What is an HDR photo?

An HDR photo is one that carries instructions for a screen that can go brighter than white. It is a normal picture plus a second, hidden layer — the gain map — telling an HDR display how much further to push the highlights. On an ordinary screen you just see the normal picture. Below you can turn one of your own photos into that format and see the difference for yourself.

  1. Your photo

    Drop a photo here — or click to choose

    JPGPNGWEBP

    Your files are never uploaded — everything runs on your device.

  2. HDR model

  3. Adjust & export

Try it on one of your own photos

  1. Add your photo

    Drop a JPG, PNG or WebP. It loads straight into your browser — nothing is uploaded.

  2. Dial in the highlight boost

    Choose how much brighter the highlights should glow on an HDR display. Shadows and midtones stay exactly as they were.

  3. Download the Ultra HDR JPEG

    You get a single JPEG with an embedded gain map. HDR screens brighten the highlights; SDR screens show your original look.

What HDR does, and what it doesn't

It changes brightness, not detail

HDR on a photo is about how bright a highlight is allowed to get on your screen — a specular reflection, a lamp, sunlight on water. It is not extra sharpness and not extra colour information hiding in the file.

One file, two screens

A gain-map JPEG (Ultra HDR / JPEG-R) is a standard JPEG with a second, embedded grayscale image plus metadata. An HDR display multiplies the base picture by that map; an SDR display ignores it entirely and shows the base. The same file works in both places.

It cannot bring back what was clipped

A normal photo holds no data beyond white, so a highlight that was already blown out stays blown out. What this authors is an HDR look — existing highlights allowed to glow brighter — not detail recovery.

The model behind it

Powered by GMNet, an MIT-licensed inverse tone-mapping model that predicts the highlight detail an SDR photo never recorded. The result is written as a gain map, the same mechanism phones use for their own HDR stills.

Frequently asked questions

What is an HDR photo?
A photo that tells a capable display it may render parts of the image brighter than ordinary white. In the Ultra HDR format that instruction travels as a gain map embedded in an otherwise normal JPEG, so the same file looks correct on an HDR screen and on an ordinary one.
What does HDR do on a photo?
On an HDR screen, the highlights — reflections, lights, bright sky — open up and glow past the white point, while shadows and midtones stay where they were. On a standard screen it does nothing at all: you see the base image, which is meant to match the original.
Why does my HDR photo look the same as the original?
Almost certainly because the screen you are looking at is not an HDR one. Open the same file on an HDR phone or an HDR monitor and the highlights will visibly brighten.
Does this recover blown-out detail?
No. A standard photo has no data beyond white, so clipped highlights cannot be restored. This authors a gain map that makes the existing highlights glow brighter on HDR displays — an HDR look, not detail recovery.
Are my photos uploaded anywhere?
No. Everything — decoding, the gain map, and assembling the final JPEG — runs entirely in your browser on your own device. Your photo is never uploaded, and nothing is kept once you close the tab.
Which model does it use?
GMNet, in a 512-pixel variant — one trained on real camera captures and one on synthetic data, so you can pick whichever suits the photo. It runs on WebGPU in your browser, and the output is a standard gain-map JPEG that HDR displays understand.

Wondering what the difference actually is, or why HDR looks washed out on your monitor? HDR vs SDR — the one difference behind the fifteen bullet points, what the formats mean, and why every comparison image online is necessarily fake.