To improve contrast together with the arrangement of index elements and to deal with a CRT in large size as well.
49 pieces of index fluorescent bodies are arranged on a display screen, for example, and an index signal is detected by an index detection amplifier 12 by detecting beam scanning using a photodetector 114. Based on this index signal, a distortion quantity detection circuit 13 detects distortion quantity, it is calculated by an arithmetic circuit 14, and a convergence correction circuit 16 is controlled. The index expectation signal is supplied from a control circuit 15 to the arithmetic circuit 14. When an index expectation signal and a phase are deviated at the position of a specified index fluorescent body, convergence correction is performed by discriminating it that the display screen is distorted at that fluorescent body position. Since it is not necessary to always perform index detection but it is enough only to perform the index detection at that fluorescent body position, contrast is improved.
FUJIWARA MASANORI
SAKAMOTO TSUTOMU
MIHARA HISAYUKI
OBAYASHI TOSHIO
ANDO MORIO
MASAKI TOSHIYUKI
TOSHIBA AVE KK