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Exclamation What is Color Volume ?

Note: I previously posted this 'article' back in June 2016, but given the recent increased interest in the subject of Color Volume, not to mention the many misconceptions about it, I decided to revisit it again. I also added a lot of additional info, illustrations, and pictures to it.

A TV's color is determined by its "Color Depth", "Color Gamut", and "Dynamic Range".

Color Depth (or "Bit-Depth", e.g. 8-bit, 10-bit, 12-bit) determines how many distinct color variations (tones/shades) can be viewed on a given display.

Color Gamut (e.g. WCG) determines which specific colors can be displayed from a given "Color Space" (Rec.709, Rec.2020, DCI-P3) (i.e. the color range).

Dynamic Range (SDR, HDR) determines the luminosity range of a specific color - from its darkest shade (or tone) to its brightest.

The overall brightness range of a color will be determined by a display's "contrast ratio", that is, the ratio of luminance between the darkest black that can be produced and the brightest white.

Color Volume is the “Color Gamut” + the “Dynamic/Luminosity Range”.

A TV's Color Volume will not only determine which specific colors can be displayed (the color range) but also that color's luminosity range, which will have an affect on its "brightness", and "colorfulness" (intensity and saturation).


Color Depth

Color Depth, also known as bit depth, is either the number of total bits used to indicate the color of a single pixel (bpp), in a bit-mapped image or video frame buffer, or the number of bits used for each of the red, green and blue color components that make up a single pixel.

A TV's Color/Bit Depth determines the total/maximum amount of distinct colors that it can display. This does not mean that the image necessarily uses all of these available colors, but that it can instead specify colors with that level of precision.

A "Full-Range" 8-bit RGB signal (0-255) refers to the number of color tones/shades (256) that are available in each of the Red, Green, and Blue channels (for a total of 16.78 million possible color variations - ranging from Blacker-than-Black to Whiter-than-White). Note: 8 bits per channel equals 24 bits per pixel (bpp).

For a "Limited-Range" 8-bit RGB signal (16-235), a total 10.65 million color variations will be available. Note: The human eye can discriminate up to ten million distinct colors.

A 10-bit RGB signal has a Full-Range color depth of 0-1023 (1,024 color tones/shades available in each of the Red, Green, and Blue channels for a total of 1.07 billion possible color variations).

For a "Limited-Range" 10-bit RGB signal (64-940), a total 674.53 million color variations will be available.

Note: Generally speaking, the broader the dynamic/luminosity range of the display and content, the more "bits" are needed to avoid seeing "color banding" or "posterization" in the displayed image. 'Banding' occurs more easily in regions of gradual color transitions, such as smooth skies, because the human visual system has different sensitivities at different brightness levels and is particularly sensitive to small changes over large areas of nearly uniform brightness.





Now taking it a step further, a 12-bit RGB signal would have a Full-Range color depth of 0-4095 (4,096 distinct color tones available in each of the Red, Green, and Blue channels for a total of 68.72 billion possible color variations).

Spoiler!

Note: Standard Dynamic Range (SDR) content is usually encoded with an 8-bit Color Depth, whereas High Dynamic Range (HDR) content is usually encoded with a Color Depth of either 10-bit (e.g. HDR10) or 12-bit (e.g. Dolby Vision).

Color Space

The Color Space, sometimes referred to as the "Color Model" (or "Color System"), is a specific organization and representation of colors.

The Color Model is an abstract mathematical model which simply describes the range of colors and represent them as tuples of numbers or color components (e.g. RGB). The Color Space relates numbers to actual colors. Each color in the system is represented by a single dot.

Color Spaces are often represented using two-dimensional slices from their full 3D shape - luminance (brightness) being the third dimension. 'Luminance' is the relative lightness or darkness of a particular color, from black (no brightness) to white (full brightness). These "slices" are useful for everyday purposes because they allow you to quickly see the entire boundary of a given cross-section.

The most saturated vivid colors are located at the outer rim of the region; the least saturated colors are at the center. "Saturation" describes the intensity (purity, strength) of a color's hue (chroma). When a color is fully saturated, it is considered to be in its purest (truest) version.

Spoiler!

The tongue-shaped or horseshoe-shaped two-dimensional "CIE 1931 Color Space" diagram represents all of the 'chromaticities' visible to the average human eye at a specifically defined level of luminance and is usually referred to as "the gamut of human vision".

"Chromaticity" is an objective specification of the quality of a color regardless of its luminance. The CIE 1931 colour chart was the first defined standard that showed the link between the three primary colours of red, green and blue and the way that those colours are actually seen by our eyes and thus provided an overall range from which various Colour Spaces could be created.

Note: The "International Commission on Illumination" - also known as CIE from its French title, la "Commission Internationale de l'Éclairage" - is devoted to worldwide cooperation and the exchange of information on all matters relating to the science and art of light and lighting, colour and vision, photobiology and image technology.



Note: It is impossible to accurately depict the gamut/range of human color vision on a computer monitor.



The next diagram [see Spoiler!] shows the chromaticities of "black-body light sources" (white light) of various temperatures, and "lines of constant correlated color temperature" (specific white points).

Spoiler!

Tech Note: "White" has no definite position in this diagram; rather it is defined according to the color temperature (measured in "Kelvin") which refers to the color of the light source that's being displayed on your screen. In order for your TV to adhere to the director's vision, it needs to reproduce white as closely as possible to the ISF recommended D65 (Daylight 6500K) which is similar to ambient daylight at midday (on a cloudy day). D65 is the standard used throughout the film and TV world.



TV's use additive color mixing with primary colors of red, green, and blue, each of which stimulates one of the three types of the eye's photo-receptors (color-sensitive cones) with as little stimulation as possible of the other two. This is called an "RGB" Color Space.

An RGB Color Space is represented on the "chromaticity diagram" by a triangle joining the coordinates for the three primary colors. Other colors could, in principle, be used, but with red, green and blue the largest portion of the human vision color space can be captured.

