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completed pytorch image classification guide

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# Image Classification in Pytorch
# Image Classification in PyTorch
related_spaces: https://huggingface.co/spaces/nateraw/quickdraw
related_spaces: abidlabs/pytorch-image-classifier
tags: VISION, RESNET, PYTORCH
## Introduction
Image classification is a central task in computer vision. And building better classifiers to classify what object is present in a picture is an active area of research, as it has applications stretching from autonomous vehicles to medical imaging.
Image classification is a central task in computer vision. Building better classifiers to classify what object is present in a picture is an active area of research, as it has applications stretching from autonomous vehicles to medical imaging.
Such models are perfect to use with Gradio's *image* input component, so in this tutorial we will build a web demo to classify images using Gradio. We will be able to build the whole web application in Python, and will look like this (try one of the examples!):
<iframe src="https://hf.space/gradioiframe/abidlabs/pytorch-image-classifier/+" frameBorder="0" height="450" title="Gradio app" class="container p-0 flex-grow space-iframe" allow="accelerometer; ambient-light-sensor; autoplay; battery; camera; document-domain; encrypted-media; fullscreen; geolocation; gyroscope; layout-animations; legacy-image-formats; magnetometer; microphone; midi; oversized-images; payment; picture-in-picture; publickey-credentials-get; sync-xhr; usb; vr ; wake-lock; xr-spatial-tracking" sandbox="allow-forms allow-modals allow-popups allow-popups-to-escape-sandbox allow-same-origin allow-scripts allow-downloads"></iframe>
Let's get started!
### Prerequisites
Make sure you have the `gradio` Python package already [installed](/getting_started). We will be using a pretrained image classification model, so also install `torch`.
Make sure you have the `gradio` Python package already [installed](/getting_started). We will be using a pretrained image classification model, so you should also have `torch` installed.
## Step 1 — Setting up the Image Classification Model
First, you will need a sketch recognition model. Since many researchers have already trained their own models on the Quick Draw dataset, we will use a pretrained model in this tutorial. Our model is a light 1.5 MB model trained by Nate Raw, that [you can download here](https://huggingface.co/spaces/nateraw/quickdraw/blob/main/pytorch_model.bin).
If you are interested, here [is the code](https://github.com/nateraw/quickdraw-pytorch) that was used to train the model. We will simply load the pretrained model in PyTorch, as follows:
First, you will need a image classification model. For this tutorial, we will use a pretrained Resnet-18 model, as it is easily downloadable from [PyTorch Hub](https://pytorch.org/hub/pytorch_vision_resnet/). You can use a different pretrained model or train your own.
```python
import torch
from torch import nn
model = nn.Sequential(
nn.Conv2d(1, 32, 3, padding='same'),
nn.ReLU(),
nn.MaxPool2d(2),
nn.Conv2d(32, 64, 3, padding='same'),
nn.ReLU(),
nn.MaxPool2d(2),
nn.Conv2d(64, 128, 3, padding='same'),
nn.ReLU(),
nn.MaxPool2d(2),
nn.Flatten(),
nn.Linear(1152, 256),
nn.ReLU(),
nn.Linear(256, len(LABELS)),
)
state_dict = torch.load('pytorch_model.bin', map_location='cpu')
model.load_state_dict(state_dict, strict=False)
model.eval()
model = torch.hub.load('pytorch/vision:v0.6.0', 'resnet18', pretrained=True).eval()
```
Because we will be using the model for inference, we have called the `.eval()` method.
## Step 2 — Defining a `predict` function
Next, you will need to define a function that takes in the *user input*, which in this case is a sketched image, and returns the prediction. The prediction should be returned as a dictionary whose keys are class name and values are confidence probabilities. We will load the class names from this [text file](https://huggingface.co/spaces/nateraw/quickdraw/blob/main/class_names.txt).
Next, you will need to define a function that takes in the *user input*, which in this case is an image, and returns the prediction. The prediction should be returned as a dictionary whose keys are class name and values are confidence probabilities. We will load the class names from this [text file](https://git.io/JJkYN).
