What aspect of a thermal printer affects its output quality when measuring resolution?

The aspect that most directly affects the output quality of a thermal printer when measuring resolution is the number of heating pins. In thermal printing, the resolution is typically defined by the density of the dots that the printer can produce, which is fundamentally reliant on the number of heating elements or pins that create these dots on the thermal media.

More heating pins allow for finer detail and a higher resolution, as more dots can be created in a given area, resulting in sharper images and clearer text. For example, a thermal printer with more heating pins can achieve resolutions as high as 300 dpi (dots per inch) or more, while those with fewer pins may only be capable of lower resolutions, leading to coarser and less defined prints.

Other factors such as print speed, thermal ribbons, and the type of paper can influence the overall performance and quality but do not inherently determine the resolution capability of the thermal printer itself. Therefore, when evaluating resolution specifically, the number of heating pins is the critical factor to consider.