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Better Pixels in Professional Projectors
White Paper
Better Pixels in Professional Projectors
January, 2016
By
Chris Chinnock
Insight Media
3 Morgan Ave., Norwalk, CT 06851 USA
203-831-8464
www.insightmedia.info
In collaboration with
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Better Pixels in Professional Projectors
Table of Contents
Introduction ................................................................................................................4
What are Better Pixels? ..............................................................................................4
Consumer TV vs. Professional Projection .................................................................................. 4
Higher Brightness ....................................................................................................................... 5
Benefits & Trade-offs ..........................................................................................................................................5
Uniformity .................................................................................................................................. 6
Benefits & Trade-offs ..........................................................................................................................................6
Enhanced Resolution .................................................................................................................. 6
Benefits & Trade-offs ..........................................................................................................................................9
High Dynamic Range and Contrast ............................................................................................ 9
Benefits & Trade-offs ........................................................................................................................................ 11
Wide Color Gamut (WCG) ....................................................................................................... 12
Benefits & Trade-offs ........................................................................................................................................ 13
High Frame Rate (HFR) ........................................................................................................... 14
Benefits & Trade-off .......................................................................................................................................... 15
Bit Depth ................................................................................................................................... 15
Benefits & Trade-offs ........................................................................................................................................ 16
3D.............................................................................................................................................. 17
Benefits & Trade-offs ........................................................................................................................................ 18
Summary ................................................................................................................................... 18
Implications for the Capture, Processing and Distribution of Better Pixel Content18
Better Pixel Capture .................................................................................................................. 18
Better Pixel Processing ............................................................................................................. 19
Better Pixel Distribution ........................................................................................................... 20
Implementing a Better Pixel Projector.....................................................................20
Applications for Better Pixels ..................................................................................21
Cinema ...................................................................................................................................... 22
Design ....................................................................................................................................... 26
Training & Simulation .............................................................................................................. 26
Rental & Staging ....................................................................................................................... 26
Corporate .................................................................................................................................. 27
Conclusion ...............................................................................................................27
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Table of Figures
Figure 1: Various TV/Cinema Resolution Standards ..................................................................... 7
Figure 2: Snellen, Simple and Hyper Acuity (Source: Arris) ......................................................... 8
Figure 3: Range of natural and human luminance values (Source: Dolby) .................................. 10
Figure 4: Reduction in dynamic range through the capture-to-display pipeline (Source: Dolby) 10
Figure 5: HDR vs. SDR Images (Source: 20th Century Fox)....................................................... 11
Figure 6: Various Color Standards on the 1931 CIE Chromaticity Diagram and u’v’ color spaces
....................................................................................................................................................... 12
Figure 7: 24 vs. 48 frames per second .......................................................................................... 14
Figure 8: Various EOTFs being Considered for HDR Content and Display................................ 16
Figure 9: System Contrast Formula (Source: RealD, Technology Summit on Cinema) .............. 23
Figure 10: System Contrast Ratio (Source: RealD, Display Summit 2015) ................................. 24
Figure 11: Theater Contrast for Various APLs and Scattering/Reflectivity Parameters (Source:
Barco) ............................................................................................................................................ 25
Table of Tables
Table 1: Acuity vs. Resolution and Viewing Angle (Source: Arris) .............................................. 8
Table 2: The Need for Better Pixels in Professional Projection Applications .............................. 21
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Int r o du c t i o n
This white paper will provide an overview of a range of video enhancements that are
emerging now in the consumer TV and professional AV industries. These are collectively called
“better pixels” as they will improve the viewing experience – in some cases, quite dramatically.
The objective of the paper is to define what these “better pixel” features are, how they will
benefit professional users and the implications for the entire content-to-display pipeline. The
key professional application for video content today is cinema, so we will mostly focus on
this. However, the technology is starting to spread to other advanced professional markets like
simulation, medical, military, etc. – which is why this paper is important
While the focus of the paper is on professional projection, no discussion of better pixels can
take place without an understanding of the consumer television market and how better pixels are
expected to be adopted there. In reality, the consumer TV and professional AV markets are
pushing each other in the development, standardization and deployment of better pixel hardware
and software.
W h at ar e Bette r P i xe l s?
Consumer TV vs. Professional Projection
The term “Better Pixels” has arisen to describe a basket of advanced imaging and display
technologies. In consumer TV’s, these have centered on the development of what is being
termed Ultra high Definition (UHD) Phase 2.
UHD Phase 1 has focused on increasing the resolution of consumer TVs from 1920 x1080 to
3840 x 2160 – sometimes referred to as Ultra High Definition, UHD or 4K. Content is mastered
using the 709 color gamut (like HDTV content), usually with 8-bits per color and 30 frames per
second. It is basically HD content with standard dynamic range and color volume but with more
pixels.
UHD Phase 2 maintains the same UHD resolution, but seeks to add additional better pixel
parameters that include:
• High Dynamic Range (HDR)
• Wide Color Gamut (WCG)
• High Frame Rate (HFR)
UHD Phase 2 is being driven by Hollywood for the creation of new content. The first UHD
TVs with some of these advanced features are in the market today, with many more coming.
The first cinemas to support these attributes are also established already, including the Dolby
Vision cinemas and new IMAX cinemas.
