Configuration file

The config folder presents a few examples of configuration files for NiftyNet applications.

This page describes commands and configurations supported by NiftyNet.


In general, a NiftyNet workflow can be fully specified by a NiftyNet application and a configuration file. The command to run the workflow is:

# command to run from git-cloned NiftyNet source code folder
python [train|inference|evaluation] -c <path_to/config.ini> -a <application>


# command to run using pip-installed NiftyNet
net_run [train|inference|evaluation] -c <path_to/config.ini> -a <application>

net_run is the entry point of NiftyNet, followed by an action argument of either train or inference:

  • train indicates updating the underlying network model using provided data.
  • inference indicates loading existing network model and generating responses according to data provided.

The <application> argument

<application> should be specified in the form of user.path.python.module.MyApplication, NiftyNet will try to import the class named MyApplication implemented in user/path/python/

A few applications are already included in NiftyNet, and can be passed as an argument of -a. Aliases are also created for these application (full specification can be found here: SUPPORTED_APP): The commands include:

# command
net_run -a niftynet.application.segmentation_application.SegmentationApplication -c ...
# alias:
net_segment -c ...
# command
net_run -a niftynet.application.regression_application.RegressionApplication -c ...
# alias:
net_regress -c ...
# command
net_run -a niftynet.application.autoencoder_application.AutoencoderApplication -c ...
# alias:
net_autoencoder -c ...
# command
net_run -a niftynet.application.gan_application.GANApplication -c ...
# alias:
net_gan -c ...

Overriding the arguments

In the case of quickly adjusting only a few options in the configuration file, creating a separate file is sometimes tedious.

To make it more accessible, net_run command also accepts parameters specification in the form of --<name> <value> or --<name>=<value>. When these are used, value will override the corresponding value of name defined both by system default and configuration file.

The following sections describes content of a configuration file <path_to/config.ini>.

Configuration sections

The configuration file currently adopts the INI file format, and is parsed by configparser. The file consists of multiple sections of name=value elements.

All files should have two sections:

If train action is specified, then a [TRAINING] section is required.

If inference action is specified, then an [INFERENCE] section is required.

Additionally, an application specific section is required for each application (Please find further comments on creating customised parser here):

  • [GAN] for generative adversarial networks
  • [SEGMENTATION] for segmentation networks
  • [REGRESSION] for regression networks
  • [AUTOENCODER] for autoencoder networks

The user parameter parser tries to match the section names listed above. All other section names will be treated as input data source specifications.

The following sections specify parameters (<name> = <value> pairs) available within each section.

Input data source section

Name Type Example Default
csv_file string csv_file=file_list.csv ''
path_to_search string path_to_search=my_data/fold_1 NiftyNet home folder
filename_contains string or string array filename_contains=foo, bar ''
filename_not_contains string or string array filename_not_contains=foo ''
filename_removefromid string filename_removefromid=bar ''
interp_order integer interp_order=0 3
pixdim float array pixdim=1.2, 1.2, 1.2 ''
axcodes string array axcodes=L, P, S ''
spatial_window_size integer array spatial_window_size=64, 64, 64 ''
loader string loader=simpleitk None


A file path to a list of input images. If the file exists, input image name list will be loaded from the file; the filename based input image search will be disabled; path_to_search, filename_contains, filename_not_contains, and filename_removefromid will be ignored. If this parameter is left blank or the file does not exist, input image search will be enabled, and the matched filenames will be written to this file path.


Keywords used to match filenames. The matched keywords will be removed, and the remaining part is used as subject name (for loading corresponding images across modalities).

See also: input filename matching guide


Keywords used to exclude filenames. The filenames with these keywords will not be used as input.

See also: input filename matching guide


Regular expression for extracting subject id from filename, matched pattern will be removed from the file names to form the subject id.

See also: input filename matching guide


Interpolation order of the input data.


If specified, the input volume will be resampled to the voxel sizes before fed into the network.


If specified, the input volume will be reoriented to the axes codes before fed into the network.


Array of three integers specifies the input window size. Setting it to single slice, e.g., spatial_window_size=64, 64, 1, yields a 2-D slice window.


Specify the loader to be used to load the files in the input section. Some loaders require additional Python packages. Default value None indicates trying all available loaders.

This section will be used by ImageReader to generate a list of input images objects. For example:

path_to_search = ./example_volumes/image_folder
filename_contains = T1, subject
filename_not_contains = T1c, T2
spatial_window_size = 128, 128, 1
pixdim = 1.0, 1.0, 1.0
axcodes = A, R, S
interp_order = 3

Specifies a set of images (currently supports NIfTI format via NiBabel library) from ./example_volumes/image_folder, with filenames contain both T1 and subject, but not contain T1c and T2. These images will be read into memory and transformed into “A, R, S” orientation (using NiBabel). The images will also be transformed to have voxel size (1.0, 1.0, 1.0) with an interpolation order of 3.

