Proper White Balance for AP

[OutsideTheMatrix]

Hi, I've been searching around the web for the proper white balance to use for AP and I've been seeing different solutions:

1. Daylight White Balance- 5300K

2. Tungsten White Balance- 3000K (to neutralize light pollution and sky glow)

3. Fluorescent White Balance- 4000K (to neutralize moonlight)

4. Custom White Balance taken off a dark part of the sky (to get rid of light pollution or sky glow)

5. Manual White Balance and set color temperature to 3900K

6. Auto White Balance (also helps with LP, but is "hit or miss")

I know with RAW we don't have to worry about WB, but I want to save a JPG alongside and be able to review it on the LCD- so which of the above is the best WB to use for light polluted skies? I want A-type stars to appear white, not G type stars since according to this table, A type stars should be white.

http://oneminuteastronomer.com/708/star-colors-explained/

That table indicates that white stars have a surface temp of 7500K, whereas daylight WB is around 5300K; does this mean that if I use Tungsten WB I will get A-type stars to appear white? (5300-3000=2300+5300=7600K).

 

[Allien]

Bump

 

[rnclark]

Hi, I've been searching around the web for the proper white balance to use for AP and I've been seeing different solutions:

1. Daylight White Balance- 5300K

Best if you want natural color and stars where you can see color that matches what people with normal vision see.

2. Tungsten White Balance- 3000K (to neutralize light pollution and sky glow)

Great if you want everything to look blue (the night sky is not blue) (unnatural)

3. Fluorescent White Balance- 4000K (to neutralize moonlight)

Great if you want mostly blue (unnatural)

4. Custom White Balance taken off a dark part of the sky (to get rid of light pollution or sky glow)

White balance is a multiply. Light pollution is added light which should be subtracted. Any site that says use white balance to reduce light pollution doesn't understand the physics and in my opinion should be avoided. It results in variable white balance with scene intensity. This is all to common on the internet. See:

Verifying Natural Color of the Night Sky, Clarkvision.com

5. Manual White Balance and set color temperature to 3900K

Again bias everything to blue and unnatural.

6. Auto White Balance (also helps with LP, but is "hit or miss")

Gives every scene a different white balance. Forget about doing a mosaic.

I know with RAW we don't have to worry about WB, but I want to save a JPG alongside and be able to review it on the LCD- so which of the above is the best WB to use for light polluted skies? I want A-type stars to appear white, not G type stars since according to this table, A type stars should be white.

http://oneminuteastronomer.com/708/star-colors-explained/

That table indicates that white stars have a surface temp of 7500K, whereas daylight WB is around 5300K; does this mean that if I use Tungsten WB I will get A-type stars to appear white? (5300-3000=2300+5300=7600K).

The sun is 5995 K (best fit outside the atmosphere) and solar type stars appear yellow-white to the eye. The above site is using above the atmosphere colors.

The 5300 K (daylight) is a correction for atmospheric transmission. So daylight white balance is best in my opinion. See my 6-part series on color in the night sky:

Color of the Night Sky, Clarkvision.com

Roger

 

[OutsideTheMatrix]

Hi, I've been searching around the web for the proper white balance to use for AP and I've been seeing different solutions:

1. Daylight White Balance- 5300K

Best if you want natural color and stars where you can see color that matches what people with normal vision see.

2. Tungsten White Balance- 3000K (to neutralize light pollution and sky glow)

Great if you want everything to look blue (the night sky is not blue) (unnatural)

3. Fluorescent White Balance- 4000K (to neutralize moonlight)

Great if you want mostly blue (unnatural)

4. Custom White Balance taken off a dark part of the sky (to get rid of light pollution or sky glow)

White balance is a multiply. Light pollution is added light which should be subtracted. Any site that says use white balance to reduce light pollution doesn't understand the physics and in my opinion should be avoided. It results in variable white balance with scene intensity. This is all to common on the internet. See:

http://www.clarkvision.com/articles/nightsky-natural-color-vs-bad-post-processing/

5. Manual White Balance and set color temperature to 3900K

Again bias everything to blue and unnatural.

6. Auto White Balance (also helps with LP, but is "hit or miss")

Gives every scene a different white balance. Forget about doing a mosaic.

I know with RAW we don't have to worry about WB, but I want to save a JPG alongside and be able to review it on the LCD- so which of the above is the best WB to use for light polluted skies? I want A-type stars to appear white, not G type stars since according to this table, A type stars should be white.

http://oneminuteastronomer.com/708/star-colors-explained/

That table indicates that white stars have a surface temp of 7500K, whereas daylight WB is around 5300K; does this mean that if I use Tungsten WB I will get A-type stars to appear white? (5300-3000=2300+5300=7600K).

The sun is 5995 K (best fit outside the atmosphere) and solar type stars appear yellow-white to the eye. The above site is using above the atmosphere colors.

The 5300 K (daylight) is a correction for atmospheric transmission. So daylight white balance is best in my opinion. See my 6-part series on color in the night sky:

http://www.clarkvision.com/articles/color.of.the.night.sky/

Roger

Thanks, Roger...what I was thinking was, would Cloudy (6000K) WB be better since it is close to the 5995K you mentioned? Would that give us the best colors?

 

[Astrozoid]

Hi, I've been searching around the web for the proper white balance to use for AP and I've been seeing different solutions:

1. Daylight White Balance- 5300K

2. Tungsten White Balance- 3000K (to neutralize light pollution and sky glow)

3. Fluorescent White Balance- 4000K (to neutralize moonlight)

4. Custom White Balance taken off a dark part of the sky (to get rid of light pollution or sky glow)

5. Manual White Balance and set color temperature to 3900K

6. Auto White Balance (also helps with LP, but is "hit or miss")

I know with RAW we don't have to worry about WB, but I want to save a JPG alongside and be able to review it on the LCD- so which of the above is the best WB to use for light polluted skies? I want A-type stars to appear white, not G type stars since according to this table, A type stars should be white.

http://oneminuteastronomer.com/708/star-colors-explained/

That table indicates that white stars have a surface temp of 7500K, whereas daylight WB is around 5300K; does this mean that if I use Tungsten WB I will get A-type stars to appear white? (5300-3000=2300+5300=7600K).

For a stock, unmodified camera, daylight white balance is correct.

