add: guide on kerascv conversion tool. (#2169)

* add: guide on kerascv conversion tool.

* Apply suggestions from code review
Co-authored-by: Pedro Cuenca <pedro@huggingface.co>
Co-authored-by: Kashif Rasul <kashif.rasul@gmail.com>
Co-authored-by: Suraj Patil <surajp815@gmail.com>

* address additional suggestions from review.

* change links to documentation-images.

* add separate links for training and inference goodies from diffusers.

* address Patrick's comments.

---------
Co-authored-by: Pedro Cuenca <pedro@huggingface.co>
Co-authored-by: Kashif Rasul <kashif.rasul@gmail.com>
Co-authored-by: Suraj Patil <surajp815@gmail.com>

docs/source/en/_toctree.yml

@@ -18,6 +18,8 @@
       title: Configuring Pipelines, Models, and Schedulers
     - local: using-diffusers/custom_pipeline_overview
       title: Loading and Adding Custom Pipelines
+    - local: using-diffusers/kerascv
+      title: Using KerasCV Stable Diffusion Checkpoints in Diffusers
     title: Loading & Hub
   - sections:
     - local: using-diffusers/unconditional_image_generation

docs/source/en/using-diffusers/kerascv.mdx

+<!--Copyright 2023 The HuggingFace Team. All rights reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with
+the License. You may obtain a copy of the License at
+
+http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on
+an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the
+specific language governing permissions and limitations under the License.
+-->
+
+# Using KerasCV Stable Diffusion Checkpoints in Diffusers
+
+<Tip warning={true}>
+
+This is an experimental feature.
+
+</Tip>
+
+[KerasCV](https://github.com/keras-team/keras-cv/) provides APIs for implementing various computer vision workflows. It
+also provides the Stable Diffusion [v1 and v2](https://github.com/keras-team/keras-cv/blob/master/keras_cv/models/stable_diffusion)
+models. Many practitioners find it easy to fine-tune the Stable Diffusion models shipped by KerasCV. However, as of this writing, KerasCV offers limited support to experiment with Stable Diffusion models for inference and deployment. On the other hand,
+Diffusers provides tooling dedicated to this purpose (and more), such as different [noise schedulers](https://huggingface.co/docs/diffusers/using-diffusers/schedulers), [flash attention](https://huggingface.co/docs/diffusers/optimization/xformers), and [other 
+optimization techniques](https://huggingface.co/docs/diffusers/optimization/fp16).
+
+How about fine-tuning Stable Diffusion models in KerasCV and exporting them such that they become compatible with Diffusers to combine the
+best of both worlds? We have created a [tool](https://huggingface.co/spaces/sayakpaul/convert-kerascv-sd-diffusers) that
+lets you do just that! It takes KerasCV Stable Diffusion checkpoints and exports them to Diffusers-compatible checkpoints.
+More specifically, it first converts the checkpoints to PyTorch and then wraps them into a
+[`StableDiffusionPipeline`](https://huggingface.co/docs/diffusers/api/pipelines/stable_diffusion/overview) which is ready
+for inference. Finally, it pushes the converted checkpoints to a repository on the Hugging Face Hub. 
+
+We welcome you to try out the tool [here](https://huggingface.co/spaces/sayakpaul/convert-kerascv-sd-diffusers)
+and share feedback via [discussions](https://huggingface.co/spaces/sayakpaul/convert-kerascv-sd-diffusers/discussions/new). 
+
+## Getting Started 
+
+First, you need to obtain the fine-tuned KerasCV Stable Diffusion checkpoints. We provide an
+overview of the different ways Stable Diffusion models can be fine-tuned [using `diffusers`](https://huggingface.co/docs/diffusers/training/overview). For the Keras implementation of some of these methods, you can check out these resources:
+
+* [Teach StableDiffusion new concepts via Textual Inversion](https://keras.io/examples/generative/fine_tune_via_textual_inversion/)
+* [Fine-tuning Stable Diffusion](https://keras.io/examples/generative/finetune_stable_diffusion/)
+* [DreamBooth](https://keras.io/examples/generative/dreambooth/)
+* [Prompt-to-Prompt editing](https://github.com/miguelCalado/prompt-to-prompt-tensorflow)
+
+Stable Diffusion is comprised of the following models:
+
+* Text encoder 
+* UNet 
+* VAE 
+
+Depending on the fine-tuning task, we may fine-tune one or more of these components (the VAE is almost always left untouched). Here are some common combinations:
+
+* DreamBooth: UNet and text encoder 
+* Classical text to image fine-tuning: UNet 
+* Textual Inversion: Just the newly initialized embeddings in the text encoder
+
+### Performing the Conversion
+
+Let's use [this checkpoint](https://huggingface.co/sayakpaul/textual-inversion-kerasio/resolve/main/textual_inversion_kerasio.h5) which was generated
+by conducting Textual Inversion with the following "placeholder token": `<my-funny-cat-token>`. 
+
+On the tool, we supply the following things: 
+
+* Path(s) to download the fine-tuned checkpoint(s) (KerasCV)
+* An HF token 
+* Placeholder token (only applicable for Textual Inversion)
+
+<div align="center">
+<img src="https://huggingface.co/datasets/huggingface/documentation-images/resolve/main/diffusers/space_snap.png"/>