A CSV file with the matched filenames and extracted subject names will be generated to T1Image.csv in model_dir (by default; the CSV file location can be specified by setting csv_file). To exclude particular images, the csv_file can be edited manually.

This input source can be used alone, as a T1 MRI input to an application. It can also be used along with other modalities, a multi-modality example can be find here.

The following sections describe system parameters that can be specified in the configuration file.


Name Type Example Default
cuda_devices integer array cuda_devices=0,1,2 ''
num_threads positive integer num_threads=1 2
num_gpus integer num_gpus=4 1
model_dir string model_dir=/User/test_dir The directory of the config. file
dataset_split_file string dataset_split_file=/User/my_test ./dataset_split_file.csv
event_handler string or a list of strings event_handler=model_restorer model_saver, model_restorer, sampler_threading, apply_gradients, output_interpreter, console_logger, tensorboard_logger


Sets the environment variable CUDA_VISIBLE_DEVICES variable, e.g. 0,2,3 uses devices 0, 2, 3 will be visible; device 1 is masked.


Sets number of preprocessing threads for training.


Sets number of training GPUs. The value should be the number of available GPUs at most. This option is ignored if there’s no GPU device.


Directory to save/load intermediate training models and logs. NiftyNet tries to interpret this parameter as an absolute system path or a path relative to the current command. It’s defaulting to the directory of the current configuration file if left blank.


File assigning subjects to training/validation/inference subsets. If the string is a relative path, NiftyNet interpret this as relative to model_dir.


Event handler functions registered to these signals will be called by the engine, along with NiftyNet application properties and iteration messages as function parameters. See Signals and event handlers for more details.


Name Type Example Default
name string ''
activation_function string activation_function=prelu relu
batch_size integer batch_size=10 2
smaller_final_batch_mode string pad
decay non-negative float decay=1e-5 0.0
reg_type string reg_type=L1 L2
volume_padding_size integer array volume_padding_size=4, 4, 4 0,0,0
window_sampling string window_sampling=uniform uniform
queue_length integer queue_length=10 5
keep_prob non-negative float keep_prob=0.2 1.0


A network class from niftynet/network or from user specified module string. NiftyNet tries to import this string as a module specification. For example, setting it to will import the ToyNet class defined in niftynet/network/ (The relevant module path must be a valid Python path). There are also some shortcuts (SUPPORTED_NETWORK) for NiftyNet’s default network modules.


Sets the type of activation of the network. Available choices are listed in SUPPORTED_OP in activation layer. Depending on its implementation, the network might ignore this option .


Sets number of image windows to be processed at each iteration. When num_gpus is greater than 1, batch_size is used for each computing device. That is, the effective inputs at each iteration become batch_size x num_gpus.


When total number of window samples are not divisible by batch_size the class supports different modes for the final batch:

  • drop: drop the remainder batch
  • pad: padding the final smaller batch with -1
  • dynamic: output the remainder directly ( in this case the batch_size is undetermined at “compile time”)


Type of trainable parameter regularisation; currently the available choices are “L1” and “L2”. The loss will be added to tf.GraphKeys.REGULARIZATION_LOSSES collection. This option will be ignored if decay is 0.0.


Strength of regularisation, to help prevent overfitting.


Number of values padded at image volume level. The padding effect is equivalent to numpy.pad with:

           volume_padding_size[2], 0, 0),

For 2-D inputs, the third dimension of volume_padding_size should be set to 0, e.g. volume_padding_size=M,N,0. volume_padding_size=M is a shortcut for 3-D inputs, equivalent to volume_padding_size=M,M,M. The same amount of padding will be removed when before writing the output volume.


Type of sampler used to generate image windows from each image volume:

  • uniform: fixed size uniformly distributed,
  • weighted: fixed size where the likelihood of sampling a voxel is proportional to the cumulative intensity histogram,
  • balanced: fixed size where each label has the same probability of being sampled,
  • resize: resize image to the window size.

For weighted and balanced, an input section is required to load sampling priors. As an example in the demo folder, sampler parameter is set to label, indicating that the sampler uses label section as the sampling prior.


Integer specifies window buffer size used when sampling image windows from image volumes. Image window samplers fill the buffer and networks read the buffer. Because the network reads batch_size windows at each iteration, this value is set to at least batch_size * 2.5 to allow for a possible randomised buffer, i.e. max(queue_length, round(batch_size * 2.5)).


The probability that each element is kept if dropout is supported by the network. The default value is 0.5, meaning randomly dropout at the ratio of 0.5. This is also used as a default value at inference stage.

To achieve a deterministic inference, set keep_prob=1; to draw stochastic samples at inferece, set keep_prob to a value in between 0 and 1.

