LRGB Module Use

Notes from users, documentation addendums.

LRGB Module Use

Postby Guy » Sun Feb 26, 2017 11:48 am

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

LRGB Module

Purpose:
  • To allow the loading of separate files representing, for example, Luminance and Red, Green and Blue colour channels.
Description:
The LRGB module is used to load and combine multiple files into a single image. Either standard luminance, Red, Green and Blue data or a combination of narrow-band data using different filters.
It can also be used to extract the Red, Green or Blue channel from a colour image.

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.
The processing tutorial video M33 in LRGB discusses the LRGB module between 0m17s and 1m00s.

When to use:
  • At the start of processing if you need to load files representing different channels - either traditional LRGB or other combinations such as Hubble Pallette (SII, Ha, OIII)
Method:
  1. Preparation:
    • All the image files must be aligned (registered). When stacking, use one image as a reference for the others.
    • If a luminance file has been loaded, any Red, Green or Blue file subsequently loaded must be either exactly the same size or exactly half the size of the luminance file. This allows luminance channels to be 1x1 binned while R,G and B files can be 2x2 binned. In all other cases all loaded files must be the same dimensions.
  2. The LRGB module can be set to interpolate any missing channels. Just set Channel Interpolation on and load what channels you have.
  3. If you have any Luminance data, load that first.
  4. Load any Red, Green and Blue data you have, making sure each file has completed loading before loading the next.
  5. If there is a difference in exposure time between Red, Green and Blue data set the Ratio settings accordingly.
  6. If you have problems loading data because of the error: 'The dimension of the bitmap you're trying to load differ from the previously loaded file bitmap(s). ...' then check the dimensions of individual data files by loading them in StarTools individually. The dimensions are listed to the right of the file name at the top of the screen.
  7. If there is a Luminance channel present you can reduce the noise in the colour information by adjusting the smoothing of the colour channels using the 'RGB Blur' control.
What result to look for:
  • Make sure all the channels are properly aligned. In rare cases it is possible for the registration to be out.
  • Ensure that all the colour channels appear. If any colour is missing try reloading it and make sure it finishes before continuing.
After Use:
Continue with your preferred workflow.

Special Techniques:

Loading Narrow Band data using the Hubble Palette
  1. You might first want to create a weighted synthetic luminance (B&W) frame first. See the description: weighted synthetic luminance for Hubble palette.
  2. Load the SII data into the Red channel.
  3. Load the Ha data into the Green channel.
  4. Load the OIII data into the Blue channel.
See also the description: LRGB & Hubble palette

Combining luminance and RGB Images
This is one way of combining luminance and RGB image data.
There is an alternative way of combining luminance and RGB images described in Layer Module Use under the heading 'Combining Luminance and RGB images'.
  1. Load the LRGB module
  2. Load the synthetic luminance data.
  3. Load Red channel with RGB data
  4. Load Green channel with RGB data
  5. Load Blue channel with RGB data
  6. Increase RGB Blur to reduce colour noise
  7. Keep.
Processing Ha,R,G,B using a synthetic luminance frame
See also the description:Ha,R,G,B ->synthetic luminance
  1. Create the weighted average synthetic luminance frame as described in the Layer module here
  2. Process the synthetic luminance frame for maximum detail as you would normally - for example:
    • Load the luminance data if necessary - indicate it is Linear - this turns Tracking on. If already loaded, make sure Tracking is on - turn Track on if necessary.
    • AutoDev to see what we have
    • Crop
    • Wipe
    • AutoDev
      Try to get maximum detail...
    • Decon
    • HDR
    • Sharp
    • Life - Isolate Preset
    • Contrast
    • Tracking off - Denoise
    • Save this file
  3. Process the RGB channels (but not the Ha)
    • Load LRGB module
      • Load Red channel data
      • Load Green channel data
      • Load Blue channel data
      • Keep
    • Crop - exactly the same as for the luminance - the files must be exactly the same size as the luminance.
    • AutoDev
    • Wipe
    • AutoDev
    • Save this RGB data File
  4. Combine the synthetic luminance and RGB image data as described in the 'Combining luminance and RGB Images' section above.
  5. Load the Color module to do colour balancing
    • Increase saturation - so that we can see changes easily
    • Adjust RGB Bias sliders
    • Max RGB
    • Cap Green if needed.
    • Keep
  6. Wipe - to confirm the colour balance (optional).
  7. Use the Sharp module with a star mask to sharpen the image.
  8. Life - Isolate preset (optional).
  9. Save
Re-centering blue back onto stars
To recentre a smeared blue channel back to align with the red and green channnels try the following as described in Fringe killer filter add blue back to central star
  1. Optionally Bin the image - then save it.
  2. In the LRGB module click Blue and navigate to the file just saved. This will load only the Blue channel of the saved image. The other channels will be automatically set due to 'Channel Interpolation'. You end up with a black & white representation of the blue channel
  3. Process this image so that you reduce the bloating of the stars in the blue channel
    • Do AutoDev or Develop - this allows us to see what we are doing.
    • You could then use the Decon module - set to 'De-ring Mask Gaps, Show Result', set Iterations to 1, set Radius to 3.2 (as appropriate).
  4. 'Keep' the result.
  5. Use Restore selecting 'Linear, Wiped, Deconvolved' option - this reverts to an image which is Linear but which retains the deconvolution you did.
  6. Save the image.
  7. Use the LRGB module to load the Red and Green channels (binned the same amount) and load the saved image into the Blue channel.
  8. You should now have an image with a better focused blue channel. Process as normal.
  9. When using the Color module, the Scientific mode may have problems with the star cores as they have artefacts in the blue channel due to the deconvolution. Either:
    • Reduce Bright Saturation right down and set Saturation Amount to 100% or lower. This will avoid recovering colour in the highlights, or
    • Use a star mask to mask out the stars - they then won't be involved in setting the colour balance, or
    • Use Artistic mode
  10. Keep the results.
Description of Controls:

