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mike1485

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  1. Dear fellow astrophotographers Since our first release of the Generalised Hyperbolic Stretch script, there has been a huge uptake in its use, due to the control and flexibility provided by the unique equations and methodology. We are grateful for the interest shown and the constructive feedback we have received. We are now pleased to offer the GHS 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. Like the script, we are providing the new process free of charge. To obtain the GHS process module you only need to have the current ghsastro repository in your managed repositories list – the address is: https://www.ghsastro.co.uk/updates/. Once downloaded, the GHS process will also be available as an External Scriptable Object making it easy to incorporate into your own PixInsight scripts. Full updated documentation is available from within the module, describing its features and use. We will continue to make the script available for download from the same repository address. The script has been modified to take advantage of the new process where possible/available. As ever, we welcome all comments and feedback. Clear skies and happy stretching! Mike Cranfield and Dave Payne
  2. Hi Mark Thanks for giving GHS a go and posting this question, I'm sure you are not alone in this sort of question so let me have a go at some pointers - watching the videos should give some more and better help. Are you only moving the D slider? If so this will give the blow out you describe. For your first stretch you will likely need to set the second "b" slider to something large - eg 8 - 10. You should also set the SP slider to where the pixel values move from background to subject (usually somewhere just left or right of the histogram peak depending upon the subject) - check out the videos for how to use the preview readout to determine this value. Your first stretch will protect the stars well but will likely leave a low contrast image. Your second stretch needs to set SP at a value where you want to add contrast (eg interesting part of the nebulosity or spiral arms of the galaxy etc) then set a mid value for b (3-5 may work). Then use the D slider to apply the stretch. This should start making the image look good but you can carry on adding contrast/tweaking at will. Check out the videos for more help on this. I hope you can get this working OK for you - blown out centres is absolutely not a feature of GHS when used in this way! My collaborator, Dave Payne, and I did a video for TAIC last weekend which you can access here. There is a practical run through of using the GHS script to stretch an image of M51 which starts at 53 minutes in, that might help illustrate the above. Let us know how you get on. Mike
  3. I am pleased to announce the release of Generalised Hyperbolic Stretch (GHS) V2.2.0. GHS is a Pixinsight script that provides an integrated environment to facilitate the design, appraisal and application of stretches to your images. The script helps avoid star-bloat and allows highly targeted addition of contrast throughout your images. The principal new feature in this version is the addition of a comprehensive pixel enquiry facility on the preview image. By clicking anywhere on the preview, you will see a readout for pixel values in the area you have clicked. This can be used directly to set relevant parameter values for your stretch. In this way you can design your stretches in a far more intuitive and precise way to achieve the exact results you want. More detail on the new features is available on the GHS website (https://www.ghsastro.co.uk/v2-2-0-notes/) and via the tooltips from within the script. A tutorial video is also in the process of production and will be available shortly. If you have the GHS repository (https://www.ghsastro.co.uk/updates/) set up in your list of managed repositories, then you will pick up the new version next time you start up Pixinsight. If you prefer to install manually, the files are available at the GHS Github repository (https://github.com/mikec1485/GHS/releases/tag/v2.2.0/). As ever, feedback is always welcome. Also, David Payne and I have been invited on to The Astro Imaging Channel on YouTube for a live show presenting GHS on 29 May 2022. Building on a brief explanation of the fundamentals of image stretching, we will be exposing the “secret weapons” of GHS and demonstrating how these have been implemented in the new GHS V2.2.0 to allow creation of “designer stretches”. The live show starts at 9:30pm EDT, or if that time doesn’t suit, it will be available afterwards for view at the TAIC YouTube channel (https://www.youtube.com/c/TheAstroImagingChannel/). Happy stretching and clear skies. Mike Cranfield
