Harmonic Detective

Support

Frequency-domain image analysis for iPad and Mac

Getting started

• Load an image — pick a bundled test image, or load one from Photos, Files, or the camera. The FFT spectrum computes automatically and a Region of Interest (ROI) appears on it.
• Adjust the ROI — drag it on the spectrum to move it, or drag its edge to resize. The Modified and Mask views update live.
• Scale slider — controls how strongly the selected frequency band is filtered (0–10).
• Modifier vs. Isolator — Harmonic Modifier scales a band in place; Harmonic Isolator keeps only the selected band.
• Add ROI — add ellipse, rectangle, or annulus regions; they combine by union masking. (Working with more than one region at a time is a Pro feature.)
• Rotation modes — “Filter frequencies” keeps the ROI fixed on screen; “Track features” locks the ROI to the feature as you rotate.
• GPU / CPU — switch the FFT processor in Settings. GPU (Metal) is the default; the app falls back to CPU automatically where Metal is unavailable.
• Export — save the modified image to Photos or Files, or export the raw FFT mask for MATLAB / Python. (Pro.)

Free & Pro

Harmonic Detective is free to download and explore. The free app is the full on-screen instrument: load any image, see its live FFT spectrum, draw one region, use the Modifier and Isolator, rotate, and zoom — with a set of built-in test images to try it on. Nothing is time-limited.

A one-time Pro unlock ($9.99, no subscription) adds saving & exporting your result to Photos or Files, working with multiple frequency regions at once, and exporting the raw FFT mask for MATLAB / Python. One purchase covers iPad and Mac. You can restore a previous purchase from the paywall’s Restore Purchase button.

Built-in manual

Tap the ? icon in the app for a full, searchable user manual that covers every feature — no internet connection required.

Frequently asked

Do I need an account or internet connection? No. The app is fully offline and requires no sign-in.

Why does the camera / photo permission appear? Only when you explicitly capture a photo or save a result. Images are processed on-device and never uploaded. See the Privacy Policy.

The GPU option looks disabled. Metal isn't available in the iOS Simulator; on a real device or Mac the GPU path is used.

Contact

Still stuck, or have a feature request? Email ios-support@slick-engineering.com — we usually reply within a couple of business days.