5.1 Don't be Frightened by LSI!

This is the chapter most readers will probably want to skip, but for those who are curious about the geek speak used by camera designers, press on! Understanding how light from a scene transforms into an image through a camera can be simplified if we think of the camera as a linear shift-invariant (LSI) system. That's a bit of a mouthful, but the concept is pretty straightforward, so let's look at the first part to understand a linear system. When an operator, say a dog, encounters an input, say a biscuit, we get a response - in this example let's say it's a "woof." If the operator encounters another input, say a cupcake, we might get a different response - this time let's say it's a "bark." But now we want to combine the inputs, so in this example we give the dog a biscuit and a cupcake. If the dog's response is simply the combination of the two responses given for the individual biscuit or cupcake, a "woof" and a "bark," we have a linear system. In other words, the response of a linear system to the sum of inputs is simply the sum of the individual responses. Easy, right?