What are some issues with convolutional neural networks?

Convolutional Neural Networks (CNNs) face several challenges, including computational inefficiency, limitations in handling spatial hierarchies, and struggles with generalization across diverse data. These issues arise from their architectural design and reliance on specific assumptions about input data. While CNNs remain powerful for tasks like image recognition, understanding their limitations helps developers choose appropriate solutions or alternatives.

One major issue is computational inefficiency, especially with deep networks. CNNs require significant processing power due to the large number of convolutional operations and parameters. For example, models like VGG-16 use over 138 million parameters, leading to high memory usage and slow training times without specialized hardware like GPUs. Even inference can be costly in real-time applications, such as object detection in video streams. Additionally, convolution operations often redundantly process overlapping regions in input data (e.g., sliding filters across an image), which can waste resources. Techniques like separable convolutions or model pruning help mitigate this, but they add complexity and may reduce accuracy.

CNNs also struggle with spatial hierarchy limitations. While pooling layers reduce feature map sizes and add translation invariance, they discard precise spatial information. This makes tasks requiring fine-grained localization—like medical image segmentation or detecting small objects in satellite imagery—challenging. For instance, a CNN might identify a tumor in an X-ray but fail to outline its exact boundaries. Furthermore, fixed-size convolutional kernels may not adapt well to objects at varying scales or orientations. A cat viewed from an angle might be misclassified if the model hasn’t learned rotated features. Architectures like Feature Pyramid Networks (FPNs) address this by combining multi-scale features, but they increase model complexity.

Finally, CNNs often require large amounts of labeled training data and struggle with generalization. In domains like rare disease diagnosis, where labeled datasets are small, CNNs may overfit. Even with data augmentation, synthetic variations (e.g., rotated images) may not cover real-world edge cases. Transfer learning helps by pretraining on datasets like ImageNet, but domain mismatch can persist: a model trained on daytime photos may fail on nighttime imagery. Additionally, CNNs can be overly sensitive to adversarial attacks—subtle input perturbations, like noise patterns invisible to humans, can cause misclassification. This limits their reliability in security-critical applications like autonomous driving. While regularization techniques (e.g., dropout) or adversarial training can improve robustness, they don’t fully eliminate these vulnerabilities. Developers must weigh these trade-offs when deploying CNNs in production systems.