Demystifying HDR

HDR Demystified…. How Sony TV, once again proved that they are the best?

Today’s market is flooded with 2nd wave of 4K TVs (UHD-1 Phase 2, or Ultra HD Premium TVs/ Dolby Vision UHD TVs) and you would have noticed that all the TV OEMs are talking about HDR or High Dynamic Range as the highlight of their TVs. So in this edition of TG guru, let us understand what exactly is meant by HDR and how it transforms video quality. HDR is going through a format war between Dolby Vision and HDR10. Dolby Vision which is supported by LG, Philips, Vizio and movie streaming content providers Netflix, Amazon etc. and the rival HDR10 is supported by Samsung, Sony and most other TV vendors. I will explain in detail what these formats are and how it compares and which will win (ex: Blu-ray vs HDVD) or may end up in peaceful co-existence like Dolby and DTS. It is interesting to note that Blu-ray disc association has selected HDR10 as mandatory requirement and Dolby Vision as optional. If you want to jump to the findings before knowing the details of both formats, here it is. Dolby Vision defines the entire chain from mastering, to display, a little futuristic in design, more of aspiration goal, and is proprietary. HDR10 is more practical and is achievable using current TV technologies. Read the rest of the article to understand the details from the basics to the latest.

For the last few years, Samsung, LG and Panasonic challenged the dominance of Sony and made better TVs and introduced OLED TVs to consumers. LG took the lead with their range of OLED TVs and snatched the crown from others and almost succeeded in taking it to “Reference TV” level status to which other TVs are compared. “Reference TV” status is lying vacant with the demise of Pioneer Kuro Series Plasma TVs, a few years ago.

Sony may be the first one to demonstrate OLED TVs as a concept a decade back, but never brought OLED tech to mainstream. Sony sticks to LED – LCD TVs for its consumers. Meanwhile with OLED TVs LG could demonstrate they could achieve black, blacker than anybody else (0.0005nits) by switching OFF the entire OLEDs for dark scenes. But 3 months back Sony demonstrated with LED/ LCD they could achieve an amazing level of brightness up to 4000 nits in last CE exhibition and launched a mainstream Z9 D series of their flagship TVs which is currently the best TVs around, available in India too. It is considered as VFM (Value for Money) at 5 Lakhs (expected price) for the entry level 65” 4K TV! So let us look at what is so great about these TVs and how they compared with others. The basic question for one is, do you want to get a TV technology which is futuristic (Dolby Vision) for which its display is not capable of reproducing (!) with current technologies or a TV with a more practical approach where capability (HDR10) and display technology matches currently.

Evolution of the Television

TVs have evolved in the last 60 years. From CRT Black and white TVs to Color TVs, then LCD HD TVs to OLED 4K and 8K TVs. TVs are meant for reproducing the picture as realistic as possible. To simplify it there are four basic parameters we can improve to produce a better video.

  1. How many? How detailed the picture is (resolution) 576P, 720P, 1080P, 2160P etc.
  2. How Fast? How fast the picture can be redrawn / refreshed? Refresh rate: 25Hz/ 30/50/60/100/120 Hz
  3. How Bright: How bright the brightest parts of the picture appear and how much detail you can still see in the shadows (dynamic range) 0.1nit to 10000 nit
  4. What Color: How many of the possible colors that your eyes can see can actually be reproduced (color gamut) – Rec. 709, DCI-P3., Rec. 2020

Let us look into each one of this in detail.

  1. How detailed the picture is? (Resolution)

The resolution of the TV has gone up a lot over the years from SD (NTSC 480P/PAL 576P) to 4K (3840 X 2160P) which improved clarity of the picture.

  1. How fast the picture can be redrawn? Refresh rate

In the early days of TV the refresh rates was fixed at the rate matching the utility power frequency to reduce the interference. So 60 HZ (NTSC)/50HZ (PAL) field rate is translated into 30Hz / 25Hz refresh rate for the interlaced scanning and later when LCD technology made it possible to do away with interlaced scanning to adopt progressive scanning, the refresh rate was progressed to 60Hz / 50Hz. Even though the video source is still using either 60i / 50i or 60P/50P the manufactures of Digital TV started offering pseudo 100/200/400 Hz (PAL) 120/240/480 Hz (NTSC) refresh rate in the TV display either by inserting additional extrapolated frames or by simply repeating the frames to improve the viewer’s experience for fast action scenes. As the Ultra High Definition TV (4K) progresses (UHD-2 Phase 2) the source refresh rate is also made to improve – 120Hz to give smoother picture.

If you want to see refresh rate in action check the following videos

https://www.youtube.com/watch?v=KTY9uDD0x14&ab_channel=Techquickie

and https://www.youtube.com/watch?v=mssESTnWtUo&ab_channel=SonyCanadaTraining

  1. How bright? How bright the brightest parts of the picture appear and how much detail you can still see in the shadows

This is one of the most important parameter of the TV since human eye is very sensitive to luminance variation rather than the variations in chrominance (color). One should understand this in detail to understand what exactly the High Dynamic Rate and current 2nd wave of 4K TVs in the market.