Note that your JPEGs will still not have a neutral sky color. It will be colored from local light pollution or airglow, which is present everywhere all the time. This is actually the correct color of the sky, it just is not aesthetically pleasing, and not really how we want the images to look (we want them to look like they would if observed or photographed above the Earth's atmosphere).

So, daylight white balance gives you correct color. But then you have to subtract the foreground sky color (light pollution and/or airglow) to achieve a neutral sky background color with correct star colors, and, in theory, correct colors for everything else.

If you have a modified camera, none of the built-in white balance settings will be correct, including daylight.

With a modified camera, for the JPEGs to be correct, you have to use a custom white balance set on a digital gray card shot in direct sunshine on a clear day at noon (preferably in the summer). And still the sky will be red/brown. If you just want the JPEGs to look like they have a neutral sky color (but star colors and other colors will be inaccurate), you can set a custom white balance on the sky itself.

Or, you can determine corrections to apply in post processing to apply a daylight white balance to a modified camera as I have outlined here:

http://www.astropix.com/HTML/I_ASTROP/CUSTOMWB.HTM

Jerry

 

[OutsideTheMatrix]

Hi, I've been searching around the web for the proper white balance to use for AP and I've been seeing different solutions:

1. Daylight White Balance- 5300K

2. Tungsten White Balance- 3000K (to neutralize light pollution and sky glow)

3. Fluorescent White Balance- 4000K (to neutralize moonlight)

4. Custom White Balance taken off a dark part of the sky (to get rid of light pollution or sky glow)

5. Manual White Balance and set color temperature to 3900K

6. Auto White Balance (also helps with LP, but is "hit or miss")

I know with RAW we don't have to worry about WB, but I want to save a JPG alongside and be able to review it on the LCD- so which of the above is the best WB to use for light polluted skies? I want A-type stars to appear white, not G type stars since according to this table, A type stars should be white.

http://oneminuteastronomer.com/708/star-colors-explained/

That table indicates that white stars have a surface temp of 7500K, whereas daylight WB is around 5300K; does this mean that if I use Tungsten WB I will get A-type stars to appear white? (5300-3000=2300+5300=7600K).

For a stock, unmodified camera, daylight white balance is correct.

Note that your JPEGs will still not have a neutral sky color. It will be colored from local light pollution or airglow, which is present everywhere all the time. This is actually the correct color of the sky, it just is not aesthetically pleasing, and not really how we want the images to look (we want them to look like they would if observed or photographed above the Earth's atmosphere).

So, daylight white balance gives you correct color. But then you have to subtract the foreground sky color (light pollution and/or airglow) to achieve a neutral sky background color with correct star colors, and, in theory, correct colors for everything else.

If you have a modified camera, none of the built-in white balance settings will be correct, including daylight.

With a modified camera, for the JPEGs to be correct, you have to use a custom white balance set on a digital gray card shot in direct sunshine on a clear day at noon (preferably in the summer). And still the sky will be red/brown. If you just want the JPEGs to look like they have a neutral sky color (but star colors and other colors will be inaccurate), you can set a custom white balance on the sky itself.

Or, you can determine corrections to apply in post processing to apply a daylight white balance to a modified camera as I have outlined here:

http://www.astropix.com/HTML/I_ASTROP/CUSTOMWB.HTM

Jerry

Thanks Jerry! Question, what is the WB to use to make the sun appear yellow like we see with our eyes or to make sunlke stars like Alpha Centauri appear yellow? Is "white star" reserved to for stars with a temperature of between 6000-7500K (F type stars like Procyon?)

 

[Astrozoid]

Hi, I've been searching around the web for the proper white balance to use for AP and I've been seeing different solutions:

1. Daylight White Balance- 5300K

2. Tungsten White Balance- 3000K (to neutralize light pollution and sky glow)

3. Fluorescent White Balance- 4000K (to neutralize moonlight)

4. Custom White Balance taken off a dark part of the sky (to get rid of light pollution or sky glow)

5. Manual White Balance and set color temperature to 3900K

6. Auto White Balance (also helps with LP, but is "hit or miss")

I know with RAW we don't have to worry about WB, but I want to save a JPG alongside and be able to review it on the LCD- so which of the above is the best WB to use for light polluted skies? I want A-type stars to appear white, not G type stars since according to this table, A type stars should be white.

http://oneminuteastronomer.com/708/star-colors-explained/

That table indicates that white stars have a surface temp of 7500K, whereas daylight WB is around 5300K; does this mean that if I use Tungsten WB I will get A-type stars to appear white? (5300-3000=2300+5300=7600K).

For a stock, unmodified camera, daylight white balance is correct.

Note that your JPEGs will still not have a neutral sky color. It will be colored from local light pollution or airglow, which is present everywhere all the time. This is actually the correct color of the sky, it just is not aesthetically pleasing, and not really how we want the images to look (we want them to look like they would if observed or photographed above the Earth's atmosphere).

So, daylight white balance gives you correct color. But then you have to subtract the foreground sky color (light pollution and/or airglow) to achieve a neutral sky background color with correct star colors, and, in theory, correct colors for everything else.

If you have a modified camera, none of the built-in white balance settings will be correct, including daylight.

With a modified camera, for the JPEGs to be correct, you have to use a custom white balance set on a digital gray card shot in direct sunshine on a clear day at noon (preferably in the summer). And still the sky will be red/brown. If you just want the JPEGs to look like they have a neutral sky color (but star colors and other colors will be inaccurate), you can set a custom white balance on the sky itself.

Or, you can determine corrections to apply in post processing to apply a daylight white balance to a modified camera as I have outlined here:

http://www.astropix.com/HTML/I_ASTROP/CUSTOMWB.HTM

Jerry

Thanks Jerry! Question, what is the WB to use to make the sun appear yellow like we see with our eyes or to make sunlke stars like Alpha Centauri appear yellow? Is "white star" reserved to for stars with a temperature of between 6000-7500K (F type stars like Procyon?)

Roger can probably better answer this question, but our eyes evolved under sun light, and we see sunlight as white. But our eyes are very adaptable to all kinds of light of different color temperatures.

Think about it, do you see the Sun as yellow when it is high in the sky on a clear summer day? No, you don't see it at all because it is too bright to look at. You see it as red when it is setting if it is not too bright to look at, but that is because of Rayleigh scattering.

