Astro Pixel Processor – Mosaic Color (RGB) Processing

Astro Pixel Processor – RGB-Ha Mosaic

Overview

This is an overview of the processing steps to create a color mosaic using red, green, blue, and hydrogen alpha channels. Note, these setting may not work with your data and should be used as guidelines. This is my attempt to document the overall process when creating an RGBHa Mosaic Image using APP. These notes are created for the Astro Pixel Processor (APP) 1.075 version which is the latest when this article was written. Also note that these settings deviate from the default settings.

Here is a process overview:

  • Process channels (Red, Green, Blue, Ha7) as a separate panel
    • R,G,B,HA – lights
    • Bias – all channels
    • Flat – all channels
    • Dark – RGB 120s channel, and Ha7 using 60s channel (depends on what exposure times used.
  • Create Bad Pixel Map (for each panel (part)
  • Create Master Bias, Dark, Flat (these master files will be applied to the other panels/parts during the processing of the other parts)

Panel/Part Processing

This step will need to be done for each part/panel of the mosaic. The idea is to create a fits image for each channel (R, G, B, and Ha7) using identical processing. These will later be used to create a mosaic representing each channel. Again, note that your settings may be different in processing your images.

  • Calibrate –> default
  • Analyse Stars –> default
  • Register –> default
  • Normalize –> default Integrate (non-default settings)
  • Integrate per channel
  • Local Normalization Correction (LNC)
    • 1st degree LNC
    • LNC iterations – 1
  • Outlier Rejections
    • LN winsor clip
      • Kappa – 3.0
      • iterations – 1
    • Create outlier rejection map – checked

Putting it all Together

Once the panels are processed, it’s time to create directories for each Color/Filter Channel. Create the new data folders and copy/rename each channel/filter based upon parts. For example:

Mosaic_Panel_Processed
├── Blue
│   ├── Part1_Blue.fits
│   ├── Part2_Blue.fits
│   └── Part3_Blue.fits
├── Green
│   ├── Part1_Green.fits
│   ├── Part2_Green.fits
│   └── Part3_Green.fits
├── Ha7
│   ├── Part1_Ha7.fits
│   ├── Part2_HA7.fits
│   └── Part3_Ha7.fits
└── Red
    ├── Part1_Red.fits
    ├── Part2_Red.fits
    └── Part3_Red.fits

Each of the above files were copied and renamed from the final process channel image name and copied to the above directory paths:

part1
|
├── St-avg-600.0s-LNWC_1_3.0_none-x_1.0_LZ3-NS-full-eq-add-sc_BWMV_nor-AAD-RE-noMBB-Hydrogen-alpha_1stLNC_it1.fits
├── St-avg-960.0s-LNWC_1_3.0_none-x_1.0_LZ3-NS-full-eq-add-sc_BWMV_nor-AAD-RE-noMBB-Blue_1stLNC_it1.fits
├── St-avg-960.0s-LNWC_1_3.0_none-x_1.0_LZ3-NS-full-eq-add-sc_BWMV_nor-AAD-RE-noMBB-Green_1stLNC_it1.fits
└── St-avg-960.0s-LNWC_1_3.0_none-x_1.0_LZ3-NS-full-eq-add-sc_BWMV_nor-AAD-RE-noMBB-Red_1stLNC_it1.fits

part2
|
├── St-avg-600.0s-LNWC_1_3.0_none-x_1.0_LZ3-NS-full-eq-add-sc_BWMV_nor-AAD-RE-noMBB-Hydrogen_alpha_1stLNC_it1.fits
├── St-avg-960.0s-LNWC_1_3.0_none-x_1.0_LZ3-NS-full-eq-add-sc_BWMV_nor-AAD-RE-noMBB-Blue_1stLNC_it1.fits
├── St-avg-960.0s-LNWC_1_3.0_none-x_1.0_LZ3-NS-full-eq-add-sc_BWMV_nor-AAD-RE-noMBB-Green_1stLNC_it1.fits
└── St-avg-960.0s-LNWC_1_3.0_none-x_1.0_LZ3-NS-full-eq-add-sc_BWMV_nor-AAD-RE-noMBB-Red_1stLNC_it1.fits

part3
|
├── St-avg-600.0s-LNWC_1_3.0_none-x_1.0_LZ3-NS-full-eq-add-sc_BWMV_nor-AAD-RE-noMBB-Hydrogen-alpha_1stLNC_it1.fits
├── St-avg-960.0s-LNWC_1_3.0_none-x_1.0_LZ3-NS-full-eq-add-sc_BWMV_nor-AAD-RE-noMBB-Blue_1stLNC_it1.fits
├── St-avg-960.0s-LNWC_1_3.0_none-x_1.0_LZ3-NS-full-eq-add-sc_BWMV_nor-AAD-RE-noMBB-Green_1stLNC_it1.fits
└── St-avg-960.0s-LNWC_1_3.0_none-x_1.0_LZ3-NS-full-eq-add-sc_BWMV_nor-AAD-RE-noMBB-Red_1stLNC_it1.fits

APP Mosaic Processing

This process will take the images created and create the mosaic image the each of the R,G,B, and Ha Channels.

  • LOAD
    • add the processed “Lights” parts/panels
  • ANALYSE STARS
    • automatic #stars target: set to 2600 (best for mosaics
      • Note Ha7 channel will have less star density
  • REGISTRATION
    • dynamic distortion – checked
    • Quadrilaterals
      • Scale start 1
      • Scale stop 10
    • Same Camera/Optics – Unchecked (since each part has already been processed).
    • Mosaic Mode – Checked
    • Registration Model
      • projective
  • NORMALIZATION
    • Mode Advanced
    • add-scale
    • BMV
  • Integration (typical, may need changes in MBB)
    • Integrate per channel
    • weights – equal
    • integrate – average
    • Composition, mode – full
    • Local normalization Correction, LNC degree – 4th degree LNC
      • LNC iterations 3
    • Multi-band blending
      • enable MBB – checked
      • 10%
    • outlier rejection, no rejection

Using the above settings, integrate each channel: Red, Green, Blue, Ha7 by selecting the three parts and then “integrate”. This will create a mosaic for each channel. Verify each image by reviewing after completion. Adjust if necessary the integration parameters (MBB, LNC, etc).

Then use the Tools to “combine RGB” images. For the Ha7 channel, assign to the desired color channel and review the combined images. Once done, you can save and play around with adjusting the image with APP processing menu on right side.

I normally save the final processed image as a TIFF image so that I can further process it using Light Room.

Final Results

Below is a three panel mosaic combined using the above data. I’ve assigned the Ha7 channel to “green”.

NGC6992 RGB/Ha7 with Ha7 Channel assigned to Green.