Pre-processing is a vital step on the journey to producing an astrophoto worthy of printing and hanging on your wall. It covers everything after gathering data with your telescope and camera, but before actually editing an image. It might not sound like there’s room for much there, but it includes folder organisation; weeding out poor quality subframes; using calibration frames; and integration (sometimes called stacking).
Most beginners use the software Deep Sky Stacker (DSS) for their pre-processing, and while it can produce decent results (and is free!) I really like PixInsight (review here). I found that my pre-processing took a big step up when I switched from DSS to PixInsight, and unlike DSS, PixInsight can also be used for processing your integrated image, which is what we produce as the final step of pre-processing. So, you can do all your astro processing in PixInsight if you like.
However, PixInsight is famously tricky for beginners to get a handle on. After reading lots of tutorials and trying different approaches for myself, I’ve found a good pre-processing workflow for deep sky objects that works well for me and my OSC camera (but it should be fine for Mono too). I’m writing this guide in case it’s helpful for you! I’m using a PC, but it should be easy enough to apply to macOS too. My standard caveat is that you should always try things for yourself, and don’t be afraid to tweak my recommendations to better suit how you like to work. Note also that my method is best for data that’s been produced using a proper astrocamera rather than a DSLR; this is because astrocameras use the FITS file format that embeds lots of useful metadata. PixInsight uses this to good effect.
At first glance this workflow might seem quite long and complex, but it’s really not that bad, and once you get into the flow of it I think it feels quite natural. If you’ve come across a better way of doing something, I’d be very interested to hear about it. Either comment at the end of the post, or use the Contact page.
Some useful terminology
Subframe
These are individual images taken with your camera.
Calibration
This is when we use calibration frames to improve the quality of our Light frames; most notably by removing noise. I use Bias, Dark, and Flat frames. Explaining these is beyond the scope of this guide, so if necessary get Googling!
Target
What we’re imaging. For example, M42.
Lights
Subframes of your Target. I almost always shoot 120-second Lights, and always at minus 10 degrees C.
Project
This is what I call everything encompassing data acquisition, pre-processing, and processing a Target. “My current Project is M42”.
Filter
The filter you used when collecting your data. These are the filters I use, and the names I assign them:
| No filter, i.e. collecting RGB data (as I’m using an OSC camera) | RGB |
| Optolong L-Ultimate | Ult |
| Askar Colour Magic D2 | D2 |
Session
This is important, so pay attention! It links with Calibration. I define a Session as all the Light Subframes collected until you do something that means you need to take new Flat frames, i.e. rotate your camera; physically remove your camera; or change / remove filters. A Session is not necessarily a single night. In fact, I heartily recommend long integration times, which involves imaging the same target for weeks on end. If you keep your telescope as a closed system (so you’ve not introducing, removing, or jiggling dust about) then you could complete an entire Project with a single Session totalling many nights.
You can take Flats at any point during a Session. It might be at the very start, before you take a single Light; or maybe at the beginning of your seventh night of imaging, while you’re waiting for cloud to clear; or maybe after you’ve finished capturing your final Light. But as soon as you do anything mentioned above that means you need new Flats, you’ve just started a new Session.
The fewer Sessions you have, the easier pre-processing is. Consider multi-session projects once you’ve mastered single-session.
Part 1: folder organisation
I know I know, it’s not too exciting, but believe me when I say that good computer folder organisation is the foundation to stress-free pre-processing. You need to know where to save all your Subframes, both Light and Calibration, and where to tell PixInsight to save files you’re working on. Get this right from the beginning and you can thank me later!
Here’s an example folder structure that’s suitable for a single Session project. It’s for data collected using an Optolong L-Ultimate filter (hence the folder named “Ult”), but it’ll work for any filter — just change that particular folder name accordingly. Say you’re using an IDAS NBZ filter; name the folder something like “NBZ”. I’ll give you example folder structures for multi-session and multi-filter projects later.
Let’s talk about these folders in a bit more detail.
Astro
The main folder on your harddrive where you store all your Projects.
.Calibration
I use a “.” in a folder name when I want it to appear first in the alphabetical folder list, which makes it easier to find. This makes sense for our Calibration folder as we’ll be using it a lot. Within .Calibration we have a folder called Bias. This is where you should put all your Bias frames. I use 50 of them. As with all Calibration frames, remember they should have been taken at the same temperature as your Lights. I use -10 degrees C for everything. That makes it easy. We also have a folder called Dark. You guessed it, this is where we put our Dark frames. I have 50 each for multiple exposure times (10s, 30s, 60s, 120s, 180s, 300s), although in reality I almost always shoot 120s Light subframes, so only every really use my 120s Darks.
