Bit depth explained: 8, 10 or 16 bit — and why gradients get stripes (banding)

What bit depth measures

Bit depth (color depth) says how many brightness levels an image can distinguish per color channel. More levels = finer transitions:

16.7 million colors sounds like more than enough — and for the finished image it usually is. The problem doesn't appear in the number of colors, but in the fine gradations within a smooth transition.

Why gradients get stripes (banding)

Picture a sky fading from light blue to dark blue — over maybe 2000 pixels of height. If that transition would need more fine brightness steps than the 256 levels of 8 bit can provide, the image has to “jump”: instead of a stepless gradient, visible stripes appear — banding. Each stripe is a region forced to share one of the 256 available levels. Compression makes it worse, because it lumps fine differences together even more.

Three ways against banding

1. Edit at higher bit depth. If you push a gradient hard (exposure, contrast), work in 16 bit — then enough intermediate levels survive, and only the final export drops to 8 bit.
2. Add a little noise (dithering).A touch of fine noise visually “breaks up” the hard step edges — the eye reads the gradient as stepless again. Many export dialogs offer this.
3. Choose a modern format. WebP and AVIF often handle gradients more gently than a heavily compressed JPG; AVIF also supports 10 bit.

When higher bit depth really matters

• Editing with strong adjustments — 16 bit as headroom against banding and tonal breaks.
• RAW photography — cameras deliver 12–14 bit so there's room in shadows and highlights.
• HDR content — uses 10 bit and more to represent the extended brightness range.

And for the normal web?

Reassurance: 8 bit is enough for the vast majority of web images. JPG and standard PNG are 8 bit, and for photos that's sufficient — banding only appears in large, smooth areas. Higher bit depth is a matter of editing and special outputs, not the normal delivery format. If your final JPG shows visible banding, combine a “high quality setting” (less compression, see JPEG artifacts) with a bit of dithering.

In short

• Bit depth = levels per channel, not just total colors.
• Banding happens when smooth gradients run out of levels.
• Edit in 16 bit, dither, or use a modern format.
• 8 bit is fine to deliver — depth matters for editing/HDR.