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There is no "correct" when you are shifting images from infrared to visible. But the "real science" part is probably done with a perceptually uniform color map. Or in the many cases where the image we see is actually a composite of many images taken with the narrow-band IR filter at different central wavelengths, the image might be presented with gaussians of different color corresponding to the different wavelength images. Or each wavelength is considered separately.

As others have hinted, the real science is going to be less pretty.

For example, some algorithm might filter the raw images and extract objects matching some properties, fit them, and then run every reasonable manipulation of that filter to give the fit an error bar. Or they will compare spectra from many galaxies to understand their composition, again running every reasonable variation of the calculation to get some kind of uncertainty.

The end science result will be a graph of some kind in a paper, but it costs very little extra to make these beautiful images on the side.

Photoshop is literally just a matrix transformation engine for data that is highly optimized for ease of use, extensibility, and making visual representations of that data.

Would be awesome to see if anyone can do machine learning using photoshop

> Thanks, but how is the sausage made then?

I can't tell you because I wasn't looking over the shoulder of whoever made the image, but at a guess they started off from a black and white image, then turned it into an RGB image and change the various hues until relevant details became easier to see. The reason that that works is because a large scale structure has areas that emit at roughly the same intensity so you can bring these out by colorizing such a range with a gradient around a single hue.

This is not an automated process because a computer would not know what we humans find 'interesting structures', if you could put that into some form of definition then you might be able to automate the process in the same way that black-and-white images are automatically colorized (which works, but which is sometimes hilariously wrong).

As for the sausage, how it is made is interesting, how it tastes is from a PR perspective probably more interesting. And regardless you could argue that anything that differs from an utterly black square is 'not truthful'.

>so we get an image that depicts a reality we can visually process

Since we can't visually process spectrums other than visible, there's no "correct" way to show the image.

No, there's none of that. These pictures aren't being used for any kind of science. They're 100% PR pieces, made to look pretty - which is fine!

Which makes me wonder how all these galaxies and nebulas would look like in real life. Would they look similar to how they colored it? Are those images maybe potraying a completely wrong reality?

Depends quite a lot on how you look.

If you use an optical telescope to look at the Orion Nebula, you'll see it, but it'll appear pretty much grey. (No scope and it'll be what looks like a bright star, with perhaps a little bit of a blobby nature.) Hook a standard SLR camera up to the telescope and do a long exposure, though, and the reds and blues become readily apparent.

Here's one I took with a standard camera and a 6" scope: https://www.instagram.com/p/CMtHMicBwvI/

You can see different images of the Horsehead nebula and the differences in how colors are presented. They vary substantially, but not in any way that matters, at least to me on an aesthetic level. It's more like the difference between different white balances (which are, to some extent and in some contexts, arbitrary) in a terrestrial image.

https://en.m.wikipedia.org/wiki/Horsehead_Nebula

Maybe one or another of them is more "true to life" but since human eyes never evolved to view this stuff, there's no reason to think that the best and most informative view of an astronomical object is the visible light one.

If you were to fly into these nebula in some kind of spaceship they wouldn't be any brighter than they appear in the night sky from Earth. They would just look way way bigger. The frustrating thing is that our eyes start to respond differently to colours when the light is really really faint. So we would probably perceive them as a grayish green haze. If the image was brightened artificiallythen we would see it as mostly red, with some browns and blues.

There is no "in real life." The size, sensitivity, and spectral response of human eyes is a response to the radiation conditions on Earth, as enhanced by evolution.

If the Sun had been redder or bluer and your eyes were the size of your head or much smaller, everything would look very different.

The Webb images are infrared so "in real life" you'd never see them as shown here. You'd see whatever was visible in optical wavelengths.

This isn't just a quantitative difference. Those science fiction imagined alien worlds covered in little tiny technological lights - just like Earth - are a fantasy. Aliens might see UV instead of optical frequencies, and Earth would look like Venus to them - an opaque planet covered by a thick haze. They might light their spaces with UV, which we wouldn't be able to see so their planet would look dark to us.

And so on.

You are obviously missing the point. They want to know what it would look like to a human observer.

It's the wrong question to ask because a 'human observer' would see absolutely nothing. The age of the objects you are looking at is such that you are looking into the past not at something the is still there in the present, so if we were to transport you there you would not recognize the various objects in visible light at all, too much time has passed.

At this level 'distance' = 'time'.

This isn't true at all, many of the objects are not far away.

The Carina Nebula (imaged) is 7,500 light years away. It is still there.

It seems like people are going through mental gymnastics to avoid answering the question. If someone asked what a famous black and white photo like raising the flag would look like in person, would people give the same nonsense answers? e.g. "There is no "in real life", "the past cant be seen"

For the Carina Nebula[2] :

"Several filters were used to sample narrow and broad wavelength ranges. The color results from assigning different hues (colors) to each monochromatic (grayscale) image associated with an individual filter. In this case, the assigned colors are: Red: F444W, Orange: F335M, Yellow: F470N, Green: F200W, Cyan: F187N, Blue: F090W"

This is in comparison to the human eye, which sees 630 nm for red, 532 nm for green, and 465 nm for blue light.

