Live stacking Save button, 4 sub-options ??

[jonstarrysky]

Hi, appreciate any feedback on this. So we have 4 options, top to bottom:

1. Save as 16 Bit Stack
2. Save as Raw (32-bit) Stack
3. Save with Adjustments
4. Save Exactly as Seen

Despite the clear info on the SharpCap manual I'm a bit unsure which options to save my Live Stacks from my 294MC camera set to 16 bit RAW in SharpCap (the sensor its self is 12 bit).

My workflow is to do the Live Stack histogram stretch and colour adjustment in SharpCap, then export in .png format for final tweaks in Affinity Photo 2 (Curves, Background subtraction, HLVG, NoiseXTerminator) i.e. #3 or #4

Example below of a recent "Save Exactly as Seen", before and after some final tweaks in Affinity Photo 2

https://www.cloudynights.com/gallery/im ... e-as-seen/
https://www.cloudynights.com/gallery/im ... -postproc/

Ideally to also save a master file where the histogram stretch can be done later eg using the Ritson "Normalized Tone Stretch" in Affinity Photo. Or in SharpCap itself at a late time. But no saving of individual raw frames to stack later.

My observations are #3 and #4 generate images which visually look exactly the same. Maybe the file size is a bit bigger for #3 and could in theory contain more detail.
I have found that #1 is incompatible with the Ritson "Normalized Tone Stretch" in Affinity Photo.

Maybe a good workflow would be to export #3. Potentially being more than 8-bit it might be a more ideal starting point for final image tweaks eg at the lower grey levels ?? And to consider also exporting #2, for maximum compatibility for potential more involved processing at a later date including Histogram stretch.

I guess also #4 being 8-bit is a guarantee the image file will open in any software. But if #3 is saved then #4 is not that important.

Not sure what #1 achieves for me unless if can be reopened in SharpCap to do the Live Stack histogram stretch later ?

Finally, is there a way of configuring a one-click multiple save operation where pre-defined combinations including one or more of #1,2,3,4 are saved in succession ? Would definitely help

Thx, Jon

[admin]

Hi Jon,

first the easy part - yes you can configure multiple saves (in recent update versions of SharpCap 4.1). In the right hand most tab of live stacking you have some options, including checkboxes for which of those 4 formats are going to be saved if the stack is 'auto saved'. The same options apply to 'Bulk Save', which is activated by pressing <CTRL> and clicking the save button.

As to the output formats, the 16 and 32 bit stacks contain (to some approximation) the same image data - however the 32 bit stack is the full state of the stack at the detail level it is stored internally in SharpCap, while the 16 bit stack is the same data downsampled and rescaled to the 16 bit range. The 16 bit file is smaller, and has better compatibility with a number of image processing applications (some don't like 32 bit FITS). It's also worth noting that it will usually take a *lot* of stacked frames before the pixel noise level drops below the 16 bit quantization threshold, so in most cases the 32 bit stack is simply using more file size to record the pixel noise in greater detail... However, it does look like some of the Affinity algorithms from James Ritson are designed for 32 bit images, so that would be the way to go if you plan to use those.

The differences between 'with adjustments' and 'exactly as seen' are twofold

1) 'with adjustments' gets a 16 bit image, 'as seen' gets 8 bit. This makes 'as seen' handy for sharing on social media, etc, but 'with adjustments' better for further tweaks/processing.

2) 'as seen' includes adjustments from the display stretch mini histogram, 'with adjustments' does not. In general, that's not important as you tend not to use the mini histogram stretch when live stacking, but for some high contrast targets (M42, M31, etc), using the second stretch can help deal with the contrast in the image.

Hope this helps,

Robin