Let us start from the basics, how the real World looks like in terms of the variation in brightness and the capability of our eyes, how much variation we can really understand.

The following picture in the left gives an idea about the difference between the capabilities of Human visual System (HVS) to perceive the variations in brightness in the real World.

The brightness varies from 10-8 to 108 nits from a pitch dark night to a very bright sunlight. One nit is defined as one candela per square meter, or one candle power per square meter cd/m2. Out of these humans can see only a brightness variation of 10-4 to 106 with all our cones, rods and pupil adjustments. Current HD TV can show only up to 100nits.

Following figure gives the nits in the real World.

Current HD TVs uses 8 bit colors and can show a brightness variation of 100 nits. But Ultra HD TV demands 10 bits to 12 bits of colors and high dynamic range of brightness minimum 1000 nits. OLED TVs can show dark scenes better than any other TV employing LCD/LED combinations. OLED TVs can switch OFF LEDs covering the dark scenes if demands achieving a perfect black. But LCD/ LED TVs cannot achieve this because LCD are not emitting lights and LED are used for backlit so effectively some lights will leak diluting the scenes or wiping off the shadow regions when the conventional edge lit LEDs are used . In the other end of brightness spectrum LED lit LCDs shine since it can go very high, easily more than 1000nits whereas OLED cannot go beyond 600nits. In short both can have very good range, but it is yet different, OLED TVs are very good when ambience light is low or night viewing where LCD / LED set shines even in bright day light. So you choose between them depending on your viewing habits and ambience lights of the TV room.

  1. What color? How many of the possible colors that your eyes can see can actually be reproduced (color gamut)

From the days of CRT tubes we were following 8 bits of color with Re. 709 color gamut which is around 36% of colors visible to us. But Ultra HD demands Rec. 2020 color gamut with 12 bits of color covering almost 70% of visible colors. None of the current display technologies support this, so as an interim solution TV manufacturers agreed to support DCI P3 color gamut covering 45% of visible colors which is supported by studio video equipment for many years.

Refer to the following figure to understand the difference between Rec. 709 (8bits), DCI-P3 (10 bits) and Rec. 2020 (12 bits) records used in color gamut applications in TV.

Visit the following video to understand more about color gamut.

https:/ /www.youtube.com/watch?v=Z1TR4WbHN5o&ab_channel=TWiTNetcastNetwork

Dolby Vision vs HDR 10

Following bullet points gives the difference between HDR 10 and Dolby Vision. Dolby Vision was unveiled in 2014 and is little futuristic in its goal.

  • Dolby Vision mastering supports up to 10,000 nits peak brightness, with a current 4,000 nit peak brightness target
  • HDR10 mastering supports up to 4,000 nits peak brightness, with a current 1,000 nit peak brightness target
  • Dolby Vision mastering supports up to 12-bit color depth, HDR10 is mastered for 10 bits
  • Dolby Vision mastering supports up to the BT.2020 color space, HDR10 is mastered for DCI-P3

It is a proprietary technology which requires the products to be certified by Dolby. Dolby vision aiming at very high standards (as given below) which covers the entire echo system from source (mastering) to display which our current hardware cannot support. So systems which supports Dolby Vision needs a Dolby vision chip in all equipment in the chain to enable the best video the current hardware is capable of. For example the current best studio TV display (costs as much $40,000) supports 4000nits whereas Dolby mastering video can support up to 10,000 nits display if engineers can make such display in the future. HD10 adopts a much practical approach where it can match with the current TV tech and it can be upgraded in all TV by a firmware upgrade. Dolby vision requires a special hardware so TVs cannot be upgraded to support it.

Dolby Vision HDR 10
1 Brightness (Theoretical) 10000 nits 4000 nits
2 Brightness (Current Goal) 4000 nits 1000 nits
3 Color (mastering) 12 bits 10 Bits
4 Color Gamut (mastering) Rec 2020 DCI-P3
5 LG OLED TV (nits) 0.0005 – 540 0.0005- 540
6 Sony Z9D TV (nits) NA 0.05 – 2000
7 Resolution (4K) 3840 X 2160 3840 X 2160

Currently LG, Philips, TLC etc. supports Dolby Vision but LG’s best OLED TVs can go only up to 540 nits so Dolby vision needs to scale down a lot to match the TV. Currently there are fewer titles which supports Dolby Vision format mainly available as online video streaming services such as Netflix.

Sony , Samsung and most other TV manufactures support HDR 10 and Ultra HD Blu-ray made HDR10 support mandatory and Dolby Vision optional. There are no Ultra HD Blu-ray player currently in the market which support Dolby Vision. So there are plenty of movies in Ultra HD format available in Blu-ray with HDR10 support. Almost all the studios promised support for HDR10 whereas Universal is the only studio announced support for Dolby Vision. This forced Netflix to make its own Dolby Vision Content – Marco Polo TV Show is an example of this which is mastered in 4K with Dolby Vision. This also forced LG who was in Dolby Vision camp to support both formats Dolby Vision and HDR10 in their TVs with a firmware upgrade. So one would think going for a TV which supports both format will be the best. Mostly it is not, since the current crop of Dolby Vision supported main stream TVs are OLED TVs which cannot go beyond 800 nits brightness. But mains stream LED backlit LCD TVs are able to go up to 1500 nits.

