I am a mathematician trying to understand some signal processing terms. My first question regards the terms 'even' and 'odd' filters. What does this mean? Does it reference the fact that upon a Fourier transform, there is a cosine and a sine function, which in turn are even and odd? If not, a link to a reliable source would be appreciated.
Second question: What is a quadrature? I have heard the term used for the phase shift between two Fourier transforms, the method for dividing a frame into four parts, and taking a gradient-like subtraction from vertical, horizontal, and both diagonal directions. Is it all of these at once? Also, a link to a reliable source would be great.