Update Cascade documentation (#7257)

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* update

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* Update docs/source/en/api/pipelines/stable_cascade.md
Co-authored-by: Sayak Paul <spsayakpaul@gmail.com>

* update

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---------
Co-authored-by: Sayak Paul <spsayakpaul@gmail.com>
Co-authored-by: Kashif Rasul <kashif.rasul@gmail.com>

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

@@ -12,13 +12,13 @@ specific language governing permissions and limitations under the License.
 
 # Stable Cascade
 
-This model is built upon the [Würstchen](https://openreview.net/forum?id=gU58d5QeGv) architecture and its main 
-difference to other models like Stable Diffusion is that it is working at a much smaller latent space. Why is this 
-important? The smaller the latent space, the **faster** you can run inference and the **cheaper** the training becomes. 
-How small is the latent space? Stable Diffusion uses a compression factor of 8, resulting in a 1024x1024 image being 
-encoded to 128x128. Stable Cascade achieves a compression factor of 42, meaning that it is possible to encode a 
-1024x1024 image to 24x24, while maintaining crisp reconstructions. The text-conditional model is then trained in the 
-highly compressed latent space. Previous versions of this architecture, achieved a 16x cost reduction over Stable 
+This model is built upon the [Würstchen](https://openreview.net/forum?id=gU58d5QeGv) architecture and its main
+difference to other models like Stable Diffusion is that it is working at a much smaller latent space. Why is this
+important? The smaller the latent space, the **faster** you can run inference and the **cheaper** the training becomes.
+How small is the latent space? Stable Diffusion uses a compression factor of 8, resulting in a 1024x1024 image being
+encoded to 128x128. Stable Cascade achieves a compression factor of 42, meaning that it is possible to encode a
+1024x1024 image to 24x24, while maintaining crisp reconstructions. The text-conditional model is then trained in the
+highly compressed latent space. Previous versions of this architecture, achieved a 16x cost reduction over Stable
 Diffusion 1.5.
 
 Therefore, this kind of model is well suited for usages where efficiency is important. Furthermore, all known extensions
@@ -30,13 +30,154 @@ The original codebase can be found at [Stability-AI/StableCascade](https://githu
 Stable Cascade consists of three models: Stage A, Stage B and Stage C, representing a cascade to generate images,
 hence the name "Stable Cascade".
 
-Stage A & B are used to compress images, similar to what the job of the VAE is in Stable Diffusion. 
-However, with this setup, a much higher compression of images can be achieved. While the Stable Diffusion models use a 
-spatial compression factor of 8, encoding an image with resolution of 1024 x 1024 to 128 x 128, Stable Cascade achieves 
-a compression factor of 42. This encodes a 1024 x 1024 image to 24 x 24, while being able to accurately decode the 
-image. This comes with the great benefit of cheaper training and inference. Furthermore, Stage C is responsible 
+Stage A & B are used to compress images, similar to what the job of the VAE is in Stable Diffusion.
+However, with this setup, a much higher compression of images can be achieved. While the Stable Diffusion models use a
+spatial compression factor of 8, encoding an image with resolution of 1024 x 1024 to 128 x 128, Stable Cascade achieves
+a compression factor of 42. This encodes a 1024 x 1024 image to 24 x 24, while being able to accurately decode the
+image. This comes with the great benefit of cheaper training and inference. Furthermore, Stage C is responsible
 for generating the small 24 x 24 latents given a text prompt.
 
