Workflow tutorial: using SIRIL 1.4 including GraXpert, Cosmic Clarity Suite Pro and Veralux python scripts

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Updates January 2026

The rapid development of Veralux Python scripts has been breathtaking this month. As a result I am adding some updates to this page. These can be found at the bottom of this original post - as a postscript. Any future updates will appear in the same place. 

This post was published 13.12.25

Optimal workflow using SIRIL with COSMIC CLARITY SUITE PRO, GRAXPERT and AFFINITY PHOTO

I have written a previous post about my SIRIL workflow which you can find here  https://undersouthwestskies.blogspot.com/2025/01/a-beginners-guide-to-using-siril-some.html

This post was updated early December 2025, late December 2025. 

In this post I 

·       share my more simplified, reorganised workflow - which is based on SIRIL vs 1.4, and the python scripts for Cosmic Clarity Suite (by Seti Astro), Veralux and GraXpert. 

·       Try to give notes and tips which will help beginners

·       Share some useful, helpful YouTube tutorials

So, let’s get stuck straight in to my latest workflow: PLEASE NOTE - screenshots will be added when I process my next image - so please bear with me until then 

NOTE: I am assuming you have a little knowledge of how to organise your images – if you are going to be using SIRIL – if you are new to SIRIL the jump down to the bottom to watch one or two of the videos first.

Below is a simple graphic image which simplifies my workflow approach: 

and here is a simple infographic I tried to design based on SIRIL and not using the latest cosmic clarity and veralux python scripts 

A.      Organisation:

1.      Organise your folders into one folder called SIRIL and then sub folders for – lights, biases, darks and flats

2.      Set your home directory top menu bar left hand side

3.      Choose scripts – siril script files  - OSC pre-processing.ssf  to start the stacking process

 

B.      Crop and gradient removal:

1.      Be in autostretch mode on bottom task bar

2.      Load results.fits file produced from your stacking script – find in your home directory

3.      Crop edges to remove stacking artefacts

4.      Tools – astrometry  - image plate solver  on the pop up window:

a.      In pop up window - search catalogue number; (S box = if southern hemisphere image); click metadata from image; check – siril solver, solution order – cubic, flip image, auto-crop for wide field, star catalogue auto, catalogue limit – auto.

5.      Background extraction – image processing – python scripts - AutoBGe seti

a.      use default settings in the pop up window initially i.e. sample points 100, polynominal 2 RBF smoothness – 0.1.  (L-Enhance note - Use degree 2 to avoid flattening extended Ha regions).

b.      On the pop up window – can opt to click add exclusion area – (this is what you don’t want extracted) – free hand draw in around nebula area to be excluded – if make a mistake – click clear selection and start again – then when ready click process

c.      Use undo/redo arrows to compare before and after to see the changes

NOTES: background extraction

1.      Can use GraXpert for BGE  – GraXpert uses AI model - don’t do denoise now just BGE – severe gradients <0.5; mild gradients >0.5

6.      If using SIRIL BGE – grid tolerance 3, squares off nebula and bright stars; click dither to on; subtraction on; polynominal – increase for very bad gradients – RBF tab – smoothing default 0.5

 

C.     Colour calibration:

1.      NOTE – must have done image plate solver before doing colour calibration

2.      Autostretch mode on lower menu bar

3.      Remove chromatic aberration – python script - aberration remover – can do now or after colour calibration – either

4.      Plate solve image – if not already done above MUST DO BEFORE COLOUR CALLIBRATION WORK  - needs internet connection - astrometry - image plate solve

5.      Colour calibration – image processing tab – colour calibration - Spectrophotometric colour calibration

a.      SPCC – needs internet – tick the following: average spiral galaxy, one shot colour, osc sensor – closest, osc filter – optolong L pro OR if narrow band – check narrow band box and enter your filter details ( L enhance details for table – see below; tick background reference to auto detection.

b.      Settings if using L-enHance filter - – wavelength : blue OIII – 500; Green HB – 486; red H-alpha 656.3 and BW – OIII green 24; red 10; Blue 24

 

D.     Cosmic clarity sharpening  before denoise

a.       DO BEFORE STRETCHING I.E. LINEAR DATA

                                                  i.      stellar = stars only; non stellar = background and other objects - do both stellar and non stellar on pop up window OR experiment using undo/redo arrows – use GPU, clear input directory, (stellar sharpening  - 0.5 default and play with slider; or move first slider to 0.20 to 0.25; non stellar slider to 0.80; non stellar strength to 3. Zoom in a check – use undo and redo buttons to see differences made

b.      OPTIONAL – could do DENOISE now – scripts – python scripts - CC denoise – use RGB channel; check GPU and Clear input directory.     ** New veralux silentium python script is also a denoise option - must be done on linear images i.e. before image is stretched. To get this new script - go to scripts tab and get scripts and then go down the list - select the veralux script bar and check the box at the end. NOTE: as of late december 2025 - note that under scriupts tab - veralux now has its onw heading

c.      Now find output folder in Cosmic Clarity home folder on C drive and delete files as you go.