Luminance button
Allows you to navigate to and load the Luminance file.
  • Make sure the file has finished loading before continuing.
  • If loading a colour (RGB) image - converts the image to greyscale.
Red Button
Allows you to navigate to and load the Red channel file.
  • If a luminance file has been loaded then any Red, Green or Blue file subsequently loaded can be either the same size or exactly a quarter of the resolution of the luminance file. This allows luminance channels to be 1x1 binned while R,G and B files can be 2x2 binned. In all other cases all loaded files must be the same dimensions.
  • Make sure the file has finished loading before continuing.
  • If loading a colour (RGB) image - extracts the Red channel.
Green Button
Allows you to navigate to and load the Green channel file
  • If loading a colour (RGB) image - extracts the Green channel.
Blue Button
Allows you to navigate to and load the Blue channel file
  • If loading a colour (RGB) image - extracts the Blue channel.
Channel Interpolation
The LRGB module can be set to interpolate any missing channels.
  • Just set Channel Interpolation On and load what channels you have. This feature can be used to:
    • Generate a missing green channel in the case of an Ha/Hb composite
    • Generate a greyscale from a single Ha, Hb, OIII or SII frame which may later be turned into a false colour image using the Color module.
  • Default is On
Luminance File
Shows the path of any file loaded in the Luminance channel.
  • Default is None.
Red File
Shows the path of any file loaded in the Red channel.
  • Default is None.
Green File
Shows the path of any file loaded in the Green channel.
  • Default is None.
Blue File
Shows the path of any file loaded in the Blue channel.
  • Default is None.
RGB Blur
Allows you to reduce the noise in the colour information by adjusting the smoothing of the colour channels using the 'RGB Blur' control.
  • Set so that the blur is virtually undetectable.
  • The reduction in noise can be significant because the eye is much less sensitive to the colour information than the luminance.
  • Default is 1.0 pixel. Range is 1.0 to 5.0 pixels.
  • Only works if there is a Luminance channel present.
Cap Green
Removes any green colour information from the image.
  • Very few objects in space are green - so often green elements are due to noise and so can be removed.
  • Default is No.
Red Ratio
Allows you to compensate for differences between the exposure times of Red, Green and Blue channels.
  • Set to the amount the channel should be multiplied by to attain the same exposure duration as the other channels.
  • For example, If Red is a 30 minute exposure and Green and Blue were 45 minute exposures then set the Red Ratio to 1.5 to compensate.
  • Default is 1.00. Range is 1.00 to 10.00.
Green Ratio
Allows you to compensate for differences between the exposure times of Red, Green and Blue channels
  • Set to the amount the channel should be multiplied by to attain the same exposure duration as the other channels.
  • Default is 1.00. Range is 1.00 to 10.00.
Blue Ratio
Allows you to compensate for differences between the exposure times of Red, Green and Blue channels
  • Set to the amount the channel should be multiplied by to attain the same exposure duration as the other channels.
  • Default is 1.00. Range is 1.00 to 10.00.
Background Notes:
Aligning LRGB subframes using Regim
To make sure the L, R, G, B images are all aligned the same. we need to select a single reference frame for all images.
  • In Regim images can have different dimensions. The output file dimensions will be that of the reference file.
  1. Under the Preprocessing menu select the Preprocessing option.
  2. Set the standard Calibration, Register and Combination settings under the relevant tabs.
  3. Under the 'Files' tab select the luminosity reference light frame first.
  4. Select all other relevant lights, darks, flats etc.
  5. Select only the 'do calibration' and 'do register' checkboxes in the preprocessing dialog and do the registration.
  6. All files registered to the reference frame will be .fit files and have the prefix “Reg_”.
  7. Open the preprocessing dialog again and select all the "Reg_*.fit" files you want to combine and Add to images - exclude the reference frame if you want.
  8. Select only the 'do combination' checkbox.
  9. Run the combination.
  10. Save the image.
  11. Repeat for Luminosity, Red, Green and Blue data using the same reference frame.
  12. The result should be 4 files all aligned exactly the same.
Aligning LRGB subframes using Deep Sky Stacker (DSS)
To make sure the L, R, G, B images are all aligned the same. We need to select a single reference frame for all images.
  • In DSS all files to be stacked must have the same dimensions, number of colours, number of channels, only one master dark, offset and flat.
  • Make sure you use the 'Standard Mode' setting in the 'Result' Tab of the Stacking Parameters in DSS.
  • Note: The reference sub-frame appears to be ignored if not included in the stack - can anyone confirm this?
  1. Load the reference (luminosity) sub-frame into DSS.
  2. Right-click on it and select 'Use as reference frame'.
  3. Load relevant Lights, Darks, Flats etc. into DSS.
  4. Stack as normal and save the image.
  5. Repeat for Luminosity, Red, Green and Blue data using the same reference frame.
  6. The result should be 4 files all aligned exactly the same.
Guy
 
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