Spatially Variant PSF Deconvolution (SVDecon) Module Use (v1.8)

[Guy]

Here are some notes relating to using this module. It is not the only way to use the module and experimentation is encouraged.
They relate to StarTools version 1.8.506alpha and later.
Please let me know if anyone sees any errors or has any additional advice they think helpful.
I will update this post as needed.
To see a full alphabetical list of module topics click here

Spatially Variant PSF Deconvolution (SVDecon) module (v1.8)
Purpose:

• The SVDecon module tries to reverse the effects that atmospheric turbulence and, optionally, the optical train, has on the data. It allows recovery of detail in seeing-limited data sets that were affected by atmospheric turbulence and diffraction. It can model the variation in the effects across the image.

Description:
The SVDecon module allows the modification of the deconvolution algorithm across the image. By deconvolving selected sample stars across the image a mapping of how the atmospheric and optical distortion - and hence deconvolution algorithm - varies across the image.
There are three modes of operation:
3 Modes:

1. When no star samples are selected - uses one synthetic atmospheric distortion model for the whole image - As pre v1.7 StarTools did. A number of synthetic models are available to choose from. This is useful in Lunar, Planetary and Solar imaging where there is a large starless area in the central part of the image.
2. When one star sample is selected - uses that sample to as the basis to calculate the custom (atmospheric + optical) distortion model PSF for the whole image - with an option to to further compensate for the optical distortion by choosing a synthetic optical distortion model - Similar to StarTools v1.7
3. When multiple star samples are selected - uses the samples to define how the custom (atmospheric + optical) distortion model PSF varies across the image. There is an option to further compensate for the optical distortion by choosing a synthetic optical distortion model.

For a good description see SVDecon: Detail Recovery through Spatially Variant Distortion Correction
The SVDecon module is noise-aware and is able to generate its own de-ringing mask. De-ringing will still try to coalesce singularities.

Useful Sources
SVDecon: Detail Recovery through Spatially Variant Distortion Correction
Links and Tutorials

When to use:

• The SVDecon module should be used after the final global stretch (Develop or AutoDev) and local stretch (Contrast, Sharp and HDR) modules:
• SVDecon will be able to achieve better results the closer you get to a final image - since it has better information from tracking.
• The HDR module (and to some extent the new Sharp module) can exacerbate any residual ringing.
• If there is no oversampling, or if there is a lot of noise, the benefit of this module will be limited.
• Use only once.

Example Workflow (v1.8):AutoDev-{Lens}-Bin-Crop-Wipe-AutoDev (or FilmDev)-{Contrast/HDR/Sharp/SVDecon}-Color-{Shrink/Filter/Entropy/SuperStr/NBAccent/}-Track/NR(Unified-Denoise)-{Flux/Repair/Heal/Layer/Synth}

Key: {...} optional modules

Method
For DSOs - using Mode 3 - multiple star samples selected:
This is a way of using the module which should give good results in most cases:

1. Load the module
2. At the 'Apodization Mask Generation' prompt select 'Auto-generate mask' to create an apodization mask - a form of star mask - or use the ApodMask preset to create one - this selects the stars to be processed, and acts as a guide for the de-ringing algorithm.
3. Select a preview area rectangle in the image to see the effect of changes - this speeds up analysis. Choose a bright, detailed and noise-free area.
4. Click on 'Sampling' button to show the possible sample stars.
5. Keeping Zoom at 100% - should allow the stars should be large enough to evaluate and for you to position the sliders at the edge of the image easily to cover the whole image in 6-9 segments.
6. Select samples - at least two from each segment
7. Samples should be green without red centres. See 'Choosing sample stars' below.
8. Add more samples if there is a lot of variation in the way the stars are deformed.
9. Put a sample in any area where the stars have been deformed in a slightly different way.
10. Adjust 'Sampled PSF Area' so that the blue area just surrounds the selected stars green pixels.
11. Increase 'Sampled Iterations' until you see no further improvement
12. Set 'Synthetic Iterations' to 'Off' unless you want to use an optical PSF model
13. Zoom in and out so you can see the effect in the detail and as a whole.
14. Toggle top "Pre Tweak/Post Tweak" button to see effect of last adjustment if needed.
15. Normally other default values work well - but you can experiment if you want.
16. When done, select 'All' to apply this to the whole image - this may take some time.
17. Press 'Keep'.

