Exactly, there are two other reasons why cameras "see" green better than any other colour, the first is the sensor itself single sensor cameras / CMOS chips have tightly packed Red, Green and Blue photo diodes, the alignment of which gives a slightly higher number of Green senors to any other, see image:
Valid for location recorded content - but single-sensor cameras are kind of unheard of in studios (other than very cheapskate operations using BlackMagic cameras). The Sony F55 briefly had a life as a location 4K camera - but OB providers were all waiting for 2/3" 3 sensor cameras to arrive (and they did in the shape of the HDC4300) as large single-sensor cameras with shallow DoF are not a good mix for fast moving sports coverage.
You've missed the real point.
Most studio operations use 8 or 10 bit digital YCbCr 4:2:2 subsampled chroma for studio signal routing (not equal bandwith RGB - even though RGB cameras with 3 CCDs can normally deliver a full RGB equal bandwith signal at the camera head - unless pixel-offsetting has been used).
In SD 601 Y=0.587G + 0.299R + 0.114B
In HD 709 Y= 0.715G + 0.212R + 0.072B
As you can see there is a lot more green information in the high-bandwidth luminance channel than there is blue (red isn't used because of lips). If you want a clean chroma-key you get a cleaner result from using green. If you look at the maths, you have between 59 and 72% of the green signal in the double-bandwidth luminance channel, whereas you only have 0.07 to 0.14% of the blue signal in that channel (In 8 bit that would be somewhere between 16 and 32 levels between 0% and 100% blue meaning any blue HF detail has a very low number of quantisation states (8 bits carrying a 7% max signal doesn't give you many levels to play with...) The bulk of the blue signal information is carried in the Cb signal which is half the horizontal bandwith of the luminance, Y, signal.
This is also why chroma-key from a 4:2:0 or 4:1:1 format is usually not recommended (i.e. the various DV flavours and the low-bitrate MPEG2 LongGOP stuff like XD Cam 4:2:2 33Mbs)
In the days of analogue studios, you could usually get a high quality RGB or YPbPr analogue component signal from the camera CCU to feed to the mixer (you didn't key off the composite source that was the fill) and this was able to deliver a high quality clip from blue or green. With digital studios you are often better off with green. Downside was, of course, you couldn't chroma-key from anything other than the live cameras (you couldn't get a good quality chroma key from a composite 1" or 2" VT
recording of the source camera - so if you wanted to key in post-production you had to use a second VTR to record the key signal generated by a chroma-key box 'live')
Things changed when got Beta SP and CRV component sources arrived which could be connected to the chromakey inputs of vision mixers of course...
Last edited by noggin on 18 March 2016 5:39pm