According to Mathworld, a "pencil" is all lines thru a point:
http://mathworld.wolfram.com/Pencil.html
However, a "pencil of planes" is a line.

I want to quote the following from the paper:

"The significance of the plenoptic function is this:
The world is made of three-dimensional objects, but these
objects do not communicate their properties directly to
an observer. Rather, the objects fill the space around them
with the pattern of light rays that constitutes the plenoptic function, and the observer takes samples from this
function. The plenoptic function serves as the sole communication link between physical objects and their corresponding retinal images. It is the intermediary between
the world and the eye."

I think that Adelson is being overly metaphysical when he says this. This plenoptic function reminds me of the ether, a stationary material medium that pervades all space, which you might have heard about during an introduction to Einstein's theory of special relativity.

Although it is beneficial to talk about a function whose dimensions correspond to basic visual properties, it might be a better idea to simply talk about embedding basic visual measurements in a vector space instead of making deeper philosophical claims regarding the existence of the plenoptic function.

I guess this is pretty trivial, but I'm sort of confused about their use of the term "pencil." I had always taken it to mean "a one-parameter family of lines." But here they use it to refer to the set of all lines passing through a point in E3. But this is a 2-dimensional family, right (spherical coordinates, or the cartesian coordinates of a picture plane)?

This discussion board is for any thoughts/questions you might have on the physiology of vision and "the plenoptic function and the elements of early vision" by Adelson and Bergen