Bit depth is a term we hear floating around a lot in the worlds of photography and video. And, with the latter of those two topics, many confuse bit depth with bitrate. But what exactly is bit depth? In this video from ZY Productions, we look at the topic of bit depth to find out exactly what it means, and how it affects your images.
One thing to note when we typically talk about bit depth and “8-bit images” is that we’re talking 8 bits in each of the three red, green and blue colour channels. So, 24-bits in total. But what is it? In practical terms, it’s the number of shades of grey between pure black and pure white within each of those colour channels.
A bit is basically a binary on-off switch. And each bit in binary is analogous to a “stop” when we talk about light measure. Each stop of light you add to your scene doubles the amount of light, and so with each bit you add to a number you get doubles the total number of potential values. 1-bit is 2 values, off or on, pure black & white. 2-bit is 4 values; Black, white and a couple of shades of grey. 3-bit is 8 values, 4-bit is 16, and so on. By the time we reach 8-bit, we’re up to 256 values. But that’s 256 values per colour channel. With three colour channels, that’s 256 (red) x 256 (green) x 256 (blue) for a total of around 16.7 million individual colours. When we add 2 more bits, it doesn’t sound like a lot, but each extra but doubles the value. 9-bit is 512, 10-bit is 1024. That’s 1,073,741,824 potential colours. When we start getting into things like 12-bit and 14-bit raw, that’s 4,096 and 16,384 values per colour channel respectively. For the 16-bit raw capability of many medium format cameras, that’s 65,536 total potential values from pure black to pure white for each colour channel.
8 bits per colour channel: 16,777,216 total colours10 bits per colour channel: 1,073,741,824 total colours12 bits per colour channel: 73,876,521,536 total colours14 bits per colour channel: 4,398,046,511,104 total colours16 bits per colour channel: 281,474,976,710,656 total colours
So, essentially, more bits means more colours, a lot more subtle tone between different colours and shades with much less banding. It also often means the potential for more dynamic range. This is why medium format guys rave about the subtlety of tones they can see in their 16-bit raw images. Ultimately, even though you might be delivering 8-bit video or photos in the end, higher bit depth raws and footage will offer you a much better starting point to create a final result that better matches your vision.
