IEEE Consumer Electronics Magazine - October 2015 - 82

different colors so that highly saturated colors are obtained.
The problem here is the inability of OLEDs to emit photons at
a single frequency and achieve pure colors. Recently, quantum
dots LEDs (QD LEDs) have tried to address this limitation by
using molecule-sized semiconductors that absorb short wavelengths of light and emit a narrow spectrum of light at a longer
wavelength [38]. Their emission wavelength is easily tuned by
changing the size of the quantum dots to achieve the entire visible spectrum of wavelengths (see Figure 1). OLEDs and QD
LEDs can significantly increase the color gamut that a display
can achieve. However, increasing their peak luminance (for
instance, to 4,000 results in high power consumption and heat
problems. For the above reasons, there is no HDR prototype
display today that can achieve full BT.2020 color gamut and
high peak luminance at the same time.
Achieving high peak luminance in displays is mostly constrained by the power consumption and heat management. In
particular, this is the case if we want to manufacture HDR
projectors for digital cinema. Increasing the peak luminance
of the projector would require brighter lamps, which is not
always a viable solution since brighter lamps usually generate
more heat that needs to be dissipated and are more expensive.
To address this issue, Hoskinson et al. [39] proposed an optical design that adds a low-resolution secondary mirror array
to convert a single lamp into a multitude of light sources. This
mirror array steers light away from dark areas and redirects it
to bright areas to achieve a higher peak luminance. To drive
the mirror array, a light allocation algorithm is used that

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Metadata
Color and Tone
Inverse Color and
Mapping
Tone Mapping
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allows underexposing some areas to achieve a higher dynamic
range. A prototype based on the same design but using a laser
instead of a lamp was recently presented in [40]. In this system, the peak luminance depends on the ratio between the
number of bright and dark pixels in the image to be displayed.
The more dark pixels exist in the image, the higher the peak
luminance will be since the light is redirected from dark pixels to bright ones. Note that in terms of color gamut, lasers
have the same capability as quantum dots.

COLOR/TONE MAPPING AND
INVERSE COLOR/TONE MAPPING
As discussed earlier in the distribution pipeline, the color and
dynamic range of content need to match those of the display
so that content is interpreted and reproduced properly. In case
adaptation is required, the distribution pipeline is equipped
with a mapping process to expand or reduce the dynamic
range and color gamut of the content, as illustrated in
Figure 15. When the display's dynamic range is smaller than
that of the content, a TMO is applied to reduce the dynamic
range of the content so that it matches the display capabilities. Over the last two decades, many TMOs have been developed [1]. The main tone-mapping schemes include global,
local, edge-aware, and simulation of the HVS. Global operators compute a monotonously increasing tone map curve
[41]. Local operators map a pixel depending on information
from its spatial neighborhood [42]. Edge-aware operators
separately compress the edges and the image's background

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Color and
Tone Mapping

Inverse Color and
Tone Mapping

Metadata

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Distribution
(b)

(a)

FIGURE 17. (a) The distribution of LDR content with metadata to reconstruct HDR content and (b) the distribution of HDR content with
metadata to reconstruct LDR content.

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and
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FIGURE 18. (a) Simulcast and (b) scalable distribution when several inputs of the same content are available.

82 IEEE Consumer Electronics Magazine

october 2015

HD/UHD
TV (LDR)

Table of Contents for the Digital Edition of IEEE Consumer Electronics Magazine - October 2015