astrovale
member
Reged: 02/19/06
Posts: 65
Loc: Rimini, Italy
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Hi guys,
I've been asking myself a question for quite some time now:
Why do we use orange as false color in our h-alpha images?
Is there a specific reason? is this reason purely aesthetic or is there a "scientific" reason to do it? Does it increase contrast? I see that also professional observatories do it (although not all of them) so there must be a better reason than just "it looks good" or "everyone else does it".
Why not using a red color similar to what the eye sees at the eyepiece of an h-alpha scope? Or a green color used to enhance contast in white light (as the continuum filter used to increase contrast in Baader Herschel prisms).
Lately I've been experimenting with a shade of red (you can see an example here: http://www.amun-ra.org/NOAA_HA/11026/NOAA-11026_20090923_1114_halpha.jpg ) and I don't think it is less contasted than its orange counterpart, so I would like to know what you guys think about this question.
I know it is not a very interesting problem, but hey we gotta find something to do until the next active area besides cleaning filters and processing old movies 
As a provocation I attach 4 images in R, G and B and one in the "usual" orange hue. I think the green one looks very good 
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www.amun-ra.org
Solar Imaging Website
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astrovale
member
Reged: 02/19/06
Posts: 65
Loc: Rimini, Italy
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Blue
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www.amun-ra.org
Solar Imaging Website
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astrovale
member
Reged: 02/19/06
Posts: 65
Loc: Rimini, Italy
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Green 
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www.amun-ra.org
Solar Imaging Website
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astrovale
member
Reged: 02/19/06
Posts: 65
Loc: Rimini, Italy
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Conservative
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www.amun-ra.org
Solar Imaging Website
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swisswalter
sage
Reged: 03/29/09
Posts: 404
Loc: Eastern-Switzerland
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hi luca
i vote for the red one :-)
walter
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only dust in the wind, TAK on GM8, Lunt 60, DMK31,still greenhorn, but as a golfer used to be humble
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Jim Rosenstock
Post Laureate
Reged: 07/14/05
Posts: 3713
Loc: MD, south of the DC Nebula
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I'm "conservative".
Go figure. 
Jim
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DavidM
sage
Reged: 03/25/06
Posts: 217
Loc: Sohar, Oman
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I thought the orange was the closest to the view through the eyepiece, though if I ever got a view like those images through my eyepiece I might fall off my chair!
Does anyone know if there a specific RGB value that exactly replicates the colour of 6562 angstroms?
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David
16" Meade Lightbridge
70 mm Coronado Helios 1 H-a scope
8" Celestron 8iSE
80 mm Orion EON
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old_frankland
professor emeritus
Reged: 03/28/05
Posts: 515
Loc: San Francisco Bay Area
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I think the blue and green, particularly the green makes it far easier to interpret what is going on. Red is actually a poor color as the human eye is less sensitive in that part of the spectrum, and I find it hard to sort out fine structure, especially when a dark shade of red is used.
Excellent comparison project, Luca. Thanks for posting.
My two cents.
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Cheers,
Jim
Livermore CA
http://www.lafterhall.com/astro.html
3" APO, 4" ED refractor, 9" SCT, GM8
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swisswalter
sage
Reged: 03/29/09
Posts: 404
Loc: Eastern-Switzerland
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hi david
656,2 nm must be deep red
walter
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only dust in the wind, TAK on GM8, Lunt 60, DMK31,still greenhorn, but as a golfer used to be humble
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snowdragonusa
Pooh-Bah
Reged: 09/04/07
Posts: 1128
Loc: Denver, CO
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I think the reason for using orange is because our star is a yellow/orange star. Deep sky astrophotographers can use a variety of color palettes to show there work (like with narrowband images), and so can solar photographers. In general though, we tend to color our photos in the 'natural' colors of the subject when possible.
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Adam
12" LX200R, AT80LE
Lunt 60mm Ha & CaK solar scopes
DMK41.AS, DSI Pro, DSI-C, LPI
Denver Astronomical Society
Brighton Astronomical Group
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Oldfield
Postmaster
Reged: 03/20/02
Posts: 5816
Loc: Hong Kong
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frankly, I love green myself.
I think most people imagine sun as in orange, and that's why we made it orange.
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The Home Astronomer from a city where most people are proud of the light pollution
Toys: Orion 100ED, Ranger with NGF-CM, SM40/BF10, TG-SP II, LXD55, DMK 31AF03, Canon 10x30 IS...
My observation log and ideas My General Blog
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DavidM
sage
Reged: 03/25/06
Posts: 217
Loc: Sohar, Oman
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Thanks Walter. Hmm, if H-a is deep red, why does the sun look orange in my eyepiece? Is it the brightness that makes it look orange, or am I missing something here because I am moderately red-green colourblind?
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David
16" Meade Lightbridge
70 mm Coronado Helios 1 H-a scope
8" Celestron 8iSE
80 mm Orion EON
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PeteLawrence
Carpal Tunnel
Reged: 02/07/06
Posts: 2292
Loc: Selsey, UK
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H-alpha red just looks indistinct and it's difficult to see detail. Blue and green show lots of detail but they just look, well, wrong. To me they look as if they're waiting for the other channels to be added
IMO greyscale works better than blue or green.
Orange plays to our natural perception of what the Sun looks like naturally. It also gives an excellent feeling of warmth to the image which helps reinforce the fact that it's correct - even though it's not.
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Best regards,
Pete Lawrence
http://www.digitalsky.org.uk
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Matt Wastell
super member
Reged: 07/05/09
Posts: 139
Loc: Paddington, Brisbane, Australi...
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With images like yours (I love your site) you can post in whatever colour the hell you like.
