[PixArt-Alpha] Introduce resolution binning (#5739)

* feat: add resolution binning
Co-authored-by: lawrence-cj <jschen@mail.dlut.edu.cn>

* rename

* debug

* add :test

* remove unused variable

* set resolution_binning to False.

---------
Co-authored-by: lawrence-cj <jschen@mail.dlut.edu.cn>

src/diffusers/pipelines/pixart_alpha/pipeline_pixart_alpha.py

@@ -19,6 +19,7 @@ import urllib.parse as ul
 from typing import Callable, List, Optional, Tuple, Union
 
 import torch
+import torch.nn.functional as F
 from transformers import T5EncoderModel, T5Tokenizer
 
 from ...image_processor import VaeImageProcessor
@@ -43,7 +44,6 @@ if is_bs4_available():
 if is_ftfy_available():
     import ftfy
 
-
 EXAMPLE_DOC_STRING = """
     Examples:
         ```py
@@ -60,6 +60,42 @@ EXAMPLE_DOC_STRING = """
         ```
 """
 
+ASPECT_RATIO_1024_BIN = {
+    "0.25": [512.0, 2048.0],
+    "0.28": [512.0, 1856.0],
+    "0.32": [576.0, 1792.0],
+    "0.33": [576.0, 1728.0],
+    "0.35": [576.0, 1664.0],
+    "0.4": [640.0, 1600.0],
+    "0.42": [640.0, 1536.0],
+    "0.48": [704.0, 1472.0],
+    "0.5": [704.0, 1408.0],
+    "0.52": [704.0, 1344.0],
+    "0.57": [768.0, 1344.0],
+    "0.6": [768.0, 1280.0],
+    "0.68": [832.0, 1216.0],
+    "0.72": [832.0, 1152.0],
+    "0.78": [896.0, 1152.0],
+    "0.82": [896.0, 1088.0],
+    "0.88": [960.0, 1088.0],
+    "0.94": [960.0, 1024.0],
+    "1.0": [1024.0, 1024.0],
+    "1.07": [1024.0, 960.0],
+    "1.13": [1088.0, 960.0],
+    "1.21": [1088.0, 896.0],
+    "1.29": [1152.0, 896.0],
+    "1.38": [1152.0, 832.0],
+    "1.46": [1216.0, 832.0],
+    "1.67": [1280.0, 768.0],
+    "1.75": [1344.0, 768.0],
+    "2.0": [1408.0, 704.0],
+    "2.09": [1472.0, 704.0],
+    "2.4": [1536.0, 640.0],
+    "2.5": [1600.0, 640.0],
+    "3.0": [1728.0, 576.0],
+    "4.0": [2048.0, 512.0],
+}
+
 
 class PixArtAlphaPipeline(DiffusionPipeline):
     r"""
@@ -495,6 +531,38 @@ class PixArtAlphaPipeline(DiffusionPipeline):
         latents = latents * self.scheduler.init_noise_sigma
         return latents
 
+    @staticmethod
+    def classify_height_width_bin(height: int, width: int, ratios: dict) -> Tuple[int, int]:
+        """Returns binned height and width."""
+        ar = float(height / width)
+        closest_ratio = min(ratios.keys(), key=lambda ratio: abs(float(ratio) - ar))
+        default_hw = ratios[closest_ratio]
+        return int(default_hw[0]), int(default_hw[1])
+
+    @staticmethod
+    def resize_and_crop_tensor(samples: torch.Tensor, new_width: int, new_height: int) -> torch.Tensor:
+        orig_height, orig_width = samples.shape[2], samples.shape[3]
+
+        # Check if resizing is needed
+        if orig_height != new_height or orig_width != new_width:
+            ratio = max(new_height / orig_height, new_width / orig_width)
+            resized_width = int(orig_width * ratio)
+            resized_height = int(orig_height * ratio)
+
+            # Resize
+            samples = F.interpolate(
+                samples, size=(resized_height, resized_width), mode="bilinear", align_corners=False
+            )
+
+            # Center Crop
+            start_x = (resized_width - new_width) // 2
+            end_x = start_x + new_width
+            start_y = (resized_height - new_height) // 2
+            end_y = start_y + new_height
+            samples = samples[:, :, start_y:end_y, start_x:end_x]
+
+        return samples
+
     @torch.no_grad()
     @replace_example_docstring(EXAMPLE_DOC_STRING)
     def __call__(
@@ -518,6 +586,7 @@ class PixArtAlphaPipeline(DiffusionPipeline):
         callback_steps: int = 1,
         clean_caption: bool = True,
         mask_feature: bool = True,
+        use_resolution_binning: bool = True,
     ) -> Union[ImagePipelineOutput, Tuple]:
         """
         Function invoked when calling the pipeline for generation.
@@ -580,6 +649,10 @@ class PixArtAlphaPipeline(DiffusionPipeline):
                 be installed. If the dependencies are not installed, the embeddings will be created from the raw
                 prompt.
             mask_feature (`bool` defaults to `True`): If set to `True`, the text embeddings will be masked.
+            use_resolution_binning:
+                (`bool` defaults to `True`): If set to `True`, the requested height and width are first mapped to the
+                closest resolutions using `ASPECT_RATIO_1024_BIN`. After the produced latents are decoded into images,
+                they are resized back to the requested resolution. Useful for generating non-square images.
 