.Template
This will make your life easier! Once you’ve made your first Target file structure, copy all the (empty) folders and paste them here. Then, whenever you start a new Target, just copy / paste the template folders to start you off.
NGC 7822
This is the Target I’m using for this example. Each Target has its own folder, as shown in the chart. When possible use short names, e.g. M45 instead of The Pleiades. We’ll see why later.
2023
You may re-image a particular Target over multiple years, so the next folder is named after the year in which you completed gathering your data. For example, if your Project ran from 6 July to 18 August 2022, make a folder named 2022. If your Project ran from 1 December 2022 to 3 February 2023, name the folder 2023.
.Finished
This is where we’ll save the final, completed, full edited image. (I’ll write guides for full processing later).
Ult
This folder is named after the filter that was used when you collected your data for the Session. I use Ult for Optolong L-Ultimate data, as shown in this example. I use RGB when I haven’t used any filters, because I’ve collected RGB data, and D2 for Askar Colour Magic D2 data. You’ll need your own names if you’re using different filters, but you get the idea. More on multi-filter projects later!
- Flats
This is where you should save all the Flats for your Session. I use 20 Flats per Session. - Source
This is where you should save all the Lights for your Session. If, like me, you aim for long integration times, then this folder will gradually grow over the timeframe of a Project to eventually house several hundred Lights. - Blinked
This is where we’ll save Lights that we’ve Blinked. More on this later. - Approved
This is where we’ll save our Lights that have gone through the SubframeSelector process. More on this later. - WBPP
This is where we’ll save files produced by the WeightedBatchPreprocessing process. More on this later. - WiP
WiP stands for Work in Progress. This is where we’ll save our Integrated Master Light, ready for full processing. More on this later.
I know that seems like a lot, but it’ll make sense once we actually start pre-processing! Before we continue, you should have:
- Made the file structure for your Project
- Put your Bias and Dark Subframes into the correct places within .Calibration
- Put your Flats into 1. Flats
- Put your Lights into 2. Source
Part 2: pre-processing a single-filter, single-session Project
Step 1: Blink
We only want good quality Lights to go into our final Integrated image — our cake should have the finest ingredients! So, the first thing we need to do when pre-processing is weed out any Lights that are obviously of a poor quality. Blink is a tool that will help us with this.
Once you’ve loaded PixInsight, go to PROCESS -> <All Processes> -> Blink. This will load the Blink module. Then, highlight all the files you have in 1. Source, and drag and drop them onto the Blink workspace [1]. This will load them. If you’ve got a lot of Lights then this could take a few minutes.
Once they’ve loaded, you’ll see all the Lights listed, and an image of whichever one is currently highlighted [2]. Use the control buttons [3] to skip through them quickly, like an animation; pause; and move forwards and backwards. The objective here is to spot any Lights that are obviously no good, most likely because of cloud. When you come across one of these bad Lights, uncheck its box from the list. This will remove it from the pool, i.e. it’ll be skipped when you’re using the control buttons [2].
Note that plane or satellite trails are not a reason to remove a Light from the pool. PixInsight’s integration process will remove these trails very effectively.
Once you’ve skimmed past all your Lights once or twice and weeded out the obviously bad ones, highlight the BlinkScreen [2] and zoom in a few steps. I use my mousewheel for this. Then repeat the process of skimming through all the Lights, but this time you’re looking for any Subframes with stars that are obviously out of focus; or with stars that are actually little lines, probably due to guiding or tracking errors. Remove all these by unchecking their boxes, as before.
How many Lights you uncheck depends on your data, but it could potentially be the majority of your data if you had bad weather. If you’re cutting a lot of Lights due to star issues, then you may want to look into improving your mount’s guiding / tracking.
Once you’ve done your weeding, highlight the filenames of all the Lights that are still checked, i.e. seem to be good quality. You can click and drag over multiple files, and Ctrl_click to select multiple ones as well.
Then, click on the Save icon [4] and select your folder 3. Blinked.
Tip: if you ever open Blink and it’s already populated with Lights, you can use the little icon immediately to the left of Save [4] to remove them.
