A fast way to make a PSF-image
A commonly used technique in processing astro images is deconvolution. Light that has travelled through the atmosphere and telescope optics has spread-out by the time it reaches the sensor. For example a star, which theoretically should be a point-source of light, is more like a small dish of light. The light is convoluted. Deconvolution is the process to mathematically reconstruct the original signal again. The result is that stars look smaller and sharper, with the light more concentrated in the center. And while the biggest effect can be seen on stars, also high contrast structural elements can show up more prominent. It is often seen as a sharpening technique, although this is technically not correct.
Deconvolution is a labour-intensive process. Several support images are required. One of those support images is the Point-Spread-Function, or PSF. This is a tiny image of only one star, which statistically best describes the way the light has been spread-out in the system. A PSF-image can be created using the Process>Image>DynamicPSF process. This is a time-consuming process. You need to identify 10-25 stars in the image, and some say even a larger number is required. They must be bright enough, but not too bright, should all have the same statistical spread (e.g. Moffat or Gaussian, etc), and they should ideally be close to your main object. Usually you select many more than required, and remove the ones that don’t fit the criteria. Overall this can take quite some time.
A much faster solution comes in the form of a script called PSFImage, developed by Hartmut Bornemann, which automates the process of PSF image creation. The script can be found here and needs to be installed in PixInsight. To install the script, the file (psfimage.js) is copied to the directory \\Applications\PixInsight\src\scripts. In PixInsight, select Script>Feature Scripts… In the menu that appears, click the button Add and select the folder where the new script file has been copied to. When clicking Open, the system compares the scripts in that folder with the ones that are already installed and will highlight the new script. Now click the button Regenerate and the script will be installed. Now the script can be selected from within PixInsight under Script>Render>PSFImage.
Running the script is very easy. The first step is to select which function to use. The default Moffat is the one that will be used 99% of the time. Default values for sensitivity typically work well. If the script selects too many stars to analyse, the sensitivity can be increased. Also, some people may like to increase the minimum amplitude to 0.1 or 0.2. Once you’ve got the settings right, you click the button ‘Evaluate’, and the computer starts analysing the image of the active view. This requires a reasonable amount of computing power, so allow for some time to complete the process. Once it is done, the only thing you need to do is click the button ‘Create’, and a PSF image is created that can be used directly in the deconvolution process.
There are also scripts designed to automate the whole process. Unfortunately, at AstroWorldCreations, the result with them has been inconsistent. But the PSFImage script has been working fine so far and reduces the time it takes to do a full deconvolution.