Using Starnet++ in Siril

Click on any image to see a closer view

The following will show a workflow (that is not absolutely rigid) but will work. Practice and you will master it.

 Open your autosave.tif in Siril

Click on Autostretch so you can see what the image contains (remember that Autostretch only affects the preview and does not change the underling data)

Click on Image Processing and Geometry

Select Rotate&Crop (you are not going to rotate, just crop)

Pull the red edges of the crop box into the image to get rid of any unwanted stuff at the edges

Click on apply when you have selected the crop area

Click on Image Processing and Star Processing

Select StarNet Star Removal

Make sure the two boxes shown are checked and click Execute

 

A progress bar will move slowly at the bottom right and the stars will eventually be removed

Click on Image Processin and Background extractio

Use the left click button to put selection points all over the image but not on any nebulae or other structures. If you need to, you can remove a point by right clicking on it.

Click on Compute Background and you will see it change and most gradients will be gone

Click on apply and the selection points will go.

Select Linear rather than Autostretch

The image will become darker and will need stretching

Select Image Processing and Asinh Transformation and pull the slider(s) a little

Select Image Processing and Generalised Hyperbolic Stretch Transformations. Pull the sliders as shown and click Apply

You will have to pull the sliders again as shown and click Apply.

Select Image Processing and Histogram Transformation

Pull the sliders from the left and right and Click apply

Repeat. The idea is to darken the background a bit and to brighten the nebula a bit. Finish by pulling the left slider up the the histogram and click Apply

We now have an image with the nebulae showing and the background darkish

Select Image Processing and Star Processing

Select Star Recomposition

You will be presented with two charts that are empty, the left one is for Background Stretch Parameters and the right one is for Star Stretch Parameters.

When the Star removal stage was done, the computer stored the starless image and the starmask (stars) images probably in your pictures folder. 

To load the starless data and the starmask data into the Star Recomposition dialogue click on the two folder symbols to the right of the words None.

This will put both he starless background and the stars back together in the image on the left. However, they can be adjusted independently. The sliders should be pulled for each control until the background looks OK and the stars are bright enough, but not too overwhelming. You may want to click Apply and stretch one or the other, or both some more. When you have done, click Close.

You may want to use Image Processing and Histogram Transformations again at this stage clicking Apply to set the effect.

Finish with the left slider up against the edge of the histogram Click Apply to set the effect.

You might want to gently apply some colour saturation

Then, at the top of the Window Click on Save as a different filename and give it a sensible name

It can still be saved as a 32 bit image

Once saved, it can be opened in the Gimp for some last tweeking and to reduce its bit depth.

REMEMBER when you open a colour FITs file in Gimp to click on the NAXIS as shown in the image below or it will not be a colour image.

Here the Levels are being adjusted to darken the background a bit and increase the mid tones a bit

Now we change the bit depth to 8 bits

Making sure the Perceptual gamma is selected, click on Convert.

Click on Export as and choose a sensible filename and type .png is best as you can make it uncompressed

Make sure that the result is going into the folder you want, and most importantly, make sure that compression is set to zero, you will see that you can save this as default so your png files will always be uncompressed.

Your final image

This has been to show a workflow that will take stars away, allow the starless image to be manipulated and then the stars put back to any extent you want. It also shows that Gimp can and should be used at the end for final tweaking and to get the final image in the right format: 8 bit, png with a sensible name, in a folder where you can find it.