** If you use the new veralux silentium denoise script - I tend to use the default settings. when the preview box appears - it shows the settings in effect. To see the original image just press and hold down the space bar. the red box on the preview screen can also be moved about and acts as a zoom in function - so drag and drop it to the area you want to focus on. 

E   OPTIONAL stretching now – using Veralux hypermetric Stretching  NOTE – SEE F BELOW BEFORE DECIDING

a.      MUST DO PLATE SOLVING AND SPCC COLOUR BEFORE HAND

b.      Linear view – then Scripts – python scripts – processing – Veralux hypermetric stretching

c.      Settings for pop-up window:

a.      Processing – ready to use

b.      Sensor calibration – top one or canon 600d or 709re recommended.

c.      Click live view – use mouse scroll wheel to zoom in and out

d.      Target background – start 0.10 (0.2 is default) (lower the number the more contrast and darker the image – higher the number the less contrast and brighter the image)

e.      Log D – strength of stretch – leave at default 2.00

f.        Click auto calculate

g.       Protect B – how protected stars are during stretch – leave on default

h.      Star core recovery – leave default 3.5

i.        Process

j.        Make adjustments and experiment with setting inputs until happy

k.       If over saturated use the slider – but RECOMMENDATION IS DON’T TOUCH THE SLIDER – chromatic preservation colour one  - after alteration click auto calculate again

l.        Can also now apply curves transformation if image looking too washed out etc – or wait until starnet

d.      If choose scientific – then after do series of transform curve stretches in siril to bring up contrast and colour – s curves to raise darks, MT and HL’s

F. Star removal: I always DO BEFORE STRETCHING so I'd do section E above AFTER doing the starnet separation

1.      Optional first step: Image processing – star  processing desaturate stars

2.      Image processing – star processing - Starnet – tick prestretch in pop up window

3.      Stretching starless nebula – keep linear below in bottom menu

a.      OPTIONS: either Veralux hypermetric stretch as above OR Cosmic Clarity statistical stretch – see below

                                                  i.      Statistical stretch – in linear mode - target median 0.11 for anything not filling entire frame; normalise- no curves adjustment; if fully fills frame target median at 0.25 starter.

                                                 ii.      Stretch until: - Nebula structure is visible      Background is not clipped   Stars not blown out – NB if done colour correction already must check linked stretch box.
Now the image is nonlinear and ready for detail work.

b.      NOTE – CAN STILL DO OLD WAY IF DESIRE – SEE BELOW:

                                                  i.      OR – asinh stretch first followed by HTF stretch –  (HTF stretch using lhs and middle triangles or placing points on curve line to get shallow s curve  - watch clipping % - ensure no clipping of data –  ( can use ROI – draw box on part of nebula – right click select |ROI – select ‘set to selection’ and do adjustments; to remove – go back to menu and click ‘clear ROI’

                                                 ii.      OR Can also retry with curves adjustment ticked – try boost slider at 0.5 – the greater the boost the more contrast and fainter detail at expense of more noise and artefacts - 

                                               iii.      OR can do curves transformation – tiny iterative changes and repeat image processing – stretches – curves transformation – click on line and drag up or down – aim shallow s curve – don’t clip data – make very small adjustments – repeat gently LESS is MORE 

EXPERIMENT WITH EACH UNTIL HAPPY – use undo/redo arrows

4.      Complete denoise now – scripts – python scripts – processing – cosmic clarity denoise Denoise

a.      In pop up windopw - full strength – do zoom in and undo/redo to check difference

b.      alternative is denoise in siril  - if using GRaXpert – default stretch 0.5 so try 0.8

 

(NOTE – could try  SETI ENHANCER if you have it downloaded — Star Control, Detail Boost, Color Punch at this stage -
Load the denoised stretched image into SETI Enhancer.

·        Star Reduction - Use after stretch, not before.   Strength: 10–30%    Helps separate the nebula from crowded star fields      Avoid “donut-shaped” stars—dial back if seen

·        Nebula Detail Enhancement   Use:   Local contrast      Midtone sharpening    Texture boost
Moderate levels keep it natural.