Having a specifically defined Color Space is needed so that images can be accurately and consistently reproduced. Without some form of agreed upon standard how would anyone know what a specific colour was supposed to look like? Without this standard how was a program maker, a broadcaster or a TV manufacturer supposed to know what colours to use? This adherence to colour standards is vital in ensuring that what is being produced, broadcast and displayed is correct and retains the content creator's original intentions.




The Color Space is essentially the "container" that determines the maximum color range a digital device can work in but is "device-independent". It defines all possible or realizable colors which can be made from the color combinations that fall within its boundaries. The larger the Color Space, the more colors a particular device can potentially display and the more saturated those colors can be.

Colors that fall outside the chromaticity triangle are said to be "out-of-gamut".


Color Gamut

The Color Gamut defines the specific range of colors (or subset of colors) that a digital device (e.g. TV, computer monitor) can display/reproduce from within a given device-independent reference Color Space and is expressed as a percentage of that Color Space (e.g. 98% of Rec.709; 95% of DCI-P3; 73% of Rec.2020).

Spoiler!

Similar to how an artist might mix their primary colors on a palette in order to visualize the range of colors they have to draw from, the Color Gamut is effectively just a digital palette; except these colors are much more precisely organized and quantified.

Note: "Color Gamut" is often also used to refer to the larger "Color Space" - in which case the two terms are used interchangeably.

The Color Gamut establishes a definite "footprint" within the reference Color Space and is a useful method and tool for users to understand the color capabilities of a particular digital device.



To have an idea of the ability of a display to represent colors that are "true to life", it is important to know how much of a given Color Space their Color Gamut actually covers. Most SDR (Standard Dynamic Range) content uses the more narrow Rec.709 Color Space while most HDR (High Dynamic Range) content uses the much broader Rec.2020 Color Space. [more on "Dynamic Range" later]

Now since most modern displays' Color Gamut usually covered the entire Rec.709 Color Space (or more), there really was no need to differentiate between the two terms because, in this case, Color Gamut did, more or less, equate to Color Space.

However, with Rec.2020, that is no longer the case. No current display's Color Gamut can cover the entire, much wider, new Color Space; not even close. Which is one reason we usually refer to a display's Color Gamut as covering only a certain percentage of a specified Color Space (i.e. P3 or Rec.2020).


Rec.2020 (or BT.2020)

Even though it is usually only referenced when talking about Color Space, and compared to the old Rec.709 and DCI P3 color spaces, it actually specifies and defines more than just the Color Space (as did Rec.709 before it - Rec.709 has been the industry standard for broadcast TV and Blu-ray since the advent of High Definition displays).

Recommendation ITU-R BT.2020-2, which dates back to August 23, 2012 and was revised in October 2015, is a set of standards that defines, in addition to "color space", various other aspects of Ultra HD TV such as display resolution, frame rate, chroma sub-sampling, and bit depth. It is the new standard for UHD displays and players.

The overall standards developed for Rec.2020 were intended to be future proof, so some of them, such as the full Color Space and 8K resolution, are currently unattainable by today's displays.

DCI (Digital Cinema Initiative) P3 is the Color Space currently used by the film industry for Digital Cinema.

That said, UHD HDR movies and shows that are graded for a home release are currently being mastered with a P3 color gamut; however, they are delivered in a BT.2020 "container". Put differently, all UHD HDR content is encoded as BT.2020 for home delivery and every UHD HDR TVs, players, and streaming devices use the Rec.2020 Color Space.

The Ultra HD Alliance (UHDA), specifies that a TV needs to be able to display a minimum of 90% of DCI P3 to receive the "Ultra HD Premium" certification (see "ULTRA HD PREMIUM" Specs).


Dynamic Range

Dynamic Range is - according to Wikipedia - "the ratio between the largest and smallest values that a certain changeable quantity can assume".

When it comes to displays, it refers to its overall brightness range or luminosity range, that is, the ratio of luminance between the darkest black that can be produced and the brightest white (i.e. its "contrast ratio"). 'Brightness' is the relative lightness or darkness of a particular color, from black (no brightness) to white (full brightness).

Note: The presence of any ambient light in a room will significantly impact a TV's perceived contrast ratio.

The human eye is able to easily see objects in both starlight (although "colour differentiation" is greatly reduced at low light levels) and in bright sunlight, even given the fact that on a moonless night objects receive only a very small fraction of the illumination they would on a bright sunny day.

Since it can dynamically adapt to different brightness levels by closing and opening the pupil, the human eye can perceive scenes with a very high dynamic contrast ratio, anywhere from 1,000,000-17,000,000:1 (or 20-24 stops of light), far surpassing the capabilities of a single camera image.



Spoiler!

However, our eyes cannot perform these feats of perception at both extremes of the scale at the same time - it takes time for them to adapt and adjust to different brightness levels - their dynamic range in a given scene is actually quite limited. Nonetheless, it is still higher than the "static" brightness range of most display technology.

At any given time, the eye's static contrast ratio is somewhere between 1,000-15,000:1. In situations of extreme low-light viewing (where our eyes have adjusted to use rod cells for "scotopic/night vision"), our visual system can accommodate an even larger brightness range.

If we consider our eye's instantaneous (static) dynamic range - where our pupil opening is unchanged, like looking at one region within a scene, letting our eyes adjust, and not looking anywhere else - most estimate that our eyes can see anywhere from 10-14 stops of dynamic range, which definitely surpasses most compact cameras (5-7 stops), but is surprisingly similar to that of digital SLR cameras (8-11 stops).


A digital or film-based image can only record so much detail between the darkest shadows of a scene and the brightest highlights, and eventually will render tones at the end of this scale as an effective black or white simply because there is not enough detail available (details in the bright and dark parts of the image will be clipped). The ability to produce a wider luminosity range, or to have a greater range of tones available between black and white, is what is sought when comparing the dynamic range of different cameras or displays.

In practice, it is difficult to achieve the full dynamic range experienced by humans using electronic equipment. Electronically reproduced video often uses some trickery to fit original material with a wide dynamic range into a narrower recorded dynamic range that can more easily be stored and reproduced. In other words, the extended luminosity range of a high dynamic range image has to be compressed to fit into a lower dynamic range to be made visible. This method of rendering is called "tone mapping".

