Scott Wilkinson (0:00)

In this episode of Home Theater Geeks, I talk about a new way to represent color reproduction. It's very cool and very geeky, so stick around.

Leo Laporte (0:11)

This episode brought to you by Red Canary when cybersecurity threats hit fast, you need an MDR partner that moves faster. Red Canary delivers 24.7expert MDR support, total visibility, and actionable insights. Plus it helps you detect four times more threats so you can stay ahead with without burning out. Red Canary clears the noise and has your back every hour, every incident. Get the backup you deserve. Visit redcanary.com difference to learn more podcasts.

Chris Chinnock (0:44)

You love from people you trust.

Leo Laporte (0:47)

This is Twit.

Scott Wilkinson (0:59)

Hey there, Scott Wilkinson here, the Home Theater geek. In this episode I'm going to talk about something that gets pretty geeky. But hey, this is Home Theater Geek. So totally appropriate. I want to start by thanking my colleague and friend Chris Chinnock, who is the president of Insight Media, an information and service company for the professional and consumer display industries, as well as cinema and broadcast and all sorts of things like that. Chris wrote an excellent white paper on the subject that I'm going to be talking about today, and he has graciously allowed me to use the graphics that he included in that white paper. We're going to include a URL link to the to his website, insight media.info where there's all sorts of interesting information. He and I have been colleagues for many, many years and he really knows his stuff, so I'm really glad that he allowed me to use his material as the research basis for what I'm going to talk about today. Now, most video geeks have seen what is commonly called a color gamut graph or diagram, also known as the CIE chromaticity diagram, which we can see in graphic number one. So this horseshoe shape that you see here represents all the colors that someone with normal vision can see. The curved boundary that you can see there represents single wavelength or monochromatic colors which only lasers can reproduce. All the colors that are inside that horseshoe shape are combinations of various amounts of different colors. Now, within this horseshoe shape you can see three triangles and a dot. They represent different color what are typically called color gamuts. The dashed line is the BT 2020 color gamut, which is the one used in HDR content, although that's the extreme and it's not usually used to its full extent. The dotted triangle, the smallest one is what's called REC709, more correctly, BT709. That's the color gamut of HDTV. And now we have UHD TV or 4K, which is between those two. The solid line, solid lined triangle that you see there is some display that is the actual representation of what that particular display can reproduce. And I'd say it looks fairly close to DCI P3, so it's probably a 4K TV. Now there's a problem with this diagram. It represents color reproduction at only one brightness level, which is roughly half of the display's capability from darkest to brightest. At much lower or higher brightness levels, the range of colors, this solid triangle you see here would be very much smaller. Now, a better way to represent colors from a video display is using what's called a color volume, which is a three dimensional shape, kind of an odd shape that includes brightness information. We can see that in the next graphic. You can see this is an odd sort of shape. The brightness is represented in the Z axis, the vertical axis. And it's been. The brightness values have been what's called normalized to extend from zero, which is the darkest the display can go to 100, which is the brightest the display can go. Regardless of what the actual nits of the display are. The brightness, which is represented with a parameter called L star, goes from 0 to 100. The X and Y axes, the horizontal axes are called A star and B star and they represent the red green axis and the blue yellow axis. So that's a very accurate way to just to describe or represent how the colors of a video display are reproduced. But it's cumbersome to work with. For one thing, it's three dimensional. To really see it, you need to have to hold a physical object in your hand. Now, it's difficult, it's also difficult to compare two displays. How does this display compare to that one? If you're looking at this three dimensional thing, especially if it's in, you know, represented as it is right here on your screen in two dimensions. So that's really hard to do until now. This is what I want to talk about today. It's very, very cool. It's a new way to represent color volume in two dimensions. It was developed by Dr. Kenichiro Masaoka, who is the principal research engineer at NHK, which is Japan's public broadcasting system. He's also the inventor of the BT 2020 color gamut, which is the gamut that's used in high dynamic range HDR content. Ultimately, for the most part, the color space or range that's used in HDR is a little bit less than BT 2020. That is the absolute maximum that A color range could achieve, and the only way to do that is with lasers. But in any event, he's the inventor of BT 2020, and he's also the inventor of what are called gamut rings. So we start with a color volume in this graphic. It's letter A. So it looks like sort of what we saw just there before. Next, it divides the shape into 10 slices, which you can see in B. And each of those slices is 10 brightness units thick. Okay, so we go from 0 to 100 in brightness, and we slice it into. Into 10 slices. And then as we see in letter C, those slices are squished into one unit of brightness. So I guess they're average. I don't know the exact math of this. Okay, then we take in letter D, the bottom left, we take the second lowest slice and cut a hole in it so that the lowest slice can. You can see through the second slice, you can see what's in the lowest slice. And you do that all the way up. You do that with each of the slices, and each. So each higher slice is stretched with a hole in it to wrap around all the lower ones. And that includes the. The top one, number 10, if you will. You have to really stretch it out a lot so that you can see it with all the previous ones sort of inside of it. And that's really what we see in letter F. On the lower right is what are called gamut rings. Each of these lines is. Is a ring. It's not really circular, but it. It. It is a ring. And so each band, if you will, represents 10 units of brightness. So at the center of this figure in number F, letter F, that's zero brightness. And that makes sense because it's black. There's no light there at all. And then as you go out from the center, it gets brighter and brighter and brighter until you get to the very most outermost one, and that's at 100% brightness, or the brightest the display can be. And so that lets you see a color volume in two dimensions. It's not unlike a topographical map. If you've looked at maps of. Of an area on the earth, you might notice that in some cases, there are lines that are drawn on that map, and those lines represent a given elevation. And so you can see how the elevation changes on a topographical map, just like you can see how color representation changes at different brightness levels in this gamut ring representation.