For Lunar/Planetary targets - using Mode 1 - no star samples selected:

1. Click the 'Plnt/Lnr' button
2. Don't try and select a sample star
3. Select a Synthetic PSF model to model the atmosphere.
4. Increase 'Dyn. Range Extension' to increase the dynamic range.
5. Increase the 'Synthetic Iterations' until no improvement is seen.
6. Adjust the 'Synthetic PSF Radius' until ringing occurs - then back off a little.

What result to look for:

• Elements should appear more focused as the blurring effect of atmospheric turbulence is compensated for.
• Edges should look more distinct and without the exaggerated coalescing caused by increasing the radius a lot.
• If there are ringing artefacts around the stars it indicates the 'Synthetic PSF Radius parameter' or 'Sampled Iterations' may be too high.

Ways of getting better results:

• The SVDecon module works best when there is little noise - Bin your oversampled data to improve the SNR if needed - but consider leaving some degree of oversampling to allow deconvolution to bring out finer detail. See the Bin module notes for a discussion of the issues relating to Bin vs. deconvolution.
• Data that is not oversampled is not a candidate for deconvolution if the aim is to reverse seeing-related issues.

After Use:

• Use the Color module.

Special Techniques:

Severely and non-uniformly deformed stars:

• Use as described in the method
• Increase 'Spatial Error' and 'Sampled Iterations' together to improve the stars shape.

Description of Controls:

Mask:
An apodization mask is needed if star samples are to be taken. It is not needed for planets or lunar images.

• The apodization mask identifies the light sources that will be processed.
• The apodization mask is also used to identify the potential samples in the sample view.
• You can touch up the mask in order to remove unwanted low quality stars in the blue sampled area of a sample star.
• The apodization mask identifies the boundaries of the pixels associated with a star. Only the pixels inside the boundaries are used by the module.
• It is important to include as much of the stellar profile as possible. If too few pixels are chosen there may be 'ringing' around deconvolved stars

All:
If you selected a preview area - this will apply the deconvolution to the whole image.

Plnt/Lnr:
If the image is of Planetary and Lunar and other non-DSO subjects

• Selecting this mode clears the apodization mask
• 'Synthetic Iterations' are increased to 50x
• 'Synthetic PSF Radius' is increased to 10.5 - something more suitable to high magnification.
• 'Sampled Iterations' are automatically set to 'Off' (0), and the sampling mode disabled, when this is selected.
• Star samples, if any, would not help for these sorts of images where there is a large starless area in the centre of the image.

ApodMask:
This allows the automatic generation of an apodization mask.
Options are:

• Auto-generate mask
• Auto-generate extra sensitive mask

Sampling/Result:
Toggles between sampling view and result view.
Sampling view allows the selection of sample stars used for creating the PSF models.
It provides useful information to help you select good sample stars:

• Sampling View:
  • All candidate stars are outlined in white.
  • Red pixels within the outline show low quality areas
  • Yellow pixels within the outline show borderline usable areas.
  • Green pixels show high quality areas.
  • Blue pixels show the sampled area around the sample star.
• Results View:
  • Shows the results of deconvolution.
  • Hold the left mouse button to toggle highlighting sample stars on and off.
  • To disable a sample star just click on it.

Selecting Sample Stars
Sample star selection is critical as the star is the basis on which the custom (atmospheric + optical) distortion model PSF is calculated.

• Choosing Good Sample Stars:
  • Stars rather than other objects
  • Stars that are circular or oval - and similar in outline to other stars nearby
  • Stars not sitting on any nebulosity.
  • Stars that are well separated from other stars
  • Good samples are green stars without a red or yellow centre.
  • Acceptable samples are green stars with a yellow centre.
• Sample Star number and distribution:
  • The number of samples needed depends on the how severe the variation of the PSF across the image is.
  • When sampling it is important to provide samples over the whole image.
  • The selection of high quality samples is secondary to the coverage over the whole image.
  • So make sure you sample over the whole image even if some of the samples are of lower quality.

Sampled Iterations:
When one or more samples have been selected this parameter specifies the number of times the deconvolution algorithm is repeated.

• Only relevant when one or more samples are chosen.
• You can switch off sample modelling by setting this parameter to 'Off'(0)
• Increasing this parameter will make processing take longer.
• Increase this value incrementally if further improvement can be seen - there will be a point beyond which you will not get a better result.
• Increasing this parameter too far can lead to ringing and increased noise grain. The ringing needs to be minimised here. Any remaining noise grain can be handled by the denoise module later.
• Default is 10, Range is Off (0) to 199

Sampled PSF Area:
When using sampling - specifies the area around the stars centre that is sampled.

