The Panasonic GH4 is very good for photography and produces high quality images for its generation. You can read my in-depth review of the GH4 here. While I do cover video, all my reviews are centered around the photographic capabilities of the camera.
Now specifically compared to the Canon EOS 1200D which is from around the same time-frame, you will see some improvements, mostly in terms of dynamic-range where the GH4 can capture one more stop than the 1200D. Low-light performance is about the same, although at high ISO, the larger APS-C sensor of the 1200D delivers a small advantage.
The nice thing though is that the GH4 is much more sophisticated and has tons of features not found on the 1200D. It is faster, has much more efficient controls and a larger 100% coverage viewfinder. A full list of features is shown on the first page of the review linked above.