Working with Mosaic File Sizes - Forums

Topic starter

Feb 8, 2024

First off, apologies if this question falls under one of the unsupported topics. The question itself is more asking how other's deal with the issue rather than to discuss platform limitations.

I just created my first mosaic, and wanted to export it out of PI and into Astrobin/Lightroom/Etc. The mosaic is 3x3 at 230FL shot with a ZWO 2600MC. My typical process is to export as a TIF into Lightroom for a few adjustments and then export with watermark. The challenge is that the TIF file that is generated is larger than what the format will support. I can save as a JPG from PixInsight, but am still unable to import in Lightroom. Photoshop will accept the JPG, but no matter what I do I am unable to reach a file size that can be uploaded into Astrobin.

If you create mosaics, how do you get the file size down to something reasonable that all applications/platforms can work with and not lose too much detail? I can see that detail may matter less for the shorter focal lengths, but what if I wanted to do a 12-panel at 2800FL?

Thanks,

Jeramie

Well Written Respectful Engaging

Richard

Feb 8, 2024

Ultimately, it depends on the intended display resolution you are aiming for. Within PixInsight is a process called "Integer Resample" which allows you to resize an image to a given dimension, resolution or downsample factor

If you choose a downsample factor of 2, this is essentially the same process as a 2x2 bin. You can choose to either take the average, maximum, minimum or median of the pixels to create your lower resolution image. As you may have figured out, this process will lose information since you are rescaling the image size but it really does not matter if you are viewing the image on a display (it is only noticeable once you zoom in).

Helpful Concise

Wei-Hao Wang

Feb 8, 2024

What’s the actual file size that troubles you in LR and PS? 2600 has about 24 mega pixels. That means roughly 144 MB for 16 bit color. Even if you do a 3x3 mosaic, the mosaic would have something like 1 GB to 1.2 GB at most. That’s well under Photoshop’s file size limit for TIFF (4GB). Furthermore, although TIFF’s official size limit is 4 GB, I found Photoshop has no problem reading non-standard TIFF that’s larger than that. It just can’t save TIFF larger than 4 GB. So there shouldn’t be no problem at all.

All that being said, 4GB or even 400MB is too large for Astrobin. I very often do mosaics. I try to downsize my mosaics to within 40MB for Astrobin. If my mosaic is really really huge and downsize it to <40MB would wipe out all the interesting details, I use Gigapan instead. Astrobin isn’t really optimized for viewing super large images.

Helpful

Jeramie

Topic starter

Feb 15, 2024

@Wei-Hao Wang Apologies for taking so long to get back to this.

Wei-Hao Wang:
What’s the actual file size that troubles you in LR and PS?

When I went back and looked at the individual panels of the mosaic, they are 2.5GB in size. When I build the individual columns that bumps to 9.6GB. The final XISF is close to 10GB. When I attempt to export this out to TIFF at 16-bit, it fails.

I did enjoy the process of creating the mosaic and with my C11 I'll need to become more educated on the process as I use it at longer focal lengths.

Thanks for the reply.

Well Written Respectful Concise

Wei-Hao Wang

Feb 15, 2024

The file sizes that you just mentioned is way too large. I guess you drizzled it 2x. (Drizzled 2600 images in 64 bit color would be roughly 2.4 GB.)

The drizzle part aside, if the 10GB XISF is in 64 bit, reducing it to 16 bit would bring the file size to 2.5 GB. That's well within TIFF's 4GB limit, so it shouldn't fail. Something else must be wrong.

If you switch to C11, then I will suggest not to drizzle. The focal length is long enough for your 2600 to sample the FWHM very well, so the need for drizzle is much lower. This will help to keep the file size manageable.

Helpful Respectful Concise