So if you could somehow dim the brightness of the sun perfectly without altering it's color balance, what color would you see when it was high in the sky? I would say it would be white because your eyes would adapt and your brain/eye/vision/consciousness system adapts to make the brightest thing in the scene as white.

I'm curious as to what Roger will have to say on this, he's much more knowledgeable about this than I am.

Jerry

 

[OutsideTheMatrix]

Hi, I've been searching around the web for the proper white balance to use for AP and I've been seeing different solutions:

1. Daylight White Balance- 5300K

2. Tungsten White Balance- 3000K (to neutralize light pollution and sky glow)

3. Fluorescent White Balance- 4000K (to neutralize moonlight)

4. Custom White Balance taken off a dark part of the sky (to get rid of light pollution or sky glow)

5. Manual White Balance and set color temperature to 3900K

6. Auto White Balance (also helps with LP, but is "hit or miss")

I know with RAW we don't have to worry about WB, but I want to save a JPG alongside and be able to review it on the LCD- so which of the above is the best WB to use for light polluted skies? I want A-type stars to appear white, not G type stars since according to this table, A type stars should be white.

http://oneminuteastronomer.com/708/star-colors-explained/

That table indicates that white stars have a surface temp of 7500K, whereas daylight WB is around 5300K; does this mean that if I use Tungsten WB I will get A-type stars to appear white? (5300-3000=2300+5300=7600K).

For a stock, unmodified camera, daylight white balance is correct.

Note that your JPEGs will still not have a neutral sky color. It will be colored from local light pollution or airglow, which is present everywhere all the time. This is actually the correct color of the sky, it just is not aesthetically pleasing, and not really how we want the images to look (we want them to look like they would if observed or photographed above the Earth's atmosphere).

So, daylight white balance gives you correct color. But then you have to subtract the foreground sky color (light pollution and/or airglow) to achieve a neutral sky background color with correct star colors, and, in theory, correct colors for everything else.

If you have a modified camera, none of the built-in white balance settings will be correct, including daylight.

With a modified camera, for the JPEGs to be correct, you have to use a custom white balance set on a digital gray card shot in direct sunshine on a clear day at noon (preferably in the summer). And still the sky will be red/brown. If you just want the JPEGs to look like they have a neutral sky color (but star colors and other colors will be inaccurate), you can set a custom white balance on the sky itself.

Or, you can determine corrections to apply in post processing to apply a daylight white balance to a modified camera as I have outlined here:

http://www.astropix.com/HTML/I_ASTROP/CUSTOMWB.HTM

Jerry

Thanks Jerry! Question, what is the WB to use to make the sun appear yellow like we see with our eyes or to make sunlke stars like Alpha Centauri appear yellow? Is "white star" reserved to for stars with a temperature of between 6000-7500K (F type stars like Procyon?)

Roger can probably better answer this question, but our eyes evolved under sun light, and we see sunlight as white. But our eyes are very adaptable to all kinds of light of different color temperatures.

Think about it, do you see the Sun as yellow when it is high in the sky on a clear summer day? No, you don't see it at all because it is too bright to look at. You see it as red when it is setting if it is not too bright to look at, but that is because of Rayleigh scattering.

So if you could somehow dim the brightness of the sun perfectly without altering it's color balance, what color would you see when it was high in the sky? I would say it would be white because your eyes would adapt and your brain/eye/vision/consciousness system adapts to make the brightest thing in the scene as white.

I'm curious as to what Roger will have to say on this, he's much more knowledgeable about this than I am.

Jerry

I'm wondering too because on the OBAFGKM scale aren't F type stars generally considered to be white?

Basically, something like this:

O- deep blue

B- light blue

A- bluish-white

F- white

G- yellowish

K- orange

M- red

 

[Jon Rista]

Hi, I've been searching around the web for the proper white balance to use for AP and I've been seeing different solutions:

1. Daylight White Balance- 5300K

2. Tungsten White Balance- 3000K (to neutralize light pollution and sky glow)

3. Fluorescent White Balance- 4000K (to neutralize moonlight)

4. Custom White Balance taken off a dark part of the sky (to get rid of light pollution or sky glow)

5. Manual White Balance and set color temperature to 3900K

6. Auto White Balance (also helps with LP, but is "hit or miss")

I know with RAW we don't have to worry about WB, but I want to save a JPG alongside and be able to review it on the LCD- so which of the above is the best WB to use for light polluted skies? I want A-type stars to appear white, not G type stars since according to this table, A type stars should be white.

http://oneminuteastronomer.com/708/star-colors-explained/

That table indicates that white stars have a surface temp of 7500K, whereas daylight WB is around 5300K; does this mean that if I use Tungsten WB I will get A-type stars to appear white? (5300-3000=2300+5300=7600K).

For a stock, unmodified camera, daylight white balance is correct.

Note that your JPEGs will still not have a neutral sky color. It will be colored from local light pollution or airglow, which is present everywhere all the time. This is actually the correct color of the sky, it just is not aesthetically pleasing, and not really how we want the images to look (we want them to look like they would if observed or photographed above the Earth's atmosphere).

So, daylight white balance gives you correct color. But then you have to subtract the foreground sky color (light pollution and/or airglow) to achieve a neutral sky background color with correct star colors, and, in theory, correct colors for everything else.

If you have a modified camera, none of the built-in white balance settings will be correct, including daylight.

With a modified camera, for the JPEGs to be correct, you have to use a custom white balance set on a digital gray card shot in direct sunshine on a clear day at noon (preferably in the summer). And still the sky will be red/brown. If you just want the JPEGs to look like they have a neutral sky color (but star colors and other colors will be inaccurate), you can set a custom white balance on the sky itself.

Or, you can determine corrections to apply in post processing to apply a daylight white balance to a modified camera as I have outlined here:

http://www.astropix.com/HTML/I_ASTROP/CUSTOMWB.HTM

Jerry

Thanks Jerry! Question, what is the WB to use to make the sun appear yellow like we see with our eyes or to make sunlke stars like Alpha Centauri appear yellow? Is "white star" reserved to for stars with a temperature of between 6000-7500K (F type stars like Procyon?)

Roger can probably better answer this question, but our eyes evolved under sun light, and we see sunlight as white. But our eyes are very adaptable to all kinds of light of different color temperatures.