·        Color Enhancement
Increase nebula saturation       Adjust hue sliders for Ha/OIII separation      Use vibrance before saturation
Avoid boosting star colours too strongly

·        Background Balancing
Use background equalizer if available     Ensure background is smooth and neutral
Remove remaining gradients)

G. Process starmask:

1.      Could Desaturate stars now – see above where outlined previously

2.      Can do Asinh stretch or  htf stretch – keep mild – use square and eyedropper Asinh Stretch:  Broadband: 5–15 L-Enhance: 3–8    Black point: 0.001–0.003   

3.      If doing GHS: Stretch: 0.8–1.2     Midtones:  Broadband: 0.3–0.5  L-Enhance: 0.2–0.35

Stop here.  Do not adjust saturation, HDR, clarity, sharpening. OR

4.      Could Reduce star size now – image processing - morphological transformation – selection – strength 5 – 20%

5.      Optional Slight saturation boost  - image processing – colour saturation: do globally

H. Star re-composition:

1.      Image processing – star processing – star re-composition

2.      On pop up histograms - RHS is starmask; LHS is starless

3.      Do black point adjustment to starmask to reduce number of stars

4.      Adjust blend to avoid halos and bright stars – inspect fine details – zoom to check edges

5.      Final noise reduction – optional light GraXpert or cc denoise – avoid over-smoothing background or killing faint dust

Final tweaks:

1.      Vibrance, colour balance

2.      Final cropping/rotation  to choice

3.      Green noise check – SCNR (Green Noise Removal) – BEST = SIRIL   Broadband: Strength: 0.60–0.75  L-Enhance:  Use none or mild (0.20–0.35)      OIII contains green, so don't destroy it.

4.      Export 16 bit TIFF

PS Videos that I found useful: 

Look for AstroIslander's part 2 and 3 as well 

Updates January 2026

The rapid development of Veralux Python scripts has been breathtaking this month. As a result I am adding some updates to this page: 

1. Here is a revised work flow that I have been using, based almost entirely on the Veralux suite in SIRIL. It is mainly 'narrowband imaging' orientated. 

2. NARROWBAND WORKFLOW USING VERALUX SCRIPTS

This is a new work flow I am trying after using my Optolong L-enHance filter

BASIC WORK FLOW ORDER:

•      Crop
•      Plate solver 
•      Scripts - siril scripts - AutoBge 
•      scripts - siril scripts - CC sharpening 
•      Starnet removal - tick pre-stretch box
•      On starless image in linear mode - run Veralux Alchemy (see notes below) 
•      Complete Veralux Hypermetric Stretch and possible follow up > image processing - stretches - curves transformation to brings darks down slightly and brighten slightly highlights ) shallow 'S' curve) 
•       SAVE image
•       OPTIONAL: Image processing – filters – CLAHE (toggle preview on/off; play about with slides) SAVE
•       Veralux star recomposer – load RGBstars; load veralux alchemy linear fit file
•       Python scripts – processing – HDR multiscale
•       Veralux Vectra colour grading
•       Possible final image processing - stretches - curves transformation
•       Finishing in Affinity Photo 

3. Some notes about Veralux Alchemy

 Alchemy is for use when narrowband imaging. It leads to proper channel normalization, mixing without destroying colour integrity and structure.            

Useful if you are using one shot colour camera and optolong L-enHance

DON’T DO COLOUR CALIBRATION BEFORE USING ALCHEMY SCRIPT

LINEAR ONLY – MUST BE USED BEFORE STRETCHING DATA

ALCHEMY

·          Select sensor or OSC preprocessing

·       Enable Quantum On Mixing box

·       Normalisation – enable BG neutralization; enable Auto signal Fit

·       OIII – boosts blue (double click slider returns to default)

Palette Mixer

·       Default grey box setting = HOO

·       Sliders do the blends – so note the %’s

·       Pseudo HOO – changes slider %’s (50% green)

·       HSO preset = 100% OIII

SELECT YOUR PRESET then play with normalization OIII  slider

4. Veralux Vectra notes 

Perceptual colour grading with LCH (Lightness, chroma, Hue) for final astrophotography polish

VECTRA is a final step tool  - smoother colour transitions, refined saturation, balanced tonal

MUST BE USED ON IMAGE THAT HAS BEEN STRETCHED

Use either at end of work flow OR before star recomposer

VECTRA

•       Two tabs – primary (RGB) and secondary (YCM)
•       Sliders for each – can shift hue and/or saturation
•       Enable vector scope box – watch vector scope when using slider as well as image change
•       Know which areas of image want to enhance in advance of use
•       Same for using saturation sliders
•       AIM: to do final colour work on image
•       Shadow authority slider – prevents background changes – most of time sits far LHS – can affect colour of image target – so use very tiny steps  - keep watching for background changes
•       Enable white star integrity on images with stars – disable on starless images 

5. Veralux Star Recomposer notes 

Adds stars back into starless image after Starnett++ removal – replaces star recomposition