+</div> 
+
+As soon as you hit "Submit", the conversion process will begin. Once it's complete, you should see the following:
+
+<div align="center">
+<img src="https://huggingface.co/datasets/huggingface/documentation-images/resolve/main/diffusers/model_push_success.png"/>
+</div> 
+
+If you click the [link](https://huggingface.co/sayakpaul/textual-inversion-cat-kerascv_sd_diffusers_pipeline/tree/main), you
+should see something like so: 
+
+<div align="center">
+<img src="https://huggingface.co/datasets/huggingface/documentation-images/resolve/main/diffusers/model_repo_contents.png"/>
+</div> 
+
+If you head over to the [model card of the repository](https://huggingface.co/sayakpaul/textual-inversion-cat-kerascv_sd_diffusers_pipeline), the
+following should appear: 
+
+<div align="center">
+<img src="https://huggingface.co/datasets/huggingface/documentation-images/resolve/main/diffusers/model_card.png"/>
+</div> 
+
+<Tip>
+
+Note that we're not specifying the UNet weights here since the UNet is not fine-tuned during Textual Inversion.
+
+</Tip>
+
+And that's it! You now have your fine-tuned KerasCV Stable Diffusion model in Diffusers 🧨
+
+## Using the Converted Model in Diffusers 
+
+Just beside the model card of the [repository](https://huggingface.co/sayakpaul/textual-inversion-cat-kerascv_sd_diffusers_pipeline), 
+you'd notice an inference widget to try out the model directly from the UI 🤗
+
+<div align="center">
+<img src="https://huggingface.co/datasets/huggingface/documentation-images/resolve/main/diffusers/inference_widget_output.png"/>
+</div> 
+
+On the top right hand side, we provide a "Use in Diffusers" button. If you click the button, you should see the following code-snippet: 
+
+```py 
+from diffusers import DiffusionPipeline
+
+pipeline = DiffusionPipeline.from_pretrained("sayakpaul/textual-inversion-cat-kerascv_sd_diffusers_pipeline")
+```
+
+The model is in standard `diffusers` format. Let's perform inference!
+
+```py
+from diffusers import DiffusionPipeline
+
+pipeline = DiffusionPipeline.from_pretrained("sayakpaul/textual-inversion-cat-kerascv_sd_diffusers_pipeline")
+pipeline.to("cuda")
+
+placeholder_token = "<my-funny-cat-token>"
+prompt = f"two {placeholder_token} getting married, photorealistic, high quality"
+image = pipeline(prompt, num_inference_steps=50).images[0]
+```
+
+And we get: 
+
+<div align="center">
+<img src="https://huggingface.co/datasets/huggingface/documentation-images/resolve/main/diffusers/diffusers_output_one.png"/>
+</div> 
+
+_**Note that if you specified a `placeholder_token` while performing the conversion, the tool will log it accordingly. Refer
+to the model card of [this repository](https://huggingface.co/sayakpaul/textual-inversion-cat-kerascv_sd_diffusers_pipeline)
+as an example.**_
+
+We welcome you to use the tool for various Stable Diffusion fine-tuning scenarios and let us know your feedback! Here are some examples 
+of Diffusers checkpoints that were obtained using the tool: 
+
+* [sayakpaul/text-unet-dogs-kerascv_sd_diffusers_pipeline](https://huggingface.co/sayakpaul/text-unet-dogs-kerascv_sd_diffusers_pipeline) (DreamBooth with both the text encoder and UNet fine-tuned)
+* [sayakpaul/unet-dogs-kerascv_sd_diffusers_pipeline](https://huggingface.co/sayakpaul/unet-dogs-kerascv_sd_diffusers_pipeline) (DreamBooth with only the UNet fine-tuned)
+
+## Incorporating Diffusers Goodies 🎁
+
+Diffusers provides various options that one can leverage to experiment with different inference setups. One particularly
+useful option is the use of a different noise scheduler during inference other than what was used during fine-tuning. 
+Let's try out the [`DPMSolverMultistepScheduler`](https://huggingface.co/docs/diffusers/main/en/api/schedulers/multistep_dpm_solver)
+which is different from the one ([`DDPMScheduler`](https://huggingface.co/docs/diffusers/main/en/api/schedulers/ddpm)) used during
+fine-tuning.
+
+You can read more details about this process in [this section](https://huggingface.co/docs/diffusers/using-diffusers/schedulers).
+
+```py
+from diffusers import DiffusionPipeline, DPMSolverMultistepScheduler
+
+pipeline = DiffusionPipeline.from_pretrained("sayakpaul/textual-inversion-cat-kerascv_sd_diffusers_pipeline")
+pipeline.scheduler = DPMSolverMultistepScheduler.from_config(pipeline.scheduler.config)
+pipeline.to("cuda")
+
+placeholder_token = "<my-funny-cat-token>"
+prompt = f"two {placeholder_token} getting married, photorealistic, high quality"
+image = pipeline(prompt, num_inference_steps=50).images[0]
+```
+
+<div align="center">
+<img src="https://huggingface.co/datasets/huggingface/documentation-images/resolve/main/diffusers/diffusers_output_two.png"/>
+</div> 
+
+One can also continue fine-tuning from these Diffusers checkpoints by leveraging some relevant tools from Diffusers. Refer [here](https://huggingface.co/docs/diffusers/training/overview) for 
+more details. For inference-specific optimizations, refer [here](https://huggingface.co/docs/diffusers/main/en/optimization/fp16).
+
+## Known Limitations 
+
+* Only Stable Diffusion v1 checkpoints are supported for conversion in this tool. 
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