Calibration keeps failing

You see

In the Camera Calibration dialog, you enter points and click Solve. The result shows low Quality, high RMSE, or the solve fails entirely.

What is happening

The solver looks for a consistent transform from image-pixels to reference-mm. If the points you provided are inconsistent (typos, mis-identified features, too few points), the solver cannot find a clean fit.

Fix

If you have only 2 points

Two points is the absolute minimum and produces a fragile fit. Add 2-4 more points spread around the image. Quality improves significantly with redundancy.

If your points are all close together

Solve quality depends on spread. Points clustered in one corner of the image cannot constrain the rest. Spread points across the full image area.

If one point is mis-typed

A single coordinate typo in one point throws off the entire fit. Re-check each point's pixel and reference coordinates. Even a 5-pixel error can show up as high RMSE.

If your reference grid is not regular

If you used a printed grid that has uneven spacing (poor print, paper stretched), the solver sees inconsistent reference positions. Use a digitally-perfect grid or a chessboard pattern.

If lighting changes between points

If image brightness changes drastically (you adjusted exposure mid-calibration), the visual position of features may shift slightly. Keep lighting consistent.

If the lens is the wrong kind

Some lenses (very wide-angle fisheye) introduce non-linear distortion that simple solvers cannot fit well. Use a lens with less distortion, or accept the lower quality.

Verify it worked

• Quality > 90%.
• RMSE under a few pixels.
• The saved calibration produces an undistorted captured image.

Still stuck?

• Camera Calibration dialog reference.
• Calibrate the camera guide.
• Post in the Facebook group with the camera model, lens info, and your calibration target.