I've been searching for the ideal pocket camera for a couple of years. I've tried most brands and sensor sizes. Leica is the best by far but unfortunately for most of us unless its our prime camera its far too expensive as a second or third camera in one's kit.
A pocket camera must be just that, a camera that fits comfortably in a shirt pocket, sometimes a big pocket. Point and shoot cameras are not for serious photographers. Despite the robust advertising their image quality is awful with poor resolution, washed out colours and low contrast,.... and they will not fit in a shirt pocket. I've tried working with these small sensor images in photoshop but there is not much that can be done to make the images respectable.
So I looked at the 1" sensor cameras. Not bad for image quality and most do fit in a shirt pocket but alas the sensor is still too small and they are fixed lenses. The mirrorless cameras are good to excellent for image quality in the 1.5X and full frame sizes. The camera body fits in a shirt pocket alright but not with a lens attached. Indeed the lenses for mirrorless cameras in 1.5X and full frame are just as big and heavy as the lenses for the digital single lens reflex cameras.
Finally I settled in on the 4:3 or 2X cameras. I field tested the Panasonic Lumix DMC-GX85K and am generally satisfied with the performance although I only have the low end kit lenses to work with. Eventually I will get the Leica 15mm lens to hang on the end of my Lumix and I will have a true shirt pocket camera that can take professional photographs on the street or in the bush.
I already have the Sony A99ii 42mp full frame and Sony A77 24mp 1.5X for nature photography but for those nature hikes and walks around my city the Lumix is the ticket, at least for me.
First Field Test of Panasonic Lumix DMC-GX85K with Kit Lenses