UPDATE 8/29/16: I see that OpenSeadragon is linking here. LATEST Openseadragon images are here on Tumblr. (Thanks again Ian Gilman for making that possible!)
For now, I’ve put aside my goal of high-speed image tiling for portraits. Instead, I’m trying to get a reliable (manual shooting) work-flow for 4×5 imaging for landscapes or still-life photography.