In this post, we will delve into the world of masks and explore how they can be used in various tasks such as noise reduction and sharpening. We’ll investigate how to create and apply masks using PixInsight, and discover the benefits of using range selection tools to create targeted masks.
Understanding Masks
Before we start it is essential to grasp the concept of masks. A mask, in essence, is a powerful tool that allows us to selectively control our image processing. It’s a black and white representation of an image where the black pixels are protected, and the white pixels are where we can apply processing. By applying a mask, we can protect or exclude certain regions from being processed, which is particularly useful when dealing with complex images.
Think of it like this: when you want to apply a specific effect or adjustment to your image,
you may not want to affect the entire image. You might want to preserve certain details while applying the effect elsewhere. That’s where masks come in – they help you isolate specific areas of your image and apply processing only where needed.
A mask can be quite binary, either white or dark, or smoother, with gradual changes from white to black. Each type of mask has its place and within PixInsight we have various tools at our disposal to create those masks.
Applying Masks in PixInsight
Now that we have a solid understanding of masks, let’s dive into applying them in PixInsight. As mentioned, masks are powerful tools that allow us to selectively control our image processing. By creating and applying masks, we can protect or exclude certain areas of an image from processing.
To apply a mask in PixInsight, you’ll need to drag it under the target image’s name as shown in the image to the left. You’ll know you’ve successfully done this when the target image’s name turns brown.
Alternatively, with your target image selected, go to the Mask menu and choose your appropriate mask from the dropdown menu.
Once applied, you can see how the mask is affecting your image by looking at the preview.
It is worth pointing out here that when you first apply a mask to an image that your image will likely turn mostly red, as seen here. This is a visualisation of the mask, remember the phrase “red hides and white applies”. If you would prefer to actually see your image, (honestly who doesn’t), then you can hide the mask visualisation using the show/hide mask button in the menu bar at the top of PixInsight.
Note: It is essential to remember that masks need to be nonlinear, even when working with linear data.
Mastering Mask Techniques
Now that we’ve covered how to apply masks in PixInsight, let’s dive deeper into mastering mask techniques. One of the most useful tools for creating masks is the Range Selection tool. This powerful tool allows us to create a series of masks based on brightness values, which is particularly useful when doing noise reduction and sharpening.
By adjusting the lower and upper limit sliders, we can control where the black and white points are, allowing us to select the appropriate luminance range for the mask we want to create. The mask itself will be extremely binary, with a harsh transition from black to white. However, by introducing some fuzziness and smoothness, we can make the transitions less harsh.
Another extremely useful tool for mask creation is the Game Script, created by Herbert Walter. This tool allows us to quickly and efficiently create elliptical masks to cover our galaxies, but it’s not just limited to that. It’s also an effective tool for working on halos and filters.
Game is an acronym for Galaxy Mask Editor.
Once applied, you can see how the mask is affecting your image by looking at the preview. As we discussed earlier, it’s essential to remember that masks need to be non-linear, even when working with linear data.
Conclusion
In this post we covered how to create and apply masks, so that we can protect or exclude certain areas of an image from processing, which is particularly useful when doing noise reduction and sharpening.
As we move forward in our image processing journey, it’s essential to continue learning and refining our skills. Remember, practice makes perfect, so don’t be afraid to experiment and try new things!
If you have any questions or would like to learn more about using masks in PixInsight, please feel free to contact me or ask in the comments below!
