Starship Asterisk*

I so often wonder what colors are really like. Occasionally it says something is a false color image, but I have no idea what a non-false image looks like. today's posting of M57- is it really black and white, or is it really the colors it shows, since it does not say it is a false color image. All the gorgeous nebulae, are they really that color when they don't say false color? Besides being hopeful to get an explanation here, I think it would be really nice if the apod would devote a couple of days to that, sometime, show the real color image next to the false, and most of all to say more often what is what.
(and what is bbcode?)
Thanks,
Life

Well, with a lot of astronomical images, what's happening is that they're taking multiple snapshots of the subject, each snapshot through a filter for a specific frequency. So each of these are going to be black-and-white images on their own.

What they'll do then is take these black and white images, and colour each one appropriately for the frequency of light in which it was taken. Then they combine the images, resulting in a colour composite.

Whether or not it's a false-colour image is determined by which colour they're choosing for each frequency-specific image. Sometimes they'll choose colours that will result in something approximating a natural light image, other times they'll use non-realistic colours in order to highlight certain details.

Also bear in mind that cameras see the world differently than eyes do. A lot of these images are of much higher contrast and saturation than what a human eye would see, looking at the same scene.

"True" color images (like the Ring Nebula shot) simply mean that the colors are as received by a visible light CCD or as they appear from a time exposure on ordinary visible light color film, with no filtering or color alteration, and no display of wavelengths outside the visible spectrum.

Stars and planets have pronounced recognizable color variations viewed directly or through a telescope. But most nebulae (even "colorful" ones like M57) just look like blue-white-grey fuzzy blobs viewed directly through even a large optical telescope. Viewing them on the monitor plugged into the CCD allows for vastly enhanced contrast, where the colors become clearly visible.

Life, our eyes are simply not sensitive enough to detect colors from the feeble light emitted by a distant nebula. Cameras have the advantage of absorbing a continuous flow of photons...and therefore far more detail can be detected. Even a five minute exposure can show more color and detail than your eyes could reveal on their own (regardless of the instrument you were looking through).



At the risk of repeating a thread from way back, I think that it is interesting that what we define as "true" color is in fact only our eye's interpretation of the EM spectrum. Remember, we only perceive a tiny portion of the spectrum; there's a heck of a lot more going on than "meets the eye," so to speak.

On the other hand, to make sense of the universe observed through a large portion of the EM spectrum we would probably need to have brains as large as the radio telescope-sized eyes such perception would require!

Each element, such as hydrogen and oxygen, have light reflected off of them at different wavelengths (or frequencies as Qev has explained). When filtering out light from different wavelengths, you are left with just the light coming from one wavelength, let's say oxygen. Then they'll do the same for the hydrogen. You can continue this on for several other common elements known to be found in a nebula, galaxy, etc. After this is done, you can color each picture whatever color you'd like (but they do try to pick standard colors for the elements). Once that has been done, like Qev stated, you create the color composite by putting each of those photos on top of each other in layers, creating the beautiful scenes we see. You can also add layers of "colored" radio / xray emissions for added "oomph" to the picture!

Life, I know what you mean...sometimes you wonder if what we're seeing is at all similar what it would be like to gaze upon the real thing.
That said, snowflakes are pretty enough to our eyes, but it takes a microscope to see the uniqueness of their amazing fine structure.
False colour pictures allow our minds to 'see' the finer structures that our limited eyes can't physically let us indulge in...
...but you're right too, it would be nice to see comparison images; they'd certainly help to understand the need for and wonder of the false images.

... you know, i'd sign up for false-colour enhanced eyeballs in a heartbeat...imagine the optical & chemical spectra around us...you'd always know who dealt it! ;p

Yo, Orca!

Our brains process sight and other sensory input in an essentially analog fashion. They would not need to be any larger or more powerful to handle a broader spectrum. Spectrum limitation is defined by what the cells in the retina detect.