1.       In pop-up window load starmask and load starless image

2.       Linear for most images except galaxies

3.       Sensor profile – canon EOS modern

4.       Use star intensity slider

5.       Profile hardness = stars pinpoint level – default = 6

6.       Colour physics = star colour intensity

7.       Advanced tab –

a.       Core – removes artifacts around stars

b.       Reduction – reduces star size

c.       Optical healing – reduces halos around stars to improve colour  

Workflow tutorial - using SIRIL - some notes to get you started

An updated version of this post can be now found at:  https://undersouthwestskies.blogspot.com/2025/12/beginner-tutorial-workflow-for-using.html

 My beginners guide to basic editing in Siril

As a beginner to astronomy and astrophotography, and with a limited budget for spending on the hobbies, I am always on the lookout for ‘free’ software. Two fantastic programs are SIRIL and GraXpert. My post editing workflow uses these two and I do ‘finishing’ edits in Affinity Photo, which I have had for a few years now.

Like any new programs, the initial learning curve can be steep and so I found this to be with SIRIL. However, two things came to my rescue. Firstly, this YouTube channel: Deep Space Astro – a fantastic channel; I made so many notes and went through his videos so many times, step by step, whilst actually processing an image in Siril.

https://www.youtube.com/@DeepSpaceAstro

And then this book – “Astrophotography Image Processing with GraXpert, Siril and Gimp” by Max Dobres FRAS.

I discovered this book via a Facebook post on an astrophotography group in November which showed a similar flow diagram to one I was already working on to summarise my own workflow (I am a bit of a visual learner) which is below:

My diagram above now amended, incorporates some of the elements of that original flow diagram I saw in the Facebook astrophotography group.  

Max's book was fascinating. There was much I knew already from the videos and my internet reserach notes  but then there were constant snippets on his pages, where I thought "Oooooh"! And his screen grab images were really helpful. 

So below, I now share my SIRIL, GraXpert and Affinity Photo work flow.

As always, I provide a caveat which is this: Like you, I am a beginner. I am finding my feet slowly but surely in the new to me fields of astronomy, astrophotography, and photo editing in AF. If I have made any mistakes below then please accept my humble apologies and drop me a comment at the end of the post so that I can correct it immediately.

These are my notes from the videos, internet research etc. I have had them printed off and they’ve sat alongside my laptop EVERY TIME I do any post editing of deep space objects since late 2023. They are written in a shorthand but it should be fairly clear. I have made minor alterations in light of what I have read in Max’s book. He goes into great detail and includes really help diagrams and screen grab images. If you get stuck, then DeepSpaceAstro on YouTube will have a video about it, no doubt. If you want to develop further – its worth getting Max’s book off Amazon.

 

Good luck, if you use these notes and please do let me know how it goes. If you think there should be amendments, then drop me a comment.

 

S.I.R.I.L instructions – my work flow 

Firstly, open Siril and familiarise self with home screen. Select console tab on right hand side.

1.                   STEP ONE - STACKING

a.       Create a new folder on hard drive – called Siril

b.       Create four new folders within this Siril folder  – name them ‘biases’, ‘flats’, ‘lights’, ‘darks’

c.        Click on HOME (top left hand side) – change directory folder to this Siril folder created in (a) above

d.       Select SCRIPTS on top menu – select ‘OSC processing’ – run this script

e.       Watch progress of stacking on the console tab, right hand side

f.         When it has finished, load up newly created ‘results.fits’ file from this home Siril folder

g.       At this stage, if need to free up hard drive space, can delete newly created ‘process’ and ‘masters’ folders from the master Siril folder

h.       NOTE:  if not using calibration frames – SCRIPT – select right one; and ensure you have left flats, darks, biases folders empty

2.                   STEP TWO - IMAGE PROCESSING

a.       With ‘results.fits’ image open in screen, on bottom menu select auto-stretch to preview data and review in RGB

b.       Now preview separate R, G, B channels and then return to RGB channel

3.                   STEP THREE – SWITCH TO USING GRAXPERT FOR BACKGROUND EXTRACTION

a.       DO THIS BEFORE ANY STRETCHING OF THE IMAGE in Siril

b.       Load up saved ‘results.fits’ image created in Siril folder

c.        Select advanced tab on RHS and switch on AI ‘Background Extraction’ and ‘AI Denoise’

d.       Change bottom panel stretch to 30%

e.       Step 1 - Crop to remove any artifacts. Immediately save this image as ‘results.GxpCrp.fits’

f.         Return to 15% stretch at bottom tab

g.       Step 2 - Background extraction tab – select AI – smoothing to 0.5% - click ‘calculate background’

h.       When done change top tab to ‘gradient corrected’. (Original on this tab shows pre BG). Now save image as  ‘results.GxpCrpBge.fits’

i.         Step 3 - Denoising tab – default strength is 0.5 – can experiment with 0.8 or 0.9; click ‘denoise’ – zoom in to see changes (hold down control and use mouse wheel). When done save image as ‘results.GxpCrpBgeDno.fits’

j.         Change top tab to denoise gradient

k.       (NOTE: can do Bottom tab – saturation (adds more colour to image) now or leave to Siril)

l.         Return to SIRIL and reopen this saved image ‘results.GxpCrpBgeDno.fits’ and continue SIRIL work flow

