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Why do People Colour Nebulaes etc in Post Processing?

sabana

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ollypenrice

ollypenrice

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I think there is 2 camps basically, 1) Artistic and 2) Scientific.

One wants aesthetics the other wants correctness.

I like both camps :) But I would clearly state on the image what is and what isn't so there is no doubt.

No, this is not correct either. Essentially it contains the same misunderstanding as the original post.

You'll see two kinds of imaging on here, 'RGB' and 'narrowband.'

RGB first. The imager uses red, green and blue filters to photograph (read 'measure') the object's light output in each colour. When these images are combined you get what the eye would see if you could look at the object in a telescope with a fast enough F ratio and large enough aperture to trigger the eye's colour receptors. No such telescope exists, or barely. We can make them big enough but we can't get the f ratio fast enough. However, RGB imaging is true colour imaging. Photoshop has nothing whatever to do with it and the idea of 'colouring in' is utterly absurd. Two other filters are commonly used to enhance RGB images. One is Luminance. This collects the full visible light spectrum without distinguishing between colours and gets a lot of signal fast becasue it is not discriminating. This will 'light up' the image correctly and bring more detail more quickly.

An imager may also use a narrowand filter, usually H alpha, which enhances the red. This means that faint traces of ionized hydrogen lost in the plain RGB will become visible as will lovely contrasts and structural details lost in a coarse red filter. The Ha is always declared by the imager.

Narrowband; you image the object in filters which trace the presence of different gases. By colouring each gas arbtrarily you make, in effect, a scientific colour map of the object - like a geological map with red for granite, blue for limestone or whatever.

Those of us who passionately devote night after sleepsless night to the meticulous construction of accurate and error-free astrophotos can be more than a bit touchy abut ill-informed criticism but the OP framed his/her point as a question and now I think it has been comprehensively answered.

All digital images are produced through filters, instant cameras, the lot. Equally all colour wet film images relied on chemists brewing up emulsions which were sensitive to different colours. Colour astro imaging is not different at all from any of these. If I take daytime image in my one shot colour astro camera and use an autobalance routine the picture looks like the object I've imaged. What's the problem?

Olly

PS It is also misleading to say that everyone perceives colour differently. We do perceive it slightly differently and some people, most obviously 'colour blind' people have anomalous colour vision. But for it to be perceptible as anomalous there has to be a considerable commonality in the experience of the majority. Plenty of experments can demonstrate that our colour vision is shared and consistent to quite a high degree, though is not absolute. Commonality of sensory experience has a huge role to play in collective survival and so is genetically selected in.

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umadog

umadog

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Olly is right. Colour vision is pretty constant across individuals. The point at which it appears to differ is when colour detection approaches threshold and some observers report seeing colour and others don't. In this instance, the colours in question are incredibly fleeting.

I just googled images of the orion nebula. None of them look like they've been extensively altered "unfairly" in Photoshop. Some look a little "different" because they have HDR-like effects added or have been taken with narrow-band filters. Both of these are fair, however, since they are bringing out real details which wouldn't otherwise be visible to the eye. This, of course, is the point of AP.

The AP has probably misunderstood what most APers are doing. To the OP: why not just send us some links showing the images you are "unhappy" with? This discussion is now becoming unproductive without such material.

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AWR

AWR

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I wonder what a Honeybee sees when it looks at the night sky , i bet its no the same as us :)
( Referring to 'real colurs'): And how do you know this?

Do you have some secret way to see the 'real' colours?

If so, please post some images and enlighten us all.

I like these points.

I'm colour-blind (red-green cone) and at least a couple of times per week at school (I'm a teacher), I get asked "What colour does it look to you?" I try to explain that colour is subjective. It is a secondary quality. It doesn't exist outside of our brain.

If we assume that our physics is correct then we have objects emitting/reflecting some kind of energy. We can use waves to help us explain this phenomenon. We are fortunate in that a small percentage of these waves trigger a response in our eyes. This information is transmitted as an electrical/chemical signal to our brain. It is our brain which 'colours' these signals, helping us to make sense of them. Only at this point does colour exist.

Sound can also be described using waves. Here though our brain uses volume and pitch to interpret these signals rather than intensity and hue. In the future it may be possible to 'swap the leads over'; to see in sound and hear in colour!

Should imagers then be trying to recreate the stimulus received by our eyes from looking at objects with their images? This too creates a problem. This stimulus depends on what we are looking through (12" dob? 5" Mak?); on where we are looking from (Funnily enough, everything looks orange from London) and on how far away the object is.

