Generative AI models are now a part of our daily lives. They have advanced rapidly in recent years, and the results went from a funky image to a highly photorealistic one relatively fast. With all these models like MidJourney, StableDiffusion, and DALL-E, generating the image you have in your mind has never been easier.
It’s not just in 2D as well. We have seen quite remarkable advancements in 3D content generation in the meantime. Whether the third dimension is time (video) or depth (NeRF, 3D models), the generated outputs are becoming closer to real ones quite rapidly. These generative models have eased the expertise requirement in 3D modeling and design.
However, not everything is pink-bright. The 3D generations are becoming more realistic, yes, but they still lag way behind the 2D generative models. The large-scale text-to-image datasets have played a crucial role in expanding the capabilities of image generation algorithms. However, while 2D data is readily available, accessing 3D data for training and supervision is more challenging, resulting in a deficiency in 3D generative models.
The two major limitations of existing 3D generative models are the lack of saturation in colors and the low diversity compared to text-to-image models. Let us meet with DreamTime and see how it overcomes these limitations.
DreamTime shows that the limitations observed in the NeRF (Neural Radiance Fields) optimization process are primarily caused by the conflict between uniform timestep sampling in score distillation. To address this conflict and overcome the limitations, it uses a novel approach that prioritizes timestep sampling using monotonically non-increasing functions. By aligning the NeRF optimization process with the sampling process of the diffusion model, an aim is made to enhance the quality and effectiveness of the NeRF optimization for generating realistic 3D models.
The existing methods often result in models with saturated colors and limited diversity, posing obstacles to content creation. To address this, DreamTime proposes a novel technique called time-prioritized score distillation sampling (TP-SDS) for text-to-3D generation. The key idea behind TP-SDS is to prioritize different levels of visual concepts provided by pre-trained diffusion models at various noise levels. This approach allows for the optimization process to focus on refining details and enhancing visual quality. By incorporating a non-increasing timestep sampling strategy, TP-SDS aligns the text-to-3D optimization process with the sampling process of diffusion models.
To evaluate the effectiveness of TP-SDS, the authors of DreamTime conduct comprehensive experiments and compare its performance against standard score distillation sampling (SDS) techniques. They analyze the conflict between text-to-3D optimization and uniform timestep sampling through mathematical formulations, gradient visualizations, and frequency analysis. The results demonstrate that the proposed TP-SDS approach significantly improves the quality and diversity of text-to-3D generation, outperforming existing methods.
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Ekrem Çetinkaya received his B.Sc. in 2018, and M.Sc. in 2019 from Ozyegin University, Istanbul, Türkiye. He wrote his M.Sc. thesis about image denoising using deep convolutional networks. He received his Ph.D. degree in 2023 from the University of Klagenfurt, Austria, with his dissertation titled “Video Coding Enhancements for HTTP Adaptive Streaming Using Machine Learning.” His research interests include deep learning, computer vision, video encoding, and multimedia networking.