CCG Diffusion: Combinatory Categorial Grammar-Driven Compositional and Syntactically Disambiguated Text-to-Image Generation

Ryosuke Yamaki, Daichi Mochihashi, Nobutaka Shimada, Seitaro Shinagawa, Tadahiro Taniguchi

Text-to-image generation models do not explicitly receive the syntactic structure of the prompt, i.e., which word modifies which and where each phrase attaches. Consequently, they often struggle to bind attributes to the correct objects, to depict spatial relations and counts correctly, and to render syntactically ambiguous prompts in the intended interpretation. Existing syntax-based control methods mainly address attribute binding and have limited ability to control spatial relations and counts or to specify the interpretation of syntactically ambiguous prompts. They rely on phrase-structure or dependency grammars and require additional rules or constraints on the tree structure to extract modification relations between words or to specify a syntactic interpretation. We propose CCG Diffusion, a training-free method that controls image generation using Combinatory Categorial Grammar (CCG). In CCG, the category of each word carries rich syntactic information: it specifies what the word combines with and what phrase it forms. Modification relations between words can therefore be read directly from a CCG parse. Moreover, prepositional phrase (PP) attachment ambiguity, a…