in one embodiment a reference pattern 159 might include an image that is geometrically defined to resemble the shape of a grain kernel a piece of straw or both u2014 as shown or some other component expected to flow across the plate member the reference pattern 159 may include such shapes being located at specified locations along the plate member 142 a such as at or near the corners thereof the reference pattern 159 may be formed such that the geometric shapes also exhibit a fluorescent signal similar to that of the component they are emulating in operation the reference pattern 159 is taken into account by the image processors 158 a and 158 b and may be subtracted from the overall image projected from the plate member 142 a as a u201c background u201d an algorithm may then be employed by the image processors or by another processor not shown to look for u201c grain like u201d components by examining the images to ascertain geometric characteristics of individual components of the residual material for example an algorithm may be used to search for components having substantially round circular geometric profiles and associate such profiles with grain kernels 151 b the algorithm may also be used to check for abnormalities such as oddly shaped components exhibiting a fluorescent signal other than that which is expected for a particular geometric profile the monitoring apparatus 150 may therefore determine the amount of a given component e g the first component 144 which is present in a flow path of residual material it is noted.