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Old 26th July 2016, 23:12   #1  |  Link
johnmeyer
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Join Date: Feb 2002
Location: California
Posts: 2,343
Long GOP Artifacts

Fog is a problem for long GOP compression. I'm trying to salvage some spectacular footage taken at 2:00 a.m. under the midnight sun by a DJI Inspire drone in the park on the north side of Iceland. Here is a sample from the original 4K footage, cut with ffmpeg:

DJI Inspire Drone Video Long GOP Jerkiness.MOV

As you will see, the car's motion is smooth, but amorphous objects like the dark ground and the fog are "pulsing." I'm pretty sure this is caused by the inability of the interframe compression algorithm to track the featureless fog, and therefore the pixels associated with that "object" drift aimlessly during for seven frames, and then get harshly moved when an I frame happens every 8 frames. The car and the mountains in the background are perfectly smooth.

My goal is to reduce this harshness. One idea is to either sense (don't know how to do this) or at least mark the start of each GOP (I can afford to take the time to do this, if needed), and then replace the frames on either side with some sort of motion-estimate version. This won't fix everything, but it might reduce the impact of having the position of the fog moved all at once.

For those of you who look at this, you might want to brighten it a bit (increase the top half of the histogram). When brighter, the artifacts really pop out. Also, I have no problem fixing the sensor noise in the shadows, adjusting the gamma, and adding some "punch." It is only the GOP issue that I'm trying to solve.

Any other ideas or thoughts on how to approach this would be welcome.

Last edited by johnmeyer; 26th July 2016 at 23:16. Reason: typo
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