Tone mapping is a technique used in image processing to "map" one set of color tones to another in order to approximate the appearance of high dynamic range images in a medium that has a more limited dynamic range. One of the goals of tone mapping is to be able to reproduce a given scene or image onto a display device such that the "brightness sensation" of the image to a human viewer closely matches the real-world "brightness sensation".

Most displays have a limited dynamic range that is often inadequate to reproduce the full range of light intensities present in natural scenes. Tone mapping addresses the problem of strong contrast reduction, from the scene radiance to the displayable range, while preserving the image details and color appearance important to appreciate the original scene. This is often done at the cost of reducing the global contrast of the scene, but the local contrast is maintained and the image as a whole continues to look natural.

When viewing a real-world scene, our eyes can focus on different parts of the scene and dynamically adapt and adjust for the different light levels of those different areas - our pupils open and close for the different brightness regions of the scene, giving them the ability to make out tons of detail in both the dark parts and bright parts of the scene.

Additionally, the human brain has an amazing ability to take-in all those details, intelligently interpreting the information from our eyes, and "create" a single mental picture that takes into account all those details.

High Dynamic Range (HDR)

When the term "dynamic range" is mentioned, most people automatically think of HDR.

Now given the fact that there are already countless articles/posts and dedicated threads on this Forum on the subject of HDR - not to mention an entire section set aside for it HERE - I'm not going to spend much time on it in this article.

"SDR" (Standard Dynamic Range) movies and TV shows are graded and mastered based on a maximum brightness level of around 100 nits (cd/m²) for the home and around 48 nits for cinema, and a minimum brightness level of 0.1-0.01 nits. [A "nit" is a unit used to measure brightness and is equivalent to a candela per square meter.]

One of the problems with restricting maximum brightness to 100 nits is that the brighter the color, the closer it becomes to white (the brightest color) - so bright colors become less saturated. For example, the brightest saturated blue on an SDR display is a mere 7 nits, so a blue sky will never be as bright or as saturated as it should be.

In contrast, HDR movies are currently being graded and mastered to a maximum brightness level of 1000-4000 nits.

Note: The human visual system can actually detect brightness levels as high as 100,000,000 nits or as low as 0.000001 nits.

With the available maximum brightness of today’s HDR capable displays, a content creator now has the available brightness range needed to represent a sky that is both truly bright and fully saturated, making it seem more natural and much closer to the real-world scene.



Note: The PQ or Perceptual Quantizer (published by the Society of Motion Picture and Television Engineers as SMPTE ST 2084) EOTF (Electro-Optical Transfer Function), that both HDR10 and DolbyVision are based on, actually allows for a peak brightness level of up to 10,000 nits (and minimum brightness levels as low as 0.0001 nits) - think of it as headroom for future expansion [see Spoiler!]. Brighter displays are coming!

Spoiler!

Now some of you might be thinking at this point that 4000 nits is already way too bright (never mind 10,000 nits), but consider this: the ambient brightness of a sunny day with clear blue skies is between 7000-10,000 nits (between 3000-7000 nits for overcast skies and indirect sunlight). 10,000 nits is also the typical brightness of a fluorescent tube - bright, but not painful to look at.

The natural world has a much broader range of color and brightness than current broadcast TV, Blu-rays, and Cinema systems support. A bright sunny day can have specular highlights that reach over 100,000 nits. Direct sunlight is around 1,600,000,000 nits.




Also, bear in mind that those maximum nit values usually only apply to "specular highlights" (small areas of the screen) and are only present in some scenes not all - the overall brightness level of the entire movie will still be around 100-120 nits. This means that the APL (Average Picture Level) of an HDR movie will not be significantly different than for an SDR movie. Increasing the available dynamic range simply gives you more headroom to play with.

Note: An HDR image or video does not guarantee a greater dynamic range unless this greater dynamic range is also present in the original content or scene.

Below are a couple of simulated images showing the differences between SDR and HDR.



Here are a few more simulated images that show the differences between HDR and SDR.

Spoiler!

Here is a quote [see Spoiler!] from Stephen Nakamura a colorist with "Company 3" in LA, who has worked with really high profile directors and cinematographers and knows more about HDR than most people. He has graded in HDR movies like Exodus: Gods and Kings (the first ever movie to be HDR graded); Tomorrowland (Disney’s first HDR grade and a movie made for the format); The Martian; and Joy.

Spoiler!

Now, as Stephen Nakamura pointed out, just because an HDR scene can be a lot brighter (with brighter highlights) and more colorful than an SDR scene it doesn't mean that it should be. The important thing for a colorist when grading for HDR is in trying to preserve the 'creative intent' of the director.

As he puts it, "it’s really all about the aesthetics, so when I grade my movies for HDR, I make sure that I keep the same feel that the cinematographer and the director had intended for the movie... it could look the same [as the SDR grade] or maybe just one scene could look different... again you can take advantage of all of [HDR's available brightness and color] or you can take advantage of none of that... it definitely allows you more creative freedom, that’s for sure".

As an example, if you look at the two simulated images below [see Spoiler!] the correct image that is actually preserving the director's 'creative intent' in this case is the one on the left. Even though the image on the right is a lot brighter, with much brighter specular highlights, and much more colorful, it doesn't reflect the "look" the director was aiming for or the "mood" he was trying to achieve for that particular scene. Brighter doesn't always mean better.

Spoiler!

In essence, High Dynamic Range is about the potential of brighter whites with more detailed "specular highlights" and deeper blacks with more "shadow detail".

But more importantly, HDR, combined with a Wide Color Gamut (WCG), is about having the ability to reproduce the world around us as accurately, realistically, and detailed as possible on a display.


Color Volume

So what is Color Volume?

The concept of "color" can be divided into two parts: chromaticity and brightness.

For example, the color 'white' is a bright color, while the color 'grey' is considered to be a less bright version of that same 'white'. In other words, the chromaticity of white and grey are the same while their brightness (luminance) differs. As previously mentioned, "brightness" is the relative lightness or darkness of a particular color, from black (no brightness) to white (full brightness).

