The CatWalk XT system detects footprints by video recording the animal from below while it traverses a glass plate. While other methods rely upon error-prone technologies to recognize characteristics of footprints from a video image, CatWalk XT uses the Illuminated Footprints Technology™ to capture actual footprints.
So what does this mean? Footprints are illuminated where the paw actually touches the glass. A green LED light emitted inside the glass plate is internally reflected, except at those areas where the animal makes contact with the glass plate. Where the paws touch the glass, light is refracted on the opposite side. The high speed color camera that is positioned underneath the glass plate captures these illuminated areas and sends the data to a computer running the CatWalk XT software.
The great advantage of this type of paw print detection is that it is impossible to falsely detect parts of the feet (or of the rest of the body) as part of the print. The system does not overestimate the print size or misinterpret the form. You do not have to black out parts of the body, such as the knees, to prevent false identification.
In addition, if more body weight is exerted on a particular paw, the corresponding footprint area becomes more fully covered by the sole which results in an increase in brightness. This allows subtle differences in weight bearing between the four paws to be detected.