Light Field measurement of a Virtual Images

A virtual image is an image that is produced into space without a physical entity representing the image-plane. Typically wearables and heads-up displays will produce virtual images, and due to the involved optical components, the shape of the images will be distorted in all three dimensions. This 3D-distortion is giving information about the device's quality-status and will impact the customer-experience especially when it comes to Augmented Reality functions. A robust measurement method is mandatory and required. A light-field-measurement system has been built having the potential to reconstruct images and analyze this feature. It is able to measure and recreate the origin of light vectors (intended and scattered) in spatial and angular information above human perceptual resolution. The extended scope of this project is the creation of a catalog on light fields from projection systems to allow virtualization of devices and enables a retrospective comparison of devices according to the new standards in perceptual sciences.

The specifically built Goniometer test standwith six degrees of freedom with translation resolution 0.05 mm and rotation resolution 0.0002 degrees. A LMK (Leuchtdichtemesskamera) will give luminance distribution L(x,y), color and chromaticity in measuring images, then lighting parameters such as illuminance E(x,y) and the luminous intensity I(x,y) can be derived. Camera parameters will be stored in a world coordinate system compensated for positioning imperfections of the device, with the final virtual images stored in a world coordinate view.


The calculated light field vectors generated from each pixel within an angular range of approx. 20°x10°, create 8 GB data with 13 Bit resolution. Thereafter by means of image reconstruction (inverse radon transform) algorithm, the light field data will be used for reconstruction of the light source radiation characteristics and geometry. Contrast analysis of the reconstructed data allows the identification of the image plane. A modified radon-transformation enables the reconstruction of vector-fields giving insight into the scattering function of the plane.



The aim of the project is to create a full digital-twin of the device useful in design-simulations as if it is seen from any observation point within the specified angular range.

Figure: a) Goniometer in measuring arrangement for real and virtual light field detection; b) Light field from 9 measuring positions and reconstruction of the luminance volume. c) Section in the area of the virtual image with preliminary reconstruction details Checkerboard

Ansprechpartner: Sravan Shelam