Fast-SCNN: Fast Semantic Segmentation Network

12 Feb 2019  ·  Rudra P. K. Poudel, Stephan Liwicki, Roberto Cipolla ·

The encoder-decoder framework is state-of-the-art for offline semantic image segmentation. Since the rise in autonomous systems, real-time computation is increasingly desirable. In this paper, we introduce fast segmentation convolutional neural network (Fast-SCNN), an above real-time semantic segmentation model on high resolution image data (1024x2048px) suited to efficient computation on embedded devices with low memory. Building on existing two-branch methods for fast segmentation, we introduce our `learning to downsample' module which computes low-level features for multiple resolution branches simultaneously. Our network combines spatial detail at high resolution with deep features extracted at lower resolution, yielding an accuracy of 68.0% mean intersection over union at 123.5 frames per second on Cityscapes. We also show that large scale pre-training is unnecessary. We thoroughly validate our metric in experiments with ImageNet pre-training and the coarse labeled data of Cityscapes. Finally, we show even faster computation with competitive results on subsampled inputs, without any network modifications.

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Results from the Paper


Task Dataset Model Metric Name Metric Value Global Rank Result Benchmark
Semantic Segmentation Cityscapes test Fast-SCNN Mean IoU (class) 68% # 82
Semantic Segmentation Cityscapes val Fast-SCNN + Coarse + ImageNet mIoU 69.19 # 74
Semantic Segmentation DADA-seg Fast-SCNN mIoU 26.32 # 13
Semantic Segmentation DensePASS Fast-SCNN mIoU 24.6% # 34
Semantic Segmentation EventScape Fast-SCNN mIoU 44.27 # 9
Thermal Image Segmentation PST900 Fast-SCNN mIoU 47.2 # 17
Semantic Segmentation SynPASS Fast-SCNN mIoU 21.30% # 7

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