Automatically correct color distortion in underwater photos with “Sea-thru”

When diving you’ll notice that the colors start acting up: everything will become more washed out (and look more green/blue) from the moment you look down in the water, and everything will become darker as you descend. Colors like red go first: at a depth of 10m it looks brown. To correct this, underwater photographers like myself use red filters or software in post-production. The cleverly named “Sea-Thru” is an algorithm that can do this automatically:

Sea-thru’s image analysis factors in the physics of light absorption and scattering in the atmosphere, compared with that in the ocean, where the particles that light interacts with are much larger. Then the program effectively reverses image distortion from water pixel by pixel, restoring lost colors.

Here’s a comparison gif:

It comes with one big caveat though:

One caveat is that the process requires distance information to work.

I’m pretty sure that you’ll only need to do this once per type of water. With my own GoPro it usually takes me a dive or two to get my settings right and then I can continue on using with the same settings (at the same location and under the same conditions)

Scientific American: Sea-thru Brings Clarity to Underwater Photos →

Gone Diving

Right now I’m packing my bag, as I’m leaving for vacation tomorrow. I’ll be going on a 10 day diving-trip to Tulum (Mexico) with my diving club Bubbledivers. It’s the first time I’m going to Mexico, and the first time I’ll be diving the Cenotes.

Cenote diving in Tulum (All Mexico 365)

It’s a welcome vacation, as I’ve been really busy the past three months, both on a personal as a professional level:

  • Getting our first employee up and running (along with all extra HR-related work that comes along with that, something I wasn’t made for I must admit)
  • Mentoring a student employee
  • Attending meetups and conferences such as Fronteers Conference and Full Stack Europe (both of which were wonderful)
  • Creating a new workshop “React from Scratch” and adapting a few talks for Full Stack Europe (that got me pumped!)
  • Spending time with the family
  • Gathering and preparing lots of stuff – from a bed and clothes to a card design and domain name – for our soon-to-be-born son (due January 2020)
  • Attending no less than 4 weddings in 6 weeks time (!)
  • Catching up with RSS feeds and blogging out interesting links (I failed at the latter 😅)
  • …and – in between – doing some actual work

👋 See you in 11 days, fully recharged!

The Thistlegorm Project

One of the most famous wrecks to dive on is that of the SS Thistlegorm, a British merchant steam ship that was sunk by German bombers on 6 October 1941 near Ras Muhamad (Red Sea, Egypt).

The University of Nottingham, Ain Shams (Cairo) and Alexandria University have joined forces to create a 3D model of the ship’s wreck. Spread out over 12 dives they’ve collected 24,307 high resolution image files (amounting to 637Gb of data) and have recorded several 360° videos.

360 video of a dive on the SS Thistlegorm

💁‍♂️ SS Thistlewhat?

In September 1941, during WW2, the SS Thistlegorm and HMS Carlisle could not transit through the Suez Canal to reach the port of Alexandria due to a collision in said canal. Awaiting unobstructed passage of the canal they moored at a location the Allies labeled “Safe Anchorage F”.

In the night of October 5 to October 6 1941 the Germans dispatched two Heinkel He-111 aircraft from Crete to locate Allied troop carriers, but failed to do so. On their way back however they spotted the SS Thistlegorm and bombed it. By pure chance the bombs hit cargo hold #4, which also contained (part of) the ammunition the ship was holding, resulting in a huge explosion which made the ship sink fast.

Plan of the SS Thistlegorm (click to enlarge)

The fact that the ship is so famous is because of several reasons:

  • At a depth of 30m it rests at an accessible depth.
  • The wreck sits upright, making it also accessible (wrecks that don’t sit upright can make you nauseous)
  • Even though Jacques Cousteau discovered the wreck in the late fifties it was forgotten for a long time. It only became a dive site in the late nineties, which means things were left intact for over 4 decades.
  • It’s a wreck with lots of things to see. Since it was left untouched for a long time, most of the cargo is still in place: trucks, boots, motorbikes, rifles, shells, airplane wings, tanks, steam locomotives, … they’re all still there just like they were stored at the time of the explosion. (Note that much has been salvaged over the past 20 years though, unfortunately)
  • The wreck can easily be penetrated, with one or more exits always in sight.

One of the motorbikes aboard the Thistlegorm

In March earlier this year I did two dives on the SS Thistlegorm. I can confirm that it truly is a beautiful wreck to dive on. Beware the possible strong currents though 😉

The conversion of the 2D images to a 3D model was done using a piece of software called Agisoft Photoscan Pro, and amounted for quite a lot of time:

  • 42 (1008hrs) days of local computing runtime
  • 23 days (556hrs) of cloud computing runtime
  • 65 (1560hrs) days of continuous computer processing in total

The result is amazing though: not only have they created 3D scenes of the exterior of the wreck’s site (embedded at the top of this post), they’ve also created 3D models of the various floors of the SS Thistlegorm. If you have a Cardboard Viewer you can watch ‘m in true VR style.

