"How do IQ compare between the two?"
Well, in one word: different.
Problem is you (me) can´t really compare both, side by side. Simply because they are so different. But i assure you, both are very good, each in it´s own way.
You must understand that Ricoh has it´s own IQ marks, same for Samsung.
While the IQ from the GRD3 is persistently the same, the IQ from the NX1 varies across the focal length, slightly. But that´s not all, to be more precisely, not all for me.
Most important thing beside IQ is imho the feeling of an camera. With the GRD3 you have an tool in your hands with a vast aquarel palette. Just think about customizing functions, noise settings, various focus modes, bracketing, function keys and more and more. All this with it´s prime 1.9 lens...way ahead of many other cams.
With the EX1 you get modern technique packed in perfect body, paired with very good design and gorgeous display, not to forget the sharp lens. But...and there is a big but: overall control of all those functions are quite minimalistic and very dependable of each other. Sure it has manual modes A, S, M and P (without shift). But the creative functions, when activated, blocks many other custom modes. Some users are really annoyed and have a big ? on face when camera gives no feedback about blocked modes. But people adopt quickly new situations, so anyone who likes the EX1 could and would easily forgive that issue. Even Samsung could, if they would want, address it with a slightly changed FW, but i guess for sure they won´t do that, it´s simply against they´r philosophy.
Now back again to your question about IQ. I only can tell you that both are very good, maybe the best you can get right now from any compact camera on market. Finally it´s just a matter of taste or affiliation witch one people buy. I could not resist and bought recently the EX1. My GRD3 is now soon almost 1 year old...but still in my heart.
Final words from me, both are unique cameras worth the money, and as i wrote before, GRD3 is the pencil of an artist while EX1 is the canvas to be painted
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nemo66...