What is Ultra HDR and how does it work?
Written for photographers, Android and iPhone users, and web developers curious why modern .jpg files glow on OLED displays and how the format works
Short answer
Ultra HDR (standardized in Android 14 and ISO/TS 21496-1) is a backward-compatible JPEG file format that stores two images inside one .jpg file: a normal 8-bit Standard Dynamic Range (SDR) photo that opens on every device ever made, plus a smaller secondary 'gain map' image tucked into the metadata header. On an HDR OLED phone or laptop screen, the display multiplies the base image by the gain map so sunlit clouds, lamps and reflections shine several times brighter than standard webpage white.
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For decades, digital photography was stuck in a catch-22: camera sensors could record 12 to 14 stops of light from deep shadows to bright neon signs, yet standard .jpg files only held 8 bits per channel (0 to 255). Every time engineers proposed a new 10-bit or 16-bit HDR file format (like JPEG XL, AVIF or HEIC), older websites, email clients and upload portals refused to open it.
Google’s Ultra HDR format (introduced in Android 14 and now aligned with Apple and Adobe via the ISO 21496-1 gain-map standard) solved that compatibility wall with a clever container trick: put the HDR instructions inside the metadata of a normal 8-bit .jpg file.
The 3 parts inside an Ultra HDR .jpg file
According to Google’s Ultra HDR specification, here is what happens when you open the file on different devices:
| Display & software | What it reads from the .jpg file | What you see on screen |
|---|---|---|
| Older monitor, printer or legacy app | Reads Part 1 (Primary 8-bit SDR JPEG) and ignores the MPF trailing bytes. | A completely normal, well-exposed SDR photograph with no washed-out colours. |
HDR display at partial headroom (e.g. laptop indoors at 70% brightness, 2x HDR headroom) | Reads Part 1 + Part 3, and scales the logarithmic gain map partially to match the display’s current available brightness headroom. | Sunlit highlights and lamps lift smoothly without clipping. |
OLED phone or MacBook XDR display (4x to 8x HDR headroom) | Applies the full hdrgm:GainMapMax boost to highlight pixels. | Specular highlights (sun reflections, neon signs, fireworks, clouds) shine with lifelike intensity. |
Why Ultra HDR beats older 10-bit HDR formats for everyday sharing
Before gain maps, 10-bit HDR images (like PQ or HLG video frames) stored absolute brightness values. When an app tried to show a 10-bit PQ image on a normal 8-bit monitor, it had to guess how to tone-map the highlights on the fly, which is why HDR screenshots used to look grey, dull or neon orange.
In Ultra HDR, the phone camera’s image signal processor (ISP) has already computed the ideal 8-bit SDR rendition at the moment you pressed the shutter and saved it as the primary JPEG. The gain map only tells HDR screens how to reconstruct the extra highlight headroom on top of that finished SDR base.
How to inspect or flatten an Ultra HDR file in your browser
If you want to see whether a .jpg file contains an Ultra HDR gain map, or if you want to strip the HDR glow so the image renders at normal SDR brightness on a website, use our local browser tools:
- Open the photo metadata remover and drop your JPEG file onto the inspection box.
- Check the metadata report for XMP (where hdrgm tags live) and secondary container segments.
- Click Save clean copy to strip all metadata and secondary gain-map blocks while keeping the primary 8-bit SDR JPEG bytes intact with zero re-compression, or open the file in the image brightener if you want to adjust shadows and contrast before exporting a fresh SDR file.
For practical examples of when to keep HDR and when to convert to SDR for web uploads, see our HDR image converter guide.
Questions
What file extension does an Ultra HDR image use?
An Ultra HDR image uses the standard .jpg or .jpeg extension. Because the primary image stream inside the file is a valid baseline 8-bit JPEG, any app or website that does not understand Ultra HDR simply displays the normal SDR base image.
How much larger is an Ultra HDR JPEG than a regular JPEG?
Typically only 10% to 25% larger. Because the human eye is less sensitive to fine spatial edges in pure luminance boost maps, the secondary gain-map JPEG is usually stored at one-quarter resolution (1/2 width by 1/2 height) and single-channel greyscale.
Is Apple’s iPhone HDR photo format the same as Android Ultra HDR?
Both use the exact same gain-map principle, and both Apple and Google converged on the ISO 21496-1 gain-map metadata standard so iPhones, Android phones and Chrome/Safari browsers can render each other’s HDR gain maps.
Why does an Ultra HDR photo lose its HDR glow after I crop or resize it in some editors?
Any editor that decodes only the primary 8-bit JPEG onto a standard sRGB canvas and saves a new file discards the secondary MPF gain-map stream and XMP hdrgm tags, turning the output into a normal SDR JPEG.
How can I remove the HDR glow from an Ultra HDR photo without re-compressing the base image?
Drop the Ultra HDR .jpg file into our in-browser Photo Metadata Remover and click Save clean copy. Stripping the XMP and MPF metadata segments removes the gain map while keeping the original 8-bit SDR JPEG bytes intact.
Keep reading
How to convert HDR photos to standard SDR (and why they glow on screens)
Why phone HDR photos glow blindingly bright on some screens and look washed out on others, and how to flatten them to standard SDR in your browser.
GuideHow to brighten a dark photo without blowing out the highlights
Raising Brightness washes out skies and skin. Lift Shadows first, then restore a touch of Contrast and Colour in your browser.
GuideWhat is a WebP file and how do you open or convert it?
Why saved web images end in .webp, how WebP compares with JPG and PNG, and how to convert WebP without uploading your file.
