With the rise of 4k TVs and computers and the PS4 and Xbox Project Scorpio, the differences in these acronyms is becoming a more common curiosity.
4k refers to the resolution that is quickly becoming the standard for content. Current HDTVs have a 1080p resolution (1080 horizontal lines of vertical resolution, the p stands for progressive scan) which is 1920x1080 where as 4k TV have 4 the size of the pixels for a resolution of 3840x2160 allowing for a sharper image with better clarity. HDR stands for High Dynamic Range. Many think HDR plays a bigger role increasing from normal HD content rather than seeing the same content in 4k resolution. HDR refers to a much larger spectrum of contrast between light and dark and a greater range of bright, vivid colors.
Your Tv just being labeled HDR does not mean that it is however. HDR was pushed to the public before there was a clear industry standard resulting in several TVs claiming to be HDR with hitting the quality bar one would expect from the feature. Those standards have been refined as of 2016 and they now fall under the category UHD Premium. So long as your TV claims to be Ultra HD Premium than it has been held to these standards, meaning your TV hits the minimum requirements for resolution (4k) and the proper quality of HDR to be considered Ultra HD.
However there are 2 HDR standards in the current market. Both are considered HDR Premium but only one works for console gaming. HDR10 is the opensource standard and is much more adopted by TV manufacturers and supported by developers. Dolby Vision is the higher end closed version, it offers higher quality but is not in as many TVs and many current TVs are not even good enough to process the higher end of Dolby Vision so all those extra visuals it offers are not even being used. If you are looking for a truly HDR gaming experience Xbox OneS and PS4 Pro only support HDR10. There is now a software version of Dolby Vision giving the possibility of Dolby Vision coming to consoles in the future but it is not guaranteed.
Another aspect to look for when it comes to a 4k HDR TV is input lag. With so much processing in these TVs to create the best possible picture, they can lag more than current HD TVs when outputting the signal. In gaming, particularly competitively, this becomes an issue when every millisecond matters. There are some TVs with lag as low as 20 or 30 milliseconds which is the desired range for 4k HDR gaming. Many TVs also have a "gaming mode" which lowers that input lag but sacrifices some of the picture quality.
HDR quality is also not the most consistent experience and, while consoles are supposed to auto-detect your TV's capabilities, but that isn't always the case and in many cases you will have to tell your console to output the 4k HDR manually and for the PS4 Pro enable it manually for each individual game in the game's options and not every game offers HDR resolution. Ensuring these on your TV side of the settings is a bit more difficult. First you need to make sure you are using HDMI 2.0 as opposed to regular HDMI. If you are going into an HDR ready TV then you should not have any problems but if you are using an HDMI switcher that is not HDMI 2.0 ready or HDR compatible, then you are not getting an HDR signal. This is also critical if you have a PlayStation VR headset plugged in at all times as the headset will not allow an HDR signal to pass through. After that, there is still the chance you will have to adjust your TV settings manually. Many HDR TVs do not enable HDR by default and in many cases you will have to manually adjust it for each individual input. Even then, some of the HDR presets turn on other features like dynamic contrast which will actually undo some of the effects of HDR thanks to flattening out the colors.
This is one of the areas where the industry is fairly far behind on making things easier for consumers. Some TVs do not offer very accessible means of switching between HDR and non-HDR content. If you view non-HDR content with HDR settings it will cause the image to look muted and washed out and this goes for the other way around as well. On some TVs you have to manually switch between a number of settings when you switch between content essentially setting your TV up all over again every time you switch off. You will have to double check individual TV settings and seek guides online to ensure you are getting the top quality image you paid for. Make sure these are current as these TVs are getting continuous firmware upgrades for their systems. In the end you will be rewarded with the results as the difference between HDR and non-HDR content is rather notable.
Non-gaming 4k content is still developing and there is not a large selection available but it is still an option from sources such as Amazon and Netflix with Netflix even offering a UHD search filter and a separate upgrade payment to watch UDH with HDR. Youtube is currently offering a rather large amount of 4k content and recently added HDR support. The Xbox One S and Project Scorpio also come equipped with a 4k UHD Blu-ray player which supports HDR color and contrast.
It is all particular to the individual's setup and whether you are moving to full HDR content and output or just supporting a single system, so be ready for a bit of work and testing and possibly more work to get it up and running and outputting at full strength.
Information provided via The Know - http://www.youtube.com/watch?v=6-YmLb1Nzt0