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White Balance For Astrophotography: Which Setting To Use?

Raise of hands: who knows the struggle of getting true colors in your photography?

Dull colors and color casts are one of the most common issues in color photography. 

Color treatment is quite a technical area in photography. It depends on many factors: from the image format to in-camera white balance, from color calibrated monitors to printer color profiles and paper quality.

For many of us, understanding what White Balance is and how it works is enough, and this is what this article is about.

But before learning how we can balance colors and remove a color cast from our image, let’s start from the beginning. 

Let’s start with a beautiful Universe, full of light and colors.

different white balance temperatures
A tiny portion of our Milky Way in the Cygnus constellation, packed with bright stars and colorful nebulae. Divided into different white balance colors.

A Beautiful Universe: Reality Or Illusion?

How wonderful the Universe is, with all those stars, colorful nebulae, galaxies, and stellar explosions that outshine entire galaxies. How beautiful is it up there, isn’t it?

Here is a fascinating fact: The Universe is dark. There is no “light”. The stars don’t shine, nebulae and galaxies are not colorful, the Sun is not bright. The Universe is pitch black.

The Universe lights up only when there is a set of eyes to detect the electromagnetic radiation it contains, and a brain to interpret what the eyes detect. 

What we call Light and Colors exist only in our brains, and different eyes and brains see the Universe in a different way. In a sense, we create the beautiful Universe we see.

And, we see the Universe differently than our digital cameras and telescopes do.

different types of electromagnetic radiations
The Cygnus constellation as it would look to us if we could see it with the different types of electromagnetic radiations, from gamma rays (left) to radio waves (right).

Visible Light And Colors

Visible light is just electromagnetic radiation coming from a very narrow region of the electromagnetic spectrum, which ranges from gamma-rays to radio waves. 

Electromagnetic Spectrum
The visible part of the electromagnetic spectrum. (Image credit: Wikimedia Commons)

It has been calculated we can only see the 0.0035% of the entire electromagnetic spectrum

We can only see radiations of wavelengths ranging from about 400nm to 700nm, and our brain interprets the different wavelengths as different colors. 

High energy visible light has small wavelengths and to us looks blue or violet. Low energy visible light, instead, has a longer wavelength, and it appears red. 

Finally, white light is the result of an even mix of all the different shades of colors we can see.

Our unique way to see the Universe in colors means we can assign to visible light properties such as Color Temperature and consider it to be Warm or Cold.

The Color Temperature

Color Temperature is a property of visible light, and it is related to the concept of black body radiation. 

Stars are a good approximation of the ideal concept of black bodies. The surface temperature of a star determines the color it glows with: relatively cold stars look reddish, while the hotter ones look white or blue.

star color temperature map
The color of stars as a function of their surface temperature. (Image credit: Wikimedia Commons)

The color temperature of a light source is the temperature at which a black body glows with light of the same color.

For example, the tungsten filament in a light bulb has a color temperature of 3200K, where K stands for Kelvin, the unit of the absolute scale for temperature. 

The higher the temperature of the black body, the higher is the energy of the emitted light, and the more blue-ish the light becomes.

With reddish light, the color balance is shifted towards low energy visible light, resulting in an abundance of red, orange, and yellow.

Warm And Cold Light

Here is where things get confusing. 

“Warm” and “cold” are used in connection to the “mood” we associate to a colored light and has nothing to do with the color temperature of the light.

Blue has a high color temperature, but we consider it to be a “cold” light. And orange/red light is “warm”, even if the color temperature is lower than that of blue light.

Mood and color temperature
Mood and color temperature for different kinds of light sources.

I think the origin of this has to do with the fact that under direct sunlight, which looks like yellow, we stay warm. A freezing icy lake looks blue. Fire burns us and looks red. Hot metal glows red-hot. 

Cold and warm WB is often used creatively in portraiture and landscape photography to convey particular feelings and moods. A blue-ish WB can be used to indicate sadness (we do say “feeling blue”) or chilly/stormy weather.

underexposed and cooled the image to convey a feeling of defeat
I underexposed and cooled the image to convey a feeling of defeat in this portrait.

What Is White Balance In Photography?

White Balance (WB) in digital cameras can be seen as the process of removing unwanted (unrealistic) color casts from a digital image.

In short, WB is a color treatment of the image so that colors that should be neutral (gray and white) look neutral in the image, regardless of the light source.

With a proper WB, the colors in the image will be much more similar to how you saw them in real life.

Our brain, in fact, is very good at compensating for color casts due to a colored light source, much more than your digital camera Auto White Balance (AWB) is. 

And this is why digital cameras come with a wide array of settings to get the WB just right.

There are two ways to change the color balance in the image

  1. By altering the yellow/blue ratio with the WB.
  2. By altering the green/magenta ratio with what is known as Tint.

Finally, this color treatment can be done in-camera or during the editing.

How Does White Balance Work?

The idea is simple: say you take an intimate portrait using candlelight. 

The light of a candle has a color temperature of 1200K, so it casts a red/orange glow.

If you want to compensate for this color cast and have neutral colors, your camera has to boost the blues to balance the abundance of red/orange in the scene.