Think about it, do you see the Sun as yellow when it is high in the sky on a clear summer day? No, you don't see it at all because it is too bright to look at. You see it as red when it is setting if it is not too bright to look at, but that is because of Rayleigh scattering.

So if you could somehow dim the brightness of the sun perfectly without altering it's color balance, what color would you see when it was high in the sky? I would say it would be white because your eyes would adapt and your brain/eye/vision/consciousness system adapts to make the brightest thing in the scene as white.

I'm curious as to what Roger will have to say on this, he's much more knowledgeable about this than I am.

Jerry

I'm wondering too because on the OBAFGKM scale aren't F type stars generally considered to be white?

Basically, something like this:

O- deep blue

B- light blue

A- bluish-white

F- white

G- yellowish

K- orange

M- red

If you are looking for optimal color balance, then it really would be G type stars that should be white. G-type stars are really "yellow-white", and generally much whiter than yellow.

There is a way to get "proper" color balance reference to our Sun. It is called G2V calibration, as that is the specific type of our Sun. G2V calibration, which can be done with eXcalibrator (free) and Photoshop, PixInsight, and a number of other programs, will use star catalogs and plate solving to identify G2V type stars within your image (if there are any, usually there are with wider field images, maybe more difficult with narrow field images like galaxies; Galaxies are better balanced by determining an aggregate white point from the collective stars in the galaxies in the image anyway), and determining the white point from them. You can then simply plug the provided red, white and blue white point value into whatever program you are using to calibrate.

There is documentation on how to use eXcalibrator with Photoshop, if that is what you are interested in doing.

One caveat. G2V calibration is not infalliable. It can fail, especially if not enough stars of the right type are found, or if you end up having to use the NOMAD catalog (which tends to be often) which can require additional calibration of the catalog stars itself. You should know if the results are off, they will look decidedly too red, blue, or green if that happens.

 

[Jon Rista]

Oh, I guess I should add. The presence of light pollution can make it more difficult to determine the correct white balance. I usually image at a dark site when there is no moon in the sky at all these days, so I am able to get pretty good star color calibration most of the time. I have imaged with a 25% moon in the sky on occasion. I've found that, particularly when trying to do G2V calibration, but even with PixInsight's self-referenced calibration (which seems to be more adaptive), that I cannot always get good color balance.

This was the case with my M78 wide field image from early last year:

The color of this image, as you might be able to tell on your own, is a bit too "cool". It was affected by the cool white-blue color cast added to the sky by the moon. I do have some color diversity in the stars, however it is not usually the same richness and diversity I am usually able to get, and the warmer-toned stars that should appear more orangeish appear softer, yellower. I performed multiple calibrations on this image, and multiple gradient extractions using different techniques, as well as color cast correction. While all of those helped to a degree, they were unable to fully correct the color.

These were shallower exposures than I usually get these days as well, and that may have also affected my ability to calibrate. Regardless, sometimes it doesn't really matter what you do, if you had LP, sometimes your just stuck dealing with some degree of incorrect color. It often doesn't matter much to the end results, the image above is still a good image. To me, someone who likes a more diverse color palette in my images, it just isn't quite what I wanted.

 

[rnclark]

Hi, I've been searching around the web for the proper white balance to use for AP and I've been seeing different solutions:

1. Daylight White Balance- 5300K

2. Tungsten White Balance- 3000K (to neutralize light pollution and sky glow)

3. Fluorescent White Balance- 4000K (to neutralize moonlight)

4. Custom White Balance taken off a dark part of the sky (to get rid of light pollution or sky glow)

5. Manual White Balance and set color temperature to 3900K

6. Auto White Balance (also helps with LP, but is "hit or miss")

I know with RAW we don't have to worry about WB, but I want to save a JPG alongside and be able to review it on the LCD- so which of the above is the best WB to use for light polluted skies? I want A-type stars to appear white, not G type stars since according to this table, A type stars should be white.

http://oneminuteastronomer.com/708/star-colors-explained/

That table indicates that white stars have a surface temp of 7500K, whereas daylight WB is around 5300K; does this mean that if I use Tungsten WB I will get A-type stars to appear white? (5300-3000=2300+5300=7600K).

For a stock, unmodified camera, daylight white balance is correct.

Note that your JPEGs will still not have a neutral sky color. It will be colored from local light pollution or airglow, which is present everywhere all the time. This is actually the correct color of the sky, it just is not aesthetically pleasing, and not really how we want the images to look (we want them to look like they would if observed or photographed above the Earth's atmosphere).

So, daylight white balance gives you correct color. But then you have to subtract the foreground sky color (light pollution and/or airglow) to achieve a neutral sky background color with correct star colors, and, in theory, correct colors for everything else.

If you have a modified camera, none of the built-in white balance settings will be correct, including daylight.

With a modified camera, for the JPEGs to be correct, you have to use a custom white balance set on a digital gray card shot in direct sunshine on a clear day at noon (preferably in the summer). And still the sky will be red/brown. If you just want the JPEGs to look like they have a neutral sky color (but star colors and other colors will be inaccurate), you can set a custom white balance on the sky itself.

Or, you can determine corrections to apply in post processing to apply a daylight white balance to a modified camera as I have outlined here:

http://www.astropix.com/HTML/I_ASTROP/CUSTOMWB.HTM

Jerry

Thanks Jerry! Question, what is the WB to use to make the sun appear yellow like we see with our eyes or to make sunlke stars like Alpha Centauri appear yellow? Is "white star" reserved to for stars with a temperature of between 6000-7500K (F type stars like Procyon?)

Roger can probably better answer this question, but our eyes evolved under sun light, and we see sunlight as white. But our eyes are very adaptable to all kinds of light of different color temperatures.

Think about it, do you see the Sun as yellow when it is high in the sky on a clear summer day? No, you don't see it at all because it is too bright to look at. You see it as red when it is setting if it is not too bright to look at, but that is because of Rayleigh scattering.

So if you could somehow dim the brightness of the sun perfectly without altering it's color balance, what color would you see when it was high in the sky? I would say it would be white because your eyes would adapt and your brain/eye/vision/consciousness system adapts to make the brightest thing in the scene as white.

I'm curious as to what Roger will have to say on this, he's much more knowledgeable about this than I am.

