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. 2016 Feb 1;11(2):e0145955. doi: 10.1371/journal.pone.0145955

Table 4. The features and their correlations with PM2.5 index in our dataset.

Features Beijing Shanghai Phoenix
DC PC DC PC DC PC
Transmission 0.81 -0.78 0.60 -0.60 0.32 -0.32
ROI contrast 0.82 -0.76 0.40 -0.40 0.28 -0.29
Image entropy 0.63 -0.54 0.42 -0.46 0.24 -0.24
Image contrast 0.43 -0.43 0.52 -0.55 0.13 -0.12
Sky smoothness 0.34 -0.29 0.32 -0.31 0.28 -0.30
Sky color 0.43 -0.43 0.20 -0.21 0.09 -0.08
Solar zenith angle 0.13 -0.01 0.12 -0.11 0.10 -0.04