Arsenal offers users several different modes. You can control your camera using the Arsenal app on your phone or you can put your phone and your tripod away and use Arsenal's handheld mode.
When shooting with a tripod and the Arsenal app, Arsenal uses a few things to determine settings.
Arsenal reads a live view photo from the sensor. Arsenal's AI uses the live view photo to find similar photos in its data set. The settings that were used to take the similar photos are clustered and the centroids of the main cluster are used as the "base settings". Using those base settings, Arsenal's AI can figure out what settings the photographers were trying to optimize for. For obvious reasons, Arsenal can't just apply those settings to the current scene. So it starts with the base settings and adjusts those settings based on a number of factors. This includes amount of light, camera shake, dynamic range, and depth of field required. These "environmental constraints", as we call them, are then used to adjust the base settings into something that works well for the current scene. When using the smart screen in the app, those settings are applied when you press the trigger button.
When you're in handheld mode on a DSLR, things behave a bit differently. Because the mirror is down (so you can see through the viewfinder), no light is hitting the main sensor, so we can't take a live view frame whenever we need. Instead of pulling a live view frame from the sensor, we use the last photo to compute the similar photos, dynamic range, and color range. The other environment constraints can be computed from the camera's metering and Arsenal's accelerometer. As the camera's metering or Arsenal's accelerometer detect changes, smart mode recalculates settings using the last photo and the new environmental data. The one thing we can't compute for in handheld mode that we do compute when using the app is subject motion (how fast something is moving in the frame, so we know how fast the shutter needs to be if the similar photos stop the motion). This can be estimated pretty accurately though by looking at the similar photos (football players only move so fast, race cars move so fast, birds, etc...).
Most of the data we pull from the sensor doesn't change that quickly, so really you only need to take another test shot when you change to a new subject. You'll see when in handheld mode that Arsenal is constantly updating settings based on the environmental constraints and the last photo.
Arsenal will usually get a good photo even if you don't take a test shot after you change subjects. Usually most of the things it would optimize would be pretty similar, unless you're really changing to a drastically different type of shot. That said, we still recommend taking a test photo whenever changing subjects in handheld mode on DSLRs. Please email us at firstname.lastname@example.org if you have any questions about handheld mode.