Make an image glow — with light, not a halo
Most glow effects paint bright pixels around a shape. This changes how the image is encoded, so the part you choose can render brighter than the page it sits on.
- Nothing is drawn onto your artwork
- Works on logos, text, product shots and photographs
- Optional halo if you want visible spread as well
- Free, and processed entirely in your browser
This is a free online tool that makes an image glow using real HDR luminance instead of a drawn halo. The difference is not stylistic. A CSS glow or a blurred layer adds bright pixels, but those pixels are still ordinary white, so they can never out-shine the page they sit on. Re-encoding the same pixels as Rec.2100 PQ gives them absolute luminance — 1,600 nits stays 1,600 nits regardless of what white the interface uses — and that is what produces a highlight brighter than the surface around it. Runs in your browser, free, with no watermark.
Free, with no account and no watermark. Your image is processed in your browser and never uploaded — read how HDR glow works.
Painted glow versus real HDR
These two look similar in a screenshot and behave completely differently on a capable display. Both panels below are honest about what they are.
Painted glow
A blur and a halo drawn around the letters. Every pixel is ordinary white, so it can never exceed the brightness of this page.
Real HDR luminance
Nothing added. The same artwork, re-encoded at 4,000 nits, using headroom the page around it never touches.
Your display has no HDR headroom, so both panels look similar and the left may even look brighter. That is the honest result: the difference exists in the file, not in the rendering your screen can produce.
Why a painted halo cannot go further
In an ordinary sRGB image, pixel values are relative. 255 means “as bright as white gets here”, and the operating system decides what that is — typically around 203 nits. A halo made of 255s is exactly as bright as the white background behind it. It reads as a glow only because it is soft and surrounds something.
Under PQ, values are absolute. A pixel does not say “as bright as white”; it names a luminance in nits on a scale running to 10,000. So the image can ask for 1,600 nits while the interface around it is still being drawn at 203, and the display honours both.
When each one is the right choice
Use a painted halo when
- The design must look identical to everyone
- You want visible spread and softness as the effect itself
- The output is print, or a video that will be re-encoded
Use real HDR when
- You want the bright part to actually stand out on modern screens
- The artwork should stay untouched
- It is going somewhere HDR survives, like a feed post or your own site
Questions
Can I just use a glow effect in Photoshop or Canva?
You can, and for many designs you should — a painted halo is predictable and works on every screen. What it cannot do is exceed white, because everything it draws is ordinary SDR pixels. If you want the bright part to actually out-shine the interface, the encoding has to change.
Can I combine the two?
Yes, and it often looks best. The editor has an optional halo that spreads light around the selected core, and that halo carries HDR luminance too — deliberately lower than the core, because a surround as bright as its centre reads as a flat blob rather than as light.
Does this work on photos as well as graphics?
Yes, though flat graphics hold up better. In 8-bit PQ, adjacent code values are far apart in luminance near the top of the range, so smooth gradients band where solid shapes do not. For photographic content the HDR PNG export is the safer choice.
Why does my exported file look washed out in some apps?
That app is ignoring the file's colour signalling and reading PQ code values as if they were sRGB. It is a viewer limitation rather than a fault in the file — the same file will look correct in a colour-managed browser.
Is there a size or usage limit?
No. It is free, with no account, no watermark and no export cap, and every export re-renders from your full-resolution original rather than from the preview.
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.