It can be helpful to simplify accidentals when analyzing an interval.
the quality of the interval is the same as the quality of the interval without accidentals:
In the previous example all the seconds are major. It's easier to analyze the first one without accidentals.
make the sharp note natural and the double-sharp note sharp. The quality of the interval remains the same:
In the previous example, both fifths are augmented.
make the flat note natural and the double-flat note flat. The quality of the interval remains the same:
Both fourths in the previous example are augmented.