Image analysis: Problems,progress and prospects

Over the past 25 years, many ad hoc techniques for analyzing images have been developed and the subject has gradually begun to develop a scientific basis. This paper outlines the basic steps in a general image analysis process. It summarizes the state of the art with respect to each step, points out limitations of present methods and indicates potential directions for future work.     

Low-loss waveguides fabricated in BK7 glass by high repetition rate femtosecond fiber laser

For the first time femtosecond-laser writing has inscribed low-loss optical waveguides in Schott BK7 glass, a commercially important type of borosilicate widely used in optical applications. The use of a variable repetition rate laser enabled the identification of a narrow processing window at 1 MHz repetition rate with optimal waveguides exhibiting propagation losses of 0.3 dB/cm and efficient mode matching to standard optical fibers at a 1550 nm wavelength. The waveguides were characterized by complementary phase contrast and optical transmission microscopy, identifying a micrometer-sized guiding region within a larger complex structure of both positive and negative refractive index variations.     

Digital connectedness: An algebraic approach

Let E be the incidence matrix of a graph G having m nodes; then the number of connected components of G is equal to m ? r, where r is the rank of E. In particular, if G represents an adjacency relation between points in a digital picture (or higher-dimensional array), this shows that the connected components of points can be counted by computing the rank of E. Two proofs of this result are given, one based on results from algebraic topology and the other based on a self-contained graph-theoretic argument. The former proof can be generalized to yield a method of counting holes.     

Some results on fuzzy (digital) convexity

The definition of fuzzy convexity is reviewed and some results on projections of convex and fuzzy convex sets are established. Digital fuzzy convexity is defined and relationships among alternative definitions are investigated.     

Supply curves of conserved energy for California's residential sector

A new method of presenting the potential for conservation is discussed. Supply curves of conserved energy provide a consistent accounting framework for assessing diverse conservation measures. They also permit simple comparison of conservation measures among themselves and with conventional energy supplies. The technique is applied to California's residential sector and illustrative policy conclusions are presented. Roughly 34% of the natural gas and 25% of the electricity used by the residential sector could be saved at costs of conserved energy below current marginal prices.     

Some experiments on variable thresholding

Chow and Kaneko proposed a method of variable thresholding in which an image is divided into windows; thresholds are selected for those windows that have bimodal histograms; and these thresholds are interpolated to define a variable threshold for the entire image. This method was applied to several TV images of machine parts; the results obtained appeared to be considerably better than the results of thresholding at a fixed level. An extension of the method was defined that allowed histograms to be either bimodal or trimodal; this yielded some further improvement in the results, but was also more sensitive to shadows. Finally, an adaptive quantization scheme, based on histogram peak sharpening, was applied to two of the images; the results do not seem to be as good as those obtained using variable thresholding.     

Symbolic pixel labeling for curvilinear feature detection

This paper describes a method of detecting thin curvilinear features in an image based on a detailed analysis of the local gray level patterns at each pixel. This allows operations such as thinning and gap filling to be based on more accurate information.