Step 2: SubframeSelector
We removed the obviously bad Lights with Blink, but we can use a powerful PixInsight tool called SubframeSelector to be really sure we’re only using good quality data.
Load it up by going to PROCESS -> <All Processes> -> SubframeSelector. A few windows will appear, but for now we’re most interested with the one in the screenshot above.
First, make sure that the Routine is set to Measure Subframes [1]. It should be by default.
Then click Add Files [2] and select the files from 3. Blinked. This will load all the Lights that made the grade after using the Blink process. Their filenames will appear in [3].
We then want to set three of the System Parameters [4].
1. Subframe scale. You can calculate this using the top box on this CCD Calculator. You can Google your camera’s pixel size, and you probably know your telescope’s focal length already — if not, easy to find out online. Input these two numbers, and CCD Calculator will give you the resolution, which is the number you type into the Subframe scale box in PixInsight.
This example shows that the Subframe scale of my previous imaging rig (ZWO ASI2600MC Pro camera and Askar FRA400 telescope) is 1.94:
This example shows that the Subframe scale of my current imaging rig (ZWO ASI2600MC Pro camera and Askar 130PHQ telescope) is 0.78:
2. Camera gain
You can work out your Camera gain by opening one of your Light Subframes in Pixinsight. Double-click on a blank part of PixInsight’s grey background, and then select any one of your Light Subframes from 3. Blinked. It will be displayed on your screen, but will likely look all or almost all black [1]. Don’t worry about that!
Next, go to PROCESS -> <All Processes> -> FITSHeader. This will load up FITSHeader, which will analyse your Subframe [2]. Use the drop-down arrow [3] to load your chosen Subframe. You’ll then see a lot of information displayed. Scan down until you see EGAIN [4]. In the example above it’s 0.24, to two decimal points (which is fine). This is the number to put into SubframeSelector’s Camera gain box.
If you always use the same Gain on your camera (I always use Gain 100) then you use this EGAIN number any time you use SubframeSelector. Run any of your Subframes, including Calibration Subframes, through FITSHeader and you’ll see they have the same EGAIN.
3. Camera resolution
An easy one this, just search online for your camera’s specifications. My ZWO ASI2600MC Pro is 16-bit.
Note down your answers to Subframe scale, Camera gain, and Camera resolution, then you can just put the numbers in straight away every time you use SubframeSelector. You’ll only need to work them out again if you change something, like your camera, camera gain, or telescope. It’ll become muscle-memory after a while. Whenever I load SubframeSelector, I type in 0.78, 0.24, 16-bit. Easy!
Now press the little blue circle button just below [5] on the SuframeSelector screenshot. PixInsight will analyse your Light Subframes. This may take a while, depending on the number of Subframes and the speed of your computer. It could easily take over an hour, so maybe take a break. Why not read some fascinating astrophotography articles while you wait?
…some time later…
When complete, PixInsight will display its SubframeSelector Measurements window.
At the top is a list of all the Lights, and at the bottom is graph that compares them based on a particular criterion. We’re going to use two criteria to judge our Lights: FWHM and Stars. We’ll start with FWHM. Click on the dropdown menu [1] to order the list of Lights by FWHM; then do the same with the dropdown menu at [2] to update the graph view.
FWHM stands for “Full Width Half Maximum”, and is a measure of how big or small stars appear. Big stars are likely to be out of focus, while small stars are probably in focus. You may have come across FWHM before as part of autofocus routines, where your electronic autofocusser keeps adjusting until the stars have the smallest possible FWHM, i.e. they’re sharp and in focus.
There’s no hard rule here for which Lights don’t make the grade; it depends on how strict you want to be. But in general, it’ll be fairly obvious in the graph view if any are bad. See how there’s a big spike early on, where a Light reaches a FWHM of 4.4? That got past me during the Blink process, but Subframe Selector has picked it up. I often remove anything above the light grey area of the graph.
To remove Lights from the pool, check the FWHM values in [3]. They’ll be in order, because we selected FWHM in the dropdown menu [1]. Remember with FWHM that the lower the number the better. So, scroll all the way down and at the bottom you’ll come to the poorest quality Lights according to their FWHM values. Highlight the ones in the list that you want to axe and then go to the buttons by [4]. Use the green tick to flag them for removal later.
