Is downsampling lossless?

It's a lot simpler. Downsampling loses information. Upsampling is lossless when the factor is an integer (taken you also remember the factor), but some information is lost when the factor is not an integer. Upsampling could theoretically lose more information than downsampling, for very specific resampling factors.

What is downsampling of a data sequence?

The process of reducing a sampling rate by an integer factor is referred to as downsampling of a data sequence. We also refer to downsampling as decimation. The term decimation used for the downsampling process has been accepted and used in many textbooks and fields. ^ Crochiere, R.E.; Rabiner, L.R. (1983). "2". Multirate Digital Signal Processing.

Does downsampling increase resolution?

Downsampling does not increase the signal resolution (in your words), it actually will decrease it. Oversampling is followed by digital low-pass filtering and then by decimation/downsampling. Oversampling does not change the information content of the signal at its final sample rate.

How does up- or downsampling work?

In other words, techniques like up -or downsampling are orthogonal to this. Assuming the model is better than random, you can intuitively see that increasing the threshold for positive classification (which leads to less positive predictions) increases the model's precision at the cost of lower recall and vice versa.