Bit stands for “binary device” and refers to the smallest piece of information. It has a value of either 0 or 1. In digital photography, 0 is assigned to black, and 1, to white.
How Bits Record Color
Users of digital image editing programs such as Adobe Photoshop are familiar with different-value bit images. The very common 8-bit image has 256 available tones, ranging from 00000000 (value number 0, or black) to 11111111 (value number 255, or white). Notice that there are eight numbers in each of those sequences. This is because 8 bits equal 1 byte, and 1 byte can represent 256 different states (or colors). Therefore, by switching the combination of those 1s and 0s in the bit sequence, the computer can create one of 256 variants of color (2^8th power, with 2 coming from the binary code of 1s and 0s).
Understanding 8-Bit, 24-Bit, and 12- or 16-Bit
JPEG images are often referred to as 24-bit images. This is because this file format can store up to 8 bits of data in each of three color channels (RGB, or red, green, and blue). Higher bit rates such as 12 or 16 are used in many DSLRs to create a more dynamic range of colors. A 16-bit image can have 65,653 levels of color information (2^16th power), and a 12-bit image can have 4,096 levels (2^12th power). DSLRs use most of the tones on the brightest stops, which leaves very few tones for the darkest stops (where the human eye is at its most sensitive). Even a 16-bit image, for instance, will have only 16 tones to describe the darkest stop in the photo. The brightest stop, in comparison, will have 32,768 tones!
About Printing Black and White Images
The average inkjet printer works on the 8-bit scale, too. When printing black and white images on your inkjet, don’t set it to print using only the black inks (grayscale printing). This is a great way to save ink when printing out text, but it will not produce a good photo print. The average printer has one, maybe two, black ink cartridges and three color cartridges (in CMYK). The computer transmits the data of an image to be printed using those 256 variants of color. If you were to rely on only the black ink cartridges to handle that range, the details of the picture would be lost, and gradients would not print correctly. It simply cannot produce 256 variants using a single cartridge. Even though the black and white photograph is an absence of color, it still relies on those very fine-tuned 8-bit color channels to form all of the different tones of black, gray, and white. If you’re a photographer, this reliance on color channels is important to understand if you want a digital photograph with the look of a black and white photograph that was produced by film on paper.
