Step1X-3D: Towards High-Fidelity and Controllable Generation of Textured 3D Assets (2505.07747v1)

Abstract: While generative artificial intelligence has advanced significantly across text, image, audio, and video domains, 3D generation remains comparatively underdeveloped due to fundamental challenges such as data scarcity, algorithmic limitations, and ecosystem fragmentation. To this end, we present Step1X-3D, an open framework addressing these challenges through: (1) a rigorous data curation pipeline processing >5M assets to create a 2M high-quality dataset with standardized geometric and textural properties; (2) a two-stage 3D-native architecture combining a hybrid VAE-DiT geometry generator with an diffusion-based texture synthesis module; and (3) the full open-source release of models, training code, and adaptation modules. For geometry generation, the hybrid VAE-DiT component produces TSDF representations by employing perceiver-based latent encoding with sharp edge sampling for detail preservation. The diffusion-based texture synthesis module then ensures cross-view consistency through geometric conditioning and latent-space synchronization. Benchmark results demonstrate state-of-the-art performance that exceeds existing open-source methods, while also achieving competitive quality with proprietary solutions. Notably, the framework uniquely bridges the 2D and 3D generation paradigms by supporting direct transfer of 2D control techniques~(e.g., LoRA) to 3D synthesis. By simultaneously advancing data quality, algorithmic fidelity, and reproducibility, Step1X-3D aims to establish new standards for open research in controllable 3D asset generation.

• The paper introduces a two-stage VAE and diffusion-based approach to generate high-fidelity 3D textured assets from single-view imagery.
• It employs a robust data curation and mesh processing pipeline that filters millions of assets and refines geometry for consistent texture mapping.
• Experimental results demonstrate superior geometry-image alignment with high CLIP scores and effective user-controlled generation via LoRA.

Step1X-3D presents an open framework designed to address the challenges in 3D asset generation, specifically data scarcity, algorithmic limitations, and ecosystem fragmentation. The framework aims for high-fidelity, controllable generation of textured 3D assets from single images and promotes reproducibility through open-source release of data, models, and training code.

The framework consists of three main components:

1. Data Curation Pipeline:
   • Processes over 5 million 3D assets from public (Objaverse, Objaverse-XL, ABO, 3D-FUTURE) and proprietary collections.
   • Implements a multi-stage filtering process to remove low-quality data based on texture quality (using rendered albedo maps, HSV analysis), single-surface detection (using Canonical Coordinate Maps and checking pixel matches), small object size, transparent materials (alpha channel detection), incorrect normals, and mesh type/name filters.
   • Ensures geometric consistency by converting non-watertight meshes to watertight representations. An enhanced mesh-to-SDF conversion method is introduced, incorporating the winding number concept to improve the conversion success rate, particularly for non-manifold objects.
   • Samples points and normals for VAE training, including a Sharp Edge Sampling (SES) strategy from Dora (2412.17808) to capture details. Samples different point sets (volume, near-surface, on-surface) with TSDF values for supervision.
   • Prepares data for the diffusion model by rendering 20 random viewpoints (with varying elevation, azimuth, focal length) for each model, applying data augmentations (flipping, color jitter, rotation).
   • Results in a curated dataset of approximately 2 million high-quality assets, with around 800,000 derived from public data planned for open release.
2. Step1X-3D Geometry Generation:
   • Employs a two-stage approach: a 3D Shape Variational Autoencoder (VAE) and a Rectified Flow Transformer diffusion model.
   • 3D Shape VAE: Based on the latent vector set representation from 3DShape2VecSet (2308.06721), adapted for scalability using a perceiver-based encoder-decoder architecture (2107.11701, 2308.06721). Utilizes Farthest Points Sampling (FPS) on both uniform and salient points to initialize latent queries. Incorporates Sharp Edge Sampling and Dual Cross Attention from Dora (2412.17808) to preserve geometric details. The encoder processes point positions (with Fourier positional encoding) and normals. The decoder uses cross-attention to predict TSDF values for query points in 3D space. Trained with an MSE loss on TSDF values and a KL divergence term for latent space regularization. Reconstructs meshes from TSDF using Marching Cubes [1998marching] and uses Hierarchical Volume Decoding (2503.16302) for faster inference.
   • Rectified Flow Transformer: Adapt the MMDiT architecture from FLUX [flux2024] for 1D latent space processing. Uses a hybrid dual-stream/single-stream block structure for handling latent and condition tokens. Omits spatial positional embeddings for latent sets but keeps timestep embeddings. Uses DINOv2 (2304.07193) and CLIP (2103.00013) image encoders to extract conditional tokens from preprocessed single-view images, injected via parallel cross-attention.
   • Training: Trained using a flow matching objective (Rectified Flow) (2210.02747, 2209.03003), predicting the velocity field. Uses a logit-normal sampling strategy to increase weight for intermediate timesteps. Employs Exponential Moving Average (EMA) for parameter updates. Trained in two phases: initially with a smaller latent set size (512) for fast convergence, then scaled up (2048) with a reduced learning rate for capacity and precision.
3. Step1X-3D Texture Generation:
   • Follows the geometry generation stage.
   • Geometry Postprocess: Uses the trimesh toolkit [trimesh] for mesh refinement: ensuring watertightness (with hole-filling), remeshing for uniform topology (subdivision and Laplacian smoothing), and UV parameterization using xAtlas [xatlas].
   • Texture Dataset Preparation: Curates a 30,000-asset subset from the cleaned Objaverse data, rendered from six canonical views to produce albedo, normal, and position maps at 768x768 resolution.
   • Geometry-guided Multi-view Images Generation:
     • Uses a diffusion model fine-tuned from MV-Adapter (2412.03632) (which is based on SD-XL (2204.06125)) to generate consistent multi-view images from a single input view and target camera poses. MV-Adapter's epipolar attention enables high-resolution generation (768x768), and its attention architecture balances generalization, multi-view consistency, and condition adherence.
     • Injects geometric guidance (normal and 3D position maps from the generated geometry) via image-based encoders and cross-attention mechanisms to improve detail synthesis and texture-geometry alignment.
     • Implements a texture-space synchronization module during inference within the diffusion model. This involves unprojecting latent representations to UV space, fusing information from multiple views based on view direction and normal cosine similarity, and re-projecting back to latent space. This helps maintain cross-view coherence and reduces artifacts.
   • Bake Texture: Upsamples the generated multi-view images to 2048x2048, inversely projects them onto the mesh's UV map, and uses continuity-aware texture inpainting (similar to techniques in Hunyuan3D 2.0 (2501.12202) and Paint3D (2403.17709)) to address occlusions and discontinuities, producing seamless texture maps.