In the screenshot above, I’ve flagged every Light with a FWHM higher than 3.4 for removal. I’ll actually remove them after I’ve checked a second value…
I said that lower FWHM means better-focussed stars, and that is true, but there’s a catch. Sometimes, wispy high-altitude cloud can partially obscure your image and make stars appear smaller than they are, thereby giving them a low FWHM value. To check that this isn’t happening, we can judge our Light Subframes by their Stars value. Use the two dropdown menus [1] and [2] to select Stars.
The list of Lights is now ordered by the number of Stars visible, and the graph shows this as well. Note there are some little red crosses in the graph; these are the Lights we flagged for likely removal based on their FWHM.
With Stars, the higher the number the better, so it’s good that most of those red crosses are fairly low on the graph. But look, there’s a cluster to the left that has a few red crosses, but also quite a few Lights that appeared sharp based on their FWHM, but don’t have many stars; thin cloud is likely the culprit.
My general rule of thumb is to remove any Lights that have under half the number of Stars than the highest ranking, but again it’s not a hard rule. Going by that with these data though, I’d flag every Light with fewer than 130 stars for removal by highlighting them and clicking the green tick mark [4].
At the top-left of the screen, just below the first dropdown menu, we can see at a glance how many Light s we’re left with, as a total number and a percentage of what we started with. In this case, we’re left with 341, which is 79.12% of our initial Lights. This is about what I normally have. Remember, just using Blink we thought that all of these Lights were good. SubframeSelector really gets you focussed on raising the quality of your data. It’s also a reason I aim for really long integration times. I try to collect around 30 hours per Target, as I know that Blink and SubframeSelector will probably whittle down about 1/3 of that, leaving me with a decent 20 hours.
At this point you might decide to be a bit more ruthless, and flag more for removal; or perhaps be more lenient and put a few back in. I tend to round down so that the total time of all my Lights will be a nice round number; for example, 600 120-second Light Subframes, totalling 20 hours exactly.
Now we return to that first SubframeSelector window.
Use the dropdown menu [1] and change it it Output Subframes. Note that all the Lights will still be ticked despite that fact we flagged some removal; don’t worry about that. Then go to Directory [2] and use the little folder icon at the right to select where you want to save the Light Subframes that made your grade; that should be 4. Approved. Finally, click on the little blue circle button at the bottom-left. Give PixInsight a few minutes to complete the process.
Once complete, open the 4. Approved folder and check that there are the expected number of Lights there. In this case, we approved 341 Lights, so we should see 341 in the folder.
Step 3: WeightedBatchPreprocessing
Almost there! Now we’ve got all the finest ingredients. WeightedBatchPreProcessing (WBPP) is like the pot that we’ll put everything into, give it a stir, and then produce our high quality Integrated Master Light. To load WBPP, go to SCRIPT -> Batch Processing -> WeightedBatchPreprocessing. It can sometimes take a while to load.
If there are files already loaded then we’ll need to remove them to give ourselves a clean slate. In turn, click on the Bias, Darks, Flats, and Lights tabs at the top left; then click the button labelled “X Clear”.
Use the buttons with the green + symbols [1] to add our files:
- Click on the Bias button and add the Bias Subframes from .Calibration -> Bias.
- Click on the Bias button and add the Darks Subframes from .Calibration -> Darks.
- Click on the Flats button and add the Flats Subframes from 1. Flats.
- Click on the Lights button and add the Lights Subframes from 4. Approved.
Now click the button labelled SELECT [2] and choose your preferred option; I recommend “Maximum Quality”, given all the effort we’ve gone to!
Click on the Diagnostics button [3] and PixInsight will flag any issues. The top message about long file path limitations is a stock message that appears every time; it doesn’t mean a problem has been detected. PixInsight doesn’t like very long file path names, which is why it’s good to keep the folder names short if you can. Click OK to leave the Diagnostics window.
Then we want to choose the Output Directory [4] as 5. WBPP.
Finally, click the Run button at the bottom-right to set WBPP going! Warning: it will likely take a very long time, during which your computer will be sloooooow. I have a powerful PC but still leave WBPP running overnight. The WBPP execution monitor lets you follow its progress. Don’t worry if you used a filter but see the wording “NoFilter” in any of the descriptions. It won’t affect anything.
The above example took 5 hours 46 minutes 35 seconds to complete. Note that 30 Light Subframes failed to Register; I’m not sure why this is, and need to look into it. Almost all were successful though, so it’s not a big issue. Click DONE.
