Sometimes, when taking two screenshots of the same page with the same PC in Chrome I get slightly different bitmaps for text.
This is an example diff:

The reason might be that antialias is not always the same. These are the two zoomed screenshots:

I can notice some color in the former that is absent in the latter.
Using setDiffSizeTrigger() doesn't help because it only counts the total number of points and this value can be very big when there is a long paragraph.