  Recent breakthroughs in text-to-image synthesis have been driven by diffusion
models trained on billions of image-text pairs. Adapting this approach to 3D
synthesis would require large-scale datasets of labeled 3D data and efficient
architectures for denoising 3D data, neither of which currently exist. In this
work, we circumvent these limitations by using a pretrained 2D text-to-image
diffusion model to perform text-to-3D synthesis. We introduce a loss based on
probability density distillation that enables the use of a 2D diffusion model
as a prior for optimization of a parametric image generator. Using this loss in
a DeepDream-like procedure, we optimize a randomly-initialized 3D model (a
Neural Radiance Field, or NeRF) via gradient descent such that its 2D
renderings from random angles achieve a low loss. The resulting 3D model of the
given text can be viewed from any angle, relit by arbitrary illumination, or
composited into any 3D environment. Our approach requires no 3D training data
and no modifications to the image diffusion model, demonstrating the
effectiveness of pretrained image diffusion models as priors.