Controllable Generation:

Step1X-3D leverages the structural similarity between its VAE+Diffusion architecture and 2D image generation models (like Stable Diffusion) to enable direct transfer of 2D control techniques (e.g., ControlNet (2302.08543), IP-Adapter (2308.06721)) and parameter-efficient adaptation methods (like LoRA (2106.09685)) to 3D. As part of the open-source release, LoRA is implemented for geometric shape control based on labels (e.g., symmetry, detail level). This allows fine-tuning specific aspects of generation without training the entire model, achieved by training a small LoRA module applied to a condition branch, enabling efficient injection of conditional signals. Future updates are planned for skeleton, bounding box, caption, and image prompt conditions.

Experiments and Results:

Evaluations are conducted on a diverse benchmark of 110 images, comparing Step1X-3D against state-of-the-art open-source (Trellis (2412.01506), Hunyuan3D 2.0 (2501.12202), TripoSG (2502.06608)) and proprietary (Tripo-v2.5, Rodin-v1.5, Meshy-4) methods.

• Visual Quality: Step1X-3D generates plausible geometry (shown with normal maps) and texture (shown with multi-view renders) that maintain strong similarity to input images, complete occluded regions, and exhibit good texture-geometry alignment across various styles and complexities.
• Controllable Generation: Demonstrated through LoRA fine-tuning for symmetry and geometric detail control (sharp, normal, smooth), showing the model adheres to these controls, particularly in frontal views.
• Quantitative Comparisons: Using multimodal embeddings (Uni3D (2310.06773), OpenShape (2310.06779) with SparseConv (2405.14979) and PointBERT (2202.01655) backbones) for geometry-image alignment (Uni3D-I, OpenShape$_{sc}$-I, OpenShape$_{pb}$-I) and CLIP-Score (2103.00013) for texture semantic alignment. Step1X-3D achieves the highest CLIP-Score and ranks among the top methods in geometric metrics, demonstrating robust performance.
• User Study: Participants rated objects on geometric plausibility, similarity to input, texture clarity, and texture-geometry alignment on a 5-point scale. Step1X-3D performs comparably to the best methods but the paper indicates that all methods still have significant room for improvement towards production-ready quality.
• Visual Comparisons: Side-by-side comparisons with SOTA methods, using pose-normalized renders in Unreal Engine, show Step1X-3D produces comparable or superior geometric and textural results.

Limitations:

Current limitations include the grid resolution (256^3) used for mesh-to-TSDF conversion, which limits geometric detail, and the texture pipeline's current focus on albedo generation, lacking support for relighting and Physically Based Rendering (PBR) materials. Future work aims to address these aspects.

By combining a high-quality dataset, a novel two-stage 3D-native architecture, and mechanisms for controllable generation rooted in 2D paradigms, Step1X-3D provides a strong foundation and open resources for advancing the field of 3D asset generation.