Narrowband imaging - And the creation of colour.... is it science?

[swag72]

I've read threads from time to time where people question the 'authenticity' of narrowband images. They are classed as false colour as you can in effect assign the specific filters as different channel combinations to get certain palettes (SHO is the Hubble Space telescope palette for example).

I think it is widely agreed that within the channel combination one is at least able to see that a specific colour represents a specific gas (In the case of HST mentioned above, the blue represents the distribution of OIII gas). While the colour itself may be 'false' and not what we would see if we could, it is an accurate representation of what gas lies where within a target.

What about the gases not being accurately represented and processing technique being used to make a false colour image? So the image would have nothing scientific to say about the gas distribution within an image, but it would be an artistic impression of a false colour image. Would we be able to tell them apart? Is this a valid method to create a 'pleasing image' while acknowledging that it was created in a more synthetic way? Talking of synthetic........ do we mind a synthetic green channel being used in an RGB image?

 

[ollypenrice]

You don't have to use the term 'false colour.' If, instead, you use the term 'colour mapping' then the negative implications of the word 'false' are avoided and the true nature of the colour mapped image becomes transparent. It could be  described as 'true colour mapping' because the colours truly map the gasses.

What you are going on to discuss is not colour mapping at all, because the colours would be used only for atistic effect. This would truly be false colour because the colour would have no link with reality. Since we already have the term 'false colour' (which is misleading, as I say above) then we'd need a new term like 'imaginary colour.' How would people react to this? Let's wait and see - but I predict everything from approval to apoplectic rage! 

Watching with interest from astride a distant fence!!!

Olly

[PhotoGav]

Great question Sara.

That was almost the first question that everybody asked during my exhibition: are the colours real? I had a mix of LRGB and Ha/OIII bi-colour images, with two Hubble palette images. My answer was that, apart from the Hubble images, the colours were a close approximation to what is really out there. I do map my Ha to a deep red colour and aim for a bluey colour with the OIII (though it often comes out quite white), so I think it was safe to say that. I guess your golden images, Sara, could not be termed 'real', change that to a deep red and it would be nearer to the colour of Ha at 656nm. So, the question of colour depends on what we are trying to do with our images? Are we trying to make accurate records of objects in space, with colours matching the wavelengths of the light captured? 

Is it 'science'? That is the real question. I am inclined to think that our images are not scientific, we 'play' with them to make them look as good as we can imagine them to be. However, they do show an interpretation of the real data that we gather. Nothing added or removed, it is what is, or was, out in space. What use do these images serve other than as an interesting and beautiful view of the worlds beyond Earth? What scientific use could our images have, whether 'approximate real colour' or 'mapped colour'?

Anyone....

[ChrisLX200]

The colour mapping is purely a visual aid to the human eye in differentiating structure, and there is some element of aesthetics as well, but there would be nothing 'scientifically' wrong with having all the channels mapped to a different shade of Red although doing so certainly wouldn't help the human eye to see structure in the image (however, it would make no difference to a computer that could accurately read colour temperature and so would be perfectly acceptable). I'm rather used to reading colour-mapped images for the information contained within but for those with an artistic eye I imagine they would jar somewhat!

ChrisH

[steppenwolf]

This is a fascinating question and one that I have considered in the past. As soon as you enter the world of 'colour mapping', the colours will of necessity be 'false' even though they accurately display the distribution of different types of emission and the presence of dust. However, I agree that it is, unfortunately, true that the use of the word 'false' does have negative connotations but I'm not sure that it is the 'wrong' word as such as the colours do not correctly represent the portion of the light spectrum that the emissions would normally reside in.

Personally, I have no problem with using colour mapping (or tone mapping as it is also called) to bring out the detail in a narrowband image. I also don't see a problem with manipulating LRGB data in the same manner if it releases more detail in the image.

Much of what astrophotogaphers produce is presented in an artistic way rather than a purely scientific way so taking this to a further stage does not seem to be much more than an extension of personal preference with regard to how an image should look. I do, however feel that it is important that such images are correctly described and not passed off as accurately representing emission distributions.

[ChrisLX200]

Well as an example of my earlier post, below is a colour-mapped image designed purely to reveal structure. There is no way one could claim these represent 'real' colours and of course that is not their purpose - it is to differentiate one material from another. Narrow-band images serve (to me anyway) a similar function but the image data of course must be accompanied by an explanation of what the image is showing.

ChrisH

[Stu]

Even for a visual observer this is very interesting

Which colour is assigned to which channel is surely fairly arbitrary, but in order to bring some scientific validity to the images, is it possible to follow some form of calibration or standard process by which you display the varying intensities of signal in a way which is measurable rather than artistic?

Not sure if that makes sense, but I guess it would mean that you would be aiming to apply linear or scaled stretches to things so the final intensity of a pixel represents something directly related to the true object??