Consider the eagle -- he has far sharper eyesight than we do (solely due to the sharp angle of his macula, creating a higher cross-sectional density of cones = higher resolution), and his cerebrum is tiny and unable to think much in the way of thoughts (bird brain). Of course, his cerebellum is disproportionately large, 'cause flying is rather more complicated than walking.

Our eyes were designed (or evolved) to readily detect the limited portion of the mid- to high-energy EM spectrum that readily penetrate our atmosphere, that are readily reflected by most ordinary objects around us, and that do not destroy cells. Seeing in UV is not very useful, since we would say "look at all those colors", then go blind shortly afterward; also only highly reflective surfaces reflect enough to be useful.

IR has its uses, but they are completely different, since much of that spectrum is radiated rather than reflected at everyday temperatures, and the best parts are only good to about 15 km under optimal viewing conditions. In daylight, the visible spectrum gives you the most useful data.

Randal, I was talking about viewing the "entire spectrum" of EM radiation, including the very low-energy waves.

To detect a wavelength of EM radiation, your receiving device (be it your eyes, radio tower, telescope, ect.) must be at least 1/4 the wavelength of that radiation. Since radio waves can be huge, one-inch eyeballs would not be able to detect them. Hence the vast size of radio telescopes.

Radio astronomy has become a vital tool in modern research (it allows observers to view past interstellar dust, for example). I assumed that the conversation was about observing the cosmos, not just getting around here on Earth.

Seeing in UV is not very useful, since we would say "look at all those colors", then go blind shortly afterward;

That does make sense; the "visible" part of the spectrum is where the wavelengths are as energetic as they can be without becoming ionizing radiation.

If we could see UV, it'd safe to assume we'd evolved that ability and therefore would be unlikely to go blind at 'seeing all those colours'...?


I think therefore i am anthropic

randall cameron wrote:Seeing in UV is not very useful, since we would say "look at all those colors", then go blind shortly afterward

...No blinder than if we were to point out the outdoor colours on a sunny day. UV is absorbed by our retinas whether we detect it or not.

damn your smarty pants!

... nicely pointed out

life wrote:I so often wonder what colors are really like. Occasionally it says something is a false color image, but I have no idea what a non-false image looks like. today's posting of M57- is it really black and white, or is it really the colors it shows, since it does not say it is a false color image. All the gorgeous nebulae, are they really that color when they don't say false color? Besides being hopeful to get an explanation here, I think it would be really nice if the apod would devote a couple of days to that, sometime, show the real color image next to the false, and most of all to say more often what is what.
(and what is bbcode?)
Thanks,
Life

I'm wondering if some of the APOD prints are in real color. Whether or not most of the renderings are really great.
Orin

Granted, we would need much larger eyes to see radio waves. But brain size would not have to change. In fact, resolution with longer waves generally declines, meaning less data to process.

Also, the size of radio telescopes is related to "light grasp", ability to detect very faint sources, like giant optical telescopes, not specifically to wavelength. Most of the sources they are looking at are tens of meters wavelengths or less. Minimum size of omnidirectional antennae (e.g., radio and TV antennae) is related to wavelength.

What you could see in radio would be something else again. Most things would be totally "dark", but electrical devices would emit magnetic halos according to the EMF they emit. Radars, power stations and high tension lines would probably be as "blinding" as arc welders. Watching lightning might be hazardous. Some of the longer waves ("shortwave") would bounce of the clouds and earth.

Would this be useful, particularly throughout the pre-electricity bulk of human history? Probably not, since we can see lightning and aurorae anyway, and there is not much else out there to see in the naturally occurring radio spectrum.

I'm wondering if some of the APOD prints are in real color. Whether or not most of the renderings are really great.
Orin

Most of the image we see anywhere around us, from TV to billboards, the web to the daily papers, has been enhanced somehow...boosted colour/contrast, sharpened/smoothed out complexions, cropped to stimulate or calm...

Might well be the case that without all the digital enhancement, a fair percentage of people wouldn't be quite as fascinated by the images on APOD?