An apparatus comprises memory configured to store, at least partly, labelling information of a convolutional artificial neural network, and at least one processing core configured to generate, from an input data item, partial feature maps of the convolutional artificial neural network in accordance with the labelling information, generate, from the partial feature maps, inputs to a plurality of weak classifiers to generate a classification decision, wherein the labelling information identifies at least one of the following: elements of the feature maps that generate the inputs, and elements of the feature maps that are used to generate the elements that generate the inputs.