Today’s Question: In looking at the specifications of different cameras, some offer full 16-bit per channel support, while others indicate they only support 14-bit or even 12-bit. How important is this camera specification in terms of image quality?
Tim’s Quick Answer: The bit depth of the camera determines the total number of color and tonal values the camera can reproduce. This primarily translates into smoother gradations of tone and color with a higher bit depth.
More Detail: When a camera’s image sensor records the light levels for a photographic image, it is converting an analog signal (based on light levels) into discrete digital values. During that analog-to-digital conversion, the bit depth determines how precisely the values are recorded. You can think of this as being similar to the precision of having more decimal places for a number. A price of $5 is not as precise as $4.9, and $4.99 would be more precise still.
A higher bit depth means there are more individual color and tonal values available for the final image, which in turn translates to smoother gradations of tone and color, as well as a greater ability to capture subtle details.
If you are using your camera’s JPEG capture option, the photos can only be stored as 8-bit per channel, because that is all that the JPEG file format supports. That translates to only 256 shades of gray for a JPEG image that is converted to black and white, or 16,777,216 total possible color and tonal values in a color image. This is regarded as being at about the limit of human vision in terms of discerning individual colors.
In other words, 8-bit per channel can yield excellent image quality for a color photo. However, when you apply adjustments to an image, a certain amount of detail is lost. With relatively strong adjustments, especially for a black and white image, there is a risk of “posterization”, meaning the loss of smooth gradations of tone and color. This will be exhibited as banding in the image, such as in a clear sky that should be represented by a very smooth gradation.
So, especially if you’ll need to apply relatively strong adjustments, a higher bit depth can be very helpful. For reference, a 12-bit per channel sensor provides 4,096 shades of gray and more than 68 billion possible color values. A 14-bit per channel sensor provides 16,384 shades of gray, or more than 4 trillion possible color values. And at 16-bits per channel, there are 65,536 shades of gray, or more than 281 trillion possible color values.
I would say that if you often convert photos to black and white, a higher bit depth offers tremendous value, and I would recommend opting for a camera with the highest bit depth possible. For color photography the issue is much less critical, especially if you don’t generally need to apply very strong adjustments to your photos. The higher bit-depth is good, but wouldn’t be the most important feature on my list if you only tend to process photos in full color.