Jerry

This is an interesting question that is somewhat complex because of the eye+brain adaptability. But we don't always see the brightest thing as white. For example, in a red sunset, the sun is still the brightest and does not appear white, and a white sheet of paper held up the to sunset rays will still appear reddish. So while there is an "auto white balance" of sorts with our eyes, it is limited such that we still perceive color when only one or limited colors are present. On other words, out eye auto white balance is much better than digital camera auto white balance.

The subtle difference between white and yellow white is much more difficult to establish because of this adaptability of the eye. The perceived color could depend on what other colors are around at the time. Perhaps a pinhole projection of the sun into a black or neutral gray room would show the color if one stayed in the room for a while before projecting the sun. I predict it will appear yellow-white but would not bet on it.

Using a white balance of 6000 K with an unmodified camera would be appropriate for cameras imaging above the atmosphere. But down on Earth the atmosphere absorbs more blue than red, so the color balance is adjusted lower to 5300 K. So daylight white balance at 5300 K is the best to use.

Using pixinsight and G2V stars or galaxies on linear data that some here do is an incomplete color calibration. We had a recent thread on that here where sharpkmelly showed one needs to apply a color matrix multiply to get good color, and that matrix is camera dependent. Stock cameras with raw converters like photoshop's ACR or lightroom apply the matrix multiply. Need to find that thread...

Use of galaxies is also not that accurate, as galaxy color varies a lot between galaxies and galaxy type. I have a bunch of galaxy spectra and when I get some time I'll do an article on the natural color of galaxies.

The best color accuracy for natural color and is also the easiest to apply is to use stock digital cameras with standard raw converters (like ACR) and use daylight white balance.

Roger

 

[Jon Rista]

First off, Roger, you have never used PixInsight with G2V, so your claim that they are inaccurate or incomplete is bogus. You really need to do it yourself before you can actually make that claim.

I have worked with the matrices that Sharkmelly identified. They are no more or less accurate than calibrating in PI with it's built in calibration routines, or with a G2V routine using a companion program.

Here is my Seagull Nebula image, where I applied G2V calibration using eXcalibrator and PI, and manually enhanced color saturation:

Here is the same data using Sharkmelly's matrix transformation and standard calibration (I actually performed this processing several times, using various different matrices for a few different Canon full frame DSLRs...I actually believe this is the 6D matrix, which amplified the reds less than the proper 5D III matrix):

I found the results done with the matrix transformation, which redistributes information among the three color channels to account for the non-square nature of each color filter's bandpass, to result in far too much saturation, particularly in the reds. I feel I lost a lot of the impact that the faint blue reflection nebulas had, drowned in far too much Ha. This was without any additional steps to increase the saturation either. This image feels very much like an astro-modded DSLR, and I've stuck with my unmodded 5D III for a reason...I prefer it's natural color as PixInsight calibrates it.

Oh, one additional note about using the matrix approach. It results in significantly more color noise. I had a lot of problems finding ways to reduce the excess noise without affecting detail. I was unable to. I also found that I did not like how bright star halos looked, either. I reviewed these results with sharkmelly, and we did not find any alternative way to apply the matrix to avoid these problems.

These nebula are not very bright objects in reality, so it is VERY difficult to claim that one of these images is more accurate than the other. I think regardless of which approach you take, you have to accept the fact that none will be truly accurate. Every approach to color calibration is incomplete, and entirely open to subjective opinion (or, for that matter, widely varying monitor calibrations, something we very rarely take into account when discussing the accuracy of a calibration...but something which can greatly affect what each of us observes when viewing anyone's images. It may entirely be that some people see my manual calibration of the image above as too undersaturated, while the matrix calibration is better saturated...)

 

[OutsideTheMatrix]

Hi, I've been searching around the web for the proper white balance to use for AP and I've been seeing different solutions:

1. Daylight White Balance- 5300K

2. Tungsten White Balance- 3000K (to neutralize light pollution and sky glow)

3. Fluorescent White Balance- 4000K (to neutralize moonlight)

4. Custom White Balance taken off a dark part of the sky (to get rid of light pollution or sky glow)

5. Manual White Balance and set color temperature to 3900K

6. Auto White Balance (also helps with LP, but is "hit or miss")

I know with RAW we don't have to worry about WB, but I want to save a JPG alongside and be able to review it on the LCD- so which of the above is the best WB to use for light polluted skies? I want A-type stars to appear white, not G type stars since according to this table, A type stars should be white.

http://oneminuteastronomer.com/708/star-colors-explained/

That table indicates that white stars have a surface temp of 7500K, whereas daylight WB is around 5300K; does this mean that if I use Tungsten WB I will get A-type stars to appear white? (5300-3000=2300+5300=7600K).

For a stock, unmodified camera, daylight white balance is correct.

Note that your JPEGs will still not have a neutral sky color. It will be colored from local light pollution or airglow, which is present everywhere all the time. This is actually the correct color of the sky, it just is not aesthetically pleasing, and not really how we want the images to look (we want them to look like they would if observed or photographed above the Earth's atmosphere).

So, daylight white balance gives you correct color. But then you have to subtract the foreground sky color (light pollution and/or airglow) to achieve a neutral sky background color with correct star colors, and, in theory, correct colors for everything else.

If you have a modified camera, none of the built-in white balance settings will be correct, including daylight.

With a modified camera, for the JPEGs to be correct, you have to use a custom white balance set on a digital gray card shot in direct sunshine on a clear day at noon (preferably in the summer). And still the sky will be red/brown. If you just want the JPEGs to look like they have a neutral sky color (but star colors and other colors will be inaccurate), you can set a custom white balance on the sky itself.

Or, you can determine corrections to apply in post processing to apply a daylight white balance to a modified camera as I have outlined here:

http://www.astropix.com/HTML/I_ASTROP/CUSTOMWB.HTM

Jerry

Thanks Jerry! Question, what is the WB to use to make the sun appear yellow like we see with our eyes or to make sunlke stars like Alpha Centauri appear yellow? Is "white star" reserved to for stars with a temperature of between 6000-7500K (F type stars like Procyon?)

Roger can probably better answer this question, but our eyes evolved under sun light, and we see sunlight as white. But our eyes are very adaptable to all kinds of light of different color temperatures.

Think about it, do you see the Sun as yellow when it is high in the sky on a clear summer day? No, you don't see it at all because it is too bright to look at. You see it as red when it is setting if it is not too bright to look at, but that is because of Rayleigh scattering.

