Nondestructive Computed Tomography Volumetric Void Acceptance Criteria for Heavy Polymer Sections
Computed tomography volumetric void acceptance requires zoning heavy polymer walls by stress field, setting pore limits below 0.1% in tensile skins.
Local Gradient Thresholding
Meaning
Image segmentation algorithms applied during computed tomography data processing identify material interfaces by calculating grey-value spatial rate changes across adjacent voxels. Volumetric metrology software uses local gradient thresholding to separate plastic material from background air or internal voids based on derivative intensity peaks rather than fixed grey levels. The algorithm governs surface determination accuracy, edge definition, and void volume calculation in complex moulded parts.
Its function stops at dynamic interface detection, applying no control to raw X-ray emission parameters or mechanical scan motion.
Segmentation Algorithm
Advanced image analysis software isolates material boundaries by analyzing local derivative intensity transitions across neighbouring voxels. Applying local gradient thresholding compensates for beam hardening artifacts that cause uneven grey values across thick plastic sections.
Threshold Boundary
Global thresholding methods that assign a single grey-value cutoff to an entire scan volume systematically miscalculate wall thicknesses in parts with variable density. In thick polyoxymethylene mouldings, beam attenuation causes center regions to appear artificially dense compared to outer edges. Utilizing local gradient thresholding evaluates localized intensity gradients, capturing true part dimensions and fine void boundaries regardless of global grey-value drift.
High noise levels in low-dose scans can create false gradient spikes that require smoothing filters prior to edge extraction.
Edge Definition
Inaccurate surface determination skews wall thickness measurements and introduces systematic error into non-destructive quality signoffs. Selecting local gradient thresholding routines preserves sub-voxel edge accuracy across variable wall thicknesses and mixed-material assemblies.