Astro Pixel Processor – Mosaic Color (RGB) Processing

Astro Pixel Processor – RGB-Ha Mosaic


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:

├── 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:

├── 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

├── 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

├── 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
    • automatic #stars target: set to 2600 (best for mosaics
      • Note Ha7 channel will have less star density
    • 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
    • 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.

First RGB/Ha Image

Finally, a clear night that was not below -15C/5F. It’s been a tough winter here in Minnesota. Back in January I got a Mini ZWO filter wheel and filters for my ZWO asi178mmc camera and just recently got a chance to test the new setup. During this period of no-imaging, I was able to build a Dew System for both my guide and main telescope and review my cable management (more on this later).

I wanted to image a simple target and test the the overall function of the filter wheel, focuser integration in EKOS/Kstars. I didn’t want to spend a lot of time imaging as this was a test. So, the simplest and colorful image to test the new setup was Imaging Orion’s Nebula (M42).

The M42 images were taken using the following exposures:

  • Red – 8 x 120s
  • Green – 8 x 120s
  • Blue – 8 x 120s
  • Ha 7nm – 5 x 120s
  • Dark , Flats, Bias Frames processed.
  • I used Astro Pixel Processor (APP) for processing and did some post processing with Adobe Light room.

Below Shows the results:

I am sure that I can process the image data better, and will go back and examine the overall color processing using APP. I will get the process flow better and there are some questions regarding the Ekos focusing routines that I need to better understand and setup as I found that Ekos was focusing quite often during the imaging. I also used the Ekos Scheduler to execute the image capturing process.

Image Gallery

This gallery is my basic Astronomical Deep Sky Gallery.  I’ll be updating this regularly.  Started to add some color images. (Updated May 17, 2019)

Latest Images and a Look Back

I started out taking astronomical images back in the mid 1990’s using CCD imaging.  This was when  CCD cameras were very expensive and not very practical for the amateur astronomers.   I found a book about making your own CCD camera, The Cookbook Camera by Richard Berry.  I built several of these camera CB-245 and modified the cooling system. The cookbook  CCD resolution was 378×242 pixels (my current camera has 3097×2080). 

Andromeda Galaxy – M31 (Old Cookbook Camera Image)

By the mid 2000’s they became obsolete.  I then purchased a Meade DSI pro camera and continued imaging.

Andromeda Galaxy – M31 (Meade DSI Pro CCD)

Fast forward to the present, I got back into the hobby and found that the prices have come down quite a bit.  I purchased a ZWO asi 178MMC camera which is cooled and the price point was which I could afford.  I’ve been re-learning and purchasing new equipment.

I have finally got a number of “good” images that is a vast improvement from my old Cookbook days and Meade DSI Pro cameras.  It’s been some learning curves with the equipment and software. I will be writing some useful articles about using Linux with Indi Library Drivers and my setup.  I will cover the lessons that I have learned during this process.

Andromeda Galaxy – M31 (ZWO asi178mmc)
IC5146 – Cocoon Nebula

NGC 6992 – Veil Nebula

Dumbell Nebula – M27
Veil Nebula (ngc 6992/6995)

CCD Imaging with the LX200 8 inch f/5


It’s that time of year where I like to take out the telescope. Bugs are dying off, less humidity, and nights are longer.  I have a pedestal mount that I attached during these months. I hopefully will build a simple enclosure to help expedite the setup time. The scope is remotely controlled and I used a CCD imager as my eyes. Even though this scope is up in age, it works well and guides well.  I’ll upload some of my astronomy projects as time permits.

M101 – Pinwheel Galaxy, Meade dsi pro