Accurate measurement and identification of fibers using magnified digital images relies mainly on the quality of the fiber image. At a given power of magnification, a light microscope has a limited depth of field that may not cover the entire depth space of a fiber sample on the slide and thus disallows all fibers in the image from being well focused, regardless of focus positions. This paper introduces an image-fusion technique to solve mal-focused fibers in a microscopic image to ensure optimal image quality for fiber measurements. This new technique utilizes multiple images of the same view taken at consecutive depths, calculates a focus measure of every pixel in each image, and constructs a matrix to register the image layer that has the maximum focus measure for every pixel. The matrix can be further modified and then used as a map to reconstruct a new image that contains only the best-focused pixels out of the captured images. The fused image combines selected features of multi-focus images so that unfocused fibers can be realistically amended and blurring fiber edges can be sharpened. Compared to the data measured from a single-focus image, the data taken from the fused image can greatly improve the accuracy of fiber thickness measurements.

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