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Semantic Segmentation — FCN, U-Net, DeepLab and Medical Imaging

Computer VisionSegmentation🟢 Free Lesson

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Computer Vision

Semantic Segmentation — Pixel-Level Understanding of Images

Semantic segmentation assigns a class label to every pixel in an image, enabling fine-grained scene understanding. It is critical for autonomous driving, medical imaging, and robotics.

  • U-Net Dominates Medical — Encoder-decoder with skip connections excels on small medical imaging datasets
  • Dice + BCE is Standard — Combined loss functions handle class imbalance and optimize overlap directly
  • mIoU is the Metric — Mean Intersection over Union across all classes is the primary evaluation measure

Semantic Segmentation — FCN, U-Net, DeepLab and Medical Imaging

Semantic segmentation assigns a class label to every pixel in an image, enabling fine-grained scene understanding. It is critical for autonomous driving, medical imaging, and robotics.


Segmentation Types

Segmentation Types Comparison🚗🚶🚗🚗OriginalSemanticInstancePanopticCar (all same)Car₁, Car₂Person

Fully Convolutional Network (FCN)


U-Net Architecture

U-Net Architecture: Encoder-Decoder with Skip ConnectionsEncoder (Downsampling)64×H×W128×H/2256×H/4512×H/81024×H/16BottleneckDecoder (Upsampling)512×H/8256×H/4128×H/2C×H×WOutputSkip Connections (Concatenate)

DeepLab

Atrous (Dilated) ConvolutionStandard 3×3Rate=1Dilated 3×3 (r=2)Rate=2, larger receptive fieldDilated 3×3 (r=4)Rate=4, even largerASPPRate=1Rate=6Rate=12Rate=18Paralleldilatedconvolutions

Loss Functions for Segmentation


Evaluation: IoU


Applications

Semantic Segmentation ApplicationsMedical Imaging• Tumor segmentation• Organ delineation• Cell counting• Retinal vessel analysis• Skin lesion analysisU-Net dominates hereAutonomous Driving• Road segmentation• Lane detection• Pedestrian detection• Sky/building parsing• Free space estimationReal-time requiredOther Domains• Satellite imagery• Agricultural monitoring• Industrial inspection• AR/VR scene understanding• Robot navigationDeepLab for speed

Summary

  • Semantic segmentation assigns a class label to every pixel
  • FCN introduced fully convolutional architecture for pixel-wise prediction
  • U-Net with skip connections dominates medical imaging
  • DeepLab uses dilated convolution for multi-scale context
  • Dice + BCE loss handles class imbalance
  • mIoU is the standard evaluation metric

Next: RNN Deep Dive

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