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Contributing to ITK

This page documents how to develop ITK using Git.

Note: Git is an extremely powerful version control tool that supports many different "workflows" for indivudal development and collaboration. Here we document procedures used by the ITK development community. In the interest of simplicity and brevity we do not provide an explanation of why we use this approach. Furthermore, this is not a Git tutorial. Please see our GitHelp guide for third-party documentation.


Before you begin, perform initial setup:

  1. Register for Gerrit access and possibly for Git push access.
  2. Optionally download our one page PDF desk reference.
  3. Follow the download instructions to create a local ITK clone:
   $ git clone git://
  1. Run the developer setup script to prepare your ITK work tree and create Git command aliases used below:
   $ ./Utilities/

Note that ITK defines some useful Git aliases, such as pullall or prepush, through the script for general Git tasks in ITK.

Note that if you answer y to the question "Do you want to test push access to [y/N]:", you will most likely receive the following error message: "Permission denied (publickey). fatal: Could not read from remote repository.". Only a few experienced contributors have push access. Having push access is not necessary to contribute to ITK.

You may visit the Pro Git: Setup resource in GitHelp for further information on setting up your local Git environment.


ITK development uses a branchy workflow based on topic branches. Our collaboration workflow consists of three main steps:

  1. Local Development
  2. Code Review
  3. Integrate Changes


Update your local master branch:

   $ git checkout master
   $ git pullall

Create a Topic

All new work must be committed on topic branches. Name topics like you might name functions: concise but precise. A reader should have a general idea of the feature or fix to be developed given just the branch name.

To start a new topic branch:

   $ git fetch origin

For new development, start the topic from origin/master:

   $ git checkout -b my-topic origin/master

For release branch fixes, start the topic from origin/release, and by convention use a topic name starting in release-:

   $ git checkout -b my-topic origin/release

(You may visit the Pro Git: Basic Branching resource in GitHelp for further information on working with branches.)

Edit files and create commits (repeat as needed). Add a prefix to your commit message (see below).

   $ edit file1 file2 file3

(To add data follow these instructions.)

   $ git add file1 file2 file3
   $ git commit

(You may visit the Pro Git: Recording Changes resource in GitHelp for further information on making changes and committing snapshots.)

Note: If your change modifies any of the modules in the Modules/ThirdParty directory, please read our UpdatingThirdParty guide.

Standard prefixes for ITK commit messages:

  • BUG: Fix for runtime crash or incorrect result
  • COMP: Compiler error or warning fix
  • DOC: Documentation change
  • ENH: New functionality
  • PERF: Performance improvement
  • STYLE: No logic impact (indentation, comments)
  • WIP: Work In Progress not ready for merge

Share a Topic

When a topic is ready for review and possible inclusion, share it by pushing to Gerrit. Be sure you have registered for Gerrit access.

Checkout the topic if it is not your current branch:

   $ git checkout my-topic

Check what commits will be pushed to Gerrit for review:

   $ git prepush

Push commits in your topic branch for review by the community:

   $ git gerrit-push

(If the topic adds data see this note.)

or if you started the topic from the release branch:

   $ git push gerrit HEAD:refs/for/release/my-topic

Find your change in the ITK Gerrit instance and add ITK reviewers.

Revise a Topic

If a topic is approved during Gerrit review, skip to the next step. Otherwise, revise the topic and push it back to Gerrit for another review.

Checkout the topic if it is not your current branch:

   $ git checkout my-topic

To revise the most recent commit on the topic edit files and add changes normally and then amend the commit:

   $ git commit --amend

(You may visit the Pro Git: Changing the Last Commit resource in GitHelp for further information on revising and rewriting your commit history.)

To revise commits further back on the topic, say the 3rd commit back:

   $ git rebase -i HEAD~3

(Substitute the correct number of commits back, as low as 1.)

Follow Git's interactive instructions. Preserve the Change-Id: line at the bottom of each commit message.

Return to the Share a Topic step to share the revised topic.

(You may visit the Pro Git: Changing Multiple Commits resource in GitHelp for further information on changing multiple commits -i.e. not only the last one, but further back in your history-, and the Pro Git: Rebasing resource on taking all the changes that were committed on one branch and replaying them on another one.)

Test a Topic

When a patch is submitted, it is tested across the three major platforms before being merged and tested on many platforms and configurations on the nightly dashboard.

If tests fail on a submitted topic, see the Revise a Topic step on how to submit a revised version. After a topic is merged, please check the next day's nightly dashboard to ensure there are not any regressions. If there are any new warnings or errors, submit a follow-up patch as soon as possible.

When a patch is submitted, macOS-Clang, Windows-MSVC, and Linux-GCC builds will start. Once they have finished, the build robots will make a comment on the patch with a link to their results visualized in CDash and mark the patch set as Verified +1 or Not Verified -1. The results are submitted by the Kitware Build Robot Gerrit user.

Builds can be spawned by adding the following comments to a patch set in Gerrit.

  • request build: all
  • request build: osx
  • request build: linux
  • request build: windows
  • request build: python
  • request build: power8
  • request build: cpp11
  • request build: cpp14

Merge a Topic

Only authorized developers with Git push access to may perform this step.

After a feature topic has been reviewed and approved in Gerrit, merge it into the upstream repository.

Checkout the topic if it is not your current branch:

   $ git checkout my-topic

Merge the topic, which is originally forked off the master branch, to master branch:

   $ git gerrit-merge

(If the merge conflicts follow the printed instructions to resolve them.)

For bug fixes that are ready to be included in the next patch release, please post a message in the ITK discussion for assistance.

Here are the recommended steps to merge a topic to both release and master branches, assuming the topic branch is forked off the release branch:

   $ git checkout release
   $ git merge --no-ff my-topic
   $ git push origin release

and do:

   $ git checkout master
   $ git merge --no-ff release
   $ git push origin master

to merge the release branch back to master.

Delete a Topic

After a topic has been merged upstream, delete your local branch for the topic.

Checkout and update the master branch:

   $ git checkout master
   $ git pullall

Delete the local topic branch:

   $ git branch -d my-topic

The branch -d command works only when the topic branch has been correctly merged. Use -D instead of -d to force the deletion of an unmerged topic branch (warning: you could lose commits).