About GHS

In September 2021, Dave Payne proposed the use of generalised hyperbolic equations to stretch astronomical images.  He asked for help in turning his idea into a script and Mike Cranfield answered that call.

The resulting script, GHS version 1, was launched in December 2021. This was followed in March 2022 with version 2 which incorporated several improvements including a real time preview.

The take up of GHS amongst the astrophotography community has been gratifyingly strong; in summer 2022 a version was launched by Adrian Knagg-Baugh and Cyril Richard for the popular Siril processing software.

In November 2022 we issued GHS as a process module for PixInsight. This brings the benefits of the GHS equations, offered by the script, and integrates fully into the PixInsight environment, including the real-time preview and the readout functionality, as well as taking advantage of the performance improvements possible with compiled multi-threaded code.

Dave and Mike’s collaboration continues with new developments and videos planned in the coming months – stay tuned!  

We welcome feedback from the wider Pixinsight community using GHS.  Dave and Mike are both active on astrophotography forums responding to questions and suggestions. This all helps us to make this tool as useful as possible. 

GHS repository

Installing GHS

To install GHS into Pixinsight, add the repository information as follows:

  • If you have GHS Version 1 installed then first remove this*, then …
  • From within Pixinsight go to: Resources>Updates>Manage Repositories
  • In the Manage Update Repositories dialog, click the Add button
  • In the URL box type the GHS repository URL shown alongside
  • In the Add Pixinsight Repository dialog, click the OK button
  • In the Manage Update Repositories dialog, click the OK button
  • Go to Resources>Updates>Check for Updates
  • Pixinsight should find the latest version of GHS and download it.
  • You will then need to exit PixInsight and will be asked if you wish to install updates.  
  • Answer yes to this and PixInsight will install updates and restart.
  • When you restart you will see the GHS script in the script menu under Utilities.
  • If you are running PixInsight 1.8.9-1 or later, you will also have the GHS module in the process menu under Intensity Transformations.

(*To uninstall Version 1: In Scripts>Feature Scripts…, uncheck Utilities>GeneralisedHyperbolicStretch, then click Done.  Next navigate to your PixInsight>src>scripts folder/directory and delete the file named GeneralisedHyperbolicStretch.js)


GHS is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, version 3 of the License.

GHS is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

A copy of the GNU General Public License should have been included with your installation of Pixinsight. Alternatively, you can click on the gnu opposite.

Mike Cranfield

I have had a long standing interest in astronomy as well as being a keen photographer.  So it has been a natural step more recently for me to get into the hugely rewarding (if at times frustrating!) hobby of astrophotography.

Pixinsight has been my solution of choice for processing images.  I believe one of it’s key strengths is the large number of people willing to share their experience and knowledge to help other users.  I am pleased to add my own contribution to this by developing the GHS script and making it available to the Pixinsight community.

Dave Payne

I am a recent retiree who immensely enjoys exploring space with my telescope, eyepieces and cameras, and sharing the results with others with similar passions.  Coming from a science background, but not astronomy I have enjoyed learning about both astronomy and the skill involved in astrophotography, both data acquisition and image processing.  I have to say how wonderful, helpful and collaborative the community is, both locally, with my membership in the Victoria, B.C. Centre of the Royal Astronomical Society of Canada, and further afield through collaborations such as you see here.  I have particularly enjoyed collaborating with Mike on creating this script, however I have to point out that Mike has done the lion’s share of work and provided the magic in the creation of this script – particularly version 2.   I look forward to being able to practise more public outreach with astronomy, as well as inspire interest in science and math in others.