The development of these solutions will increase image quality and in turn, will drive
adoption of higher image quality video in other professional projection markets like simulation,
rental and staging, corporate, theme parks, museums, medical, government and intelligence,
military and more.
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However, the definition of “better pixels” in professional projection is a goes wider than the
UHD Phase 2 definition. Key elements here include:
• Higher Brightness
• Enhanced Resolution
• High Dynamic Range (HDR) and Contrast
• Wide Color Gamut (WCG)
• High Frame Rate (HFR)
• Uniformity
• Bit Depth
• 3D
Let’s now take a look at each of these better pixel elements in greater detail to understand
what each means and what the benefits are, but also, what are the consequences of implementing
the feature.
Higher Brightness
Increased brightness is a key feature of a better, more realistic, viewing experience. This is
trivial for small, direct view displays; but becomes a challenge when going to large, immersive
screen sizes. Higher brightness also allows, as a component of High Dynamic Range for parts of
the image to literally be brighter than current images, which has an impact on viewers.
For example, in the consumer TV segment, most standard dynamic range (SDR) TVs offer
300-400 nits of peak luminance. The new HDR TVs offer 600-900 nits of luminance. This level
can even go higher for small areas of the TV to deliver bright specular highlights, for example.
The same thing is happening in cinema projectors, especially for 3D viewing. For example,
conventional cinema projectors with Xenon lamps project 3D images in the 3-4 fL (10-14 nits)
range compared to 2D movies which are about four times as bright. The light loss is a result of
the optics and filters needed to create the left and right eye images for 3D. Many have
complained about the noticeably low light levels with 3D.
The solution is here today in the form of 6p (six primary) RGB laser projectors. These
systems feature laser light sources operating at six primary wavelengths – 2 in the blue, red and
green. Each pair of RGB wavelengths can encode the left or right eye image, which are
separated at the viewer by glasses with corresponding spectral filters (note that other 3D
technologies could also be used). Because the lasers can be ganged together to increase light
levels, 3D projection can now occur at 14 fL (48 nits) – the same as with 2D projection.
Benefits & Trade-offs
Increasing the brightness for 3D projection is a huge benefit for the consumer and the impact
is significant. Why? - Because human perception of brightness is non linear. In the above
example, the brightness of the image increased 4X but our perception of this increase is higher as
we are in a dark environment in the theater.
This effect works the other way in bright ambient environments. Increasing the output of a
projector from 4000 to 8000 lumens, for example, is noticeable, but the image is not perceived as
twice as bright.
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These perceived changes are not only impacted by the absolute brightness levels and
ambient illumination, but also by the screen technology and other complex human visual
adaptation parameters like the changing of the iris diameter.
Also note that the human visual system perceives luminance on the screen in nits (or cd/m²).
In the case of a projected image, this needs to be translated back to lumens out of the lens. To go
from 3fL to 10fL 3D in cinema does not seem like a big task – but it is as the light source for the
projector must be more than 3X as bright. Without a technical evolution like laser illumination,
that means effectively installing 3 projectors.
Uniformity
Peak brightness and uniformity are tied somewhat. Brightness levels need to be appropriate
for the environment. That means very bright elements in a pitch dark room can be painful, while
too dim an image causes eyestrain and poor image quality. For a projection system, the projector
lumen output and the screen size, gain and material all play significant role in determining that
right brightness level.
Uniformity is an important parameter for any display, but is often not measured in detail in
flat panels, while it is in projectors. The uniformity drop off from center to edges can be
noticeable in some lamp-based projection system, rolling off to 50-75% of the peak brightness at
the screen center. The advent of RGB laser systems for projectors has really changed the
uniformity capability with uniformity of 95% not uncommon now.
The uniformity is impacted by the screen characteristics such as the screen material and
gain. A matte white screen acts like a Lambertian reflector scattering light uniformly in a
hemisphere. But many screens have gain which increases the light reflect near the surface
normal and reduces the light in the mid to extreme angles. That is fine for a long narrow theater,
but can be problematic for other venues. Gain screens create hot spots that are brighter than the
rest of the image – thus appearing as a non-uniform image. Sometimes screens are curved to
reduce this effect; but curving has a negative effect on contrast. Screens need to be considered as
part of the uniformity consideration, especially for multi-blended projector applications.
Benefits & Trade-offs
The lack of uniformity is not always that noticeable until you see a uniform gray or color on
the screen. Or, it can be very noticeable for higher gain screens or when viewing from an
oblique angle. The hot spots can be very distracting.
Moving to laser-based projectors with higher lumen outputs that allow for lower gain
screens offers a clear benefit for end users.
Enhanced Resolution
Figure 1 shows some important resolutions currently being used (both mainstream and state-
of-the-art) in different video applications:
• 720 x 480 - Standard Definition (SD) or DVD
• 1920 x 1080 - Full High Definition (FHD)
• 3840 x 2160 - Quad High Definition (QHD) or Ultra HD (UHD) or 2160p
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• 4096 x 2160 - DCI-4K or 4K
Figure 1: Various TV/Cinema Resolution Standards
The first three resolutions are now common in consumer TVs while the DCI-4K resolution
is reserved for cinema and cinema-related applications.
As noted earlier, UHD Phase 1 is really about ONLY increasing the resolution to UHD, and
to date, this represents the vast majority of UHD or 4K content, as well as the available flat
panels and projectors in consumer and professional applications.
In professional projection, the definition of “enhanced resolution” is less defined. UHD and
4K projectors clearly qualify, but there are also many projectors with resolutions between FHD
and UHD or 4K. In addition, some projectors can do “image shifting” to create higher resolution
images from lower resolution microdisplay. Finally, many applications feature blending of
multiple projectors to create large screens that can have well in excess of 4K pixels.
Professional projection systems require a screen (front or rear) and the size of the screen and
the viewer distance has a big impact on the “perceived resolution.” For example, the on-screen
pixels from a 4K projector are twice the size when moving from a 100” to a 200” screen. And,
the perception of resolution is also dependent upon how far away the viewer is from the screen.
Can a viewer see the difference between a 100” image viewed at 10 feet if the projector has
4K or FHD resolution? Conventional wisdom suggests that the limit of visual acuity for a person
with 20/20 vision is one arc-minute of resolution. This math says that the 20/20 viewer probably
can’t tell the difference in resolution in the above example, all other factors being equal. But this
idea of Snellen or 20/20 reading acuity is based on the physical layout of the rods and cones in
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the eye. When looking at an eye chart, it is measuring the eye’s ability to recognize symbols and
their orientation with a human perception level of about 30 cycles (pixels) per visual degree.
Beyond this are two other levels of acuity. Simple acuity refers to the retina’s maximum
Nyquist limit, which is about 60 cycles/degree. Hyperacuity is the ability to notice even finer
details such as the misalignment of line segments (vernier acuity) beyond 60 cycles/degree
(Figure 2).
Figure 2: Snellen, Simple and Hyper Acuity (Source: Arris)
What we “see” from a display depends upon the native resolution of the display and how far
away we are (which determines the viewing and cycles/degree). Table 1 shows various
combinations of display resolution and viewing angle along with the corresponding acuity type.
Table 1: Acuity vs. Resolution and Viewing Angle (Source: Arris)
What this table means is that increasing the resolution of the display allows you to see fine
details even from a long distance (smaller viewing angles). As a result, the benefits of more
pixels depend upon the content. Content that has low spatial frequencies (i.e. not a lot of details
and edges), or –fast- moving components will not look substantially better with increasing
resolution. Typically static content with lots of details and edges (e.g. a spreadsheet) will look
noticeably sharper and crisper as you increase the pixel count.
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A crucial part of this story is Barten’s Contrast Sensitivity Function: while the above table
might hold only for pixel on/pixel off (white vs. black pixels/lines), the sensitivity to detail also
depends on the contrast of the detail – so it may be that for detail with lower contrast, the
pixel/degree limit may be lower.
Perceived resolution will also be impacted by the room ambient levels as this can decrease
contrast and impact our acuity. It also depends upon the screen technology. Not all screens
support higher resolution images. For example, some light rejecting screens use prismatic
elements that limit their use to HD, not 4K resolutions.
Benefits & Trade-offs
Having more pixels in the projector allows the possibility to deliver an increase in perceived
resolution to the end user. Sometimes these benefits are tangible like the ability to display fine
details that may be critical for the task at hand. Sometime the benefits are more subtle like the
“feeling” the image is crisper, sharp or focused.
Perceived resolution is dependent upon the projector resolution, screen, viewer location,
room ambient and the content – and these cannot always be controlled. Developing a definition
for “better resolution” is therefore quite difficult. Since most content today is projected in the
Snellen acuity range, perhaps a definition of “better resolution” is one where the projection
solution allows the delivery of images that are in the Simple acuity range. This is a concept we
seek industry feedback on.
When does offering a “better resolution” solution make sense? Clearly, if viewers are seated
close to the screen, you don’t want them to see pixels, so increasing resolution may make sense
in such situations. When viewers are further back, the need for increased resolution become
more content and cost dependent. If the increase in crispness is important and there will be high
spatial frequency content, than more pixel can be warranted. However, there is always a cost to
increasing resolution in terms of complexity, system volume, bandwidth and dollars.
High Dynamic Range and Contrast
The real world contains a wide range of luminance values – about 15 orders of magnitude in
cd/m2 or nits (Figure 3). The human visual system can cover most of this range, but not
simultaneously. Our eyes adapt to the average light level so that our steady state luminance
range is more like 3.7 orders of magnitude (103.7= 5011:1).
The steady state adaption of the human visual system is complex and not tied to just the
average illumination level of a particular scene. For example, if the viewer is focused on a bright
object, the eye will adapt to that luminance level quickly, making it harder to see darker details.
So what happens when content is captured by a camera, processed, distributed and displayed
on a TV or projector? Figure 4 shows how the colors and range of luminance (contrast) is
reduced through this process. One of the reasons why a TV or projector doesn’t look exactly like
the real world is the fact that the colors, brightness and range of luminance are reduced. Note
that 3D parameters like depth perception and parallax are also important parameters to achieve
this realistic look and feel.
