Supernova
Back to HDR PNG Converter
✦ § 00 — Overview

How HDR PNG Conversion Works

Supernova converts standard images into HDR PNGs that glow on HDR displays. On compatible browsers/displays, preview shows the converted HDR output directly; otherwise it falls back to fast SDR preview while the final download stays full HDR PQ.

§ 01 — The pipeline

The Pipeline

1. Decode your image into raw 8-bit RGBA pixels via Canvas
2. Live preview path: on compatible browsers/displays, render a downscaled converted HDR PNG; otherwise use a fast SDR approximation for responsive updates
3. Export path: apply look controls in linear light, remap boost to HDR luminance, then PQ-encode to 16-bit BT.2020
4. Wrap in a PNG with HDR metadata chunks (cICP, cHRM, iCCP)
§ 02 — Controls

The Controls

  • Boost — HDR export brightness control. 1.0≈100 nits, 4.0≈1600 nits, 10≈10000 nits in the final PNG.
  • Saturation — primary color intensity control shown in the main panel for quick edits.
  • Advanced — Exposure, Temperature, Tint, Gamma, Contrast, Blacks, Whites, Clarity, Highlight Saturation, Highlight Roll-off, Shadow Lift, Shadow Glow, and Vibrance for finer grading.
  • Preview behavior — preview uses the converted HDR PNG when the browser/display supports it, with automatic SDR fallback otherwise.
§ 03 — Transfer

What is PQ?

PQ (Perceptual Quantizer) is the transfer function behind HDR10 and Dolby Vision. Unlike gamma (~2.2) which tops out at 100 nits, PQ maps luminance up to 10,000 nits.

Its curve allocates more precision to dim regions where our eyes are most sensitive — far more efficient than gamma for HDR's wide brightness range.

γ 2.2PQLinear lightEncoded signal0101
§ 04 — Metadata

The Metadata

A valid HDR PNG needs metadata so the display knows how to interpret the pixels:

  • cICP — declares BT.2020 primaries + PQ transfer. The primary HDR signal.
  • cHRM — BT.2020 chromaticity coordinates as fallback.
  • iCCP — embedded ICC profile for broadest compatibility. Triggers EDR on macOS.
RGBBT.2020sRGBxy
§ 05 — Support

Compatibility

Requires an HDR display and a supported browser. On SDR displays, the image renders as a normal PNG.

ChromecICPFull HDR rendering
EdgecICPFull HDR rendering
SafariICC / EDRmacOS only
Firefox—No extended brightness
§ 06 — Privacy

Privacy

100% client-side. No uploads, no server, no analytics. Your images never leave your device.

§ 07 — Guides

Related Guides