But you need to look at the range, OLED TVs have a range of 0.0005 nits to 540nits and best LED / LCD TVs have a range of 0.05 nits to 1500 nits. So the dynamic range is almost same, OLED TV can reproduce absolute black which LED/ LCD TV cannot. So OLED TVs are ideal for rooms with less ambient light whereas the latest LCD/LED TVs perform better in a room with good ambient lights. For comparison remember that the current HD TVs can go maximum only up to 100 nits. 540 nits or 1500 nits are very bright and the aspirational goal for Dolby Vision is 10000 nits which cannot be achieved by any TV with the current technology. I do not think anybody wants to go beyond that where you need sunglasses to look at very bright scenes in your TV!

Since only LG OLED TVs support both Dolby Vision and HDR10 the comparison is given below which is little skewed. Nevertheless it brings out the superiority of Dolby Vision over HDR 10 when all other things remains same.

Now let us look at Ultra HD evolution.

Ultra HD Evolution

4K TV is going through an evolution, UHD 1- Phase 1 and UHD-1 Phase 2. UHD -2 is 8K TV which will be launched by 2022 or so. UHD-1 Phase 1 mainly talked only about a bump in resolution from 1080P to 2160P, refresh rate, brightness levels (SDR) and sound remains the same as before. It was ended by 2015. In UHD-Phase 2 we can see the adoption of HDR, high refresh rates and next generation audio Dolby AC-4 which supports object based audio.

Sony launched Z series their flagship product Z9 D TV or ZD9 TV

Sony so far was using X series as their flagship product moniker. There were a few years when there was no lunch of X series TVs. Now Sony has come back with their flagship product Z9D or ZD9, instead of using X , they jumped to Z which inovolves the jump in quality too. Initially they showed an LCD/ LED backlit TV exhibiting 4000 nits in a London CE show and later launched the main stream prodcut Z9D TV which exhibits a brighness in the range of 1500 to 2000 nits, much beyond other main stream TVs offer. Let us look at how Sony has achieved this feat.

LCDs cannot generate light by themselves, they need a backlit, a light soucrce which is provided by CFL or LEDs and LCD function as the filter to allow the rigjt amount of light to pass through . The arrnagement of LEDs behind the LCD screen can be edge lit or full array as shown below. Most of the current LED TVs in the market provides edge lit LEDs, meaning there a few LEDs placed in the edge within the frame which is used to light the entire video scene. This is cheaper as well as make the TV thinner. Black scenes are produced by the LCD which filter out lights, but always some amunt of light will be leaked, so we cannot achieve 100% black for any scenes, unlike OLED where the pixel itself is generating the light, so it can be put it off for black scenes.

Now look at another scenario where the backlit LEDs are arranged in an array behind the screen and can be controlled as small groups so as to form a coarse picture of the scene behind the LCD filter so that the resulting picture can reproduce more darker pictures. TV manufactures tried this array of LEDs with local dimming before edgelit LEDs became popular. It was more costly as well as resulted in thicker TVs. Moreove the video processing chip needs more power to do this extra step of forming a coarse B/W picure for the LEDs so called local dimming.

Now Sony has come out with a solution by inventing a new Backlit Master Drive techonilogy. It uses a set of LEDs called calibrated beam approach where the LED lights are precisley controlled to emit narrow beams to reduce the halo effect found in conventional LEDs. These are controlled by a new DSP chipc alled X1 extreme, together these gives an excellent result shown in their concept TV reaching 4000nits.

Sony’s Z9D 4K TVs this year incorporates three potentially key new technologies: object-based HDR remaster, dual database processing, and Super Bit Mapping.

The first one gives out good picture range and dua data base proessin gives better upscaled video from SD sas well as HD video source. Super Bit Mapping 4K HDR technology up-converts 8-bit (Full HD) and 10-bit (4K) sources to 14-bit levels of gradation in a bid to deliver a smoother, more natural image free of the striping/banding issues that can appear over areas of subtle color blends on other TVs. So Sony effectively able to produce excellent pictures which goes up to 2000 nits in this main stream TVs. At the end Sony Z9 series of TV looks like OLED on steroids, so LED/ LCD technology strikes back!

https://www.youtube.com/watch?v=KymaqNGSFY8&ab_channel=Sony

If you do not have much content in HDR , do not worry ,Sony TV enhances the non-HDR HD content to new heights, a new extrapolation and up scaling techniques.

To get a better understanding compare the pictures shown below with HDR (left) and without HDR (right).

For more visit http://www.sony.co.in/electronics/4k-resolution-4k-upscaling-tvs?cpint=SG_PRODUCT_DETAILS_PRI-TOUT-PDP-Z9D-EN_GL-2016-06-M05-SOREAL#X1Extreme

After a few irregular postings in the last 3 months, I regained interest and put some effort in writing this article. I hope you have enjoyed reading this as much as I enjoyed penning it down. Pease send your feedback.

-Tomy

Posted in: HDR

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