 

NOTE: How to do background extraction in Siril

If working on Background extract in SIRIL:

1.                   With newly created image file ‘results.fits’ – open either green, red or blue channel tab but NOT the RGB one.

2.                   Image processing top menu – click ‘Background extraction’

3.                   On new pop up dialogue box - Change grid tolerance to 3 if there are missing orange squares on part of image background OR left click in that area to add a square. Keep only the BG squares – take squares off nebula and around really bright stars. To remove a star - right click on square to remove. Click dither. Keep on subtraction. Now click ‘compute background’ button – and then click apply

4.                   NOTES: (polynominal tab – select 1 to 4 depending on how bad a gradient is – worse the gradient  the higher the number to select). (RBF tab – recommended to use – smoothing = how aggressively applied – 0.5 is default setting)

If working on denoising in Siril

1.                   Select ‘Auto-stretch’ mode on bottom tab

2.                   Top tab – image processing – ‘noise reduction’

3.                   In new pop up dialogue box - Check ‘salt and pepper’ box. Colour denoising – off. Modulation 0.5

4.                   Default setting is ‘no secondary denoising stage’ – modulation 1 = full noise reduction – zoom in 100% on image and hit apply – experiment and do undo and redo to see changes

5.                   However, Anscombe VST OR data adaptive is better method - do trial and error between them – use undo/do buttons. Too much smoothing or smearing at edges of nebulae on new image – undo - adjust modulation slider – redo

6.                   Save image under new file name – this means can always go back a step and eload previous image if something goes wrong

4.                   STEP FOUR - COLOUR CALIBRATION IN SIRIL

a.       Make sure have image open - ‘results.GxpCrpBgeDno.fits’

b.       Set lower tab to ‘autostretch’

c.        Top tab – image processing – select colour calibration – select ‘Photometric calibration’

d.       In new dialogue box - search for DSO by entering its catalogue number e.g M101 or M42. Alter focal length inputs or use metadata within photo box to set the focal length details if used ASIair. Tick ‘flip image’ if need be. Select ‘auto’ under ‘catalogue limit’. Then click apply

e.       NOTE: BG reference – choose one of the colour channels – draw square on image in area representing best background area – Tick use current selection on dialogue box – BG neutralisation – do white reference on bright white star – apply

f.         Go to RGB and use backwards and forwards arrows on top menu to toggle between before and after changes.  When happy save this refined image as ‘results.GxpCrpBgeDnoPcc.fits’

5.                   STEP FIVE - DECONVOLUTION IN SIRIL

a.       Bottom tab – select ‘Linear

b.       Top tab - Image processing – ‘deconvolution’

c.        In newly popped up dialogue box – Default is  ‘blind deconvolution’ to generate PSF image – click apply

d.       NOTE: for experienced people - Other option to try – ‘PSF using stars’

e.       OR: see below –

f.         Deconvolution  MUST USE LINEAR NON STRETCHED IMAGE  so ensure in linear mode on bottom tab

                                                   i.      Simple option approach a - hamburger icon top right – image info – dynamic PSF – blind DC box ticked(essentially as steps above)

                                                 ii.      Approach b – image processing – ‘star processing’ – ‘full resynthesis’ – click the cog wheel. Drag the pop-up dialogue box to RHS

                                                iii.      Back on the image - create green ‘selection box’ over centre of image – right hand mouse click - crop;

                                                iv.      Image processing – star processing – cog wheel – dynamic psf – click ‘detect stars icon’ – aiming for white star that appears in top RHC to be unclipped in PSF preview box i.e. star is fully within the box and has some blackness all around it

                                                 v.      On resulting chart – click column a to sort from dimmest to brightest stars – want to keep only those 0.1 to 0.7 amplitude – fill in boxes at bottom to get this range; profile type to ‘moffat’.

