London (Video)

Fixing my low-light video from London, shot with a GH2.

I uploaded to Vimeo a short video of my trip to London when I went to Europe last year. Well, it’s actually a video of only one night in London since it was very exhausting to do and decided not to shoot any more video and instead enjoy my trip after that. That’s why even though I titled it “London” you can only see a few landmarks from what I was able to cover from my long walk that night.

I’ve always really liked night video so I gave it a try that night with a hack on my GH2 to get better compression in low light, the problem is that I don’t have any good low-light lenses so the footage was pretty noisy. I was using very high ISO and many of the shots I did with ETC mode enabled where even noisier since the camera only uses the 1080p inner portion of the sensor to achieve an extra close-up by cropping out the rest, so the noise is bigger. I mostly used a Canon FD 50mm f1.8 which is not that bad for low light, but I always used it at f2.5 since I don’t like the softness and the colour fringing when it’s wide open. So after putting together the video I decided to go back and work on denoising and trying to “restore” the footage.

First thing I did in some shots was to fix the ugly flickering/strobing because of shooting 24p video in Europe. In daylight it would be no problem but since I was shooting at night with lots of street lights there were lots of flickering. I tried shooting at different shutter speeds which would help in some situations but I still had to do some fixes in post. I shot most of the footage using a tripod, so it was easier to fix those flickering problems.

I averaged around 6 to 12 frames, depending on how bad the flickering was. It was great as long as there was nothing moving, like people or cars, so I had to do some masking of moving subjects which don’t really get much of the flickering since they are moving and you can’t really see much as in flat areas.

What it looks like straight from the camera.

This is a comparison only with the averaging. There’s no extra denoising or any colour grading. The difference is subtle in stills but in video the light flickering is extremely annoying. You can see three darker bars in the left side of the frame in the original still. Those were moving vertically across the frame. (Click on the images to see the full size)

Also one thing I noticed was that interpreting the footage as rec709 was automatically giving it a nice curve lift making the details in the shadows more visible and looking more cinematic in these night shots. Usually I would manually go and do that, but with rec709 is a single click away and then from there I can do the extra tunning in the grading. When looking back at the regular sRGB, the blacks look so crushed and very DSLR-like.

The cool thing I noticed with the average thing is that it was helping a lot with reducing noise, so I decided to try the same technique in some of the noisier shots and it was great. Averaging around 3 to 4 frames was good enough for reducing the noise and some moving things like shadows, light reflections or clouds were looking fine even with the averaging.

So what I’ve been experimenting with this night footage is loading as rec709, applying a denoise, averaging frames to get rid of light frequency issues and reduce the noise even more, some small sharpening, grading and then applying some film grain so it looks more organic and less soft. I added a bit of extra grain (probably too much) so that Vimeo has extra detail to compress from.