250 miles, 800 photographers, 107,000 photos and four million files: Building the Catalan Way Gigaphoto

  • Interview with Galdric Peñarroja, coordinator of the 250 mile long Gigaphoto of the Catalan Way, published Tuesday

Liz Castro
03.04.2014 - 13:40

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We spoke with Galdric Peñarroja, from the Catalan National Assembly Secretariat, who coordinated the construction of the Gigaphoto of the Catalan Way, which was the celebration of Catalonia’s National Day, last September 11, 2013, in which some 1.6 million people held hands from one end of Catalonia to the other, about 250 miles away. The Gigaphoto was published on Tuesday.

Give us the numbers behind the Gigaphoto: photographers, photos, gigabytes?

We had to stitch together 107,000 pictures which is quite a lot, and then we used 800 photographers, with 800 assistants, to cover the 400 kilometers in 45 minutes which is the time that the human chain was held together. The whole final image weighs 295 gigabytes, which is not the size of the image but rather all of the files that comprise the program that we use to view the image, which is over four million files.

How did you build the Gigaphoto?
We spent several months trying to find software that we could use, that could make it easy, something we could afford, and that could still stitch the pictures and get decent results. We were thinking about something like Google Street View, and there are a lot of programs like that, but they’re designed to work with 360° images. We thought naively at the beginning, that it would be easier to work in 2D and we found in the end that it is actually far more difficult. And none of these programs could do it. So in the end, after a lot of research, we ended up contacting VICROB, a research group at the University of Girona, which do computer vision and robotics. They have a lot of experience working with large images. Not exactly the kind of images that we wanted.

The problem is that we did the opposite of what you should do when you want to stitch images together. When you do a Gigapan, made up of several smaller images stitched together, what you have to do is take pictures of things that aren’t moving and you have to take the pictures all from the same point, so they have the same perspective. We did the opposite. We were shooting people, who were moving, from quite close, they were having fun, and to cover the 400 kilometers, every time the photographer took a picture, they moved some meters to take the next one. So that makes all the pictures have a different perspective. Which makes the final photo of the Gigaphoto of the Catalan Way unique and very difficult.

Does that explain the repeated backgrounds behind the people in the Gigaphoto?
That’s because of the perspective. You have to choose: either a correct alignment of the people or of the background. Both things at the same time are impossible. The people are closer to the camera, so when you move four meters, you have a completely new batch of people, but the background is the same, because it’s far away. And you simply have to choose, and obviously we chose the people.

The Gigaphoto website went live yesterday at 17:14h and then crashed…
We had to do the presentation in the afternoon, because all of the things that the Assemblea does are put together by volunteers, we all work, so though it would’ve been better for the media to do it in the morning, we had to do it in the afternoon. We chose 17:14 (quarter past five) because it was the same time that the Catalan Way happened. We had a countdown on the website, so there was a lot of anticipation. And because the website doesn’t load images, that’s a lot of information. We had it prepared with virtual servers that can handle a lot of connections, but we collapsed the networks because they couldn’t handle that much information going back and forth.

All the photographers were volunteers?
Some of them were professionals, most were just amateurs. And then we spent another six months, well, 45 minutes shooting the pictures, and then six months stitching the photos together. I saw the final web actually running, an hour yesterday at 1 in the morning. Of course I’ve seen previews.

What problems did you encounter?
A part from the people moving and having the camera moving as well, there was also the problem of having 800 photographers, with 800 different levels of knowledge, ways of shooting. The manual that we made was very simple and clear, but everyone shot slightly differently and as well we had 800 different cameras and formats and that adds a lot of work. Plus the huge number of pictures that we had to manage.

Did you have problems with file formats?
Since it was all volunteers, everyone shot with their own cameras. So that means that the size of the images was different and some cameras had different aspect ratios (3:4). And so it meant different file sizes, file formats.

Are you missing any segments?
Not that we know of. We checked a lot. There were some places that we were missing pictures. We spent a lot of time recontacting photographers to get missing pictures. For example, sometimes we found there were missing sections at the end, so we contacted the photographer of that section. Sometimes the photographer didn’t have enough time. The instructions were made so that you could take the pictures in 20 minutes, so you had 25 more minutes of spare time in case something went wrong. In some places, people couldn’t finish, but everyone was aware, so they called the photographer in the next section who went back and shot the rest. But it took time to discover all these things, but we went back and found all the images that we were missing in the first set of images.

How many files make up the Gigaphoto in the end?
The images that we finally used number 107,000, but we worked with more, because we had in some sections we had different sets. Some photographers did it twice just to make sure. In some places they had two photographers. Every section had its own history. All of the image files, in the Photo Viewer, you have to break the images into small sections, so you can upload the image and watch it. So when you see the image in the website, the computer is not showing the whole image, that would’ve been too slow.

Have you counted the people who participated?
We didn’t make it for that purpose but anyways you can count the people using the Gigaphoto, but only the people in the first row. What happened actually on September 11, in a lot of places, especially in the sections in towns and cities, is that there was a line, and there was actually a crowd behind the line, in some places there was four or five lines, and sometimes a whole concentration of people. So you can count the people in the first row but you’ll have to do an interpretation of all of the people who were there.

Have you found a lot of celebrities or politicians in the Gigaphoto?
We know that a lot of famous people participated. Some of them we know where they want because they announced it. But we didn’t have time to look for that, but as we were working, we found famous people and funny things, but we were very busy and would chat with other people on the team, but nobody actually wrote it down because we didn’t really have time for that.

In the Catalan Way, there were a lot of families, parents with children, grandparents, everybody, and they took a lot of pets, lots of dogs in the chain. You can see the whole family. And in one particular place, there’s a dog in the chain, the owners are holding the dog, it’s actually flying, the dog’s face looks like he doesn’t know exactly what’s happening. And we also saw there’s a place with a father and a daughter, and in between them they’re holding the girl’s teddy bear. Two funny things that I remember.


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Fes-te de VilaWeb, fem-nos lliures.

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