Fig. 1. YOLOv4 network structure

Fig. 2. Mish activation function

Fig. 3. MRI image of spine

Fig. 4. Histogram of gray value before and after transformation. (a) Original drawing; (b) histogram equalization; (c) CLAHE

Fig. 5. Images before and after equalization. (a) Original drawing; (b) histogram equalization; (c) CLAHE

Fig. 6. Average RIOU of different anchor frames

Fig. 7. Depthwise separable convolution

Fig. 8. Optimized YOLOv4 network structure

Fig. 9. Loss curves. (a) YOLOv4; (b) YOLOv4-disc

Fig. 10. YOLOv4-disc P-R curve. (a) Healthy; (b) protrusion; (c) swollen

Fig. 11. AP values of different networks

Fig. 12. Comparison of missed inspection. (a) YOLOv4; (b) YOLOv4-disc

Fig. 13. Comparison of repeated detection. (a) YOLOv4; (b) YOLOv4-disc

Fig. 14. Comparison of nonoptimal shooting positions. (a) YOLOv4; (b) YOLOv4-disc