So if you could somehow dim the brightness of the sun perfectly without altering it's color balance, what color would you see when it was high in the sky? I would say it would be white because your eyes would adapt and your brain/eye/vision/consciousness system adapts to make the brightest thing in the scene as white.

I'm curious as to what Roger will have to say on this, he's much more knowledgeable about this than I am.

Jerry

I'm wondering too because on the OBAFGKM scale aren't F type stars generally considered to be white?

Basically, something like this:

O- deep blue

B- light blue

A- bluish-white

F- white

G- yellowish

K- orange

M- red

If you are looking for optimal color balance, then it really would be G type stars that should be white. G-type stars are really "yellow-white", and generally much whiter than yellow.

There is a way to get "proper" color balance reference to our Sun. It is called G2V calibration, as that is the specific type of our Sun. G2V calibration, which can be done with eXcalibrator (free) and Photoshop, PixInsight, and a number of other programs, will use star catalogs and plate solving to identify G2V type stars within your image (if there are any, usually there are with wider field images, maybe more difficult with narrow field images like galaxies; Galaxies are better balanced by determining an aggregate white point from the collective stars in the galaxies in the image anyway), and determining the white point from them. You can then simply plug the provided red, white and blue white point value into whatever program you are using to calibrate.

There is documentation on how to use eXcalibrator with Photoshop, if that is what you are interested in doing.

One caveat. G2V calibration is not infalliable. It can fail, especially if not enough stars of the right type are found, or if you end up having to use the NOMAD catalog (which tends to be often) which can require additional calibration of the catalog stars itself. You should know if the results are off, they will look decidedly too red, blue, or green if that happens.

Thanks for the indepth response! Is G2V calibration better than direct calibration where I can just enter the Kelvin temperature manually into the camera?

I'm also confused about these star catalogs, why don't we calibrate off of F stars, if they are considered "pure white" rather than G type stars, which are yellowish-white?

I believe surface temps of F type stars is around 6500K, if I entered that as the WB temp, would not sunlike stars appear yellow-white?

 

[OutsideTheMatrix]

Oh, I guess I should add. The presence of light pollution can make it more difficult to determine the correct white balance. I usually image at a dark site when there is no moon in the sky at all these days, so I am able to get pretty good star color calibration most of the time. I have imaged with a 25% moon in the sky on occasion. I've found that, particularly when trying to do G2V calibration, but even with PixInsight's self-referenced calibration (which seems to be more adaptive), that I cannot always get good color balance.

This was the case with my M78 wide field image from early last year:

The color of this image, as you might be able to tell on your own, is a bit too "cool". It was affected by the cool white-blue color cast added to the sky by the moon. I do have some color diversity in the stars, however it is not usually the same richness and diversity I am usually able to get, and the warmer-toned stars that should appear more orangeish appear softer, yellower. I performed multiple calibrations on this image, and multiple gradient extractions using different techniques, as well as color cast correction. While all of those helped to a degree, they were unable to fully correct the color.

These were shallower exposures than I usually get these days as well, and that may have also affected my ability to calibrate. Regardless, sometimes it doesn't really matter what you do, if you had LP, sometimes your just stuck dealing with some degree of incorrect color. It often doesn't matter much to the end results, the image above is still a good image. To me, someone who likes a more diverse color palette in my images, it just isn't quite what I wanted.

Excellent image, but a question.....if the moon is in the sky, is it good to white balance off the moon, since it shines by reflected sunlight?

I wonder if directly entering a kelvin temperature for WB would have helped you in your image.

 

[OutsideTheMatrix]

Hi, I've been searching around the web for the proper white balance to use for AP and I've been seeing different solutions:

1. Daylight White Balance- 5300K

2. Tungsten White Balance- 3000K (to neutralize light pollution and sky glow)

3. Fluorescent White Balance- 4000K (to neutralize moonlight)

4. Custom White Balance taken off a dark part of the sky (to get rid of light pollution or sky glow)

5. Manual White Balance and set color temperature to 3900K

6. Auto White Balance (also helps with LP, but is "hit or miss")

I know with RAW we don't have to worry about WB, but I want to save a JPG alongside and be able to review it on the LCD- so which of the above is the best WB to use for light polluted skies? I want A-type stars to appear white, not G type stars since according to this table, A type stars should be white.

http://oneminuteastronomer.com/708/star-colors-explained/

That table indicates that white stars have a surface temp of 7500K, whereas daylight WB is around 5300K; does this mean that if I use Tungsten WB I will get A-type stars to appear white? (5300-3000=2300+5300=7600K).

For a stock, unmodified camera, daylight white balance is correct.

Note that your JPEGs will still not have a neutral sky color. It will be colored from local light pollution or airglow, which is present everywhere all the time. This is actually the correct color of the sky, it just is not aesthetically pleasing, and not really how we want the images to look (we want them to look like they would if observed or photographed above the Earth's atmosphere).

So, daylight white balance gives you correct color. But then you have to subtract the foreground sky color (light pollution and/or airglow) to achieve a neutral sky background color with correct star colors, and, in theory, correct colors for everything else.

If you have a modified camera, none of the built-in white balance settings will be correct, including daylight.

With a modified camera, for the JPEGs to be correct, you have to use a custom white balance set on a digital gray card shot in direct sunshine on a clear day at noon (preferably in the summer). And still the sky will be red/brown. If you just want the JPEGs to look like they have a neutral sky color (but star colors and other colors will be inaccurate), you can set a custom white balance on the sky itself.

Or, you can determine corrections to apply in post processing to apply a daylight white balance to a modified camera as I have outlined here:

http://www.astropix.com/HTML/I_ASTROP/CUSTOMWB.HTM

Jerry

Thanks Jerry! Question, what is the WB to use to make the sun appear yellow like we see with our eyes or to make sunlke stars like Alpha Centauri appear yellow? Is "white star" reserved to for stars with a temperature of between 6000-7500K (F type stars like Procyon?)

Roger can probably better answer this question, but our eyes evolved under sun light, and we see sunlight as white. But our eyes are very adaptable to all kinds of light of different color temperatures.

Think about it, do you see the Sun as yellow when it is high in the sky on a clear summer day? No, you don't see it at all because it is too bright to look at. You see it as red when it is setting if it is not too bright to look at, but that is because of Rayleigh scattering.

