COCO数据集80个类的实例数量（训练集）。在网上没找到具体数字，自己写了代码计算了一下。
person 257249
bicycle 7056
car 43532
motorcycle 8654
airplane 5129
bus 6061
train 4570
truck 9970
boat 10575
traffic light 12841
fire hydrant 1865
stop sign 1983
parking meter 1283
bench 9820
bird 10537
cat 4766
dog 5500
horse 6567
sheep 9223
cow 8014
elephant 5484
bear 1294
zebra 5269
giraffe 5128
backpack 8713
umbrella 11265
handbag 12341
tie 6445
suitcase 6112
frisbee 2681
skis 6616
snowboard 2676
sports ball 6299
kite 8801
baseball bat 3273
baseball glove 3747
skateboard 5536
surfboard 6091
tennis racket 4803
bottle 24070
wine glass 7839
cup 20574
fork 5474
knife 7759
spoon 6158
bowl 14323
banana 9195
apple 5776
sandwich 4356
orange 6302
broccoli 7261
carrot 7758
hot dog 2883
pizza 5807
donut 7005
cake 6296
chair 38071
couch 5779
potted plant 8631
bed 4192
dining table 15695
toilet 4149
tv 5803
laptop 4960
mouse 2261
remote 5700
keyboard 2854
cell phone 6420
microwave 1672
oven 3334
toaster 225
sink 5609
refrigerator 2634
book 24075
clock 6320
vase 6577
scissors 1464
teddy bear 4729
hair drier 198
toothbrush 1945