Color Gamut Demystified

When searching for a new display, you may get confused a bit when confronted with the various ways manufacturers describe their abilities to show more colors. You'll hear terms such as True Color, Wide Color Gamut, Cinematic Color, 4K Color, etc. Let's break down what matters and spend a little time explaining it. When it comes to calibrating a display, Color Gamut is the industry term used for the range of colors available on a display. Simply put, Color Gamut is the number of colors available on your display. And color gamut can be measured using several different standards. The standards that we're concerned most with are Rec.709 (HDTV), DCI-P3 and Rec.2020.

full?d=1518715200.png


The chart above is what we use to calibrate displays. Pay no attention to the inner triangle at this time, just look at the full color triangle that has a hump for a point out towards green. That humped triangle represents the colors that our eyes are able to see in a two dimensional format. Luminance is something that can be measured and displayed in a different fashion which I'll get to later. So going back to the inner highlighted triangle, this triangle represents Rec.709 which is the standard that came out for HDTV. You can see from the chart that displays were only capable of showing less than half of the visible spectrum. It should be noted that before Rec.709 the standard was Rec.601 or SMPTE-C. But I don't intend to make this a history lesson and manufacturers should not be listing this old standard as a spec for any current display. You can see that gamuts on HDTV displays were clearly lacking in the green and red areas of the visible spectrum.

This brings us to today. A lot of manufacturers use the term Wide Color Gamut (WCG) to describe their color gamut. But what does Wide Color Gamut mean exactly? That's a good question and one in which I'm sure we will see several different responses but I view the term as meaning a color gamut larger than Rec.709. It does mean that and it also means a higher bit depth too. Bit depth is the gradation of color from one to another. This means that higher bit depth displays will display more gradations or shades of color from one to the other. So not only are you increasing the number of colors by making the triangle larger, you're also increasing the amount of shades or gradations of each color within the triangle. Make sense? I'll get more into bit depth later in a different post as well.

full?d=1518715200.png


The above image represents the standard where most displays are at today - DCI-P3. It is roughly 26% larger than the Rec.709 standard pushing out more towards the green hump of the visible spectrum and down a bit more towards red. DCI stands for Digital Cinema Initiative and it is the standard used for content delivered to your local digital cinemas. What makes this important is the biology of the human eye. Our eyes see red and green better than we see blue therefore it is relatively easy to see the benefit of an expansion of the gamut into the green and red areas of visible colors.

full?d=1518715200.png


This image represents Rec.2020 or the standard of the future. Outside of some production displays used in mastering content, no displays are capable of displaying Rec.2020 yet. But you can see that the standard does push even further out towards green and red covering most of the visible spectrum. While evaluating a display by eye the difference may not jump out at you unless compared to a Rec.709 display side by side. And the major improvements will be in the green and red portions as those are the areas where the improvements have benefit most. Color gamut has expanded primarily in the green and red areas of our visible spectrum.

Which brings us to evaluating color gamut on displays and how to quantify it. The way to evaluate a display and to relay that in layman's terms is currently being done via a Color Volume measure. Color Volume measures the colors within the triangles above while also adding the third dimension measure (luminance) to the equation. A display is then evaluated as to what percentage of each particular standard it is capable of reproducing. If you have read my LG C7 OLED review here, you have seen these particular measures. Here's a graphic depiction of 3D Color Volume:

full?d=1517362368.gif


The animated gif (courtesy of Bruce Lindbloom's color site) starts out showing the two dimensional Rec.709 triangle and then rotates into showing the three dimensional aspect of adding luminance to the equation.

So when you're looking for a new display and it declares that it is capable of Wide Color Gamut, ask the salesman "How wide?"
 
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Matthew J Poes

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Thanks Steve! This is a great read.
 

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Yep... quite illuminating and colorful, if I say so myself... and I do! :bigsmile:
 

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wow, very insightful. I can sound smart around my husband when we go shopping for a new TV. He'll be impressed with all this jargon.
 

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Great work Steve! Great breakdown of one of the more important aspects of TV advancement! :T
 

Matthew J Poes

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Hey Steve, can you clarify something for me.

How does wide color gamut differ from deep color. Was anything related to deep color implemented?

A lot of projectors from say 2008 on were noted as having an overly wide and inaccurate color space. Is there any way to make use of that or was the excessively wide color gamut still not close enough to DCI-P3 to make use of?
 

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No PJ from was capable of greater than the Rec709 spec... it could be they were just widely innacuarte out of the box?
 

Matthew J Poes

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I know they didn't support beyond that but they did support things like RGBs and were noted in some reviews as being capable of reproducing more green, in particular, than was needed for rec709. Because they were mapped wrong they also were inaccurate. I'm really asking if it's possible to take advantage of that. I assume it would require custom mapping and a special device to fool the player into thinking it's a UHD display.
 

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Well, you still have to calibrate to 709 and the movies are mastered to that spec, so I can't really see how anything additional in the green spectrum would be helpful. You can't float your target green, because you'll be off from what the mastering monitors displayed (thus not having the correct color in your home)... and the projector isn't capable of processing DCI, so you can't feed it any material utilizing the larger color space.
 

