This article intends to help filmmakers successfully navigate the rapidly evolving technology associated with on-set HDR workflows in order to help facilitate decision-making on our productions. While we encourage the viewing of HDR images early in the production process, it is not a Netflix requirement to have HDR monitoring on-set.
Netflix is available to assist in navigating production-specific workflow decisions in collaboration with key production stakeholders. Please reach out to your Netflix contacts with any questions or concerns specific to your production.
For general information on the HDR format, see: "What is HDR?"
Table of Contents
- Signal Distribution & On-Set Equipment Recommendations
What are the Benefits of HDR Monitoring On-Set?
Early viewing of HDR images can inspire creative decision-making and allow the development of robust technical workflows. While most Netflix titles have been finishing in HDR for some time, HDR images aren’t typically seen by creative leads and crews until far into post-production. This late-stage review of HDR can reveal visual issues that were not evident during on-set monitoring in SDR (Standard Dynamic Range), resulting in unplanned work in VFX, unexpected redelivery costs, and unintended creative compromise.
Visual issues revealed when finishing in HDR commonly center around:
Depending on the dynamic range and content of the scene, additional detail may be seen in the shadows and highlights in HDR that were hidden or not as visible with SDR monitoring (i.e. windows that may have appeared clipped before, equipment in the shadows, light filaments, or highly reflective / specular surfaces).
The additional contrast in HDR can increase the perception of sharpness which can potentially affect skin and clothing texture. This increase in perceived sharpness may impact makeup, costume, or set design choices. Additionally, the higher contrast available in HDR can make images more susceptible to motion artifacts such as judder, which can affect camera movement choices.
The wider color gamut in HDR can reveal color casts on surfaces, skin tones, or lighting sources that would not be visible in SDR. Also, since cameras vary in behavior when shooting highly saturated colors, these colors will often appear different in HDR compared to SDR. These considerations can affect lighting, makeup, costume, set design, or lens and camera filter choices.
HDR monitoring on-set can help in identifying these problems early, allowing productions time to make any adjustments necessary to build confidence in the final look and preserve creative intent.
What are the Potential Challenges of HDR Monitoring On-Set?
While HDR adoption varies globally, it is likely to become the preferred format for monitoring images on-set. For those currently implementing HDR workflows on-set, here are some of the challenges commonly faced:
- While HDR on-set monitoring does not imply the need for more crew members, it does require more time for talking and testing across production departments to align on unique requirements and working styles.
- HDR monitoring may require additional equipment which can mean added cost during production. These added costs should be weighed against the potential cost-saving benefits that can come from discovering image-related issues early on, as listed in the section above.
- The market of available monitors can be tricky to navigate, with manufacturers still catching up to production needs. Marketing often outpaces actual performance, making it challenging for the industry to set minimum requirements for these products.
HDR Monitoring Approaches
Having HDR monitoring for every display on-set for the entire length of a production is still out of reach for most productions due to cost and technical limitations. Here are three common approaches for HDR monitoring today:
Camera Tests (e.g. Hair & Makeup Tests)
Camera tests for hair and makeup are typically the first time images are evaluated and sent through the entire production pipeline. Some productions choose to monitor in HDR during the test shoot day or at a picture finishing facility immediately afterward. Then, they continue with on-set SDR monitoring during production. This is usually the lowest cost approach to HDR monitoring.
Limited Run HDR Monitoring On-Set
In a Limited Run workflow, the HDR reference monitor is only on-set for certain weeks of the production schedule (ideally the first two weeks of production). This helps key stakeholders gain a better understanding of how the final image will be displayed in HDR. Once these stakeholders are comfortable with the format, they can stop using the HDR display and continue the remainder of the production using SDR monitors.
One HDR Monitor On-Set
Rather than make every monitor on-set HDR, this approach uses a single HDR reference monitor for the full run of production. Regular access to said monitor can help key stakeholders continually guide how their creative decisions will be manifested in HDR. The other monitors on-set, such as those in the “video village”, receive an SDR signal.
Technical Considerations for On-Set HDR Monitoring
Panel and Backlight Types:
LCD stands for liquid crystal display. LCDs are a panel technology that utilizes a backlight and an LCD layer that modulates the light to create a color image. LCD technology is common among SDR displays and mobile devices because of its low cost and decent image quality.
However, since the LCD layer has to ‘block’ the backlight that is always on, it is difficult to produce the deep black levels necessary for HDR. Also, because the LCD layer uses polarization to block or allow light to get through, LCDs suffer from limited viewing angles. This means color and luminance may vary perceptibly depending on the angle at which the LCD screen is viewed, potentially creating problems in an on-set environment.
