As the Spark only shoots jpg, the results are fixed, and this includes the noise reduction. Spark doesn't have the same noise reduction algorithm that the Mavic Air does, so as you shoot into shade, details become painterly. In my experience, in bright light, Spark does great, albeit jpg only.
Mavic, needs to be shot in AEB mode, as it's next to impossible to grade your shot on iPad, or
Crystalsky. Raw also, as you have no sharpening added and less noise fixed to image. Mavic HAS to be focused, unlike Spark or M Air. If you go from Video to stills, recheck focus always as the AF will slip. Best solution I have found, is use AF at start of flight, making sure you were given focus confirmation, then switch back to MF, and stay in MF. There are issues where the Mavic may try to reacquire focus during a hover and miss.
Before I shoot stills, I always refocus. Mavic has a portrait orientation for the sensor, which is great for panos, (taking V orientation to stitch to a landscape later on).
If you are shooting in mixed light, expose for the shadows if possible the Mavic has a bit more head room on highlights on stills at base ISO. But again shoot in AEB mode. You will waste images, but attempting to get 1 perfect exposure from the camera is IMO harder to do. The Mavic on 5 AEB will give you a range of -1.34 to +1.34 exposure stops, I would prefer more, but that is is.
Stay away from higher ISO's, anything higher than base to 400 is way to noisy and details are lost to noise. The chip in the camera is not a high ISO chip, even though they are there, it's just to small a light gathering area.
Shoot stills in tripod mode, remember to come out of tripod mode before you come back as it will slow your speed down.
Stay away from A mode, as it's going to pick a higher ISO in low light and thus give you more noise. I always shoot in M mode.
Use a raw converter that knows about the Mavic lens corrections like ACR or Lightroom, both do a very good job on the raw. Again the jpg are fixed, no changes really can be made.
As a still photographer, not video shooter by trade, I have been impressed by the Mavic camera. At 12MP you need to stitch to get a larger print, but if you shoot in raw, and use AEB, the camera can produce some impressive results.
Paul Caldwell