I guess most imagers are trying to 'best' represent the data captured by their equipment. As this equipment can see more than us and is usually in a different location from us, there is no sense to the term 'real colour'.

The criteria we will use to judge their success are complicated. Especially as our eye/brain/colour chains may all be different. A simple phrase, "Wow, that looks nice", hides a lot more than is at first apparent. If I look at M42 from outside my house, without scope, I see a uniform orange sky. If I were somehow to be able to be 'at' M42, I doubt I would notice anything, it would be too diffuse. I don't want to look at an image of M42 which looks like either of these!

Andrew

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SlipperySquid

SlipperySquid

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One thing to note Sabana is that not all the images posted are from professionals the majority of us look at this as a hobby and are not to make any scientific discoveries.

So this is the place we come to learn from those more knowledgeable than ourselves? So obviously there will be some horrors to the eyes that could make them burst capillaries if stared upon to long but as they say practice makes perfect!

Anyway point of fact is that the beautiful pictures, in all there glorious colour are what attract more and more people to venture out and take a good look at the night sky. I just want to take nice pictures I don't want to change the world :)

Anyway here's a picture I did last night of the moon with slight photoshop enhancements, some would say I've gone to far with the saturation but to my eye it looks ok? I think the colour brings out areas that a monochrome image would not?

post-17960-133877717652_thumb.jpg

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gdheib0430

gdheib0430

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Eh Matt to be honest don't take this the wrong way but I really thing your stars are a little over exposed and the focus is a little off...the crater detail on the moon looks fantastic I think I almost can pick out the Apollo 18 site in this photo.

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rocketandroll

rocketandroll

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This smacks of the worst kind of trolling but... go on... I'll bite :-)

I think the original post and follow ups have all sounded (intentionally) antagonistic, arrogant and provocative... so I'm probably just fueling the fires by even responding but... I'll give my 2p.

So... coloured astro images are 'wrong' is the jist... you can't say (and it seems, acording to you, no one knows) what the 'true' colours of any given DSO actually are... well, if we're talking about what the human eye could see if it were more sensitive, then there would be colour and, given that they are designed to capture light in similar ratios to the human eye I'd say a DSLR should give a fairly accurate representation of that.

DSO's aren't grey. Most appear feint and grey visually through a scope, but if we're going down the route of 'only what the eye can see' then we shouldn't do long exposure photos at all... in fact, taking your logic to it's obvious end... 90% of DSO's shouldn't be imaged at all because they are too feint to be seen without a camera of some kind therefore whatever we see in a photo is 'not to be trusted'.

I've imaged M42 for example with two different cameras through three different scopes... it always comes out similar colours, pink, maroon and a little violet/mauve in there too.

I always look at a lot of images of a subject and see if the colours that are coming out of the stacking software (as raw as it gets) are looking similar to the average everyone else seems to get, and in general I won't try and change the colour at all. Just enhance it a little.

Sure, there are some colour ****'s out there who will tell you your picture of XYZ is 'wrong' because it's meant to be a different shade of red... but I take that with a big pinch of salt... I don't like altering the colour of my images to match someone else's idea of what colour a given object should be.

RGB imaging is potentially even more accurate as you get real data as to the ratio of different colours coming from a given object.

Narrowband isn't for everyone, personally I think some of the Hubble pallette images are stunningly beautiful and knowing what elements are represented by each colour just ADDS TO the scientific value and interest of an image... I can't see anyone say that it detracts from it by showing information that can't otherwise be seen?!

Yes, a lot of us are in this to create attractive looking images. I love the reaction I get from friends and family when I show them a new image I've taken. I don't however (and I don't know of anyone who does) alter the colour pallette of their image to try and make it more attractive... the vast majority of people are out to give a realistic representation of the colours of these objects and the stars in and around them.

Who is it for you (or anyone) to say that someone is 'ruining' an image that THEY have taken by 'childishly colouring it in'? To suggest people are 'colouring in' monochrome images like crazed toddlers is frankly pretty insulting to the hundreds of people on here who put incredible work into creating stunning images for everyone to see and glean information from.

As for the comments about only monochrome art and photography having any value.... I'm not even going to waste my time arguing that one :-) That's probably the funniest thing I've heard on SGL since I joined :-)

Ben

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umadog

umadog

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Sabana, I'm still confused. I don't understand what point you are making with that image. There is no information on that page stating what that is an image of or why it is "false colour." How can it be judged? Why is it objectionable?