[ChrisLX200]

4 minutes ago, Stu said:

Even for a visual observer this is very interesting

Which colour is assigned to which channel is surely fairly arbitrary, but in order to bring some scientific validity to the images, is it possible to follow some form of calibration or standard process by which you display the varying intensities of signal in a way which is measurable rather than artistic?

Not sure if that makes sense, but I guess it would mean that you would be aiming to apply linear or scaled stretches to things so the final intensity of a pixel represents something directly related to the true object??

Well you don't have to - you already have the calibrated data in terms of digital information, you won't be measuring anything from the visible image which is merely a construct made from it, and it is purely an aid to get an overall view. In other words - do the patterns thus created offer any additional insight?

ChrisH

[steppenwolf]

Quote

but in order to bring some scientific validity to the images, is it possible to follow some form of calibration or standard process by which you display the varying intensities of signal in a way which is measurable rather than artistic?

Stu, this is done by some imagers already by using a G2V star to set the 'white balance' of the actual imaging system in use - different weightings are then used to exposures through each filter to compensate, thus producing a calibrated start point for imaging.

[PhotoGav]

Interesting pic Chris... I'm still trying to work out which bit of what creature it is! I've got as far as 'it's a leg'. I'm guessing this is an image from the day job?

 

[ChrisLX200]

Another example from radio data - nothing in visible light at all, and presented in a way that would not appear as a visible artifact even if it were. Below is an FFT spectrogram of the radio reflection from the ion trail of meteor strike in the upper atmosphere. The axies are time x frequency, the colour gamut is intensity. However, looking at the data as presented one can imagine a meteor strike producing a hot explosion (as indeed it does) and this might be interpreted as being a picture of that. Well it is - but not in any visual sense. When you understand _what_ is being displayed then you can correctly interpret the data contained within. The vertical line at the beginning of the upper trace is in fact the rapid deceleration of the meteor, the rest shows the dispersion of the ion cloud as the upper atmospheric winds disperse it over time.

ChrisH

[swag72]

Interesting thoughts  I certainly like the terminology 'colour mapping' instead of false colour.

Is it possible therefore to create an artistic image without any reference to gas distribution? One where perhaps the colours would be used to highlight specific area of interest within a target (as in Chris' more scientific example) yet are not a representation of gases or specific mapping ...... something placed in a more arbitrary fashion to highlight areas of interest.

I feel that while this approach would cause the purists some angst, it may be a way to create a pleasing image for 'the masses' as long as people are not trying to pass something off as something it isn't ..... if that makes sense!

[ChrisLX200]

8 minutes ago, swag72 said:

Interesting thoughts  I certainly like the terminology 'colour mapping' instead of false colour.

Is it possible therefore to create an artistic image without any reference to gas distribution? One where perhaps the colours would be used to highlight specific area of interest within a target (as in Chris' more scientific example) yet are not a representation of gases or specific mapping ...... something placed in a more arbitrary fashion to highlight areas of interest.

I feel that while this approach would cause the purists some angst, it may be a way to create a pleasing image for 'the masses' as long as people are not trying to pass something off as something it isn't ..... if that makes sense!

You're free to do whatever you like Sara! Once you depart from the claim of 'True Colour' (which itself is fraught with controvesy - like the perceptive differences from one person to another) then the objective of the presentation becomes clarity and aesthetics.

ChrisH

[StuartJPP]

When I first took up an interest in astrophotography I didn't particularly like mono or NB images. I was almost exclusively an (L)RGB man. NB seemed "fake" and RGB seemed more real, almost like we would be able to see it if our eyes were 1000 times more sensitive. However as time has progressed, I now like mono and NB images as well, some are awesome and there is more science behind them, indicating the types of emission and the delicate filaments that can't be represented in RGB alone.

I am not a total convert, but I certainly appreciate them much more than I ever did...

[pete_l]

I can't say the depiction of colours worries me. In the same way that the orientation of "up" doesn't.

If colour is used to produce a striking effect, or to reveal / accentuate detail, then that's fine. I don't think people use actual images and examine them visually for "scientific" purposes any more.

By processing the images: brightening them, expanding the dynamic range and sharpening them, we have already moved outside of true images. Just so long as we don't go to the extent of some of the images you see in telescope advertisements, we should be able to retain our credibility.

The one area where a caveat would be needed is to remind the viewer that this is NOT what they'd see through the eyepiece.

[ChrisLX200]

You will often see Radio data, Gamma, IR, X-ray images (and others) overlaid on top of visible light images. Each on their own may tell a story but when combined provide much more insight into what's happening.

ChrisH

[swag72]

But what about if what you were seeing had no scientific merit at all? If the colours you saw were nothing to do with gas distribution but just more to do with artistic thoughts as to where the colour would 'look nice' .....................