                                                vi.      Click ‘detect stars’ icon

                                              vii.      Reduce PSF box down out of sight in RHC of screen

                                             viii.      Top tab - Image processing – deconvolution – select PSF from stars – generate PSF; then click download arrow alongside generate PSF button to save this image. Save as ‘results.GxpCrpBgeDnoPccDecon.fits’

                                                ix.      Bring back dynamic PSF box into view from bottom RHC – now doing test settings on the cropped image and when finally done will click undo right back to where image was uncropped – meanwhile on cropped image select ‘Richard lucy algorithm’ and ‘non blind deconvolution’ – start with default settings – keep other algorithm to gradient descent – click apply

                                                  x.      Zoom in and check for star fringing, ringing etc – (control hold down and use mouse wheel); toggle before and after arrows in top menu to judge change

                                                xi.      Click undo arrow and increase gradient step size a little and repeat zoom in to see effect

                                              xii.      Repeat this pattern until happy with changes – note the settings used

                                             xiii.      Click undo now until returning to uncropped image – in Deconvolution box put in settings and click apply on full image. Save any alterations as  ‘results.GxpCrpBgeDnoPccDecon.fits’

 

6.               6. STAR SEPARATION/STRETCH/RECOMBINATION WORKFLOW USING USING STARNETT++ in SIRIL

 

NOTE: if you haven’t downloaded STARNET++ add on into your Siril program – do so now. 

a.       Top tab - Imaging processing – ‘star processing’ – ‘starnet++ removal’

b.       On new pop-up dialogue box – tick ‘pre-stretch linear image’  and ‘generate star mask’ – make sure still in linear mode on bottom bar – then click execute

c.        Stretching the new Starless NEBULOSITY image which is the one that should be on screen now (NOTE YOU CAN DO THIS IN AFFINITY PHOTO – SEE NOTES AT END OF THIS SECTION)

                                                   i.      start in linear mode on bottom tab

                                                 ii.      on top tab – image processing  – ‘histogram transformation’ (MTF)

d.       In new popup dialogue box - Click on cog symbol – if happy with changes to image then click  ‘apply’. If not happy click ‘reset’ and then following below

                                                   i.      Set ‘zoom amount’ in box (top tab LHC) to 1. Adjust middle triangle on base of histogram  leftwards as far as can go. Now increase the zoom number value at top to create more space at base of histogram – slide the middle triangle leftwards again until gaining pleasing image; TIP – keep this first stretch slightly dark to avoid blowing out any cores – if happy with image  – click ‘apply’ and image as ‘results.GxpCrpBgeDnoPccDeconStarless.fits’ 

e.       Alternative from AFTER step(b) above

                                                   i.      stretch line sliders below the histogram graph area  until ‘nebulosity’ appears on black image; use -/+ button to do black point adjustments  OR

                                                 ii.      middle triangle at base of histogram  to LHS to get histogram off LHS. Then alter shadow slider in to base of histogram – keep figures on right at 0 to 0.1. Choose colours menu and do appropriate for each colour as prefer (can draw box onto part of nebula – hone in on different parts of it – then go to symmetry point – hit eyedropper on LHS – then move stretch slider)

                                                iii.      SAVE FILE TWICE– firstly, as results.GxpCrpBgeDnoPccDeconStarless.fits’. Then resave again but this time as results.GxpCrpBgeDnoPccDeconStarless.tiff’  (as tiff 16 bit unsigned).

                                                iv.      NOTE: advanced action - could at this point – open tiff file in affinity photo an do some levels and curves adjustments. Save as 16 bits Tiff file and then bring back to Siril. Open it and immediately save it as fits file! This is one which will then carry on with in Siril.  

7.                   STEP SEVEN - GHS STRETCHING AND COLOUR SATURATION IN SIRIL

 

The aim of a GHS stretch, as I understand it, is to stretch the pixel values out across the whole range of brightness. We do a series of stretches to different areas of image to bring out detail and improve contrast where interesting features lie.  Starting with an overall stretch, successive stretches are applied to different areas to maximise the potential of image. Principles of GHS:  ‘S’ curves (to flatten either end of pixel distribution and boost mid-range pixels.) Done by a) defining symmetry point (sp) = centre of curve and b) local intensity – the range of the S curve. Slider adjusts strength of stretch. AIM: to bring out most detail and contrast in image

a.       Bottom tab – make sure selected linear mode

b.       Top tab - Image processing – ‘GHS’

c.        In pop up window

                                                   i.      Symmetry point to 0.5 or click middle of line on histogram; zoom level is ‘1’

                                                 ii.      Method one: if focusing on nebulae or galaxies – focus on outer rim details:

1.       GHS rim detail – left mouse click on image to draw box in area of interest e.g. outer rim detail

2.       Click on dropper symbol to set the SP value

3.       Stretch factor slider moved to get level of detail required

4.       Local stretch factor slider moved to modify extent of stretch factor slider

5.       Go back and forth between two until pleasing result (could try Local stretch slider full across to rhs and then Stretch factor slider until nebula appears – stop before background gets too grey); aiming to form an S curve on histogram – click ‘apply’ when happy

