  In this paper we approach the novel problem of segmenting an image based on a
natural language expression. This is different from traditional semantic
segmentation over a predefined set of semantic classes, as e.g., the phrase
"two men sitting on the right bench" requires segmenting only the two people on
the right bench and no one standing or sitting on another bench. Previous
approaches suitable for this task were limited to a fixed set of categories
and/or rectangular regions. To produce pixelwise segmentation for the language
expression, we propose an end-to-end trainable recurrent and convolutional
network model that jointly learns to process visual and linguistic information.
In our model, a recurrent LSTM network is used to encode the referential
expression into a vector representation, and a fully convolutional network is
used to a extract a spatial feature map from the image and output a spatial
response map for the target object. We demonstrate on a benchmark dataset that
our model can produce quality segmentation output from the natural language
expression, and outperforms baseline methods by a large margin.