Local Dimming LCDs:
In order to help LCDs produce HDR images, a backlight technology called ‘local dimming’ is often used. This utilizes multiple backlight ‘zones,’ which can individually turn on and off in order to increase the effective dynamic range of the image. When there is a dark area of the frame, the backlight zones in that area can dim or turn off to produce a pure black. In bright areas of the frame, those zones can turn on to help produce specular highlights.
While local dimming is almost always a good thing, the number of zones and the dimming algorithm can have a significant effect on the viewing experience. Good local dimming can effectively increase the dynamic range of LCD displays, but the added cost of additional backlights and the dimming algorithm needed can have an exponential effect on the cost of the display. Less expensive displays often achieve their lower cost by including too few backlights or employing an inadequate dimming algorithm, which can lead to display issues such as “blooming” or “halo” effects where there is a perceptible backlight glow around high contrast areas such as small bright objects or white text over black.
Global Dimming LCDs:
Some products, which lack local dimming capabilities, utilize a technology called ‘global dimming.’ This means that during a dark shot, the entire backlight is dimmed and during a bright shot, the entire backlight is turned up. Global dimming can have serious negative implications for on-set HDR reference monitor use. With both SDR and HDR monitoring, one of the most common workflows on-set is to ‘lock off’ the camera on a scene and adjust lighting based on a static image. Because the entire backlight is changing dynamically based on image content, a global dimming display is particularly unreliable on static images, providing little to no consistency from set up to set up.
Image courtesy of Flanders Scientific Inc.
Dual-layer LCDs, sometimes referred to as ‘dual-cell’ LCDs, utilize two layers of LCD in front of the backlight. Dual-layer LCDs avoid the need for local dimming. While one of the LCD layers is used to modulate the overall luminance, the second LCD layer introduces the color subpixels. This separates the tasks of light and modulation to provide a fairly reliable, stable image.
OLED stands for organic light-emitting diode. Compared to LCD displays, where there is a backlight producing light and an LCD layer modulating it, OLEDs have the advantage of each individual pixel in the display being able to turn on or off to produce light or black. This means that OLEDs can produce near-perfect black levels with better viewing angles than LCDs.
NOTE: Not all monitors that claim to be HDR are actually HDR. When planning an HDR on-set workflow, beware of “BSDR” or “Bright SDR” monitors. These products are often marketed as “HDR-capable” because they can interpret an HDR signal type. While some of these BSDR displays can get as bright as HDR monitors, the dynamic range is still as limited as an SDR monitor and the technology itself should still be considered SDR.
Viewing Environment Considerations
There are pros and cons to each display technology, depending on how they will be used in a given production. LCDs can typically achieve higher peak brightness due to the backlight nature, which may be important in a sunny outdoor setting or brighter overall viewing conditions. In a more controlled, darker viewing environment, the enhanced black level performance of OLED pixels can add significantly to the overall dynamic range on a static image and offer a wider viewing angle.
Viewing angle is an important consideration for any display, especially on-set, where there are often multiple viewers of the same monitor standing at different angles. Factors that affect viewing angle include the display type (see “Panel and Backlight Types” above), the reflectivity of the screen (matte vs. glass), the viewing environment, and monitor position. In a perfect world, the display luminance and color should be the same when viewed from any angle--horizontal or vertical.
Size & Form Factor
The physical dimensions, weight, ergonomics, durability, and noise of displays are all factors that should be taken into consideration when designing an HDR viewing environment.
Image courtesy of Panavision
- Power Consumption & Fan Noise
- HDR monitors consume a lot of power and often require fans, which can be noisy. This can be problematic, depending on monitor proximity to the set.
- Currently, the technologies that drive a high-quality HDR monitor can add weight to the monitor itself. Smaller and lighter units, while easier to transport and set up, are often more fragile and challenging to repair on location.
- Operational Temperature Range
- When working in more “extreme” conditions, it’s best to follow the manufacturer’s guidance for optimal temperature ranges.
- Rack and VESA Mountability
- Because of their weight, some HDR monitors may require more robust mounting solutions than others, which can impact considerations around equipment transport and selecting viable locations for the viewing environment on-set.
Luminance & Contrast Ratio
While SDR monitors are typically calibrated to 100 nits, the minimum peak luminance for color grading in Dolby Vision HDR is 1000 nits (a ‘nit’ is a term used to describe luminance or brightness of a display). Ideally, an HDR on-set monitor should have the same peak luminance as the final reference monitor, but this is not always possible with today’s available technology. When considering an HDR monitor for on-set use, a higher priority than peak nit level is a display’s ability to simultaneously (and sustainably) produce bright white levels and sufficiently dark black levels so as to reveal accurate image data in the highlights and shadows.
