[docs] Clarify guidance scale in Qwen pipelines (#12181)

* add clarification regarding guidance_scale in QwenImage

* propagate.

docs/source/en/api/pipelines/qwenimage.md

@@ -86,6 +86,12 @@ image.save("qwen_fewsteps.png")
 
 </details>
 
+<Tip>
+
+The `guidance_scale` parameter in the pipeline is there to support future guidance-distilled models when they come up. Note that passing `guidance_scale` to the pipeline is ineffective. To enable classifier-free guidance, please pass `true_cfg_scale` and `negative_prompt` (even an empty negative prompt like " ") should enable classifier-free guidance computations.
+
+</Tip>
+
 ## QwenImagePipeline
 
 [[autodoc]] QwenImagePipeline

src/diffusers/pipelines/qwenimage/pipeline_qwenimage.py

@@ -480,6 +480,11 @@ class QwenImagePipeline(DiffusionPipeline, QwenImageLoraLoaderMixin):
                 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.
+
+                This parameter in the pipeline is there to support future guidance-distilled models when they come up.
+                Note that passing `guidance_scale` to the pipeline is ineffective. To enable classifier-free guidance,
+                please pass `true_cfg_scale` and `negative_prompt` (even an empty negative prompt like " ") should
+                enable classifier-free guidance computations.
             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*):

src/diffusers/pipelines/qwenimage/pipeline_qwenimage_edit.py

@@ -597,6 +597,11 @@ class QwenImageEditPipeline(DiffusionPipeline, QwenImageLoraLoaderMixin):
                 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.
+
+                This parameter in the pipeline is there to support future guidance-distilled models when they come up.
+                Note that passing `guidance_scale` to the pipeline is ineffective. To enable classifier-free guidance,
+                please pass `true_cfg_scale` and `negative_prompt` (even an empty negative prompt like " ") should
+                enable classifier-free guidance computations.
             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*):

src/diffusers/pipelines/qwenimage/pipeline_qwenimage_img2img.py

@@ -568,6 +568,11 @@ class QwenImageImg2ImgPipeline(DiffusionPipeline, QwenImageLoraLoaderMixin):
                 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.
+
+                This parameter in the pipeline is there to support future guidance-distilled models when they come up.
+                Note that passing `guidance_scale` to the pipeline is ineffective. To enable classifier-free guidance,
+                please pass `true_cfg_scale` and `negative_prompt` (even an empty negative prompt like " ") should
+                enable classifier-free guidance computations.
             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*):

src/diffusers/pipelines/qwenimage/pipeline_qwenimage_inpaint.py

@@ -698,6 +698,11 @@ class QwenImageInpaintPipeline(DiffusionPipeline, QwenImageLoraLoaderMixin):
                 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.
+
+                This parameter in the pipeline is there to support future guidance-distilled models when they come up.
+                Note that passing `guidance_scale` to the pipeline is ineffective. To enable classifier-free guidance,
+                please pass `true_cfg_scale` and `negative_prompt` (even an empty negative prompt like " ") should
+                enable classifier-free guidance computations.
             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*):