Modern professional cameras can capture 11-14 f-stops of luminance, but this wide dynamic
range is not preserved. In the production process, this range is “squeezed down” to a smaller
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dynamic range. In television, the current practice specifies that the peak luminance of the
mastered content will not exceed 100 nits while the black level is set at around 0.1 nits. In the
cinema, the DCI specification calls for a 2D luminance of 48 nits (14 fL) and a 3D luminance of
24 nits (7 fL). Other professional content may have a wide range of peak luminance and black
levels.
Figure 3: Range of natural and human luminance values (Source: Dolby)
Figure 4: Reduction in dynamic range through the capture-to-display pipeline (Source: Dolby)
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The specifications for standard dynamic range (SDR) content were developed in the CRT
days where mastering CRTs had the same luminance range as consumer TVs. From a practical
standpoint, a luminance range of 0.1 to 100 nits made sense as it matched the display technology.
As LCD TVs and projectors became more prevalent, this mastering range was not changed.
Instead, if the display had higher peak luminance, the content was simply scaled from the 100
nits to whatever peak level the display offered. The dynamic range of the display may have
improved, but the basic dynamic range of the content remained the same.
High Dynamic Range or HDR changes the way content is mastered so that it now has a
greater range in luminance values. Then, HDR displays can show this wider range to great
effect. This is illustrated in Figure 5.
Figure 5: HDR vs. SDR Images (Source: 20th Century Fox)
HDR is an increase in the contrast ratio. This often means an increase in the peak luminance
as well as a decrease in the lowest luminance levels. In theatrical projection for example, it is
mainly a reduction in the black levels, while for TVs, it is a change in both.
There is no definition of an HDR display, but in projection, sequential contrast in excess of
perhaps 5,000:1 without a dynamic iris, would probably be considered to be HDR contrast. But
intraframe contrast is also important and what checkerboard pattern you use matters as well.
These remain non-standardized attributes at this time.
Benefits & Trade-offs
The added value of HDR is twofold: more realism and more creativity. Matching the
dynamic range of the human visual system better and showing more detail in dark scenes makes
the perception of the digital image more realistic. Furthermore, having more degrees of freedom
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adds value to the creative process. Like the painter having a bigger pallet, HDR gives more
options to the digital content creator.
The challenge with transmissive display technologies (flat panel or projection) and HDR is
the desire to increase brightness and reduce black levels simultaneously. That is quite hard to do,
and has a direct impact on cost and complexity. Emissive approaches offer greater long term
potential for HDR.
Wide Color Gamut (WCG)
Wide Color Gamut (WCG) is a term that is applied to content or displays that have a color
gamut beyond the existing color standard. For consumer TV and most professional applications,
this means beyond Rec.709. For cinema, this means beyond DCI-P3.In both markets, the
Rec.2020 gamut is considered the target for WCG.
Figure 6: Various Color Standards on the 1931 CIE Chromaticity Diagram and u’v’ color
spaces
Rec.2020 is the largest color space and does the best job of showing all of the colors
available in nature (Pointer’s gamut), plus many additional colors (neon lights, LED lights,
computer generated colors, etc.).
The left image of Figure 6 shows how three color standards are overlaid on the horseshoe of
visible colors using the 1931 CIE xy method. The right side of the figure shows another way of
showing the same information but using the u’v’ coordinates. The u’v’ space is an improvement
on the xy space as it is more linear than xy.
As can be seen, P3 and 2020 expand the colors visible on the display considerably beyond
Rec.709. A typical example is the color cyan, as appearing in nature in sky- and ocean-colors.
This is most noticeable in the expanded red and green colors and the saturation of these colors
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(closeness to the edge of the horseshoe). The 3 color points (R, G and B) of Rec.2020 are located
exactly on the boundary locus of the 1931 CIE chromaticity diagram. This means that they can
only be reached by perfectly monochromatic sources.
Benefits & Trade-offs
Displaying content in the P3 or 2020 color gamut has clear advantages over content
displayed in 709. Not only is it possible to show more colors, but these colors can be more
deeply saturated. People clearly see more saturated colors, offering a solid benefit.
Deeply saturated color also offer an addition benefit known as the Helmholtz-Kohlrauch
(HK) effect. This effect means that deeply saturated colors look brighter than the same color
when less saturated – even if both have the same luminance. The strength of the effect varies by
color, but can contribute to the perception that the image is up to 30% brighter. That’s a
significant benefit to moving to a P3 or 2020 color space.
There are several challenges in the move the WCG. One is realizing displays that can
achieve the 2020 gamut. Quantum dots are the leading candidate in flat panels and RGB lasers
or LED are viable in projection. But the 2020 color gamut has no tolerances so no display
current can say it is 2020-compliant. This needs to change.
Secondly, there will be a much bigger need for color remapping algorithms. That means
taking content that is mastered in one color volume and displaying it in a display with a different
color volume.
In the cinema market, movies are mastered in the P3 color gamut and shown on projectors
that are calibrated to show P3 colors. But the RGB laser projectors can create colors that are
outside of the P3 gamut and are close to the full 2020 color gamut.
Stretching to colors from the P3 master to the wider colors available in the RGB laser
projector will probably not happen in the cinema because of the tight control of the creative
process and respect for reproducing the director’s intent. But as 2020-capable projectors and
display show up in homes theme parks, museums and other venues, additional issues will arise.
