class weights formula for imbalanced dataset

Question

class weights formula for imbalanced dataset

safa

2021年5月2日 17:51

I am trying to make some semantic segmentation. I have 7 imbalanced classes in my case. I found several methods for handling Class Imbalance in a dataset is to perform Undersampling for the Majority Classes or Oversampling for the minority classes. but the most used one is introducing weights in the Loss Function. And I found several formula to calculate weights such us: wj=n_samples / (n_classes * n_samplesj) or wj=1/n_samplesj

which is the best one?

Topic weight-initialization loss-function class-imbalance deep-learning

Category Data Science

SoheilStar · Accepted Answer · 2021年5月2日 17:51

I really don't suggest Under/Oversampling as it would change the distribution of dataset. we should consider distribution as a useful feature of dataset. so I think the weighted loss would have better performance in most cases. if you're using TF/Keras, this link would be useful. you can use a variety of loss functions, like the below one, to apply the weight.

tf.nn.weighted_cross_entropy_with_logits(
    labels, logits, pos_weight, name=None
)

A value pos_weight > 1 decreases the false negative count, hence increasing the recall. Conversely setting pos_weight < 1 decreases the false positive count and increases the precision.

class weights formula for imbalanced dataset

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