question about 32-bit color

[compusic]

by searching this forum, can't find the answer.

It seems "32-bit color depth" is used to refer to different color depth, very confusing. can someone make it clear?

well, I just give some examples I have encountered.

for crt or lcd display, 32-bit means 24-bit RGB and the extra 8-bit is for transparence, right?

and some softwares process video data in 10-bit resolution for each channel, and this is also called by someone as 32-bit color, though only 30-bit is used, and the eatra 2-bit may or may not be used for transparence.

some file format allows 32-bit color for each channel, and the total depth without transparence is 96-bit.

but some NLE softwares have 32-bit color option for export or render, and don't tell whether it's 10-bit or 8-bit for each channel, such as Premiere.

[edDV]

For Premiere type editors it goes something like this.

24 bit can be RGB or YCbCr with 8 bits for each pixel per component.
32 bit adds an 8 bit alpha channel for pixel level transparency

RGB is usually sampled 4:4:4 @13.5 MS/s with Alpha adding another 4 for 4:4:4:4.

YCbCr is usually sampled 4:2:2 with Cb and Cr half sampled at 6.75 MHz
If Alpha is added you have 4:2:2:4.
Alpha is fully sampled and behaves just like a second luminance channel.

In CCIR-601 it was possible to do YCbCrA in 4:4:4:4. This was useful for higher color accuracy (Pantone chip calibrated) and smoother special effects manipulation.

All of the above uses 8 bit per component and dates back to the middle 1980's. This all became standardized as ITU-REC-601 and formed the basis for MPeg2, DV, DVD, DVB and ASTC.

Premiere Pro, Final Cut Pro, Avid XPress, Vegas and others can now handle 10bit and higher YCbCr or RGB. 10bit is common for post houses. Special SDI (SMPTE-259M/292M) real time hardware cards are usually used to support these higher bit depths (e.g. Aja and BlackMagic).

High definition video uses the same bit depths but increases horizontal sample rates and number of lines. HD also comes in RGBA and YCbCrA flavors.