Debayering, Nebulosity & Altair colour cameras

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Debayering, Nebulosity & Altair colour cameras

Post by turfpit » Sun Mar 18, 2018 2:14 pm


I usually use Nebulosity to calibrate, debayer, align and stack my deep sky frames.

When selecting Batch > Batch Demosaic + Square RAW color the Manual Demosaic Setup window appears.

manual-demosaic-setup.PNG (5.88 KiB) Viewed 54 times

The question becomes - "for Matrix offset, what are the correct values for X & Y?" The possible values are X = 0 or 1, Y = 0 or 1 or 2 or 3 (8 combinations).

The notes below describe how I arrived at the X, Y values for a 183C camera as suggested in this post. The notes below were tested by forum user JThree against a 178C - thanks Jerry.

Summary Findings
For an Altair 183C camera, use X = 1 and Y =1
For an Altair 178C camera, use X = 1 and Y = 1

With Nebulosity 4.1.7 (and the recent 4.1.8 beta) the Altair drivers are dated 19 Nov 2015, so of course the Altair 183C and other recent Altair cameras are not recognised.

Use the following steps to update the drivers (for a 64-bit Windows installation):
  • Rename C:\Program Files (x86)\Nebulosity4\altaircam.dll to altaircam-old.dll (think regression).
  • Copy C:\Program Files\SharpCap 3.1\Altaircam.dll to C:\Program Files (x86)\Nebulosity4\Altaircam.dll.
  • Start Nebulosity, select Altair Astro from the cameras list and capture say 5 frames.
  • Open one of the frames in FITS Liberator and click the Image Headers tab. XOFFSET and YOFFSET are the values for X & Y in the Manual Debayer Setup window. See the yellow highlight in the attachment FITS-Nebulosity.png. FITS headers can also be inspected under the File > FITS Header Tool in Nebulosity.

FITS-Nebulosity.png (31.17 KiB) Viewed 54 times

SharpCap 3.0 users should replace SharpCap 3.1 with Sharpcap 3.0 in the second bullet above. The altaircam.dll file in Sharpcap 2.9 is an older date, so this procedure is unlikely to work for the latest Altair cameras and SharpCap 2.9.

In the Manual Debayer box, Pixel Size can be left as X=1, Y=1 for a square pixel. Color Control can be left as a diagonal of 1’s.

This should be enough to use Nebulosity for the Debayer process.

For a 32-bit Windows system, Nebulosity and SharpCap both reside in C:\Program Files.

If anyone follows this process for a different model of camera, please post your X,Y results here as they may help others.


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