Gray uniformity and the dirty screen effect: a practical check

How this is calculated

Look for four things on the gray pattern. Vignetting is a gradual darkening toward the corners or edges, common on large LCDs. Clouding is soft, uneven patches of lighter or darker gray, usually from an uneven backlight. Tint shift is when one side of the screen looks warmer or cooler than the other. The dirty screen effect, or DSE, is a blotchy, smudged texture that looks like dirt on the glass. You often don't notice it until something pans across the screen, like a sports broadcast or a game camera turning over grass or sky. Start with mid gray at 128, then try darker levels around 40 and lighter levels around 200. Different problems show at different levels. Sit at your normal distance and keep your head still while you look, since viewing angle changes brightness, especially on large or curved screens. If you see something, switch to real content that matches: a slow pan in a game, a hockey or football broadcast, or a large solid colored window you drag across the screen. DSE that you only see on a test pattern rarely matters. DSE that follows you around the ice rink does.

Verdict

Expect some falloff toward the edges, especially on screens larger than about 32 inches (81 cm). Treat the gray pattern as a way to find candidates, then confirm them with panning content. A colorimeter is the only way to put numbers on uniformity, and reviewers who measure it report that even good panels vary by several percent from center to corner.