Should't justify mean pixel perfect?

Question

Until now I thought justify meant that the text will start and end at the same pixel, but i was surprised a few hours ago, when I saw this:

I got similar results in 2 computers (win7+chrome, ubuntu+firefox), and not just at this place, there are more similar bugs on the same site.

After my second chec I thought this is general and I just haven't noticed yet, but other sites don't show this strange behaviour. Also refreshing the site and restarting the browser didn't solved it.

Has anybody else noticed this? What causes this?

Answer 1

The points previously made about this being a perceptual issue are valid, but also a bit accepting of a best-case scenario where the justification is being done right/well in the first place. It's worth nothing that proper text justification is actually rather hard, and the algorithms used by browsers just aren't that great. This Hacker News thread has a bunch of notes and links that should be of interest.

Answer 2

Actually that could well be intended behaviour. As with kerning it's about the appearance, rather than being pixel perfect. With justification the appearance that's trying to be achieved is of a straight edge on both sides of the text column.

Letting a letterform with an uneven right edge like "k" stick out past the straight edge of a letter like "n" helps to give that appearance visually. This is because of Gestalt psychology, which deals with how we perceive shapes, and you can see it happening at the start of lines as well:

It wouldn't surprise me if Webkit handles the nuances of text reproduction like this better than IE's engine—it's a feature in desktop publishing software like Adobe InDesign.

Answer 3

It should be because of the character width is variable, a pixel is the smallest unit here, and fill the spaces, with, spaces can sometimes compute a float which is rounded.

Anyway, you should really not worry about this as the main reason would readability and not a design vagary.