Color Volume includes all colors throughout the entire luminosity range (not just at one specifically defined level of luminance). It is represented by a three-dimensional graph (sometimes referred to as a "3D Color Gamut"). Put simply, the higher the color volume, the better the display can express a vast range of vivid, accurate colors.

“Color Gamut” + “Dynamic/Luminosity Range” = “Color Volume





The next image below [see Spoiler!] compares the Color Volume of two different TVs. The TV on the left has greater Color Volume than the the one on the right. Note the added brightness and vibrancy in the colors.

Spoiler!

Climbing the Staircase

Now coming back to the original premise of my article – that a TV's color is determined by its "Color Depth", "Color Gamut", and "Dynamic/Luminosity Range" (and by extension, its "Color Volume") – I will use an illustration to further explain/illustrate this and show how each component relates to the others.

Now, bearing in mind that no illustration is perfect, I want you to picture a staircase.

Now imagine that the overall height of the staircase represents a color’s luminosity range – from its darkest shade/tone to its brightest. The bottom of staircase would essentially be "true" black, while the top of the staircase would represent "true" white. (Hey! Kinda like a 'Stairway to Heaven')

Now imagine that the overall width of the staircase represents a color’s gamut or range. Each individual "step" of the staircase would represent different brightness levels going from black (or a color’s darkest shade) at the bottom to white (or a color’s brightest tone) at the top.

Tech Note: Even though the overall, maximum width (color gamut/range) of the staircase would remain "fixed" in this case, the width of each individual step (brightness level) in the staircase would vary – narrower at the top and bottom; wider towards the middle (the color gamut, or range of "displayable" colors, will always be broader towards the middle of the brightness range).

Now imagine that the total number of steps in the staircase represents the color depth or bit-depth (the overall number of individual brightness levels/steps in the "grayscale"). The total number of steps (distinct color tones) in this case would be determined by the "bit-depth" (e.g. 256 steps for an 8-bit full-range color depth; 1,024 steps for a 10-bit color depth; and so on).



Spoiler!

If you were to increase the overall height (dynamic/luminosity range) of the staircase, with the overall width (color gamut) and the overall number of steps (color/bit depth) staying the same, the actual height of each one of those individual steps would have to increase.

This could potentially lead to each steps being too tall (which could result in "color banding" or "posterization" becoming visible in the displayed image). This is why it is always a good idea to increase the number of "steps" (bits) when increasing the overall "height" (luminosity range) of a staircase.

If you were to increase the overall width (color gamut/range) of the staircase, with the overall height (luminosity range) and the overall number of steps (color depth) staying the same, then the average width (color gamut) of each individual step would, consequently, be increased.

If you were to increase the number of steps (color/bit depth) in the staircase, with the overall height (luminosity range) and the overall width (color gamut) staying the same, then the average height of each one of those individual steps would, consequently, decrease but the overall size (color volume) of the staircase would remain the same.

However, increasing the number of steps (the bit-depth) would reduce the chances of seeing "color banding" or "posterization" in the displayed image (due to the increased number of distinct values available in each of the Red, Green, and Blue channels) - which would result in much smoother color gradients.

Now if you were to increase both the "height" (luminosity range) and the "width" (color gamut) of the staircase, you would in effect be increasing the overall size (color volume) of the staircase, but the number of steps (bit-depth) would remain the same. The number of steps (bits) in the staircase would have no effect on the overall size of the staircase (its color volume).

I hope you have found this article enlightening (pun intended).

Thank you for reading!

Be sure to check out the second part of my article in the next post below.

Also, please feel free to post a comment.

Richard

You can also check out my article "Light and our Perception of Color"

Last edited by King Richard; 05-21-2017 at 03:40 AM.
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post #2 of 54 Old 04-12-2017, 01:18 AM - Thread Starter
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Arrow Why is Color Volume Important ?

If you haven’t already done so, please be sure to read the first part of my article, "What is Color Volume" (post #1)

As stated in part one of my article, Color Volume is a color’s "Gamut" (chromaticity) plus its "Dynamic or Luminosity Range" (brightness). It includes all colors throughout the entire luminosity range (not just at one specifically defined level of luminance) and is represented by a three-dimensional graph (sometimes referred to as a "3D Color Gamut").




Why is it Important?

Color Volume, the palette of all available colors at all available intensities, is quickly becoming an effective way to measure the precision of colors.

One of the reasons Color Volume matters more today than in years past is because to properly reproduce HDR WCG content on modern UHD TVs, you not only need a display that can get really bright, but one that can also maintain richly saturated colors in those bright areas. Note: Wide Color Gamut (WCG) coverage is also important at low luminance levels not just at high luminance levels.




From Rec.709 SDR to Rec.2020 HDR

In the past, with SDR (Standard Dynamic Range) content, which was graded using the Rec.709 Color Space and a maximum brightness level of around 100 nits, illustrating a display’s Color Gamut on a 2D Color Space usually proved satisfactory as calibrated displays all behaved in a similar manner. Colors were generally well saturated at one luminance level, typically around 75% of the display’s peak luminance.

However, in the HDR (High Dynamic Range) and WCG (Wide Color Gamut) era where luminance levels and color spectrums differ greatly, the 'rules' have changed. A 2D Color Gamut is no longer sufficient to express a display’s ever increasing capabilities – especially when you consider that they are now capable of reaching much higher peak brightness levels (exceeding 1000 nits).

Therefore, new methods of evaluating a display’s performance, which took into account their increased capabilities, needed to be established in order to ensure that the HDR content that was being produced, broadcast and displayed was correct and retained the content creator’s original intentions.


Evaluating Display Capabilities

The International Committee for Display Metrology (ICDM) came up with a method of evaluating a display’s performance which they called Volume-Color-Reproduction Capability (VCRC).

Quote:
This method is particularly important for displays showing video and/or broadcast images, owing to the wide range of luminance levels inherent in the content of those images.

An approximate color gamut volume is calculated for characterization of color reproduction capability of a display in a three-dimensional color space. Luminance and chromaticity of colors are measured at a centered window occupying 4% of the screen area with 40% gray level background (e.g. gray level 102 of 0 to 255 levels).

