ResNet (Residual Network)
ResNet is a deep convolutional neural network (CNN) architecture proposed by Kaiming He et al. in 2015, also described in “Overview of CNNs and Examples of Algorithms and Implementations” ResNet introduces innovative ideas to effectively train very deep networks. ResNet is an approach that introduces innovative ideas to effectively train very deep networks and achieve amazing performance in computer vision tasks.
1. skipped connections (Residual Connection):
The most important element of ResNet is the Residual Connection. Normal convolutional neural networks convey information layer by layer, and the information is modified step by step. However, ResNet introduces skip connections and directly conveys information in intermediate layers by adding inputs directly to outputs. This method reduces the gradient loss problem and facilitates training of very deep networks.
2. Residual Block:
The ResNet architecture consists of modules called Residual Blocks. Each residual block contains skipped connections, which ensure information transfer. The residual block consists of a regular convolutional layer, a batch normalization layer, and an activation function (ReLU).
3 Stack of convolutional layers:
In ResNet, many residual blocks are stacked. Models such as ResNet-50, ResNet-101, and ResNet-152 have hundreds of convolutional layers.
4. reduction of pooling layers and total concatenation layers:
ResNet reduces the number of pooling and all-joining layers compared to traditional convolutional neural networks. This reduces the computational cost of the model and allows lighter models to be built.
5. pre-training and transition learning:
ResNet is pre-trained on large data sets, and its trained models are widely used for transition learning. When applied to other tasks, it is common to recalibrate the pre-trained weights as initial values.
ResNet can train very deep networks, and its performance often outperforms other models, making it a widely used method in computer vision. The idea of ResNet’s architecture led to fundamental advances in the training of deep learning models and has had a significant impact on the design of subsequent models.
Specific procedures for ResNet
To understand the ResNet model, we briefly describe the specific steps.
1. input image preprocessing:
The input to ResNet is usually a normalized image. Typical preprocessing steps include image sizing, mean subtraction, and standard deviation normalization.
2. convolution layer:
The first layer of ResNet usually begins as a regular convolution layer. These convolution layers extract low-level features from the image.
3. Residual Block:
The central element of ResNet is the residual block. The residual block is stacked on top of the regular convolutional layer and contains the following elements
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- Skip Connection: The inputs are directly added to the outputs. This skip connection directly conveys the information of the intermediate layer.
- Convolutional Layer: Typically contains two convolutional layers and batch normalization.
- Activation function (ReLU): Typically, ReLU is used as the activation function.
4. stack deepening:
Multiple residual blocks are stacked to increase the depth of the network. This allows for the extraction of advanced features. A typical ResNet model has tens to hundreds of residual blocks.
5. reduction of pooling layers:
ResNet reduces the number of pooling layers (e.g., maximum pooling) compared to traditional models, reducing the computational cost of the network.
6. reduction of all coupling layers:
ResNet reduces the final number of all coupling layers, reducing the size of the model and improving computational efficiency.
7. output layer:
In the final output layer, a softmax activation function is applied for class classification. This generates a probability distribution of images belonging to different classes.
8. learning and optimization:
ResNet is trained on large data sets and trained using optimization algorithms (usually gradient descent).
9. evaluation and prediction:
After training is complete, ResNet makes predictions on new images. It interprets the probability distribution of the output layer and estimates the class of the image.
The key elements of ResNet are skip connections and residual blocks, which allow training very deep networks and reduce the gradient loss problem. ResNet is widely used in computer vision and will be a successful method for high-performance image classification, object detection, segmentation, and other tasks.
ResNet Application Examples
ResNet has been widely applied in many computer vision tasks and has been successfully used in a variety of applications due to its high performance and deep network design. The following are examples of ResNet applications.
1. image classification: ResNet has been very successful in image classification tasks on large datasets such as ImageNet, classifying different classes of images with high accuracy; versions such as ResNet-50, ResNet-101, and ResNet-152 are widely used.
2. Object Detection: ResNet is used as the backbone of the object detection model, which is also described in “Overview of Object Detection Techniques, Algorithms and Various Implementations” ResNet is integrated into object detection architectures such as Faster R-CNN as described in “Overview, Algorithms, and Examples of Implementations of Faster R-CNN” and YOLO (You Only Look Once) as described in “Overview, Algorithms, and Examples of Implementations of YOLO (You Only Look Once)” to help detect object location and class
3. Semantic Segmentation: Combining global average pooling and a convolutional layer, ResNet is also used for semantic segmentation tasks. A class label is assigned to each pixel in the image to achieve highly accurate segmentation. For more information, see also “Overview of Segmentation Networks and Implementation of Various Algorithms.
4. Face Recognition: In face recognition systems, parts of ResNet are used to extract facial features for face recognition and face identification. Applications include security systems, access control, and social media face detection. See also “Overview of Access Control Technologies, Algorithms, and Examples of Implementations” for more information.
5. Image Caption Generation: ResNet features are used as input to image caption generation models to help generate descriptive text about images.
