One aspect of image quality is resolution, or image sharpness.
People tend to prefer a sharply focused image.
That is true even if symbol size and contrast ratios are such that sharp focus might not seem to be important. Stimulation of the visual system produces measurable electrical activity in the brain. The voltage differences between two electrodes placed on the scalp can be recorded. The evoked potential produced by an image of higher resolution is, within limits, stronger and more clearly defined than one produced by an image of lower resolution but similar contrast and equal total light output. One of the problems in recommending a specific level of resolution is that visual performance over the range of spatial frequencies that are of interest does not change with differences in resolution so long as modulation is held constant.