• The area should contain only one sampled star.
• All the pixels that belong to the sample star should just fit into the area - with not much background.
• The sampled area is shown in blue - grow or shrink the area to ensure the samples just fit around the star(s).
• Default is 15x15 pixel area, Range is 7x7 to 25x25 in 2 pixel increments.

PSF Resampling:
Controls if and how the Point Spread Functions are re-sampled.

• Resampling tends to reduce the development of ringing artifacts and can also improve results.
• There are 3 modes:
  • None - No resampling or reconstruction - samples are used as they are.
  • Intra-Iteration - All samples are resampled at their original location
  • Intra-Iteration + Centroid Tracking Linear - All samples are resampled after their locations have been recalculated
• Default is None

Synthetic Iterations:
Controls the use of the Synthetic PSF Model.

• Synthetic Iterations are automatically set to 'Off' (0) when a sample is selected.
• Use a synthetic model if no samples are selected - e.g. for Planetary/Lunar images.
• You can optionally use a synthetic model to model the Optics when one or more samples are selected.
• You can switch off synthetic PSF modelling by setting this parameter to 'Off'(0)
• For Planetary/Lunar images it may help to Increase this value significantly - into the hundreds.
• Default is 10, the 'Plnt/Lnr' preset sets it to 50, Range is Off(0) to 500

Synthetic PSF Radius:
The size of the turbulence blurring that the deconvolution algorithm (specified by the 'Synthetic PSF Model' setting) will try and remove:

• This value can be increased until ringing starts to occur on small non-overexposed stars - then back off a little.
• Related to the seeing - Seeing-induced blur is normally 3-4.5 arc-seconds. The camera/lens combination gives a resolution between 1 and 5 arcsec/pixel depending on the equipment combination.
• Under the same seeing conditions a wide field image will have a smaller blur. A narrow field image will have a larger blur.
• Adjust the Radius until just before the smaller stars start showing signs of ringing.
• Default is 1.5, the 'Plnt/Lnr' preset sets it to 10.5, Range is 1.0 to 20.0 pixels

Synthetic PSF Model:
Defines which model of atmospheric turbulence or optical blurring is used in the reversal process:

• If no samples are selected the model chosen is the one applied to the whole image. In this case choose one of the atmospheric models unless the image was taken in space.
• If one or more samples are selected then the Synthetic model is by default switched off. It can be enabled by increasing 'Synthetic Iterations' from 0 [Off].
• If one or more samples are selected then there is only one model available - the one to model the optics - the 'Circle of Confusion'. With sampling the combined atmospheric and optical distortion model is calculated from the sample. The option to additionally use the 'Circle of Confusion' synthetic PSF model allows additional tweaking to the optical model if needed.
  The PSF Model used for the atmosphere will be derived from the sample star(s).
• Default is Moffat Beta=4.765 (Trujillo) (Atmosphere) with no samples selected, Circle of Confusion (Optics) when samples are selected.
• Range is:
  • Gaussian Beta=Infinite (Atmosphere) - Model used in Decon previous to StarTools 1.6
  • Circle of Confusion (Optics Only) - models basic focusing assuming no atmosphere (e.g. in space).
  • Moffat Beta=5.5 (Atmosphere)
  • Moffat Beta=5.0 (Atmosphere)
  • Moffat Beta=4.765 (Trujillo) (Atmosphere) - Uses a Moffat distribution with Beta factor 4.765. Recommended by Trujillo et al (2001)
  • Moffat Beta=4.5 (Atmosphere)
  • Moffat Beta=4.0 (Atmosphere)
  • Moffat Beta=3.5 (Atmosphere)
  • Moffat Beta=3.0 (Saglia, FALT) (Atmosphere) - Uses a Moffat distribution with Beta=3.0. As implemented in the FALT software at ESO.
  • Moffat Beta=2.5 (IRAF) (Atmosphere) - Uses a Moffat distribution with Beta=2.5. As implemented in the IRAF software by USNOAO.

Spatial Error:
This control helps when stars are badly deformed by allowing the algorithm to reconstruct stars from pixels that are further away than normal.

• Increase this value in cases where the PSF is heavily distorted
• This can be due to: astigmatism, field curvature, tracking error, or other issues causing stars to severely deform.
• Default is 1.00, Range is 1.00 to 2.00

Deringing Amount:
This parameter sets the strength of the deringing algorithm.

