Archive for May 26th, 2015

Action Camera Video Compression vs. License Plates

Having recently mounted a Cycliq Fly6 rear-facing camera (more about this later) on my Tour Easy’s seat, I had high hopes it might produce more legible images than the Sony HDR-AS30V helmet camera. Although these still images have been compressed a bit, that doesn’t affect the conclusions; the video files aren’t any more readable.

The Fly6 shows where the driver laid on the horn:

Rt 376 at Cedar Valley - 2015-05-22 13:34 - Seat - 1

Rt 376 at Cedar Valley – 2015-05-22 13:34 – Seat – 1

The next two come from the Sony HDR-AS30V helmet camera:

We couldn’t hear what the passenger said above the horn, but it didn’t sound friendly:

Rt 376 at Cedar Valley - 2015-05-22 13:34 - Helmet - 1

Rt 376 at Cedar Valley – 2015-05-22 13:34 – Helmet – 1

However, the driver gave us about as much clearance as can reasonably be expected with oncoming traffic:

Rt 376 at Cedar Valley - 2015-05-22 13:34 - Helmet - 2

Rt 376 at Cedar Valley – 2015-05-22 13:34 – Helmet – 2

Traffic generally hits the 40 mph = 60 ft/s speed limit on that curve and we’re rolling at 10 mph =  15 ft/s, so the relative motion might be upwards of 45 ft/s. The Fly6 runs at 30 frame/s = 1.5 ft and the AS30V at 60 frame/s = 0.75 ft. Although the exposure time is much shorter than the frame time, you can see plenty of motion blur in all the images.

The Fly 6 captures 1280×720 video @ 30 frame/s with variable bit rate compression, saving a separate file every 10 minutes on the dot. The files range from 300 MB to 600 MB, more or less.

The AS30V captures 1920×1080 @ 60 frame/s with constant bit rate compression, plopping a 4 GB file every 22 minutes and 43 seconds.

The Fly6 seems to preserve more image detail than the AS30V, but it’s probably a factor of the native resolution and compression method. The cameras provide absolutely no control over any image functions or settings; they do what they do and you get what you get.

The video compression algorithms seem overwhelmed by the number of pixels that change from frame to frame: asphalt and leaves generally have blocky compression artifacts, particularly in low light, and license plate text generally gets compressed into a blur.

When the camera remains stationary and the image doesn’t change, the compression artifacts largely disappear and the images become crisp and beautiful. Unfortunately, that’s not generally the situation while we’re riding.

I want to apply “low resolution OK here” masks to parts of the frame, leaving more bits for the critical parts. Perhaps applying thin tape to the top third of the frame would help?

Meanwhile, back on the road, nearly all drivers understand the rules and act accordingly; this was a rare occurrence.

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