Photosensitivity Prevention Best Practice Guideline For Branded Productions

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Please note, this doc contains visual examples with strobing effects that may affect photosensitive readers.

 

CONTEXT

This guidance outlines how Photosensitive viewers may be affected by flashing or strobing material in your content, as well as the steps that can be taken to avoid harmful flashes and minimize Photosensitivity risks.

 

WHY DOES NETFLIX CARE ABOUT PHOTOSENSITIVITY IN CONTENT?

We want to provide a stunning viewing experience for all users, on all devices, in any viewing environment. Being mindful of the ill-effects that flashing or strobing patterns can cause for some viewers is an important part of achieving this experience. 

 

WHAT IS PHOTOSENSITIVITY?

Photosensitivity is any negative physical effect that is caused or aggravated by strobing, flashing or quickly changing patterns, luminance or chrominance. It can lead to headaches, eyestrain, nausea and, in some people, seizures. The tests that are run to determine whether content may cause seizures are called Photosensitive Epilepsy (PSE) Tests.

 

Further information, including guidance for how viewing environments can be configured to mitigate Photosensitivity risks, can be found here via the Epilepsy Foundation.

 

IS MY CONTENT REQUIRED TO PASS A PSE TEST?

Please refer to the Netflix Branded Delivery Specification for the most up-to-date requirements.

Netflix conducts testing to the ITU-R BT.1702-3 standard. Our current delivery specifications only require testing for Netflix branded animated titles.  For live action content, Netflix may request testing when the title meets certain criteria such as a high volume of visual effects, heavy action, scenes with strobing lights, and/or is intended for a higher risk audience. Photosensitive Epilepsy is most common in children and viewers under the age of 20.

 

If tested content fails PSE testing and cannot be fixed, an advisory may be applied for our audiences, allowing them to make an informed decision on how and what they watch. This warning appears in an overlay following other ratings information and is displayed when a viewer begins playing an episode or feature:

 

“Some scenes have a strobing effect that may affect photosensitive viewers.”

 

Ultimately, our goal is to avoid issues like these, with the guidance below intended to help productions proactively avoid potentially harmful content.

 

WHAT ELEMENTS IN A PIECE OF CONTENT MAY AGGRAVATE PHOTOSENSITIVITY IN AUDIENCES?

• Rapidly changing brightness at a rate of more than 3 times per second that occupies 25% of the image. This is commonly called a “luminance flash error.”
• Rapid transitions to and from a highly saturated red, at a rate of more than 3 times per second. This is commonly called a “red flash error.”
• Flashing or strobing patterns that don’t violate the thresholds above, but continue for an extended period of over 5 seconds. This is commonly called an “extended flash error.”
• Contrasting and tight patterns (i.e. bars or shapes with little space between light and dark portions), even if static, but especially when the pattern rapidly moves and changes. This is commonly called a “spatial pattern error.”

 

HOW ARE PHOTOSENSITIVITY RISKS DETECTED?

Video content can be run through software tools to analyze if it contains potentially harmful flashes, patterns or chrominance changes. These tools exist both as standalone applications and as a part of many commercially available automated QC tools. 

 

Please note that there are online testing tools which require content to be uploaded. These tools should not be used for content security reasons. Approved testing tools and formats are noted in the appendix below.

 

WHAT ARE SOME EXAMPLES OF POTENTIALLY HARMFUL ON SCREEN EVENTS?

While certain scenarios, such as a scene that takes place in a club with strobing lights, present immediately recognizable risks, many PSE failures are flagged during scenes where flashing or strobing patterns may not be immediately apparent. Common examples include:

• Strobing or flickering lights
  • This could include broken street lights or neon signs.
• Light being emitted from a TV or display on screen
• Explosions
• Camera flashes
• Muzzle flashes
• Lightning and thunder
• Concerts
• Reflections on windows
  • Can be especially problematic if camera movement turns these reflections into a shifting pattern.
• Car chases
  • Can be especially problematic if vehicles are moving through structures where light may be intermittently blocked, resulting in strobing effect. For instance, when a high speed chase occurs on a suspension bridge or past densely packed buildings.
• Graphics and title sequences
  • Can be especially problematic if graphics have flashing or flare effects, are animated to move rapidly across screen, and/or produce a tight pattern.
• Quick camera movements
• Rapid edits
  • Can be especially problematic if cuts are quickly made between bright and light scenes.
• Contrasting patterns like polka dots or tightly packed alternating stripes
• Sunlight being intermittently blocked by tree leaves or other objects moving in the wind
• A siren and or visual warning alarm going off that emits red light
  • Even at a slower cadence, transitions into and out of a highly saturated red can cause a PSE test failure.

Visual examples are below. Please note, these clips contain items with a strobing effect that may affect photosensitive readers.

• The following two shots show more apparent examples of potentially harmful flashes resulting from VFX:

• Action scenes frequently fail PSE testing for a variety of reasons, including the examples provided above. A common factor that may be overlooked in these situations is how the surrounding environment can produce a strobing effect as characters and vehicles move through it. Note how arches in the setting below cause rapidly alternating flashes during a car chase:

 

WHAT STEPS CAN BE TAKEN TO IDENTIFY AND AVOID POTENTIALLY HARMFUL CONTENT?

