Visual defect and dead-pixel detection on TV panels

Need

A dead pixel is one among the millions on the screen; if the camera sampling is not matched to the pixel pitch of the panel, moiré appears in the image and masks a single-pixel defect. Mura is a low-contrast patch with no sharp boundary. Ambient light and reflections on the panel hide both defects.

Solution approach

In a dark room the panel shows black, white and grey test screens in turn; the pattern generator triggers the camera at each change and one frame covers the whole panel. No lighting is added: the panel is the light source. Pixels darker than their neighbours are counted on white, bright pixels on black; on grey, the luminance difference left after low-pass filtering is the mura contrast.

Process steps

1. 01

   Test screen

   The panel shows a uniform test screen: black, white or grey; the pattern generator triggers the camera.

2. 02

   Acquire

   The camera captures the whole screen in a single frame in the dark.

3. 03

   Analyse

   The image is scanned for pixels and regions that deviate from their neighbours.

4. 04

   Decide

   Defect count and contrast are compared with the limits; the result is shown on the stack light.