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Moiré Patterns in Video Conferencing

Watch What You Wear When On Video

By Paul Konikowski, CTS-D

As I religiously watched Nightly Business Report with Tyler Mathisen and Susie Gharib last Friday, I could not help but notice the dapper suit coat that Tyler was wearing. Unfortunately, the reason I noticed his coat was because of the wavy moiré pattern his coat created in the YouTube video stream, see below. The moiré pattern is instantly recognizable when Tyler comes on about 40 seconds into the program:

I can not say if this pattern was detectable on high-definition or standard-definition television sets, because I recently “cut the cord” of cable television, and now watch NBR online. The YouTube video stream is decent, but not high definition, and it could be the down-sampling that caused the moiré pattern. Here is another YouTube video that illustrates the moiré effect when two similar sets of parallel lines intersect:

What happened in Friday’s NBR video was Tyler’s coat had vertical and horizontal lines that intersected with the horizontal scan lines of the video stream. Video is traditionally recorded as of horizontal lines of pixels, and each pixel is essentially a sample of the actual color or pattern being recorded. So when these sampling lines intersect with Tylers’ coat lines, a moiré pattern emerges in the video.

I was surprised to see this happen on such a long-running business news show on PBS and other stations, but maybe the pattern was not visible on the professional 1080p cameras and broadcast monitors? Maybe they did not notice until it was uploaded to YouTube? My guess is that Tyler only had one coat with him, so there was little they could do about it before they started airing. Hopefully, CNBC and Tyler learned a lesson, and he will try to avoid those patterns in the future, at least when on video.

This video lesson applies to all of us, not just television newscasters. For example, if you are working at or attending an online university, you certainly do not want moiré video patterns that distract from the teaching. Corporate video conference systems like GotoMeeting, Webex, Polycom and Cisco are also prone to moiré patterns, and many people use Skype, Facetime, or Google Hangouts to video conference with family and friends. So how can you avoid it? First, avoid wearing shirts or ties with small parallel lines. How small depends on the resolution of the camera, the sampling rate, and the distance. Since there are so many variables, just avoid parallel lines, or plaid or checkered outfits (like Tyler Mathisen in the first video).

In addition to avoiding moiré patterns, and watching what you wear, you should always think about two things whenever you video conference: sound and lighting. Is there any background noise from windows, televisions, or other people talking? You should reduce this background noise before you start any conference call by closing windows and doors. You should also close the blinds or shades and turn on all of the lights, as this will help with the room acoustics as well as the lighting. Sunlight is the enemy when it comes to indoor video, because the contrast is too much, so its best practice to use artificial lighting from above, ideally angled towards the faces.

If possible, you should always do a test video call beforehand, and ask the “far end” how you look and sound to them on video. Tell them exactly why you are asking, and ask them to be honest. It’s the video conference equivalent of asking a friend, “do I have anything stuck in my teeth?” after eating a big meal. In the end, everyone wins.

If you have any questions about moiré patterns, video conferencing, lighting, or room acoustics, please don’t hesitate to comment below, or write me directly at pkav.info @ gmail dot com.

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