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How False Color Astronomy Works
StartsWithABang writes: When you look out at the nebulae in the night sky — especially if you're seeing them with your eye through a telescope for the first time — you might be in for a big surprise. These faint, fuzzy, extended objects are far dimmer, sparser and more cloud-like than almost anyone expects. Yet thanks to some incredible image processing, assigning colors to different wavelengths and adjusting the contrast, we can make out detailed structures beyond what even your aided eye could ever hope to perceive. Here's how the magic happens, and what it teaches us.
Just add paint!
I know I should've expected it given it's on medium, and it's been submitted to /. by its own author, but that's a really bad article. It's full of irrelevant details, stupid comparisons and misleading crap. I understand the concept of "science evangelism" but could you please do it without acting like a total buffoon?
They are more art than science, providing an illusion of reality.
Nope, they are coded with the relation color = abundance of atomic component. Colors are a stimulus, they do not exist outside of all of our brains. What is real is the wavelength, and that, for instance, the transition of an electron from the 3rd to 2nd layer of the structure of the Hydrogen atom will emit a photon at 656nm, which we call red.
One disadvantage of the FITS format is that raw images typically need to be manipulated to show anything.
Nothing to do with the FITS format. That's the same type of information all RAW formats have : unprocessed data, as close as possible to the signal coming from the sensor after quantization, with ideally no processing, offset or other adjustments performed.
It made for great imagery, but wasn’t a true representation of how Jupiter looks.
Our vision is also subjective, it permanently adapt to lightning and ambient color conditions. There is no such thing as a true image representation. Especially in the mentioned case (a magazine), where it is desirable to have an image which pops the eye rather than a blob of washed out colors.
So what's the news here?
P.T. Barnum said it so I won't repeat it.
In the amateur astrophotography community some people image-process to death by using brush tools to selectively enhance specific features. An example: "Paint" a galaxy with a brush tool to make it stand out from the background. In my humble opinion, this is unacceptable. One other example: Wrong color balance in wide-field Milky Way shots, resulting in blue night skies. The night sky can't be blue for any aesthetic reason. At least, inform your viewers that your images are (heavy) processed.
Thierry Legault, an acclaimed astrophotographer says about image processing:
Furthermore, an astronomical image is something fragile, and it is dangerous (and unuseful) to torture it to extract details. Image processing softwares are now so powerful that they look like Ferraris...but don't drive them like Ayrton Senna ! Actually the best is to process an image as little as possible: the first quality of an amateur in this field is its moderation. Just take a look at the planetary images of the HST: they are detailed but very smooth and natural, no trace of the over-processing that damages so many amateur images. If a raw image is good, a slight processing must be sufficient for showing its contents. And if a processed image shows too few details, it is not a problem of processing but a problem of acquisition.
(From http://www.astrophoto.fr/ip.html)
While the images are certainly pretty, and also certainly scientifically useful, nonscientists generally expect to look at a color image and see what they'd see if they were looking at it out the window.
Instead of showing us "image" vs "enhanced image" of the crab nebula, I'd rather that they took some pictures of things we see regularly - a person, for example - and show us the results of the SAME image-processing on these familiar images, so we could judge if the 'enhancement' is trivial or substantially changing the image.
-Styopa
It's done the same way as real colour is done: you assign a colour to a frequency of light and make the brightness of the colour depend on intensity.
Really. That's all your eye does too. And photographic emulsion or CCD cameras.
They respond with a certain efficiency to a range of light frequencies and overlap their resposes. The end result we call "red" "green" and "blue" by convention. Mixing the intensity then produces a colour impression.
No different here. Just the response curves are different and extend much further.
yea all that images are photoshoped
When you need to decide what color to make sulfur II so you can tell it from hydrogen alpha, and the merits of using hydrogen beta over oxygen III.
1) Raw B&W intensities through a non-filer or color filter.
2) "True color" processing to match the colors on a reference image painted on a probe wall. Took a while to confirm the Martian sky and sunsets are different colors than Earth counterparts.
3) "Enhanced color" contrast jacked up to reveal more details like cracks and nodules.
The use of enhanced images, illustrations, artists' conceptions, and diagrams in science education cuts both ways.
Even when I was growing up (in the 1950s) my first impressions of astronomy were formed by illustrations of the solar system--shown from a point of view outside the system, with the orbits displayed as brightly colored, ellipses, and the planets on a scale a thousand times larger than the scale of the orbits.
Something like this helps the child understand what it is that astronomers discovered, and what the spatial relationships actually are. That's good. On the other hand, it leaves them completely unprepared to see Jupiter or Venus out in the backyard on a clear summer night.
And it leaves them unable to appreciate the discovery, the sheer intellectual achievement of someone like Kepler. He figured that out? He didn't have any picture of ellipses? Just from measurements of positions of bright little dots of light that look like they're pinholes in a dome a few hundred feet away? Doing three dimensional trig with nothing but pencil and paper?
My first impressions of Halley's Comet were highly magnified photographic time exposures made by big observatories. The tail, viewed with my eye on the printed page, was bright and probably subtended thirty degrees of visual arc.
I don't think there's any layperson in the world who hasn't been disappointed and upset by their first view of a real comet in the real sky. It should be a wonder, a miracle, a creepy sort of thing--your left brain knows it isn't really a portent, but your right brain is sure it is. Instead, it's like a Peggy Lee refrain: "Is that all there is to a comet?"
What a thrill it ought to be to recognize the Andromeda Nebula with the naked eye. But not if you were expecting a sort of Fourth of July fireworks Catherine wheel instead of a faint smudge.
Understanding the scientific results is worthwhile, but it is almost more important to understand the bedrock experiential reality, and the discovery process.
I know that Jupiter has moons because one night I saw four little stars all in a line right next to it, and next night I saw them again but they'd moved. There is something terribly important in the direct experience, the personal verification. Good buddies, Galileo and me. I've seen something in the sky that wasn't moving around the earth, and so I know Galileo was right.
Last year I finally got around to buying the right kind of telescope for what I wanted to do, a wide aperture low-power "richest field" telescope. With it, I've seen the Andromeda Nebula for myself better than I've ever seen it before.
Boom! No guessing, no squinting, no waiting for a perfectly dark night, THERE IT IS. I'll have to take someone's word for its being a spiral. But I've seen it, me, with my own eyeball. Big faint oval, small bright center. No time exposures, no false color, no computer processed CCD imagery.
It's there, it's really there, I've seen it with my own eyes, not in a planetarium, not in a book, and the light from that sucker had to leave two and a half million years ago to get here just for me to see it. Wow.
"How to Do Nothing," kids activities, back in print!