You’ll then see the Smart Report. If you had any issues then you might like to Save this, but if not just click DONE.
The WeightedBatchPreprocessing window will then appear again. Go ahead and close it by clicking the Exit button at the bottom-right.
Now we want to load up our integrated Light file, called a Master Light. Double-click anywhere on PixInsight’s grey background, then navigate to 5. WBPP.
Then double-click to open the master folder.
This next step is optional, but I like to do it because I find it interesting. Double-click on the file that has the largest file size. It’ll be a masterLight, but without the suffix _autocrop. Three images will load up, and they’ll likely look completely black. This is ok. Click in the top window so that it’s selected (i.e. its top bar is blue not grey). Then click on the little icon of a computer screen with a nuclear symbol, above the [1] in this screenshot:
This shows all the digital noise that’s been removed from your Mater Light file during the WBPP process. There’s so much of it! Makes going through every step and having an overnight wait worth it, I think. OK, go ahead and close those three images. Now back to the necessary steps.
Double-click anywhere on PixInsight’s grey background, then navigate to 5. WBPP. Then double-click to open the master folder. (You may be there already if you followed the above optional step). This time we want to open the file that has _autocrop as its suffix. It’s normally the last of the three files.
Two images will be displayed. Go ahead and close the top one.
The remaining image is actually our fully Integrated Master Light — that’s right, the result of all our efforts so far! But it likely looks completely black. That’s normal. We need to apply an autostretch to get a rough preview. To do this, go to PROCESS -> <All Processes> -> ScreenTransferFunction.
Make sure the Master Light window is selected, i.e. its top bar is blue not grey. Look at the icons to the right of [1] in the screenshot below. The top one shows a chain. Click on this so it’s deselected. Then click on the nuclear symbol. This will apply an autostretch to your Master Light file, and you’ll get a preview of your data. Exciting! Note that once you’ve fully processed your image, it’ll look much much better.
Now click FILE -> Save As. Navigate to 6. WiP. Name your file with the prefix of the filter that you used, then _integrated. In this example I’d type Ult_integrated. The file type should be XISF, which it will likely be as default. Then click Save.
You’ll see an options box. All the defaults should be ok, but for reference this is what you want:
Click OK. Congratulations! You’ve now completed your pre-processing. That Integrated file, safely saved in 6. WiP, is the one you’ll go onto fully process.
Optional extra step: we created a lot of files during pre-processing, and they’ll be filling our harddrive. We can delete ones we don’t need. Normally I do this after I’ve completely finished a Project, but I’ll take this opportunity to outline what’s safe to delete in case you need to do it earlier. Basically, we want to keep the files that will be needed if we decide to reprocess our data in the future. Anything else we can delete.
- Keep everything in 1. Flats.
- Delete everything in 2. Source.
- Delete everything in 3. Blinked.
- Keep everything in 4. Approved.
- Delete everything in 5. WBPP. (Double-check you’ve got your Master Light saved in 6. WiP first!)
- Keep everything in 6. WiP.
This way, you’ve got your Flats and all your best quality Lights. These are needed if you want to run WBPP again. You’ve also got your freshly integrated Master Light.
Part 3: pre-processing a multi-filter Project
What if your Project involves more than one filter? For example, maybe you want to add RGB stars to your L-Ultimate data. Or, perhaps you want to use an Askar D2 to gather Sulphur II data to add into the mix. Well the good news is that your pre-processing is no more complex that what we’ve already covered. Combining data happens during the processing stage, not pre-processing. The difference in pre-processing comes from the file structure, and where you save your files.
Use the screenshot above as a guide. I’ve started with the Year of your Project, just to keep the chart more manageable. Run through pre-processing the data for each filter separately, following all the steps from Part 2. Note that each filter should have its own set of Flats.
When you have each Integrated Master Light, save it in .WiP. Note that this folder is in a slightly different position in our folder hierarchy compared to before. This will just make it a bit easier when you’re combining them during processing.
Part 4: pre-processing a multi-filter, multi-session Project
This is the most complex option: pre-processing a Project that involves multiple filters, and also multiple Sessions. Still, it’s not too hard if you follow a good workflow. Let’s just remind ourselves of what a Session is:
I define a Session as all the Lights collected until you do something that means you need to take new Flats i.e. rotate your camera; physically remove your camera; or change / remove filters. A Session is not necessarily a single night.
