RAW or JPEG? Which one when?

Kim Letkeman wrote:

The jpeg data has gamma, sharpening, contrast and noise reduction already applied. And it is compressed into blocks that are invisible to the eye, but not always invisible to processing algorithms.

So anything you do in layers is now risking artifacts and posterization ... whether non destructive or not. The destruction is already wrought when before you start ...

You can get a great image from a JPEG .... but it can be much harder than with RAW, and I have seen cases where the JPEG just had to be abandoned as it could not support what I wanted to do. One reason why my "great JPEG experiment" ended permanently some years ago.

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http://kimletkeman.blogspot.com