Method and apparatus for measuring color purity of a color display

摘要

PURPOSE:To enable high-precision measuring of color purity by determining two electron beam central positions in both positive and negative directions of an external magnetic field and besides determining an electron beam central position as an internal division point of them where a magnetic field is not applied. CONSTITUTION:Contours 17 and 18 of luminous parts (superposed part of 15 on 15', that of 15 on 15'') are extracted in a state where electron beams 15 are moved in both positive and negative directions by an external magnetic field. Elliptical equations are assumed for the contours 17, 18, and polynominals are adapted by coordinate values of a point row of obtained contours and next coefficients of the polynominals are assumed. Ellipses 19, 21 equivalent to the obtained contours are provided, and concurrently short axis directions 20, 22 of their ellipses are determined. Cross points of the short axis directions 20, 22 and their corresponding equivalent ellipses are determined respectively in the quantity of two, so that dots 23 and 24 are obtained. Further, polynominals of circular equations are adapted on the basis of edges 23 and 24 of these dots so as to assume a luminous dot shape (a central position and a radius) 25 (which corresponds with a luminous dot 16). Color purity can be thus measured with high precision.