Stop Calling Them “False Color” Images!

Last week we discussed astronomical imaging and even had our workshop attendees have a go at processing images. Such an exercise is instructive because it crystalizes the idea that colors in astronomical images are neither real nor false. Instead, they’re representative of the filters, structure, and anything else astronomers are trying to pull out of the image data.

Afterward we had a discussion about what the term “false color” really means and that perhaps the term “false” isn’t a very good term to use to describe enhanced images. The discussion turned out to be rather timely because astronomer and imaging scientist Robert Hurt just put a blog post up today where he criticizes the use of the term “false color”. In it, he suggests that the term was invented in a much more mature time when the public had a favorable view of and trust in scientists. Since then, he conjectures, public support and trust of science has fallen flat and the term “false” now implies something intended to be misleading and deceitful. I’m curious if there is any hard polling data that supports or refutes this claim, but I do not disagree with the concern here.

Before I show you what I mean, let’s consider the fact that our eyes only see a tiny sliver of the electromagnetic spectrum

We can only see a teeny tiny part of the electromagnetic spectrum, so how are we supposed to represent the colors we cannot see in an image we're supposed to look at?
We can only see a teeny tiny part of the electromagnetic spectrum, so how are we supposed to represent the colors we cannot see in an image we’re supposed to look at?

As you can see, all of the colors you and I will ever be able to perceive, from the deepest violet to the reddest red imaginable, occupy just a teeny, tiny sliver of the entire electromagnetic spectrum. There are all sorts of colors we’ll never be able to see with our eyes, but we can still detect them with modern-day instruments. These instruments were first showed off to the public during the Voyager missions to the outer planets in the late 1970’s and 1980s. Consider this lovely image of Saturn:

Three Voyager 2 images, taken through ultraviolet, violet and green filters, were combined to make this photograph. And no, it isn’t false, it’s just translated into something we can see. Image credit: NASA/JPL

Pretty isn’t it? Obviously, that’s not how Saturn would appear to our unaided eye if we were flying by along with Voyager, but Voyager captured it in ultraviolet, violet, and green filters. Good for Voyager, but our eyes are simply not capable of pulling off such a stunt. So how can we visualize what Voyager recorded? The answer is to substitute a color we can see for a color we cannot see (in this case, perhaps swapping red in for ultraviolet). This technique doesn’t hide the ultraviolet; quite the opposite – it shows us where the ultraviolet light is coming from!

So let’s describe such images as being rendered in representative color or translated color instead of false color because those colors aren’t being used to falsify anything.

And when we do capture objects in the same colors we do see, perhaps we could refer to those images as being rendered invisible color:

Hubble Space Telescope image of Saturn, processed to appear very similar to how it would look to our eyes. Image credit: NASA/ESA

Even the press release refers to this as Saturn in Natural Colors. Natural to to you and me, perhaps, but what about a Mantis Shrimp? It can see in color bands far beyond the visible and I’m pretty sure he’d be feeling pretty shortchanged if all he saw of Saturn was this washed out-image. Perhaps a better term for this would be Saturn in visible colors instead of in natural colors. Because let’s face it, ultraviolet and infrared happen in nature, too.

All of this is to say that the colors in astronomical images are real, but they may just be being used to represent a color we cannot see with our eyes that nonetheless reveals something truly amazing about the subject in question.

Bottom line, there are no “false color” images and there are no “true color” images. There are only images that convey the wonders of the cosmos to our woefully limited eyes, so let’s drop those false terms once and for all, shall we?