Multi-focus image fusion for enhancing fiber microscopic images

Abstract

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.

Multi-focus image fusion for accurate measurement of nonwoven structures

“…, n), and G i ðx, yÞ the grayscale value of the pixel. The gradient magnitude of the pixel can be calculated by its horizontal and vertical components as follows [12,14] …”

“…where PFI is the fused image generated from this pixel-based fusion algorithm [12], whose pixels have the highest sharpness values among the layers. Figure 4(a) displays the PFI of the 100 multi-focus images of the nonwoven sample shown in Figure 3.…”

Fusing multifocus images for yarn hairiness measurement

“…A driving device was installed to control the movement of the microscope platform along the x-y axis direction that could move the yarn through the microscope. 20 The power of magnification of the objective lens was set at 4×. A digital camera (C200, BEION) was mounted on the top of the microscope to capture images with a size of 800 × 600 pixels, which approximately covered an actual area of 1 × 0.75 mm 2 on the yarn surface.…”

“…Therefore, the yarn sample was forwarded 10 times at a 1-mm interval to yield the measurements in 1-cm sections. At each stop, 10 images were grabbed at different depths of view by adjusting the z-axis of the microscope, 20 and then were fused into one sharp image where the protruding fibers were all well focused. Figure 2 shows two example images of a polyester yarn with hairy fibers protruding from the yarn core captured at different focal points.…”

“…Multifocus image fusion is one of the fusion methods that uses a set of images of the same scene captured at various focal planes of a camera to construct a clear and shape image in which all objects are focused. 19 Multifocus images comprise complementary information that can be seamlessly merged into one image more suitable for microscopic analysis of material properties, and they have been successfully used as accurate measurments of fiber diameters which could improve the fiber measurement accuracy by more than 20% 20 for nonwoven structures with respect to the fiber orientation in the nonwoven fiber. 21 In this new application for yarn hairiness measurement, the yarn passing through the microscope is intermittently advanced, and at each stop the yarn segment is imaged multiple times on different focal planes.…”