The short explanation
Content mastered at 1000 nits arriving at a display capable of 600 has to be squeezed. Done crudely, everything above the ceiling clips to flat white and highlight detail disappears. Done well, the curve is rolled off gradually and most of the detail survives.
Where you run into it
Who does the tone mapping determines the result. With HDR10 the display does it, using one static figure for the whole title. With Dolby Vision the display does it with scene-by-scene guidance. With LLDV the source does it and hands over a finished picture.
That is why the same film can look meaningfully different depending on which route it takes through your chain — and why the numbers you advertise about your display are not a formality.
How the DR HDMI 8K handles it
The DR HDMI 8K does not tone-map; it decides who does and what they are told. By controlling the HDR flags and the Dolby Vision data block — primaries, luminance range, interface type — you choose whether the display or the source handles the mapping, and on what assumptions. On a projector, that choice is often the difference between a washed-out picture and a good one.
Want to test your own HDMI chain?
The DR HDMI 8K is sold through the HDFury.eu web shop.