Null-text Guidance in Diffusion Models is Secretly a Cartoon-style Creator

Classifier-free guidance is an effective sampling technique in diffusion models that has been widely adopted. The main idea is to extrapolate the model in the direction of text guidance and away from null-text guidance. In this paper, we demonstrate that null-text guidance in diffusion models is secretly a cartoon-style creator, i.e., the generated images can be efficiently transformed into cartoons by simply perturbing the null-text guidance. Specifically, we proposed two disturbance methods, i.e., Rollback disturbance (Back-D) and Image disturbance (Image-D), to construct misalignment between the noisy images used for predicting null-text guidance and text guidance (subsequently referred to as null-text noisy image and text noisy imageb respectively) in the sampling process. Back-D achieves cartoonization by altering the noisb level of the null-text noisy image via replacing xt with xl + Δ t. Image-D, alternatively, produces high-fidelity, diverse cartoons by defining xt as a clean input image, which further improves the incorporation of finer image details. Through comprehensive experiments, we delved into the principle of noise disturbing for null-text and uncovered that the efficacy of disturbance depends on the correlation between the null-text noisy image and the source image. Moreover, the proposed methods, which can generate cartoon images and cartoonize specific ones, are training-free and easily integrated as a plug-and-play component in any classifier-free guided diffusion model. The project page is available at https://nulltextforcartoon.github.io/.