PSB File doubles in size through Flattening

[Ocean 11]

I have a PSB file 46 000 x 25 000 pixels at 2.17 GB with fifty layers.

After flattening the file size increases to 3,49 GB.

With regular sized images I work with TIFF, and file size after flattening is always about 20% or less of the layered file.

Why has the file size almost doubled in PSB through flattening?

PS: the layers consisted of JPG files.

[D Fosse]

https://forums.adobe.com/people/Ocean+11  wrote

PS: the layers consisted of JPG files.

What does that mean? Are they linked smart objects?

[Ocean 11]

No, each layer was a jpg photograph (not a Tiff), and the whole document was psb file.

[Mike_Gondek]

Are you keeping the file format psd or psb after flattening.

If you are going to .tif, can we see what compression settings you may or may not have used.

[Ocean 11]

Yes, the file is still psb after flattening.

I thought 46 000 pixels wide would be too large for a TIFF or PSD.

[Mike_Gondek]

Can you post a screenshot showing your art & layers, or anything else helpful so we know you construct or save this (layers on or off).

For me the files get smaller with flattening, and tried with both smart objects and cloud objects.