====== SplitInput ======
This module splits an input stack of images into equally sized subsets of images based on a selected splitting method. This can be useful, to  

===== Parameters and I/O =====

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^ Parameters                 ^ Description     ^
| Mode                       | Select a mode (see below). |
| -> Header key              | If "Split by headerkey" is selected as mode, the user needs to specify a header key here. |
| Number of outputs          | Select the number of outputs/stacks, the input shall be split into. |

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^ Modes                      ^ Description     ^
| Split by headerkey         | If selected, the specified header key is used to sort the data, before the set is split into equally sized subsets. |
| Randomize                  | The images will be randomly split into the selected number of outputs stacks. All output stacks will be equally sized. |
| Equally spaced             | The original stack with its original sorting will be split into equally sized stacks. |