Digital image analysis of fluid inclusions

Fluid inclusions commonly exist in the cracks of rock masses. From a microscopic point of view, the fluid inclusion plane (FIP) is the crack plane while the fluid inclusion line (FIL) is the intersecting line between a specific plane (horizontal or different) and the FIP. These microscopic compositions or structures not only provide valuable information on the deformations and/or fractures of rocks but also reflect the trend, length and width of cracks. This paper presents the digital image analysis of fluid inclusions in rocks and discusses the characteristics of FILs. For the image analysis, the original digital images photographed by the microscope equipped with a digital camera on a heating–freezing platform were first converted into grayscale images and then broken into blocks using quadtree decomposition and region segmentation. For each block, the inflection point, derivative, frequency and color-based methods were used to detect the edges of fluid inclusions. To better define the boundaries of fluid inclusions, the dilation, erosion, seed filling, boundary connection and smoothing techniques were used to, respectively, extend edges, connect discontinuous points, fill pores in the outlines, eliminate irrelative parts in neighboring positions, smoothen projecting parts around the outlines and aggregate smaller inclusions into larger ones. After the boundaries of fluid inclusions were defined, the blocks were re-assembled and the edge points and lines of fluid inclusions were then defined in a global coordinate system. Based on the geometrical properties of the fluid inclusions, such as the centroid positions, areas and long-axis directions, FILs and their configuration parameters (such as length, mean width and abundance) were obtained with the least-squares method. All of these procedures were coded into a program and could be automatically run. The digital image analyses of fluid inclusions may provide valuable information about the relationships between the FIL networks and the crack properties.