You convert an iPhone photo to JPG and the glowing sky suddenly looks flat. The converter did not break your image; it stripped the hidden brightness map and wide colour space that standard JPG files cannot hold.
Standard JPG files cannot hold your iPhone's extra brightness data. When you view a photo on a modern iPhone, the screen physically brightens just for the highlights in that picture. A traditional JPG has no way to tell your monitor to do that.
Conversion forces 10-bit colour and Display P3 down into 8-bit sRGB. Apple captures over a billion colour shades in a wide gamut. Browser converters map those down to 16.7 million shades so the resulting JPG looks normal on every screen and web form.
Washed-out colours happen when a tool ignores the colour profile instead of converting it. If neon reds or deep greens turn grey after conversion, the software stripped the Display P3 tag without recalculating the pixel values for sRGB.
When you take a photo in bright sunlight, your iPhone does not just save one picture inside the HEIC container. It saves a standard dynamic range (SDR) base image alongside a secondary monochrome image called an HDR gain map. When you open the Photos app on an XDR display, iOS reads the base image and uses the gain map as a multiplier, pushing individual pixels on the physical screen far brighter than the white background of the app itself.
Traditional JPEG encoders—including the standard HTML5 canvas inside your web browser—only output an 8-bit baseline image. When you convert a HEIC file, the decoder reads the main image track and discards the auxiliary gain map track. The sunbeams, neon signs, and reflections that literally glowed on your phone are flattened down to standard white (RGB 255, 255, 255). The detail is still there because Apple tone-maps the base image before saving it, but the physical blinding brightness is gone.
Brightness is only half of the shift. The other half is colour depth and colour space. Modern iPhones encode HEIC images using 10-bit HEVC inside the Display P3 colour gamut. Display P3 covers much deeper reds, oranges, and vibrant greens than the older sRGB standard used across the web.
| Property | iPhone HDR HEIC | Standard Browser JPG |
|---|---|---|
| Bit depth per channel | 10-bit (1,024 levels) | 8-bit (256 levels) |
| Total possible colours | 1.07 billion | 16.7 million |
| Colour space | Display P3 (wide gamut) | sRGB (standard web gamut) |
| Highlight headroom | Auxiliary HDR gain map | Clamped at peak white (255) |
When a converter turns that 10-bit P3 image into an 8-bit JPG, two things happen. If the tool simply drops the P3 ICC profile without converting the numbers, any sRGB viewer will misread the pixel values, making the whole photo look dull and desaturated. If the tool converts the colour space properly—as browser canvas pipelines do—most colours match closely, though extreme neon shades are pulled inward to the nearest colour sRGB can actually represent. This happens alongside other container changes, just like when you convert a HEIC with transparency to a solid JPG.
Before you blame a converter for ruining a sunset photo, check what the underlying base image looks like on your iPhone with the screen booster turned off. You can toggle this directly in iOS without altering your files:
What you see on your screen now is the exact tone-mapped SDR base image that a good HEIC to JPG converter will give you.
If a photo looks too dark or flat once the HDR headroom is gone, you can adjust it before or during your workflow so the 8-bit JPG still has punch:
When you drop a file into the HEIC to JPG converter, it decodes the 10-bit image in your browser memory and uses your browser's native colour management engine to map Display P3 smoothly into standard 8-bit sRGB. You lose the proprietary iPhone screen glow, which standard JPGs cannot carry, but your skin tones, skies, and shadows stay accurate without that grey, washed-out shift.
Your photos are decoded in your own browser — open the converter and see.
First published: 27 October 2026