Add real HDR brightness to an ordinary image
Select regions or colours in your image and encode them as HDR highlights in a Rec.2100 PQ file. It does not invent detail that was never captured — it makes what you choose genuinely bright.
- Rec.2100 PQ output with correct colour signalling
- Automatic detection, or select exactly what should glow
- Verified after encoding, not just intended
- Free, and the image never leaves your browser
This is a free online HDR image generator. It converts an ordinary SDR photo or graphic into a real Rec.2100 PQ file, signalled with cICP 9 16 0 1 in PNG or a Rec.2100 PQ ICC profile in JPEG, so a colour-managed viewer reads it as HDR rather than as an unusually bright sRGB image. Brightness is encoded as absolute luminance in nits against a 203-nit diffuse white, which is what lets selected regions exceed the white of the interface displaying them. Every export is read back and its signalling verified before you download it. Free, with no account.
Free, with no account and no watermark. Your image is processed in your browser and never uploaded — read how HDR glow works.
What this does, precisely
It is worth being exact, because this corner of the market is full of overstatement. This tool does not reconstruct photographic dynamic range. If a sky was blown out when the shutter fired, that information is not in the file and no amount of processing brings it back.
What it does is different and genuinely useful: you choose regions or colours, and those are re-encoded with real absolute luminance in an HDR container. A highlight you select at 1,600 nits is a highlight the display will render at 1,600 nits worth of instruction, subject to its own headroom.
The pipeline
- Decode the transfer function first, so all arithmetic runs on linear light. Multiplying gamma-encoded values is the documented cause of exports that open as dark grey.
- Honour the source primaries rather than assuming sRGB — a Display-P3 screenshot read as sRGB is wrong before anything else happens.
- Work in CIE XYZ, which is linear-light and unbounded, so a value that overflows Rec.2020 is still valid while it is being reasoned about.
- Raise luminance in the exposure domain, so a mask ramp reads as a smooth falloff rather than a hard ring.
- Fit each pixel into the signal volume by desaturating at constant luminance, never by clipping a channel.
- Apply PQ exactly once, at the very end.
Export formats
Questions
Does this turn an SDR photo into a true HDR photo?
No, and be wary of anything claiming it does. Detail that was clipped when the photo was taken is gone and cannot be invented. What this does is take regions you select and encode them as genuine HDR highlights within a Rec.2100 PQ file.
What is the difference between this and an HDR filter in a photo app?
Most so-called HDR filters are local contrast and tone adjustments that stay entirely inside SDR. Nothing they produce can exceed the display’s normal white. This changes the encoding, so the output carries absolute luminance instructions the display acts on.
Can I use it on photographs?
Yes, with more care than a logo. Photographs are classified automatically and given a more conservative starting brightness, because 8-bit PQ bands in smooth gradients. For a photo with large soft areas, the HDR PNG export holds up better than the JPEG.
What if my image already contains HDR?
It is detected and handled as HDR rather than being read as sRGB. That matters — reading PQ samples as sRGB would clamp a 4,000-nit highlight down to ordinary white and destroy the HDR the file already had. The existing information is preserved and the glow applied on top.
How do I know the output is really HDR?
Every export is read back after encoding and its signalling verified — the cICP tuple or ICC profile, the chroma sampling, the encoded peak and whether an SDR fallback is readable. The result panel shows each check.
What are the numbers?
Every figure below is either a published constant or a value this tool computes. None is an estimate, and each one is traceable to the standard beside it.
| Measurement | Value | Source |
|---|---|---|
| Diffuse white reference | 203 nits | ITU-R BT.2408 |
| PQ maximum | 10,000 nits | SMPTE ST 2084 |
| 8-bit PQ code for diffuse white | 148 | Computed |
| 8-bit PQ code for 1,600 nits | 205 | Computed |
| Rec.2020 white ceiling | 10,000 nits | Computed |
| Rec.2020 green ceiling | 6,780 nits | Computed |
| Rec.2020 red ceiling | 2,627 nits | Computed |
| Rec.2020 blue ceiling | 593 nits | Computed |
| Blue's share of Rec.2020 luminance | about 6% | Computed |
| LinkedIn logo size | 400 × 400 px | Measured |
| LinkedIn post and ad size | 1200 × 627 px | Measured |
| LinkedIn JPEG re-encode | quality 90, 4:4:4 | Measured |
| Price | Free, no account | This site |
Where do these figures come from?
This tool implements published standards rather than an in-house approximation of them. Each specification below defines part of what the exported files contain.
- ITU-R BT.2100
Defines the HDR system this tool encodes into — BT.2020 primaries with the PQ transfer function.
- ITU-R BT.2408
Sets diffuse white at 203 nits, which is the reference every brightness figure here is measured against.
- SMPTE ST 2084
The PQ transfer function itself: absolute luminance from 0 to 10,000 cd/m², independent of display.
- ITU-T H.273
The code points behind cICP 9 16 0 1 — colour primaries, transfer characteristics, matrix and range.
- W3C PNG Third Edition
Specifies the PNG cICP chunk, which is how an HDR PNG declares itself without an ICC profile.