Is 32-bit color depth enough?
Most monitors that I see these days support 32-bit color depth. I can tell the difference between 16-bit, 24-bit, and 32-bit color depth but I am wondering if the human eye could tell the difference between 40-bit, 48-bit, etc. color depth?
You have to be a little careful with the definitions.
24 bit per pixel and 32 bit per pixel
â€œ24 bitâ€ usually means 24 bits total per pixel, with 8 bits per channel for red, green and blue, or 16,777,216 total colours. This is sometimes referred to as 24 bit RGB.
â€œ32 bitâ€ also usually means 32 bits total per pixel, and 8 bits per channel, with an additional 8 bit alpha channel thatâ€™s used for transparency. 16,777,216 colours again. This is sometimes referred to as 32 bit RGBA.
24 bit and 32 bit can mean the same thing, in terms of possible colours. Itâ€™s also worth noting that transparency doesnâ€™t need to be sent to your display, because displays are opaque (you canâ€™t see through your display to whatâ€™s behind it, unless youâ€™re Tony Stark).
32 bit per channel
Also, 32 bit occasionally means 32 bits per channel (128 bits total per pixel). And, a lot of the time 32 bit per channel uses floating point numbers, rather than integers. (Iâ€™m happy to add more detail on floating point vs integer, if youâ€™d like.)
The OpenEXR format supports 32 bit float channels. That might sound excessive, but itâ€™s often used for VFX and rendered material, where heavy processing or colour correction may be involved, and large files are less of a concern.
16 bit per pixel or 16 bit per channel?
â€œ16 bitâ€ can typically mean two different things: 16 bits per pixel or 16 bits per channel. 16 bits per pixel works out to be 65,536 possible colours, and it definitely looks worse than 24 bits per pixel. 16 bits per channel means 281,474,976,710,656 total colours â€” well beyond human perception, but handy for processing.
RGB or CMYK?
All the above information assumes youâ€™re working with RGB or RGBA images. If an image is CMYK, it could be 8 bit per channel and 32 bit per pixel, with 8 bits for cyan, magenta, yellow and black channels.
I am wondering if the human eye could tell the difference between 40-bit, 48-bit, etc. color depth?
I think 8 bit per channel (24 bit per pixel) is on the fringe of what the human eye can easily distinguish, but thatâ€™s only part of the story. Processing can cause rounding and clipping, so additional colour depth can push errors beyond the point where humans and display technology can see them.
That is one of the reasons why itâ€™s common for RAW camera formats to be 10, 12 or even 14 bits per channel, which works out to be 30, 36 or 42 bits per pixel. Itâ€™s also common for those working on photos to import RAW to a 16 bit per channel document for further manipulation. Pro video recording can be 10 bits per channel or higher, too.
And, in cases where you might not think thereâ€™s any processing going on, there might be â€” colour management alone can introduce additional processing.
8 bits per channel means thereâ€™s only 256 levels of intensity, which really isnâ€™t much. Common causes for rounding errors to be visible when using 8 bits per channel:
- Using gradients stacked on top of each other, where layers arenâ€™t 100% opacity.
- Gradients drawn without decent dithering.
- Shadows with large blurs.
- Blurred objects.
- Blending modes and other compositing of two or more layers.
bpp vs bpc
Now might be a good time to mention the shorthand thatâ€™s often used for
bits per pixel,
bits per channel,
bpc. Itâ€™s common to write
32bpp etc when talking about these things, to remove the ambiguity of saying
Dynamic range and gamma
Dynamic range should also be factored in. Itâ€™s typical for displays to target sRGB (gamma of 2.2). Wider dynamic range means the number of possible values are stretched further, so more colour resolution is needed.
Is 8 bits per channel enough for final asset delivery?
Yes, most of the time, depending on the use.
Is 8 bits per channel enough for creation?
Sometimes. But, often it is not.
Please note: Iâ€™ve added some more information relating to digijim and Warren Youngâ€™s comments below.