What 10-bit video means for what you see

The number appears on every 4K film and almost nobody explains it. It is the difference between a clean night sky and one full of visible steps.

Bits are shades, not resolution

Bit depth has nothing to do with how many pixels there are. It is how many shades of each colour the file can describe. 8-bit manages 256 per channel, around 16.7 million colours in total. 10-bit manages 1,024 per channel — over a billion.

Where you notice it

Anywhere colour changes gradually: a sunset, a dark interior, smoke, a wall lit from one side. In 8-bit those gradients arrive as visible bands. In 10-bit they are smooth, because there are enough shades to describe the change.

Getting it on screen

A 10-bit file needs a player that decodes 10 bits and passes them through rather than flattening to 8. AIX Player does, and tone-maps HDR on your graphics card so highlights and shadows keep their detail on an ordinary monitor.

Where you will actually notice it

Not in a bright, busy scene — there is too much going on to see the difference. You notice it in gradients: a sunset fading through orange to blue, smoke drifting through a shaft of light, a wall lit from one side, the dark corners of an interior. In 8-bit these arrive as visible steps, sometimes called banding. In 10-bit the same gradient is smooth, because there are enough shades to describe every stage of the change.

Why 10-bit files are barely larger

It sounds as though four times the shades should mean a much bigger file, but it does not work that way. Smooth gradients compress more efficiently than banded ones, so much of the extra data pays for itself. A 10-bit encode is often within a few percent of its 8-bit equivalent, and occasionally smaller — which is why there is no real reason to prefer 8-bit when both exist.

What a player has to do with it

Carrying 10 bits through to the screen is the part that gets skipped. A player that decodes 10-bit and then flattens it to 8 before display gives you the banding back, and the file gets blamed for it. AIX Player keeps the depth through decoding and tone mapping, so what reaches your monitor is as smooth as the file allows.

Worth knowing