3.4 Chromostereoscopy

Chromostereopsis

Chromostereoscopy, or colour stereoscopy, is a three dimensional viewing system that does not rely entirely on binocular parallax and convergence. This method is based on the visual phenomenon of chromostereopsis. When chromostereopsis is positive, blue objects appear to be at a greater depth than red objects. Einthoven (1885) was the first scientist to study the chromostereopic effect. He attributed this effect to transverse chromatic dispersion and the asymmetrical relation of the visual and optical axes. The visual and the optical axes of the eyes are not the same. Rays of light imaged on the fovea strike the corneal surface at an angle. As a result, the cornea and the two lens surfaces act as prisms. Shorter wavelengths (blue) are refracted more than longer wavelengths (red). On the retina, blue light is focused towards the nose while red light is focused towards the temples. Therefore, the red object will appear to be closer than the blue object.

Visual and optical axes

Chromostereopsis can be enhanced by using principles of refraction (Newton, 1704). Light passing through a prism is refracted by an amount dependent on the wavelength of the light and the speed at which it travels through air and the glass of the prism. Using the principles of chromostereopsis, Richard Steenblik developed ChromaDepth^TM 3-D glasses in 1986. These glasses became commercially available in 1992. The lenses of these glasses are clear plastic, but act like thick glass prisms. They combine refraction and diffraction in a system of high precision micro-optics. The lenses shift image colours in different directions for each eye thereby creating a stereo perception from a single image.

Prism

3-D image exploiting chromostereopsis

The method by which chromostereopsis can be used to create 3-D imagery is to encode depth into an image by means of colour and then to decode the colour by means of optics such as the ChromaDepth^TM glasses. In this way 3-D images can be created and presented in a variety of mediums including print, film, video and computer graphics. A 3-D display technique using the ChromaDepth^TM glasses has been used to enhance qualitative analysis of remotely sensed data combined with geoscientific data (Toutin and Rivard, 1997).

Qualitative analysis using 3-D display