Quantifying homogeneity of high-consistency pulp from light-transmission imaging

Abstract Currently, robust and reliable methodologies for quantifying the homogeneity of high-consistency fiber suspensions are lacking, despite the critical importance of such characterization for numerous applications. This study introduces a reproducible image-analysis approach that enables objective quantification of the homogeneity of high-consistency fiber suspensions (20–45 wt.%) based on light-transmission images. A fiber-type-specific calibration confirmed that gray-value contrasts can be related to local solid-content variations within the calibrated range, enabling a physically interpretable evaluation of transmission images rather than a purely relative grayscale analysis. Agglomerates are identified using a regression-based thresholding approach, allowing them to be defined as significant local densifications relative to the surrounding bulk pulp background. This approach ensures reproducible and comparable segmentation of the samples. Characteristic values are derived from both the segmented and non-segmented images, including the significant area fraction, object size, multiscale fluctuation, gray-level, and spectral texture. When applied to raw pulps, the selected values consistently describe the expected trends: inhomogeneity increases with increasing solid content and is higher for longer fibers than for shorter fibers. The proposed methodology provides a robust framework for benchmarking homogenization processes in high-consistency fiber suspensions. It further enables subsequent studies linking structural heterogeneity to the mechanical performance of fiber-based materials.