Compensating lateral chromatic aberration of a colour fringe projection system for shape metrology

In this paper we demonstrate a technique to compensate for lateral chromatic aberration between the red, green and blue channels of a colour fringe projection system. For measurement of colourful artefacts it is important to be able to combine data from the different colour channels to accurately quantify the artefact's form, with colour capture also providing colour texture information that can be mapped onto the form data. However, the use of conventional refractive lenses in the projection and imaging systems introduce dispersion and hence lateral chromatic aberration that modifies the measured phase differently in each of the colour channels. A linear compensation model is proposed using phase maps from the different colour channels to enable the magnitude of lateral chromatic aberration to be calibrated. The required performance of the technique is established via simulations and the use of the technique over a typical depth of field has been confirmed experimentally. Results from a white reference plane, a telephone and a colourful painting show that the proposed method compensates lateral chromatic aberration from the captured shape data. The probability of calculating the correct fringe order by unwrapping the phase between the different colour channels is typically 99.9%.