Another example: overcast days, have a bluish light. If you want to compensate for this light, you will set your camera to use the cloudy WB. This will boost the yellows to compensate for the blue color cast in the scene.

You can easily see how this compensation works by intentionally choosing the wrong WB setting. 

Say you are photographing with natural light: if you use the WB for a Tungsten light (orange light), the camera will boost the blue to compensate for the orange color cast. 

But, since daylight is more white than red, the camera overcompensates the reds and the result is a heavy blue color cast in your image.

How different WB settings alter the colors of a photo
How different WB settings alter the colors of a photo.

Saving In RAW File: Does White Balance Make A Difference?

The WB is an image treatment, much like noise reduction or image profiles and sharpening. 

When you shoot in RAW, you are recording the image as seen by the sensor, and in-camera WB settings are not applied.

This means you can successfully tweak the WB in the editing stage.

Instead, when you use the JPEG format, the in-camera white balance setting is applied to the image. You can still tweak the colors by editing the JPEG but in a less efficient way.

If you use JPEG, you should really get the WB right in-camera.

Still, even if you shoot in RAW format, WB settings are applied to the preview embedded in the RAW image. This is what you see on your camera screen.

Should I Use Auto White Balance?

Auto White Balance (AWB) is quite a convenient way to fix the white balance, and it works fairly well in many cases.

Yet, in particularly difficult light conditions, such as if you are shooting in a woods, or on the snow, you may want to use a custom white balance

If you are shooting RAWs, don’t bother with the in-camera WB, but since you have to pick one, use AWB.

How Do You Choose White Balance On Your Camera?

If you need to have better control of the WB of your JPEG image, somewhere in your camera software you will find several WB settings. 

Where to find them, though, depends on the camera model and brand, so refer to the user guide.

The most common WB presets you can choose from are:

  • Sunny
  • Cloudy
  • Shade
  • Tungsten Light
  • Fluorescent Light
  • Flash Light
  • Custom WB

If you need to choose one, look at your scene and determine the kind of dominant light you have.

Use A Gray Card For Accurate White Balance

If you want to remove the guessing from setting the WB, you can use a neutral (18%) gray card, commonly available on the internet and in all shops of photographic material.

white balance card

A set of neutral gray, white, and black cards to correctly set the WB for your images.

The workflow can vary depending on your needs, but here is the basic one.

  1. Set your camera to save images in RAW format, place the card next to your target and take a test shot.
  2. Take away the gray card and take your photo.
  3. On your computer open the test shot and with the eyedropper tools for the WB sample the gray card in the photo.
  4. Now you have a proper white balance: apply the settings to your image without the card and you are good to go.

Color checkers are also a great tool if you really need accurate colors.

Color Checker for white balance

A classic color checker passport also features a gray card.

This video explains how to use a gray card or a color checker to set your WB and colors.

Gray cards can also be used to properly expose your scene. Here is a nice, short video about setting the exposure by using a gray card.

What Is The Best White Balance For Night Shots?

In astrophotography we shoot in RAW format, so the in-camera WB setting used is not important

Most of the time I use Sunny WB (the stars are basically suns) as the AWB will display on the LCD camera images with a strong blue color cast.

Also, because of light gradients and light pollution, it is much better to fix the white balance during the editing than in the camera.

This way, you can perform local white balance adjustments to the image using masks and/or local tools such as brushes.

A common mistake when editing a night shot is to a blue sky: the natural dark sky is not blue, nor is it pure black, instead it is a neutral mix of colors.

effect of different WB on an image shot of Neowise comet
The effect of different WB on an image shot at 4 a.m. to capture the C/2020 F3 (NEOWISE) comet.

The same is true for deep sky images: you don’t want to have a “cold” dark sky. If anything, use a slightly warm WB.

effect of using a cold and slightly warm WB with a deep sky image
The effect of using a cold (top) and slightly warm (bottom) WB with a deep sky image: the bottom one looks more natural.

Adjusting White Balance In Photoshop

In Photoshop, you can adjust the WB of an image by using the White Balance tool layer. But I prefer to use the Adobe Camera Raw Filter.

white balance control inside of Adobe Camera Raw
The interface of Adobe Camera Raw (ACR).

With Adobe Camera Raw (ACR) and Adobe Lightroom you have the usual sliders, but also an eyedropper tool and even AWB.

With the eyedropper, you can sample a portion of the image that should contain a neutral color, and the program will apply the proper corrections to remove the color cast. 

You can keep sampling different areas of the image until you are happy with your color balance.

Conclusion

Understanding how white balance works is very important in photography. WB is not used only to have “true” colors, but can also be used creatively to convey a particular mood.

If you shoot in RAW, you can decide your WB in the editing stage, as in-camera WB settings are not applied to the image. If you shoot JPEG, then in-camera WB are applied, and you should take care to pick the right settings.

For astrophotography, you will shoot RAW, so just set your camera to use AWB or daylight/sunny WB and fix that during editing. Just remember that the night sky is not a cold/blue-ish sky, so use a slightly warm WB.

About Andrea Minoia

Andrea Minoia works as a researcher in a Belgian university by day and is a keen amateur astrophotographer by night. He is most interested in deep sky photography with low budget equipment and in helping beginners along their journey under the stars.