For example, if a near-2020-capable display is available and content is mastered in a smaller
color volume like P3 or 709, operators may be tempted to stretch the colors to the wider color
gamut. This will create an image that is not what the content creator intended, but it will be done
nonetheless. Developing algorithms that do this well without distorting other colors and ruining
flesh tones will be desirable. Such gamut mapping algorithms should be carefully evaluated for
each application.
In addition, there will be the need to reduce color volume. This will occur when 2020
master content is played back on a P3 or 709 display or P3 content played back on a 709 display.
For these scenarios, there are two types of solutions: clipping or perceptual rendering.
Clipping means the saturation of the color, which is beyond the capabilities of the display,
are reduced to what the display can natively produce. This is usually done be reducing the
saturation by calculating a vector from the color back to D65 and seeing where it intersects the
edge of the native color volume. The color is then displayed with this reduced saturation level.
A second method to deal with out-of-gamut colors is called perceptual rendering. Here, the
idea is to try to select a new color or series of colors that might look similar to the original color.
In other words, if a pixel with cyan is out of gamut, maybe a combination of blue and green at
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the right saturation and luminance levels within the native gamut of the display can approximate
the original cyan color. These colors may be created by spatial dithering (flashing) or temporal
dithering. Again, this requires more sophisticated processing, but these techniques provide the
freedom for display manufacturers to differentiate their performance.
High Frame Rate (HFR)
High frame rate means different things to different groups of people. For those offering
content now at 30 fps, going to 60 fps is high frame rate. But the UHD phase 2 specification
calls for UHD content to be able to be mastered and delivered at 120 fps.
Figure 7: 24 vs. 48 frames per second
In the theatrical world, high frame rate (HFR) means going from 24 to 48 or 60 fps. This
has already been pioneered on The Hobbit movies to mixed reviews. The next Avatar movie is
probably going to be in HFR but reports suggest this will be in variable frame rate from 24 to 60
fps. From a technology viewpoint, going to 2K at 120fps or 4K at 60fps is perfectly possible, as
are variable frame rates.
High frame rates need to consider the capture and display techniques. Higher frame rates
result in less blurring, but the speed of the object and the capture frame rate determine the
amount of blurring. In addition to frame rate, one must consider the shutter angle in capture and
playback. This impacts perception of motion blur and judder.
A number of groups are working on developing techniques that allow for capture of content
at high frame rates of 120 or 240 fps, with processing techniques that can create finished content
at various frame rates and shutter angles. Such tools would expand the creative tool box
allowing traditional 24 fps 180-degree shutter angle “film like” content with all kinds of other
combinations going up from there. This requires more post production, but can be used to create
new looks and experiences. Projection systems are particularly adept at being able to adapt to
these new capabilities.
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Benefits & Trade-off
Reduction of motion blur is generally accepted to be a desired outcome as it increases the
clarity of the image and makes viewing of faster moving objects less objectionable.
However, for movies, the 24 fps rate is likely to be mainstream for some time. Films have a
certain look that includes the motion blur. Movies are often about suspending belief so having
content that looks too “real” can be a negative and not a positive.
Increasing frame rate has its consequences technically too. Mainly, the bandwidth of the
image processing to display pipeline needs to support the higher frame rates.
In addition, some solutions may employ frame rate conversion algorithms (like converting
24 fps content to 60 fps content) which can introduce many type of artifacts and change the
entire “look” of the content. The viability of these should be carefully assessed for each
application.
Bit Depth
Bit depth refers to the number of digital bits devoted to image quality. It typically refers to
the bit depth per color in an RGB video format, so 8-bits per color is a 24-bit video – standard
today. 8 bits per color means that for every color channel (like R, G or B), there are 28=256
distinct video levels between black and white. In total, there will be 28*28*28=16.777.216
different combinations, potentially representing unique colors.
Capture systems and some post production processes work with 12- or even 16-bits per
color, but most professional HDTV work today is done at 10-bits per color, with the final
rendering done at 8 bits for distribution to the end user in many consumer and professional
applications.
Digital Cinema requires content mastered in 16 bits and delivered to the theaters with 12-
bits per color. Professional content varies from 8 to 12 bits, depending upon the need and
application.
The distribution of code values over the luminance ranges is called the “gamma curve”. The
name ‘gamma’ comes from the exponent used in representing luminance coding in video levels:
L=Vγ. Since in many cases the shape of this curve is not exactly a power law, a more generic
term is used: Opto-Electric Transfer Function (OETF) at the side of the camera, that encodes
optical properties into signal codes, and Electro-Optical Transfer Function (EOTF) at the display
side, that translates video signals into linear-to-light optical parameters. And for HDR in
particular, new OETF and EOTFs curves are needed. That’s because the existing curves were
designed for standard dynamic range content and simply scaling these code values to an
expanded range won’t work. Why? Two reasons.
For one, the curves were designed to try to have steps between code values be about the
same from a visual perception point of view. Stretching them messes up this relationship.
Secondly, expanding the range with only 8 bits per color does not provide enough gradation
between steps. The result is “banding” or posterization in content. This may be familiar as
discrete bands in a sky scene or shadow details, for example.
As a result, HDR content needs at least 10-bits per color for the finished product. But the
gamma curve issue is still a bit undecided.
