  Many questions remain in turbulence research---and related fields---about the
underlying physical processes that transfer scalar quantities, such as the
kinetic energy, between different length scales. Measurement of an
ensemble-averaged flux between scales has long been possible using a variety of
techniques, but instantaneous, spatially-local realizations of the transfer
have not. The ability to visualize scale-to-scale transfer as a field quantity
is crucial for developing a clear picture of the physics underlying the
transfer processes and the role played by flow structure. A general technique
for obtaining these scale-to-scale transfer fields, called the filter approach,
is described. The effects of different filters, finite system size, and limited
resolution are explored for experimental and numerical data of two-dimensional
turbulence.
