The Ins and Outs of HDR ― What is HDR?
An easy-to-follow explanation of HDR, covering everything from the basics to the latest trends
1. What is HDR?
HDR stands for High Dynamic Range, and allows a wider range of brightness (dynamic range), from darkest to brightest, to be displayed compared to existing SDR (Standard Dynamic Range).
As shown in the images below, when content is displayed in SDR, shadows tend to have crushed blacks and bright areas tend to have washed out whites, while HDR allows for a more natural and realistic display, without sacrificing the tones in the bright or dark areas.
HDR has drawn attention as a next-generation high-quality imaging technology, and content produced in HDR is now available through video streaming services like Netflix and on UHD Blu-ray discs.”
The Five Elements of High Image Quality
Of these, resolution, bit depth, frame rate, and colour gamut have already been standardized under the 4K/8K UHD broadcast standard BT.2020. (A 4K/8K ultra-high-definition TV broadcast standard planned for implementation from the end of 2018. The current full HD standard is known as BT.709.) Only brightness, which remains standardized at the same 100 cd/m² set for the full HD broadcast standard BT.709, has not seen its standards raised.
Because of this, production work to date has required compression of high-brightness portions of images to match the characteristics of the display device, resulting in an image that differs from the original scene. However, in recent years, improvements in display technologies have led to an expansion in dynamic range that can be displayed, enabling brightness and colour rendition that are truly like that seen in the real world.
This is why so much attention is focused on HDR of late.
Resolution refers to the number of pixels in an image. At a given screen size, the higher the resolution is, the more pixels there are, allowing for finer detail to be displayed. 4K UHD resolution is 3840 x 2160, meaning that four times the amount of image data is shown compared to standard full HD.
Bit depth refers to the number of colours each pixel can display. The greater the bit depth, the more colours can be displayed, for smoother and more natural gradations. For example, an 8-bit display can show roughly 16.77 million different colours, while a 10-bit display can show roughly 1.07 billion colours.
Frame rate refers to the number of images shown in a single second. Films are generally shot at 24p (24 images, or frames, per second), while standard TVs generally run at 60i or 30p (30 frames per second).
The BT.2020 standard for 8K broadcasts includes definitions for frame rates of up to 120p, for movement that is virtually as smooth as the real world.
Colour gamut refers to the range of all colours that can be displayed. The chart to the right shows the range of all RGB values that can be perceived by the human eye. The triangles show colour gamuts: the larger the triangle, the greater a number of colours can be displayed.
The 4K/8K broadcast standard BT.2020 (Rec.2020) covers a much wider colour gamut than the existing full HD broadcast standard BT.709 (Rec.709).
Brightness refers to the range of the intensity of the image lighting that can be displayed. The difference in scale between the darkest and the brightest objects the human eye can perceive (dynamic range) is commonly said to be 1012, yet display devices have traditionally only been able to display a range of up to 103. HDR expands this dynamic range to 105 — a hundredfold increase over display devices to date — allowing for light and shadow to be represented in a manner much closer to what the human eye can perceive.
2. Gamma Curves
BT.2100 — a New International Standard for HDR
HDR stands for High Dynamic Range, and allows a wider range of brightness (dynamic range), from darkest to brightest, to be displayed compared to existing SDR (Standard Dynamic Range).
As shown in the images below, when content is displayed in SDR, shadows tend to have crushed blacks and bright areas tend to have washed out whites, while HDR allows for a more natural and realistic display, without sacrificing the tones in the bright or dark areas.
HDR has drawn attention as a next-generation high-quality imaging technology, and content produced in HDR is now available through video streaming services like Netflix and on UHD Blu-ray discs.”
| BT.709 (Current Full HD Standard) | BT.2020 (4K/8K Standard) | BT.2100 (4K/8K HDR Standard) | |
|---|---|---|---|
| Resolution | Full HD | 4K, 8K | HD, 4K, 8K |
| Bit Depth | 8 bit | 10 or 12 bits | 10 or 12 bits |
| Frame Rate | Up to 60p | Up to 120p | Up to 120p |
| Colour Gamut | Rec.709 | Rec.2020 | Rec.2020 |
| Brightness (Dynamic Range) | SDR | SDR | HDR |
Two Gamma Curves
In order to properly display HDR images, it’s not enough to simply raise the level of brightness — it’s crucial to display colour and tones in a way that matches human eyesight. Colour and tones are affected by an input-output characteristic called gamma that each input and output device has.
The BT.2100 standard provides two gamma curves as standards for different types of production work.
- For Internet Streaming and Movies: PQ (Perceptual quantization)
- For Broadcast TV: HLG (Hybrid Log-Gamma)
The PQ gamma curve is based on the characteristics of human visual perception, and is most suitable for the production of movies or streaming video content on the internet, where reproduction accuracy is key. On the other hand, the HLG gamma curve is intended to allow for display on existing SDR TVs without looking out-of-place, and is most suitable for broadcast TV and live video feeds.
