Player-Led versus Display-Led Dolby Vision
Dolby Vision is considered the “best” High Dynamic Range (HDR) solution. It includes HDR metadata that gives compatible displays frame-by-frame brightness and contrast information to ensure the best picture possible. But few people realize that there are two different implementations of Dolby Vision – player-led and display-led (or TV-led). So, how do they work and which is the best?
How Dolby Vision Works
Dolby Vision starts with a base layer of HDR10 (on disc, this is always true, streaming can be different). This means, even if your display cannot display Dolby Vision, it can decode the HDR10 base layer. Dolby Vision is a metadata layer on top of the HDR10 base. This metadata describes scene-by-scene or frame-by-frame the brightest and darkest pixels in the image.
To do this, the player and the display have to talk. They do this during the HDMI handshake. During this handshake, the display will tell the player what it is and maybe how bright it can get, the player will then tell the display what signal it can send. Together, they will decide whether the Dolby Vision image will be player-led or display-led.
Player-Led Dolby Vision
Usually, with player-led Dolby Vision, the display tells the player what model it is or how bright it can go. The player then needs to interpret that into how to tone-map the image before it sends it to the display. This, in theory, should work just fine. Unfortunately, players aren’t as smart as we’d like them to be.
Most player-led Dolby Vision solutions don’t really have the ability to know map exactly to your display’s abilities. The display may communicate that it has a maximum output of 750 nits. Most players have what amount to lookup tables for tone mapping. They may have one for 750, but more likely they don’t. They certainly have one for 1000 nits (since that is HDR10 mastering default) and maybe 500 nits. So it has to decide which to choose. If it chooses 500 nits, then some of the bright detail will be lost (as it adjusts 750 down to 500).
Display-Led Dolby Vision
Alternatively, there is display-led Dolby Vision. In this case, when the HDMI handshake is made, the display tells the player to send it the full information. The display then tone-maps the Dolby Vision information. In theory, this should work better. The display knows how bright it can get and it should be able to tone-map the image more accurately.
Houston, We Have a Problem
When looking at display-led or player-led Dolby Vision, it is easy to wonder which is the best. Well, the problem is that you don’t often know which type of Dolby Vision you are getting. If you have display-led Dolby Vision, you are getting the very best HDR out there (as of this writing). But if you are getting player-led Dolby Vision, you likely aren’t. In that case, you’d be better off using dynamic tone-mapping.
Author’s Note: And if the disc doesn’t have Dolby Vision, then you are stuck with HDR10. This means you are relying on the content on the disc to be correct. There have been many cases where the encoding has incorrectly identified the peak brightness. It may say that it was mastered to 1000 nits peak brightness but there is nothing higher than 800 nits on the disc. In this case, you’d definitely be better off using dynamic tone-mapping.
We’ve talked about dynamic tone-mapping before. Dynamic tone-mapping ignores the metadata and actually looks at each frame as it comes off the disc. Each frame is then tone-mapped to the capabilities of the display. If you’re shopping for a projector, you’ll want to look at JVC and LG. Their projectors do true frame-by-frame tone mapping. Sony projectors do something similar, and it looks very good, but it still utilizes the metadata.
If you are shopping for a flat panel, you’ll want to look at LG and Sony OLEDs. They both do dynamic tone-mapping but in slightly different ways. The LGs attempt to retain all the highlight detail but also brighten shadows. This gives you as much detail as possible but at the expense of strict accuracy. The Sony OLEDs tries to keep everything as accurate as possible but sometimes clip the very brightest highlights in doing so. If you are on the market for an LCD display, you’ll want to look at Sony LCDs and Samsung QLEDs.
If you want a standalone box, there is no Ultra HD Blu-ray player that does dynamic tone-mapping, The only way to get it is to connect a computer to your display running the MadVR program or buy a Lumagen Radiance video processor. At nearly $5000 a pop, it’d be cheaper to buy a new display.
- Display-led Dolby Vision
- Dynamic tone-mapping
- Player-led Dolby Vision
- Base HDR10
Generally, if you can get display-led Dolby Vision, you are getting the very best HDR possible. It is matched to the capabilities of your display and will most faithfully recreate the image as the creator intended. If you can’t ensure that the content is display-led (or you have a display that can’t do Dolby Vision), your best bet is a display that can do dynamic tone-mapping. If you have the ability to do Dolby Vision but don’t have access to dynamic tone-mapping, just use Dolby Vision and hope it is display-led. Lastly, if you don’t have access to Dolby Vision or dynamic tone-mapping, you are just stuck with base HDR10. It may not be the most accurate, but it is probably better than non-HDR. Probably.