PatternFab

Software for making DIC speckle patterns physical: an optimized pattern in, a fabrication file out, with the manufacturing constraints already applied.

Build from source Source on GitHub

Free and open source, LGPL-2.1-or-later · Qt and VTK · sister tool to SurView DIC

The PatternFab window: a 175-speckle pattern over a 30 by 20 mm specimen, manufacturing constraints on the left with a constraint report reading no tiling needed and zero violations, and export buttons for SVG, DXF, PNG and STL.

Capabilities

A good speckle pattern is designed digitally and then has to survive being made. PatternFab is the step in between: it applies the real constraints of the process you will use, and writes the file that process needs.

Vector patterns read directly, raster patterns via contour and blob detection
Minimum feature size checked against the chosen process
Bleed compensation applied before export, not after the fact
Stencil and stamp bridging checked, so a cut stencil holds together
Tiling checked for the periodicity it would inject
SVG and DXF for a laser-cut stencil
PNG at a caller-supplied DPI for direct-write or decal transfer
STL relief for a 3D-printed stamp or a silicone-cast mold
Per-pixel correlation confidence from a real camera noise model
2D stencil and 3D relief previews of what will be written

Specification

What the software does, in the terms the process needs.

Reads

Vector speckle primitives as JSON (shape, centre, radius) with the specimen's physical parameters, or a raster PNG or TIFF pattern through contour and blob detection.

Physical parameters

Specimen width and height in mm, imaging resolution in px/mm, and target speckle size in mm. Every constraint and every export is computed in millimetres from these, never in pixels of the source picture.

Constraints

Minimum feature size, bleed compensation and minimum bridge width, each in mm, each reported as a count of violations rather than silently applied.

Non-periodicity

A pattern too small for the specimen has to be tiled, and tiling a random field makes it periodic, which is the one thing correlation cannot tolerate. The report states whether tiling is needed before anything is written.

Writes

.svg and .dxf stencils, .png at any DPI from 50 to 4800, and .stl relief with a chosen base thickness and bump height.

Uncertainty

A design-time per-pixel DIC correlation confidence, combining local intensity gradient with a measured camera sensor noise model rather than a pattern-only heuristic. In the library and the command-line driver today; not yet in the window.

Architecture

A headless patternfab-core library with no dependency on interactive widgets, wrapped by a thin Qt application and a command-line driver. The library is unit-tested directly.

Built on

Qt 6 (window, and QSvgGenerator for SVG), VTK 9 (relief mesh and STL), dime (DXF), nlohmann/json. The same Qt and VTK stack as FreeCAD, ParaView and SurView DIC.

Licence

LGPL-2.1-or-later. Fully open source, no proprietary tier.

The fabrication methods

The methods themselves are published work by other people, not inventions of this project. PatternFab's contribution is the software bridge from a pattern to the file each method needs.

Stamp or mold

An STL relief, resin-printed as a stamp directly or as a mold to cast silicone from. The strongest method for medium and large speckle. FDM printing alone cannot hold fine features at a 0.4 mm nozzle, which is why the mold path exists.

Diani, Geraud, Coq et al., "Stamps for Pattern Applications for DIC or Markers Tracking", Experimental Techniques, 2026.

Direct-write

A PNG at the correct DPI, driving a modified 3D printer that dispenses ink through a syringe in a Poisson-disc distribution. Suited to fine speckle.

Yang, Tao, Franck, "Smart DIC Patterns via 3D Printing", Experimental Mechanics, 2021.

Decal transfer

The same PNG, printed to water-slide transfer paper. Confirmed stable under impact loading and large strain, and the fastest method to apply.

Quino et al., "Speckle patterns for DIC in challenging scenarios", Measurement Science and Technology, 2020.

Stencil

SVG or DXF for a laser cutter, with bridging checked so the cut stencil holds together. Spray through a stencil is the weakest reproducible method, with edge bleed, halo and clogging: PatternFab supports it, and says plainly that a stamp or a transfer is better where either will do.

Screenshots

The sample pattern that ships with the source: 175 Poisson-disc speckles over a 30 by 20 mm specimen, imaged at 40 px/mm.

The 2D stencil preview showing the speckle field over the specimen, with the constraint report reading zero minimum-feature violations and zero bridging violations.

What will be cut, and whether it holds

The constraint report answers the three questions that decide whether a pattern can be made at all: does it cover the specimen in one application, is any feature smaller than the process can hold, and does any bridge fall below the minimum width.

Set the constraints in millimetres for your own process. The report and the previews follow immediately, before anything is written.

The 3D relief preview: the pattern as a stamp, a rectangular base plate with a raised bump at every speckle, rendered in the window.

The stamp, before it is printed

The same pattern as a relief, with the base thickness and bump height you will print, rendered in the window through VTK rather than left to the slicer to reveal.

This is the geometry that goes into the STL, not an impression of it.

Build

PatternFab builds from source on Ubuntu 26.04 and equivalents.

sudo apt install libvtk9-dev libvtk9-qt-dev \
    qt6-base-dev qt6-base-dev-tools qt6-svg-dev \
    libdime-dev nlohmann-json3-dev

git clone https://github.com/katalystnord/patternfab.git
cd patternfab
cmake -S . -B build -G Ninja -DCMAKE_BUILD_TYPE=Release
cmake --build build

./build/gui/patternfab-gui examples/sample_pattern.json

The last line opens the sample pattern already loaded, which is the screenshot above. The window needs a VTK whose GUISupportQt is built against Qt6; Ubuntu 24.04 and older ship one built against Qt5, and one process cannot hold both. Build with -DPATTERNFAB_BUILD_GUI=OFF there, and the library, the command-line driver and the whole test suite still build and run.

Sister tool

PatternFab and SurView DIC are two ends of one workflow: the speckle pattern PatternFab makes is the pattern SurView measures.

Fabricate the pattern

PatternFab

An optimized pattern into a stamp, a stencil, a decal or a direct-write file, with the manufacturing constraints applied before anything is made.

This tool.

Measure the pattern

SurView DIC

Speckle images in, displacement and strain fields out, with every point's reliability reported and full provenance carried into ParaView and FreeCAD.

SurView DIC

Licence and credits

PatternFab is free software under the GNU Lesser General Public License, version 2.1 or later, the same licence FreeCAD uses in the same ecosystem.

Built on Qt and VTK, with dime for DXF and nlohmann/json.

The fabrication methods are the published work of the authors cited above. PatternFab implements the software bridge to them and claims none of them.