Synth Module Use

Notes from users, documentation addendums.

Synth Module Use

Postby Guy » Wed Apr 12, 2017 5:21 pm

Here are some notes relating to using this module. It is not the only way to use the module and experimentation is encouraged.
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

Synth Module

Purpose:
  • To allow the user to adjust, augment or even replace stars in an image by the modelling of a telescope's diffraction of starlight.
Description:
This module can be used to:
  • Make stars brighter and tighter. However the Magic module may be more appropriate if this is all you need to achieve.
  • Re-model stars to show physically correct starlight energy distribution.
  • Accurately model diffraction spikes.
Useful Sources
The Unofficial guide is also a good source of help. It relates to version 1.3.5 so there may have been some changes. The notes below relate to StarTools version 1.4.

When to use:
  • Can only be used when Tracking is off. Towards the end of the workflow.
  • Only use once.
Example Workflow:
AutoDev-{Band/Lens}-Bin-Crop-Wipe-AutoDev(or Develop)-{As needed: Decon/Sharp/Contrast/HDR/Flux/Life}-Color-{Filter}-Denoise-{If needed: Layer/Magic/Heal/Repair/Synth}
Key: {...} optional modules

Method:
  1. Select the 'Newtonian' or 'Refractor' Preset according to the telescope used to take the image.
  2. Set the Aperture value to that of the telescope used to take the image.
  3. Set the Focal Length to that of the telescope used to take the image.
  4. The default values may be sufficient for the other settings - but adjust any that you know are wrong.
  5. Press 'Next'.
  6. Define a star mask - Mask-Auto-Stars-Do-Keep
  7. Set the Blur parameter so the diffraction pattern of the stars are consistent with the blur in the image caused by the atmosphere.
  8. Set the Image Diameter value to the angular size of the image.
  9. Set the Overlay Mode to 'Hybrid, Keep Stars'
  10. The default values may be sufficient for the other settings - but experiment if you want.
  11. 'Keep' the desired result.
What result to look for:
  • Ensure the stars have the same sharpness as the rest of the image. If not, adjust the Blur parameter.
Ways of getting better results:
  • The Synth module works best on images which are sharp and have low noise.
After Use:
  • Consider using other modules that require Tracking to be off - like Heal, Magic and Repair.
Description of Controls:

Screen 1 - Specify the parameters of the virtual telescope

Newtonian preset
Sets default values relevant to a Newtonian reflector telescope.
  • With this preset it may only be necessary to set Aperture and Focal Length. The default values of other settings may be Ok in most cases.
Refractor preset
Sets default values relevant to a refractor telescope.
  • With this preset it may only be necessary to set Aperture and Focal Length. The default values of other settings may be Ok in most cases.
Aperture
Sets the scope's aperture. Apart from being a factor in the concentration of starlight and the diffraction limit, this setting also influences the relative size of all other components.
  • Default is 200mm. Range is 50mm to 1050mm
Focal Length
Sets the scope's focal length.
  • From this and the Aperture setting the FoV of the scope is derived.
  • From the FoV and the angular size of the image object, the virtual stars' light concentration is estimated.
  • Default is 1200mm. Range is 50mm to 10050mm
Sample Size
Sets the accuracy of the diffraction pattern.
  • Larger sizes yield more accurate simulations, at the expense of increased computing time.
  • Default is 2048 x 2048 pixels. Range is 512x512, 1024x1024, 2048x2048, 4096x4096 pixels.
Vanes
Sets the number of spider vanes present.
  • This setting is the main influence on the number of distinctly visible diffraction spikes.
  • Default is 4 [Newtonian], 0 [Refractor]. Range is 0 to 4.
Vane Width
Sets the width of the virtual spider vanes.
  • This setting influences the frequency of the occurrence of the 'rainbow patterns' in the spikes.
  • Default is 1.6mm, 0.00mm [Refractor]. Range is 0.0 to 100.0 mm.
Vane Support Width
Sets the width of the virtual spider vanes.
  • This setting has a subtle influence on the central flare's diffraction pattern.
  • Default is 1.6mm, 0.00mm [Refractor]. Range is 0.0 to 100.0 mm.
Backscatter
Sets how much light is reflected back by the primary mirror and mirror Clips onto the Central Obstruction, the Vanes and the Vane Supports and subsequently emitted as diffused light.
  • The setting dulls down the brightness of the diffraction spikes and parts of the central flares.
  • Default is 2%. Range is 0 to 100%.
Central Obstruction
Sets the size of the Central Obstruction as a percentage of the full aperture.
  • This setting greatly influences the diffraction pattern.
  • A setting of 0% effectively turns the virtual scope into a refractor.
  • Default is 25% [Newtonian], 0% [Refractor]. Range is 0 to 100%.
Dispersion
Sets the strength of the dispersion - the subtle way the different wavelengths (colours) are diffracted differently.
  • This setting effectively controls the strength of the 'rainbow effect' in the diffraction spikes.
  • Note that stars that do not emit equal amounts of light in all wavelengths will generate 'rainbows' with different colour balances.
  • Default is 100%. Range is 0 to 100%.
Screws
Sets the number of evenly distributed screws around the edge.
  • These screws block light in the optical tube assembly.
  • This setting subtly affects the central flare's diffraction pattern.
  • Default is 12 [Newtonian], 0 [Refractor]. Range is 0 to 50.
Clips
Sets the number of clips present around the edge to hold the primary mirror or lens in place.
  • This setting subtly affects the central flare's diffraction pattern.
  • Default is 3 [Newtonian], 0 [Refractor]. Range is 0 to 20.
Clip Size
Sets the size of the clips that hold the primary mirror or lens.
  • This setting subtly affects the central flare's diffraction pattern.
  • Default is 10mm [Newtonian], 0mm [Refractor]. Range is 0 to 100mm.
Focuser
Sets the size of the optional focuser.
  • This setting subtly affects the central flare's diffraction pattern - adding a faint but distinct spike.
  • Default is None. Range is None, 1.25, 2 and 3 inch.
Focuser Travel
Sets the amount of inward travel of the focuser.
  • This setting subtly affects the central flare's diffraction pattern - adding a faint but distinct spike.
  • Default is 20mm [Newtonian], 0mm [Refractor]. Range is 0 to 100mm.
Focuser Angle
Sets the angle at which the focuser is mounted on the optical tube assembly.
  • This affects the angle of the faint but distinct spike caused by the inward travel of the focuser.
  • Default is 120 [Newtonian], 0 [Refractor]. Range is 0 to 360.
Screen 2 - Set the parameters of the image.

