8 Bit vs. 16 Bit

      The difference between an 8-bit and a 16-bit image file is the number of tonal values that can be recorded. (Anything over 8 bits per channel is generally referred to as high bit.) An 8-bit-per-channel capture contains up to 256 tonal values for each of the three color channels, because each bit can store one of two possible values, and there are 8 bits. That translates into two raised to the power of eight, which results in 256 possible tonal values. A 16-bit image can store up to 65,536 tonal values per channel, or two raised to the power of 16. The actual analog-to-digital conversion that takes place within digital cameras supports 8 bits (256 tonal values per channel), 12 bits (4,096 tonal values per channel), 14 bits (16,384 tonal values per channel), or 16 bits (65,536 tonal values per channel) with most cameras using 12 bits or 14 bits.
     When working with a single exposure, imaging software only supports 8-bit and 16-bit-per-channel modes; anything over 8 bits per channel will be stored as a 16-bit-per-channel image, even if the image doesn’t actually contain that level of information. When you start with a high-bit image by capturing the image in the RAW file format, you have more tonal information available when making your adjustments. Even if your adjustments—such as increases in contrast or other changes—cause a loss of certain tonal values, the huge number of available values means you’ll almost certainly end up with many more tonal values per channel than if you started with an 8-bit file. That means that even with relatively large adjustments in a high-bit file, you can still end up with perfectly smooth gradations in the final output.

    Working in 16-bit-per-channel mode offers a number of advantages, not the least of which is helping to ensure smooth gradations of tone and color within the image, even with the application of strong adjustments to the image. Because the bit depth is doubled for a 16-bit-per-channel image relative to an 8-bit-per-channel image, this means the actual file size will be double. However, since image quality is our primary concern we feel the advantages of a high-bit workflow far exceed the (relatively low) extra storage costs and other drawbacks, and thus recommend always working in 16-bit-per-channel mode.