1. In a digital medium environment to generate improved training data to train a model to label pixels, a method implemented by a computing device, the method comprising: selecting, by the computing device, an object from a plurality of objects of a structured object representation included with an image, the structured object representation defining a hierarchical relationship the plurality of objects within the image; displaying, by the computing device, the selected object in a user interface; receiving, by the computing device, an input originated through user interaction with the user interface, the input labeling the displayed object; and training, by the computing device, a model using machine learning to label pixels, the training based at least in part on a plurality of said labelled objects for a plurality of said images.