This example demonstrates learning a superpixel CRF for semantic image segmentation. To run the experiment, please download the pre-processed data from: http://www.ais.uni-bonn.de/deep_learning/downloads.html

The data consists of superpixels, unary potentials, and the connectivity structure of the superpixels. The unary potentials were originally provided by Philipp Kraehenbuehl: http://graphics.stanford.edu/projects/densecrf/

The superpixels were extracted using SLIC. The code for generating the connectivity graph and edge features will be made available soon.

This example does not contain the proper evaluation on pixel level, as that would need the Pascal VOC 2010 dataset.

```
import numpy as np
try:
import cPickle as pickle
except ImportError:
import pickle
from pystruct import learners
import pystruct.models as crfs
from pystruct.utils import SaveLogger
data_train = pickle.load(open("data_train_dict.pickle"))
C = 0.01
n_states = 21
print("number of samples: %s" % len(data_train['X']))
class_weights = 1. / np.bincount(np.hstack(data_train['Y']))
class_weights *= 21. / np.sum(class_weights)
print(class_weights)
model = crfs.EdgeFeatureGraphCRF(inference_method='qpbo',
class_weight=class_weights,
symmetric_edge_features=[0, 1],
antisymmetric_edge_features=[2])
experiment_name = "edge_features_one_slack_trainval_%f" % C
ssvm = learners.NSlackSSVM(
model, verbose=2, C=C, max_iter=100000, n_jobs=-1,
tol=0.0001, show_loss_every=5,
logger=SaveLogger(experiment_name + ".pickle", save_every=100),
inactive_threshold=1e-3, inactive_window=10, batch_size=100)
ssvm.fit(data_train['X'], data_train['Y'])
data_val = pickle.load(open("data_val_dict.pickle"))
y_pred = ssvm.predict(data_val['X'])
# we throw away void superpixels and flatten everything
y_pred, y_true = np.hstack(y_pred), np.hstack(data_val['Y'])
y_pred = y_pred[y_true != 255]
y_true = y_true[y_true != 255]
print("Score on validation set: %f" % np.mean(y_true == y_pred))
```

**Total running time of the script:**
(0 minutes 0.000 seconds)

**Download Python source code:** `image_segmentation.py`