Make any color glow in HDR
Pick a colour from your image — or one region of it — and encode only that as an HDR highlight, with its hue held as closely as the colour volume allows.
- Detected palette, or sample any pixel with the eyedropper
- See the exact-colour brightness ceiling for your specific colour
- Preserve, Balanced and Max glow decide what gets traded
- Glow several colours at once, each at its own brightness
This is a free online tool for making any colour glow in HDR, not just white. Pick a colour from the detected palette or sample one from the image, and only those pixels are re-encoded with real absolute luminance. Each colour has a ceiling it cannot pass while staying exactly itself: Rec.2020 white reaches 10,000 nits, green 6,780, red 2,627, and blue only 593, because blue carries roughly 6% of the luminance. The tool computes that limit for your specific colour and lets you decide whether to hold the hue or trade saturation for brightness. Free, in your browser.
Free, with no account and no watermark. Your image is processed in your browser and never uploaded — read how HDR glow works.
Why saturated colours have different brightness limits
Making a colour brighter without changing it means scaling all three of its linear components by the same factor — that is what keeps chromaticity fixed. The limit arrives when the largest of those three components reaches the top of the PQ range.
Because luminance is a weighted sum of the three, and the weights are wildly uneven, colours run out at very different points. Green carries most of the luminance, so it gets far before any channel saturates. Blue carries almost none, so its blue channel hits the ceiling while the light output is still modest.
These are encoding-gamut limits computed from the BT.2020 matrix and PQ’s 10,000-nit component ceiling — not claims about any particular monitor. A real display will usually reach less.
How we preserve brand colours
The naive approach is to scale the colour until a channel clips and let it clip. That produces an uncontrolled hue shift: the clipped channel stops rising while the others keep going, so a bright orange slides toward yellow without anyone choosing that.
Instead, when a request goes past what the colour can hold, the colour is blended toward the neutral of the same luminance. Because the BT.2020 luma coefficients sum to one, that blend holds brightness exactly constant while chroma falls — so brightness and saturation become two separate dials rather than one uncontrolled outcome.
Preserve, Balanced and Max glow
All three run the same solver and differ only in how they weight hue error, chroma error and brightness shortfall. On fully saturated sRGB blue asked for 1,600 nits, against a ceiling of 806:
Colour error is measured as ΔE ITP in ICtCp, which stays meaningful above diffuse white where ordinary SDR difference metrics do not.
Glow one region, not every matching pixel
Colour alone is often not what someone means. In a photograph with a red jacket, a red sign and a red car, clicking the jacket should light the jacket.
Sampling with the eyedropper sets the scope to the connected region by default: the selection grows outward from the pixel you clicked, through neighbouring pixels that match, and stops at the edge of that object. Choosing a colour from the palette does the opposite and selects every matching pixel, because picking a swatch means the colour rather than the thing.
Matching itself is perceptual rather than exact. JPEG turns one flat brand colour into thousands of slightly different values, so an equality test would select almost nothing and leave speckled holes through the logo.
Questions
Can HDR glow be coloured at all?
Yes. Rec.2100 PQ encodes each channel independently, so a colour can carry absolute luminance exactly as white can. What differs is how far it can go: the ceiling depends on the colour’s chromaticity, not on the format.
Why can’t my blue be as bright as white?
Under the BT.2020 luminance coefficients blue contributes about 5.9% of the luminance, red 26.3% and green 67.8%. Scaling a colour up without changing it drives its largest channel into the PQ ceiling first, and for a saturated blue that happens while the overall luminance is still low.
Will my exact brand colour be preserved?
In Preserve mode, yes — brightness is capped at the point where the colour would have to change, and the chromaticity comes through untouched. Balanced and Max glow trade some saturation for more brightness, and the panel shows you how much.
Can I glow two colours at once?
Yes. Each selection is a layer with its own brightness, colour behaviour and match settings, and each is solved against its own colour limit. Where two selections overlap the result is blended between them rather than added.
How do I glow only one object, not every pixel of that colour?
Sample the object with the eyedropper and set the scope to “This region”. The selection then grows outward from the pixel you clicked through connected matching pixels, so a red jacket lights up without the red sign behind it.
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.