• First see if you can minimise the ringing being generated - by reducing the 'Synthetic PSF Radius' parameter or 'Sampled Iterations' parameter.
• Increasing this value increases the effect of the deringing algorithm.
• Try increasing the 'Deringing Detect' setting from its default if increasing here does not have enough effect.
• Default is 0.80, Range is 0.00 to 1.00

Dyn. Range Extension:
This parameter allows the reallocating of dynamic range so that reconstructed highlights can show their detail correctly.

• Increase this parameter from 1.0 if significant new detail has been created.
• Increase it until the clarity of the new detail stops improving.
• Default is 1.00, Range is 1.00 to 3.00

Deringing Detect:
Specifies the aggressiveness of a de-ringing filter used to damp down ringing artifacts around the stars.

• Higher values will remove more artifacts - but will also remove some of the darker detail enhancement.
• Default is 50, Range is Off(0) to 100

Linearity Cutoff:
Defines at what point we assume the dynamic range of the sensor used is no longer linear.

• Sets the threshold for the red and yellow areas in the sample view.
• Default is 85%, Range is 0% to 100%

Deringing Fuzz:
Controls the smoothness of the transition between the de-ringed areas and the surrounding parts of the image.

• Default is 20.0 pixels, Range is 1.0 to 40.0 pixels

Background Notes

Sample Stars and deconvolution
Sample Stars: Good candidates for sample stars have the following characteristics:

• Are set in an even background.
• Are neither over-exposed or dim.
• Ideally their profile covers most of the linear dynamic range of the image.
• Ideally they are located towards the centre of the image.

Spatial variation of the Point Spread Function
The spatial variance of the Point Spread Function can be due to any issue which has deformed the stars in a non-uniform way - such as:

• field rotation
• field curvature
• tracking error
• coma
• camera mounting stability
• some other issue which has deformed the stars in a non-uniform way

Apodizaton mask
The big difference between the apodisation mask and other masks is in the way it is used.
The apodization mask has the following functions:

• To identify the boundaries of the stars where the local PSF function is applied.
• To help in the selection of sample stars - if used.
• As a guide for the de-ringing algorithm.

The apodisation mask is generated in the same way as other masks:

• You can use the Mask module to adjust the mask once created
• You can also generate an apodisation mask manually using the Mask module:
  - Generate Apodization mask:
  Mask Module: Clear-Invert-Auto-Stars- Set Threshold to 95%, all else at default. -Do-Grow x1-Keep
  - Generate Extra sensitive Apodization mask:
  As above but Grow x2

Deconvolution and Oversampling
Deconvolution is used to undo the blurring effect of an unstable atmosphere and an imperfect optical train, however this can amplify noise and introduce artefacts including ringing. It works best on data which is oversampled and has a high signal to noise ratio.
However, data that is on the cusp of being oversampled, where faint stars are spread over 3 pixels, may still benefit from a small amount of deconvolution. Every optical system, no matter how expensive, spreads a point light over multiple pixels to a degree (see Airy disk). SVDecon can reverse this spreading as well - just take it easy - it is very easy to overdo this.
For further details regarding oversampling, binning and deconvolution see the Bin module background notes.

Deconvolution and singularities
Singularities in the data are those areas where there is a discontinuity in the valid data - where the valid data is missing - such as in the saturated white cores of stars. These areas normally cause bad ringing artefacts.
StarTools uses a novel de-ringing algorithm which ensures stars are protected from the Gibbs phenomenon (also known as 'panda eye effect'), while actually being able to still coalesce singularities, such as over-exposed white cores of stars, into point lights.

Tracking
Tracking in StarTools is the name given to the way in which StarTools gathers information about the signal and its evolution through different modules.
It provides each module with as much information as possible to allow it to get the best results.
Each module can:

• Understand how each pixel has been modified by previous modules.
• Influence data earlier in the processing chain (e.g. linear data) and re-apply the modifications made since then.
• Use the information gained from previous modules to understand how the signal has been changed and where the noise is.

Some benefits of Tracking:

• Deconvolution only works on linear data - but the SVDecon Module is used after the data has been stretched.
• In the SVDecon module we look at the result of a stretched and processed image and apply deconvolution on the linear data and watch its effect on the processed image.
• Noise reduction is applied at the end of processing where Tracking has gained the most information about noise.
• Noise reduction is automatically targeted most at the areas where it is needed.

Lunar/Planetary/Solar
The SVDecon module behaves slightly differently with Lunar, Planetary and Solar images when it comes to reconstructing highlights.
With these images if a reconstructed highlight requires more dynamic range it is allocated it. The reconstructed highlights are not allowed to over-expose. The dynamic range of the complete image is adjusted to accommodate the new highlights.
With DSOs, if a reconstructed highlight is not given any more dynamic range and is allowed to over-expose.
Also, these images do not require an aggressive deringing strategy.

