MiWORD of the Day is… Domain Shift!

From looking at the image from two different domains, could you tell what are they?
Hmmm? Is this a trick question or not, aren’t they the same? You might ask.
Yes, you are right. They are all bags. They are generally the same object, and I am sure you can easily tell just at a glimpse. However, unlike human beings, if you let a machine learning model read these images from two different domains, it would easily get confused by them, and eventually, make mistakes in identifying them. This is known as domain shift in Machine Learning.

Domain shift, also known as distribution shift, usually occurs in deep learning models
when the data distribution changes when the model reads the data. For instance, let’s say a deep learning model is trained on a dataset containing the images of backpacks on domain 1 (see the backpack image above). The model itself would then learn the specific features of the backpack image from domain 1 like the size, shape, angle of the picture taken etc. When you take the exact same model to test or retrain on the backpack images from domain 2, due to a slight variation in the background angle, the data distribution of the model encounters shifts a little bit, which would most likely result in a drop in model performance.

Deep learning models, such as a CNN model, are also widely used in the medical
imaging industry. Researchers have been implementing deep learning models in image
classification, segmentation and other tasks. However, because different imaging centers might use different machines, tools, and protocols, the datasets on the exact same image modality across different imaging centers might differ. Therefore, a model might experience a domain shift when it encounters a new unseen dataset which has variation in the data distribution.

Me: “What can we do if a domain shift exists in a model between the source and target dataset?”
Professor Tyrrell: “Try mixing the target dataset with some images from the source dataset! ”

Less serious:
Mom: “I heard that your brother is really good at physics, what is your domain?”
Me: “I used to be an expert on Philosophy, but now due to my emerging interest in AI, I shift my domain to learning Artificial Intelligence.”
Mom: “Oh! A domain shift!”

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