In the case of drawing multiple Monte Carlo samples, the user can run the inference command mutiple times, with each time a different save_seg_dir, for example:

python inference ... --save_seg_dir run_2 --keep_prob 0.5.


Intensity based volume normalisation can be configured using a combination of parameters described below:

(1) Setting normalisation=True enables the histogram-based normalisation. The relevant configuration parameters are:

histogram_ref_file, norm_type, cutoff, normalise_foreground_only, foreground_type, multimod_foreground_type.

These parameters are ignored and histogram-based normalisation is disabled if normalisation=False.

(2) Setting whitening=True enables the volume level normalisation computed by (I - mean(I))/std(I). The relevant configuration parameters are:

normalise_foreground_only, foreground_type, multimod_foreground_type.

These parameters are ignored and whitening is disabled if whitening=False.

More specifically:

Name Type Example Default
normalisation boolean normalisation=True False
whitening boolean whitening=True False
histogram_ref_file string histogram_ref_file=./hist_ref.txt ''
norm_type string norm_type=percentile percentile
cutoff float array (two elements) cutoff=0.1, 0.9 0.01, 0.99
normalise_foreground_only boolean normalise_foreground_only=True False
foreground_type string foreground_type=otsu_plus otsu_plus
multimod_foreground_type string multimod_foreground_type=and and

Boolean indicates if an histogram standardisation should be applied to the data.


Boolean indicates if the loaded image should be whitened, that is, given input image I, returns (I - mean(I))/std(I).


Name of the file that contains the normalisation parameter if it has been trained before or where to save it.


Type of histogram landmarks used in histogram-based normalisation (percentile or quartile).


Inferior and superior cutoff in histogram-based normalisation.


Boolean indicates if a mask should be computed based on foreground_type and multimod_foreground_type. If this parameter is set to True, all normalisation steps will be applied to the generated foreground regions only.


To generate a foreground mask and the normalisation will be applied to foreground only. Available choices:

otsu_plus, otsu_minus, thresh_plus, thresh_minus, mean_plus.

Strategies applied to combine foreground masks of multiple modalities, can take one of the following:

  • or union of the available masks,
  • and intersection of the available masks,
  • all masks computed from each modality independently.


Name Type Example Default
optimiser string optimiser=momentum adam
sample_per_volume positive integer sample_per_volume=5 1
lr float lr=0.001 0.1
loss_type string loss_type=CrossEntropy Dice
starting_iter integer starting_iter=0 0
save_every_n integer save_every_n=5 500
tensorboard_every_n integer tensorboard_every_n=5 20
max_iter integer max_iter=1000 10000
max_checkpoints integer max_checkpoints=5 100


Type of optimiser for computing graph gradients. Current available options are defined here: SUPPORTED_OPTIMIZERS.


Set number of samples to take from each image volume.


The learning rate for the optimiser.


Type of loss function. Please see the relevant loss function layer for choices available:

The corresponding loss function type names are defined in the ApplicationFactory


The iteration to resume training model. Setting starting_iter=0 starts the network from random initialisations. Setting starting_iter=-1 starts the network from the latest checkpoint if it exists.


Frequency of saving the current training model saving. Setting to a 0 to disable the saving schedule. (A final model will always be saved when quitting the training loop.)


Frequency of evaluating graph elements and write to tensorboard. Setting to 0 to disable the tensorboard writing schedule.


Maximum number of training iterations. The value is total number of iterations. Setting both starting_iter and max_iter to 0 to save the random model initialisation.


Maximum number of recent checkpoints to keep.

Validation during training

Setting validation_every_n to a positive integer enables validation loops during training. When validation is enabled, images list (defined by input specifications) will be treated as the whole dataset, and partitioned into subsets of training, validation, and inference according to exclude_fraction_for_validation and exclude_fraction_for_inference.

A CSV table randomly mapping each file name to one of the stages {'Training', 'Validation', 'Inference'} will be generated and written to dataset_split_file. This file will be created at the beginning of training (starting_iter=0) and only if the file does not exist.

To exclude particular subjects or adjust the randomly generated partition, the dataset_split_file can be edited manually. Please note duplicated rows are not removed. For example, if the content of dataset_split_file is as follows:


Each row will be treated as an independent subject. This means:

subject 1065 will be used in both Training and Validation stages, and it’ll be sampled more frequently than subject 1040 during training; subject 1071 will be used in Inference twice, the output of the second inference will overwrite the first.

Note that at each validation iteration, input will be sampled from the set of validation data, and the network parameters will remain unchanged. The is_training parameter of the network is set to True during validation, as a result layers with different behaviours in training and inference (such as dropout and batch normalisation) uses the training behaviour.

During inference, if a dataset_split_file is available, only image files in the Inference phase will be used, otherwise inference will process all image files defined by input specifications.

