Before long, we’ll be getting a lot of spectacular imagery from the Webb. This is a good time to remind ourselves just what those colorful images really represent.
The sensors on these instruments simply count photons, so the ‘color’ is artificial, or ‘false color’, assigned by the computer. Since the Webb’s sensors operate primarily in the infrared (the spectral range is from yellow, to far into the IR), objects which are yellow, orange and red can be registered in their true color. Light from the IR parts of the spectrum will have to be simulated by the software. For example, the near infrared may be represented as green, and the far infrared as blue. Intermediate frequencies will be some blend of G or B, and the dividing line between the two will be arbitrarily set by the investigators, depending on which phenomenon they are studying and how it manifests itself in the data. The human eye can only see R, G and B, and combinations of those three primary colors.
So we can look forward to some really gorgeous color images, but we must keep in mind that those colors are ‘false’, that is, they have been chosen for convenience. They do not reflect the colors of what is actually out there. False color is not fake, it represents reality, but it is how we have to represent a reality the human eye cannot detect. Different investigators may choose to assign different combinations of R, B, G to different frequencies, depending on what they want to emphasize, or even their own personal esthetic sensibility.
When I worked with LANDSAT data, we assigned the R gun on the CRT’s to the near infrared, because it caused vegetation (which is highly reflective in the IR) to show up as red, not green. It was the industry standard, or convention, but it still caused a lot of confusion when trying to explain it to management dildoes. We just had to say “vegetation shows up as red”. As you can imagine, it will be really confusing when we’re looking at light from Webb that is invisible to the human eye. And since the universe is really cold, There’s a lot of data out there in far IR part of the spectrum. The LANDSAT platform had 7 sensors, B, G, and R plus several others in the Infrared. We found it most useful to concentrate on the B, G, and near IR bands, as this combination carried the most information. So we assigned them the B, G, and R color phosphors on the CRTs. If we wanted to look at data on the other bands, we had to assign them to the same three guns. The sensor had seven bands, but the eye can only see three at a time! Needless to say, the color images we studied did not resemble at all the scenes we would see with the human eye from an orbiting spacecraft.
Keep this in mind when we get our first exposure to the coming data avalanche from the JWST. I don’t know about you, but I can’t wait!