What Is Bit Depth?

Bit depth tells you how much room a file sets aside for every piece of color information it stores. More bits mean finer steps between one shade and the next. Fewer bits mean the file has to round colors off to the nearest value it can describe.

Which files carry a bit depth

Bit depth, also known as color depth, turns up in bitmapped images and in video. That covers JPEG, PNG, TIFF, BMP, GIF and camera RAW files, plus the video stream inside formats like MP4 and MOV. The value is decided by whatever produced the file: the camera or scanner that captured it, or the program that saved or exported it. You cannot type it in by hand, and changing it means re-saving the file.

Depending on the field, the number describes either a single pixel as a whole or one color component of that pixel. Some reports list it per channel, as 8 8 8 for the red, green and blue components of a photo. Others add those up and show the total, 24. Audio files use the same word for a different measurement: there, a bit depth of 16 or 24 describes how finely each sound sample is measured, not color.

What the numbers mean

The value sets the number of tones the file is able to describe. The higher the number, the more tones, and the smoother the transition between them. Common values include:

• 1 - two tones only, pure black and white, as used by fax-style TIFF scans
• 8 - 256 tones, typical for a grayscale image or an image with a fixed color palette
• 24 - 8 bits each for red, green and blue, which gives 16,777,216 possible colors
• 32 - the same three channels plus 8 bits of transparency
• 48 - 16 bits per channel, used by scanners, RAW conversions and edit-friendly TIFF files

Grayscale images usually sit between 1 and 8 bits, although higher values exist. Color images normally run from 8 bits upwards. Video is commonly 8 bits per channel, with 10 bits used for high dynamic range material.

Why it matters for your file

Bit depth is the difference between a smooth sky and a sky that breaks into visible bands of color. At low depths there simply are not enough steps to describe a gentle gradient, so the file shows stripes. A high depth also gives you headroom: a 16-bit-per-channel image survives heavy brightness and color correction that would tear a shallower one apart.

It costs space. Every extra bit per pixel makes the uncompressed data larger, so a 48-bit TIFF is far heavier than an 8-bit version of the same picture. It can also cost compatibility, because older software may refuse a 16-bit-per-channel file, and 10-bit video needs a player that supports it.

For archiving, it is worth checking before you convert. Reducing bit depth throws tones away for good, and raising it again later does not bring them back. The field says nothing about you or your device, only about how the file stores its colors, so there is no privacy question here.