         Examples:
 
@@ -591,6 +664,10 @@ class PixArtAlphaPipeline(DiffusionPipeline):
         # 1. Check inputs. Raise error if not correct
         height = height or self.transformer.config.sample_size * self.vae_scale_factor
         width = width or self.transformer.config.sample_size * self.vae_scale_factor
+        if use_resolution_binning:
+            orig_height, orig_width = height, width
+            height, width = self.classify_height_width_bin(height, width, ratios=ASPECT_RATIO_1024_BIN)
+
         self.check_inputs(
             prompt, height, width, negative_prompt, callback_steps, prompt_embeds, negative_prompt_embeds
         )
@@ -709,6 +786,8 @@ class PixArtAlphaPipeline(DiffusionPipeline):
 
         if not output_type == "latent":
             image = self.vae.decode(latents / self.vae.config.scaling_factor, return_dict=False)[0]
+            if use_resolution_binning:
+                image = self.resize_and_crop_tensor(image, orig_width, orig_height)
         else:
             image = latents
 

tests/pipelines/pixart/test_pixart.py

@@ -89,7 +89,8 @@ class PixArtAlphaPipelineFastTests(PipelineTesterMixin, unittest.TestCase):
             "generator": generator,
             "num_inference_steps": 2,
             "guidance_scale": 5.0,
-            "output_type": "numpy",
+            "use_resolution_binning": False,
+            "output_type": "np",
         }
         return inputs
 
@@ -120,6 +121,7 @@ class PixArtAlphaPipelineFastTests(PipelineTesterMixin, unittest.TestCase):
             "generator": generator,
             "num_inference_steps": num_inference_steps,
             "output_type": output_type,
+            "use_resolution_binning": False,
         }
 
         # set all optional components to None
@@ -154,6 +156,7 @@ class PixArtAlphaPipelineFastTests(PipelineTesterMixin, unittest.TestCase):
             "generator": generator,
             "num_inference_steps": num_inference_steps,
             "output_type": output_type,
+            "use_resolution_binning": False,
         }
 
         output_loaded = pipe_loaded(**inputs)[0]
@@ -189,8 +192,8 @@ class PixArtAlphaPipelineFastTests(PipelineTesterMixin, unittest.TestCase):
         inputs = self.get_dummy_inputs(device)
         image = pipe(**inputs, height=32, width=48).images
         image_slice = image[0, -3:, -3:, -1]
-
         self.assertEqual(image.shape, (1, 32, 48, 3))
+
         expected_slice = np.array([0.3859, 0.2987, 0.2333, 0.5243, 0.6721, 0.4436, 0.5292, 0.5373, 0.4416])
         max_diff = np.abs(image_slice.flatten() - expected_slice).max()
         self.assertLessEqual(max_diff, 1e-3)
@@ -219,6 +222,7 @@ class PixArtAlphaPipelineFastTests(PipelineTesterMixin, unittest.TestCase):
             "num_inference_steps": num_inference_steps,
             "output_type": output_type,
             "num_images_per_prompt": 2,
+            "use_resolution_binning": False,
         }
 
         # set all optional components to None
@@ -254,6 +258,7 @@ class PixArtAlphaPipelineFastTests(PipelineTesterMixin, unittest.TestCase):
             "num_inference_steps": num_inference_steps,
             "output_type": output_type,
             "num_images_per_prompt": 2,
+            "use_resolution_binning": False,
         }
 
         output_loaded = pipe_loaded(**inputs)[0]