x-height is the height of the lowercase letters, disregarding ascenders or descenders, typically exemplified by the letter x. The relationship of the x-height to the body defines the perceived type size. A typeface with a large x-height looks much bigger than a typeface with a small x-height at the same size.
The typefaces with large x-height render well in busy backgrounds by
allowing counters of an optimum size which aid legibility. Especially,
the letters with three horizontal strokes such as a,e,s benefit from
Typefaces with large x-height are more legible when viewed at a distance because the large x-height results in large counters. However, too large x-height can lead to the misrecognition of letters.
The x-height should be optimised to get a right
balance between the ascender and the counter size keeping in mind
the deterioration caused by rounding and irradiation.
The impact of x-height ceases to exist width of the letter
is small. Hence these two factors should be considered in tandem.
In the case of letters with two horizontal strokes (o,z,b,d,p,q)
large x-height does not affect the legibility much.
Use of large x-height in some cases might lead to misrecognition among the letters if the x-height overpowers the ascenders
height (see image ), which usually get suppressed by rounding at
the edges because of irradiation thereby decreasing the legibility.
Ascenders play a huge role in letter recognition as compared to descenders.
x-height does not help if the counters are narrow and strokes merge into each other when viewed at an angle.