I like the green one - I see more in it!
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Look up, look good!
http://www.freewebs.com/mattwastellastroimages/index.htm
Matt
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astrovale
member
Reged: 02/19/06
Posts: 65
Loc: Rimini, Italy
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Thanks guys for sharing your opinions. I also had another thought, while my pc was churning in the background working on some old video: CaK pictures are presented in blue to resemble the eyepiece image: I wonder how they wold look in orange! I don't have a CaK filter (for now  ) so I can't experiment, but I bet they would look nice.
I agree with Pete that greyscale is probably the best option, but I'm tempted to break the rules here to try to find a false color that makes details easier to detect. Then I also agree with Adam that orange is the most pleasant within the "right" colors for a star like our own, but that could be applied in a later stage.
I personally like the green and blue like Jim, so expect to see some funky images in the future guys!
Ciao
Luca
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www.amun-ra.org
Solar Imaging Website
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astrovale
member
Reged: 02/19/06
Posts: 65
Loc: Rimini, Italy
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Love your post Matt! Thanks a lot for the comment!
Luca
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www.amun-ra.org
Solar Imaging Website
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ragebot
Carpal Tunnel
Reged: 08/26/05
Posts: 1672
Loc: Tallahassee, FL, USA
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Quote:
Hi guys,
I've been asking myself a question for quite some time now:
Why do we use orange as false color in our h-alpha images?
SNIP
I suspect there are multiple reasons.
Historically the first solar observers could only view the sun through haze, fog, or cloud cover; often times around sunset when the sun did appear as an orange ball. Both Carrington and Maunder recount how their early interest in solar observing started when viewing the sun under the conditions I described above.
The early solar photographers had only B&W technology; and it was really not very good compared to what we have now. Even some of the early color pix paled compared to what even the cheapest digital sensor can provide today.
Most current photographers would confirm that almost all the images we see today are as much the result of post processing as what was used to capture the image. It is quite common to use something like CS to manipulate the RGBL channels of the image; and in some cases eliminate of drastically alter the values in a channel. It should come as no surprise that the original color of the image is also changed using such a work flow.
As others have pointed out the human eye is normally most sensitive around the green wave length, and in fact sometimes B&W images reveal the most detail. But this does vary from person to person (minor or major color blindness and other considerations); so what one person likes best may not be what another person likes best.
I started out with a PST, moved on to a DS SM40, put those filters on an ED80, and finally got a SO sub .3A setup on a 5in OTA. The color of the sun in all three OTAs is different; somewhat from how dim the image is, but probably some what from the band pass as well. Still one of these images in an EP is probably close to the deep read a HA filter should produce, even after my personal vision changes it.
I suspect the some what standard orange of many images is more the result of post processing of digital images than anything else.
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Meade ETX 90, Meade AR5, Orion ED80, Atlas GT, 8 in Newt, Coronado DS SM40, Garrett 10.5X70, Sigma SD10, SD14, Canon 1D2, Xti, Nikon CP4500, C-14
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solarGain
super member
Reged: 07/18/09
Posts: 135
Loc: London & la Palma, Canary Is.
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Luca Hi. I think its time for a Warhol special. With so many artists universally mimicking the color palette could we have our own helio-chrome screen-saver so that on cloud cover days we have our own life-saver there in the background!!! As always...
Edited by solarGain (11/02/09 01:17 PM)
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Davidgojr
sage
Reged: 08/09/08
Posts: 329
Loc: San Antonio, TX
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I see the same level of detail in all of the images that astrovale presented. Therefore, I guess it comes down to preference.
I personally like the h-alpha red colorized images. While the eye is much less sensitive to red light than other colors like green, it makes no difference when the image is bright enough. I like seeing images that look as though I was seeing them at the eyepiece. From a scientific point of view, it just feels like the color reproduction is nice and accurate.
I also like the orange color since it is what I think about whenever I view images of the sun and just looks natural. It also coincides nicely with the yellow-orange colorization of our star.
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David
San Antonio, TX
Orion XT6, White Light Solar, H-alpha Coronado PST
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Evokal
member
Reged: 02/12/09
Posts: 42
Loc: Manitou Springs, CO
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Quote:
H-alpha red just looks indistinct and it's difficult to see detail. Blue and green show lots of detail but they just look, well, wrong. To me they look as if they're waiting for the other channels to be added
IMO greyscale works better than blue or green.
Orange plays to our natural perception of what the Sun looks like naturally. It also gives an excellent feeling of warmth to the image which helps reinforce the fact that it's correct - even though it's not.
Interesting...
My theory is that blue and green are generally considered cooler colors because of their association with water (green is slightly warmer being mixed with yellow). We associate yellow orange, and red with fire and heat ('red hot' for example) Orange is slightly cooler than yellow and red cooler than orange). Purple is the final cooling into blue to complete the circle. I think blue and green only seem wrong due to association, because we all know (most of us at least) that the sun emits every possible color in addition to ones we can't even see.
What's strange about the light-color spectrum is that it isn't a circle at all. The purple wavelength (high energy) is vibrating the most intensely and red (low energy) the most lazily... Personally, I would like to see it morph from one color to another! 
I believe contrast would be enhanced in this way because certain colors bring out brighter areas better and vice-versa concerning dark areas. Too bad it's not possible on CN! IMO I prefer any color over no color. That in no way affects my appreciation of a good photograph though!
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Michael Huwe
Lunt 60mm Doublestack w/ B1200 BF
"Might the sun be a metaphor of the compassion we can only reflect if we turn in that direction, revealing every flaw? I wonder this every time I see a full moon light up the night around me..." -Anonymous
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