Quote:
Originally Posted by ppppenguin
Why 4 tubes? 2 main reasons. One is registration, as mentioned above. The other is more subtle relating to gamma and constant luminance. The late Ivan James of EMI was a great proponent of constant luminance and may well have influenced the design. Here's Poynton's view on the subject:
http://www.poynton.com/notes/video/C...luminance.html
Later designs used "highs out of green" and suchlike, recognising that green is a reasonable proxy for luminance. |
Besides EMI and Marconi, the four-tube concept (as laid out here) was also applied by U.S. maker General Electric on their PE-250, PE-350 and PE-400 studio cameras; as well as by RCA (not as successfully, as described above) on their infamous TK-42 and TK-43 cameras. And of course, on the two American companies' respective film chain cameras (G.E. PE-24/240/245 and RCA TK-27).
The later attribute (on three-tube cameras), I've noticed was referred to as "contours out of green."