Harmonic Detective
A real-time 2D Fast Fourier Transform workbench for images — a scientific instrument, not a photo filter.
Overview
A scanned fingerprint with a printer's halftone grid baked into it. A microscopy image with scan-line banding. A photo of a screen, striped with moiré. The pattern degrading your image lives in the frequency domain — and most photo apps can't touch it, because they never leave pixel space.
Harmonic Detective loads an image, shows its frequency spectrum, and lets you draw a region of interest directly on that spectrum — then scale or extract exactly the frequencies you selected. Four synchronized views keep the original, spectrum, result, and mask in step, so you always see the math, never a black box.
- Platform
- iPhone · iPad · Mac (Universal)
- Engine
- Metal GPU FFT · CPU-validated
- Privacy
- 100% on-device · no account
- Price
- $9.99 once · no subscription
- Status
- Live on the App Store
Features
Four Synchronized Views
Original, FFT magnitude, modified result, and mask panes stay in sync — a 2×2 grid on iPad and Mac, a tabbed layout on iPhone — with a log-scaled contrast slider auto-ranged to each image's real dynamic range.
Frequency-Domain ROI Tools
Draw ellipse, rectangle, or annulus regions directly on the spectrum. Place several at once — color-coded and combined by union masking — and move or resize by touch on iPhone/iPad, or click-and-drag on Mac.
Harmonic Modifier & Isolator
Scale a selected frequency band 0–10× to attenuate or boost a periodic pattern, or isolate it to see what it alone contributes. Masks preserve full conjugate (Hermitian) symmetry, so filter gain is exact — no mirror-band artifact.
GPU-Accelerated FFT Engine
A Metal (MPSGraph) engine transforms arbitrary image sizes with no padding — 2–3 ms at 400×400, 5–8 ms at 2750×2750 — with an Accelerate/vDSP CPU path validated to match it bin-for-bin.
Two Rotation Modes
Filter frequencies keeps the region fixed on screen while the filtered result changes as you rotate; Track features locks the region to a rotating feature. The FFT is computed once and reused — rotating never triggers a recompute.
Export for Further Analysis
Save the modified image to Photos or export a PNG to Files — and export the raw FFT mask as a binary float array with metadata, for MATLAB, Python, or your own pipeline.
Specifications
- Platforms
- Universal — iPhone, iPad & Mac (Apple silicon + Intel)
- FFT Engine
- Metal / MPSGraph (GPU) · Accelerate / vDSP (CPU fallback)
- ROI Shapes
- Ellipse · Rectangle · Annulus — multiple, color-coded, union-masked
- Processing Modes
- Harmonic Modifier (scale 0–10×) · Harmonic Isolator (extract band)
- Export
- Save to Photos · PNG to Files · raw FFT mask (binary float array)
- Privacy
- 100% on-device — no account, no network, no analytics
- Price
- $9.99 one-time — no subscription, no in-app purchases, no ads
Use Cases
Some patterns are nearly impossible to touch in pixel space but trivial in the frequency domain — a regular pattern collapses to a few bright points in the spectrum, where you can select and filter it directly.
Periodic Noise Removal
Halftone dots, scan-line banding, and screen-door moiré all live at discrete points in the frequency domain. Notch them out and the image comes back clean.
Texture & Pattern Isolation
Extract a repeating structure — textile weave, sensor pattern, printed screen — to study it on its own, or scale it down to subtract it from the image.
Moiré & Halftone Analysis
Photos of screens and printed material carry regular interference patterns. See exactly where they sit in the spectrum and filter by band, not by guesswork.
Forensics, Microscopy & DSP
Built for the frequency-domain tasks a forensic image analyst, microscopist, or signal-processing engineer already knows by name — on real data, with no presets and no AI.
Frequently Asked
It's a real-time 2D Fast Fourier Transform (FFT) workbench for still images. Load an image, see its spatial-frequency spectrum, draw a region of interest directly on that spectrum, and either scale or extract exactly the frequencies you selected — to remove periodic noise, isolate textures, or study repeating patterns.
Neither. There are no presets and no AI. You choose the frequency band and whether to scale or isolate it, and you see the math happen across four synchronized panes — original, spectrum, modified result, and mask.
It's a Universal app for iPhone, iPad, and Mac (Apple silicon and Intel) — one $9.99 purchase unlocks the full app on all three. No subscription, no in-app purchases, and no ads.
No. Every computation happens on-device. There's no account, no sign-in, and no network access of any kind — the app makes no network calls. It requests camera access only when you capture a photo, and photo-library access only when you save a result.
Save the modified image to Photos, export it as a PNG to Files, or export the raw FFT mask as a binary float array with metadata — for use in MATLAB, Python, or your own analysis pipeline.
It's available now on the App Store — a $9.99 one-time Universal purchase that unlocks the full app on iPhone, iPad, and Mac (Apple silicon and Intel), with no subscription, in-app purchases, or ads.
Availability
Harmonic Detective is available now on the App Store. One $9.99 purchase unlocks the full app on iPhone, iPad, and Mac (Apple silicon and Intel) — no subscription, no in-app purchases, no ads.
Download on the App Store- App Store · iPhone & iPad
Touch to place and resize regions on the spectrum; 2×2 grid on iPad, tabbed layout on iPhone. - Mac App Store · Apple silicon + Intel
Native Mac app with click-and-drag regions and the full 2×2 synchronized grid.