Thresholding of noisy shoeprint images based on pixel context

In a typical shoeprint classification and retrieval system, the first step is to segment meaningful basic shapes and patterns in a noisy shoeprint image. This step has significant influence on shape descriptors and shoeprint indexing in the later stages. In this paper, we extend a recently developed denoising technique proposed by Buades, called non-local mean filtering, to give a more general model. In this model, the expected result of an operation on a pixel can be estimated by performing the same operation on all of its reference pixels in the same image. A working pixel’s reference pixels are those pixels whose neighbourhoods are similar to the working pixel’s neighbourhood. Similarity is based on the correlation between the local neighbourhoods of the working pixel and the reference pixel. We incorporate a special instance of this general case into thresholding a very noisy shoeprint image. Visual and quantitative comparisons with two benchmarking techniques, by Otsu and Kittler, are conducted in the last section, giving evidence of the effectiveness of our method for thresholding noisy shoeprint images.

A geotechnical description of fresh cement grout - filtration and consolidation behaviour

The removal of water from three Portland cement grouts by pressure filtration is examined, and the consolidation behaviour of the filtered material clarified. The filtration takes place by the laying down of a very stiff filter cake through the removal of excess water. The behaviour due to further loading resembles that of a re-constituted silt. For stress levels above the filtration pressure the calculated permeability values are similar to those from the filtration phase only if the data sampling rate was sufficiently rapid to discriminate the first portion of the observed primary consolidation curve. The change in void ratio for incremental loading is roughly linear with the change in the logarithm of the vertical effective stress. The characterisation of fresh cement paste using standard soil mechanics models is both appropriate and useful, at least during the first few hours after mixing.