TIFFs of different file size

Hi, a question just popped up: a few days ago, I saved a coupe of photos of fireworks, as compressed TIFs, their size was about 40-45 MB each, 16 bit rgb.
Today I saved a photo of a flower, same settings, but its size is more than 90 MB.
How is this possible? I thought RT uses a lossless compression for TIFs.
And I thought that the file size of TIFs only depends of the number of pixels they contain (and bit depth and compression method).
This could only make sense if RT used a lossy compression for TIFs, couldn’t it?
Thanks and regards form Vienna
b

I think the number of different pixels count too

Try to photograph solid white or black (low iso, short time, with covered lens). What is the the tiff size? If it is small, then You got the reason.

When you click the save button in RT, the save dialog contains a checkbox for “uncompressed tiff.” Perhaps this is it?

I payed much attention to that, I think thats not it. The flower just does not go unter 90 MB, no matter what I do.

No, as @cuniek already wrote above…

Out of curiosity - I opened a file in RT, made it totally black (curves) and saved as 16 bit tiff (uncompressed). 94 MB. Then I made another save - this time with compression (lossless). 135 kB.

In other words - If Your image has a lot of solid color, the compression (even when lossless) is very effective.

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OK. I tried the same with Affinity. Same Result: 18 MB for 16 MP, 16 bit.