In the case of our pretrained model, it will look like this:
```python
from pathlib import Path
import requests
from PIL import Image
from torchvision import transforms
LABELS = Path('class_names.txt').read_text().splitlines()
# Download human-readable labels for ImageNet.
response = requests.get("https://git.io/JJkYN")
labels = response.text.split("\n")
def predict(img):
x = torch.tensor(img, dtype=torch.float32).unsqueeze(0).unsqueeze(0) / 255.
with torch.no_grad():
out = model(x)
probabilities = torch.nn.functional.softmax(out[0], dim=0)
values, indices = torch.topk(probabilities, 5)
confidences = {LABELS[i]: v.item() for i, v in zip(indices, values)}
return confidences
def predict(inp):
inp = Image.fromarray(inp.astype('uint8'), 'RGB')
inp = transforms.ToTensor()(inp).unsqueeze(0)
with torch.no_grad():
prediction = torch.nn.functional.softmax(model(inp)[0], dim=0)
confidences = {labels[i]: float(prediction[i]) for i in range(1000)}
return confidences
```
Let's break this down. The function takes one parameters:
* `img`: the input image as a `numpy` array
* `inp`: the input image as a `numpy` array
Then, the function converts the image to a PyTorch `tensor`, passes it through the model, and returns:
Then, the function converts the image to a PIL Image and then eventually a PyTorch `tensor`, passes it through the model, and returns:
* `confidences`: the top five predictions, as a dictionary whose keys are class labels and whose values are confidence probabilities
* `confidences`: the predictions, as a dictionary whose keys are class labels and whose values are confidence probabilities
## Step 3 — Creating a Gradio Interface
Now that we have our predictive function set up, we can create a Gradio Interface around it.
In this case, the input component is a sketchpad. To create a sketchpad input, we can use the convenient string shortcut, `"sketchpad"` which creates a canvas for a user to draw on and handles the preprocessing to convert that to a numpy array.
In this case, the input component is a drag-and-drop image component. To create this input, we can use the convenient string shortcut, `"image"` which creates the component and handles the preprocessing to convert that to a numpy array.
The output component will be a `"label"`, which displays the top labels in a nice form.
The output component will be a `"label"`, which displays the top labels in a nice form. Since we don't want to show all 1,000 class labels, we will customize it to show only the top 3 images.
Finally, we'll add one more parameter, setting `live=True`, which allows our interface to run in real time, adjusting its predictions every time a user draws on the sketchpad. The code for Gradio looks like this:
Finally, we'll add one more parameter, the `examples`, which allows us to prepopulate our interfaces with a few predefined examples. The code for Gradio looks like this:
```python
import gradio as gr
gr.Interface(fn=predict,
inputs="sketchpad",
outputs="label",
live=True).launch()
inputs="image",
outputs=gr.outputs.Label(num_top_classes=3),
examples=["lion.jpg", "cheetah.jpg"]).launch()
```
This produces the following interface, which you can try right here in your browser (try drawing something, like a "snake" or a "laptop"):
This produces the following interface, which you can try right here in your browser (try uploading your own examples!):
<iframe src="https://hf.space/gradioiframe/abidlabs/draw2/+" frameBorder="0" height="450" title="Gradio app" class="container p-0 flex-grow space-iframe" allow="accelerometer; ambient-light-sensor; autoplay; battery; camera; document-domain; encrypted-media; fullscreen; geolocation; gyroscope; layout-animations; legacy-image-formats; magnetometer; microphone; midi; oversized-images; payment; picture-in-picture; publickey-credentials-get; sync-xhr; usb; vr ; wake-lock; xr-spatial-tracking" sandbox="allow-forms allow-modals allow-popups allow-popups-to-escape-sandbox allow-same-origin allow-scripts allow-downloads"></iframe>
<iframe src="https://hf.space/gradioiframe/abidlabs/pytorch-image-classifier/+" frameBorder="0" height="450" title="Gradio app" class="container p-0 flex-grow space-iframe" allow="accelerometer; ambient-light-sensor; autoplay; battery; camera; document-domain; encrypted-media; fullscreen; geolocation; gyroscope; layout-animations; legacy-image-formats; magnetometer; microphone; midi; oversized-images; payment; picture-in-picture; publickey-credentials-get; sync-xhr; usb; vr ; wake-lock; xr-spatial-tracking" sandbox="allow-forms allow-modals allow-popups allow-popups-to-escape-sandbox allow-same-origin allow-scripts allow-downloads"></iframe>
----------
And you're done! That's all the code you need to build a Pictionary-style guessing app. Have fun and try to find some edge cases 🧐
And you're done! That's all the code you need to build a web demo for an image classifier. If you'd like to share with others, try setting `share=True` when you `launch()` the Interface!