So if you could somehow dim the brightness of the sun perfectly without altering it's color balance, what color would you see when it was high in the sky? I would say it would be white because your eyes would adapt and your brain/eye/vision/consciousness system adapts to make the brightest thing in the scene as white.

I'm curious as to what Roger will have to say on this, he's much more knowledgeable about this than I am.

Jerry

This is an interesting question that is somewhat complex because of the eye+brain adaptability. But we don't always see the brightest thing as white. For example, in a red sunset, the sun is still the brightest and does not appear white, and a white sheet of paper held up the to sunset rays will still appear reddish. So while there is an "auto white balance" of sorts with our eyes, it is limited such that we still perceive color when only one or limited colors are present. On other words, out eye auto white balance is much better than digital camera auto white balance.

The subtle difference between white and yellow white is much more difficult to establish because of this adaptability of the eye. The perceived color could depend on what other colors are around at the time. Perhaps a pinhole projection of the sun into a black or neutral gray room would show the color if one stayed in the room for a while before projecting the sun. I predict it will appear yellow-white but would not bet on it.

Using a white balance of 6000 K with an unmodified camera would be appropriate for cameras imaging above the atmosphere. But down on Earth the atmosphere absorbs more blue than red, so the color balance is adjusted lower to 5300 K. So daylight white balance at 5300 K is the best to use.

Using pixinsight and G2V stars or galaxies on linear data that some here do is an incomplete color calibration. We had a recent thread on that here where sharpkmelly showed one needs to apply a color matrix multiply to get good color, and that matrix is camera dependent. Stock cameras with raw converters like photoshop's ACR or lightroom apply the matrix multiply. Need to find that thread...

Use of galaxies is also not that accurate, as galaxy color varies a lot between galaxies and galaxy type. I have a bunch of galaxy spectra and when I get some time I'll do an article on the natural color of galaxies.

The best color accuracy for natural color and is also the easiest to apply is to use stock digital cameras with standard raw converters (like ACR) and use daylight white balance.

Roger

Thanks, Roger, I see why we use 5300K rather than 6000K now. As a hypothetical let's say I used 5300K and directly imaged the sun (something you aren't supposed to do), would the sun appear to be the same color as what it looks like with the unaided eye (yelliowish-white)?

 

[rnclark]

Thanks, Roger, I see why we use 5300K rather than 6000K now. As a hypothetical let's say I used 5300K and directly imaged the sun (something you aren't supposed to do), would the sun appear to be the same color as what it looks like with the unaided eye (yelliowish-white)?

In theory, yes.

 

[Jon Rista]

Oh, I guess I should add. The presence of light pollution can make it more difficult to determine the correct white balance. I usually image at a dark site when there is no moon in the sky at all these days, so I am able to get pretty good star color calibration most of the time. I have imaged with a 25% moon in the sky on occasion. I've found that, particularly when trying to do G2V calibration, but even with PixInsight's self-referenced calibration (which seems to be more adaptive), that I cannot always get good color balance.

This was the case with my M78 wide field image from early last year:

The color of this image, as you might be able to tell on your own, is a bit too "cool". It was affected by the cool white-blue color cast added to the sky by the moon. I do have some color diversity in the stars, however it is not usually the same richness and diversity I am usually able to get, and the warmer-toned stars that should appear more orangeish appear softer, yellower. I performed multiple calibrations on this image, and multiple gradient extractions using different techniques, as well as color cast correction. While all of those helped to a degree, they were unable to fully correct the color.

These were shallower exposures than I usually get these days as well, and that may have also affected my ability to calibrate. Regardless, sometimes it doesn't really matter what you do, if you had LP, sometimes your just stuck dealing with some degree of incorrect color. It often doesn't matter much to the end results, the image above is still a good image. To me, someone who likes a more diverse color palette in my images, it just isn't quite what I wanted.

Excellent image, but a question.....if the moon is in the sky, is it good to white balance off the moon, since it shines by reflected sunlight?

I wonder if directly entering a kelvin temperature for WB would have helped you in your image.

The data is RAW, so any WB setting is simply stored in the RAW heater metadata, it is not applied to the data in-camera. RAW editors CAN use that setting to automatically apply a WB, however I do not do that myself. I've disabled such settings in PixInsight so I can perform a more proper calibration (which is actually a multi-step process, requiring gradient extraction (as they can taint color and result in improper calibration), background neutralization, and white point calibration.

I do not believe that setting WB on the moon would have helped. The light from the moon is a POLLUTANT. It is extra unwanted signal being added to your data as the light from the moon scatters through our atmosphere. I believe the true color of objects in deep space comes from the objects in deep space. I believe the best way to calibrate that information is by the stars around the objects your imaging, at the very least, if not specifically just the G2V stars.

 

[Jon Rista]

If you are looking for optimal color balance, then it really would be G type stars that should be white. G-type stars are really "yellow-white", and generally much whiter than yellow.

There is a way to get "proper" color balance reference to our Sun. It is called G2V calibration, as that is the specific type of our Sun. G2V calibration, which can be done with eXcalibrator (free) and Photoshop, PixInsight, and a number of other programs, will use star catalogs and plate solving to identify G2V type stars within your image (if there are any, usually there are with wider field images, maybe more difficult with narrow field images like galaxies; Galaxies are better balanced by determining an aggregate white point from the collective stars in the galaxies in the image anyway), and determining the white point from them. You can then simply plug the provided red, white and blue white point value into whatever program you are using to calibrate.

There is documentation on how to use eXcalibrator with Photoshop, if that is what you are interested in doing.

One caveat. G2V calibration is not infalliable. It can fail, especially if not enough stars of the right type are found, or if you end up having to use the NOMAD catalog (which tends to be often) which can require additional calibration of the catalog stars itself. You should know if the results are off, they will look decidedly too red, blue, or green if that happens.

Thanks for the indepth response! Is G2V calibration better than direct calibration where I can just enter the Kelvin temperature manually into the camera?

I'm also confused about these star catalogs, why don't we calibrate off of F stars, if they are considered "pure white" rather than G type stars, which are yellowish-white?

I believe surface temps of F type stars is around 6500K, if I entered that as the WB temp, would not sunlike stars appear yellow-white?

