An ideal imitation of the human eye enables the precise measurement of near-eye and head-mounted display quality

The all-new 2021 version of the Almalence Human Eye Simulator. Optically clear. Eye Tracking ready.

To assess the quality of head-mounted displays, it is necessary to capture images which exactly match with what a human eye would perceive. Indeed, a capturing device has to be capable of accurately replicating the human eye’s optical properties. If they are not, then this could lead to some drastic irregularities – a mismatch of entrance pupil diameter, for instance, would lead to quite different blurs and aberrations, or even sometimes visible Fresnel rings, which are not apparent to the human eye. Once you do have a capturing device in place that can match the optical properties of the human eye, however, then now comes the real challenge: the device has to be recognized as an “eye” by eye trackers – otherwise, there will simply be no chance of capturing a correct picture, as a wrong picture would be displayed in the first place, in case the HMD uses eye position-dependent rendering techniques like foveated rendering or dynamic aberrations correction – which have recently been becoming standard for high-quality near-eye displays.

Almalence, a pioneer in designing the eye-imitating cameras, has now begun to roll out an all-new and updated version of its powerful eye simulator, better than ever and ideally suited for near-eye display picture capturing and quality measurement tasks. It features made-to-order, optically clear eye corneas, flawlessly creating a perfect match to the form of a real, human eye that is indistinguishable for eye trackers – unlike other, off-the-shelf parts and solutions, which commonly result in deviations from the proper shape. A clear aperture for up to a 120° FOV enables the seamless capture of up to the entire field of view in one shot, without ever compromising the contrast and MTF of the true visible picture.

The ideal profile of both visible and IR light absorption and reflection is painstakingly implemented, in order to make the simulator’s iris look exactly like a natural iris to an eye tracker. An additional IR-cut filter also prevents unwanted reflections from the camera lens, which may spoof eye tracker readings.

Auto-focus capability, to avoid having to manually adjust the focal point when moving the “eye” inside head-mounted displays that exhibit a significant field curvature.

The platform encapsulates multiple capturing camera designs, including a 100° field of view camera which enables the user to capture the entire visible FOV in one shot. This feature is also quite useful for geometry distortion measurements. Specially designed narrow 78- and 34-degree FOV cameras are also included, engineered for high-precision optical measurements, including apparent resolution, chromatic aberrations, and more.

A monochromatic camera can also optionally be used with the eye simulator, in order to resolve ambiguity in color channel mixing between the HMD display and CFA filters inside the camera.

Almalence has also developed a powerful software for the processing and transforming of captured images, so that they can readily be used for correct measurements of geometry, MTF, channel crossing, and other quality characteristics, with industry-standard tools such as ImaTest. Together with a 6-DOF robo-arm and its controlling software, all of the above-mentioned features seamlessly combine to present a complete, easy-to-implement tool for head-mounted displays, picture quality assessment, and the profiling of geometry and aberrations correction.

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