[PDF: VOLUME-COLOR-REPRODUCTION CAPABILITY]



Tech Note: Color Volume in L*a*b* color space - the L* dimension represents the perceptual measure lightness. a* dimension represents a perceptual uniform color transition from red to green over gray, while b* dimension represents a perceptual uniform color transition from blue to yellow over gray. For each L*a*b* volume, different horizontal cross sections are automatically computed and the overall volume is deduced.


Measuring Color Volume Today

With SDR, when you wanted to find out how many colors a display could show, you would just measure 8 key color points (Black, White, Red, Green, Blue, Cyan, Magenta, and Yellow) at one predetermined luminance level and that would tell you how much of that 2D Color Gamut that display covered.

But now with HDR, it’s a whole new ballgame. To be clear, Color Volume is a much better metric for measuring colors when it comes to High Dynamic Range and Wide Color Gamut. To measure the 3D Color Volume you need to take far more than the 8 measurements you take for the 2D Color Gamut. For Color Volume, you can measure 140 points or more, taken at different luminance levels.

There are a number of different ways to measure and report Color Volume, each with its own advantages and disadvantages, however, the fact is that there are currently no actual 'standard' for how to measure and report it.

If you were to measure the DCI-P3 Color Gamut on two different TVs, they may both measure at 100% of that Color Space, but after adding a luminance (L) value they can appear very different. One display might be able to reach a Color Volume of 100% of DCI-P3 when the other only gets to 67%.

Various workflows are currently being implemented to enable TV calibrators and product reviewers to accurately measure Color Volume. One of those workflow options is from SpectraCal’s (Portrait Displays) CalMAN calibration software.

The measurements are done using the L*a*b* method. The Color Volume coverage of the display, for the Rec.709, DCI-P3 and Rec.2020 Color Spaces, is determined by first specifying a "Peak Luminance Target" and then measuring a minimum of 140 different points with this peak brightness level selected. This reports what percentage of each specific Color Space is being met.

Screenshots below [see Spoiler!] are from the CalMAN 5.8 calibration software.

Spoiler!

"Rtings.com" has now, as of Feb, 2017, started testing TVs for their "Color Volume Coverage" for both the DCI-P3 and the Rec.2020 Color Spaces.

Quote:
We are now measuring the color volume of TVs as it is important for good HDR performance. We have tested all 44 of our 2016 TVs... We test to see how much of the DCI-P3 and the Rec. 2020 color volume TVs can cover... A high coverage of color volume is beneficial for HDR [and WCG] video sources such as UHD Blu-rays, streaming video, and HDR video games. These are the only types of content which take advantage of this increased color volume...

The color volume is significant because most TVs can only produce very saturated colors at a small range of luminance levels. When a TV can't provide vivid colors in very dark or bright scenes, it results in loss of detail. Colors outside of the reproduction capabilities are reduced in saturation or brightness through a tone-mapping process dependent on the TV...

The way luminance is perceived as brightness is not linear. The range of colors displayed at low luminosities (dark scenes) is just as important as for high luminosities (bright scenes), so we linearize the measured luminosities... This linearization is done with the Perceptual Quantizer (PQ) EOTF...

For a color volume measurement to be significant it should correspond to the way we perceive colors at different luminosity levels. The eye is much more sensitive to small changes in luminosity of a dim light compared to a bright one; so although the measured change in luminosity may be the same, the bright source with less perceivable difference should have less impact.

[rtings.com: Color Volume of TVs]

The important thing is, we now have new tools available that can be used to measure Color Volume and report on how well a display performs with HDR WCG content. These measurements are far more accurate and indicative of real-world performance.


Brightness and Color Accuracy

One of the problems with restricting maximum brightness to 100 nits (with SDR content) is that the brighter the color, the closer it becomes to white (the brightest color) - so bright colors become less and less saturated.

As an example, the brightest saturated blue on a 100 nit display is only 7 nits, so a blue sky will never be as bright or as saturated as it should be. In contrast, at 600 nit maximum brightness (peak white), blue would be 43 nits; at a peak brightness of 4000 nits, blue would be 289 nits; at a peak brightness of 10,000 nits, blue would be 722 nits.



Again, in order to accommodate the increasing variation in display capabilities, including their much higher levels of overall brightness, luminance was integrated as a third dimension into the traditional 2D Color Gamut diagram to create the 3D Color Volume. This 3D measurement illustrates how a display reproduces colors at all of the luminance levels of its luminosity range.

A display having a high Color Volume will be able to express every detail of the picture with absolutely precise color accuracy at all brightness levels, just as the director intended and as seen in a real-world scene. The range of colors displayed at low luminosities (dark scenes) is just as important as for high luminosities (bright scenes). The higher the Color Volume, the better the display can express a vast range of vivid, accurate colors.

Spoiler!


HDR: A Full Volume of Colors

HDR content is being graded and mastered at much higher maximum brightness levels than SDR content - anywhere from 1000 to 4000 nits (up to 10,000 nits in the future) - using the much larger Rec.2020 Color Space (today’s movies are currently being graded and mastered using Digital Cinema’s P3 Color Space, but are delivered in a BT.2020 'container').

Below is a quote from Patrick Griffis, VP office of the CTO for Dolby Labs.

Quote:
HDR really unleashed the whole notion of color volume. After 50 years in the world of NTSC, we have just started looking at that little horseshoe diagram [CIE Chromaticity Chart] and we forgot about how bright stuff was, because we all knew it was 100 nits.

With HDR, suddenly, we’ve taken the lid off and are able to reproduce the full volume of colors at brightness levels we could never do before. I kind of think of it as unleashing the potential of what’s possible... This is very important to understand, because it’s color volume not HDR or color gamut that is the key thing.




Mapping Color Volume

Most TVs do not feature the full Wide Color Gamut or High Dynamic Range or the peak luminance of the mastering displays. Additionally, there is more variation in device capabilities today than ever before. This means that mapping between different Color Volumes is critically important for consistent best-possible reproduction of TV imagery.

When the professional mastering display, used to grade the movies and TV shows for the home, has a bigger Color Volume than that of the target display, the colors need to be "compressed" or "re-mapped" – "tone-mapped" (for brightness) and "gamut-mapped" (for the color range) – in order to make the larger Color Volume 'fit' into the smaller one.

