The 401st Blow :: Thoughts On Media

Dan Flavin Meets iPhone Photo Aliasing

Posted in Content, Software, Technology by Noah Harlan on June 2, 2010

This past weekend I was out on Long Island and we stopped in at the Dia Center’s Dan Flavin Art Institute. If you’re ever passing through Bridgehampton be sure to take a couple minutes and visit this tiny former church and see the exhibit. It’s free and is one of the rare cultural gems of the South Fork. For those that don’t know Dan Flavin’s work, in summary, he arranged colored fluorescent lights in specific patterns, often with the aim of transforming how we respond to a space. It’s at once simple and deceptively complex and I enjoy it quite a bit.

I took a few pictures with my iPhone while walking through the exhibit and they revealed something interesting about the phone and, interesting, created a new vision of the work through the intersection of technologies. Here’s what I saw.

I took a photo of the piece untitled (to Jan and Ron Greenberg), 1972-73. Here is what the piece looks like:

untitled (to Jan and Ron Greenberg), 1972-73

(image used under Creative Commons from 16 Miles of String’s flickr stream)

When I took a photo with the iPhone, here is what I got:

Same image, but very different!

Where did those horizontal lines come from? My first guess was that it had to do with the timing of the fluorescent lights and a rolling shutter issue with the phone.

Fluorescent lights are actually not a constant light source like a regular light bulb. In actual fact a fluorescent light is constantly flickering on and off. This is why they are so unpleasant to sit under all day. The cycle of that flicker is slow enough to be a sub-conscious irritant to our brain (for some of us). This also creates issues for filming since the lights are flickering and the camera is taking a series of still photos those two things can interact in problematic ways. Colors can shift or frames can be lost to darkness.

Rolling shutter is a different issue, unique to digital technologies. The way a digital camera works is that it starts scanning at the top line of the image and quickly scans from top to bottom. The faster it can do that, the more likely it is that an image will look ok. The problem is, if things are moving quickly in the frame, they can be distorted. For example, you are shooting a street and a truck drives by very quickly. When your camera starts scanning the frame, the truck may be in one position but by the time it reaches the bottom of the frame the truck may have moved several feet forward. This means that the vertical lines on the truck will appear sloped. In very extreme scenarios this can create incredible illusions like this:

Pretty wild what’s happening to that propeller, right?

So, perhaps, I’m seeing the actual shadows created by the lights when they flicker. Except I then took this photo of my brother:

The shadows are in front!

The shadows are in front of his body as well. That seemed odd. And that lead me to think that this might be an aliasing thing in the phone meeting the flickering of the light meeting that intense pure green color.

Digital cameras have built in coding to adjust for “mistakes” in how they capture images. To counter problems like the rolling shutter, the cameras are taught to “invent” lines when they think there should be some. The problem is that sometimes, those lines are pure fantasy. Take a look at these two shots. The first is from a digital camera (a Canon EOS 7D) and the second is a raw image of the source:

Aliasing gone awry.

How it was supposed to look.

Quite a difference, eh? For a great, in-depth explanation of all this check out the post I borrowed these images from over on DVXUser.

So perhaps the iPhone is trying to resolve straight lines and in so-doing, it is inventing shadows. Any thoughts? I don’t know exactly the answer but I’m curious…

And just to leave you with one last image that is not going to give you a headache, here’s a picture I took using Red Giant’s awesome Plastic Bullet app at the same exhibit:

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