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So far, the leading candidate for wide adoption is the so-called “PQ” or Perceptual Quantizer
curve. This has been standardized as SMPTE 2084 and is part of the new Blu-ray 4K
specification. Figure 8 shows the PQ curve along with two 709 curves, and the BBC HDR
proposed curve as well.
The shape of the PQ curve was designed to match human perception over a wide luminance
range, with the bit depth extendable depending upon the range of luminance values covered. But
most importantly, for the first time a code value is tied to a specific luminance level. That means
when the content creator wants a certain pixel to be at 100 nits, a properly designed display will
reproduce it at 100 nits – if it uses the PQ curve.
Multiple other HDR transfer functions have been developed as well. Some of them are for
cameras to be used at capture; others (such as the BBC/NHK Hybrid Log Gamma) to resolve
issues of backwards compatibility.
Figure 8: Various EOTFs being Considered for HDR Content and Display
Benefits & Trade-offs
With more pixels, more colors and greater dynamic range, more bits are needed to keep the
image looking smooth and lifelike. The PQ curve for 10 bits and higher content creation and
display is desirable, but other new curves may be suitable for certain applications as well. These
need to be evaluated carefully for their impact on the ecosystem and their backward
compatibility.
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Moving to higher bit depth has ramifications throughout the acquisition, production,
distribution and consumption pipeline. Delivering 10-bits per color to the home requires a major
upgrade. Delivering it in professional applications will be challenging as well as equipment may
have to be upgraded to support this.
3D
Stereoscopic 3D is still a big element in theatrical. For consumer TVs, 3D has faded from
interest in North America and Europe, but is still popular in Asia. Virtual reality may actually be
how 3D is reintroduced to the consumer market going forward.
3D is also used in a range of specific professional applications. That includes CAD design
for automobiles, architecture or aircraft, visualization of computer generated models or 360-
degree video content, medical imaging data and much more.
To create a 3D image, the left and right stereo pairs are presented in a time sequential
manner. (This is the case for a single projector only; For dual projection, the images can be
shown simultaneously) That means the projector has to run at twice the normal rate. This fact,
plus the methods used to optically encode and decode the stereo images, leads to significant loss
of brightness. RGB laser projectors address this issue as discussed in the Higher Brightness
section.
3D projectors also need to have high stereo contrast – that is, excellent separation of the left
and right images with little overlap. High contrast projectors with appropriate “black time”
between images, is the key to high performance.
Are 3D pixels better pixels? If you can visualize or perform your task easier in 3D, then
they should be considered a better pixel. But these pixels are only “better” if the content is
acquired and processed correctly and the display system can present images with minimal
eyestrain or distortions. That is not always the case as 3D can be hard to acquire or create
correctly.
Stereoscopic 3D only provides one of the cues that humans use to see, interpret and
understand a 3D world. What 3D content provides is a single binocular stereo pair (left and right
eye images) with horizontal parallax only. In the real world, we can move our heads left and
right to acquire multiple horizontal parallax views. We can also move our heads up and down to
acquire vertical parallax.
The limitations of glasses-based stereo displays also impact the image quality. This is so
called accommodation-vergence mismatch issue. In the real world, when we look at an object
our eyes focus (accommodate) on the object and our eye “toe-in” or converge at the same time.
These fine muscle movements are calibrated by the brain help us understand how far away the
object is.
In 3D displays, the point of focus is always the display but our vergence can change
depending upon whether object is in front of or behind the screen. Accommodation and
vergence are only matched when the object is at the screen plane. Otherwise, this mismatch
causes eyestrain that can lead to the discomfort some people feel. That is why minimizing this
mismatch range is so important, but this must be done in content creation.
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Autostereoscopic displays have been developed too that allow 3D viewing without glasses.
This address one deficiency by adding more horizontal views, but in so doing, most techniques
today also introduce sweet spots and transition zone, which can be even more disturbing.
Light field displays go further and holographic displays will be ideal, but these are still quite
experimental at this stage.
Benefits & Trade-offs
3D displays offers clear benefits in entertainment and multiple professional applications – if
the content is created well and the display system is high quality. The ability to see spatial
relationships that are not possible in 2D displays is extremely powerful, but only if done
correctly. Fortunately, many of these applications are now mature enough to understand how to
best create and display 3D with high quality.
There are drawbacks of course. In addition to the human factors issues described above, 3D
requires users to wear glasses, which is not always ideal. Plus, running the display at twice the
frame rate and adding additional technology to display the left and right eye images separately,
adds complexity and cost, often leading to lower efficiency as well.
Summary
The idea of better pixels as an all or nothing proposition is the wrong way to think of it. In
reality, professional projection systems will come to market with various combinations of better
pixel attributes. These will be designed to fit specific application needs and price points and to
provide differentiation in the product line. Some combinations will be more powerful than
others, however.
HDR with 4K resolution, wide color gamut and 10-bit processing will become an
increasingly popular combination, we believe. HFR and 3D will find specialized uses.
Improvements in brightness and uniformity will be led by RGB laser and LED projectors and
will expand as these products become more mainstream.
Im pl i cati o n s fo r t h e C apt u r e , P r o ce ssi ng an d
D i str i bu ti o n o f Bette r P i xe l C o nte nt
Better Pixel Capture
The capturing of content with better pixel attributes is most mature in the movie segment.