Mask
  • Set the star mask if not already set - Mask-Auto-Stars-Do-Keep
  • Remove any noise that is also selected - by using the Shrink-Grow buttons.
  • All stars should be selected - not just a few.
Gamma Adjust
Allows adjustment of the gamma of the synthesized star layer.
  • This is a basic but effective means of reducing the virtual stars' diffraction spike and central flare.
  • Default is 1.00. Range is 0.00 to 5.00.
Core Whiteness
Sets the amount of colour the Synth module should pick up from the star.
  • Default is 67%. Range is 0 to 100%.
  • Note that this parameter is not real-time.
Blur
Sets the kernel size of the Gaussian blur that is applied to the virtual layer, prior to overlaying it.
  • This should be close to the blur in the image caused by the atmosphere.
  • Default is 1.0 pixels. Range is 1.0 to 5.0 pixels.
OTA Rotation
Sets how many degrees the point spread function (and thus the virtual stars and any diffraction artefacts) is rotated.
  • Default is 0. Range is 0 to 359.
  • Note that this parameter is not real-time.
Grow Mask
This is identical to the 'Grow' operation as found in the mask editor.
  • This parameter is best increased if the healing stage of the Synth algorithm is not getting rid of all traces of the original star.
  • Default is 0 pixels. Range is 0 to 10 pixels.
  • Note that this parameter is not real-time.
Image Diameter
Sets the angular size of the image in arc-minutes.
  • This information is used to scale the point spread function appropriately.
  • Default is 70 arc-minutes. Range is 1 to 301 arc-minutes.
  • Note that this parameter is not real-time.
Overlay Mode
Sets one of seven algorithms to be used to overlay the virtual stars.
The range is:
  • Hybrid, Remove Stars - Performs a mixture of addition and lighten-only, while removing the original stars.
  • Lighten, Remove Stars - Performs a lighten-only operation, while removing the original stars.
  • Addition, Remove Stars - Performs an addition operation, while removing the original stars.
  • Hybrid, Keep Stars - Performs a mixture of addition and lighten-only, while keeping the original stars.
  • Lighten, Keep Stars - Performs a lighten-only operation, while keeping the original stars.
  • Addition, Keep Stars - Performs an addition operation, while keeping the original stars.
  • Subtract, Keep Stars - Performs a subtraction operation, while keeping the original stars. This mode may assist in masking out stars completely, revealing detail otherwise drowned out by its glare.
  • Default is 'Hybrid, Keep Stars'.
Blend Original
Sets how much of the original image should be blended in with the synthesised version.
  • Default is 0%. Range is 0% to 100%.
Brightness Adjust
Adjusts the brightness of the virtual stars.
  • Default is 100%. Range is 0% to 400%.
Core Noisiness
This parameter attempts to compensate for noise in the stars' cores.
  • This setting is best used if the core of the stars are not perfectly white and contain noise. If the latter is the case, such stars may be (incorrectly) split into multiple smaller stars.
  • Default is 0%. Range is 0% to 25%.
  • Note that this parameter is not real-time.
Guy
 
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Joined: Thu Feb 19, 2015 8:35 am

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