If it is done right, I do believe so. There are limitations. G2V, at least if done with eXcalibrator, will not account for atmospheric extinction, nor is it capable of dealing with color shifts caused by changing transparency. Not automatically, anyway. There ARE ways to handle those issues with eXcalibrator, it is a little involved and advanced. However, in my experience, barring color casts from LP, any overhead imaging 30 degrees over the horizon at least, to the meridian, will usually calibrate well with eXcalibrator. As such, it works best with data from a good dark site, and not as well with data from the city. It also requires LRGB data, or DSLR data which has had a synthetic luminance extracted and plate solved.

As for color temperatures. A color temperature around 5500K, give or take, is going to be pure white. The sun, assuming we could actually see it with direct vision, is affected by atmospheric scattering (Rayleigh scattering), which affects the observed color. It's elevation above the horizon also affect's it's color, as the amount of scattering is dependent upon the depth of the column of atmosphere to the observer. So measured from on the Earth, our sun, when directly overhead at the zenith, would be a "yellow-white". Measured from outside our atmosphere, it should measure a fairly pure white, because none of it's light is being scattered. Near the horizon, more blue light is scattered due to the increased depth of the atmosphere, so the sun appears orange or even orangish-red.

In general, I think the discrepancy between an overhead-sun "yellow-white" vs. a true "pure white" is small enough that it does not affect color calibration enough to truly matter. It certainly affects it much less than light pollution, either from the moon or from city lighting. Depending on solar activity, even airglow and possibly aurora can affect color balance. I've even experienced fairly significant changes in the color of my sub's background skies simply due to the passage of very thin layers of clouds that I cannot even see, yet which pick up and reflect the city light from Denver fifty miles away. All of those sources of LP tend to introduce gradients and skew accurate color. These gradients are often inconsistent in color across the field, and there can be multiple layers of different gradients with different orientations. I find that these gradients have a fairly significant impact on my ability to color balance properly. As such, I spend a lot of time in PixInsight carefully identifying and extracting all of the gradients in my images before I do any color calibration. What discrepancies may result from less than perfect G2V calibration, or simply using the self-referenced calibration that PixInsight does itself (which tends to differ from G2V calibration by a fairly small amount in most cases), are not enough for me to worry about for the most part.

In the end, I'm creating art. I'm not a scientist. As much as this is a 'scientific hobby', it is still more art than science. The very very vast majority of astrophotographers are hobbyists and artists, very few are actually scientists, and even those that are are still usually not actually doing science with their astrophotography. Discrepancies in color calibration usually do not matter. They aren't significant enough, few people notice, as most aren't even attuned to what truly is "scientifically accurate" to even know what to look for. Color calibration isn't a fixed "this is correct, that aint" kind of thing in the end. Not for the artistic 'scientists' we are.

None of my images are 100% perfectly scientifically calibrated to ideal G2V, accounting for extinction and atmospheric conditions. To do that for every image would be extremely complicated, significantly more effort...and it just doesn't matter. All of these images are reasonably accurately color calibrated. I tend to opt for color diversity, rather than die hard accuracy in star colors (I usually have a good deal more whiter yellow-white stars, yellow stars, and oranger stars than bluer stars...however scientifically speaking, I should probably have even more yellow stars and many bluer stars should probably be more neutral white...but I don't think that looks as good. )

Don't worry about being so exact. These images were all taken under widely varying conditions. Some had simple gradients, some had very complex gradients. Some had a lot more LP than others (i.e. some were imaged under 20.95mag/sq" skies, others were imaged under 21.5mag/sq" skies which is almost a stop difference). Some had decent seeing, some had terrible seeing. Some are only ~3-4 hours of integration, one is over eight hours of integration.

In the end, all those various factors don't matter as much as how you deal with them when you process. I have spent more of my time over the last two years invested in learning how to deal with the data I am able to gather, as more often than not the skies are cloudy, or have a moon in them, or are riddled with bad seeing and excessively bloated stars, and imaging is simply impossible. On the rare occasions when the skies are clear, dark, and stable, you gather what data you can. You'll often make mistakes, forget to set white balance, or set it wrong. Or the skies just aren't quite as good as you thought (high, thin clouds injecting a massive orange-brown tinged gradient). Whatever the issue is...the vast majority of them can be taken care of during processing.

Acquire more. Stack more. Process more. In the end, those are the fundamental means by which you will create the best integrations, and get the best results.

 

[AustinMN]

The sun is 5995 K (best fit outside the atmosphere) and solar type stars appear yellow-white to the eye. The above site is using above the atmosphere colors.

The 5300 K (daylight) is a correction for atmospheric transmission. So daylight white balance is best in my opinion. See my 6-part series on color in the night sky:

http://www.clarkvision.com/articles/color.of.the.night.sky/

Roger

Thanks, Roger...what I was thinking was, would Cloudy (6000K) WB be better since it is close to the 5995K you mentioned? Would that give us the best colors?

Yes, 5995k would give best colors, as long as your camera is in orbit (or higher).

 

[OutsideTheMatrix]

Thanks, Roger, I see why we use 5300K rather than 6000K now. As a hypothetical let's say I used 5300K and directly imaged the sun (something you aren't supposed to do), would the sun appear to be the same color as what it looks like with the unaided eye (yelliowish-white)?

In theory, yes.

Thanks Roger- how do you feel about applying WB by color temperature?

I had an idea I want to implement-

Using this

Stellar classification - Wikipedia

en.wikipedia.org

It gives a color and temperature for the different classes of stars, since the temp for F type stars is 6,000-7,500K if I select a WB temp of (say) 6,500K will that make F type stars appear white?

See also: F-type main-sequence starCanopus, an F-type supergiant and the second brightest star in the night sky

F-type stars have strengthening H and K lines of Ca II. Neutral metals (Fe I, Cr I) beginning to gain on ionized metal lines by late F. Their spectra are characterized by the weaker hydrogen lines and ionized metals. Their color is white. About 1 in 33 (3.03%) of the main-sequence stars in the solar neighborhood are F-type stars.

Also, I noticed something interesting, when changing the WB temp, the camera sometimes changed exposure values, is that supposed to happen? That happened when I was doing infrared photography and selected a WB temp of 2000K (which is what I read you are supposed to select for infrared WB) and the exposure was 0.7 EV slower than it was when I used Auto WB for IR.