6.       Then change to a ‘linear black point stretch’ in top menu of pop up box  – slide BK point slider to close gap base of LHS of histogram curve

7.       NOTE: Stop highlights blowing out when adjusting for midtones by pulling back the highlight protection point  - on logarithmic scale the red line on histogram will be very steep where detail is but then the incline should be far less steep for rest of the histogram

                                                iii.      Method two – for GHS odust detail – draw box on area wanted to impact

1.       Set the SP point as above with box

2.       Adjust strength and local intensity values as above to get effect pleasing

3.       Move shadows and highlight protection sliders to stop highlights blowing out

                                                iv.      On both methods above -

1.       Change back to GHS at top  - logarithmic scale – check box on left – aiming to get straight line from peak to bottom lowest point (humps = areas where lower contrast needed; valleys = where more contrast needed) – click to left of very top of histogram curve to set symmetry point – now stretch slider a little; then local stretch slider to add or remove contrast and to try and smooth the line.

2.       Repeat for bottom of curve rhs – click to set symmetry point an repeat step above – use local stretch curve to add/remove contrast

                                                 v.      Method three – GHS colour stretching

1.       Aim to improve colours – turning colour buttons on and off

2.       Boost blue – a tiny amount – click off other colour channels – draw square around area of DSO that represents brightness area where we want to boost blue – click on dropper to set SP.  Play with strength and local intensity sliders to get effect as outlined above.

3.       Use shadow and highlight protection point sliders to squeeze the affected area away from edges of histogram by keeping them close to the SP

4.       May need to move SP to get blue boost in right place  - then click apply

5.       Add touch of red – use same process outlined above LESS IS BETTER

6.       Improving saturation – top right menu to colour saturation stretch. Boosts all colours. Check zoom at 1.

                                                vi.      Remember to save your image after GHS: ‘results.GxpCrpBgeDnoPccDeconStarlessGhs.fits’

8.                   If not doing colour saturation above as part of GHS work then - COLOUR SATURATION

a.       Top tab - Image processing – ‘colour saturation’ – hue on global.

b.       Amount > increases colour saturation – try between 0.25 and 0.5.

c.        Click background factor to allow sky background to be protected from colour saturation

d.       Experiment and when happy - apply

e.       Click save: ‘results.GxpCrpBgeDnoPccDeconStarlessGhsCos.fits’

9.                   ALTERING CONTRAST AND DETAIL in SIRIL

a.       Top menu tab - Image processing – ‘contrast limited adaptive histogram equalisation’ (CLAHE)

b.       Use it lightly – small adjustments to avoid introducing artefacts

c.        Use preview box to see before and after

d.       Save as ‘results.GxpCrpBgeDnoPccDeconStarlessGhsCosCon.fits’

10.                REMOVAL GREEN HUES

a.       Top menu tab - Image processing – ‘sub-chromatic green noise’

b.       After using default settings – save image as ‘results.GxpCrpBgeDnoPccDeconStarlessGhsCosConGno.fits’  If unhappy with file name this long – try saving as ‘resultsfinalstarless1.fits’

11.                Note: you can do stretching etc in affinity photo rather than here in Siril.  When you open your image in AP – you can do your curves and level adjustments, shadows/highlights etc to sort contrast. Critical is the saving bit at end – save the image in AP – export it as a tiff RETURN TO SIRIL

Open this Tiff  in SIRIL; click save down arrow and rename file as starless etc but FITs at end. Click 32 bit and now work on this fits image.

NOTE: you can do similar for working on the star image below – if AP if desire

 

12.            STRETCHING ON STAR IMAGE IN STARNET++

a.       Open the unstretched stars image from your master Siril folder – it will be labelled as resultsstarmask.fits or something similar

b.       Top tab - Image processing – ‘histogram transformation’ – making sure display option on bottom tab is LINEAR

c.        On pop-up box - zoom factor is 1 and all graph colour buttons below histogram are set to on

d.       At base of histogram - Middle ‘mid tones’ triangle slide to left until stars begin to appear on image

e.       Adjust zoom number at top - > it, triangle will move to right – move it back left again

f.         Keep going – stars will get brighter and more numerous – keep going until value in midtones box is around 0.002 and zoom value is around 60 – 70   If happy with amount of stars visible       Click apply  if unhappy – reset the histogram and start again – experiment trial and error

g.       When happy save as ‘resultsstarmaskstr.fits’ or something similar

13.            STARNET STAR RECOMPOSITION PROCESS

a.       Top menu tab - Image processing – star processing – star recomposition

b.       Load both images back up in relevant histograms. MAKE SURE RIGHT IMAGE GOES WITH RIGHT HISTOGRAM:  your stretched stars image goes in ‘star stretch parameters’. Your starless nebulosity image loads in to ‘background stretch parameters’.

