[feat]Add strength in flux_fill pipeline (denoising strength for fluxfill) (#10603)

* [feat]add strength in flux_fill pipeline

* Update src/diffusers/pipelines/flux/pipeline_flux_fill.py

* Update src/diffusers/pipelines/flux/pipeline_flux_fill.py

* Update src/diffusers/pipelines/flux/pipeline_flux_fill.py

* [refactor] refactor after review

* [fix] change comment

* Apply style fixes

* empty

* fix

* update prepare_latents from flux.img2img pipeline

* style

* Update src/diffusers/pipelines/flux/pipeline_flux_fill.py

---------

src/diffusers/pipelines/flux/pipeline_flux_fill.py

@@ -224,11 +224,13 @@ class FluxFillPipeline(
         self.vae_scale_factor = 2 ** (len(self.vae.config.block_out_channels) - 1) if getattr(self, "vae", None) else 8
         # Flux latents are turned into 2x2 patches and packed. This means the latent width and height has to be divisible
         # by the patch size. So the vae scale factor is multiplied by the patch size to account for this
-        self.image_processor = VaeImageProcessor(vae_scale_factor=self.vae_scale_factor * 2)
-        latent_channels = self.vae.config.latent_channels if getattr(self, "vae", None) else 16
+        self.latent_channels = self.vae.config.latent_channels if getattr(self, "vae", None) else 16
+        self.image_processor = VaeImageProcessor(
+            vae_scale_factor=self.vae_scale_factor * 2, vae_latent_channels=self.latent_channels
+        )
         self.mask_processor = VaeImageProcessor(
             vae_scale_factor=self.vae_scale_factor * 2,
-            vae_latent_channels=latent_channels,
+            vae_latent_channels=self.latent_channels,
             do_normalize=False,
             do_binarize=True,
             do_convert_grayscale=True,
@@ -493,10 +495,38 @@ class FluxFillPipeline(
 
         return prompt_embeds, pooled_prompt_embeds, text_ids
 
+    # Copied from diffusers.pipelines.stable_diffusion_3.pipeline_stable_diffusion_3_inpaint.StableDiffusion3InpaintPipeline._encode_vae_image
+    def _encode_vae_image(self, image: torch.Tensor, generator: torch.Generator):
+        if isinstance(generator, list):
+            image_latents = [
+                retrieve_latents(self.vae.encode(image[i : i + 1]), generator=generator[i])
+                for i in range(image.shape[0])
+            ]
+            image_latents = torch.cat(image_latents, dim=0)
+        else:
+            image_latents = retrieve_latents(self.vae.encode(image), generator=generator)
+
+        image_latents = (image_latents - self.vae.config.shift_factor) * self.vae.config.scaling_factor
+
+        return image_latents
+
+    # Copied from diffusers.pipelines.stable_diffusion_3.pipeline_stable_diffusion_3_img2img.StableDiffusion3Img2ImgPipeline.get_timesteps
+    def get_timesteps(self, num_inference_steps, strength, device):
+        # get the original timestep using init_timestep
+        init_timestep = min(num_inference_steps * strength, num_inference_steps)
+
+        t_start = int(max(num_inference_steps - init_timestep, 0))
+        timesteps = self.scheduler.timesteps[t_start * self.scheduler.order :]
+        if hasattr(self.scheduler, "set_begin_index"):
+            self.scheduler.set_begin_index(t_start * self.scheduler.order)
+
+        return timesteps, num_inference_steps - t_start
+
     def check_inputs(
         self,
         prompt,
         prompt_2,
+        strength,
         height,
         width,
         prompt_embeds=None,
@@ -507,6 +537,9 @@ class FluxFillPipeline(
         mask_image=None,
         masked_image_latents=None,
     ):
+        if strength < 0 or strength > 1:
+            raise ValueError(f"The value of strength should in [0.0, 1.0] but is {strength}")
+
         if height % (self.vae_scale_factor * 2) != 0 or width % (self.vae_scale_factor * 2) != 0:
             logger.warning(
                 f"`height` and `width` have to be divisible by {self.vae_scale_factor * 2} but are {height} and {width}. Dimensions will be resized accordingly"
@@ -624,9 +657,11 @@ class FluxFillPipeline(
         """
         self.vae.disable_tiling()
 
