03-02-2021, 07:42 PM
While the 29.97Hz frame rate of NTSC is a great nuisance in TV production it allowed the early digital TV standards to work rather well. With a 13.5MHz pixel clock you get 864 pixels per line in PAL and 858 in NTSC. Exactly. This simplified a lot of digital kit, very valuable in the early days when it was difficult.
The price for this is that the pixels aren't square in either standard, something that's a problem when interfacing with computer systems. The later HD standards all use square pixels. As a result the clocks for 25Hz and 29.97Hz are in the ratio 1000/1001. So for 1080/50i the pixel clock is 74.25MHz. For 1080/59.94i it's 74.5 * (1000/1001).
The price for this is that the pixels aren't square in either standard, something that's a problem when interfacing with computer systems. The later HD standards all use square pixels. As a result the clocks for 25Hz and 29.97Hz are in the ratio 1000/1001. So for 1080/50i the pixel clock is 74.25MHz. For 1080/59.94i it's 74.5 * (1000/1001).
www.borinsky.co.uk Jeffrey Borinsky www.becg.tv
