InsightSoftwareConsortium/ITK: ITK 6.0 Beta 2: CMake Module Targets

We are excited to announce the second beta release of ITK 6.0! This release introduces modern CMake module targets — a major build system modernization that makes it easier than ever to link ITK into your projects. Alongside this headline feature, Beta 2 delivers continued C++ modernization, Python enhancements, performance improvements, and expanded agentic engineering practices. As a beta release, we actively encourage the community to test and provide feedback as we approach the first Release Candidate. 🚀 ✨ 🎉 🔦 Highlights CMake Module Targets The most significant change in Beta 2 is the introduction of modern CMake interface library targets for every ITK module. Each module now exports a namespaced target — for example, ITK::ITKCommonModule, ITK::ITKImageGradientModule, or ITK::ITKThresholdingModule — enabling clean, explicit dependency management with proper transitive dependency resolution. Pre-defined factory meta-modules simplify linking for common IO use cases: ITK::ITKImageIO — all image IO modules (JPEG, PNG, NIFTI, DICOM, etc.) ITK::ITKMeshIO — all mesh IO modules ITK::ITKTransformIO — all transform IO modules Before (ITK 5): find_package(ITK REQUIRED) include(${ITK_USE_FILE}) add_executable(HelloWorld HelloWorld.cxx) target_link_libraries(HelloWorld ${ITK_LIBRARIES}) After (ITK 6): find_package(ITK REQUIRED) itk_generate_factory_registration() add_executable(HelloWorld HelloWorld.cxx) target_link_libraries(HelloWorld ITK::ITKCommonModule) For projects that read images, simply link the IO meta-module: find_package(ITK REQUIRED) itk_generate_factory_registration() add_executable(MyFilter MyFilter.cxx) target_link_libraries( MyFilter PRIVATE ITK::ITKImageGradientModule ITK::ITKImageIO ) UseITK.cmake (${ITK_USE_FILE}) is now deprecated in favor of these interface library targets. ITK can also be consumed via CMake FetchContent, illustrated in the new HelloFetchITK example. For full migration details, see the ITK 6 Migration Guide — also a useful reference for both humans and AI agents working with ITK projects. We especially welcome feedback on the CMake module targets during this beta period. Please report any issues you encounter with the new build system on GitHub. C++ Modernization VariableLengthVector gains a std::vector-like interface: front(), back(), data(), and a (length, value) constructor FixedArray gains front(), back(), and empty() member functions ImageConstIterator::ComputeIndex() added as the replacement for GetIndex() (now deprecated), with performance benefits from avoiding redundant offset table lookups New itk::MakeIndexRange utility functions for convenient index-space iteration SobelOperator extended to N-D with corrected 3D coefficients and a UseLegacyCoefficients option NumericTraits::GetLength is now constexpr Replaced vnl/vnl_sample.h with standard <random> across tests Expanded use of constexpr, [[nodiscard]], aggregate initialization, and range-based for loops Python Enhancements Python 3.10+ is now required for wrapping New ITK_PYTHON_RELEASE_GIL build option enables GIL release during ITK filter execution Updated bundled pygccxml to v3.0.2 Performance Improvements Tuned ImageRegionRange copy used in CastImageFilter IndexRange iterators made significantly faster via m_Position data member ImageRegionRange bypasses OffsetTable[0] (which is always 1) Prefer "with index" iterators when the index is used in each iteration, avoiding redundant ComputeIndex() calls Third-Party Library Updates GDCM 3.2.2, double-conversion 3.4.0, Expat, VXL, NrrdIO, CastXML v2026.01.30 Platform & CI Updates Updated CI to Windows 2022 images Added Linux ARM CI testing Migrated to macOS 15 runners (Apple Silicon) Support building with system Eigen3 >= 5 New ITK_FREEZE_REMOTE_MODULES option to prevent remote module updates during build Remote Module Updates CudaCommon v2.0.0 with __cuda_array_interface__ support for interoperability with CuPy and PyTorch RTK major updates: new Python applications, CUDA improvements, spectral CT documentation Remote modules updated for CMake modernization (itk_module_add_library) Agentic Engineering ITK continues to advance its agentic engineering practices, improving the developer experience with agent-friendly workflows, better CI, and review agents. In this release, copilot-swe-agent[bot] contributed the GIL release feature, NumericLocale GoogleTest coverage, bug fixes for imread and locale-dependent NRRD parsing, and more. The AGENTS.md guide and GitHub Copilot setup workflow continue to be refined. Now is as great a time as ever to contribute to ITK and learn from an active and friendly community of experienced medical imaging professionals. 