That is not to say the Nebula isn't also observable in visible light, you would just be seeing different colors and perhaps features. probably something like this visible spectrum imagine of a different part of the nebula

For the other images, what you would see in person ranges from very similar to nothing depending on the image, and pixel in the image.

[1] https://en.wikipedia.org/wiki/Raising_the_Flag_on_Iwo_Jima

[2] https://webbtelescope.org/contents/media/images/2022/031/01G...

[3] https://esahubble.org/images/heic0910e/

Yes, you're right, for that particular nebula. Of course there are other nearby objects that are interesting in that spectral range. But MIRI really shines when it comes to distant galaxies whose light is so far redshifted that it shows up as deep infrared.

Yes, but even then you can answer the question of what it would look like to the human eye if transported closer and/or back in time.

They would look different, have different colors and features. Galaxies would look more like andromeda as viewed via telescope.

What I wouldn't give for a first person view from a planet around a double star... oh well.

>a 'human observer' would see absolutely nothing

Although the accuracy of infrared, or other non-visible spectrum digital representations, could be disputed you would definitely see something similar in visible spectrum as compared to infrared, but with much more dust. Most objects that are emitting energy are doing so in many portions of the spectrum.

See this example: https://esahubble.org/images/heic1406c/

> if we were to transport you there you would not recognize the various objects in visible light at all, too much time has passed.

I think this is an old interpretation of the speed of light and spacetime, since it describes travelling very far through space and also time. So it's more of a statement about the realities of space travel than what it would be like to be there now.

As you said, distance = time, so saying that too much time has passed is the same as saying that it's too distant to see, which is kind of beside the point.

I would say that what we see in the pictures really is the nebula as it exists now, but if you tried to travel there at near the speed of light, your speed through time would increase so much that you would see it rapidly change.

The real question is, what would you see if you were there now (at the time during which the shape of the nebula matches the photo).

Responses to this question are really interesting. I usually take these kinds of evasive non answers in bad faith, thinking that people are refusing to acknowledge the validity of the question.

After some thought, I wonder if it is more an issue of neurodiversity. Perhaps some people cant imagine themselves viewing a celestial object, or can't imagine the desire to do so.

Whose real life? Some of the aliens can see better than us. ;)

These are Webb's first science images, so published papers will come out of them. Of course, those papers will have additional data and analysis to go alongside it, but they absolutely are looking at details resolved in these specific images, processed in this specific way.

So I'm not sure where the sentiment that these are just images for the public is coming from. That's certainly part of why these observations were made and processed this way, but there is science too.

"but they absolutely are looking at details resolved in these specific images, processed in this specific way."

I don't think you're correct. PR images from telescopes aren't new, so if you are correct then surely you'll be able to find papers based on older photoshopped images from Hubble.

Are you able to find any?

There are countless examples. The reason they composite the sensor layers in the first place is because they are trying to color code gases and dust for use by scientists. In some cases they are trying to highlight features that would be too dim otherwise.

Here is an example of color-coded images from Hubble being used - https://iopscience.iop.org/article/10.1086/345911/pdf - The same beautiful image used to get the public excited about space is used in Fig2 to locate where helium, nitrogen, and oxygen are in a planetary nebula. Even the 'Pillars of Creation' image was used for this sort of analysis, though it was less interesting than most images.

"Beautiful" just happens to overlap with "highest contrast and most useful for study". JWST has more sensors than ever before, so it will be more colorful than ever before.

I like to think that these cosmological structures are inherently beautiful the same way abstract mathematics is, and colorizing it is just a way to convey a sense of that beauty to most people who don't speak the language.

Because light red shifts over time/expansion, you could color these towards blue until they cover parts of the human vision space to what they would look like on earth a billion years ago or so.

In that case you could render the image differently depending on how many millions of years in the past you were interested in.

I.e these used to be human “visible” on earth, but eventually their colors shifted beyond what we can perceive with our eyes.

Many of these images are close and not redshifted.

This is manly a demonstration of the imaging capabilities of JWST. Making actual sausage is a way longer, way more boring process.

It depends on the science of course, but generally the sausage is made with specialized software that produces contour plots with error bars and what-have-you. The actual calculations will be done using just numbers, fitting models to data without any pretty pictures at all.

This likely wouldn't have made #1 on HN without "pretty pictures" (this is what astronomers calls them). Photoshop is made for pretty pictures so it would be silly _not_ to use it. :)

I don't think there's a scientific definition of "correct" for these sorts of images. How would you even define correctness?

I might be wrong but in theory you know/see what elements are involved and burned in observed objects.

Based on their distance, hence blue-/redshift, you could at least predict the visible colors we might perceive.

If you'd like to see how space telescope results look in research, you can check out published articles about Hubble.

They do have some custom tools that are publicly available. I saw some videos in the past showing how they use those tools along with Photoshop to process images.