Here, large format single-imager cameras with an RGGB pixel arrangement (Bayer pattern)
dominate. These cameras offer 12-15 f-stops of dynamic range, a wide color gamut capture and
speeds that can go up to 240 fps with 4K, 5K, 6K and even 8K resolution. This is how most
better pixel video content is being generated today, but the cameras are costly.
Also costly are the storage devices needed to capture large pixel images along with the
associated processing and on-set monitoring devices and monitors. In effect, the entire near
realtime rendering and display of HDR and WCG content is now becoming possible. This
allows content to be de-Bayered into a YCrCb or RGB format and output as RAW data or
compressed in common video formats.
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The content has a gamma curve applied – either the PQ curve or proprietary log-based
curves. On-set HDR monitors can then play back the HDR content. Most of the playback
monitors support a native P3 color gamut at this time, but most will allow Rec.2020 content to be
input with out-of-gamut pixels perceptually rendered or clipped to the P3 gamut or highlighted to
showcase them.
Development of better pixels broadcast TV equipment is much further behind. Here,
cameras are typically three chip RGB types. The experiments being done today are mostly
using modified cinema gear, however, which is not ideal for the lens requirements of broadcast
TV and many other professional applications.
Development of non-cinema cameras that can support HDR, wide color gamut, expanded bit
depth and other better pixel attributes is in the early stages of development. As a result, it is
likely that most “better pixels” content in the near term will be generated with cinema-grade
equipment.
Better Pixel Processing
The workflow upgrades needed to work with better pixels content depends very much upon
the application and the better pixel attributes that need to be managed. In the movie and post-
production environment, there is a desire for on-set near realtime playback of just captured
content. Canon, for example, has shown solutions that meet this need today and others will
follow.
Most work is done in non realtime. Here, non-linear editing software and color grading
tools need to be updated to support better pixel content. Once most content is coming in at 4K to
6K resolution with wide color gamut and high dynamic range, tools need to be able to support
this. Software solutions from a number of companies are now available to enable this workflow.
Outside of the cinema and post-production community, development of better pixels
processing is being done in specialized segments. For example, in broadcast, the move from 60
fps to 120 fps is a key better pixels area of investigation. HDR is also being looked at for
application to UHD-4K as well as HD content as the benefits are not dependent upon the
resolution. However, color gamuts are still mostly locked at 709 as this has been the standard for
a long time.
In the simulation market, high dynamic range content and projectors have been available for
some time, although they have not been called that. Here, achieving the darkest black level is
critical for good contrast so the entire image generation pipeline has been optimized to support
this workflow. So far however, this segment has paid little attention to wider color gamut. But
they do like to have 120 fps content to reduce motion blur and the potential for nausea in the
simulator.
Automotive and aircraft design is clearly interested in lots of pixels, high dynamic range and
wide color gamuts to be able to create as realistic simulations of their designs as possible to
make design decisions. The pipeline to do this exists today.
Beyond these specialized markets, there seems to be little ability to generate and process
better pixels content in a standard way and format. This will remain an issue for wider adoption
for some time.
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Better Pixel Distribution
Distribution refers to the movement of better pixels video within a professional facility or
environment, the distribution of content from one location to another, and the final connection
from the playback device to the TV, monitor or projector.
In a professional facility or environment, lightly compressed or uncompressed video is
common. Light compression formats like J2000, TICO, VC-2, DSC and others are emerging as
next generation solutions in some of these professional markets.
Realtime distribution of better pixel content remains an issue. In broadcast for example,
quad 3G-SDI is now used for 4K content at 30 fps, but other solutions will be need to move to 60
fps. IP solution, 12G SDI and other approaches are being considered with some advanced
facilities doing some initial installations. This is an expensive upgrade which will slow adoption.
For non realtime distribution from one place to another, compression is used except in the
most critical applications. This may be light compression or medium to heavy compression,
depending upon the needs of the application. Since most better pixel content is also 4K
resolution today, compression is often needed to squeeze the content into a smaller pipeline.
HEVC is the leading new codec for 4K compression for live transport over IP and other
applications like Ultra HD Blu-ray, but others are also being seriously considered. This
includes’ Google VP-9/VP-10, Cisco’s Thor and Mozilla’s Daala which are proposing royalty-
free options to the royalty-bearing HEVC codec. These codecs should support most better pixel
features, but again, will have to be carefully evaluated for an application.
Distribution using these codecs can be for cable/satellite TV, over the top TV, or
professional distribution over Internet infrastructure. Compression values will vary depending
upon the link bandwidth and/or desired video quality.
In ProAV applications, distribution is likely over IP networks using fiber or CAT cable,
HDMI, HD-BaseT or DisplayPort connections. There are many different configurations possible
and many variations in each connection scheme, so extreme caution is urged when choosing a
physical connection method. All can support 4K distribution but support for better pixel features
may be problematic.
These same connection options will also power the final display/projector link. Obviously,
the projector or display must support better pixel features if you deliver it to the display, so make
sure it does.
There is a lot more complexity to these connectivity and processing issues that are beyond
the scope of this white paper. As a result, we want to focus a little more closely on the needs of a
better pixel projector.
Im pl e m enti ng a Bette r P ixe l P r o je c to r
As we have noted already, different markets and applications require/want different better
pixel features. Development of better pixel projectors is not without its trade-offs, however.