See also StarTools help on Lunar, Planetary and Solar

Synthetic Models of the atmosphere
The way a point source has its light scattered around its actual location is called a Point Spread Function (PSF)
Deconvolution does its best to model this PSF and then reverses it to get back to the original.
Over the years synthetic models have been developed for the PSF of atmospheric blurring.
Five of these models are available to select from in the SVDecon Module.

• Gaussian (Fast)
  • Uses Gaussian distribution to model atmospheric blurring
  • Model used previous to Startools 1.6
  • Fast
• Circle of Confusion
  • Models the way a lens focuses the light of a point source assuming no atmosphere
  • Suitable for images taken outside the Earth's atmosphere.
• Moffatt Beta=4.765 (Trujillo)
  • Uses Moffat distribution to model atmospheric blurring
  • Uses a Beta factor 4.765.
  • Recommended by Trujillo et al (2001) [PDF] as best fit for prevailing atmospheric turbulence theory
• Moffatt Beta=3.0 (Saglia, FALT)
  • Uses Moffat distribution to model atmospheric blurring
  • Uses a Beta factor of 3.0.
  • This is a rough average of the values tested by Saglia et al (1993)[PDF]
  • It corresponds with findings of Bendinelli et al (1988)[PDF]
  • As a result of studying the Mayall II cluster - Implemented as the default in the FALT software at ESO.
• Moffatt Beta=2.5 (IRAF)
  • Uses Moffat distribution to model atmospheric blurring
  • Uses a Beta factor of 2.5.
  • As implemented in the IRAF software by US National Optical Astronomy Observatory.

Selection of Beta for Moffat PSF

• A Moffat PSF with a value of 10 is similar to a Gaussian PSF.
• Pixinsight defaults to a Beta of 4
• Trujillo, Saglia, Bendinelli and others all did evaluations and came to answers varying from 2.5 to 4.765
• Take your pick - try each one out and see what you think.

[jhart]

Hi,

Does the ApodMask button create a different star mask than the regular Mask button? Could you explain any difference? Before selecting sample stars is it necessary to click to create that special Apodization mask to replace the regular star mask generated when SVDecon first opens?

Thanks

[hixx]

hi,
yes the Apo mask is different. it is not just a regular star mask but will mask stars and perform a sample quality review as not all stars will qualify as potential sample equally You will be guided to creation of apod msk by default or you can just click the Apod preset button. then click sampling button to see the sample view

• Select 'Auto-generate mask' to create an apodization mask - a form of star mask - or use the ApodMask preset to create one - this masks out overexposed stars which cause ringing.
  Select a preview area rectangle in the image to see the effect of changes - this speeds up analysis. Choose a bright, detailed and noise-free area.
  Click on 'Sampling' button to show the possible sample stars.
  Keeping Zoom at 100% - should allow the stars should be large enough to evaluate and for you to position the sliders at the edge of the image easily to cover the whole image in 6-9 segments.

clear skies,
jochen

[Guy]

Hi,

I was just about to post my reply when I saw Jochen's response.

This is how I understand the use of the Apodization mask. I'm sure Ivo will respond if I've misunderstood.

Does the ApodMask button create a different star mask than the regular Mask button?

Jochen is right in that there is a difference in how the mask is used by SVDecon.
However, I think the masks are generated automatically in the same manner as any other mask.

The Apodization masks (or something very close) can be generated using the Mask Module by using these settings:

• Generate Apodization Mask:
  Mask Module: Clear-Invert-Auto-Stars- Set Threshold to 95%, all else at default. -Do-Grow x1-Keep
• Generate Extra Sensitive Apodization Mask:
  As above but Grow x2

Before selecting sample stars is it necessary to click to create that special Apodization mask to replace the regular star mask generated when SVDecon first opens?

No, the selection you made when SVDecon first opened was to create an Apodization Mask. This mask is generated in exactly the same way as the equivalent Apodization Mask generated using the 'ApodMask' button.

I hope this helps.

Guy

[jhart]

Hi Jochen and Guy,

Thanks for the great explanations about the Apod mask.

I have one further question. After the Apod mask is created, can I click the regular Mask button to edit it as needed for use there in SVDecon? It may be that the auto-generated Apod mask needs to edited with Grow (or Shrink). (It only flashes once when created and generally I would like to confirm if it covers the stars correctly too). If I then click Mask and grow/shrink as needed, can I click Keep and have that result applied as the Apod mask for SVDecon?