Advantages of the PQ and HLG Gamma Curves for HDR
| PQ (Perceptual Quantization) | HLG (Hybrid Log-Gamma) | ||
|---|---|---|---|
| Target | Internet video streaming, movies | Broadcast TV, live video | |
| Advantages | Handles brightness in absolute values of up to 10,000 cd/m²; New gamma curve based on human visual perception | Handles brightness as relative values (same as existing standards); Compatible with SDR TVs | |
| Peak Brightness | Absolute value of 1,000 cd/m²; Consistent, regardless of display device | Absolute value of 1,000 cd/m²; Consistent, regardless of display device | |
| Black Level | 0.005 cd/m² or lower | 0.005 cd/m² 0.005 cd/m² or lower | |
| Proposed by | Dolby | BBC and NHK | |
| Reference Standards | SMPTE ST 2084 and ITU-R BT.2100 | Outstanding | Good |
| Appearance on SDR TVs | Poor | Fair | |
| Live Broadcasts | Fair | Outstanding |
The graph below shows both the PQ and HLG gamma curves for HDR.
The peak brightness of PQ gamma curve is fixed at 1,000 cd/m² (or higher). To put it another way, the gamma curve is always the same, with an upper limit of 1,000 cd/m², regardless of the peak brightness of the display device, allowing for consistent image reproduction.
On the other hand, the HLG gamma curve’s peak brightness is whatever the peak brightness of the display device is. In other words, because the gamma curve varies depending on the peak brightness of the display device, it allows for acceptable viewing of HDR content even on existing SDR displays, with less image degradation.
3. HDR Workflow
A monitor environment where you can accurately check and evaluate both the brightness and colours of HDR content is absolutely indispensable to any HDR content production workflow.
The ColorEdge CG series provides the outstanding display performance needed for video production, with specialised functionality for a comfortable work environment. These monitors provide incredible support for every step of the HDR workflow, from checking the data from a shoot, to VFX and compositing work, to final colour grading.
HDR Monitor Upgrade Options
For Shooting, VFX, and Compositing Work
EIZO offers the option to upgrade most models in the current ColorEdge CG series monitor lineup to display HDR (HLG and PQ gamma curve). By enabling simplified HDR previews from the production steps, editing can be performed with a good idea of how the finished colours will look.
Applicable Models:
ColorEdge CG318-4K
ColorEdge CG248-4K
ColorEdge CG277
ColorEdge CG247X
HLG and two PQ gamma curves (PQ1000 and PQ300) are added to the built-in colour modes on each monitor to upgrade the monitor to display HDR.
In the PQ1000 display mode, a PQ gamma curve with a peak brightness of 1,000 cd/m² is compressed to fit within 300 cd/m², to match the brightness of the monitors (see the PQ1000 graph below).
In the PQ300 display mode, the brightness curve follows a PQ gamma curve with a peak brightness of 1,000 cd/m² until it reaches 300 cd/m², becoming constant for all gradations exceeding that point (see the PQ300 graph below).
By allowing for the accurate display of gradations corresponding to brightness levels of up to 300 cd/m², this gamma curve is suitable for checking the coloration of low-gradation areas. After installation, the user can press a button on the front of the monitor to easily switch between colour modes to match the task at hand.
EIZO’s HDR Reference Monitor For Colour Grading
For Shooting, VFX, and Compositing Work
The ColorEdge PROMINENCE CG3145 is the first HDR reference monitor to overcome the drawbacks that existing reference monitors face. It is perfect for final colour grading work, which requires strict colour management and a precise colour display environment.
- Size: 31.1"
- Resolution: DCI 4K (4096×2160)
- Brightness: 1,000 cd/m² (typical)
- Contrast ratio: 1,000,000:1 (typical)
- Compatible with both PQ and HLG HDR gamma curves
- Five-year warranty
4. Compatibility
We have tested the compatibility between ColorEdge 4K monitors and SDI converters for use in professional video creation.
| Manufacturer | Output / Input | Product | Monitor | ||
|---|---|---|---|---|---|
| CG3145 | CG318-4K | CG248-4K |
|||
| APANTAC | SDI-DisplayPort | Micro-4K-DP2 | Not Supported | Yes | Yes |
| AJA | SDI-HDMI | Hi5-4K-Plus | Yes (recommended) | Yes (recommended) | Yes (recommended) |
| AJA | Hi5-4K | Not Tested | Yes | Not Tested |
|
| Blackmagic Design | SDI-HDMI | Teranex Mini SDI to HDMI 12G | Yes | Yes | Yes |
4K Monitor Compatibility with Video Devices
For compatibility between ColorEdge 4K monitors and video devices, click here.
FAQs
Does CG3145 support SDI input?
No. Please refer to the above list for compatible converters.
Does CG3145 support HDR10?
CG3145 can display signal from an HDR10 output device. Please refer to the setup manual to select the appropriate gamma and colour space for HDR10.
Do other HDR CG Series monitors support HDR10?
No. HDR support for monitors other than CG3145 does not include HDR10.
Implementing 4K Monitors
Get information on EIZO 4K monitors such as compatibility with other devices and more. Click here