Astrophotography - Mosaic/Stitching Workflow

[djwalters]

Hello everyone (cc: @James Ritson):

I want to attempt to stitch a mosaic image using a number of smaller images, likely in a 2x2 or perhaps 3x3 grid. Assuming this is possible in Affinity Photo, does anyone have a recommendation for a general flow to maximize quality and minimize issues?

I can think of several approaches, but to utilize the benefits of the Astro workflow my thought was to do something like the following. I haven't tried this yet, so I'm not sure what to expect (for example, will the stitching process work well for astrophotography).

Example Workflow

1. Stack each set of captures in the Astrophotography workflow.
2. While in Astro workflow, apply filters/adjustments to each image. Select the best sequence of these to copy to remaining captures to ensure the tone/brightness/etc are the same across all image stacks.
3. Export each stack to TIFF.
4. Re-import into stitching workflow.
5. Apply any remaining required edits/adjustments as needed.

Has anyone successfully done something similar with Affinity Photo, or will I end up with a red forehead?

[James Ritson]

Hey @djwalters, I haven't experimented with mosaic stitching but I would likely try one of the two following workflows:

1. Stack each mosaic individually with the relevant calibration frames (if required)
2. Commit the stack, tone stretch the data (using whichever method you wish) then export to gamma-encoded 16-bit TIFF
3. Use File>New Panorama and stitch the separate TIFF files together
4. Continue editing

Or—and I'm not sure whether the panorama stitching process would work properly here—try stitching the linear stacked data instead:

1. Stack each mosaic individually with the relevant calibration frames (if required)
2. Commit the stack, then export to 32-bit TIFF. On the export dialog, there is no explicit preset for this, so select TIFF and then under Pixel format choose RGB 32-bit
3. Use File>New Panorama and stitch the separate TIFF files together
4. Tone stretch the resulting panorama then do any further editing as necessary

Panorama stitching will use exposure equalisation, but depending on your tone stretching method I'm not sure if using the first process may result in colour discrepancies that could look odd when the separate tiles are stitched together. That's why I think it may be worth giving the second method a try.

Hope that helps!

[djwalters]

Hi @James Ritson,

 

Thanks for the tips! I haven't had much luck yet with the weather, but when it decides to cooperate I'll try the 2nd approach first and let you know how it goes.

In the meantime, I'm building up my calibration frames. My camera (ASI6200MM) images are ~120MB each, so Bias/Dark frames can take up a lot of storage as individual images, especially if I'm looking at several Bin and exposure settings @ 30 images each. Does Affinity support creating "Master" calibration frames to lower storage requirements? I'm wondering if the normal "Stack" workflow would work for this (using mean/average)?