  4. Interesting workflow vlaiv. Thanks for sharing that.
  5. Thanks for the mention Lee - it's great to see GHS being used to good effect in your image. I think this over simplifies things vlaiv. Stretching an image will generally affect the saturation. If (r, g, b) are the red green and blue values for a given pixel then saturation is generally measured as 1 - (min(r, g, b) / max(r, g, b)). If an intensity transformation (stretch) increases all pixel values by the same proportionate amount, this formula clearly shows that saturation would be preserved. However, typically most initial stretches apply an intensity transformation that stretches lower values (eg min(r, g, b)) proportionately more than higher values (eg max(r, g, b). Hence generally you will actually lose saturation as you stretch from linear. That is why images tend to look a bit washed out when you first move to the non-linear state. One way round this would be to stretch all three channels by the same proportional amount. This is the approach used by the arcsinh stretching process. Effectively, instead of stretching each r, g, b channel separately, a single stretch ratio is calculated by reference to the average of the r, g and b values and this same ratio is applied to all three channels. In this way saturation is maintained. Many image processors like using the arcsinh process precisely because of this feature. However, it is not the arcsinh intensity transformation that preserves colour, rather it is the way it is applied - ie in a way that ensures each channel is stretched by the same ratio. This same approach has been incorporated as an option within the GHS script as the "Colour stretch" option. GHS gives the benefit of using this approach alongside a range of different intensity transformations including arcsinh and mtf (as used in Histogram Transformation) but also with the generalised hyperbolic equations which give the script its name (a family of extremely flexible equations well adapted to stretching astronomical images).
  6. I have today released version 2.1.0 of GHS. A number of features have been included in this update, including the following: Stretches are now recorded in a view’s history with a fully parameterised script instance, allowing this to be dragged and repeated on another view for example. You can now transfer the selected readout point on the histogram to the stretch parameters by clicking the reset button to the right of the relevant parameter’s slider. You can now toggle the preview between “before” and “after” by ctl-click (cmd-click on a Mac) on the preview image. The maximum zoom available on the histogram zoom slider can now be increased in the preferences dialog (use with care on slower systems!). A new stretch visualisation using a greyscale mapping has been added below the histogram – in common with other chart features, this can be turned off if preferred in the preferences dialog. The histogram display has been improved for single channel (R, G or B) stretches so the histogram of the stretched channel can more easily be judged against the unstretched channels. Plus a number of other changes/improvements/fixes. Many of the changes introduced in this release have been motivated by the excellent and helpful feedback we have received from users. I would like to take the opportunity to thank everyone who has downloaded GHS and particularly those who have taken the time and trouble to provide their feedback. Your feedback helps to make GHS as useful as it can be for everyone, and your comments help motivate Dave and I in developing the script. Clear skies and happy stretching Mike
  7. I thought people would want to know that Dave Payne has released the next in his GHS2 tutorial series. Dave's tutorial videos now cover the following: Tutorial 1: Introducing GHS Version 2 Tutorial 2: More advanced stretching Tutorial 3: More options, colour stretch and image blending Links to these videos as well as links to the excellent series prepared by Paulyman Astro can be found on the https://ghsastro.co.uk website.
  8. Something has clearly gone awry there - I don't know if this is a GHS related problem, I am not aware of the issue before. Are there any other warning/error messages earlier in the GHS session that might give a clue to what may have happened? I would exit Pixinsight and fire it up again - that should clear everything down. If it happens again and seems related to GHS, if you could try to recall what you were doing in GHS and let me know, I will take a closer look at the issue.
  9. Nice work Martin. That is a great image - thanks for sharing it. Mike
  10. Hi Budgie The repository information you need to use is: https://www.ghsastro.co.uk/updates/ The GitHub repository is available so people can download the files and install manually if they prefer but using the ghsastro repository is my recommended route as it is much easier and means you will automatically receive any updates. I hope this sorts things out for you but let me know if you are still having problems.
  11. I thought people may want to know of a couple of great new videos that have been released. Dave Payne has released the first in his GHS2 tutorial series which should be a great place to start to get acquainted with the tool. Paulyman Astro has also released a video showing how he has used the new functionality in GHS to implement an "Eric Coles" type approach to image processing which can really help make your images pop! Links to both videos can be found on the https://ghsastro.co.uk website.
  12. Thanks guys for sorting this - I have edited the instructions to suggest version 1 is removed before installing version 2.
  13. Experience seems to be that Starnet++ (even v2) works better if the image is stretched first, even if only mildly. To this end people may like to know of the GHS stretching script for Pixinsight. Using GHS your image can be stretched (remember the parameters you use) - you can then remove the stars with Starnet++ - and GHS then allows you to enter the same stretch parameters but check the "Invert Transformation" checkbox. GHS will then apply an exact mathematical inversion of the original stretch to get you back where you started, but without stars. I have just released version 2 of the GHS script if anyone is interested - the details are in this post: GHS Version 2 Release.
  14. Hi - my mistake - there should be two forward slashes after the https: I have corrected in the OP now. Sorry about that and thanks for picking it up. (1.8.8-6 should work fine). Cheers Mike
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