The capability of cameras and displays to reproduce small differences in luminance levels is constantly growing. However, we are still dealing with a limitation of the human visual system (HVS) known as the simultaneous contrast range (SCR).
ABSTRACT
In recent years, High Dynamic Range (HDR) has been improved enormously. The capability of cameras and displays to reproduce small differences in luminance levels is constantly growing. However, we are still dealing with a limitation of the human visual system (HVS) known as the simultaneous contrast range (SCR).
Compared to earlier studies, this paper focus on realworld scenarios for evaluating the SCR. In natural images bright highlights, especially in HDR, can limit the eyes’ sensitivity to detect small differences in surrounding dark areas.
The paper on hand describes a different test-image set - developed as part of current research activities by the authors - to measure the relation between the perceived SCR and the following four significant parameters: The distance or rather the viewing angle, the size of the bright highlight, the luminance of the highlight and the ambient light.
As a result, a mathematical formula is given which can help to evaluate and improve HDR viewing experiences as well as SDR down-conversions.
INTRODUCTION
The human visual system (HVS) is a very complex model, not only dealing with the eyes but also with neuronal reception, processing, and interpretation of information. It is commonly known that this system can distinguish differences in intensity within a very wide range of luminance levels using mechanical and biochemical adaptation processes. However, the adaptation processes take time.
On the contrary, the steady-state or simultaneous contrast range (SCR) of the HVS is extremely limited compared to the overall range. The range of the simultaneous visible contrast however, it not yet exactly examined.
When introducing High Dynamic Range (HDR) into the television industry, this question becomes more important. The sensitivity of cameras, as well as displays, has increased tremendously over recent years which allowing the capturing and reproduction of a contrast range several times larger than classic SDR-TV.
New technologies will even further improve this capability over the coming years.
This leads to new challenges for manufactures, as well as for content producers and raises different issues about viewers’ preferences as described in an earlier paper. With all these technological improvements the question is whether we shall reach, or have already reached, the limitations of the HVS toward the SCR.
We use the term ‘contrast range’ instead of ‘dynamic range’ in this paper, because ‘dynamic’ defines the quantisation. This could lead to a misinterpretation (just focusing only on the number of bits for the quantisation).
However, when using a non-linear OETF, e.g. a logarithmic transfer curve, a relatively small dynamic range is sufficient to capture a wide contrast range. In this case, the ‘contrast’ is more precise.
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