Hi everyone,
I have developed ExtensionToolset, a collection of scripts to support image processing and analysis in PixInsight.
Features included in ExtensionToolset:
- AdditiveColorCalibration: A high-accuracy and robust additive color calibration tool based on a background preview. In contrast to current tools, it is more robust in case the background preview contains
stars, a common situation in widefield imaging. It is not intended to replace SPCC or other tools, it should be considered as yet another tool capable of handling one specific problem case better than others.
- BTM: The Brightness and Transparency Meter is a tool that allows you to measure the night sky brightness in magnitudes per square arcsecond and the transparency in percent from a single
calibrated image and a few acquisition details. Along with these values, it also calculates the USQ (Unified Sky Quality) index, which is a measure of the quality of the night sky further
explained later in the post.
- USQCalculator: The Unified Sky Quality index Calculator allows you to calculate the USQ index based on already known night sky brightness and transparency values. This makes it easier
to compare conditions across multiple places and photographers.
- GradientStrength: for a given series of images, you can calculate the gradient strength score for each image to automatically select the best subset of images for the generation of a
LocalNormalization reference image. This is purely based on gradient strength inside the images, intended to simplify the gradient in the integrated image, not based on SNR.
- ExtensionToolsetOverview: in case you need a quick high-level overview over all features, release notes or other important information, all that is bundled here.
Installation:
For installation, add this repository to your PixInsight update repository list: https://gerriterdt.github.io/ExtensionToolset-release/
You can manage your update repository list under Resources -> Updates -> Manage Repositories -> Add.
After adding the repository, check for new updates and follow the instructions.
Usage:
Once installed, you can find the scripts in the Script menu under the entry "ExtensionToolset".
Each script includes a standardized description at the top, explaining the use case, preconditions, and results of the script.
For a full documentation of each script, you can refer to the tooltips of each individual element on the user interface of the script.
Known limitations:
- The measurement of the night sky transparency often yields accurate results, but in case you use images with a very small FOV, a low SNR, or a combination of both, the results become less accurate. Generally, larger FOV images with a better SNR are beneficial for increased accuracy. I hope to improve this in the future.
Further details about the USQ:
Since the USQ index is a new concept, I want to explain it in more detail.
Most of the time, it is hard to compare the sky quality for imaging purposes across different nights or locations. Clearly, darker skies are better, but how much better are they actually, and how much better is a dark sky if it is not as transparent as a brighter sky?
The USQ index solves this problem by combining both metrics of quality into a single index. The USQ index is a value between 0 and 100, where 0 is the worst possible sky quality and 100 is the best possible sky quality. It is proportional to the SNR of a well‑exposed image taken under these conditions.
In practice, this means that if you have calculated a USQ index of 20 for location A and a USQ index of 60 for location B, then you can expect a well‑exposed image taken at location B to have an SNR of 60 / 20 = 3 times the SNR of a well‑exposed image taken at location A with all other conditions being equal. That means that, at location A, you have to expose 3^2 = 9 times as long for the same SNR compared to location B.
Of course, there are some limitations here, but I have tried to make them as small as possible:
The USQ index is only defined for night‑sky brightness between 16.0 and 22.5 magnitudes/arcsec^2. Values outside this range are technically possible, but will leave the [0, 100] range.
While the USQ index is proportional to the SNR of well‑exposed images, it is not of great help for images that are not well‑exposed. Additionally, the proportionality is valid for most of the possible values, but it is not proportional for values very close to the boundaries, i.e. a SQM of exactly 16.0 is not perfectly in the proportional range, as the USQ will be 0. This is, however, of low practical relevance, since the boundaries are pretty wide, and we generally aim to have well-exposed images anyway.
The SNR that I have used here is the SNR of large objects, not of small objects like stars. The effects of seeing are not included in the USQ index.
I have the strong hope that the USQ index can be established as a standard measure for night‑sky quality, improving the community’s ability to compare locations and nights with each other, fostering a better understanding of the quality of images by other astrophotographers and what can be achieved by changing locations.
Troubleshooting & Feedback:
If you encounter any issues or have suggestions, feel free to reach out to me through any of the forums where I have published the initial announcement. Feedback and feature requests are always welcome!
Also, I will continue to develop more features in the future, further enhancing the ExtensionToolset. If you have any ideas or suggestions, let me know - I will be happy to consider them.
For reference, here is the original announcement in the PixInsight forum: https://pixinsight.com/forum/index.php?threads/new-scripts-extensiontoolset.26110/#post-173931
CS Gerrit
I have developed ExtensionToolset, a collection of scripts to support image processing and analysis in PixInsight.