The further upstream steps are taken to avoid potentially harmful patterns or red flashing, the more likely it is that content can be made safe for photosensitive viewers without altering creative intent. 

 

A production will have the most options at their disposal to avoid Photosensitivity issues if potentially problematic scenes are flagged prior to or during production, especially if steps can be taken to mitigate these issues on set (e.g. adjusting camera exposure settings or lighting). If potentially Photosensitivity concerns aren’t considered until Post, concessions may have to be made during editorial or VFX. If this conversation only begins at picture finishing, the only options available to a production may be severe and impacting to creative intent. This is why Netflix recommends a proactive approach.

 

From script to production to post, we recommend asking questions along the lines of:

• Are there scenes that take place in a dance club or red carpet event? 
• Are there motion graphics or title sequences with fast moving and tight patterns?
• Are there environmental factors like thunderstorms?
• Are there close ups of police sirens or broken lights that are flickering?
• What visual effects are we adding that might create potentially harmful patterns?
• Are  the words strobing, flashing, pattern, or other related terms, in the script? Are they driving a main story point?

If the answer to any of the above questions is “yes”, then we ask you to be mindful of the usage of flashing elements on screen in production, visual effects, post production and finishing. Please contact your Netflix representative if you need content specific guidance.

 

WHAT CAN I DO TO FIX A PSE TEST ERROR?

We acknowledge that there are situations where story and creative intent will result in content containing flashing effects and spatial patterns. Per our testing policy, if it is not possible to remediate a PSE test failure, Netflix may apply an advisory on service.

 

However, we do recommend that productions attempt to fix these errors and explore options for fixing failures. This can include:

• Adjusting the edit to reduce the number and/or cadence of a flashing effect.
• Creating mattes in animation or VFX that allow you to isolate flashing elements.
• Using power windows or qualifiers in color grading to isolate a flashing element or reduce red flashing.
• For VFX or animated elements, decreasing the overall area on screen that flashing effect or pattern occupies.
• Changing the colors that oscillate on screen to reduce red saturation and/or overall contrast.
• Adjusting graphics so that patterns are not as dense and/or animated to move more slowly.
• Adjusting VFX or editorial transitions to avoid rapid motion.

 

FREQUENTLY ASKED QUESTIONS

WHEN SHOULD I TEST?

If you are concerned about flashing effects and/or spatial patterns in your title, or it is one that requires PSE testing for Netflix final delivery, we recommend that you begin testing during editorial. To get actionable results, any sequence requiring testing will need at least 30 seconds of “handles” from your latest cut, ideally with near final VFX and/or animation if applicable.

 

Changes to the edit, a sequence being tested in the context of a full standalone or episode, updates to VFX/Animation, and downstream processes like color grading, can have a significant effect on the final result. With this in mind, we find that testing results at this stage of editorial provide a good leading indicator of whether certain sequences have potentially harmful effects, allowing productions to proactively address potential issues. Please note that if you test a clip of less than 30 seconds and without adequate “handles” from the cut, you are more likely to get a false positive.

 

If your title requires testing, the process for final testing and results submission is detailed below.

 

If my title requires testing, what should I submit to Netflix?

 

If your title requires PSE testing for final delivery to Netflix, coordinating testing and final results submission is the responsibility of production. It should be conducted using your final IMF Package or a high quality derivative (e.g. HDR ProRes XQ, SDR Trim ProRes HQ, DNxHR 444, etc.) and completed prior to asset delivery.

 

Final results must be submitted to Netflix via the following workflow.

 

WHO CAN TEST FOR ME?

If testing during editorial, you can either purchase one of the tools listed in the appendix or work with your Picture Finishing facility to manage testing, as this is a service these partners frequently offer. Having direct access to an approved PSE testing tool will provide the advantage of being able to quickly iterate on test results.

 

For final testing and results submission, we recommend that your Picture Finishing partner conduct testing and upload results during the final delivery process.

 

In select cases, Netflix may conduct final testing on behalf of a production. This option requires prior approval from your Netflix Post Management and Production Technology & Operations representatives.

 

IF I AM DELIVERING AN HDR TITLE, DO I NEED TO TEST BOTH THE HDR MASTER AND SDR TRIM?

Netflix only requires that either your HDR master or SDR trim is tested for results submission. Please note that not all testing software is capable of testing HDR content, please refer to the appendix below for further details.

 

APPENDIX

ACCEPTED PSE TESTING TOOLS

Please note that non-current versions of these products can be used, but may be unable to evaluate HDR content for PSE errors. Even while generally supporting automated QC evaluation of HDR content, some testing tools specifically do not contain testing algorithms compatible with ITU 1702 HDR testing standards. Please consult your product manual, product support, or Netflix PT&O Specialist, if you are unsure of which formats your product version supports.

 

Additionally, because spatial pattern parameters are not defined in older versions of the ITU 1702 standard, please take care to ensure that spatial pattern evaluation is enabled when running PSE testing.

 

As stated above, tools that require content upload and use of third party managed cloud storage or compute resources should not be used.

 

Change Log

• 2/19/25 - Updated to reference ITU 1702-3 spec (1702-2 was previously referenced) and refined guidance on common examples of failure, identification of problematic content, and potential fix methods. Also added expectations around testing HDR content and refreshed "Accepted PSE Testing Tools" section.
• 3/11/21 - Updated wording in several sections per input from Netflix Legal team.

 

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