** WARNING ** Readers are advised that this blogpost doesn't contain any flashing-images but the content of the text deals with the subject of online flashing or strobing images. **END OF WARNING**
Last year a friend and I were guests at the wedding reception of another friend of ours. On arrival, Brian suggested that he bought some drinks and I find us somewhere to park ourselves for the evening. I wandered into the function room, which had just opened, and surveyed the layout. Initially I sat at a table just inside the doorway. Then became aware that the lighting from the musical entertainment was directly in my line of vision. Without hesitation, I immediately moved diagonally across the room and chose a table in a corner. I then selected seats that I knew were definitely not in the direct line of the lighting rig.
One or two other guests may have thought that this was strange behaviour. However there was a perfectly good reason for my action. I know that Brian is an epileptic. Although he isn’t prone to seizures very often, I’m aware that flashing lights can be a source that triggers them. This knowledge comes from having an elder sibling who is also epileptic. In essence what I was doing by changing tables and seat, was minimising any potential risk for Brian, in order that he could enjoy the evening as much as everyone else. Which, I hasten to add, he did do.
I recall this tale simply because I was scrolling through my Twitter feed the other day and came across, what I thought, were some alarming animated GIFs. The animations consisted of series of dark blue and black images with white text superimposed on them. The amount of time, that each image appeared on screen, was so short that the GIFs produced a strobe lighting effect. This made me wonder whether strobing animated GIFs can cause an epileptic viewer to have a seizure.
As viewers, we’re used to hearing a TV news anchor tell us that “This report does contain some flashing imagery”, or seeing subtitles for a televised concert which informs us “The performance may include strobe lighting effects.” So should flashing animated GIFs, that appear online, carry similar warnings?
Keen to broaden my knowledge, I headed to the Epilepsy Action website to see if they had any specific information about this subject. Here, I learnt that around 3 in every 100 people with epilepsy have seizures that are triggered by flashing or flickering lights, or by particular patterns. The symptom even has its own name, photosensitive epilepsy.
In order to fully appreciate what is happening, I also needed to understand the hertz (Hz) unit of frequency. Hertz is a measurement system most commonly used to describe sine waves, musical tones, and speeds at which computers and other electronic devices are driven. Put simply, 1 Hz means one cycle per second. 100 Hz means one hundred cycles per second. The higher the number of hertz then the more frequent the oscillation. When the rate of hertz is associated with light, the result informs us of the speed of the flashing images.
Although there appear to be no fixed guidelines on this subject, the following points are worth considering:
Both natural and artificial light can be a trigger for people with photosensitive epilepsy.
Some patterns like stripes or checks can also be a trigger.
Most people with photosensitive epilepsy are sensitive to flashing images between 16-25 Hz.
Some people may be sensitive to rates as low a 3 Hz and as high a 60 Hz.
In general seizures for people with photosensitive epilepsy usually happen at the time of, or just after, looking at a trigger.
In addition, we need to remember that a Frame Animation Timeline, created in Adobe Photoshop, provides us with the default settings to animate and change frames every:
– 0.1 second (10Hz)
– 0.2 second (5Hz)
– 0.5 second (2Hz)
– 1 second (1Hz)
– 2 seconds (0.5Hz)
– 5 seconds (0.2Hz)
– 10 seconds (0.1Hz)
Adobe Photoshop also enables us to create custom timings for frame animations, for example 0.05 seconds (20Hz). So it easy to see how we can quickly create animated GIFs that have the potential of being a trigger for someone with photosensitive epilepsy.
So what can we do as designers? Personally speaking, I believe a fundamental part of what we do is consider the viewer experience. We need to create visual solutions that are inclusive. It has become second nature for those of us who work in the creative and digital industries to add subtitles to videos for the hard of hearing. Similarly we include alt-tag descriptions to website graphics and images so that screen readers can provide the visually impaired with a more fulfilling online experience. So isn’t it time for us to start thinking about people with photosensitive epilepsy during the planning stages for our next animated GIF? That dark background graphic with flashing white text may seem cool, but has the potential of being more than just a killer-looking design!
Just like I did for Brian, at the wedding reception we went to, I believe it’s time for designers to think about others. Let’s take action now and ensure that everyone can enjoy the animated online visuals we create for them.
24 July 2017
As a footnote to above blogpost, it was great to see that the BBC recently made visitors to their site aware that video footage of lightening storms in the UK contained flashing images. We should have also pointed out that most social media sites, like Twitter, have the ability to disable video autoplay. This is a function that those effected by photosensitive epilepsy should consider enabling.
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