RGB: Full vs. Limited
By Chris Heinonen on
When using a Blu-ray player or a video game system, you often have many color space selections to choose from. The most common choices available are YCbCr, 4:2:2, 4:4:4, RGB, RGB Full or Enhanced, and RGB Limited. For the most part they output the same content in different ways except for RGB Full. So what does this Color Space control mean, and how should you select it?
When an image displays on your TV, Monitor, or Projector, it uses RGB. Except for a few rare cases, every pixel on your screen is made up of Red, Green, and Blue sub-pixels. Everything sent into your display becomes RGB at some point. Not everything sent to your display is RGB to start with.
So why do we have YCbCr and RGB? That itself could be its own article, but it involves Black and White TV, the transition to color, and human visual perception. RGB treats everything equally while YCbCr allows you to treat Black and White and Color information differently. Since we have a higher sensitivity to Black and White information than to color, this allows us to compress color more (the CbCr part of YCbCr) while leaving Black and White with more detail. Our eyes can’t see the difference but we save lots of bandwidth and storage space.
RGB Full and RGB Limited are a different story. The names are confusing, as you would assume you always want the full information. Why would someone ever choose to have something limited? Well it comes down to TVs vs. PCs and how they handle a video signal.
TVs use a video range from 16-235. It considers levels below 16 to be black, and information above 235 is white. A calibrated TV will never display anything below 16 as anything other than black. Most will also treat everything over 235 as white since it should not exist in video content.
PCs are different and use a range from 0-255. There is no data below 0 or above 255 with an 8-bit video signal as there are only 256 possible values. In short, this is much simpler to understand as the TV concepts of Blacker-than-Black and Whiter-than-White do not exist.
RGB Full and RGB Limited exist because of this difference. TV programs and movies use the 16-235 range of values. Video games and PCs use the 0-255 range of values. Since TVs and PC Monitors use different scales, there has to be a way to convert between the two. Setting this RGB Full and Limited setting does that.
With a TV you should always use the RGB Limited setting. Limited refers to the values being limited to 16-235 and not the Full 0-255 scale. With TV and Movies, it leaves them untouched because they are already in the 16-235 range. When you play a video game, it will convert the 0-255 range to the 16-235 range. If it did not do this, shadow and highlights would be pure black or pure white, and the image will look off. You aren’t losing anything by using RGB Limited, but if you use RGB Full with a TV you are losing details. You’ll want to make sure you have Brightness and Contrast set correctly by using a Calibration Disc like Spears & Munsil.
The image below takes the image at the top of this piece and displays it as a TV will when using RGB Full. You see washed-out highlights while the bottom of the ramp is all black. These are highlight and shadow details we will lose.
On a computer monitor you use the opposite approach. RGB Full will display video games and other 0-255 content at the correct 0-255 range. TV, Movies and other video range content expands to use the full 0-255 range of a computer display. If you use RGB limited instead, shadows will be gray instead of black and highlights will be dull. You will not take full advantage of the dynamic range of the PC monitor and content will have a washed-out look. The image below is the opposite of that above where now we are missing highlights, they are slightly gray instead of white, while blacks are a dark gray and not black.
While poorly named, RGB Full and RGB Limited allow you to use AV devices (Blu-ray players, Video Game systems, and more) with a TV or a PC Monitor without having to keep adjusting the settings. By using this control correct, you see all the shadows and highlights you should regardless of the display. You also will not need to calibrate your TV twice because of the different types of content. Hopefully this clears up some of the misunderstandings people have about this setting.
What about HDR?
With HDR video, the good news is that you don’t need to worry about RGB Limited and RGB Full. Unlike SDR, HDR has code values that correspond to exact brightness values on-screen, and the encoding of it is designed around what is humanly perceptible. Also, by using 10-bits instead of 8-bits and assigning half of those bits for what is traditionally the SDR range of images, it has far more data than an RGB Full range image would have to essentially eliminate banding unless the banding is part of the source (due to limited storage space and bitrate issues).
Because of this, you don’t need to worry about selecting RGB Limited or Full with HDR, it will effectively ignore this choice since it doesn’t apply to HDR content. Though we still recommend using RGB Limited for SDR content for the reasons outlined in this article.
August 30, 2014 Update
I’ve noticed a lot of discussion about this and some more misconceptions about how Full and Limited RGB work with video game consoles in particular. Hopefully I can address a few more of these questions to make it easier to understand how to set this up correctly.
Q: Since video games use the Full RGB palette, shouldn’t I use Full RGB when playing video games and then Limited RGB for movies?
A: No. Most video games are designed using the Full RGB spectrum since they are designed on computers which use that. However, when you are playing a Full RGB game and your video game console is set to Limited, it takes this into account. The video levels are shifted from 0-255 down to 16-235 and the gamma curve is adjusted to match a TV as well. You aren’t losing anything as the system is accounting for this.
Q: When I choose limited, I get a washed out image. When I choose full, shadows are crushed. Which is correct?
A: If you are on a TV, then Limited is still correct. The washed-out image is caused by your brightness setting being too high. You should use a calibration disc, like the free AVS 709 disc, World of Wonder, or Spears & Munsil, to set this correctly. Then your black levels will be correct in limited, you will see shadow details, and it won’t be washed out.
Q: My TV supports Full mode, shouldn’t I use this?
A: No. TVs support Full to make them easier to calibrate. Most TVs will not display a black level below 16 because video content should never have it. By letting you see Black 15 or 14, it can make it easier to calibrate the display and get the black level correct. However, you really should not use this as your main setting as most displays are not designed to display levels below 16, and often introduce color tints when doing white levels past 240 or so. Additionally, if you restrict yourself to levels 16-235 you wind up with a brighter image with a better contrast ratio, as you can turn up the contrast level higher. Contrast Ratio is the thing your eye notices most, and so it will produce a more pleasing image.
Also, since any non-video game content will only use 16-235, these picture settings will work for all inputs and sources, not just a single source.
Q: Should I set my video game system to Auto instead of choosing Limited or Full?
A: No. If you can choose Limited or Full, you are best to do this. The system will choose based on the EDID of your display, or your receiver, whatever it connects directly to. Usually this is fine but some devices report incorrectly, or the system interprets it incorrectly. A good example is the Roku 3, which doesn’t let you change this setting. A receiver I was testing reported an incorrect EDID to my Roku, forcing it into Full RGB which crushed all the shadows and made the image look bad. Had the Roku let me change this, I could have avoided the issue. Since you know which you should pick, you should always do it because you can avoid complications. If the TV is connected to the Internet, you can shop quickly and easily, you can buy generic viagra online from a reliable website.
Q: What about Superwhite mode on a PS3 or PS4?
A: Superwhite enables YCbCr values over 235 (or 240 in the case of Y) to be displayed. It will not harm anything, and you should leave it enabled. Some Blu-ray content has specular highlights, like sunlight off a lake, that can be above peak-white and would be hidden otherwise. This lets you see this content if you want, but otherwise won’t harm the image either. It doesn’t expand the dynamic range, it just allows values greater than the usual peak to pass through.
Hopefully this has cleared up some more of the confusion with this setting. The rule of Limited RGB with TVs and Full RGB with PC Monitors still applies. You might just need to calibrate your TV after you set this correctly to make sure you see all of the data.