How many bits per channel is my laptop screen?

Question

Because of the ambiguity associated with naming schemes for color depth, I'm not sure how many types of colors my laptop screen is actually capable of displaying. In Windows 10, when I go to my display adapter properties, I see this:

32 bit almost certainly does NOT mean 32 bits per channel (RGB), but if it means either 8 or 10 bits per channel, what are the remaining 8 or 2 bits used for? In terms of, for example, a PNG image, 32 bit usually means 8 bits per channel, with an alpha channel being represented as the last 8 bits. But, to me, that makes no sense for a screen since an alpha channel has no meaning (the pixels on a screen are only red, blue and green; alpha makes no sense).

If I, for example, were to play back a video encoded using a 10 bit per channel codec, can this laptop screen actually display the extra colors? I just don't understand what kind of bit-depth my screen is actually displaying.

Answer 1

In this context, "32 bits" means 8 bits per channel, with the remaining 8 bits going unused.

Many budget laptop displays actually use 6-bit color and simulate the remaining 2 bits through temporal dithering. This functionality is internal to the display panel, though; it would not be visible through software.

Answer 2

The 32-bit does indeed mean it is 8-bits per colour channel. It is RGBA or Red, Green, Blue & Alpha.

Bear in mind though that at the stage you are configuring is the colour depth handled by the graphics card, not the display itself. At this level the alpha channel is relevant and can be used to apply transparency effects prior to the data being converted to something the display can handle.

The alpha channel is not "unused" or irrelevant, it is just used at a stage earlier than the actual display output.

Windows 7 and its "glass" user interface style made extensive use of the alpha channel and Windows 10 still does. The graphics card handles compositing and transparency effects and being able to see things that are behind other things.

The data is then effectively flattened in order to send pure RGB (or YCbCr or whatever the display wants) data.