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Old 17-08-2007, 06:01 PM
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h0ughy (David)
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Help - how do you process for the true and correct colours of M45?

this is a genuine question - how do you process your images to get the true colours of a deep space object - especially with a modified DSLR?

My intended target is M45 to start with
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Old 17-08-2007, 09:03 PM
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I just process until I think it looks nice. There are many objects I have no idea what colour they are suppose to be, so I make it so I like it

Not much help am I
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Old 17-08-2007, 09:16 PM
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I just process until I think it looks nice. There are many objects I have no idea what colour they are suppose to be, so I make it so I like it

Not much help am I
Haha, sounds good! That gave me a giggle.

Anyways, wouldn't true color just be setting white balance correctly for the dark sky, then obtaining as much data as possible.

Or with M45 you could simply mess around with the white balance till it's completely blue in the nebulosity
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Old 17-08-2007, 09:20 PM
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Quote:
Originally Posted by Ingo View Post
Haha, sounds good! That gave me a giggle.

Anyways, wouldn't true color just be setting white balance correctly for the dark sky, then obtaining as much data as possible.

Or with M45 you could simply mess around with the white balance till it's completely blue in the nebulosity
thats my point is it blue? there are a lot of over processed blues out there- what is the natural colour????
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Old 17-08-2007, 09:36 PM
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thats my point is it blue? there are a lot of over processed blues out there- what is the natural colour????
Because they're blue stars and the nebulosity reflects the blue?

http://en.wikipedia.org/wiki/Messier_45

Just wikipedia the messier object and it'll give you everything you want to know about it and more.
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Old 17-08-2007, 10:31 PM
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Dave, to a large degree the colour of the reflection nebula is determined by the frequency output of the most massive stars in the cluster and the compounds it is reflecting off. For example look at the "reflection nebula" around Antares, it isn't blue it is yellow/orange. This is not just because of the colour of Antares, but also because it isn't just reflecting off predominantely hydrogen gas, but a lot of other "contaminants" being expelled by Antares .

But 99% of the time reflection nebula are being highlighted by very big hot O and B association stars reflecting of predominantly hydrogen. If you want to get a colour that is close, then check out the spectral range of a Hertzsrung Russell Main Sequence Diagram. That should give you the best place to start.
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Old 17-08-2007, 10:34 PM
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no the wikipedia misses the mark - by heaps.
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Old 18-08-2007, 12:03 AM
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Hi Houghy!
With my modified 10D i use Astroart 4 to get the "correct color" if there is something like that...

I split the color image into the RGB components.
than, i do combine Trichromie again.
Here Astroart offers a auto color correction.
This auto correction recognizes the sky background does an analyze of the skybackground and from there it calculates the correction factors for Red Green and Blue. R with the modified camera
usually stays 1 and G and B are corrected.
This works most of the time very nice and better than all my
tries in the past with photoshop manually...
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Old 18-08-2007, 07:00 AM
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good thread!
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Old 18-08-2007, 12:00 PM
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Reflection nebula are coloured blue, emission nebular are coloured red for exactly the same reason that our sky is blue. This is not to be confused with clouds that are lit almost directly (near line of sight) by background stars.

To colour correct your image you need to find a white star (G5-G8 Spectral classification I think) and split out the RGB of the image into layres then adjust until the brightest part of the white star is white (assuming you haven't over exposed that star iun the image). There are charts online that dictate the RGB colour of all spectral types of stars so you can also use these.

Cheers
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Old 18-08-2007, 02:01 PM
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Quote:
Originally Posted by h0ughy View Post
this is a genuine question - how do you process your images to get the true colours of a deep space object - especially with a modified DSLR?

My intended target is M45 to start with
Hi h0ughy,

Don't forget the old saying about "beauty is in the eye of the beholder".

Clearly you are striving to achieve a result that is somehow more 'realistic'.
But don't forget that color perception in living organisms utilize complex
physiological and psychological mechanisms that provides another layer
of processing and abstraction over the pure physical phenomena that light
is emitted at varying wavelengths.

Therefore one has to be careful when you set the goal of achieving the "true colors"
of a deep sky object, as you would then need to articulate further what that
actually means.

For example, consider the human eye for one moment. Most of us know that
there are three types of cone cells that respond to short, medium and
long wavelengths respectively. We also know that the wavelengths that these
three types of cones respond to overlap to some extent. However, the response
of a cone also varies with the intensity of light and not just the wavelength
and at least two types of cones have to be activated in order for the brain
to perform some differential processing to perceive color and to determine the
intensity of the light.

So it is little wonder that when we view most DSO's visually through amateur
telescopes, they tend to look monochomatic.

Picking M45 as an example, as far as its "true color" is concerned, it is one
thing to observe it with the unaided naked eye from Earth, another to
view it through it from a telescope on Earth and another yet to view it from
a spacecraft 5 feet away. The intensity of light in each case will alter the
perceived color.

In the mid-80's, I had colleagues that were working on early controllers
for color laser printers. "How complex can this color perception thing be", was the
initial attitude. Turns out that color perception is an incredibly complex
area and still not completely understood. Even though we all know about the
cones in the retina, a lot of color processing goes on within the visual cortex
of the brain where various complex tuning goes on. Back in the early 70's,
there was seminal work done by people like Edwin Land (of Polaroid fame)
in this area.

On a final note, I always remember a National Geographic photograph
of color technicians attempting to tune the color of the images transmitted
back from the Viking landers. They were there with a color chip
chart matching it against an 'identical' chip chart being imaged on the side
of the lander. The response of the electronic imaging system was different
to the human eye and it was the best way to calibrate the image.

Now if one could only send a paint chip chart out to M45 you would be set.

Anyway, don't let any of the above put a damper on what you might
be attempting to do. We all know broadly what wavelengths of light
M45 is emitting and reflecting and therefore roughly what its colors might be.
However, this response also acts as a heads-up not to go looking for the
"holy grail" for some "exact, perfect, true color", as in the end color, like
beauty, is in the eye of the beholder.

Best Regards

Gary
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  #12  
Old 18-08-2007, 02:28 PM
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h0ughy (David)
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thanks David and Gary for your responses
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  #13  
Old 18-08-2007, 02:29 PM
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Quote:
Originally Posted by mostschaedel View Post
Hi Houghy!
With my modified 10D i use Astroart 4 to get the "correct color" if there is something like that...

I split the color image into the RGB components.
than, i do combine Trichromie again.
Here Astroart offers a auto color correction.
This auto correction recognizes the sky background does an analyze of the skybackground and from there it calculates the correction factors for Red Green and Blue. R with the modified camera
usually stays 1 and G and B are corrected.
This works most of the time very nice and better than all my
tries in the past with photoshop manually...
thanks Gerald
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  #14  
Old 18-08-2007, 02:55 PM
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Quote:
Originally Posted by higginsdj View Post
Reflection nebula are coloured blue, emission nebular are coloured red for exactly the same reason that our sky is blue. This is not to be confused with clouds that are lit almost directly (near line of sight) by background stars.

To colour correct your image you need to find a white star (G5-G8 Spectral classification I think) and split out the RGB of the image into layres then adjust until the brightest part of the white star is white (assuming you haven't over exposed that star iun the image). There are charts online that dictate the RGB colour of all spectral types of stars so you can also use these.

Cheers
I agree that stars are the way to go. If you can identify a bright star in your field, you can probably find out its spectral class and hence its true colour. So if you fiddle till that's right, presumably everything else will also be OK.
Geoff
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