Convert a photo to Ultra HDR

This converter turns an ordinary JPG, PNG or WebP photo into an Ultra HDR JPEG: a normal image that every app can show, plus a small gain map that tells HDR screens how much brighter each area can be. On an HDR phone, tablet or laptop the highlights glow; everywhere else you see the same photo as before. The conversion runs in your browser and the photo is never uploaded.

What the tool does

An SDR (standard dynamic range) photo stops at the screen's normal white. HDR screens can show small areas much brighter than that. The converter builds a file that uses that extra headroom without breaking compatibility:

The gain map is computed from the brightness of your photo. Dark tones and skin get no boost; brighter areas get progressively more, up to the limit you choose. Writing both the Google XMP and the ISO 21496-1 metadata is what lets one file work on Android, in Chromium browsers and on Apple systems. We checked the output with Apple's own ImageIO framework on macOS 26, which reads it as an ISO gain map.

To learn how gain maps work in general, read what Ultra HDR is.

How to use it

1. Choose a photo with the picker above (or drag it in on a computer). JPEG, PNG and WebP work everywhere; HEIC works if your browser can decode it.
2. Set the highlight boost from +1 to +3 stops, in half-stop steps. Each stop doubles the brightness, so the range is 2× to 8× on the brightest areas. The default is +2 stops (4×).
3. Choose what glows:
   • Highlights: only the brightest parts, such as sky, lamps and reflections. The most natural choice.
   • Bright areas: light tones as well, for a stronger effect.
   • Whole photo: everything, in proportion to its brightness.
4. Download the Ultra HDR JPEG. The file is saved with -ultrahdr added to its name.

How to read the result

• The result preview. If your screen reports HDR support, the tool tells you so, and in a browser that displays gain maps (recent Chrome, Edge and Safari) the highlights in the preview glow brighter than the page around them. On an SDR screen you see the standard version, which is expected.
• The gain map preview. White means the most extra brightness on HDR screens, black means unchanged. If skin or midtones look light gray and you don't want them to glow, switch back to Highlights or lower the boost.
• Inside the file. A panel lists the base image size, the gain map size, the metadata written and the final file size. The gain map adds only a small amount to the size.
• Want to double-check? Open the downloaded file in the photo metadata viewer and look for the hdrgm fields in the XMP.

Other ways to get Ultra HDR photos

• Shoot them. Recent Android phones save Ultra HDR JPEGs straight from the camera, and iPhones store their own gain maps in HEIC photos. A photo captured in HDR holds more real highlight information than any conversion.
• Desktop editors. Some photo editors can edit in HDR and export a JPEG with a gain map. They give you full control, at the cost of more steps and software to install.
• Command line. Google's open-source libultrahdr library can encode Ultra HDR files from scripts.

Use this tool when you want a quick, private conversion of an existing photo without installing anything.

Limits

• It cannot add detail that was never captured. This is an inverse tone mapping effect: the converter guesses which areas should be brighter. A sky recorded as flat white stays flat, just brighter.
• It doesn't fix a dark photo. Brighten it first with the image brightener (see how to brighten a dark photo), then convert.
• The gain map is easy to lose. Editors, compressors, social networks and messaging apps that re-encode the image often keep only the base JPEG. To shrink the file, read how to compress an image without losing quality and test the result on an HDR screen.
• Too much looks fake. At +3 stops on Whole photo, large areas glare. Moderate settings usually look better.
• Transparency is flattened. JPEG has no alpha channel, so transparent areas of a PNG or WebP become white.
• Very large photos are scaled to about 16 megapixels to stay within the browser's memory; the tool tells you when that happens.

Keep your photos private with sigil.

HDR or not, a photo can say more than you mean to share. sigil. keeps the photos you want private in a vault encrypted on your phone with a 256-bit key that only the sign you draw on a 5×5 grid unlocks. It strips EXIF and location data on import and export, and its private camera keeps new shots out of your Camera Roll. Read more about pattern encryption.