Black is source-dependent
Broadcast black, letterbox bars, faded frames, HDR transfer functions and analogue captures can have different sample levels. A universal threshold can miss real transitions or mark ordinary dark scenes.
Threshold controls
Use average/peak black and contrast-related controls together with the scan region. Excluding persistent bars, logos or noisy edges can make the measured area more representative.
Calibrate and verify
- Mark a short interval containing known black transitions and nearby dark content.
- Use calibration where available or adjust the thresholds conservatively.
- Run a short scan and inspect statistics for true and false candidates.
- Save the settings only after representative scenes behave correctly.