This is referred to as "Color Volume Mapping". The closer the Color Volume of the target display is to that of the mastering display, the less mapping is needed, thus maintaining the look of the original scene. The colors that end up outside of the target display’s 're-mapped' Color Volume will be "clipped".

Spoiler!

TVs did not typically require "Color Volume Mapping" in the past because most display devices had a gamut and dynamic range that matched the encoded signal. However, this is no longer the case with today’s HDR WCG displays.

HDR systems with Dynamic Metadata (SMPTE-2094), like Dolby Vision or HDR10+, optimize content mapping from the mastering display to the target display, providing (somewhat) future-proof scalability.

Dynamic Metadata can track content characteristics in real time (on a scene-by-scene or even frame-by-frame basis) to adaptively provide temporal consistency during rapid image brightness changes. Using dynamic tone-mapping, the system knows what the content is doing and uses that information as a guide to map it down to the display’s specific capabilities.


100% Color Volume

Color Volume was one of the hot topics at CES this year. Held in Las Vegas every year, CES is the world’s largest gathering place for all who thrive on the business of consumer technologies and where next-generation innovations are introduced to the marketplace.

Leading the charge was Samsung with their new 2017 QLED model TVs.

Note: The info below comes directly from Samsung's website, so you should take it all with a 'grain of salt'.

Quote:
Samsung’s 2017 QLED TVs... offer dramatically improved color performance, displaying DCI-P3 color space accurately and – in another world first for Samsung, QLED TVs are capable of reproducing 100 percent color volume. This means they can express all colors at any level of brightness – with even the subtlest differences visible at the QLED’s peak luminance.

Samsung Electronics’ 2017 QLED TV recently received verification from world-class testing and certification association, “Verband Deutscher Elektrotechniker” (VDE), for its ability to produce '100 percent color volume.' [LINK #1]

VDE provided verification for Samsung’s QLED TV based on the organization’s expertise in color volume testing... The designation, a first for any global TV manufacturer, illustrates how color volume is quickly becoming an effective way to measure the precision of colors... '100 percent color volume' presents color that can be expressed regardless of the different levels of brightness.

Samsung integrated a new Quantum dot material into its QLED displays which improves luminous efficiency... Utilizing new Quantum dot (QD) material, Samsung’s QLED TVs offer outstanding color volume, pinpoint color accuracy, improved brightness and the deepest blacks on an active display.

Generally, a TV’s color-rendering capabilities diminish as brightness levels go up, leading to color distortion on-screen... With better color volume, the elevated brightness of the QLED actually increases the vividness and maintains color integrity... to reproduce color volume effectively, a lot of brightness is required.

[LINK #2] [LINK #3]

QLED '100% Color Volume' Promotional Pics [See Spoiler!]

Spoiler!

Please Note: This thread is for general discussion on the subject of “Color Volume”. It is not meant to be a discussion of a particular brand/model of TV, or to “pit” one TV against another. Please save those comments for the dedicated “Owner Threads” for those specific TVs.
Furthermore, I do NOT want this thread to turn into yet another “OLED vs. LED/LCD” debate. There are already more than enough of those on this Forum. I purposely avoided making those comparisons in my article for this very reason. Thank You!


In the coming years, we will see displays having increasingly wider color gamuts, ever expanding dynamic ranges, and much higher peak luminance levels - with an ever increasing emphasis being placed on Color Volume.



If you enjoyed this article, please leave a comment below.

Thanks again for reading!



Richard
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post #3 of 54 Old 04-12-2017, 01:57 AM
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Very nice. Perhaps you could make it clearer earlier on in the "Anatomy of a CIE Chromaticity Diagram" diagram that it represents one slice taken out of the colour volume diagrams below. (a slice at the 100 nits level?) - and consequently, the label at the top "all colors visible to the human eye are in this diagram" is a bit misleading.
Also, the "notes" are in an impossibly-small font size.
Overall very nice
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Excellent work, King Richard!
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Excellent work, King Richard!
Very Nice!
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Very well done King Richard. You have taught and helped me (and I am sure others) over time.
Thanks for your efforts!
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Brilliant. Thank you for taking the time to write this.
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The most confusing thing about color volume is that it is not a volume, as measured. Instead, it is reported as a percent of the colors displayed by an idealized display of the same luminosity range. The second most confusing thing, which follows from the preceding, is that a very dim display could have a very high color volume, because its failure to produce bright saturated colors doesn't lower its color volume if the colors are outside its luminosity range. (The easy way to get a perfect color volume of 100% is to turn off the TV.)

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Originally Posted by mrtickleuk View Post
Very nice.
Thank You my friend. And thank you for your post.

Quote:
Originally Posted by mrtickleuk View Post
Perhaps you could make it clearer earlier on in the "Anatomy of a CIE Chromaticity Diagram" diagram that it represents one slice taken out of the colour volume diagrams below. (a slice at the 100 nits level?)

Actually, the fact that the 2D Color Space "CIE Chromaticity Diagram" represents only a "slice" from the full 3D Color Space (i.e. the Color Volume) is mentioned no less than 4 times in the Color Space section. Just sayin'

As to the "100 nits" number... With SDR (Standard Dynamic Range) content that is mastered at a maximum of 100 nits, the Color Space "slice" is usually taken at around 75% of the maximum luminance value (or ~75 nits). But now with HDR (High Dynamic Range) content, with maximum brightness being all over the map, that is no longer the case.

So I believe it varies (lets just say I haven't found a source that specifies a specific number of nits for HDR).

One source actually said that the Color Space "slice" is usually taken at 50% luminance (that is, a horizontal slice at the vertical midpoint of the Color Volume) But unfortunately I can't confirm that percentage number at this time.

Quote:
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...the "notes" are in an impossibly-small font size.
Sorry about the "Notes" being so small. I did it that way 1. to save space 2. to make them "stand out" from the rest of the paragraphs and 3. simply for the sake of "artistic expression".

They don't look that small at all on my computer monitor and are very "legible".

