Add image-text-to-text task guide (#31777)

* Add image-text-to-text task page

* Update docs/source/en/tasks/image_text_to_text.md
Co-authored-by: Steven Liu <59462357+stevhliu@users.noreply.github.com>

* Update docs/source/en/tasks/image_text_to_text.md
Co-authored-by: Steven Liu <59462357+stevhliu@users.noreply.github.com>

* Update docs/source/en/tasks/image_text_to_text.md
Co-authored-by: Steven Liu <59462357+stevhliu@users.noreply.github.com>

* Update docs/source/en/tasks/image_text_to_text.md
Co-authored-by: Steven Liu <59462357+stevhliu@users.noreply.github.com>

* Update docs/source/en/tasks/image_text_to_text.md
Co-authored-by: Steven Liu <59462357+stevhliu@users.noreply.github.com>

* Update docs/source/en/tasks/image_text_to_text.md
Co-authored-by: Steven Liu <59462357+stevhliu@users.noreply.github.com>

* Update docs/source/en/tasks/image_text_to_text.md
Co-authored-by: Steven Liu <59462357+stevhliu@users.noreply.github.com>

* Update docs/source/en/tasks/image_text_to_text.md
Co-authored-by: Steven Liu <59462357+stevhliu@users.noreply.github.com>

* Update docs/source/en/tasks/image_text_to_text.md
Co-authored-by: Steven Liu <59462357+stevhliu@users.noreply.github.com>

* Update docs/source/en/tasks/image_text_to_text.md
Co-authored-by: Steven Liu <59462357+stevhliu@users.noreply.github.com>

* Update docs/source/en/tasks/image_text_to_text.md
Co-authored-by: Steven Liu <59462357+stevhliu@users.noreply.github.com>

* Address comments

* Fix heading

* Update docs/source/en/tasks/image_text_to_text.md
Co-authored-by: amyeroberts <22614925+amyeroberts@users.noreply.github.com>

* Update docs/source/en/tasks/image_text_to_text.md
Co-authored-by: amyeroberts <22614925+amyeroberts@users.noreply.github.com>

* Update docs/source/en/tasks/image_text_to_text.md
Co-authored-by: amyeroberts <22614925+amyeroberts@users.noreply.github.com>

* Update docs/source/en/tasks/image_text_to_text.md
Co-authored-by: amyeroberts <22614925+amyeroberts@users.noreply.github.com>

* Update docs/source/en/tasks/image_text_to_text.md
Co-authored-by: amyeroberts <22614925+amyeroberts@users.noreply.github.com>

* Update docs/source/en/tasks/image_text_to_text.md
Co-authored-by: amyeroberts <22614925+amyeroberts@users.noreply.github.com>

* Address comments

* Update image_text_to_text.md

---------
Co-authored-by: Steven Liu <59462357+stevhliu@users.noreply.github.com>
Co-authored-by: amyeroberts <22614925+amyeroberts@users.noreply.github.com>

docs/source/en/_toctree.yml

@@ -92,6 +92,8 @@
       title: Visual Question Answering
     - local: tasks/text-to-speech
       title: Text to speech
+    - local: tasks/image_text_to_text
+      title: Image-text-to-text
     title: Multimodal
   - isExpanded: false
     sections:

