… for Codecs & Media

Tip #541: What is Bit Depth?

Larry Jordan – LarryJordan.com

Bit depth is always expressed as a power of 2.

Bit depth determines the number of steps between the minimum and maximum of a value. The bit depth number (8, 16, 24) actually describes a power of 2.

• A bit depth of 4 = 2^4 = 16 steps
• A bit depth of 8 = 2^8 = 256 steps
• A bit depth of 10 = 2^10 = 1,024 steps
• A bit depth of 16 = 2^16 = 65,536 steps

In the screen shot, the top row represents an image with a bit depth of 8. The lower image represents an image with a bit depth of 10.

NOTE: These are illustrations, actual bit depth variations don’t look quite this bad.

Where higher bit depths help image quality is in color grading, gradients and anywhere smooth shading from one value to another is important.

EXTRA CREDIT

In audio, bit depth determines the dynamic range; the amount of variation in audio levels between soft and loud. Bit depth is only meaningful in reference to a PCM digital signal (i.e. WAV or AIF). Non-PCM formats, such as lossy compression formats (i.e. MP3), do not have associated bit depths.