💾 Download Python Packages Install ITK Python packages with: pip install --pre --upgrade itk Note: Use --pre flag to install beta releases. Guide and Textbook InsightSoftwareGuide-Book1-6.0b02.pdf InsightSoftwareGuide-Book2-6.0b02.pdf Library Sources InsightToolkit-6.0b02.tar.gz InsightToolkit-6.0b02.zip Testing Data Unpack optional testing data in the same directory where the Library Source is unpacked. InsightData-6.0b02.tar.gz InsightData-6.0b02.zip Checksums and Signatures InsightToolkit-6.0b02.tar.gz.asc InsightToolkit-6.0b02.zip.asc InsightData-6.0b02.tar.gz.asc InsightData-6.0b02.zip.asc MD5SUMS SHA512SUMS 📖 Migration Guide For detailed guidance on migrating existing code to ITK 6.0, please consult the ITK 6 Migration Guide. Key changes in Beta 2 include: Modern CMake interface library targets replacing UseITK.cmake Python 3.10+ requirement for wrapping ImageConstIterator::ComputeIndex() replacing GetIndex() GIL release option for Python multithreading 🙏 Acknowledgments Thank you to the 22 contributors who made ITK 6.0 Beta 2 possible! We extend a special welcome to our 5 new contributors: Cavan Riley, Yu-An Chen, Axel Garcia, Michael Cho, and nslay. Thank you for joining the ITK community! We are grateful for Axel Garcia, Ben Boeckel, Brad King, Bradley Lowekamp, Cavan Riley, Cyril Mory, Dave Chen, Davis Marc Vigneault, Dženan Zukić, Hans Johnson, Jon Haitz Legarreta Gorroño, Lucas Gandel, Matt McCormick, Michael Cho, Niels Dekker, nslay, Paul Elliott, Sean McBride, Simon Rit, Tom Birdsong, Vladimir S. FONOV, Yu-An Chen, and the entire ITK community for their code contributions, testing, documentation efforts, and invaluable feedback. 🗣️ What's Next ITK 6.0 Release Candidate 1 Following community testing and feedback on Beta 2, the next ITK 6 release will be the first Release Candidate. Please test the beta — especially the new CMake module targets — in your workflows and report any issues. ITK 5.4 Long-Term Support ITK 5.4 will continue to receive maintenance updates as a long-term support (LTS) release, providing: Critical security patches Bug fixes for production environments Full support for Intel macOS Backward compatibility for existing applications Community Feedback We actively welcome your feedback on ITK 6.0 Beta 2! Please report issues on GitHub or the ITK Discourse forum. Feedback on the CMake module targets is especially valuable as we finalize this major change for the Release Candidate. Enjoy ITK! ITK Changes Since v6.0b01 Ben Boeckel (4): Enhancements update-common.sh: synchronize with upstream (1bc98267c9) update-third-party: sync with upstream (66a45d3bfc) Style Changes git-fetch-file: track update-common.sh (99c9c92652) thirdparty: disable exact tree matching (78982a2b08) Brad King (4): Enhancements itkexpat: Update source layout to make includes ITK-specific (8ec19eb1d6) itkexpat: Update includes to reliably use ITK's expat headers (20fd88b57b) itkexpat: Add script to import from upstream (b12ac06e7e) itkexpat: Remove source tree to make room for fresh import (4957068ebe) Bradley Lowekamp (79): Enhancements Improve initialization in Path classes (9143a4d820) Use ImageRegionRange iterator in ImageAlgorithm::Copy (5b58520f19) Use GTest::gtest and GTest::gtest_main targets (51c24a5a0f) Check IPO/LTO support once globally for all wrapper modules (48b834b5b1) Remove legacy and unused Wrapping EXECUTE_OUTPUT_PATH (ffaa0c946e) Use imported OpenCL targets from CMake (bf1566b687) Use OpenCL imported target in GPUCommon (e3b18e7142) Use target-based includes for ITK modules (87cc629cd4) Create CMake interface libraries for each ITK module (d159777773) Add modern CMake linking with ITK interface modules to examples (602a5e03c6) Configure factory meta-modules with registration properties (056d0a60ab) Link module libraries to interface modules libraries (01971b74c8) Add namespace support for all ITK targets (6dd596e53f) Update Installation Example to use ITK Interface libraries (377423ff66) enable multiple call to itk_generate_factory_registration (bf531980db) Add deprecation warning to UseITK usage. (14665e644c) Allow modules to override GENEX INCLUDE variables (f9638701f6) Remove CMake code block for unsupported versions (22d4ff4f32) Update to use PRIVATE and PUBLIC linking modes (8a4dd39dd6) MINC update script properly ignores trailing whitespace (0bad5e05c0) Enable gersemi to run on ITK CMake files in ThirdParty directory (5a8fb4c71b) teach itk_module_macro to support NAMESPACE argument (d8f37be021) Use ITK CMake interface targets for all example linking (3048ad4230) Use modern CMake interface libraries for ZLIB (8af1b5c5f6) Support installation of FILE_SET HEADER for module targets (b4399480cd) Update double-conversion to 3.4.0 (1aaaf1bef9) Update double-conversion CMake to target_includes (1fec0a4dce) Add example project which used ITK Modules and FetchContent (f8c35f0fb2) Conform GDCM to use CMAKE_*OUTPUT_DIRECTORY (d5cf8de3ed) Performance Improvements Use tuned ImageRangeRegion copy in CastImageFilter (2e8c70a449) Documentation Updates Add migration guide for new CMake Interfa