Pixel Height Ratio
Definition
The number of pixels occupied by a vertical extent (person, door, markings) in the image. Ratios between subject and reference pixel heights form the basis of proportion-based methods, corrected by a perspective factor when the positions differ.
- Measures
- Vertical pixel extent of a subject or reference in an image
- Use
- Proportion-based height estimation from CCTV
- Correction needed
- Perspective factor when subject and reference differ in position
- Common reference objects
- Doorways, marked height charts, fixed measurements in frame
Common questions
Why can't pixel height ratio alone give an accurate height estimate?+
A subject standing closer to or farther from the camera than the reference object will appear a different apparent size purely from perspective, so the raw pixel ratio must be corrected using the geometry of camera position, lens, and distance before it reflects true height.
What increases error in a pixel-height-ratio estimate?+
Low camera resolution, motion blur, an oblique camera angle, and a reference object that is not in the same depth plane as the subject all widen the uncertainty range reported alongside the estimated height.
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...
- Perspective Distortion Error
- The apparent change in size of objects at different distances from the camera due to projective geometry. A person closer to the...
- 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...