The story of Bit Depth starts with the pixel, the smallest unit of digital visual information. The word Pixel is a combination of the words picture and element. A digital image is made of a grid (rows and columns) with millions of square pixels, each with a specific coordinate on the grid. Every pixel has a small file of information attached describing its appearance.
These files contain information about how a pixel should appear, its lightness or darkness and its color. It’s a lot like the way mosaics are made. Google “pixilated image”. If we zoom way in, you can see what I’m talking about.
Pixels can represent colors in different modes, CMYK (which stands for cyan, magenta, yellow, and black), Greyscale, or RGB (which stands for red, green, and blue). Our main concern here is with the RGB mode. In this mode, each pixel is designated as one of the additive primary colors of light; red, green, or blue. To see an illustration of how RGB colors combine to form different colors, Google “additive primary colors of light”. Together, you will see the colors create white light.
The pixels, or photosites, on a CCD (charge coupled device) only record a range of tonality from pure white to pure black. To render an image in color, there are small color filters on top of the photosite sensors. The red, green, and blue filters are arranged in a pattern called the Bayer Array. Google “Bayer Array” to see what it looks like.
When the array of millions of RGB pixels are viewed together in their grid-work to form a picture, they appear as the many colors we see with our eyes.
Bit Depth is the color space, or color information of an individual pixel. It’s the number of tones of color that a pixel can represent. The higher the number of bits, the more tones and colors the pixel can display. The number of different tones a pixel can display is called its bit depth.
One bit is the smallest measure of a pixel’s color space and represents only 2 options, black and white. An example of a 1 bit image would be a photo of a black ink drawing on white paper. Printers, color monitors and many digital cameras have an 8 bit color space which will yield 256 tones per channel.
RGB color is comprised of a red, green, and blue channel. Each of these channels is 8 bits (each channel with 256 tones of black to white) so when all three are combined to produce full color, it is 24 bits.
More and more cameras and editing software are operating in 16 bits, which yields 65,536 tones of color per channel. This is called a high bit file. The larger the bit depth, the more data there is, requiring a more robust processor to handle the increase in data. You also need more memory and storage because the files for 16 bits and beyond are exponentially larger than 8 bit. For example 24 bits yields 16,777,216 colors. 48 bits has over 281 trillion distinct colors per channel.
The capacity of the digital camera’s bit depth will continue to increase over time. Photographic technology never stops growing, so we can’t stop growing! These are the tools of our art. So, we have to keep on learning, bit by bit.