Two different things
People lump “HDR” and “wide colour” together, but they are separate.
- Colour space (gamut) is the range of colours the numbers in the file can mean. Display P3 is wider than sRGB.
- Dynamic range is the span of brightness. HDR means a greater span than a normal screen shows by default.
A photo can have one without the other. You treat them differently when you convert.
Display P3
Display P3 is a wide-gamut RGB space, and the ICC registry entry for Display P3 lists Apple as the responsible organization, with the primaries and the white point (D65). It has more saturated reds and greens than sRGB. The CSS Color Level 4 specification includes display-p3 as a colour space so that web pages can use it too.
Pixel values are only meaningful together with a colour profile. An ICC profile, defined by the ICC specification, is the standard way to say which space the numbers are in. HEIC photos from iPhones usually carry a Display P3 profile.
The problem when you strip the profile
If a P3 image is saved as JPG but the profile is dropped, software assumes sRGB and the saturated colours look flatter. Or the reverse: if the pixels are already sRGB but are tagged P3, colours look too punchy. This is why “my converted photo looks dull” is such a common complaint.
What FromHEIC does by default
- It transforms pixels to sRGB using the file’s embedded profile. Colours should look right in ordinary software, at the cost of squeezing the very saturated colours into sRGB’s smaller range.
- An option keeps the original profile embedded instead. The pixels stay in that space, and software that honours profiles shows the wider colours.
Which to choose? For websites, messaging and forms, use the default. For editing in a colour-managed app or printing, keep the profile (or output TIFF, which embeds the ICC profile). Check the profile with the colour profile viewer before and after.
Bit depth
JPEG is 8 bits per channel; MDN says as much about JPEG’s colour modes. If the HEIC carries more than 8 bits, a JPG will not keep the extra precision. FromHEIC can keep that precision in one place: a 16-bit TIFF from a HEIC with more than 8 bits per channel holds the real extra tonal data. Its other outputs, including PNG and JPG, are 8-bit, and an 8-bit HEIC stays 8-bit in substance even inside a 16-bit file.
HDR and gain maps
Some HEIC files carry an auxiliary image used for HDR rendering, often called a gain map. The libheif project lists support for auxiliary images, and FromHEIC’s HDR gain map inspector reports whether a file has one, and the extract tool can pull gain maps out as separate images.
What a conversion does with it: the output is a standard single image. FromHEIC does not claim to preserve HDR rendering in JPG, PNG, WebP, AVIF or TIFF. Expect an ordinary SDR picture. If the HDR look matters, keep the original HEIC and view it in software that understands it. How a phone or app renders the gain map varies, so check the manufacturer’s documentation for your device.
A short decision guide
| Goal | Choice |
|---|---|
| Share on the web or by message | JPG with sRGB (default) |
| Keep the wide colours in an editor | TIFF, or JPG/PNG with profile kept |
| No extra loss after decode | PNG |
| Preserve HDR rendering | Keep the HEIC |
Check your result
- Open the original in the colour profile viewer.
- Convert.
- Compare in two programs. If colours differ between them, one of them is ignoring the profile.
For conversions that also look rotated wrongly, see orientation and colour. For the general format comparison, see HEIC vs JPG.