Purpose
Use a greyscale ramp when a sky, a desktop background or a game looks striped. Channel ramps are there when one colour seems to break before the others. Near-black and highlight ranges shorten the ramp so shadow and white-end steps are easier to see.
Preparation
Note vivid, cinema or night modes if they are on. You do not have to switch them off. Judge the screen the way you use it, and say so in your notes if you compare later.
What to look for
Visible strips, a sudden jump, or a colour cast along the ramp. The 8-band and 16-band modes are flat blocks on purpose, so you can see a known step beside the browser’s smooth blend.
Common false positives
Scaling, remote desktop, a JPEG screenshot, and the browser’s own blend. Do not decide bit depth from a photo of the ramp.
Limitations
Smooth mode is browser-interpolated sRGB between two exact ends. Stepped mode fills each band with an exact RGB from this site. Neither mode measures the panel. This is not an HDR test.
Questions
Why do I see steps on a smooth ramp?
The browser, graphics system and panel can all quantise a ramp. A step is a clue, not proof of bit depth. The 8-band and 16-band modes are deliberate flat strips so you can compare.
Is the smooth ramp exact at every pixel?
The ends are exact hex values. The pixels between them are interpolated by the browser in sRGB. This site does not claim a measured 1:1 ramp.
What does the shadow range mean?
It runs from RGB 0 to RGB 26, about 0–10% of 255. It is a signal level, not a reading in nits.
Can this test HDR?
No. These are ordinary sRGB values. They do not drive an HDR brightness curve.