Noise, or graininess in our photos, is the astrophotographer’s arch enemy. Destroy noise with Lightroom!
The more you increase the ISO, the warmer the air temperature and camera sensor, the greater the risk of introducing more noise to your images, likewise with increased exposure duration. Unfortunately, noise is nearly unavoidable…but, we can do something about it in post processing with Lightroom and other image processing applications. Whew!
Understanding two main types of noise
Upon inspection, you’ll find that Lightroom presents you with Luminance and Color (chrominance) noise reduction settings, found in the Details panel.
Luminance noise will appear as a more “grainy” noise, without the variety of color pixels in the image.
Color noise will be represented as multi-colored pixels in an area that should have a very uniform color.
To combat this, you first have to establish which type of noise you’re dealing with and adjust the sliders accordingly. Every photo is unique, but it’s infrequent that noise will be isolated to only one of these.
What you can do about these two types of noise
While using a zoomed-in view of your image, adjust the Luminance and Color sliders. Often, aggressive testing, or pushing beyond what you may think should be necessary, is needed to see just how much noise reduction can be applied without a significant loss of detail. You need to achieve a balance, avoid smoothing out the photo too much and losing the structure detail of the Milky Way core, while reducing the noise to a level where it looks acceptable.
Lightroom automatically applies color noise reduction when importing raw files. Which is why the default color slider is always set to 25. (With Detail and Smoothness both at 50), but will leave the Luminance setting unchanged.
Luminance noise reduction
Start here! A default setting for Luminance noise reduction can’t be specified, as it depends on each individual image. However, there is always a minimum, it seems. Once you’re happy with the level of noise reduction on Luminance, use the Detail and Contrast sliders to enhance your images further.
The Contrast slider controls luminance contrast – higher settings will help you retain more of the contrast in luminance noise reduced areas, but may be less effective in reducing luminance noise, so for MW photography we’ll keep this relatively low.
The Detail slider controls the luminance threshold, where higher values will keep more detail but might come at a cost of leaving too much noise in the image. This value is best kept around the midway mark for Milky Way photographs.
Color noise reduction
Adjusting the main Color noise reduction slider will help fix multi-colored pixels in areas where there should be relatively even color. It is often important to use color noise reduction, but, using it too much (over 50-75%) can remove too much and affect the color of the stars and reduce overall image saturation.
As with Luminance, the Detail slider in the Color panel controls the noise threshold, but specifically for the chrominance noise. Values too high here may introduce fringing on edges like stars (weird looking color pixels around areas of high contrast), so again, don’t push this too much. To combat this, using the Smoothness slider can be effective.
The Sharpening slider is seductive, but beware of this potentially nasty vixen!
When your Milky Way image is zoomed out fully, applying a hefty amount of sharpening can look great, but as soon as you zoom in and look it what you’ve done…yeah, just don’t do that. It can get ugly.
Most of time, a properly-focused and exposed Milky Way photo will not need much sharpening at all. I most often hardly use any at all, maybe around 20% at the maximum. Also, keep the Radius to around the default of 1.0 and Detail around the default of 25.
The Masking slider is very effective in making sure you don’t add too much noise in areas of consistency, like in between the stars. Overall, use Sharpening very sparingly — rather spend more time focusing!
As we’ve said, every image is unique
The shoot location, sensor, ambient temperature, and other factors all create different results. The noise reduction and sharpening adjustments are applied effectively and quickly to images, giving you a real time preview of the strength and effect on the photo.