There's nothing wrong with "false colour". Here is a shot of Centaurus A Best-Ever Snapshot of a Black Hole's Jets | Flickr - Photo Sharing! The false colour represents non-visible microwave and x-ray radiation. The image has both scientific and artistic merit. False colour is the only way we can see detail such as this. Similarly, IR images from the Spitzer are in false-colour (here's the Helix: http://smbhax.com/stuff/_helix_nebula_spitzer.jpg)

Colouring and HDR techniques do not generally impose information which was not in the original object ("colouring-in" as you put it). I have not noticed a significant number of apparently misleading images from either amateur or professional sources. I suspect it is contrast manipulations which bother you? e.g. http://www.robgendlerastropics.com/M42HeartNMCropM.jpg Even in this image, however, the photographer is just accentuating differences which are already there. In astronomy, the human eye will never see what the camera sees...

On a different note, if you're so bothered about reality why not take all of your terrestrial photos with the camera's white balance set to "sun." You'll be pretty unhappy with quality of the shots under indoor lighting since the camera is showing you what's really going whilst your brain is correcting for the colour balance of the light source. Everying will look yellow under incandescent lighting, for example. There is no right or wrong.

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stan26

stan26

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NB: I hope the people that do colour use a calibrator for their monitor. That would be an even more henious crime. I've seen some completely out of whack.

Why..? So its worth paying extra and having a calibrated monitor setup for editing pictures and posting over the internet for people to admire though mostly un-calibrated monitors and un-calibrated web browsers......? Hmm

If was to profit from my AP or frequently put them onto print for whatever reason then I would maybe consider calibration.

When I'm ruining my pictures in photoshop to be honest I haven't a clue what the correct colour shade/balance should be most of the time. Do a google image search for Orion nebula and see how many different colours come up. Which one should I believe is correct..? The important thing is, it looks good/right to me, and IMO that's all that matters end of.

Stan :)

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JAllen

JAllen

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If you take colour to be the wavelength of light then there is of course a 'correct' colour, even if it is what colour it looks like then most people will see the same thing.

The problem is that the atmosphere's transparency varies with wavelength as does the sensitivity of any sensor, be it your eyes, CCDs or film.

RGB images, or those taken with a DSLR are pretty close to the 'correct' colour. They may be a bit out, but does that really matter?

The main point seems to be regarding false colour images. Some people may take them because they look good, it's their descision, but that isn't really the point of them. HubbleSite seemed to sum it up fairly well, but they are a combination of different narrowband images. Each narrow band image shows the distribution of a certain gas using one of its transitions, such as hydrogen alpha. If you want to see how these gases relate to each other you cannot use a black and white image because you wouldn't able to tell them apart, therefore you assign a certain colour to each gas. That way you can see how the density of each varies with position.

As an unfortunate side effect you get pictures that look great that amateurs want to copy, even though the colours are wrong.

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sabana

sabana

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Heres the thing guys. There are a lot of amazing pictures taken here on this site as I've stated twice now. I know that the effort put in is huge and time consuming. What I have stated is people seem to go two ways though. Either the more relaistic type of image with greyer hues and a more limited colour gamut. Or the others (and you know who you are). Who out and out photoshop their images. I'm sorry if this offends but I only am voicing an opinion rightly or wrongly. But the closest analogy I'v eheard so far is one poster mentioning HDR in photography as an example. You either love it or hate (like Marmite). I just don't like it. But again each unto their own.

Just noticed the last post. Yes thats the point. People do copy hubble image colours even though the colours are wrong.

Nb: Don't forget Stargazing Live for the next three nights on BBC.

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John

John

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.... I'm sorry if this offends but I only am voicing an opinion rightly or wrongly....

Are you really sorry that it offends ? - you don't come across as having any regrets about that at all in the way you post :)

If you sense it does offend then you are wrong to keep voicing the opinion - this is not a forum where we welcome offensive posters :D

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Beyond_Vision

Beyond_Vision

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So Sabana by the sentence ' out and out photoshop their images' do you mean adding information that isn't there. Do you mean using pencil or brush tools to add pixels to the image?

I would love to see a few examples then. I would also love to know how you would propose to deal with data from narrowband filters. Especially how you would deal with wavelengths that are invisible to the human eye or severely attenuated compared to RGB.

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