up

Author: yiyixuxu

src/diffusers/pipelines/qwenimage/pipeline_qwenimage.py

@@ -435,7 +435,7 @@ def __call__(
         width: Optional[int] = None,
         num_inference_steps: int = 50,
         sigmas: Optional[List[float]] = None,
-        guidance_scale: float = 1.0,
+        guidance_scale: Optional[float] = None,
         num_images_per_prompt: int = 1,
         generator: Optional[Union[torch.Generator, List[torch.Generator]]] = None,
         latents: Optional[torch.Tensor] = None,
@@ -462,7 +462,12 @@ def __call__(
                 `negative_prompt_embeds` instead. Ignored when not using guidance (i.e., ignored if `true_cfg_scale` is
                 not greater than `1`).
             true_cfg_scale (`float`, *optional*, defaults to 1.0):
-                When > 1.0 and a provided `negative_prompt`, enables true classifier-free guidance.
+                Guidance scale as defined in [Classifier-Free Diffusion
+                Guidance](https://huggingface.co/papers/2207.12598). `true_cfg_scale` is defined as `w` of equation 2.
+                of [Imagen Paper](https://huggingface.co/papers/2205.11487). Classifier-free guidance is enabled by
+                setting `true_cfg_scale > 1` and a provided `negative_prompt`. Higher guidance scale encourages to
+                generate images that are closely linked to the text `prompt`, usually at the expense of lower image
+                quality.
             height (`int`, *optional*, defaults to self.unet.config.sample_size * self.vae_scale_factor):
                 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):
@@ -474,12 +479,13 @@ def __call__(
                 Custom sigmas to use for the denoising process with schedulers which support a `sigmas` argument in
                 their `set_timesteps` method. If not defined, the default behavior when `num_inference_steps` is passed
                 will be used.
-            guidance_scale (`float`, *optional*, defaults to 3.5):
-                Guidance scale as defined in [Classifier-Free Diffusion
-                Guidance](https://huggingface.co/papers/2207.12598). `guidance_scale` is defined as `w` of equation 2.
-                of [Imagen Paper](https://huggingface.co/papers/2205.11487). Guidance scale is enabled by setting
-                `guidance_scale > 1`. Higher guidance scale encourages to generate images that are closely linked to
-                the text `prompt`, usually at the expense of lower image quality.
+            guidance_scale (`float`, *optional*, defaults to None):
+                A guidance scale value for guidance distilled models. Unlike the traditional classifier-free guidance
+                where the guidance scale is applied during inference through noise prediction rescaling, guidance
+                distilled models take the guidance scale directly as an input parameter during forward pass. Guidance
+                scale is enabled by setting `guidance_scale > 1`. Higher guidance scale encourages to generate images
+                that are closely linked to the text `prompt`, usually at the expense of lower image quality. Ignored
+                when not using guidance distilled models.
             num_images_per_prompt (`int`, *optional*, defaults to 1):
                 The number of images to generate per prompt.
             generator (`torch.Generator` or `List[torch.Generator]`, *optional*):
@@ -559,6 +565,16 @@ def __call__(
         has_neg_prompt = negative_prompt is not None or (
             negative_prompt_embeds is not None and negative_prompt_embeds_mask is not None
         )
+
+        if true_cfg_scale > 1 and not has_neg_prompt:
+            logger.warning(
+                f"true_cfg_scale is passed as {true_cfg_scale}, but classifier-free guidance is not enabled since no negative_prompt is provided."
+            )
+        elif true_cfg_scale <= 1 and has_neg_prompt:
+            logger.warning(
+                " negative_prompt is passed but classifier-free guidance is not enabled since true_cfg_scale <= 1"
+            )
+
         do_true_cfg = true_cfg_scale > 1 and has_neg_prompt
         prompt_embeds, prompt_embeds_mask = self.encode_prompt(
             prompt=prompt,
@@ -613,10 +629,17 @@ def __call__(
         self._num_timesteps = len(timesteps)
 
         # handle guidance
-        if self.transformer.config.guidance_embeds:
+        if self.transformer.config.guidance_embeds and guidance_scale is None:
+            raise ValueError("guidance_scale is required for guidance-distilled model.")
+        elif self.transformer.config.guidance_embeds:
             guidance = torch.full([1], guidance_scale, device=device, dtype=torch.float32)
             guidance = guidance.expand(latents.shape[0])
-        else:
+        elif not self.transformer.config.guidance_embeds and guidance_scale is not None:
+            logger.warning(
+                f"guidance_scale is passed as {guidance_scale}, but ignored since the model is not guidance-distilled."
+            )
+            guidance = None
+        elif not self.transformer.config.guidance_embeds and guidance_scale is None:
             guidance = None
 
         if self.attention_kwargs is None: