Loading data

To efficiently handle files larger than main memory, LiberTEM never loads the whole data set into memory. Calling the load() function only opens the data set and gives back a handle; running an analysis with run() or a UDF with run_udf() then streams the data from mass storage.

See Sample Datasets for publicly available datasets for testing.

There are two main ways of opening a data set in LiberTEM: using the GUI, or the Python API.

Loading through the API

In the API, you can use libertem.api.Context.load(). The general pattern is:

ctx = Context()
ctx.load("typename", path="/path/to/some/file", arg1="val1", arg2=42)

So, you need to specify the data set type, the path, and dataset-specific arguments. These arguments are documented below.

For most file types, it is possible to automatically detect the type and parameters, which you can trigger by using "auto" as file type:

ctx.load("auto", path="/path/to/some/file")

For the full list of supported file formats with links to their reference documentation, see Supported formats below.

Loading using the GUI

Using the GUI, mostly the same parameters need to be specified, although some are only available in the Python API. Tuples (for example for nav_shape) have to be entered as separated values into the fields. You can hit a comma to jump to the next field. We follow the NumPy convention here and specify the “fast-access” dimension last, so a value of 42, 21 would mean the same as specifying (42, 21) in the Python API, setting y=42 and x=21. Note that the GUI is currently limited to 2D visualizations, while the scripting API can handle more general cases.

See also the concepts section.

Common parameters

There are some common parameters across data set types:

name

The name of the data set, for display purposes. Only used in the GUI.

nav_shape

In the GUI, we generally support visualizing data containing rectangular 2D scans. For all the dataset types, you can specify a nav_shape as a tuple (y, x). If the dataset isn’t 4D, the GUI can reshape it to 4D. When using the Python API, you are free to use n-dimensional nav_shape, if the data set and chosen analysis supports it.

sig_shape

In the GUI, you can specify shape of the detector as height, width, but when using the Python API, it can be of any dimensionality.

sync_offset

You can specify a sync_offset to handle synchronization or acquisition problems. If it’s positive, sync_offset number of frames will be skipped from start. If it’s negative, abs(sync_offset) number of blank frames will be inserted at start.

io_backend

Different methods for I/O are available in LiberTEM, which can influence performance. See I/O Backends for details.

Supported formats

LiberTEM supports the following file formats out of the box, see links for details:

• Merlin Medipix (MIB)

• Raw binary files

• NumPy files (NPY)

• Digital Micrograph (DM3, DM4) files

• EMPAD

• K2IS

• FRMS6

• BLO

• SER

• HDF5

• Norpix SEQ

• MRC

• TVIPS

Furthermore, two alternative mechanisms exist for interfacing LiberTEM with data loaded elsewhere in Python via other libraries:

• a memory data set can be constructed from a NumPy array for testing purposes. See Memory data set for details.

• a Dask data set can be constructed from a Dask array. Depending on the method used to construct the source array this can achieve good performance. See Dask for details.