Prepare the display
Use the monitor’s native resolution where possible, allow the display to settle and reduce direct reflections. Clean visible dust using the manufacturer’s instructions. A speck on the surface can look like a dark pixel but will not follow the same pattern as an electrical subpixel defect.
Compare across colors
A constantly dark point is easiest to see on bright patterns; a constantly lit point is easier on black. Red, green and blue patterns can reveal a subpixel that fails to change normally. Inspect the same location across patterns and at a sensible distance before recording a suspected problem.
Record observation rather than diagnosis
Mark the approximate position and note which patterns make it visible. The browser cannot read the physical panel, so no automatic pass or fail is issued. If the problem persists, compare the result with the manufacturer’s pixel policy and provide clear observations rather than assuming every dot has the same cause.
Run a consistent pattern sequence
Choose a starting pattern, generate the report and select Open display test. If the browser grants full screen, hide the controls with H while inspecting; if it does not, the viewer states that browser-area mode is active. Move through black, white, red, green and blue with the controls or arrow keys, then use gray and grid for broader checks.
Enable Mark positions only when you want to record a location. Click the suspected area, change pattern and compare the same position again. The tool stores observations, not camera measurements. Exit with the visible close control or Escape, and avoid pressing or rubbing the panel to test a suspicious point.
Separate screen content from panel behavior
Move a normal application window over the area after leaving the test. A defect that follows a picture or window belongs to the content or rendering path; a mark fixed to the physical panel needs a different investigation. Surface dust may change appearance with viewing angle. Document which patterns reveal the issue before classifying it, because a dark point, a bright subpixel and broad backlight unevenness are different observations.