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vise three additional metrics that quantify how accuracy is |
distributed across the classes. The metrics have been used |
in existing fairness analysis of segmentation models [19]. |
These are:1.Class-std . Standard deviation of IoUs across the 7 |
classes; |
2.Worst . IoU of the worst-performing class (Worst); |
3.Sorted 30% (bottom, top) . Mean of the bottom 30% |
and top 30% classes of the sorted class IoUs. In our |
case, 30% is 2 classes out of 7. |
Next, we describe the setup for the two transfer tasks. |
4.2. Transfer learning |
As mentioned earlier, we consider the setting of unsu- |
pervised domain adaption (UDA) that is we have a single |
task (image segmentation) on the two domains. We assume |
access to images and labels for the source (train) domain |
and only the images for the target (test) domain. This is |
a practical setting in satellite imagery since collecting im- |
ages is inexpensive due to advancements in remote sensing, |
however, annotating the segmentation labels is expensive. |
Thus, we want to be able to use the labelled source images |
to segment known but as yet unlabelled target domain. |
We consider two UDA methods which performed the |
best on the LoveDA benchmark [52] – class-balanced self- |
training ( CBST ) [59] and instance adaptive self-training |
(IAST ) [33]. CBST optimizes the generation of pseudo- |
labels used during self-training to be more balanced among |
the classes by using class-wise confidence scores. IAST |
adaptively adjusts the pseudo-label generation to improve |
the diversity of pseudo-labels and saves useful information |
from hard instances. We also use a natural method which |
ignores transfer learning and trains only with data from the |
source domain ( No adaptation ). |
For all transfer learning experiments, we use a |
DeepLabV3+ [7] network with ResNet50 encoder. An |
Adam optimizer is used with a momentum of 0.9. The batch |
size is 8 and the total training iterations are 15000. Other ex- |
perimental setup parameters are the same as in the semantic |
segmentation task. |
4.2.1 Task B - Transfer across districts |
First, we consider the scenario where a model is transferred |
across different geographical locations, which in our case |
are administrative districts. Source domain comprises of |
8 districts: Gulou, Qinhuai, Qixia, Jinghan (urban), and |
Pukou, Gaochun, Lishui, Jingxia (rural); and Target do- |
main has 4 districts: Yuhuatai, Jintan (urban), and Liuhe, |
Huangpi (rural). The ”No adaptation” and two UDA meth- |
ods (CBST, IAST) are applied to train the network on the |
source domain, and are tested on urban and rural images |
from the unseen target domain, separately. The same accu- |
racy and fairness metrics listed in Section 4.1.2 are used for |
evaluation. |
2919 |
Mean Class-std |
Model rural urban rural−urban (%) rural urban rural−urban (%) |
UNet 0.639 0.595 0.044 (6.9%) 0.106 0.0946 0.0114 (10.8%) |
DeepLabV3+ 0.632 0.597 0.035 (5.5%) 0.0982 0.0896 0.0086 (8.8%) |
Worst Sorted 30% (bottom, top) |
Model rural urban rural−urban (%) rural urban rural−urban (%) |
UNet 0.453 0.474 −0.021 (-4.4%) (0.491, 0.742) (0.480, 0.705) (0.011 , 0.037)(2.2%, 5.0%) |
DeepLabV3+ 0.473 0.473 0 (n/a) (0.504, 0.740) (0.489, 0.706) (0.015, 0.034)(3.0%, 4.6%) |
Table 1. Task A: Evaluation on single-domain semantic segmentation. Two networks, UNet and DeepLabV3+, are tested on rural and |
urban districts from the same domain as training set. For metrics, Mean, Class-std, and Worst, the better performing group (between rural |
and urban) is in bold. The difference in performance between rural and urban is shaded. Typically, performance is better for rural than |
urban. |
Mean Class-std |
Method rural urban rural−urban (%) rural urban rural−urban (%) |
No adaptation 0.364 0.486 −0.122 ( −25%) 0.200 0.135 0.065 (33%) |
CBST 0.374 0.523 −0.149 ( −28%) 0.215 0.105 0.110 (51%) |
IAST 0.376 0.493 −0.117(−24%) 0.223 0.135 0.088 (39%) |
Worst Sorted 30% (bottom, top) |
Method rural urban rural−urban (%) rural urban rural−urban (%) |
No adaptation 0.0609 0.244 −0.183 ( −75%) (0.098, 0.581) (0.317, 0.630) (−0.219,−0.049) ( −69%,−7.7%) |
CBST 0.0172 0.362 −0.345 ( −95%) (0.0943, 0.609) (0.398, 0.647) (−0.304,−0.038) ( −76%,−5.9%) |
IAST 0.0304 0.232 −0.202 ( −87%) (0.0772, 0.598) (0.327, 0.640) (−0.250,−0.042) ( −76%,−6.6%) |
Table 2. Task B: Evaluation of transfer across districts. Three methods (No adaptation, CBST, IAST) are trained source districts, and |
evaluated on target rural and target urban districts. For the metrics, Mean, Class-std, and Worst, the better performing group (between rural |
and urban) is in bold. The differences in performance between rural and urban are shaded. Models have high unfairness upon transfer. |
4.2.2 Task C - Transfer across urban and rural areas |
Second, we consider the scenario where the segmentation |
model is transferred either from urban to rural areas or from |
rural to urban areas. The source and target domain consists |
of data from the same set of districts. So for this task, the |
only source for domain discrepancy is rural and urban dis- |
crepancy. The no- adaptation method and two UDA meth- |
ods are trained on the source domain, and tested on the tar- |
get domain. Evaluation metrics are the same as earlier. |
5. Results |
We summarize results for the single-domain in Table 1. |
Both the networks (UNet, DeepLabV3+) have better over- |
all accuracy, shown with Mean IoU over the 7 classes, for |
the rural districts compared to the urban districts. Fairness |
metrics such as IoU of the worst class and mean IoU of |
30% bottom classes are comparable between rural and ur- |
ban. The worst class is Barren for both rural and urban. The |
30% bottom classes include Barren and Road for rural, and |
Barren and Forest for urban (see Table A.1 in Appendix |
for class-wise results). Rural results show higher mean IoU |
Figure 2. Task B: Mean IoU upon transfer across districts. |
Mean IoU on the union of rural and urban data from the source |
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