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360 Camera Techniques

Purple Got You Seeing Red? Why Purple Fringing is Such a Big Deal

Purple fringing
Purple fringing

There’s a commonality among 360 cameras. It’s one that seems new and unaddressed. I’ve even seen people posting on social media about the incompetence of the camera manufacturers for allowing it to happen to their camera(s) that are on the market. I even saw one person call for a boycott against a company because of it. Luckily it was a threat that gathered no steam because it all boils-down to fundamental physics. So what is it that’s got people all up in arms?  It’s chromatic aberration, or what’s become known as purple fringe.

Fringe up/down the whole tree
Purple fringe can be seen here, running the entire height of the tree. Read the article here: Review: Insta360 Nano

I take issue with calling it “purple fringing” because we are an inclusive society, we should allow things of every color into our conversations, there’s no reason to single out just purple. Purple is a great color but we should be more inclusive. We’re not monsters, we are fantastic and creative people.

I’ve teased enough. What is this thing and why hasn’t it been fixed?

The answer is simple: Prisms. Simple as that.

When you put a prism between a light source and the light’s destination, you’ll split the light into its constituent colors. Over the last few centuries, we have developed the ability to take hold of the light that is constantly bouncing from place to place from every direction around us. We have recreated one of nature’s most beautiful phenomena. We can take light and split it completely apart to reveal the entirety of the very small section of the electromagnetic spectrum that our eyes can see.

 

From white light to a rainbow
A simple optical device, prisms refract light so it’s constituent colors are visible.

 

Through the use of a simple prism that you can purchase for only a few dollars you can see that acronym some of us learned in school (R.O.Y.G.B.I.V). If you learned what that acronym means, you most likely learned the song. It goes like this:

“Red… Orange… Yellow Green Blue… Indigo and Violet, too”

Go ahead and nod at your screen if you just sang that in your head. Go ahead, nod. Nobody will judge you, people nod at their screens all the time. You’re just another person staring at a screen. You might even make a serious face like you just read something profound! That would make my day!

I’ll show you a quick demonstration. This image was taken as part of a photogrammetric model. The dot is part of a target that I use to get the software to recognize where things are in 3D space. This particular dot is far too close to the edge of the lens that it shows exactly what we’re talking about:

 

Those should be black
These markers are used to help the software understand 3D space

 

It’s important to note that the software I use cannot recognize that as a dot because, well, it’s not a dot. The edge of the lens is acting so much like a prism that it’s now a multi-colored oval.

Look at it a bit closer:

 

That dot isn't black anymore
What was a small black dot is now a multi-colored oval.

 

When I zoom-in, it becomes more apparent that that simple black dot, isn’t just purple (violet according to our song), it’s the whole visible spectrum. Notice that at its furthest from the center of the lens, it’s purple while the closer to the center of the lens it goes from yellow to orange and ending at red.

There’s a HUGE amount of history to this and the laws of optics are extremely interesting but both of those subjects take up at least three full-year college courses. Instead of diving further into it, I’ll leave it here for now.

Just remember, before you go and get all red in the face with anger over that purple (VIOLET!) that makes it all the way around your stitch-line, you’ve left out all the other colors. Instead of being angry at purple (VIOLET!), be angry at the whole visible spectrum because it’s all being split (or refracted).

Maybe if we spread that anger out so much that we wind up upset with the entirety of light itself, we might just spread our anger out so far that it’s too thin to maintain.

Now who wants to experiment by putting a filter on their camera’s stitch-line that’ll eliminate purple (VIOLET!)?

About the authorScott Nebeker is a VR content creator based in Utah whose past clients have included Fortune 100 companies and government agencies.

About the author

Scott Nebeker

Broadcasting semi-live from Salt Lake City, Utah!

4 Comments

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  • While the article correctly explains what causes chromatic aberration, it makes absolutely zero reference to achromatic lens designs such as achromatic doublets. Those are the very lens elements that are designed to correct such undesired effect. I’m including a wikipedia link about such lens designs as a starting point in case anyone is interested on the subject 🙂 https://en.wikipedia.org/wiki/Achromatic_lens

    • You are absolutely correct about that. Good call. 🙂

      A perfect example of what you mention are true macro lenses. In my example photos, I created the aberration by using magnifier filters stacked at the front of the lens. True macro lenses are designed to mitigate this as best as possible using optics alone.

      The problem with writing short form like this is that you have to skip entire chunks of the subject matter. Perhaps a follow-up?

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