Features included in ExtensionToolset:
- AdditiveColorCalibration: A high-accuracy and robust additive color calibration tool based on a background preview. In contrast to current tools, it is more robust in case the background preview contains
stars, a common situation in widefield imaging. It is not intended to replace SPCC or other tools, it should be considered as yet another tool capable of handling one specific problem case better than others.
- BTM: The Brightness and Transparency Meter is a tool that allows you to measure the night sky brightness in magnitudes per square arcsecond and the transparency in percent from a single
calibrated image and a few acquisition details. Along with these values, it also calculates the USQ (Unified Sky Quality) index, which is a measure of the quality of the night sky further
explained later in the post.
- USQCalculator: The Unified Sky Quality index Calculator allows you to calculate the USQ index based on already known night sky brightness and transparency values. This makes it easier
to compare conditions across multiple places and photographers.
- GradientStrength: for a given series of images, you can calculate the gradient strength score for each image to automatically select the best subset of images for the generation of a
LocalNormalization reference image. This is purely based on gradient strength inside the images, intended to simplify the gradient in the integrated image, not based on SNR.
- ExtensionToolsetOverview: in case you need a quick high-level overview over all features, release notes or other important information, all that is bundled here.
Installation:
For installation, add this repository to your PixInsight update repository list: https://gerriterdt.github.io/ExtensionToolset-release/
You can manage your update repository list under Resources -> Updates -> Manage Repositories -> Add.
After adding the repository, check for new updates and follow the instructions.
Usage:
Once installed, you can find the scripts in the Script menu under the entry "ExtensionToolset".
Each script includes a standardized description at the top, explaining the use case, preconditions, and results of the script.
For a full documentation of each script, you can refer to the tooltips of each individual element on the user interface of the script.
Known limitations:
- The measurement of the night sky transparency often yields accurate results, but in case you use images with a very small FOV, a low SNR, or a combination of both, the results become less accurate. Generally, larger FOV images with a better SNR are beneficial for increased accuracy. I hope to improve this in the future.
Further details about the USQ:
Since the USQ index is a new concept, I want to explain it in more detail.
Most of the time, it is hard to compare the sky quality for imaging purposes across different nights or locations. Clearly, darker skies are better, but how much better are they actually, and how much better is a dark sky if it is not as transparent as a brighter sky?
The USQ index solves this problem by combining both metrics of quality into a single index. The USQ index is a value between 0 and 100, where 0 is the worst possible sky quality and 100 is the best possible sky quality. It is proportional to the SNR of a well‑exposed image taken under these conditions.
In practice, this means that if you have calculated a USQ index of 20 for location A and a USQ index of 60 for location B, then you can expect a well‑exposed image taken at location B to have an SNR of 60 / 20 = 3 times the SNR of a well‑exposed image taken at location A with all other conditions being equal. That means that, at location A, you have to expose 3^2 = 9 times as long for the same SNR compared to location B.
Of course, there are some limitations here, but I have tried to make them as small as possible:
The USQ index is only defined for night‑sky brightness between 16.0 and 22.5 magnitudes/arcsec^2. Values outside this range are technically possible, but will leave the [0, 100] range.
While the USQ index is proportional to the SNR of well‑exposed images, it is not of great help for images that are not well‑exposed. Additionally, the proportionality is valid for most of the possible values, but it is not proportional for values very close to the boundaries, i.e. a SQM of exactly 16.0 is not perfectly in the proportional range, as the USQ will be 0. This is, however, of low practical relevance, since the boundaries are pretty wide, and we generally aim to have well-exposed images anyway.
The SNR that I have used here is the SNR of large objects, not of small objects like stars. The effects of seeing are not included in the USQ index.
I have the strong hope that the USQ index can be established as a standard measure for night‑sky quality, improving the community’s ability to compare locations and nights with each other, fostering a better understanding of the quality of images by other astrophotographers and what can be achieved by changing locations.
Troubleshooting & Feedback:
If you encounter any issues or have suggestions, feel free to reach out to me through any of the forums where I have published the initial announcement. Feedback and feature requests are always welcome!
Also, I will continue to develop more features in the future, further enhancing the ExtensionToolset. If you have any ideas or suggestions, let me know - I will be happy to consider them.
For reference, here is the original announcement in the PixInsight forum: https://pixinsight.com/forum/index.php?threads/new-scripts-extensiontoolset.26110/#post-173931
CS Gerrit