[ChrisLX200]

Just now, swag72 said:

But what about if what you were seeing had no scientific merit at all? If the colours you saw were nothing to do with gas distribution but just more to do with artistic thoughts as to where the colour would 'look nice' .....................

Then it becomes a nice painting... ;-)

ChrisH

[swag72]

And a nice painting is acceptable as long as it is stated at the onset?.......

[ChrisLX200]

Of course... ;-)

ChrisH

[Scott]

I think that as long as its clear that it is art for arts sake then theres nothing that can be wrong with it. Of course an omission of information could be seen as intentional desception and one only need ask julian wessel how that turns out

 

[gajjer]

Although I have some interest in the physics of space, my reason for selling my soul to astrophotography is to capture the beauty of the many objects out there. I am NOT trying to accurately represent reality. I don't know how I could do that.

What would my reference be? Our eyes are nowhere near sensitive enough to capture the dynamic range. We stretch some regions and compress others and even if we keep the reds red and the blues blue, they wont match the reality. But that doesn't bother me.

I'm not going to be putting them in technical journals.

If you take your average family snap, how many times have you thought - I'm sure that dress wasn't that colour. Or those flesh tones look a bit too red. And if you can't get those right, what chance is there for a nebula?

It's a representation. I love my simple picture of the Orion nebula - for it's simplicity. Then I look at Olly's million squillion gigabyte picture*   of the region and I'm gob smacked by how much is going on in that region. I could spend all day inspecting it.

They serve different purposes and which is 'correct'. It's a question that doesn't arise for me.

I just like looking at pictures. End of.

 

cheers

gaj

* I may have exagerated the size of Olly's picture. Please forgive me.

 

[ollypenrice]

1 hour ago, gajjer said:

 

cheers

gaj

* I may have exagerated the size of Olly's picture. Please forgive me.

 

You haven't exaggerated its size, assuming you're using the American definition of 'squillion' (which is red x 10^6/Richard Feynman) but you have exaggerated my involvment in it. It was more Dr O'Donoghue's image than mine. I just got my name on it by low cunning.

My take on LRGB or NB enhanced LRGB is this: it's a game with rules. Now everyone has their own relationship with rules. Only fundamentalist nutters stick to them to the letter. Only criminals ignore them entirely. (Douglas Bader said they were there for the obeisance of fools and the guidance of wise men but - he was a nutter as well. No help from him, then...)

I don't do G2V calibration but I do check my star colours against spectral type (OK, OK, not always...) and I assign Ha to red and OIII to green and blue in my LRGB/NB images. So I do have some  respect for the rules of my chosen imaging game, which I call 'natural colour.' Loosely but not arbitrarily, that is. If brought to book I might hope to avoid a custodial sentence. A bit of roundabout repair in a dayglo jacket, maybe, but not prison.

In this game of mine I am intensely jealous of NB imagers because in their game of reduced rules (Formula Libre) they can have tiny stars and fantastic nebular structure... and I hate them!  Well I don't hate Sara cos we're friends. But you know what I mean.

But, seriously, I do like what I lamely call 'natural colour imaging' because it has this in-built discipline and because the colour is three dimensional. It has three colour channels. Bi-colour just doesn't make my heart sing in the same way, though very fine it can be.

Imaginary colour, the subject of this thread, is something new. I'm the son of two artists and married to an artist. I can hardly object to art...

Olly

 

[PhotoGav]

I think we have all agreed that our images are not scientific 'evidence', so they are beautiful images of real objects out in space, not paintings from our imagination. Colour is a feature. Mono images can be stunning. Do we worry that there is no colour? (Funnily enough, a black and white image is the best representation of what a human sees of a space object anyway!). So, why not paint in Bok Globules in pink or Herbig-Haro jets in tangerine. Give it a go and this could be a whole new beginning!

[ollypenrice]

11 hours ago, PhotoGav said:

I think we have all agreed that our images are not scientific 'evidence', so they are beautiful images of real objects out in space, not paintings from our imagination. Colour is a feature. Mono images can be stunning. Do we worry that there is no colour? (Funnily enough, a black and white image is the best representation of what a human sees of a space object anyway!). So, why not paint in Bok Globules in pink or Herbig-Haro jets in tangerine. Give it a go and this could be a whole new beginning!

I'm not signing up to this agreement without caution, but yes. I regard it as important that my images be informative.  That means that the colour will approximate to that which we'd see if we had giant eyes optimized for low levels of light. It also means that my handling of dynamic range imposes the kind of data compression which our senses do automatically anyway. So, like the rest of us, I exaggerate faint signal and suppress bright signal to fit a wider dynamic range from nature into a narrower one for our eyes. But, but, we all avoid brightness inversions so what we don't do is take two features from an image and reverse their respective brightness. 

Tacitly we follow rules, the first of which is to declare what you've done.

Olly