Adding two bits

Accurate color. That’s an important thing. Herein lies the tale of adding just two bits.

Color as represented in a computer is typically made up of a 24-bit composite value arranged as 8 bits each of Red, Green and Blue (RGB). 24 bits allows for 16,777,216 combinations – and that’s enough for anything, right?

Let’s see about that. Human perception is believed to encompass 12 – 15 ‘stops’ of dynamic range from light to dark; thus at least some among us may be able to detect a full 16 bits just of light to dark. 24-bit color allows for 256 values (light to dark) of each of the three colors… hmm… 256 values is only 8 bits… only a fraction of what we can actually perceive.

Before looking to increase the range, the question is, is it really necessary for most computer applications? No. Historically website builders worked within a limited “web-safe” color palette of just 216 colors. The first two iterations of the iPhone supported 18-bit color (262,144 colors); this is still true of most feature phones on the market today – and of many older model desktop displays (including the 20-inch iMac).

Today pretty much everything outside of a few budget notebooks are using 24-bit displays, even if much of the content we view doesn’t need so many colors. But what about the applications where the extra color depth is important?

One solution might be to go for the maximum — make all the paths 16 bits; but this becomes a sizable nightmare rather quickly. 48 bit color is certainly doable – but you’ll need a very fast machine and loads of memory and Adobe Photoshop to pull this off… and you’ll have to do your work partly blind, because no [affordable] display hardware is capable of showing you the full 48 bits.

But we can quadruple the number of available colors by merely adding two bits to each of our three colors! And 30-bit is much easier for our hardware to handle.

Still, the entire workflow has to support 30-bit operations. Source – my cameras support either 12 bits/channel or more; 36 bits input. Processor is rated to handle 64-bit operations. Video card supports 24-bit, 30-bit or 48-bit output… and the newest monitor also operates in 30-bit mode. Software support – Adobe Photoshop CS5.5 handles it (admittedly a bit awkwardly), as does certain industry-specific* modeling software.

I’m doing this in Windows 7, which supports a 30-bit color path if you turn off “Aero.” If you’re on a Mac, complain to Cupertino because your O/S doesn’t support 30-bit colors, even if [some of] your hardware does.


* NDAs are “fun.”

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