Issues include:
• Size: the most important law of optical design in projectors is étendue. Étendue can
only increase through the optical path. That means that as you start increasing light
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sources for higher brightness or modulator size for higher resolution and brightness,
the projector size quickly scales up too.
• Efficiency: all the power you are not using to project on the screen is still pulled
from the power plug and internally dissipated as heat. Dual modulation designs to
achieve HDR, like Dolby Cinema, introduces even more inefficiency.
• Processing: Image processing done inside or outside the projector is needed for
image scaling, color processing, compression decoding, HDR signal decoding and
more. This can add latency and synchronization issues for multi-projector
applications using blending and/or warping.
• Lifetime: all physical components have a limited lifetime. The most critical
components are those that must manage a big thermal load. When trying to scale up
brightness, the internal load increases, as does the need to careful cooling. This is
even more critical in applications where the projector is built for professional
applications, some of them running 24/7.
• Cost & Complexity: A better pixel projector offers stunning performance, but with
increased cost and complexity.
Let’s now consider some markets where better pixel projection solutions are being
implemented.
A ppl i cati o n s fo r Bette r P ixe l s
Table 2 shows a number of better pixel attributes for projection cross referenced with a
variety of professional markets. An X indicated that that feature is highly desired in that market
segment. As can be seen, there is broad desire for improvements with these attributes.
Table 2: The Need for Better Pixels in Professional Projection Applications
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But can the industry deliver better pixel projectors? We will explore this and the
consequences in the next section.
Cinema
In the cinema market, there are several very impressive better pixel offerings. One key trend
is the use of red, green and blue lasers as the light source coupled to a 3-chip DLP engine with
4K resolution that can run at 60 fps.
In addition to the better pixel features of 4K and high frame rate of 60 fps for the cinema
market, the laser source can deliver very close to the full 2020 color gamut. That is because the
laser primaries are very near the primaries required in the 2020 specification. This is one on the
few projectors that can display this color gamut.
The laser sources are also configured to provide a 6p or 6 primary 3D capability as well.
That means there are two principal red, green and blue laser wavelengths –one set for the left eye
and one set for the right eye. Using spectral separating glasses, the user can then see the 3D
content. And, this content can now run at the standard 14 fL of peak brightness due to the high
lumen output of the projectors.
The other major advantage of the RGB laser projector is the increased uniformity of the light
out of the projector. Now, the center to edge drop off can be as little as 10% compared to over
25% in a Xenon lamp cinema projector.
Finally, content for the cinema must be mastered to DCI specification, which includes 12-
bits per color. So, the current class of RGB laser cinema projectors meet most of the checklist
items for a better pixel projector. .
To create an HDR cinema projector requires a new design to the standard 3-chip DLP prism
architecture, or a big trade off in terms of efficiency. The typical Xenon-lamp based DLP 3-chip
DLP projector has a contrast ratio of about 1800-2000:1. Moving to an RGB laser source
increases the native contrast beyond 2500:1. Further increases are possible by further aperturing
of the optical system, but with the loss of a lot of light and the thermal and electrical
consequences as well.
To solve this problem, two new designs have been developed by IMAX and Dolby which
both claim to offer HDR capabilities added to all of the other features mentioned above.
The IMAX design throws away the prism and creates a design where the 3 DLP chips are
mounted in the engine and aligned without the prism. This is to reduce scattering and other
optical issues that reduce contrast.
The Dolby design is essentially two 3-chip DLP engines in series. The first engine acts as a
normal cinema engine while the second one adds an additional level of modulation.
Neither company has published contrast specification, but it is believed the IMAX design
achieves about 8000:1 full on/off (sequential) contrast ratio, while the Dolby design should be
much higher.
Besides having a superior projector, controlling the room environment is critical for
achieving superior image quality. Even moderate levels of ambient illumination can degrade
high image contrast and desaturate the wide color gamut of the image.
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In studies conducted by RealD and Barco of the cinema environment, they noted that there
are four main contributors to the final contrast ratio reaching the eyes of the audience.
• Sequential contrast ratio - projector black state
• Projector lens veiling glare
• Auditorium ambient light level
• Auditorium contrast ratio
The sequential contrast ratio is mostly a measure of how dark the black state is in the
projector. Anyone who has been to a theater knows there is always that glow even with no
content on the screen. Black is not black. This is the area where HDR projectors can really
increase the contrast ratio.
Projector lens veiling glare happens when stray light reflects off multiple surfaces and shows
up as a glow at some other point on the screen, reducing contrast. This is calculated by
measuring the MTF from the ANSI checkerboard contrast – a conservative measurement that
yields a contrast of about 1300:1. However, measured in-theater contrast varied from 400-
1700:1.
Figure 9: System Contrast Formula (Source: RealD, Technology Summit on Cinema)
The auditorium is not as dark as you might think. Those exit lights add far more light than
commonly believed. Measured contrast was in the 850-980:1 range
Finally, the theater has a contrast ratio as well. This is minimized by have black light
absorbing walls, carpet and seats, but according to Dolby, it can still be 5% or a contrast ratio of
200:1. And that is with no people in the theater. Once you add people, their faces and clothes
reflect more light, further degrading the contrast.
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