De-Interlacing
Definition
The process of reconstructing a full progressive frame from the two interlaced fields captured by analogue video systems. Different algorithms (line doubling, weave, motion-adaptive) produce different results and must be selected and documented.
- Input
- Two interlaced fields captured by analogue video systems
- Output
- One reconstructed progressive frame
- Line doubling
- Duplicates one field's lines, fast but loses vertical detail
- Weave
- Combines both fields directly, best for static scenes
- Motion-adaptive
- Switches method locally based on detected motion
Common questions
Why does the choice of de-interlacing algorithm matter for court-presented video?+
Different algorithms make different trade-offs between spatial detail and motion artefacts. Weave produces combing artefacts on moving subjects, while line doubling halves vertical resolution, so the wrong choice can distort or obscure the very detail the examiner is trying to demonstrate.
What should be documented when de-interlacing footage for a forensic report?+
The examiner should record which algorithm was applied, the software and version used, and the reasoning for that choice, since a different reasonable choice on the same source material can visibly change what a viewer perceives in the reconstructed frame.
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