About

A gain map image encodes an SDR photo alongside a secondary brightness map. On HDR displays — Apple XDR, Android Ultra HDR, Windows Advanced Color — highlights render above SDR reference white. On SDR displays the image renders normally; the format is fully backward compatible.

Gainmaps.com demonstrates browser-based conversion. Drop any JPEG, PNG, HEIC, WebP, or AVIF into the converter. Processing runs locally in a service worker — no file leaves your device, no upload, no server.

The gainmap CLI batch-encodes images from your terminal. It targets ISO 21496-1 (Ultra HDR JPEG). Install via npm, Homebrew, or curl — see Developer docs.

The project is open source. github.com/kirkstrobeck/gainmaps →