Contrast ratio is the ratio from the peak brightness to the minimum black level of a display, usually measured in the ratio - light:dark. For example, a 1000 nit display with a black level of 1 nit, would have a 1000:1 contrast ratio. That said, when it comes to consumer displays, marketing has effectively rendered this metric meaningless, with scientifically inaccurate terms like “infinite contrast ratio” commonly used.
As such, there is no reliably marketed benchmark available to best compare the quality of these displays in terms of contrast ratio. Hands-on evaluations can help key stakeholders understand the nuance of each available option. With both SDR and HDR displays, it is critically important to test and calibrate your monitors.
Color management is a term we use to describe how the image is managed between camera and delivery. Proper color management means that color is captured and maintained throughout production and post-production at the highest quality and fidelity, increasing the likelihood that creative intent (the ‘look’) will be maintained throughout the production process and onto our service.
Having a solid color management plan is crucial for a number of reasons, but it is especially important when planning to monitor HDR on-set. This starts by using the same color management framework for both SDR and HDR signal paths, rather than different color management frameworks for each. This way, the production will be comparing SDR and HDR through the same color management framework, rather than comparing SDR and HDR with different frameworks. For example, when using ACES color management, it should be used for both SDR and HDR paths, rather than the camera manufacturer’s SDR (in-camera) and ACES for HDR (external).
See “What Is Color Management” for a more in-depth explanation of this topic.
Signal Distribution & On-Set Equipment Recommendations
- Color space: Log recommended.
- Bit depth: 10-bit minimum.
- Color subsampling: 4:4:4 or 4:2:2 minimum .
- Resolution: 4K resolution is ideal, but HD (1920x1080) resolution is sufficient.
- SDI signal:
- Minimum 10-bit 4:2:2 required for HDR monitoring.
- Signal Splitting / Distribution:
- At a minimum, have a properly rated 3G-HD-VDA (Video Distribution Amplifier) to distribute signals to multiple downstream monitors.
- A router / switcher, properly rated for the type of signal anticipated, e.g. 3G-SDI vs 12G-SDI vs HDMI can be used. Included in this would be a Router Panel for each monitor for which a signal would be distributed. This enables the operator to select what specific signal to monitor.
- The minimum specification for wirelessly transmitting an HDR signal requires systems that work in 10-bits or higher and are capable of transmitting the color space of 4:2:2.
- If you are in a multi-cam / live-to-tape situation, you may elect to use systems that enable additional enhancements for control and/or telemetry for control data.
While a light meter remains an important and effective tool to inform exposure and lighting decisions, measured lighting ratios may need to be adjusted for HDR to account for the differences in roll-off, shadows, and background details. For example, if a key light on one side of the talent’s face appears brighter in HDR than in SDR, the key light or fill light may be adjusted to achieve an appropriate balance. Implementing HDR monitoring on-set, in conjunction with the use of a light meter and other tools, can help to inform these types of lighting ratio decisions.
Scopes are often used to evaluate image signal and exposure to avoid potential clipping during on-set monitoring; however, SDR and HDR use different curves, or EOTF’s (Electro-optical Transfer Functions), for those calculations. This means that operators will have to re-train themselves on how to interpret scope outputs when working in HDR or upgrade their scopes to models that can represent an HDR signal appropriately.
Gamma (Rec. 709)
SDR signals use a 2.4 “gamma” EOTF standardized as BT.1886. This places a peak white of 100 nits at a signal level of 100%, black (0 nits) at a signal level of 0%, and the remaining range is modified using a 2.4 power function. This means that typical imagery will fall in the ‘middle’ of the scopes because the highlights and shadows were compressed in the top and bottom.
PQ (ST. 2084)
With the advent of HDR, a new EOTF was defined called PQ, which stands for Perceptual Quantizer. PQ is standardized as SMPTE ST.2084. Instead of encoding 100 nits into a simple power function, the PQ curve encodes 0 to 10,000 nits and uses a curve modeled after the human visual system’s response to luminance differences. This is done to optimize the use of every code value (CV) across the whole luminance range. This means that typical imagery will generally fall on the lower portion of the scope.
Live Grading Software and LUTs
For HDR monitoring, it is important to ensure the hardware involved in the HDR monitoring pipelines on-set (such as monitors, LUT boxes, etc) supports a minimum of 33x sized 3D LUTs which provide more precise conversion and fewer potential image artifacts.
Live grading software is highly recommended in order to provide real-time control over the image when viewing HDR on-set. Most software options support both camera native color management and ACES color management.
If Live Grading Software is not being used, or crew is not available to run such software, some options for HDR Monitoring include:
In-Camera Output or LUT
Some cameras offer the ability to use their own color management to directly output for HDR on-set monitoring. See our camera guides in Cameras and Image Capture for more information.
If there are limitations with in-camera color management, some monitors offer the ability to load LUTs directly or apply color processing internally, allowing the camera to send a log signal directly to the monitor for image processing.