EDIT: I decided to go ahead and change the "Notes:" to a larger print Size. I instead chose a different Font to make them stand out.

Thank You!

Richard
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Bravo Richard!!!!! Bravo!!!!!!!

Superb article!!!!!
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Nicely written & displayed bud, must have taken you quite a while to write it, we all appreciate it!
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Actually, the fact that the 2D Color Space "CIE Chromaticity Diagram" represents only a "slice" from the full 3D Color Space (i.e. the Color Volume) is mentioned no less than 4 times in the Color Space section. Just sayin'

As to the "100 nits" number... With SDR (Standard Dynamic Range) content that was mastered at a maximum of 100 nits, the Color Space "slice" was usually taken at around 75% of the maximum luminance value (or ~75 nits). But now with HDR (High Dynamic Range) content, with maximum brightness being all over the map, that is no longer the case.

So I believe it varies (lets just say I haven't found a source that specifies a specific number of nits). One source actually said that the Color Space "slice" is usually taken at 50% luminance (that is, a horizontal slice at the vertical midpoint of the Color Volume) But I can't really confirm that unfortunately.
Isn't it the case that it's an "angular" slice? In other words, not a perpendicular slice (relative to Y) at some given luminosity value (75 nits) in the "fat part" of the color volume, but rather a it's actually a 45 degree (or whatever) slice through the volume where one tip (maybe green?) of the 2D representation is at 75 nits (or whatever) and another tip (blue?) is like at 10 (or whatever) and red around 25. So if you kind of visualize a 3d model of the color volume (like the one you presented), rather than just "slicing" perpendicular to the Y axis (and parallel to the x and y axis), you "cut" the volume at an angle relative to the Y axis. And when you flatten it out, you still get a "fat" slice of the volume. I don't know. I'm just trying to visualize it. So maybe the 'average' luminosity is like 50% of the maximum luminance value? But there's no hard and fast luminosity across the 2D slice?

Maybe I'm not thinking about it right. But one of the visual models there seemed to show the triangles within the color volume, and they seemed to be angular slices. But maybe that has nothing to do with this whole luminance value slice issue. Sigh... it's interesting, but confusing. This was an incredibly useful write up, however. Learned a lot. Thanks.
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post #13 of 54 Old 04-12-2017, 04:40 PM - Thread Starter
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Quote:
Originally Posted by Jeffrey Suchocki View Post
Isn't it the case that it's an "angular" slice? In other words, not a perpendicular slice (relative to Y) at some given luminosity value (75 nits) in the "fat part" of the color volume, but rather a it's actually a 45 degree (or whatever) slice through the volume where one tip (maybe green?) of the 2D representation is at 75 nits (or whatever) and another tip (blue?) is like at 10 (or whatever) and red around 25. So if you kind of visualize a 3d model of the color volume (like the one you presented), rather than just "slicing" perpendicular to the Y axis (and parallel to the x and y axis), you "cut" the volume at an angle relative to the Y axis. And when you flatten it out, you still get a "fat" slice of the volume. I don't know. I'm just trying to visualize it. So maybe the 'average' luminosity is like 50% of the maximum luminance value? But there's no hard and fast luminosity across the 2D slice?

Maybe I'm not thinking about it right. But one of the visual models there seemed to show the triangles within the color volume, and they seemed to be angular slices. But maybe that has nothing to do with this whole luminance value slice issue. Sigh... it's interesting, but confusing. This was an incredibly useful write up, however. Learned a lot. Thanks.

No.

The entire "slice" is in fact taken at a single given luminance value and is therefore "perpendicular" to Y.

Thanks for your comment. (And you're welcome!)



Richard
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post #14 of 54 Old 04-13-2017, 01:13 AM - Thread Starter
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Nicely written & displayed bud, must have taken you quite a while to write it, we all appreciate it!

Thank you!

Yep! It did take quite a bit of time to write.

Including the "original" post in June of last year, and the numerous revisions of this one, I would say that I spent over two weeks in total on part 1, plus another week on part 2. This includes tons of research, fact-checking (I'm a perfectionist), locating and adding all those pics, illustrations, etc., and then finally writing and "formatting" it.

...However, I loved every minute of it.

(If I didn't enjoy writing these articles, I wouldn't be spending so much time on them - you know I don't actually get paid for this right? I wish! )

And a big Thank You! again to all who posted a comment.


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Yes absolutely! Happy Ēostre everyone: the festival of the Pagan goddess of Spring. Another festival hijacked by the Christians just like Xmas

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post #17 of 54 Old 04-16-2017, 11:17 AM - Thread Starter
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Yes absolutely! Happy Ēostre everyone: the festival of the Pagan goddess of Spring. Another festival hijacked by the Christians just like Xmas

A little off topic , however, since you brought it up...

Did you know that English is one of the only languages in the world (German being another one: "Ostern") that named the holiday after the pagan goddess Ēostre (or Ostara) [although a lot of that "history" is uncertain and up for debate].

In almost every other international language, the holiday is called by some permutation of "Pesach", the Hebrew word for the Passover holiday (or "Pascha" in Aramaic). For instance, in French (a Latin-based language and my native tongue) it is called "Pâques". So...


But you're right, it's a well know fact that most of our religious holidays have pagan roots as do things like the "Easter Bunny", the "Christmas tree", and so on.

"Interlude" over, now back to our regularly scheduled program...



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post #18 of 54 Old 04-17-2017, 09:52 AM
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Good read Richard, thanks again for the great article!
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post #19 of 54 Old 04-26-2017, 03:02 AM - Thread Starter
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Just a note to let everyone know that the First Post has been revised and expanded.

I added a lot of extra material to most of the sections - including additional info and lots more images and illustrations. I also added 2 brand new sections to it and made a few changes and improvements to some of the previous material.

I also took this opportunity to correct a few small mistakes that were bothering me and do a bit of reformatting. (Hey, I happen to be a perfectionist, with perhaps a little bit of OCD thrown-in for good measure. In fact, you will notice that a lot of my posts on the Forum often have a "Last edited by" footnote at the bottom of them - many of those "edits" are often only to correct a small spelling mistake or something stupid like that. )

Additionally, I decided to take the advice of my friend @mrtickleuk and change the print size of my "Notes" (except for the very first one), which were too small and hard for some to read (they looked fine in the browser I was using, but viewing them in a different browser I noticed they were indeed quite small). I instead used a different "Font" to make them stand out.