It’s easiest if you can collect all your data for a particular filter over one Session. My Sessions tend to last several weeks. This is what I do almost all of the time. But occasionally something crops up that changes the plan. For example, recently I was imaging M42 using my Optolong L-Ultimate filter. To keep things simple and only use one set of Flats, I wanted to gather 10+ hours over many nights all in a single Session. However, Comet C/2022 (E3 ZTF) made an appearance and I didn’t want to miss it. So, one night I took the Optolong L-Ultimate filter out so that I could image the comet in RGB. Once that was complete, I put the Optolong L-Ultimate back in place to continue imaging M42. But because I made that change, some dust in the telescope, filter or camera would have been introduced, removed, or moved. This meant I needed to take a new set of Flats for the next batch of Lights I would take. Everything up until removing the filter was one Session; after putting the filter back in was a new Session. Eventually we want all these Light Subframes to make one Integrated Master Light. PixInsight can do this!
Here’s a new folder chart. It shows the setup for a complex Project: RGB data gathered over two Sessions, and Optolong L-Ultimate data gathered over three Sessions. I’ve started the chart with the Target’s Year, just to help you focus on what’s important.
Treat each Session on its own for the majority of pre-processing, following everything outlined in Part 2 all the way to the completion of Step 2: SubframeSelector. So, for each Session you need to have gone through Blink and SubframeSelector, meaning you have good quality Light Subframes, and of course matching Flats. Once you’re confident of this, delete everything in 2. Source and 3. Blinked, only keeping the files in 1. Flats and 4. Approved.
We want to combine these Lights into one Integrated Master Light. We do that using WeighedBatchPreprocessing. Go ahead and load it up: SCRIPT -> Batch Processing -> WeightedBatchPreprocessing. It can sometimes take a while to load.
Once it’s ready, you may see files already loaded. We’ll need to remove them to give ourselves a clean slate. In turn, click on the Bias, Darks, Flats, and Lights tabs at the top left; [1] then click the button labelled “X Clear”.
Next, click the +Directory button [3]. Highlight your SESSION_1 folder and click the Select Folder button.
This will load all the Flats and good quality Lights from your Session. (This is why we deleted 2. Source and 3. Blinked; we don’t want them to be included). After a moment, PixInsight will show you its Diagnostic Messages. Skim through this to make sure its as expected: it should have found all the Flats and Lights from 4. Approved. Click OK. PixInsight is clever, and should have put them into the correct tabs.
Next, go ahead and repeat that process for your next Session. Click the +Directory button, highlight your SESSION_2 folder and click the Select Folder button. After a little while, PixInsight will have loaded all those files, just as it did with your first Session. Repeat for every Session with the same filter.
You may notice that all the Flats from your Sessions have been lumped together; and the same for the Lights. This is no good, as the Flats need to go with their corresponding Lights. Fortunately we’ve been very organised with our folder structure, so this is easy to do.
Go to Grouping Keywords [1] and ensure it’s checked. Type SESSION into the text box, then click on the green +. Hey presto, your Flats and Lights from your Sessions will now be separated; check the list [2] to be sure. If this doesn’t work, try clicking the gears icon within Grouping Keywords. If it still doesn’t work, check that you’ve put an underscore in your folder names, i.e. SESSION_1 and not SESSION1.
You may like to look at the Pipeline tab, as shown below. Note how WBPP will Integrate, Calibrate, and Debayer each Session separately; but will then run additional steps on all the Light subframes, resulting in a single Integration and Autocrop. If your Pipeline shows that you’ll end up with two or more Integrations or Autocrops, then something has gone wrong and I suggest you carefully try each step again.
Now continue with your WBPP procedure as outlined in Part 2. To recap, select Maximum Quality [3], select the Output Directory as your WBPP folder [4], run Diagnostics if you like, then click Run. WBPP will use the correct Flats to calibrate their corresponding Lights, and then integrate all the Lights into one single Master Light.
Then repeat for any other filters you used. In the end, your .WiP folder should contain one Integrated Master Light for each filter you used.
That’s it
It seems like a lot when it’s all written down in a guide like this, but PixInsight pre-processing isn’t that tricky once you get the hang of it. And you’ll produce excellent Integrated Master Lights ready for processing!
Don’t feel that you need to follow this guide slavishly. If you find a better way of doing something, great! Maybe let me know and I can improve my own workflow.
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