FAQ

Short answers to the questions people arrive with. Hit an actual error? That lives in Troubleshooting.

What is semper for?

It measures how a surface deforms from photographs — full-field displacement and strain maps, computed on your phone. It is aimed at mechanical testing and materials work in teaching and research.

What devices does it run on?

semper is an Android app.

Is it free, and do I need an account?

You sign in (Google or email), and a new account needs a one-time admin approval before you can use the app. That gate is about managing access, not payment.

Why does my account need approval?

semper is an allow-list app while it is in early release. Support is emailed automatically when you sign up; tap Check status in the app after you are approved — it does not update on its own.

Does it work offline?

Yes, once your device has been approved. Importing frames and running the correlation need no network. Only sign-in, approval checks, and cloud uploads do.

Can I use my phone camera, or a video?

You load photos you have already taken, or pick a video and semper samples it into frames (the first frame becomes the reference). For how to shoot a good speckle and lighting, see the iDICs guide below.

Are results in millimetres?

No. Displacements are in pixels — semper has no spatial calibration. Convert with your own scale factor (pixels per mm from your setup).

How accurate is it?

The engine locates each subset to roughly 1/100 of a pixel, and recommends a subset size that targets about 0.007 px displacement accuracy on your image. Real accuracy depends on your speckle, lighting, and camera — the parameters and a sweep let you check it.

Why does semper warn about JPEG?

JPEG works, but compression damages the intensity gradients correlation needs, so semper shows a non-blocking warning. Prefer PNG or TIFF. RAW and DNG import only through Files, not the gallery.

Why is speckle contrast too low?

On import the app measures your speckle. A weak pattern cannot reach the target accuracy even at the largest subset, so you see a warning and a larger subset suggestion. Treat it as feedback on the pattern, not just a slider tip: accept the larger subset, redraw the ROI over well-speckled surface, or re-shoot. For how to paint and light a speckle, see the iDICs guide below.

Is my data uploaded to the cloud?

Only if you turn on Save to cloud. The correlation always runs on the phone; cloud backup just stores the results you choose to sync, so you can restore them. See Privacy for the full picture.

Can I use semper results in a paper?

Yes. Export “Everything”, quote the VSG with any strain value, and keep the archive with your raw images — inputs, fields, and parameters together are what make the result reproducible. From a sweep you can also Save graph for an annotated lattice plot PNG.

I forgot my password — do I leave the app?

No. Forgot password mails a link that reopens semper on a set-new-password form (same password rules). Email sign-in links work the same way once App Links are verified.

Does semper send crash reports?

Only if you opt in. After the beta notice on first run you are asked once; you can change it later under Settings → Your data → Send crash reports. Declining is the default. Reports never include your images or results.

How do I reuse parameters from a sweep?

On the lattice plot, double-tap the value readout to copy that combination’s subset, step, and strain window. Start a new single-setting analysis and tap Paste params on step 2.

Something went wrong — where do I look?

Troubleshooting is indexed by the exact message the app showed you. For how-to, use the Manual; for account or private matters, email support.

Speckle, lighting, and experiment design are outside this FAQ. See the iDICs Good Practices Guide for Digital Image Correlation.