Matthew J Poes

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Well, you still have to calibrate to 709 and the movies are mastered to that spec, so I can't really see how anything additional in the green spectrum would be helpful. You can't float your target green, because you'll be off from what the mastering monitors displayed (thus not having the correct color in your home)... and the projector isn't capable of processing DCI, so you can't feed it any material utilizing the larger color space.
So I guess my thought would be that using the processor you would use to trick the player into thinking it was a UHD projector would be setup with presets. With Rec709 you would have a preset accurate for that. When a UHD source is used a custom preset would be engaged that would have custom mapped color to allow the projector to use it's slightly wider color space is an accurate way. I assume it would be accurate because it would have a true wide color gamut to work with.

HDfury makes a device that can do most of this but not the custom color mapping.

I'm sure it's not worth the effort. I suspect I could buy a projector that natively supports DCI-P3 accurately for less than the cost of all this trick hardware. My JVC RS1 wasn't that much wider than 709.
 

Matthew J Poes

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Here is an example of the color gamut of the Hd100 and shows how far off the color points these were from Rec709. I also note how close that looks to the DCIp3 color space. Seems sad you can't make use of that.

B76368BF-BE1C-45D6-9842-26B1ACA83362.jpeg
 

Todd Anderson

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Matt - you have to remember, very - very - little color information is used at those extreme points. Calibration can be performed to 75% of the space and result in great accuracy. Also, with 4K HDR you have to think in terms of color volume (three dimensionally) which then involves brightness... which your RS1 won't have as compared to new gear.

Even with that color space you're showing, you're going to be way off on the at key points, despite having some reach into blues.

If you want 4K through a PJ, just take the leap and buy a true 4K capable PJ with the appropriate processor, etc. Otherwise, I think you'll be throwing cash at something that will result in questionable performance.
 

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I have no idea how I missed all of the conversation above! I don't think I received any notifications for those posts at all. :dontknow: I think Todd answered everything nicely though. If you have any other questions Matt, I'm paying attention now. :hide:
 

Matthew J Poes

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I have no idea how I missed all of the conversation above! I don't think I received any notifications for those posts at all. :dontknow: I think Todd answered everything nicely though. If you have any other questions Matt, I'm paying attention now. :hide:
I've had the same problem. People ask questions and I never see the comments post. Seems to be a random glitch.

Anyway, I knew this would be the answer. I saw some devices coming on the market that could be used to send fake EDID data that seemed like they might allow older displays with a wide color gamut to possibly make use of the new wider color gamut if UHD disks. JVC projectors have been 10 bit end to end (and now 12 bit end to end) for quite a while, so it seemed feasible. Sounds like it wouldn't be worth the effort.

Oh well, time to save up for a new projector!
 

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Yeah it would be too many hoops to jump through and in the end it may not look right anyways.
 

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The human eye and brain can only detect 110 colors. So I take it that our current display technology isn’t able deliver everything we are actually capable of seeing?

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Wayne
 

Matthew J Poes

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The human eye and brain can only detect 110 colors. So I take it that our current display technology isn’t able deliver everything we are actually capable of seeing?

Regards,
Wayne
Did you mean 110 million?

I believe that is the number of rods in our eye. Howany colors we can detect is supposed to be less, like 10 million. I keep seeing articles though that find we can detect more shades than previously thought. One recently showed we could see more green than previously thought.
 

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The number of colors the human eye can detect varies by the year the study was done. According to CIE 1931, it can detect roughly 2.4 million different colors. That would be the big oblong triangle in the images above. However, it only takes into effect the two dimensions. Adding the third dimension - luminosity - increases that number by quite a bit. I've seen more recent numbers ranging from 10 million all the way to 100 million. I have always viewed the 10 million as the safer number myself.
 

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I got the 110 figure from an episode of Forensic Files I recently watched. Looks like they misquoted something – an internet search shows 7,000,000 or so.

Regards,
Wayne
 

Matthew J Poes

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I got the 110 figure from an episode of Forensic Files I recently watched. Looks like they misquoted something – an internet search shows 7,000,000 or so.

Regards,
Wayne
I've read so many different figures. It sounds like the definition of color gradation is ever changing.

I don't know if color science is different, but one problem in the acoustics and audio world is that there isn't actually a lot of academic research in that area. It isn't like other fields where every university from a community college to a large university has ten variations of the area of study and every academic is publishing like crazy. In my field we have literally 100's of journals we could potentially publish in. In the acoustics and audio world a lot of concepts were studied at one time with the technology of the day. Once people felt it was good enough and it no longer served a great academic purpose, the scientific community moved on, and most of the science fell on manufacturers. Unfortunately that makes a lot of that work suspect and often of questionable rigor.

I could see there being a clear motivation for scientific bias in color research right now because it would allow manufacturers to peddle ever improved color gamut's beyond the limits of what is necessary right now. We already see a lot of manufacturer supported academic research in this area promoting higher resolutions, higher dynamic range, and wider color gamuts. My feeling is that, for now, this is all a good thing, as I do think there is room for improvement (based on what little I really know about the topic). I do worry though that we are quickly heading toward a point of perfection where further improvements will net no further increase in visual quality, but allow the continued sale of the next new thing.
 
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