11-10-2025, 08:18 AM
(This post was last modified: 11-10-2025, 08:22 AM by Mike Watterson.)
Amazingly the beam index CRT was first demoed in about 1951, but technical problems not solved till late 1990s, when it was too late. One version used UV emission from the rear of the blue stripe and a photo detector at the single gun. However without more advanced electronics sequential frame or shadowmask was better. If the triple gun shadowmask had not been invented, or if colour had been added in 1935, then colour would have used sequential frames and an optical filter. The conceptually simple idea of a single gun beam indexed stripe phosphor CRT proved very difficult to implement.
Another early system (1924 and early 1950) was sequential frame colour. In one model the CRT was inside a drum with the colour filters. The single chip DLP projectors use a colour wheel and convert to sequential frame colour. Hence if you move your head suddenly you may see a rainbow effect.
Without a frame store any sequential frame colour system might have needed three times the bandwidth. NTSC, PAL and SECAM use a much lower chroma bandwidth (very much lower VHS) which helps in fitting the signal into the spectrum gaps.
PAL plus took advantage of the black bands of letterbox transmission of Widescreen for 4:3 to add a signal to improve "zoomed" letterbox on 16:9 screens. RTE used it for a while.
IMO Widescreen TVs and WS transmission (letterboxed or not) should never have existed till there was Digital HD.
Another early system (1924 and early 1950) was sequential frame colour. In one model the CRT was inside a drum with the colour filters. The single chip DLP projectors use a colour wheel and convert to sequential frame colour. Hence if you move your head suddenly you may see a rainbow effect.
Without a frame store any sequential frame colour system might have needed three times the bandwidth. NTSC, PAL and SECAM use a much lower chroma bandwidth (very much lower VHS) which helps in fitting the signal into the spectrum gaps.
PAL plus took advantage of the black bands of letterbox transmission of Widescreen for 4:3 to add a signal to improve "zoomed" letterbox on 16:9 screens. RTE used it for a while.
IMO Widescreen TVs and WS transmission (letterboxed or not) should never have existed till there was Digital HD.