-    # Copied from diffusers.pipelines.flux.pipeline_flux.FluxPipeline.prepare_latents
+    # Copied from diffusers.pipelines.flux.pipeline_flux_img2img.FluxImg2ImgPipeline.prepare_latents
     def prepare_latents(
         self,
+        image,
+        timestep,
         batch_size,
         num_channels_latents,
         height,
@@ -636,28 +671,41 @@ class FluxFillPipeline(
         generator,
         latents=None,
     ):
+        if isinstance(generator, list) and len(generator) != batch_size:
+            raise ValueError(
+                f"You have passed a list of generators of length {len(generator)}, but requested an effective batch"
+                f" size of {batch_size}. Make sure the batch size matches the length of the generators."
+            )
+
         # VAE applies 8x compression on images but we must also account for packing which requires
         # latent height and width to be divisible by 2.
         height = 2 * (int(height) // (self.vae_scale_factor * 2))
         width = 2 * (int(width) // (self.vae_scale_factor * 2))
-
         shape = (batch_size, num_channels_latents, height, width)
+        latent_image_ids = self._prepare_latent_image_ids(batch_size, height // 2, width // 2, device, dtype)
 
         if latents is not None:
-            latent_image_ids = self._prepare_latent_image_ids(batch_size, height // 2, width // 2, device, dtype)
             return latents.to(device=device, dtype=dtype), latent_image_ids
 
-        if isinstance(generator, list) and len(generator) != batch_size:
+        image = image.to(device=device, dtype=dtype)
+        if image.shape[1] != self.latent_channels:
+            image_latents = self._encode_vae_image(image=image, generator=generator)
+        else:
+            image_latents = image
+        if batch_size > image_latents.shape[0] and batch_size % image_latents.shape[0] == 0:
+            # expand init_latents for batch_size
+            additional_image_per_prompt = batch_size // image_latents.shape[0]
+            image_latents = torch.cat([image_latents] * additional_image_per_prompt, dim=0)
+        elif batch_size > image_latents.shape[0] and batch_size % image_latents.shape[0] != 0:
             raise ValueError(
-                f"You have passed a list of generators of length {len(generator)}, but requested an effective batch"
-                f" size of {batch_size}. Make sure the batch size matches the length of the generators."
+                f"Cannot duplicate `image` of batch size {image_latents.shape[0]} to {batch_size} text prompts."
             )
+        else:
+            image_latents = torch.cat([image_latents], dim=0)
 
-        latents = randn_tensor(shape, generator=generator, device=device, dtype=dtype)
+        noise = randn_tensor(shape, generator=generator, device=device, dtype=dtype)
+        latents = self.scheduler.scale_noise(image_latents, timestep, noise)
         latents = self._pack_latents(latents, batch_size, num_channels_latents, height, width)
-
-        latent_image_ids = self._prepare_latent_image_ids(batch_size, height // 2, width // 2, device, dtype)
-
         return latents, latent_image_ids
 
     @property
@@ -687,6 +735,7 @@ class FluxFillPipeline(
         masked_image_latents: Optional[torch.FloatTensor] = None,
         height: Optional[int] = None,
         width: Optional[int] = None,
+        strength: float = 1.0,
         num_inference_steps: int = 50,
         sigmas: Optional[List[float]] = None,
         guidance_scale: float = 30.0,
@@ -731,6 +780,12 @@ class FluxFillPipeline(
                 The height in pixels of the generated image. This is set to 1024 by default for the best results.
             width (`int`, *optional*, defaults to self.unet.config.sample_size * self.vae_scale_factor):
                 The width in pixels of the generated image. This is set to 1024 by default for the best results.
+            strength (`float`, *optional*, defaults to 1.0):
+                Indicates extent to transform the reference `image`. Must be between 0 and 1. `image` is used as a
+                starting point and more noise is added the higher the `strength`. The number of denoising steps depends
+                on the amount of noise initially added. When `strength` is 1, added noise is maximum and the denoising
+                process runs for the full number of iterations specified in `num_inference_steps`. A value of 1
+                essentially ignores `image`.
             num_inference_steps (`int`, *optional*, defaults to 50):
                 The number of denoising steps. More denoising steps usually lead to a higher quality image at the
                 expense of slower inference.
@@ -794,6 +849,7 @@ class FluxFillPipeline(
         self.check_inputs(
             prompt,
             prompt_2,
+            strength,
             height,
             width,
             prompt_embeds=prompt_embeds,
@@ -809,6 +865,9 @@ class FluxFillPipeline(
         self._joint_attention_kwargs = joint_attention_kwargs
         self._interrupt = False
 
