Table Of Contents
Table Of Contents

10. Skip Finetuning by reusing part of pre-trained model

There is a dilemma that pre-trained public dataset detection models need finetuning before we can apply them to our interested domain. While it is still a chanllenging task, in this tutorial we showcase a very interesting way to reuse pre-trained models.

Basically, you can grab a GluonCV pre-trained detection model and reset classes to a subset of coco categories, and it will be instantly ready to use without any tuning.

First let’s import some necessary libraries:

from matplotlib import pyplot as plt
import gluoncv
from gluoncv import model_zoo, data, utils

Load a pretrained model

Let’s get an Faster RCNN model trained on COCO dataset with ResNet-50 backbone.

net = model_zoo.get_model('faster_rcnn_resnet50_v1b_coco', pretrained=True)

Pre-process an image

Similar to faster rcnn inference tutorial, we grab and preprocess a demo image

im_fname ='' +
x, orig_img = data.transforms.presets.rcnn.load_test(im_fname)

Reset classes to exactly what we want

Original COCO model has 80 classes

print('coco classes: ', net.classes)
net.reset_class(classes=['bicycle', 'backpack'], reuse_weights=['bicycle', 'backpack'])
# now net has 2 classes as desired
print('new classes: ', net.classes)


coco classes:  ['person', 'bicycle', 'car', 'motorcycle', 'airplane', 'bus', 'train', 'truck', 'boat', 'traffic light', 'fire hydrant', 'stop sign', 'parking meter', 'bench', 'bird', 'cat', 'dog', 'horse', 'sheep', 'cow', 'elephant', 'bear', 'zebra', 'giraffe', 'backpack', 'umbrella', 'handbag', 'tie', 'suitcase', 'frisbee', 'skis', 'snowboard', 'sports ball', 'kite', 'baseball bat', 'baseball glove', 'skateboard', 'surfboard', 'tennis racket', 'bottle', 'wine glass', 'cup', 'fork', 'knife', 'spoon', 'bowl', 'banana', 'apple', 'sandwich', 'orange', 'broccoli', 'carrot', 'hot dog', 'pizza', 'donut', 'cake', 'chair', 'couch', 'potted plant', 'bed', 'dining table', 'toilet', 'tv', 'laptop', 'mouse', 'remote', 'keyboard', 'cell phone', 'microwave', 'oven', 'toaster', 'sink', 'refrigerator', 'book', 'clock', 'vase', 'scissors', 'teddy bear', 'hair drier', 'toothbrush']
new classes:  ['bicycle', 'backpack']

Inference and display

box_ids, scores, bboxes = net(x)
ax = utils.viz.plot_bbox(orig_img, bboxes[0], scores[0], box_ids[0], class_names=net.classes)

More flexible mapping strategy for reusing old weights

We also support dict for 1-to-1 class weights re-mapping So we can take advantage of this to remap some categories

net = model_zoo.get_model('faster_rcnn_resnet50_v1b_coco', pretrained=True)
net.reset_class(classes=['spaceship'], reuse_weights={'spaceship':'bicycle'})
box_ids, scores, bboxes = net(x)
ax = utils.viz.plot_bbox(orig_img, bboxes[0], scores[0], box_ids[0], class_names=net.classes)

The same story for different models

We can apply this strategy to SSD, YOLO and Mask-RCNN models Now we can use mask rcnn and reset class to detect person only

net = model_zoo.get_model('mask_rcnn_resnet50_v1b_coco', pretrained=True)
net.reset_class(classes=['person'], reuse_weights=['person'])
ids, scores, bboxes, masks = [xx[0].asnumpy() for xx in net(x)]

# paint segmentation mask on images directly
width, height = orig_img.shape[1], orig_img.shape[0]
masks = utils.viz.expand_mask(masks, bboxes, (width, height), scores)
orig_img = utils.viz.plot_mask(orig_img, masks)

# identical to Faster RCNN object detection
fig = plt.figure(figsize=(10, 10))
ax = fig.add_subplot(1, 1, 1)
ax = utils.viz.plot_bbox(orig_img, bboxes, scores, ids,
                         class_names=net.classes, ax=ax)

Feel excited?

Stay tuned for more generalized detection models with much more category knowledges than COCO and Pascal VOC!

Total running time of the script: ( 0 minutes 11.373 seconds)

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