; points are placed automatically at even spacing as you go. Good for long, smooth curves.
- DDelete — click a point to remove it.
Pen down / Pen up controls whether the next point connects to the previous one with a line. Use Pen up right before starting a new, disconnected segment of the same curve set (e.g. jumping over a gap).
Undo last removes the most recent point; Clear all empties the current curve set.
4. Multiple curves (curve sets)
If your chart has more than one curve, don't mix them into one set:
- Click + add next to "Set" to create a new curve set, and give it a Title (e.g. "Efficiency", "d=40mm").
- Switch between sets with the Set dropdown — each remembers its own points, pen state, and curve fit.
- Each set draws in its own color on the canvas so you can tell them apart; the active set's points are drawn larger.
- Delete this set removes the active set (disabled if it's your only one).
5. Curve fitting
The Fit dropdown (Off / Linear / Quadratic / Cubic) fits a polynomial through the active set's points and draws it as a dashed line, with the equation and R² shown underneath. It updates automatically as you add, move, or remove points.
6. Measuring & navigating
- Measure (top toolbar) — click two points anywhere to see the distance between them in data units.
- Pan — toggle on, then drag to move the view. You can also hold Space and drag with the mouse.
- Scroll / pinch to zoom, centered on your cursor or pinch point.
- A magnifier loupe follows your cursor for precise clicking near small tick marks.
7. Exporting your data
- Export CSV — every curve set's points, with a "set" column.
- Download curve (HTML) — a standalone interactive report: hover for coordinates, click points to select and remove them, a legend with a working fit dropdown per curve, and a data table. Opens in any browser, no internet or account needed.
Touch & tablet
Every tool works with a finger or stylus, not just a mouse: drag to pan/trace/place points, tap to click, and pinch with two fingers to zoom.
