At 4K resolution, the Sony delivers a crisp, rich detail, with few digital artifacts such as aliasing or moiré.
Compared to the Lumix GH4 we must note that although the A7s images might appear sharper, actually both cameras seem to capture the same level of detail.
Sony A7s: codec XAVC-S
Here’s one of the greatest improvements regarding Sony A7s: the codec..
Previous cameras recorded internally on AVCHD codec, which had a low transfer rate of 25Mbps, which produced highly compressed images, with poor quality and color artifacts.
Finally Sony has listened to the requests of users and has implemented a much more slid codec in the A7s: XAVC-S. Now the A7s can internally record at a maximum resolution of 1920×1080 at 50Mbps with this codec, which offers higher quality than AVCHD although it still samples color at 4: 2: 0 and records at 8 bits of color depth.
XAVC-S (the amateur version of XAVC, which reaches up to 12 bits and 4:4:4), although not perfect, offers a very acceptable quality / size ratio. It seems to be solid enough to let us do color corrections without the fear of “breaking” the image. For these tests we have used Davinci Resolve, getting fantastic results with XAVC-S from the Sony A7s.
Regardless of the internal recording, the A7s has “clean” HDMI outputs, both 1080p HD and UHD 4K. However both options are limited to 8 bits although at a significantly improved 4: 2: 2 color sampling.
An interesting factor for those who only need a 1080p finish is being able to capture in 4K and then downsample to 1080p in post. Thus not only achieve an image of higerh quality with virtually no compression artifacts, but also oversampling from 4: 2: 2 to 4: 4: 4.