How does a camera or eye detect violet if the smallest wavelength pixel element only detects blue? Since cameras have RGB sensing elements per pixel, and eyes' cones similarly detect color with red, green and blue variants. The spectral sensitivities of the eyes are something like the following, and cameras similar.:

An element cannot alone differentiate wavelengths either side - so a blue sensing element cannot tell the difference, for example, between a blue-green and blue-violet color by itself.
Have I got something wrong or am I missing something? Thanks
 A: I think I can answer my own question:
The eyes only perceive so-called visible light down to violet wavelengths precisely because the green elements do slightly register down to violet. The brain interprets blue plus a lack of green as violet.
Cameras don't 'interpret' anything. They just copy the amount of blue and (lack of) green, allow display equipment to output the same amounts of blue and (lack of) green, and the brain then interprets it for itself as violet.
A: To avoid serious confusion you should differentiate between green in the RGB coding, "green" as a human sensation and green as a more or less precise wavelength.
A wavelength of 500 nm is seen green, but there are infinite wavelength mixtures that are seen more or less green (and more or less "saturated"). No RGB coded device can reproduce a pure green, but
only some approximation thereof. Still worse for yellow: an RGB "yellow" is far from a pure spectral yellow (about 550 nm).
If you think of the chain 


*

*light source 

*detector (photo or TV camera) 

*display equipment 

*human eye

*human brain


there are four mapping (conversion) steps and none is (none can be) faithful. A detector has three sensing elements (like retina) and for whatever luminous input it outputs three analog signals. A very poor mapping indeed.
RGB coding is a digital conversion more or less precise according to the number of bits assigned to each signal conversion.
The display equipment does its best but each element (one for R, one for G, one for B) outputs a light far from monochromatic and also different from the sensitivity curve of sensing element.
The human eye acts like the original sensor in that in the retina there are three kinds of cones, with sensitivities roughly like you sketched, but surely different from those of camera. Moreover, the retina isn't made of cones alone - there are some cell layers accomplishing a first elaboration of the signals outputted from cones. 
Then via optical nerve these signals enter the brain where a most complex elaboration is done. One - only one - of the aspects of this elaboration allows for color constancy. Very simply said, this is why we attribute the same colour to an object under very different lighting conditions.
As to your interpretation of violet perception I'm not sure you're right. First, difference in sensitivities of what you call green and red cones (usually named M and L) is impressively small. Second, a monochromatic violet (say 400 nm) excites very little those cones, but M more than L (green more than red). So the retina output is significant for S (blue) cones, weak for M cones, still weaker for L ones). Maybe you're confusing with so-called "purple colours" which are not pure spectral colours but can be obtained by mixing red and blue in various
proportions.
I conclude remarking that we have only scratched the surface of this complex and fascinating subject - human colour perception.