c.        Make tint slider adjustments under each histogram. When happy with each click apply under each histogram and check progress in console tab on RHS.

d.       Save this recombined image as something like ‘M42final.fits’ or whatever target you have been imaging

Other things you can do in Siril

14.                REMOVING GRADIENTS IN SIRIL

a.       Image processing – BG extraction – Polynominal – simple gradients. The higher the number chosen, the more complex the gradient

b.       Best to use RBF method – choose small smoothing changes – default setting is 0.5

c.        The larger the number of amples per line – the longer taken to process

d.       Grid tolerance – adjust so that samples not on stars or DSO’s that do not belong to the background sky

e.       Add dither

f.         Generate creates grid – clear – clears it

g.       Correction – subtracts background sky

15.                TO REDUCE BANDING IN IMAGE

a.       Auto-stretch

b.       Image processing – banding reduction – apply (use default settings)

c.        To prevent it affecting brightness of image – tick protect from highlights box; select vertical banding if it is also present

16.                STAR REDUCTION IN SIZE

a.       Image processing – star reduction MTF – it will close image down; bottom right hand script menu – green light will show processing – when red – means finished.  Save image

b.       To compare this new image with original – open original file used before doing star reduction process; open this final one working on

c.        Use little triangle button next to open – toggle between new and original image to see differences 

d.       Want smaller – re-run process again     Save file as reduced stars_final.fit

Using affinity photo for final polishing edits

17.                GO TO AFFINITY PHOTO 

a.       curve and level adjustments for colour, contrast, brightness) and do for R,G, B individual colours as well. TINY changes.

b.       Shadows/highlights.

c.        Sharpening and denoise.

d.       Colour adjustments and saturation

e.       Other level adjustments as see fit.

f.         SAVE AS TIFF; SAVE PNG AND/OR JPEG AS WELL; SAVE AS AFFINITY PHOTO WORK FILE

18.                IF NOT DOING STARTNET++ REDUCTION in Siril

a.        go back to section 2 image processing – this will now follow on from point 11:

b.       do a histogram stretch – select linear mode on bottom menu – image processing – histogram transformation – auto-stretch cog wheel – apply. Repeat step and make fine adjustments with sliders.

c.        Colour saturation – image processing – colour saturation – experiment with different levels etc

19.                TIPS AND TRICKS IN SIRIL 

Ctrl	+O	open an image	Ctrl	+Z	Undo previous command
Ctrl	+S	Save loaded image	Shift+Ctrl	+Z	Redo previous command
Shift+Ctrl	+S	Save loaded image with new file name	Ctrl	+I	Negative transformation
Ctrl	+W	Close image	Ctrl	+east arrow	Rotate 90d clockwise
Ctrl	++	Zoom in	Ctrl	+west arrow	Rotate 90d anticlockwise
Ctrl	+-	Zoom out	Ctrl	+vertical arrow	Horizontal mirror
Ctrl	+0	Fit image to window	Ctrl	+down arrow	Vertical mirror
Ctrl	+1	Zoom image to 100%	Ctrl	+
Ctrl	+P	Open preferences	Shift+Ctrl	+A	Open plate solving dialogue
F10		Open application menu	Shift+Ctrl	+P	Open photometric colour calibration
Ctrl	+F6	Open dynamic PSF window	Ctrl	+/	Search an object in the image
Ctrl	+D	Change working directory	Shift+Ctrl	+C	Copy snapshot to clipboard
Ctrl	+F	Full screen on/off	F5		switch to plot page
Ctrl	+T	Hide/show toolbar	F6		Switch to the stacking page
F1		Switch to conversion page	F7		Switch to the output logs page
F2		Switch to sequence page	Ctrl	+Q	Quit the application
F3		Switch to pre-processing page
F4		Switch to registration page

  

I hope these notes are of help – they are my workflow – written as a beginner and as I gain further experience, I am sure I will refine them. I made the mistake of trying to get to grips with astronomy and telescopes, astrophotography, and then basic photo editing in affinity photo – all at the same time. Stupid mistake but there we go – heck of a learning journey, I guess!

As always, if you are more experienced at all this and have any useful tips regarding workflow order, please share them in the comment box below so that we beginners can see them and learn from them. Appreciated.

Clear skies. Stay safe, have fun out there.

Steve

 

PS – I can not place enough emphasis on this – two fantastic resources that beginners should know about:

Youtube channel: DeepSpaceAstro

Book: Astrophotography Image Processing with Siril, GraXpert and GIMP  by Max Dobres FRAS  

ISBN 9798338039373  Pub: 2024