Official Comment by Authors
We thank the reviewer for your appreciation of our impressive results, our method’s great versatility and clear presentation. Please see our responses to your concerns below.
1. **DMV3D vs LRM**: We would like to clarify the different contributions of LRM and DMV3D. Please note that, in DMV3D, we acknowledge LRM as prior work and have explicitly cited LRM in section 3.2. Our work makes orthogonal contributions, focusing on different challenges that are not covered by LRM. In particular, LRM focuses on the task of single-image reconstruction only and introduces the first scalable transformer model trained on massive multi-view data. However, in essence, LRM is a deterministic model that cannot model the inherent uncertainty (multiple plausible solutions exist for unseen parts of the 3D objects) in single-image 3D reconstruction. In contrast, DMV3D aims to build a general probabilistic diffusion model for 3D generation. Our framework is not only applicable to single-image reconstruction but also text-to-3D generation – a task completely uncovered by LRM.
To do so, we propose a novel single-stage multi-view diffusion framework and adopt a transformer model to achieve multi-view denoising. Again, please note that we have cited LRM (by anonymously putting it in the supplemental material) and clearly stated in Sec.3.2 that our transformer architecture is inspired by LRM to avoid any misconception about dual submission. We emphasize that the whole story of our paper, including our entire method section (Sec. 3), does not focus on the original transformer contribution made by LRM. Instead, our focus is mainly on: 1) how to build a multi-view diffusion framework for 3D generation (Sec. 3.1), 2) how to improve/extend the transformer model to support multi-view denoising (Sec. 3.2), and 3) how to enable both text and image conditioning (Sec. 3.3). These aspects are distinct from the scope of LRM. Furthermore, our transformer architecture is also different from the one in LRM in taking noisy multi-view images as input, being conditioned by the diffusion time step, utilizing a new ray-conditioning technique to better handle the diverse camera intrinsics, and supporting text conditioning.
As a result, even for the same single-image reconstruction problem, DMV3D and LRM address it in very different ways. DMV3D leverages multi-view diffusion denoising, whereas LRM performs single-view image-to-NeRF translation. The transformer inputs (multi-view noisy images vs a single-view clean image) and the inference processes (DDIM-based multi-step diffusion denoising vs single-step transformer inference) are highly different. Moreover, because of being a probabilistic generative model, DMV3D can generate multiple high-quality 3D assets given the same single image input (as shown in Fig. 1 and our project page), while LRM can only generate one single result. The probabilistic modeling introduced by DMV3D also enhances the realism and reduces the blurriness of generated textures for unseen parts; in contrast, LRM tends to generate blurred results due to mode averaging.
In sum, different from the deterministic model in LRM, our DMV3D introduces a novel probabilistic model for 3D generation and contributes 1) a novel multi-view diffusion framework 2) the general support for both text and image conditioning and 3) new architecture designs to support multi-view denoising and text/image conditioning. The contributions are made orthogonal to those of LRM and we believe these are valuable contributions to the field towards a general, practical, and high-quality 3D generative model.
2. **Novelty**: As discussed in the related work, we are inspired by the RenderDiffusion work for using a reconstructor as a denosier. Concurrent work, Viewset Diffusion, adopts the same idea from RenderDiffusion, but was only demonstrated to work on limited data lacking diversity. Our novel transformer-based 3D denoiser architecture is different from the reconstructor architecture in viewset diffusion and enables state-of-the-art results for scalable, diverse, and high-quality 3D generation.
3. **Limitations**: one limitation with our text-to-3D model is that we cannot handle complex text prompts as well as 2D diffusion models like stable diffusion, as a result of the limited scale of multi-view data compared with 2D data. Another limitation is that the generated textures at unseen views are still a bit blurry compared with input view. It will be interesting to further boost the quality of texture sharpness in future work.
4. **Training time**: despite our method being a diffusion model, we only sample a single time-step at a time to train our multi-view denoiser. This single-step setting is similar to what LRM does except our input images are noisy; hence our model trains as fast as LRM during training.