Parallel-Plane Requirement
Definition
The requirement that the camera sensor plane be parallel to the evidence-and-scale plane to eliminate keystoning distortion and allow accurate metric measurement from the photograph.
- Applies to
- Crime-scene photography with a scale
- Requirement
- Sensor plane parallel to evidence plane
- Failure mode avoided
- Keystoning distortion
- Purpose
- Accurate metric measurement from the image
Common questions
Why does keystoning specifically ruin measurement rather than just looking odd?+
Keystoning distorts the scale of the image unevenly across the frame, so a ruler or scale placed in the shot no longer represents a consistent pixel-to-millimetre ratio throughout the photograph, which invalidates any measurement taken from the image.
How do photographers verify the parallel-plane requirement is met in the field?+
A tripod with a bubble level, or a camera's built-in electronic level, is used to confirm the sensor is square to the evidence surface before the shutter is released, since the error is difficult to correct reliably after the fact.
Related terms
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- ENFSI
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- Equirectangular Projection
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- EXIF Metadata
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- Four-Tier Protocol
- The standard crime-scene photography sequence: overall (establishing), mid-range (relationship), close-up with scale, and close-up without scale. Each tier answers a distinct spatial...
- IAI
- International Association for Identification; includes the Crime Scene Certification programme requiring demonstrated forensic photography competency.
- Light Painting
- A technique where a handheld light source is moved across a scene during a long camera exposure to evenly illuminate large areas;...
- Nodal Point
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- Photo Log
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- SWGIT
- Scientific Working Group for Imaging Technologies (US); publishes multi-section guidelines on crime-scene photography, digital imaging, and specialised photographic techniques for law enforcement.