Perspective Distortion Error
Definition
The apparent change in size of objects at different distances from the camera due to projective geometry. A person closer to the camera appears larger in the frame than a person of identical height further away. Uncorrected perspective differences between subject and reference are the most common source of height estimation error.
- Cause
- Projective geometry of the camera lens
- Effect
- Objects nearer the camera appear taller than distant ones of equal height
- Common context
- CCTV-based height estimation
- Mitigation
- A reference scale placed at the subject's depth plane
Common questions
How is perspective distortion corrected in CCTV height estimation?+
Analysts either photograph a calibrated reference object at the same distance and depth plane as the subject, or apply photogrammetric reverse projection using known camera geometry, rather than comparing raw pixel heights across different depths.
Can a single fixed camera fully eliminate this error?+
No. A single camera can only be corrected for a known depth plane; any deviation of the subject's true position from the calibrated plane reintroduces error, which is why multiple reference points or stereo setups are preferred where available.
Related terms
- Ground-Plane Calibration
- A physical survey of the scene after the event, measuring reference points on the floor relative to the camera position, allowing the...
- Pixel Height Ratio
- The number of pixels occupied by a vertical extent (person, door, markings) in the image. Ratios between subject and reference pixel heights...
- Reference-Object Method
- Height estimation by measuring the pixel heights of both the subject and a reference object of known stature in the same frame,...
- Stature Estimation Uncertainty
- The combined error from pixel localisation, reference height knowledge, positional correction accuracy, and camera model assumptions, expressed as a confidence interval at...
- Vanishing-Point Method
- Using the vertical vanishing point and two horizontal vanishing points to compute the camera's effective viewing geometry, then projecting the person's image...