Make SpandrelImageToImage tiling much faster.

Author: RyanJDick

invokeai/app/invocations/spandrel_image_to_image.py

@@ -1,6 +1,4 @@
-import numpy as np
 import torch
-from PIL import Image
 from tqdm import tqdm
 
 from invokeai.app.invocations.baseinvocation import BaseInvocation, invocation
@@ -16,7 +14,7 @@
 from invokeai.app.invocations.primitives import ImageOutput
 from invokeai.app.services.shared.invocation_context import InvocationContext
 from invokeai.backend.spandrel_image_to_image_model import SpandrelImageToImageModel
-from invokeai.backend.tiles.tiles import calc_tiles_min_overlap, merge_tiles_with_linear_blending
+from invokeai.backend.tiles.tiles import calc_tiles_min_overlap
 from invokeai.backend.tiles.utils import TBLR, Tile
 
 
@@ -50,6 +48,29 @@ def _scale_tile(self, tile: Tile, scale: int) -> Tile:
             ),
         )
 
+    def _merge_tiles(self, tiles: list[Tile], tile_tensors: list[torch.Tensor], out_tensor: torch.Tensor):
+        """A simple tile merging algorithm. tile_tensors are merged into out_tensor. When adjacent tiles overlap, we
+        split the overlap in half. No 'blending' is applied.
+        """
+        # Sort tiles and images first by left x coordinate, then by top y coordinate. During tile processing, we want to
+        # iterate over tiles left-to-right, top-to-bottom.
+        tiles_and_tensors = list(zip(tiles, tile_tensors, strict=True))
+        tiles_and_tensors = sorted(tiles_and_tensors, key=lambda x: x[0].coords.left)
+        tiles_and_tensors = sorted(tiles_and_tensors, key=lambda x: x[0].coords.top)
+
+        for tile, tile_tensor in tiles_and_tensors:
+            # We only keep half of the overlap on the top and left side of the tile. We do this in case there are edge
+            # artifacts. We don't bother with any 'blending' in the current implementation - for most upscalers it seems
+            # unnecessary, but we may find a need in the future.
+            top_overlap = tile.overlap.top // 2
+            left_overlap = tile.overlap.left // 2
+            out_tensor[
+                :,
+                :,
+                tile.coords.top + top_overlap : tile.coords.bottom,
+                tile.coords.left + left_overlap : tile.coords.right,
+            ] = tile_tensor[:, :, top_overlap:, left_overlap:]
+
     @torch.inference_mode()
     def invoke(self, context: InvocationContext) -> ImageOutput:
         # Images are converted to RGB, because most models don't support an alpha channel. In the future, we may want to
@@ -100,15 +121,19 @@ def invoke(self, context: InvocationContext) -> ImageOutput:
                 )
                 output_tiles.append(output_tile)
 
-        # Merge tiles into output image.
-        np_output_tiles = [np.array(SpandrelImageToImageModel.tensor_to_pil(tile)) for tile in output_tiles]
-        _, channels, height, width = image_tensor.shape
-        np_out_image = np.zeros((height * scale, width * scale, channels), dtype=np.uint8)
-        merge_tiles_with_linear_blending(
-            dst_image=np_out_image, tiles=scaled_tiles, tile_images=np_output_tiles, blend_amount=min_overlap // 2
+        # TODO(ryand): There are opportunities to reduce peak VRAM utilization here if it becomes an issue:
+        # - Keep the input tensor on the CPU.
+        # - Move each tile to the GPU as it is processed.
+        # - Move output tensors back to the CPU as they are produced, and merge them into the output tensor.
+
+        # Merge the tiles to an output tensor.
+        batch_size, channels, height, width = image_tensor.shape
+        output_tensor = torch.zeros(
+            (batch_size, channels, height * scale, width * scale), dtype=image_tensor.dtype, device=image_tensor.device
         )
+        self._merge_tiles(scaled_tiles, output_tiles, output_tensor)
 
         # Convert the output tensor to a PIL image.
-        pil_image = Image.fromarray(np_out_image)
+        pil_image = SpandrelImageToImageModel.tensor_to_pil(output_tensor)
         image_dto = context.images.save(image=pil_image)
         return ImageOutput.build(image_dto)