+The Stage C model operates on the small 24 x 24 latents and denoises the latents conditioned on text prompts. The model is also the largest component in the Cascade pipeline and is meant to be used with the `StableCascadePriorPipeline`
+
+The Stage B and Stage A models are used with the `StableCascadeDecoderPipeline` and are responsible for generating the final image given the small 24 x 24 latents.
+
+<Tip warning={true}>
+
+There are some restrictions on data types that can be used with the Stable Cascade models. The official checkpoints for the  `StableCascadePriorPipeline` do not support the `torch.float16` data type. Please use `torch.bfloat16` instead.
+
+In order to use the `torch.bfloat16` data type with the `StableCascadeDecoderPipeline` you need to have PyTorch 2.2.0 or higher installed. This also means that using the `StableCascadeCombinedPipeline` with `torch.bfloat16` requires PyTorch 2.2.0 or higher, since it calls the `StableCascadeDecoderPipeline` internally.
+
+If it is not possible to install PyTorch 2.2.0 or higher in your environment, the `StableCascadeDecoderPipeline` can be used on its own with the `torch.float16` data type. You can download the full precision or `bf16` variant weights for the pipeline and cast the weights to `torch.float16`.
+
+</Tip>
+
+## Usage example
+
+```python
+import torch
+from diffusers import StableCascadeDecoderPipeline, StableCascadePriorPipeline
+
+prompt = "an image of a shiba inu, donning a spacesuit and helmet"
+negative_prompt = ""
+
+prior = StableCascadePriorPipeline.from_pretrained("stabilityai/stable-cascade-prior", variant="bf16", torch_dtype=torch.bfloat16)
+decoder = StableCascadeDecoderPipeline.from_pretrained("stabilityai/stable-cascade", variant="bf16", torch_dtype=torch.float16)
+
+prior.enable_model_cpu_offload()
+prior_output = prior(
+    prompt=prompt,
+    height=1024,
+    width=1024,
+    negative_prompt=negative_prompt,
+    guidance_scale=4.0,
+    num_images_per_prompt=1,
+    num_inference_steps=20
+)
+
+decoder.enable_model_cpu_offload()
+decoder_output = decoder(
+    image_embeddings=prior_output.image_embeddings.to(torch.float16),
+    prompt=prompt,
+    negative_prompt=negative_prompt,
+    guidance_scale=0.0,
+    output_type="pil",
+    num_inference_steps=10
+).images[0]
+decoder_output.save("cascade.png")
+```
+
+## Using the Lite Versions of the Stage B and Stage C models
+
+```python
+import torch
+from diffusers import (
+    StableCascadeDecoderPipeline,
+    StableCascadePriorPipeline,
+    StableCascadeUNet,
+)
+
+prompt = "an image of a shiba inu, donning a spacesuit and helmet"
+negative_prompt = ""
+
+prior_unet = StableCascadeUNet.from_pretrained("stabilityai/stable-cascade-prior", subfolder="prior_lite")
+decoder_unet = StableCascadeUNet.from_pretrained("stabilityai/stable-cascade", subfolder="decoder_lite")
+
+prior = StableCascadePriorPipeline.from_pretrained("stabilityai/stable-cascade-prior", prior=prior_unet)
+decoder = StableCascadeDecoderPipeline.from_pretrained("stabilityai/stable-cascade", decoder=decoder_unet)
+
+prior.enable_model_cpu_offload()
+prior_output = prior(
+    prompt=prompt,
+    height=1024,
+    width=1024,
+    negative_prompt=negative_prompt,
+    guidance_scale=4.0,
+    num_images_per_prompt=1,
+    num_inference_steps=20
+)
+
+decoder.enable_model_cpu_offload()
+decoder_output = decoder(
+    image_embeddings=prior_output.image_embeddings,
+    prompt=prompt,
+    negative_prompt=negative_prompt,
+    guidance_scale=0.0,
+    output_type="pil",
+    num_inference_steps=10
+).images[0]
+decoder_output.save("cascade.png")
+```
+
+## Loading original checkpoints with `from_single_file`
+
+Loading the original format checkpoints is supported via `from_single_file` method in the StableCascadeUNet.
+
+```python
+import torch
+from diffusers import (
+    StableCascadeDecoderPipeline,
+    StableCascadePriorPipeline,
+    StableCascadeUNet,
+)
+
+prompt = "an image of a shiba inu, donning a spacesuit and helmet"
+negative_prompt = ""
+
+prior_unet = StableCascadeUNet.from_single_file(
+    "https://huggingface.co/stabilityai/stable-cascade/resolve/main/stage_c_bf16.safetensors",
+    torch_dtype=torch.bfloat16
+)
+decoder_unet = StableCascadeUNet.from_single_file(
+    "https://huggingface.co/stabilityai/stable-cascade/blob/main/stage_b_bf16.safetensors",
+    torch_dtype=torch.bfloat16
+)
+
+prior = StableCascadePriorPipeline.from_pretrained("stabilityai/stable-cascade-prior", prior=prior_unet, torch_dtype=torch.bfloat16)
+decoder = StableCascadeDecoderPipeline.from_pretrained("stabilityai/stable-cascade", decoder=decoder_unet, torch_dtype=torch.bfloat16)
+
+prior.enable_model_cpu_offload()
+prior_output = prior(
+    prompt=prompt,
+    height=1024,
+    width=1024,
+    negative_prompt=negative_prompt,
+    guidance_scale=4.0,
+    num_images_per_prompt=1,
+    num_inference_steps=20
+)
+
+decoder.enable_model_cpu_offload()
+decoder_output = decoder(
+    image_embeddings=prior_output.image_embeddings,
+    prompt=prompt,
+    negative_prompt=negative_prompt,
+    guidance_scale=0.0,
+    output_type="pil",
+    num_inference_steps=10
+).images[0]
+decoder_output.save("cascade-single-file.png")
+```
+
 ## Uses
 
