Gerwin Damberg

Calibrated image appearance reproduction

Managing the appearance of images across different display environments is a difficult problem, exacerbated by the proliferation of high dynamic range imaging technologies. Tone reproduction is often limited to luminance adjustment and is rarely calibrated against psychophysical data, while color appearance modeling addresses color reproduction in a calibrated manner, albeit over a limited luminance range. Only a few image appearance models bridge the gap, borrowing ideas from both areas. Our take on scene reproduction reduces computational complexity with respect to the state-of-the-art, and adds a spatially varying model of lightness perception. The predictive capabilities of the model are validated against all psychophysical data known to us, and visual comparisons show accurate and robust reproduction for challenging high dynamic range scenes.

Comparing Signal Detection Between Novel High-Luminance HDR and Standard Medical LCD Displays

DICOM specifies that digital data values should be linearly mapped to just-noticable differences (JNDs) in luminance. Increasing the number of JNDs available requires increasing the displays dynamic range. However, operating over too wide a range may cause human observers to miss contrast in dark regions due to adaptation to bright areas or, alternatively, miss edges in bright regions due to scattering in the eye. Dolby Inc.s high dynamic range (HDR) LCD display has a maximum luminance over 2000 cd/m2; bright enough to produce significant in-eye scatter. The display combines a spatially variable backlight producing a low-resolution 8-bit ldquobacklight imagerdquo with a high-resolution 8-bit LCD panel, approximating a 16-bit greyscale display. Alternatively, by holding the backlight constant at 800 cd/m2, a standard medical LCD display can be simulated.We used two-alternative forced choice (2AFC) signal-detection experiments to quantify display quality. We explored whether the full-power HDR displays optical characteristics (scattering and low resolution backlight) have a negative effect on signal detection in medical images compared with a standard LCD. We used 8-bit test images derived from high-field MRI data combined with synthetic targets and synthetic Rician noise. We suggest signal detection performance with the HDR display is comparable to a standard medical LCD.

Efficient, high brightness, high dynamic range projection

Projection is a popular form of imaging but suffers from dim peak light levels and poor contrast, limiting effective use to dark and controlled viewing environments like the cinema (Figure 1). We introduce a novel High Dynamic Range (HDR) projection technique that achieves both dark black levels and very bright peak luminance in an energy and cost efficient implementation.

High brightness HDR projection using dynamic phase modulation

We demonstrate a new, large screen projection technology that utilizes dynamic phase modulation for light steering to achieve both black levels indiscernible from the screen in dark environments and peak luminance levels some 20 times above what conventional projectors can reach with the same light source. The human visual systems near-logarithmic brightness response to luminance is demanding on the lamp requirements in a conventional display system. With a steerable light source, excess light from dark areas in an image can be used for areas requiring higher brightness thus breaking the conventional linearity between out-of-lens-lumens and onscreen-luminance. We will demonstrate our new, full color prototype which reproduces very realistic appearing images and requires only a fraction of the energy of a traditional projector (Figure 1).

A high bit depth digital imaging pipeline for vision research

In order to achieve accurate results in user studies in the fields of Psychophysics, Experimental Psychology, Ophthalmology and clinical studies there are high demands towards an imaging pipeline presenting these stimuli in an experiment (as illustrated in Figure 1). For example, display stability and repeatability, both short term and long term are crucial when conducting research leading to robust results. Further important factors are the perceptual limits of a graphics pipeline. Here, two important elements are the achievable dynamic range and the color gamut, which would ideally approximate or exceed the capabilities of the human visual system (HVS). In an optimal solution, those stimulus dimensions would be displayed with continuous intensity levels between their respective extrema (e.g. from dark to light) when presenting them to participants.