+        init_image = self.image_processor.preprocess(image, height=height, width=width)
+        init_image = init_image.to(dtype=torch.float32)
+
         # 2. Define call parameters
         if prompt is not None and isinstance(prompt, str):
             batch_size = 1
@@ -838,9 +897,37 @@ class FluxFillPipeline(
             lora_scale=lora_scale,
         )
 
-        # 4. Prepare latent variables
+        # 4. Prepare timesteps
+        sigmas = np.linspace(1.0, 1 / num_inference_steps, num_inference_steps) if sigmas is None else sigmas
+        image_seq_len = (int(height) // self.vae_scale_factor // 2) * (int(width) // self.vae_scale_factor // 2)
+        mu = calculate_shift(
+            image_seq_len,
+            self.scheduler.config.get("base_image_seq_len", 256),
+            self.scheduler.config.get("max_image_seq_len", 4096),
+            self.scheduler.config.get("base_shift", 0.5),
+            self.scheduler.config.get("max_shift", 1.15),
+        )
+        timesteps, num_inference_steps = retrieve_timesteps(
+            self.scheduler,
+            num_inference_steps,
+            device,
+            sigmas=sigmas,
+            mu=mu,
+        )
+        timesteps, num_inference_steps = self.get_timesteps(num_inference_steps, strength, device)
+
+        if num_inference_steps < 1:
+            raise ValueError(
+                f"After adjusting the num_inference_steps by strength parameter: {strength}, the number of pipeline"
+                f"steps is {num_inference_steps} which is < 1 and not appropriate for this pipeline."
+            )
+        latent_timestep = timesteps[:1].repeat(batch_size * num_images_per_prompt)
+
+        # 5. Prepare latent variables
         num_channels_latents = self.vae.config.latent_channels
         latents, latent_image_ids = self.prepare_latents(
+            init_image,
+            latent_timestep,
             batch_size * num_images_per_prompt,
             num_channels_latents,
             height,
@@ -851,17 +938,16 @@ class FluxFillPipeline(
             latents,
         )
 
-        # 5. Prepare mask and masked image latents
+        # 6. Prepare mask and masked image latents
         if masked_image_latents is not None:
             masked_image_latents = masked_image_latents.to(latents.device)
         else:
-            image = self.image_processor.preprocess(image, height=height, width=width)
             mask_image = self.mask_processor.preprocess(mask_image, height=height, width=width)
 
-            masked_image = image * (1 - mask_image)
+            masked_image = init_image * (1 - mask_image)
             masked_image = masked_image.to(device=device, dtype=prompt_embeds.dtype)
 
-            height, width = image.shape[-2:]
+            height, width = init_image.shape[-2:]
             mask, masked_image_latents = self.prepare_mask_latents(
                 mask_image,
                 masked_image,
@@ -876,23 +962,6 @@ class FluxFillPipeline(
             )
             masked_image_latents = torch.cat((masked_image_latents, mask), dim=-1)
 
-        # 6. Prepare timesteps
-        sigmas = np.linspace(1.0, 1 / num_inference_steps, num_inference_steps) if sigmas is None else sigmas
-        image_seq_len = latents.shape[1]
-        mu = calculate_shift(
-            image_seq_len,
-            self.scheduler.config.get("base_image_seq_len", 256),
-            self.scheduler.config.get("max_image_seq_len", 4096),
-            self.scheduler.config.get("base_shift", 0.5),
-            self.scheduler.config.get("max_shift", 1.15),
-        )
-        timesteps, num_inference_steps = retrieve_timesteps(
-            self.scheduler,
-            num_inference_steps,
-            device,
-            sigmas=sigmas,
-            mu=mu,
-        )
         num_warmup_steps = max(len(timesteps) - num_inference_steps * self.scheduler.order, 0)
         self._num_timesteps = len(timesteps)