Is it possible to create a vector tile package from raster imagery?

[BradMead]

I know you can't do it directly, but is there a way to convert a raster into a format that can then be turned into a vector tile package that preserves the image quality of the raster? 

If not, what are some ways you can reduce the size of large raster files so they can be sideloaded into Collector?

[MervynLotter]

If you are only interested in converting a raster to a format that can be downloaded onto Collector then try creating a tile package (TPK) and side-loading that onto the device. Rasters are not support in vector tile packages.

For more detail, do see Go offline—Collector for ArcGIS (Classic) | ArcGIS  and https://community.esri.com/thread/90177 

If I am not editing data, then I usually create a TPK of the raster data, then include that in a MMPK with my vector data (with pop-ups and bookmarks) that is easily side-loaded onto Explorer for ArcGIS. 

[BradMead]

We have been able to sideload map tile packages, but the files weigh in at 119gb. Collector still works, but is very slow and not all that functional. I was hoping having the imagery in the vector format would decrease the size and improve performance.

[MichaelAugust]

Coincidentally, right now we're trying something similar, to publish a tile service, upload that to our Portal, then allow people to download chunks of it to Collector for offline use instead of having to side-load. If everything in your map can be offline then this might work for you:

"To author a map for offline use, the map needs to contain the following:

• Sync-enabled feature layers—These can be hosted feature layers or ArcGIS Server feature services. Feature layers that are not sync-enabled are not supported. For details on using hosted feature layers, see Allow offline editing (ArcGIS Online or ArcGIS Enterprise). For details on using ArcGIS Server feature services, see Preparing data for offline use and Tutorial: Setting up feature service data for offline use in the ArcGIS Server documentation.
• A basemap enabled for offline use—This can be from your own ArcGIS Server or a hosted tile layer. For details on enabling export of tiled map services, see Allow clients to export cache tiles in the ArcGIS Server documentation.
• (Optional) Tiled map services with export tiles enabled—See Allow clients to export cache tiles in the ArcGIS Server documentation for more information."

[JoshuaBixby · Accepted solution]

The only time that "having the imagery in the vector format would decrease the size and improve performance" is when the data was originally vector and was tiled to raster/image.  When that is the case, the benefit comes from going back to the original data and re-tiling as vector tiles instead of image tiles.  Taking remotely-sensed data like aerial or satellite imagery and trying to segment or classify it so it can be presented as vector tiles will not turn out well.