Method and arrangement for detecting free fibre ends in paper
First Claim
1. A method for detecting free fibre ends in a paper surface, the method comprisingilluminating a target sample surface, which comprises free fibre ends, from at least two directions one direction at a time, with at least one light source,obtaining for each light source direction an original reflectance image for the target sample surface with an imaging device,estimating a surface normal for each image pixel of the original reflectance image,reconstructing a reconstructed reflectance image from the estimated surface normals, andcomparing the reconstructed reflectance image and the corresponding original reflectance image and constructing a difference image, where the differences represent shadow objects of the free fibre ends in a paper surface.
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Abstract
The invention relates to a method and arrangement for detecting free fiber ends in a paper surface. The method comprises illuminating a target sample (6) surface, which comprises free fiber ends, from at least two directions one at the time, with at least one light source (1). Original reflectance images are obtained for the target sample (6) surface with an imaging device (4), and a surface normal is estimated for each image pixel of the original reflectance image. Thus it is possible to reconstruct a reconstructed reflectance image from the estimated surface normals, and to compare the reconstructed reflectance image and the corresponding original reflectance image and to construct a difference image, where the differences represent shadow objects of the free fiber ends in a paper surface.
8 Citations
18 Claims
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1. A method for detecting free fibre ends in a paper surface, the method comprising
illuminating a target sample surface, which comprises free fibre ends, from at least two directions one direction at a time, with at least one light source, obtaining for each light source direction an original reflectance image for the target sample surface with an imaging device, estimating a surface normal for each image pixel of the original reflectance image, reconstructing a reconstructed reflectance image from the estimated surface normals, and comparing the reconstructed reflectance image and the corresponding original reflectance image and constructing a difference image, where the differences represent shadow objects of the free fibre ends in a paper surface.
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16. An arrangement for detecting free fibre ends in paper, the arrangement comprising
an imaging device such as a digital systems camera, arranged to a distance from a sample holder, for obtaining original reflectance images of a target sample surface, at least two light sources attached around the imaging device, or one light source, which is attached to a supporting arm, which is arranged to rotate around the imaging device, the at least two light sources or the one light source being arranged to illuminate the target sample surface from at least two directions one direction at a time, a data processing unit, which is arranged to receive original reflectance images obtained for each light source direction from the imaging device, to estimate a surface normal for each image pixel of the original reflectance image, to reconstruct a reconstructed reflectance image from the estimated surface normals, and to compare the reconstructed reflectance image and the corresponding original reflectance image and to construct a difference image, where the differences represent shadow objects of the free fibre ends in a paper surface.
Specification