Test Patterns, End to End

What each field is checking

• Grid — a fine crosshatch. Lines should run dead straight edge to edge; a wave near a corner is lens-style geometric distortion, common on curved or budget panels.
• Grayscale and channel ramps — four smooth gradients (black-to-white, then black-to-red, -green, -blue). A visible band or step where the eye expects a smooth slope is the panel's color depth showing its limit, not a rendering glitch.
• Uniformity steps — five flat greys at 10/30/50/70/90%. Same principle as the backlight test's black field, but at brightness levels a movie or spreadsheet actually uses — clouding shows up here that pure black never reveals.
• Moiré weave — a checkerboard fine enough to fight with your panel's own subpixel grid. Fuzzy rainbow interference across it is moiré from a scaling mismatch; a scanned photo or a screen recording of a screen does the same thing.

Reading the ramps without fooling yourself

Banding on a laptop panel is usually 8-bit color depth doing exactly what it's rated for — smooth gradients are the hardest thing an LCD does, and a cheap panel will show faint steps in a sunset photo before you ever notice it elsewhere. What's worth flagging: a band that's sharp-edged and always in the same spot no matter the source material, especially near one edge of the screen — that's closer to a panel fault than ordinary quantization.