Name Type Example Default
validation_every_n integer validation_every_n=10 -1
validation_max_iter integer validation_max_iter=5 1
exclude_fraction_for_validation float exclude_fraction_for_validation=0.2 0.0
exclude_fraction_for_inference float exclude_fraction_for_inference=0.1 0.0

Run validation iterations after every N training iterations. Setting to 0 disables the validation.


Number of validation iterations to run. This parameter is ignored if validation_every_n is not a positive integer.


Fraction of dataset to use for validation. Value should be in [0, 1].


Fraction of dataset to use for inference. Value should be in [0, 1].

Data augmentation during training

Name Type Example Default
rotation_angle float array rotation_angle=-10.0,10.0 ''
scaling_percentage float array scaling_percentage=-20.0,20.0 ''
random_flipping_axes integer array random_flipping_axes=1,2 -1

Float array, indicates a random rotation operation should be applied to the volumes (This can be slow depending on the input volume dimensionality).


Float array indicates a random spatial scaling should be applied (This can be slow depending on the input volume dimensionality). The option accepts percentages relative to 100 (the original input size). E.g, (-50, 50) indicates transforming image (size d) to image with its size in between 0.5*d and 1.5d.


The axes which can be flipped to augment the data. Supply as comma-separated values within single quotes, e.g. ‘0,1’. Note that these are 0-indexed, so choose some combination of 0, 1.


Many networks are fully convolutional (without fully connected layers) and the resolution of the output volume can be different from the input image. That is, given input of an NxNxN voxel volume, the network generates a DxDxD-voxel output, where 0 < D < N.

This configuration section is design for such a process of sampling NxNxN windows from image volumes, and aggregating the network-generated DxDxD windows to output volumes.

In terms of sampling by a sliding window, the sampling step size should be D/2 in each spatial dimension. However automatically inferring D as a function of network architecture and N is not implemented at the moment. Therefore, NiftyNet requires a border to describe the spatial window size changes. border should be at least floor((N - D) / 2).

If the network is designed such that N==D is always true, border should be 0 (default value).

Note that the above implementation generalises to NxMxP-voxel windows and BxCxD-voxel window outputs. For a 2-D slice, e.g, Nx1xM, the second dimension of border should be 0.

Name Type Example Default
spatial_window_size integer array spatial_window_size=64,64,64 ''
border integer array border=5,5,5 0, 0, 0
inference_iter integer inference_iter=1000 -1
save_seg_dir string save_seg_dir=output/test output
output_postfix string output_postfix=_output _niftynet_out
output_interp_order non-negative integer output_interp_order=0 0
dataset_to_infer all|training|validation|inference dataset_to_infer=training ''


Array of integers indicating the size of input window. By default, the window size at inference time is the same as the input source specification. If this parameter is specified, it overrides the spatial_window_size parameter in input source sections.


Tuple of integers specifying a border size used to crop (along both sides of each dimension) the network output image window. E.g., 3, 3, 3 will crop a 64x64x64 window to size 58x58x58.


Integer specifies the trained model to be used for inference. -1 or unspecified indicating to use the latest available trained model in model_dir.


Prediction directory name. If it’s a relative path, it is set to be relative to model_dir.


Postfix appended to every inference output filenames.


Interpolation order of the network outputs.


String specifies which dataset (‘training’, ‘validation’, ‘inference’) to compute inference for. By default ‘inference’ dataset is used.


For evaluation of the output of an application against some available ground truth, an EVALUATION section must be present. Examples of evaluation config files are available in the config folder with the suffix _eval.ini.

The evaluation command is:

# command to run from git-cloned NiftyNet source code folder
python evaluation -c <path_to/config.ini> -a <application>

(For example, multimodal segmentation evaluation could be: python evaluation -a niftynet.applications.segmentation_application.SegmentationApplication -c config/default_multimodal_segmentation_eval.ini)

In order to run the evaluation, the input sources section must contain the details on

  • The ground truth against which to compare (label in case of the segmentation)
  • The corresponding files to evaluate (inferred)

The final evaluation file is saved in the folder indicated as input of the field model_dir in the section [SYSTEM] under the form of a csv file with indication of subject id (label if relevant) and the calculated metrics as columns.

The evaluation configuration section ([EVALUATION]) must contain:

  • save_csv_dir – Path where to save the csv file output
  • evaluations – List of metrics of evaluation to be calculated presented as a string separated by commas (e.g. dice, jaccard, n_pos_ref, n_pos_seg). Lists of possible evaluations metrics per application are available in regression evaluations, segmentation evaluations, and classification evaluations.
  • evaluation_unitsforeground, label or cc. Describe how the evaluation should be performed in the case of segmentation mostly (foreground means only one label, label means metrics per label, cc means metrics per connected component). More on this topic can be found at segmentation evaluations.