Turning a Digital Camera into an Absolute 2D Tele‐Colorimeter

Abstract

We present a simple and effective technique for absolute colorimetric camera characterization, invariant to changes in exposure/aperture and scene irradiance, suitable in a wide range of applications including image‐based reflectance measurements, spectral pre‐filtering and spectral upsampling for rendering, to improve colour accuracy in high dynamic range imaging. Our method requires a limited number of acquisitions, an off‐the‐shelf target and a commonly available projector, used as a controllable light source, other than the reflected radiance to be known. The characterized camera can be effectively used as a 2D tele‐colorimeter, providing the user with an accurate estimate of the distribution of luminance and chromaticity in a scene, without requiring explicit knowledge of the incident lighting power spectra. We validate the approach by comparing our estimated absolute tristimulus values (XYZ data in cd/m2) with the measurements of a professional 2D tele‐colorimeter, for a set of scenes with complex geometry, spatially varying reflectance and light sources with very different spectral power distribution.

Camera response function assessment in multispectral HDR imaging

“…While ISO 14524 describes a standard method for the measurement of absolute opto-electronic conversion functions of imaging systems including CRF by means of a specific test chart [2], in a similar approach Martinez et al [3] used a classic ColorChecker (CC24) to measure absolute CRF. In another work, Guarnera et al [4] exploited a projector to measure opto-electronic conversion transform. Brauers et al [5] used an integrating sphere and a precise optical setup to measure relative CRF.…”

On the Acquisition and Reproduction of Material Appearance

“…Hence, we focused on the development of an effective technique for absolute colorimetric camera characterisation, suitable for use in a wide range of applications, including image-based reflectance measurements, spectral prefiltering and spectral upsampling for rendering and to improve color accuracy in HDR imaging. As demonstrated in [14], the characterised camera can be used as a 2D telecolorimeter to obtain an estimate of the distribution of luminance and chromaticity in a scene, in physical units (cd/m 2 ). Besides the aforementioned applications, such a characterised camera can be used for radiometric compensation, to project images on unoptimised surfaces [15] while compensating for the spatially varying background (see Figure 2).…”

“…In (c), the compensated image, projected on the same surface. The estimation of the surface gamut partly relies on a camera characterised with our method[14].…”

Multilayer Perceptron to Boost Colorimetric Capacities of 2D RGB and Hyperspectral Snapshot Cameras

“…Currently, the most reliable solution to systematically measure the colour of a surface is to rely on colourimeters [8]. Nevertheless, its contrasted accuracy comes with some limitations like issues relating to measure non-flat surfaces or the inability to measure many colours at the same time [9].…”

“…Nevertheless, its contrasted accuracy comes with some limitations like issues relating to measure non-flat surfaces or the inability to measure many colours at the same time [9]. Alternatively, camera-based approaches appear as a solution to this problems [8], [10]. The setup used by most of these approaches generally requires a controlled illumination environment.…”