Local Basis Weight and Formation of Paper by Light Transmission Image Analysis, 1994 Papermakers Conference Proceedings

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A method based on light transmission coupled with computer based image analysis has been developed for determining the distribution of local basis weight and hence the formation of the paper. This technique is fast, inexpensive and accurate. The image of the sheet, obtained by a video camera, is acquired by an image analysis friendly personal computer. Nonuniformity of lighting, a side effect in this method, is removed by computer treatment if necessary. A data processing procedure was developed to convert local opacity to local basis weight. The method, tested over the range of 20 to 75 g/m2 basis weight for various furnishes and formations, has a resolution of at least 0.5 mm, with an accuracy better than 0.5 g/m2. As the basic image is captured as a 480x640 grid, this amount of data allows further statistical treatment for evaluation of formation. A frequential analysis based upon a Fast Fourier Transform (FFT) treatment of the data can extract the contour map of the flocs in the paper and provide a new Floc Formation Index (FFI) describing paper formation.