Temporal Tiling: Treating Image Tiles as a Temporal Sequence¶

The idea: instead of processing tiles independently (standard tiling), treat them as a temporal sequence where each tile knows the context of previously generated tiles — like frames in a video. This eliminates seam artifacts and maintains global coherence.

The Problem with Standard Tiling¶

Standard tiled diffusion (MultiDiffusion, Tiled Inference) processes tiles independently and blends overlaps by averaging. This causes: - Seam artifacts on smooth gradients (metal surfaces, skin) - Inconsistent lighting/color across tiles - Duplicated objects (same prompt, different tiles → same content repeated)

Approaches — From Simple to Full¶

Level 0: Overlap Averaging (MultiDiffusion)¶

Tile A [====overlap====] Tile B
       averaged in overlap zone

Level 1: Gradient Sync (SyncDiffusion, NeurIPS 2023)¶

At each denoising step, compute perceptual loss between overlapping predicted images → backprop gradients → nudge tiles toward consistency. 66% preference over MultiDiffusion. No retraining. Slow (gradient computation per step).

Level 2: Global + Local (DemoFusion, AccDiffusion)¶

Generate low-res global image first → use as structural guide for high-res tiles: - DemoFusion: skip-residual from low-res + dilated sampling for global paths - AccDiffusion v2: ControlNet from low-res + patch-content-aware prompts (avoids object duplication) - FreeScale: Scale Fusion separates self-attention into global (low-freq) and local (high-freq)

Level 3: Cross-Attention to Previous Tile (IP-Adapter Pattern)¶

After generating tile N, encode its latent. When generating tile N+1, inject previous tile features via cross-attention (like [[PixelSmile|IP-Adapter]]).

~22M extra params. Fast. But only sees immediate predecessor — error accumulates.

Level 4: Temporal Attention Modules (AnimateDiff Pattern)¶

Treat tiles as video frames. Insert temporal self-attention after each spatial block:

Spatial layers: each tile processed independently
                (temporal axis → batch dimension)
                          ↓
Temporal attention: process ACROSS tiles
                (spatial axes → batch dimension)
                          ↓
Each spatial position attends to same position in all tiles

Zero-initialized output projection → identity at start → pretrained spatial model protected.

Pros: bidirectional attention, learned consistency Cons: O(N^2) in number of tiles, requires training temporal modules

Level 5: Causal Temporal Attention (SANA-Video / GPDiT Pattern)¶

Generate tiles sequentially with causal masking — each tile attends only to previously generated tiles:

Tile 0 (top-left): generated normally
Tile 1: attends to Tile 0
Tile 2: attends to Tiles 0, 1
...

GPDiT variant: each noisy tile attends to previous CLEAN tiles (already denoised). Ablating clean-clean attention saves ~50% FLOPs.

Sparse causal (Tune-A-Video): each tile attends only to first tile + immediate neighbor. Efficient.

Level 6: NUWA-Infinity Pattern (Autoregressive Patches)¶

Microsoft's system — closest prior art to tiles-as-sequence: - Nearby Context Pool (NCP): caches previously generated patches as context for current patch - Arbitrary Direction Controller: learns optimal generation order - Global patch-level autoregressive model for inter-patch dependencies - Local token-level generation within each patch - "Render-and-optimize": each patch optimized immediately, hidden states saved as context

Level 7: Hybrid (Best of All Worlds)¶

Combine global guidance + neighbor cross-attention: 1. Generate low-res global image (DemoFusion) 2. For each tile: inject global context via skip-residual AND inject neighbor tile features via MVDiffusion-style Correspondence-Aware Attention (CAA) 3. Parallelizable (tiles depend on global + overlap, not on each other sequentially)

For SANA Specifically¶

SANA's linear attention makes temporal tiling uniquely practical:

1. Linear complexity O(N) — extending token sequence with neighbor tiles costs linearly, not quadratically
2. 32× DC-AE compression — tile latents are extremely compact (32×32 for 1024px tile)
3. SANA-Video already exists — Block Causal Linear Attention with constant-memory KV cache. Same mechanism directly applicable to tiles.
4. Causal Mix-FFN in SANA-Video caches last frame of previous block for temporal convolution — maps to last row of previous tile for spatial tiling

Minimum viable approach for SANA: Extend RoPE position encoding to include 2D tile position. When generating a tile, concatenate its tokens with tokens from overlapping regions of adjacent (already generated) tiles. Linear attention handles cross-tile consistency at O(N) cost.

Full approach: Port SANA-Video's Block Causal Linear Attention to 2D spatial tiling. Each tile = one "frame". KV cache stores cumulative statistics from previous tiles (O(D^2) memory regardless of tile count).

Key Papers¶

Memory Comparison¶