This was explained in demo website [1] that was submitted earlier today [2]
> It works by displaying a color whose brightness is way outside the standard range of sRGB color space.
> Unfortunately, this color cannot be represented with CSS colors (rgb(999,999,999) doesn’t work) or any of the widely-supported image formats. However, an HDR video can represent this color.
> It works by displaying a color whose brightness is way outside the standard range of sRGB color space.
> Unfortunately, this color cannot be represented with CSS colors (rgb(999,999,999) doesn’t work) or any of the widely-supported image formats. However, an HDR video can represent this color.
[1] https://notes.dt.in.th/HDRQRCode [2] https://news.ycombinator.com/item?id=36384625