docs/source/en/tasks/image_text_to_text.md

+<!--Copyright 2024 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.
+
+⚠️ Note that this file is in Markdown but contain specific syntax for our doc-builder (similar to MDX) that may not be
+rendered properly in your Markdown viewer.
+
+-->
+
+# Image-text-to-text
+
+[[open-in-colab]]
+
+Image-text-to-text models, also known as vision language models (VLMs), are language models that take an image input. These models can tackle various tasks, from visual question answering to image segmentation. This task shares many similarities with image-to-text, but with some overlapping use cases like image captioning. Image-to-text models only take image inputs and often accomplish a specific task, whereas VLMs take open-ended text and image inputs and are more generalist models.
+
+In this guide, we provide a brief overview of VLMs and show how to use them with Transformers for inference.
+
+To begin with, there are multiple types of VLMs:
+- base models used for fine-tuning
+- chat fine-tuned models for conversation
+- instruction fine-tuned models
+
+This guide focuses on inference with an instruction-tuned model. 
+
+Let's begin installing the dependencies.
+
+```bash
+pip install -q transformers accelerate flash_attn 
+```
+
+Let's initialize the model and the processor. 
+
+```python
+from transformers import AutoProcessor, Idefics2ForConditionalGeneration
+import torch
+
+device = torch.device("cuda")
+model = Idefics2ForConditionalGeneration.from_pretrained(
+    "HuggingFaceM4/idefics2-8b",
+    torch_dtype=torch.bfloat16,
+    attn_implementation="flash_attention_2",
+).to(device)
+
+processor = AutoProcessor.from_pretrained("HuggingFaceM4/idefics2-8b")
+```
+
+This model has a [chat template](./chat_templating) that helps user parse chat outputs. Moreover, the model can also accept multiple images as input in a single conversation or message. We will now prepare the inputs. 
+
+The image inputs look like the following.
+
+<div class="flex justify-center">
+     <img src="https://huggingface.co/datasets/huggingface/documentation-images/resolve/main/cats.png" alt="Two cats sitting on a net"/>
+</div>
+
+<div class="flex justify-center">
+     <img src="https://huggingface.co/datasets/huggingface/documentation-images/resolve/main/bee.jpg" alt="A bee on a pink flower"/>
+</div>
+
+
+```python
+from PIL import Image
+import requests
+
+img_urls =["https://huggingface.co/datasets/huggingface/documentation-images/resolve/main/cats.png",
+           "https://huggingface.co/datasets/huggingface/documentation-images/resolve/main/bee.jpg"]
+images = [Image.open(requests.get(img_urls[0], stream=True).raw),
+          Image.open(requests.get(img_urls[1], stream=True).raw)]
+```
+
+Below is an example of the chat template. We can feed conversation turns and the last message as an input by appending it at the end of the template. 
+
+
+```python
+messages = [
+    {
+        "role": "user",
+        "content": [
+            {"type": "image"},
+            {"type": "text", "text": "What do we see in this image?"},
+        ]
+    },
+    {
+        "role": "assistant",
+        "content": [
+            {"type": "text", "text": "In this image we can see two cats on the nets."},
+        ]
+    },
+    {
+        "role": "user",
+        "content": [
+            {"type": "image"},
+            {"type": "text", "text": "And how about this image?"},
+        ]
+    },       
+]
+```
+
+We will now call the processors' [`~ProcessorMixin.apply_chat_template`] method to preprocess its output along with the image inputs.
+
+```python
+prompt = processor.apply_chat_template(messages, add_generation_prompt=True)
+inputs = processor(text=prompt, images=[images[0], images[1]], return_tensors="pt").to(device)
+```
+
+We can now pass the preprocessed inputs to the model.
+
+```python
+with torch.no_grad():
+    generated_ids = model.generate(**inputs, max_new_tokens=500)
+generated_texts = processor.batch_decode(generated_ids, skip_special_tokens=True)
+
+print(generated_texts)
+## ['User: What do we see in this image? \nAssistant: In this image we can see two cats on the nets. \nUser: And how about this image? \nAssistant: In this image we can see flowers, plants and insect.']
+```
+
+## Streaming
+
+We can use [text streaming](./generation_strategies#streaming) for a better generation experience. Transformers supports streaming with the [`TextStreamer`] or [`TextIteratorStreamer`] classes. We will use the [`TextIteratorStreamer`] with IDEFICS-8B.
+
+Assume we have an application that keeps chat history and takes in the new user input. We will preprocess the inputs as usual and initialize [`TextIteratorStreamer`] to handle the generation in a separate thread. This allows you to stream the generated text tokens in real-time. Any generation arguments can be passed to [`TextIteratorStreamer`].
+
+
+```python
+import time
+from transformers import TextIteratorStreamer
+from threading import Thread
+
+def model_inference(
+    user_prompt,
+    chat_history,
+    max_new_tokens,
+    images
+):
+    user_prompt = {
+        "role": "user",
+        "content": [
+            {"type": "image"},
+            {"type": "text", "text": user_prompt},
+        ]
+    }
+    chat_history.append(user_prompt)
+    streamer = TextIteratorStreamer(
+        processor.tokenizer,
+        skip_prompt=True,
+        timeout=5.0,
+    )
+
+    generation_args = {
+        "max_new_tokens": max_new_tokens,
+        "streamer": streamer,
+        "do_sample": False
+    }
+
+    # add_generation_prompt=True makes model generate bot response
+    prompt = processor.apply_chat_template(chat_history, add_generation_prompt=True)
+    inputs = processor(
+        text=prompt,
+        images=images,
+        return_tensors="pt",
+    ).to(device)
+    generation_args.update(inputs)
+
+    thread = Thread(
+        target=model.generate,
+        kwargs=generation_args,
+    )
+    thread.start()
+
+    acc_text = ""
+    for text_token in streamer:
+        time.sleep(0.04)
+        acc_text += text_token
+        if acc_text.endswith("<end_of_utterance>"):
+            acc_text = acc_text[:-18]
+        yield acc_text
+    
+    thread.join()
+```
+
+Now let's call the `model_inference` function we created and stream the values. 
+
+```python
+generator = model_inference(
+    user_prompt="And what is in this image?",
+    chat_history=messages,
+    max_new_tokens=100,
+    images=images
+)
+
+for value in generator:
+  print(value)
+
+# In
+# In this
+# In this image ...
+```
+
+## Fit models in smaller hardware
+
+VLMs are often large and need to be optimized to fit in smaller hardware. Transformers supports many model quantization libraries, and here we will only show int8 quantization with [Quanto](./quantization/quanto#quanto). int8 quantization offers memory improvements up to 75 percent (if all weights are quantized). However it is no free lunch, since 8-bit is not a CUDA-native precision, the weights are quantized back and forth on the fly, which adds up to latency. 
+
+First, install dependencies.
+
+```bash
+pip install -U quanto bitsandbytes
+```
+
+To quantize a model during loading, we need to first create [`QuantoConfig`]. Then load the model as usual, but pass `quantization_config` during model initialization.
+
+```python
+from transformers import Idefics2ForConditionalGeneration, AutoTokenizer, QuantoConfig
+
+model_id = "HuggingFaceM4/idefics2-8b"
+quantization_config = QuantoConfig(weights="int8")
+quantized_model = Idefics2ForConditionalGeneration.from_pretrained(model_id, device_map="cuda", quantization_config=quantization_config)
+```
+
+And that's it, we can use the model the same way with no changes. 
+
+## Further Reading
+
+Here are some more resources for the image-text-to-text task.
+
+- [Image-text-to-text task page](https://huggingface.co/tasks/image-text-to-text) covers model types, use cases, datasets, and more. 
+- [Vision Language Models Explained](https://huggingface.co/blog/vlms) is a blog post that covers everything about vision language models and supervised fine-tuning using [TRL](https://huggingface.co/docs/trl/en/index).