Add support for fast image processors in add-new-model-like CLI (#36313)

* add support for fast image processors in add-new-model-like

* fix header not found add-fast-image-processor-cli

* Encourage adding fast image processor

* nit

* start improve doc

* update docs

* make requested modifs

docs/source/en/add_new_model.md

@@ -476,7 +476,7 @@ When both implementations produce the same output, verify the outputs are within
 torch.allclose(original_output, output, atol=1e-3)
 ```
 
-This is typically the most difficult part of the process. Congratulations if you've made it this far! 
+This is typically the most difficult part of the process. Congratulations if you've made it this far!
 
 And if you're stuck or struggling with this step, don't hesitate to ask for help on your pull request.
 
@@ -541,6 +541,48 @@ input_ids = tokenizer(input_str).input_ids
 
 When both implementations have the same `input_ids`, add a tokenizer test file. This file is analogous to the modeling test files. The tokenizer test files should contain a couple of hardcoded integration tests.
 
+## Implement image processor
+
+> [!TIP]
+> Fast image processors use the [torchvision](https://pytorch.org/vision/stable/index.html) library and can perform image processing on the GPU, significantly improving processing speed.
+> We recommend adding a fast image processor ([`BaseImageProcessorFast`]) in addition to the "slow" image processor ([`BaseImageProcessor`]) to provide users with the best performance. Feel free to tag [@yonigozlan](https://github.com/yonigozlan) for help adding a [`BaseImageProcessorFast`].
+
+While this example doesn't include an image processor, you may need to implement one if your model requires image inputs. The image processor is responsible for converting images into a format suitable for your model. Before implementing a new one, check whether an existing image processor in the Transformers library can be reused, as many models share similar image processing techniques. Note that you can also use [modular](./modular_transformers) for image processors to reuse existing components.
+
+If you do need to implement a new image processor, refer to an existing image processor to understand the expected structure. Slow image processors ([`BaseImageProcessor`]) and fast image processors ([`BaseImageProcessorFast`]) are designed differently, so make sure you follow the correct structure based on the processor type you're implementing.
+
+Run the following command (only if you haven't already created the fast image processor with the `transformers-cli add-new-model-like` command) to generate the necessary imports and to create a prefilled template for the fast image processor. Modify the template to fit your model.
+
+```bash
+transformers-cli add-fast-image-processor --model-name your_model_name
+```
+
+This command will generate the necessary imports and provide a pre-filled template for the fast image processor. You can then modify it to fit your model's needs.
+
+Add tests for the image processor in `tests/models/your_model_name/test_image_processing_your_model_name.py`. These tests should be similar to those for other image processors and should verify that the image processor correctly handles image inputs. If your image processor includes unique features or processing methods, ensure you add specific tests for those as well.
+
+## Implement processor
+
+If your model accepts multiple modalities, like text and images, you need to add a processor. The processor centralizes the preprocessing of different modalities before passing them to the model.
+
+The processor should call the appropriate modality-specific processors within its `__call__` function to handle each type of input correctly. Be sure to check existing processors in the library to understand their expected structure. Transformers uses the following convention in the `__call__` function signature.
+
+```python
+def __call__(
+    self,
+    images: ImageInput = None,
+    text: Union[TextInput, PreTokenizedInput, List[TextInput], List[PreTokenizedInput]] = None,
+    audio=None,
+    videos=None,
+    **kwargs: Unpack[YourModelProcessorKwargs],
+) -> BatchFeature:
+    ...
+```
+
+`YourModelProcessorKwargs` is a `TypedDict` that includes all the typical processing arguments and any extra arguments a specific processor may require.
+
+Add tests for the processor in `tests/models/your_model_name/test_processor_your_model_name.py`. These tests should be similar to those for other processors and should verify that the processor correctly handles the different modalities.
+
 ## Integration tests
 
 Now that you have a model and tokenizer, add end-to-end integration tests for the model and tokenizer to `tests/models/brand_new_llama/test_modeling_brand_new_llama.py`.
@@ -620,4 +662,4 @@ There are four timelines for model additions depending on the model contributor
 
 - **Hub-first release**: Transformers [remote-code](./models#custom-models) feature allows Transformers-based projects to be shared directly on the Hub. This is a good option if you don't have the bandwidth to add a model directly to Transformers.
 
-  If a model ends up being very popular, then it's very likely that we'll integrate it in Transformers ourselves to enable better support (documentation, maintenance, optimization, etc.) for it. A Hub-first release is the most frictionless way to add a model.
+  If a model ends up being very popular, then it's very likely that we'll integrate it in Transformers ourselves to enable better support (documentation, maintenance, optimization, etc.) for it. A Hub-first release is the most frictionless way to add a model.