I am planning to start working on "Part 2" of my article hopefully this coming weekend (which will be the 2nd Post of my Color Volume Thread that I currently have marked as "Reserved!"). I plan to have it finished sometime next week if all goes well.

So stay tuned!



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id been wondering how i was supposed to be reading those 2d color graphs, still no clue on the 3d ones, but at least im making progress, thanks!
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post #21 of 54 Old 04-26-2017, 06:27 PM - Thread Starter
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id been wondering how i was supposed to be reading those 2d color graphs, still no clue on the 3d ones, but at least im making progress, thanks!
You're welcome!

Well if you can wrap your head around those 2D "CIE Chromaticity charts", its not very difficult to understand the 3D ones (i.e. the Color Volume).

Remember, the 2D CIE Chromaticity charts represents one single two-dimensional slice (or cross-section) from their full 3D shape (3D "Color Gamut" a.k.a. Color Volume) taken at a specifically defined level of luminance or brightness.

Again, as I mentioned in my article, that "2D Chart" (the entire shape) represents all of the 'chromaticities' (colors) visible to the average human eye at that specifically defined brightness level and is usually referred to as "the gamut of human vision". The Color Space that a particular display uses (either Rec.709 or Rec.2020) is represented by different size triangles within it.

As an example, lets consider a TV with a maximum brightness of 1000 nits.

Now imagine we took a 2D color "slice" at every 10 nits brightness level, from 0 nits to 1000 nits - the first slice would be taken at 10 nits (since a slice at 0 nits would only show black) and the last slice would taken at 990 nits (since a slice taken at 1000 nits would only show white - the brightest "color").

Now if you were to take all those slices and stack them all on top of each other (starting with the darkest one and working your way up to the brightest one) you would end up with the 3D Color Gamut or Color Volume of that particular display.

Now don't forget that the slices in the middle of the stack would be broader (wider).

Hope that makes sense.

Richard

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Richard, this is great! I wonder if the boys at CNET and DIGITAL TRENDS are as well-informed on the topic as you obviously are?
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Richard, this is great!

Thank you my friend!

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I wonder if the boys at CNET and DIGITAL TRENDS are as well-informed on the topic as you obviously are?

I doubt it! (kidding)



Richard

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post #24 of 54 Old 04-28-2017, 10:53 AM
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CNET would write a 4 paragraph article, probably on 4 separate sub-pages with Next/Previous links. One or two picture on each page, and then they'd think they'd dealt with it. I've never seen anything in-depth or comprehensive on there.
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post #25 of 54 Old 05-01-2017, 08:22 AM
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Richard, when you're finished I think you should send a document in PDF format to Dave Katzmaier & Geoff Morrison at CNET, and Caleb Denison at Digital Trends.
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post #26 of 54 Old 05-16-2017, 02:37 PM - Thread Starter
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Part 2: Why is color Volume Important ?


I just wanted to let you know that I finally finished the second part of my article (post #2). If you haven’t done so already, be sure to first read the first part of my article (post #1) .

I also made further improvements to the first part (post #1) of my article, adding more information, including more pics and illustrations. I also added a lengthy Quote from professional colorist Stephen Nakamura to the HDR section.

Stephen Nakamura is a colorist with "Company 3" in LA, who has worked with really high profile directors and cinematographers and knows more about HDR than most people. He has graded in HDR movies like Exodus: Gods and Kings (the first ever movie to be HDR graded); Tomorrowland (Disney’s first HDR grade and a movie made for the format); The Martian; and Joy.

I hope you like it, thank you!



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post #27 of 54 Old 05-16-2017, 02:51 PM
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Was it really necessary to spam the same post into seemingly every thread on the front page?

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post #28 of 54 Old 05-16-2017, 03:08 PM - Thread Starter
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Originally Posted by vipergts2207 View Post
Was it really necessary to spam the same post into seemingly every thread on the front page?

Well... not every thread!



It was just the best way I could come up with at the time to let everyone know that I had finally finished part 2 of my article (a lot of people enjoyed the first part and were looking forward to the second part).

(P.S. Not everyone checks out the "main" LCD page you know. Some people just read the same one or two threads and that's it. So they would have no way of knowing about my article.)

I have just one small "correction" to make regarding your comment though, those different threads that I posted in were NOT all on the first page. They just automatically moved up to the top of the first page after I made my post (because that's just how it works). Plus, it was only 1 short post!

Just sayin'

You also have to understand that I spent probably close to 100 hrs of my own free time on this article (part 1 and 2). I don't actually get paid to write these articles you know (I wish! ). What would be the point of spending all this time writing these articles if nobody actually read them (or even knew about them).

But I apologize if I "offended" you or anyone else.


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Last edited by King Richard; 05-18-2017 at 08:44 PM.
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post #29 of 54 Old 05-17-2017, 01:07 AM - Thread Starter
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Color Volume Limitations with HLG !


Here's a paper I was just reading from "Dolby Labs" that I thought you might be interested in.

Click the LINK below.

>PDF: Color-Volume Limitations with HLG<


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post #30 of 54 Old 05-17-2017, 01:39 AM
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Originally Posted by King Richard View Post
Here's a paper I was just reading from "Dolby Labs" that I thought you might be interested in.
Seen that before. We need to point out that of course, as a competitor, it's in Dolby's interest to find any downside to any other HDR system and highlight it.

What they are completely ignoring is all the massive benefits of HLG, and what it was designed for: ie a single signal path for both SDR and HDR for broadcasting, so you don't need to have a "HDR channel" and a "SDR channel" - everyone watches the exact same broadcast and the HDR signal is backwards-compatible to SDR for normal TVs. And is isn't hampered by needing metadata, so it can be used with live broadcasts.

HLG meets its design goals admirably, and those of us with Samsung TVs who have watched the HLG demos saw no obviously visible colour issues.
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