LOCAL GRAMMAGE DISTRIBUTION AND FORMATION OF PAPER BY LIGHT TRANSMISSION IMAGE-ANALYSIS

A method based on light transmission coupled with computer-based image analysis has been developed for determining the distribution of local grammage and hence the formation of paper. This technique is fast, in expensive, and accurate. The method, tested over the range of 20 to 75 g/m(2) basis weight, for various finishes and formations, as a resolu tion of at least 0.1 mm, with an accuracy better than 0.5 g/m(2). A da ta processing procedure was developed to convert local opacity to loca l basis weight. A frequential analysis based upon a Fast Fourier trans form treatment of the data can extract the contour map of the flocs in the paper, providing a visual representation of flocs not previously available. Further processing of the power spectrum data gives a singl e number as a new floc formation index (FFI) describing paper formatio n. The FFI criterion discriminates much more sensitively between diffe rent qualities of formation than does the standard formation number, w hile not having the disadvantage of the multiple indices of second-ord er statistics.