6. Medical Image Analysis: ResNet is used to analyze medical images such as X-rays, MRIs, and CT scans for tasks such as anomaly detection, tumor detection, and disease diagnosis. For more information on anomaly detection techniques, see also “Overview of Anomaly Detection Techniques and Various Implementations.
7. image association with natural language processing: ResNet features are used for text-to-image association and image caption generation in combination with the natural language processing tasks described in “Overview of Natural Language Processing and Examples of Various Implementations.
Deep Learning Transfer Learning: ResNet’s trained models are used as a powerful starting point for transfer learning to other tasks. This allows for efficient construction of high-performance models for new datasets and tasks.” For details, please refer to “Overview of Transfer Learning, Algorithms, and Examples of Implementations.
Examples of ResNet implementations
Example implementations of ResNet are provided using deep learning frameworks (TensorFlow, PyTorch, Keras, etc.). The following is a simple example implementation of ResNet-50 using Keras.
from tensorflow.keras.applications import ResNet50
from tensorflow.keras.preprocessing import image
from tensorflow.keras.applications.resnet import preprocess_input, decode_predictions
import numpy as np
# Loading the model
model = ResNet50(weights='imagenet')
# Image Preprocessing
img_path = 'path_to_your_image.jpg' # Path to the image file
img = image.load_img(img_path, target_size=(224, 224)) # ResNet-50 expects 224x224 pixel images
x = image.img_to_array(img)
x = np.expand_dims(x, axis=0)
x = preprocess_input(x)
# Image Classification
preds = model.predict(x)
decoded_predictions = decode_predictions(preds, top=5)[0]
for i, (imagenet_id, label, score) in enumerate(decoded_predictions):
print(f"{i + 1}: {label} ({score:.2f})")The code loads the ResNet-50 model via Keras and performs class classification on a given image. The model is trained on the ImageNet dataset and returns class labels and probabilities for them.
Challenge for ResNet
ResNet is an excellent model and a method that can effectively solve the gradient loss problem in training deep neural networks. However, several challenges also exist, including the following
1. computational cost:
ResNet’s very deep networks are computationally expensive and require a high-performance GPU or TPU for training and inference on large data sets. This limits its use for general developers and in resource-constrained environments.
2. amount of training data:
Training a deep network requires a large amount of training data, and small data sets are prone to overtraining and may degrade model generalization performance.
3. tuning of hyperparameters:
Tuning ResNet’s hyperparameters (convolution filter size, learning rate, regularization strength, etc.) is necessary to find the right settings for each task and requires trial and error and experience to use the model with optimal performance.
4. memory and disk space:
ResNet’s model size is relatively large and consumes memory and disk space during deployment. Model size can be a challenge, especially for edge devices and mobile applications.
5. feature extraction and interpretability:
ResNet networks are very deep, making it difficult to understand which features are extracted by the model. There is a need to improve feature visualization and model interpretability.
6. new architectural developments:
While ResNet was innovative when it was first proposed, more efficient and higher-performing architectures (e.g., EfficientNet, described in “About EfficientNet“) have since been developed. These new architectures should be considered to replace ResNet.
Addressing ResNet (Residual Network) Issues
To address the ResNet (Residual Network) challenge, the following methods are commonly employed
1. reducing computational cost:
If the ResNet model is computationally expensive, it is important to consider lightening or pruning the model. Adjusting the depth of the model and removing extra layers can reduce the computational cost. In addition, deep learning frameworks (TensorFlow Lite, ONNX Runtime, etc.) can be used to efficiently infer models.
2. transfer learning:
ResNet’s trained models can be used for transfer learning to efficiently build high-performance models for new tasks. It is common to adjust the final layer to the new task and readjust the trained weights.
3. data augmentation and regularization:
Data expansion techniques can be used to increase the training data to reduce overlearning. It is also important to apply regularization techniques (e.g., dropout, weight decay) to improve the generalization performance of the model. For more information on data expansion techniques, please refer to “Approaches to Machine Learning with Small Data and Examples of Various Implementations,” and for more information on regularization, please refer to “Overview of Sparse Modeling, Application Examples, and Implementations.
4. model optimization:
The training process can be efficiently controlled by selecting model optimization methods and adjusting hyperparameters. For example, scheduling the learning rate or adjusting momentum can be considered.
5. model visualization and interpretability:
Techniques to improve model visualization and interpretability can be used to better understand model behavior and identify misclassification problems. For more on model visualization, see also “Deep Learning for Computer Vision with Python and Keras (4) Visualizing CNN Training Data.” Tools such as Grad-CAM and LIME, described in “Explainable Machine Learning” are also useful.
6 Adopt a new architecture:
Instead of ResNet, newer architectures (e.g., EfficientNet as described in “About EfficientNet” and MobileNet as described in “About MobileNet“) that are more efficient and perform better may be adopted. These architectures can reduce computational costs and provide equal or better performance.
7. Hardware resource provisioning:
When computational costs are high, ResNet can be efficiently trained and evaluated by using cloud-based hardware resources and high-performance hardware such as GPUs and TPUs. See also “Cloud Technology” for more information on using the cloud.
Reference Information and Reference Books
For details on image information processing, see “Image Information Processing Techniques.
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