On another subject -- and this may be getting into too much detail -- could you explain the different between the atmospheric distortion correction model (like used in the sampled models) and the optical distortion correction model (like used in the synthetic model) and when it would be better to use one or the other, or both?

Thanks again,
Jeff

[Mike in Rancho]

I am not certain if the sensitive mask is really just an extra grow? It doesn't seem like it, especially since grow can be a bit blocky, and the sensitive mask appears to create finer-grained circles about the stars.

Jeff, there is only one mask in SVD. It is the apodization mask but also serves a secondary task of assisting with the deringing. There is no longer a "bright star / leave this alone" mask as in 1.7. I believe this remains the case even when using 1.7-style synthetic modes. That mask is bye bye. The only way to block deconvolution selectively would be a subsequent undo buffer in Layer with an appropriate custom or auto mask.

Upon SVD entry, you have mask generation choices for the apod mask. Once in SVD, the apod mask button simply opens those choices up again. The mask button is the mask button like always, and pressing that will allow you to alter the apodization mask.

Indeed, it is sometimes necessary, as auto generation can sometimes miss the target, especially if your data has some wonky bright stars. Even if you will not be using them for sampling, filling those missed star masks in to cover the stellar profile could help out with the deringing.

The other nice trick with mask adjustments is the ability to remove a small star that would be within the blue sample box of a star that you really want to use for sampling. Only one star should be in the box. Helpfully too, Ivo made adjustments to the view/zoom when entering Mask to ease this process, so that what you are (were) looking at remains the same.

I am uncertain if your stated assumption is correct as to the modeling. I thought the sampling mode forced "circle of confusion" i.e. optical, whereas all of them including the atmospheric models are available in synthetic mode. But I agree, some additional info could be useful. Even reading the interim documentation, it leaves me a bit confused. Is sampling somehow optical and not atmospheric, or maybe it just doesn't make sense in the realm of variantly-sampled star profiles to be using atmospheric (or optical) modeling? (not that it necessarily matters, as it sure seems to work great. )

[Guy]

Perhaps Ivo will tell us how the masks are created.

The Apodization Mask also acts as a guide for the deringing algorithm.
I think you can block deconvolution of individual stars selectively just by removing them from the apodization mask.

If you sample one or more stars then the atmospheric PSF Model is derived from those sample stars (so clever these mathematicians!).
This means that there is no need for the synthetic atmospheric PSF models. So only the optical PSF model - 'Circle of Confusion' is left available as an option.

Guy

[hixx]

Hi,

I thought the sampling mode forced "circle of confusion" i.e. optical, whereas all of them including the atmospheric models are available in synthetic mode

I had raised the above question before with Ivo before. The idea of the SV Decon is to cover both optical and atmospheric impairments by using star sampling. This is why there should be no need for additional Synthetic models of the atmosphere. Hence these are deactivated upon using at least one star sample. Only Circle of confusion remains available in case the optical diffraction had not totally been compensated for. The synthetic atmospheric models would become instrumental for solar / lunar / planetary targets where no stars are visible.
Hope this helps,
jochen

[Mike in Rancho]

Hi,

I thought the sampling mode forced "circle of confusion" i.e. optical, whereas all of them including the atmospheric models are available in synthetic mode

I had raised the above question before with Ivo before. The idea of the SV Decon is to cover both optical and atmospheric impairments by using star sampling. This is why there should be no need for additional Synthetic models of the atmosphere. Hence these are deactivated upon using at least one star sample. Only Circle of confusion remains available in case the optical diffraction had not totally been compensated for. The synthetic atmospheric models would become instrumental for solar / lunar / planetary targets where no stars are visible.
Hope this helps,
jochen

Well good grief. Thanks! That was not clear to me at all, and I've probably read the documentation 10x.

By "available" I presumed that was just the style of deconv that was implemented by sampling. And figuring I was being a good user, I always zeroed one out to turn it off before switching between sampled and synthetic. Just tried it on some quick Double Cluster data I took recently, and sure enough, after getting my sampling settings all worked out, if I then click up synthetic iterations those turn on and make changes. I almost wonder if the Circle of Confusion line could be lit up rather than greyed out, to help let you know that it is in operation? But good enough I guess, I understand it now and if iterations are set over there that also means it is working.

So, a little synthetic can work in conjunction with SVD sampling, if needed.