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Shadow Mask Inspection

 

 

Introduction

This research was done in conjunction with LG Electronics, the objective of which was to detect defects in CRT shadow masks using physiological models of human perception. The main steps involved in this research were first to propose a physiological model which explained why human operators can detect tiny defects in shadow masks, then to construct an inspection system and develop software to simulate the physiological processes.

Shadow Masks

This research was done in conjunction with LG Electronics, the objective of which was to detect defects in CRT shadow masks using physiological models of human perception. The main steps involved in this research were first to propose a physiological model which explained why human operators can detect tiny defects in shadow masks, then to construct an inspection system and develop software to simulate the physiological processes.

 

Detecting Shadow Mask Defects

The objective of this work was to understand and model how the human operators manage to detect tiny defects in the shadow masks. The operators sit in front of a light table and examine a mask by rotating it in circular motions in front of the table. Areas where the shadow mask holes are too small are perceived as darker regions than normal and holes which are too large are perceived as areas brighter than normal. The factors which cause this percept are dealt with in the next section.

Physiological Models

 


There were three processes in particular which seem to contribute to the ability of human operators to detect the tiny defects :

  • The Persistence of Illusory Contours
  • The Bunsen-Roscoe Law (aka Bloch's Law)
  • The On-Centre and Off-Centre cells in the Retinal Ganglion