Before JPEG was JPEG
Forchammer has done research and teaching at DTU, since it was called DTH.
His heart has always been in coding. It started with image coding – before JPEG was JPEG.
Back then the graphics industry printed from film and physically drove them from A to B, so you made the film in one place and printed in another.
At some point people found that it would be more efficient to scan them. At that time, no one had even thought of PDF, but Forchhammer contributed to developing a code for the purpose, which was later adopted by PDF. So Forchhammer played a small part in the development of one of the world's most used file types.
Coding in space
As if it were not enough to have contributed to PDF, Forchhammer was also involved in the beginning of the development of JPEG2000 – a successor to JPEG, which can compress an image up twice as much as JPEG – a file type used by digital cinemas amongst others.
Based on this, Forchhammer was encouraged to help with image coding for satellites. Here Forchammer could use some of his work from JPEG2000 and create a code for space use.
In 2018 the code for space images finally made it to the International Space Station, where it’s used for the ASIM space mission, which primarily studies lightnings above the clouds. They have video cameras from which they select data to send to Earth. For this, they use the code to compress the images so that they can be sent to their colleagues on the ground.
So Forchhammer's work has reached the very outer limits of our atmosphere.
Fast as f***
Forchhammer became leader of the Coding and Visual Communication group in 2008. An important activity in the group is error-correcting codes – especially for high-speed optical communication.
These codes are usable for all digital communication. When you send bits – whether via optical fibres, the wireless mobile network or satellite, there will be errors in the transmission due to noise on the channel. To solve that problem, you need effective codes that correct those errors. So every single time you use your mobile phone, there are error-correcting codes which ensure that your communication is delivered correctly.
What's so great about optical communication is also what makes it so challenging: it’s incredibly fast. So part of the challenge of making error-correcting code for that is figuring out how to make efficient codes that can run that fast. Forchammer has made error correcting codes, running at up to 1.6 gb/second.
Error-correcting codes are also what Forchhammer and his group use in their work on encryption, which they contribute with at our basic research center SPOC, in the development of quantum key distribution. The exchange of quantum communication will, just like all other communication, be flawed, so when you want to make a quantum key that can be used digitally, you also use an error-correcting code here – and Forchammer and his group make it.
In 2020 Forchhammer and his colleagues got an award for their work at IEEE Global Communications Conference. Their contribution to the awarded paper was that they took a more fundamental look at some of the coding people work with, and created a theoretically optimal coding. The trick was that they enabled the decoding to actually run that fast. They demonstrated 400 and 800 gb/second, on which you could run an optimal decoding.
Why?
When asked why he has stayed in research, Forchammer’s answer is simple. “Because it’s exciting”. He elaborates that it's easy, when there are so many different things, you get to work with. It’s never just one thing – it’s not even just research. It’s teaching as well. Forchammer enjoys teaching young, hopeful minds, and of course the freedom, research offers, to pursue new and crazy ideas, and generally having a large influence on what you do.
Academically speaking Forchammer’s proudest achievement was two-dimensional entropy and information theory. The theory was that you could create a new type of memory based on holographic and other novel techniques.
The idea behind it was that you could write information bits at e.g. atom level, but instead of just writing the bits as 0’s and 1’s, you could pack them tighter, if you wrote fewer 1’s. So you could write a code, which allowed greater data density. If you compare this to, for instance, magnetic storage which is one-dimensional, containing several strings next to each other, then you would notice that you would have much larger data density on the strings than between the strings. It is clear that there would be something to gain by storing your data in two dimensions instead.
Why is this so great? Well, the whole thing never really “came to life”, because other types of memory became more popular, but Forchammer still states that this was great to be a part of. Forchammer explains that the thing that’s so great about information technology is that you can work with a highly relevant issue, and distill it down to a quite simple problem, which in reality is very difficult to solve.
Now-then or here-there
Forchhammer explains that there are two types of coding, one for storage, and one for telecommunication, adding that they aren’t all that different from each other. Some say, that storage coding perceives data as now-then, while telecommunication coding perceives it as here-there. In reality, it’s all mixed together in today’s Internet.
Of course the coding must fit the physical media. You do one thing if you're going to do holographic/atomic storage, and another thing if it's for optical communication. But the basic theory – whether you're communicating in a storage device or via a fiber or wireless – is the same.
From digitization to digitalization
At the start of his career, Forchhammer worked with digitization. Here he digitized images and video so that they could be handled digitally. Later, more digitalization has been added, for which digitization is the prerequisite – and it’s also part of the system for efficient handling of the digital data.
The future also holds coding for Forchhammer. He particularly emphasizes energy efficiency and quantum security. But visual communication also plays a role in two of the major projects his group is a part of.
One is aimed at video meetings, where cameras can follow a person at a virtual meeting, the other is aimed at e-commerce, where the group wants to ensure more accurate color representation of clothing in online shopping, so less clothes are returned – something which has an immense environmental impact.
Forchhammer puts it briefly: "If you look at the possibilities of use and the societal perspective, then the focus is sustainability and security".
