How to stop Photos decreasing jpg size

You write "... always seems to reduce the file size ..."

Did you check if the file size or resolution of your photos is changing after you have edited it?

Are these photos in Photos App or are they somewhere on your computer without importing them in Photos App?

Please write down file size & resolution of a few photos before you edit them.

Right click on the photo and then "Get Info" will give you the file size.

Then do some editing and compare the file size before and after.

One of the benefits of using Apple Photos App is normally that the editing is "non destructive", you are not really saving the editing steps in the JPEG as soon as you do the editing.

All steps are recorded in the Photos Library and can be reversed if needed, therefore you always have the original data.

Photo editing basics in Photos on Mac - Apple Support (CA)

Would be great if you have some examples where this is not working.

Ralf

Any time you edit a jpeg file it will be resaved with additional jpeg compression. That's the nature of the beast.

Resolution is the number of pixels/dots per inch when viewed/printed. Unless you crop an image the total number of pixels in the image does not change.

As for printed resolution it will depend on the size of the print. It's described in this article: The Myth of DPI.

How are you saving. If using drag/drop, you are only gettting a reduced quality/size preview.

You need to use file>export (for the edited version) then choose full size and max quality. If you want the file exactly as imported, file>export unmodified original.

When you choose export, the next pane should look like this (depending on version - what version of MacOS are you on?). You can also export as a TIF file which is fully uncompressed.

This discussion might help.

Photos - Apple Community

In summary: export at higher quality.

No problem. We are all slow on the uptake sometime. I find more often as time passes 😂