[Tech1] Brown balls and colour perception

[Chris Woolf]

On 04/03/2020 14:58, Geoffrey Hawkes wrote:
> .....Usually the words are in yellow on deep blue as that gives good 
> contrast and legibility. When the feed is cut, I notice that 
> momentarily the screen appears yellow. I know this is due to 
> persistence of vision but can’t remember why, other than that yellow 
> is complimentary to blue. Can you or anyone explain?
> Geoff
>
This is fatigue colour, or after image, rather than persistence. The 
large blue area depletes the blue photoreceptors in your eye - your 
brain carries on seeing blue because it "knows" it is still blue. 
However when the image changes to white, your eye cannot instantly 
provide the blue portion of that, so the screen looks heavily 
blue-depleted = yellow. As your retina refreshes the blue cones your 
white balance improves till you see a proper white screen again.

Plenty of nice examples here. 
https://www.animations.physics.unsw.edu.au/jw/light/complementary-colours.htm

A long time ago.... I was tracking a camera in TC1, going up and down 
the rail of a ship, with artists looking out "to sea". Cameraman and I, 
in the "sea", were bathed in constant blue light for an hour or so at a 
time. When we trolled out to the tea bar it took around 15 minutes 
before we could see anything the right colour again.

Chris Woolf



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