An image-based measurement technique that directly measures the crepe
pattern on a moving sheet employs a suitable arrangement of illumination,
optical elements, and an imaging device to obtain digital images of the
sheet surface. The image resolution is sufficient to represent tissue
crepe folds at the scale of the crepe. A spectral analysis of some or of
all the images reveals the crepe folding pitch. Further analysis of the
image optionally reveals other crepe structural parameters, such as the
distribution of crepe fold orientation angles and distribution of linear
fold lengths. Corrective actions can be implemented in response to
changes in the crepe structure. The pitch of creping is the primary
parameter for describing the crepe pattern; in addition, analyzing the
images with a gradient operator can yield information regarding the
orientation of the crepe folds and distribution of angles of the crepe
furrows on the hood side or equivalently of the crepe seams on the
cylinder side.