 ### Direct Use
@@ -53,7 +194,7 @@ Excluded uses are described below.
 
 ### Out-of-Scope Use
 
-The model was not trained to be factual or true representations of people or events, 
+The model was not trained to be factual or true representations of people or events,
 and therefore using the model to generate such content is out-of-scope for the abilities of this model.
 The model should not be used in any way that violates Stability AI's [Acceptable Use Policy](https://stability.ai/use-policy).
 

src/diffusers/pipelines/stable_cascade/pipeline_stable_cascade_combined.py

@@ -19,7 +19,7 @@ from transformers import CLIPImageProcessor, CLIPTextModel, CLIPTokenizer, CLIPV
 
 from ...models import StableCascadeUNet
 from ...schedulers import DDPMWuerstchenScheduler
-from ...utils import replace_example_docstring
+from ...utils import is_torch_version, replace_example_docstring
 from ..pipeline_utils import DiffusionPipeline
 from ..wuerstchen.modeling_paella_vq_model import PaellaVQModel
 from .pipeline_stable_cascade import StableCascadeDecoderPipeline
@@ -29,11 +29,10 @@ from .pipeline_stable_cascade_prior import StableCascadePriorPipeline
 TEXT2IMAGE_EXAMPLE_DOC_STRING = """
     Examples:
         ```py
-        >>> from diffusions import StableCascadeCombinedPipeline
-
-        >>> pipe = StableCascadeCombinedPipeline.from_pretrained("stabilityai/stable-cascade-combined", torch_dtype=torch.bfloat16).to(
-        ...     "cuda"
-        ... )
+        >>> import torch
+        >>> from diffusers import StableCascadeCombinedPipeline
+        >>> pipe = StableCascadeCombinedPipeline.from_pretrained("stabilityai/stable-cascade", variant="bf16", torch_dtype=torch.bfloat16)
+        >>> pipe.enable_model_cpu_offload()
         >>> prompt = "an image of a shiba inu, donning a spacesuit and helmet"
         >>> images = pipe(prompt=prompt)
         ```
@@ -260,6 +259,12 @@ class StableCascadeCombinedPipeline(DiffusionPipeline):
             [`~pipelines.ImagePipelineOutput`] or `tuple` [`~pipelines.ImagePipelineOutput`] if `return_dict` is True,
             otherwise a `tuple`. When returning a tuple, the first element is a list with the generated images.
         """
+        dtype = self.decoder_pipe.decoder.dtype
+        if is_torch_version("<", "2.2.0") and dtype == torch.bfloat16:
+            raise ValueError(
+                "`StableCascadeCombinedPipeline` requires torch>=2.2.0 when using `torch.bfloat16` dtype."
+            )
+
         prior_outputs = self.prior_pipe(
             prompt=prompt if prompt_embeds is None else None,
             images=images,