# Gainmaps

> Convert photos to HDR gain map images in your browser. Local and private — no upload, no server.

## What are gain map images?

A gain map image encodes an SDR photo plus 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 cross-platform technical name is HDR gain map image. Consumer brands include Adaptive HDR (Apple) and Ultra HDR (Android/Google).

## Browser converter

[Convert images in your browser](/convert)

Drag and drop any photo — PNG, JPEG, GIF, HEIC, WebP, or AVIF. Processing runs locally in a service worker. No file leaves your device.

## CLI

Install the gainmap command-line tool to batch-encode gain map images without a browser.

- npm: `npm install -g gainmap`
- Homebrew: `brew install kirkstrobeck/tap/gainmap`
- curl: `curl -fsSL https://gainmaps.com/install.sh | sh`

## Ultra text agent skill

Add Ultra-white HDR letterforms to headlines and logotypes using a WebGPU canvas. Available as an agent skill installable via `npx skills add kirkstrobeck/gainmaps`. Works with any coding agent that supports the skills convention.

[Ultra text demo](/text)

## Developers

CLI docs, agent skill reference, and TypeScript library API for gainmaps.

[Developers](/developers)

## Docs

What gain map images are, how the browser converter works, and how to use Ultra text.

[Docs](/docs)

## Galleries

- [Photo gallery](/photos) — 100 landscape photographs as gain map images
- [Logo gallery](/logos) — brand logos rendered as gain map images

## When to use Gainmaps

Use Gainmaps when:

- You need to convert a photo to an HDR gain map image (JPEG, PNG, HEIC, WebP, or AVIF input).
- You want to batch-encode images from the terminal without a browser: `npm install -g gainmap` or `brew install kirkstrobeck/tap/gainmap`.
- You want to add Ultra-white HDR text effects to a headline or logotype in a web project.
- You are building a tool that needs to process images into the ISO 21496-1 Ultra HDR JPEG format.

Do not use Gainmaps when:
- You need to edit or retouch image content (Gainmaps is a format converter, not an image editor).
- You need lossless conversion (the gain map JPEG format is lossy).

## API

The public JSON API is documented at /openapi.json. Main endpoints:
- GET /api/photos — list of all photos in the gallery
- GET /api/photos/{slug} — single photo record with image URLs
- GET /api/logos — list of brand logos
- GET /api/logos/{slug} — single logo record
- GET /api/version — CLI version and install commands

All endpoints return CORS-enabled JSON. Errors return {error: {code, message, hint}}.