The Thistlegorm Project →
The Thistlegorm Project: 3D Programmetry →
The Thistlegorm Project: 360 Videos →

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Using Subsurface with a Suunto Vyper on macOS (OS X)

Profile of one of the dives I did in the Maldives, displayed using Subsurface

Download the Virtual COM Port Drivers and reboot your iDevice. After that Subsurface should recognise your Suunto Vyper.

As a diver one logs all his/her dives into a paper logbook. In the paper logbook one generally notes things like the gear used, the volume of air consumed, the buddies you dove with, the diving/weather conditions, special things/animals that were encountered, a description of the dive (or a map), etc.

A photo of my paper logbook

Next to the paper logbook, modern dive computers (which divers use to keep an eye on their depth, remaining bottom time, etc.) also keep digital logs of each dive onto the dive computer itself. Over the weekend I decided to check out Subsurface, a piece of open source software for reading out scuba dives from your dive computer (created by Linus Torvalds, of all people). So I connected my Suunto Vyper to my Mac using the provided USB cable and … nothing – even though the docs state that Subsurface should automatically detect your dive computer.

Checking out System my Suunto Vyper was indeed connected, yet Subsurface would not recognize it.

“Suunto Sports Instrument”

Long story short: eventually I found a Google Groups Thread suggesting to download Virtual COM Port Drivers. One installation and a reboot later that indeed did the trick: my Suunto appeared as a mount point in Subsurface.

A mounted Vyper, yay!

In hindsight I found a note somewhere way down in the documentation about requiring drivers (“Appendix A – 17.1. Make sure that the OS has the required drivers installed”); this in contrast with earlier (and bigger) mentions in other parts of the docs of “it just works” lacking any mentions of drivers.

Subsurface →

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Diving into the Unknown

In this feature length documentary the viewers are taken into a secret operation where a group of Finnish cave divers try to retrieve the bodies of their friends from deep inside underwater cave in Norway. Now they have to face the burden of their own fears during this life-threatening mission.

It’s only mentioned very quickly in the documentary itself, but the team that recovered the two men set out just only seven weeks (~= 1.5 months) after the tragic accident happened. In the documentary you can clearly see that they are all still processing the events that happened – especially “Kai“ who was under water for about 11.5 hours in total (!), and had to return solo thinking all his friends had died – but also that they are dedicated to bringing back their lost diving buddies.

👉 FYI: If you live in Belgium you can watch “Diving into the Unknown” for free online on vrtnu, until Feb 21.

Googling a bit around, I found this interactive scrollthrough infographic (pictured above) which gives you a good overview of the events that happened — something that I found missing in the documentary itself.

There’s also this extensive longread, with extra footage and input from the survivors themselves. Here’s an excerpt of the events that lead up to the first diving accident:

The passage began to ascend. At one point, it makes a 90-degree turn right while continuing to ascend. It is a narrow section, but not the narrowest on the route.

Grönqvist went first, but having made it through he realised the the light of Huotarinen was nowhere to be seen.

He turned around and waited.

“Then I saw Jari waving his light up and down,” Grönqvist describes.

That is the sign divers use to indicate distress.

“He screamed: ‘Patte, come here!’”

Grönqvist turned back. They were now positioned face to face in the narrow passage. Huotarinen asked Grönqvist to detach one of his large bailout cylinders, which was apparently in the way. It was difficult to detach. Grönqvist moved his scooter out of the way.

“Jari kept yelling at me to come back. I shouted back that I won’t be more than a couple of seconds, calm down.”

He swam back down the narrow passage to Huotarinen and moved the bailout cylinder roughly a dozen metres ahead next to his scooter.

He thought about yanking Huotarinen in case he was stuck but was concerned it could induce panic.

“I still didn’t understand what he was doing there. Was he caught? It wasn’t until then that I noticed that the line of his scooter was stuck under a big rock. Your scooter is stuck, I shouted.”

“Jari tried to yank it free by force. That was the end of that scooter, I thought. I still didn’t understand how distressed he was.”

After the scooter came off, Grönqvist moved out of the way.

They were 111 metres below the surface.

The longread also gives a detailed explanation on how rebreathers work, how a pause of five minutes at that depth increases your dive time by over an hour, what nitrogen narcosis is, … — recommended stuff if you’re no diver, unlike me.

Diving into the Unknown →
Interactive infographic on the Plura cave and the following rescue operation →
Longread: The Finns’ fateful cave dive in Norway was a ghastly struggle →

TomTom Bandit Underwater Scene Mode

Being a diver myself (certified PADI Master Scuba Diver), this looks awesome:

The latest TomTom Bandit camera update now automatically provides colour correction while filming in the water up to a depth of 15 m without the need for any additional accessories. View the difference!

By the looks of it, mainly the white balance is adjusted.

TomTom Bandit Action Cam →

I know what you did last summer

Yes, is still a thing. Save a few posts mid July not that much has happened around here.

So, what have I been up to the past two months? Here’s a small list (saving the best for last):

  1. I reviewed a book
  2. I went diving
  3. I renovated my house
  4. I went camping with my kids
  5. I reexamined my students
  6. I went cooking with the Scouts
  7. I quit my job as a lecturer

Told you I’d save the best for last! 😉

Continue reading “I know what you did last summer”